BIOL 284 exam one review

infant fontanelle

identification

• sphenoid (anterolateral) fontanelle - superior to the sphenoid bone

• mastoid (posterolateral) fontanelle - posterior to the temporal bone

• anterior fontanelle - posterior to the frontal bone

• posterior fontanelle - anterior to the occipital bone

purpose

• fontanelles are spaces between unfused bone that are filled with fibrous membrane

• allow for the shifting of the bones during childbirth and the growth of the brain during infancy

• fontanelles typically ossify by a year old (except the anterior fontanelle which can remain present up to two years after birth)

• skull reaches adult size by eight to nine years of age

developmental curvatures of the spine

primary curvatures

• present at birth

• spine exhibits one continuous c shaped curve or anterior concavities (kyphoses) with thoracic and pelvic subsets

secondary curvatures

• develop later - as an infant begins to crawl and lift head the cervical curvature develops and walking upright develops the lumbar curvature

• spine exhibits posterior concavities (lordoses) with cervical and lumbar subsets

abnormal curvatures of the spine

causes -

• degenerative diseases

• muscle paralysis

• poor posture

• ergonomics

• pregnancy

• obesity

• congenital defects

scoliosis - lateral postural drift (to the left or right)

• most common abnormality

• exhibits as a lateral lean with uneven shoulders

• usually deviates at the thoracic level (but can also occur at the lumbar level)

• more common in young girls

hyperkyphosis (hunchback) - anterior postural drift

• exaggerated thoracic concavity

• exhibits as anteriorly hunched shoulders

• usually from osteoporosis or osteomalacia 

• can also be caused by wrestling or weight lifting on young and developing bodies

hyperlordosis (swayback) - posterior postural drift

• exaggerated lumbar concavity that bends further anterior

• exhibits as a posterior lean from the lower back that alleviates pressure on the lumbar vertebrae and compensates for increased abdominal weight

• shares similar causes as hyperkyphosis

• can also be caused by pregnancy or obesity

paranasal sinuses

bones containing paranasal sinuses 

• frontal bone (frontal sinus)

• sphenoid bone (sphenoidal sinus)

• ethmoid bone (ethmoidal sinus)

• maxilla (maxillary sinus)

functions 

• connected by the nasal cavity and lined by mucous membranes

• filled with air

• lighten the anterior portion of the skull

• act as chambers that add resonance to the voice

intervertebral discs

• an intervertebral disc is a cartilaginous pad located between the bodies of two adjacent vertebrae

• each disc consists of an inner gelatinous nucleus pulposus surrounded by a ring of fibrocartilage called the anulus fibrosus

• there are twenty-three intervertebral discs with the first between C2 and C3 and the last between L5 and S1

• intervertebral discs function to bind adjacent vertebrae together and support the weight of the body while allowing spinal mobility and absorbing shock

• when subject to excessive stress discs can rupture (known as ruptured or herniated discs)

skeletal system functions

• framework stability and support - supports the body against gravity and resistance with a rigid structure and provides scaffolding for muscles and skin

• organ protection - encases vital organs (eg. central nervous system, heart, lungs, pelvic viscera, bone marrow)

• movement - appendicular bones act as levers for muscle actions on limbs; breathing and neck muscles are anchored to axial bones

• electrolyte balance - bone is both a storage depot and source of calcium and phosphate ions which are important for electrical and chemical currents in the tissue fluid and blood

• acid and base balance - phosphate in the bone tissue buffers blood against excessive pH changes by absorbing or releasing alkaline phosphate and carbonate salts

• hematopoiesis (blood formation) - red bone marrow or myeloid tissue is the chief producer of blood cells (eg. erythrocytes, leukocytes, megakaryocytes)

• hormone secretion - bone cells secrete hormones that influence the secretion and action of insulin and moderate the stress response

components of the skeletal system

the living skeleton is made of active tissues that are full of cells and permeated by nerves and blood vessels

bones

• organs that form the strong yet slightly flexible framework of the body

cartilage

• forerunner of most bones in embryonic and childhood development

• remnants of cartilage following development form articular cartilage which is hyaline cartilage without a perichondrium

• articular cartilage covers interacting surfaces at the joints of mature bones

ligaments

• hold bones together at the joints or articulations

general features of bones

articular cartilages

• cover articular surfaces of bones in highly movable joints

• allow joints to move freely with less friction which enables painless movement

• most are made of hyaline cartilage and uniquely lack perichondrium (exceptions include the menisci of the knee, the pubic symphysis, and the intervertebral discs which contain tougher fibrocartilage laters that also lack a perichondrium)

• are avascular and aneural which cause difficulty with healing and the lack of perichondrium prohibits the regeneration of lost tissue

• these cartilages prevent osteoarthritis which is caused by wear and tear over time

nutrient foramina

• small holes in surfaces of all bones that permit blood vessels and nerves to permeate, nourish, and sustain internal bone tissue

• there are many small foramina per bone but there is usually one larger nutrient foramen for the main line of the nutrient artery or vein

• the foramina allow passage of nutrient vessels to and from the bone marrow in the core of the bone

types of bones

flat bones

• thin and curved plates that contain a spongy layer of diploe surrounded by inner and outer tables of compact bone

• protect soft organs

• examples include the parietal bones, the sternum, the scapula, ribs, and hip bones

long bones

• longer than wide

• rigid levers acted upon by muscles that are crucial for movement

• examples include the humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges

short bones

• approximately equal in length and width

• glide across one another in multiple directions

• examples include the carpals and tarsals

irregular bones

• elaborate shapes that do not fit in other bone classes

• examples include the vertebrae, sacrum, the sphenoid bone, and the ethmoid bone

sesamoid bones 

• bones developed in tendons due to stress

• a particular example is the patella

general features of long bones

diaphysis - cylinder of compact bone that provides leverage

epiphysis - enlarged ends of bone that strengthen the joint and provide added surface area for ligament and tendon attachment

epiphyseal line - slightly denser spongy bone between the epiphysis and diaphysis that is a remnant of the epiphyseal plate (areas of hyaline cartilage in the metaphysis of immature bones that enable elongation)

medullary or marrow cavity - space in the diaphysis of a long bone that contains bone marrow (mostly yellow marrow in adults)

metaphysis - area in between the diaphysis and epiphysis

periosteum - surface membrane of bone composed of two layers (an outer fibrous collagen layer and an inner osteogenic layer of osteoblasts)

endosteum - thin layer of reticular connective tissue that lines the internal marrow cavity, covers trabeculae of spongy bone, and lines the canal systems found in compact bone

compositions of bone as complex organs

• bones are composed of osseous tissue which is a connective tissue with a mineralized extracellular matrix

• mineralization or ossification (calcification) is the process of extracellular matrix hardening due to heavy deposition of calcium and phosphate crystals

• bone organs contain various tissues (eg. osseous tissue, red bone marrow or myeloid tissue, blood, cartilage, external connective tissue, nervous tissue, yellow bone marrow or adipose tissue, and simple epithelia)

• even though it appears static bone continually remodels itself and the physiology of the bones affect all other organ systems

bone membranes and their components

endosteum

• thin reticular connective tissue lining internal bone surfaces

• has cells that deposit (osteoblasts) and cells that dissolve (osteoclasts) osseous matrix

• also contains hematopoietic stem cells that produce red bone marrow

• found on all internal surfaces including the lining of compact bone surrounding the marrow cavity (cortical endosteum), lining of canals within compact bone osteons (osteonal endosteum), and the continuous lining of every spicule in cancellous bone (trabecular endosteum)

periosteum

• dual layered external sheath that covers bone except at the articular cartilages

• fibrous connective tissues of tendons and ligaments meld with the periosteum as a continuous feature

• perforating or sharpey fibers penetrate into the bone matrix to provide flexibility and structural adherence which prevents delamination or tearing with injury

• composed of two layers

1. outer fibrous layer is rich in collagen (with elastin) and vascular supplies that pass through microscopic perforating canals in bone

2. inner osteogenic layer contains osteoblasts which are important to thickening or circumferential growth of bone and the healing of fractures

bone cells

1. osteogenic or osteoprogenitor cells 

• derived from embryonic mesenchymal stem cells

• give rise to osteoblasts and osteocytes

• found in the endosteum and inner layer of the periosteum

• capable of dividing and producing more bone cells and multiple continuously to produce new osteoblasts

• increase osteogenesis during healing of injuries or experience of mechanical stress

2. osteoblasts

• direct descendent of osteogenic cells

• bone forming cells that synthesize a soft organic osteoid (bone like) template composed of collage into the matrix which hardens by mineral deposition and crystallization

• nonmitotic and cannot divide to form more osteoblasts

• found in regenerative membranes of the endosteum and inner layer of the periosteum

• contain mitochondria and endoplasmic reticula to support osteogenic role

• secrete osteocalcin (allows parasympathetic nervous system to function)

3. osteocytes

• direct descendent of osteogenic cells and osteoblasts

• former osteoblasts that retire from bone formation when trapped in lacunae

• interconnected by a network of canaliculi or microscopic tunnels that run through the dense mineral matrix to maintain cell viability

• have cytoplasmic extensions called dendrites which project through the canaliculi and extend to other osteocytes while osteocytes close to one another communicate through gap junctions since diffusion cannot occur through bone

• dissolve and deposit bony matrix in small amounts which contributes to the homeostatic regulation of bone minerals

• produce biochemical relay signals to stimulate osteoblast activity when necessary

• function as strain sensors as load stimulates sensory cilia on the dendrites and induces cells to secrete signals that regulate bone remodeling to adjust shape and density and adapt to stress

• secrete osteocalcin (allows parasympathetic nervous system to function)

4. osteoclasts

• descendent of leukocyte precursor cells that produce macrophages (monocytes)

• bone dissolving cells

• unusually large cells formed from the fusion of several cells that typically have three to four nuclei (multinucleate) 

• have an abundance of lysosomes that digest and break down cellular debris

• have ruffled membranes that face bone surface and increase surface area for resorption efficiency

• reside within pits called resorption bays

different types of lamellae

concentric lamellae

• rings of matrix that surround the central canal of an osteon

interstitial lamellae

• irregular regions of lamellae between osteons

circumferential lamellae

• parallel layers of lamellae that form around the whole bone

components of the bone tissue matrix

• matrix of osseous tissue is about ⅓ organic and ⅔ inorganic matter or minerals

• bone matrix is a composite of polymer (organic) and ceramic (inorganic) components

• matrix combines optimal mechanical properties of each component

organic matter

• synthesized by osteoblasts

• mostly collagen but includes some proteoglycans (PGs), glycosaminoglycans (GAGs), and glycoproteins

• defects in collagen found in the organic matter can cause osteogenesis imperfecta or brittle bone disease which can result in serious structural problems

• gives bone some degree of flexibility

• bones would be brittle and prone to fracture without organic material

inorganic matter

• minerals and depositions by osteoblasts

• 85% hydroxyapatite or crystallized calcium phosphate salt

• 10% calcium carbonate

• 5% other minerals and inorganic ions (eg. fluoride, sodium, potassium, and magnesium)

• deficiencies in calcium or vitamin d can cause rickettsia in children (bones curve laterally as growth plate lacks minerals and influenced by weight) or osteomalacia in adults

• structurally rigid for supporting body weight

• unable to support weight and deform in shape without inorganic portion

formation of osseous tissue matrix by deposition

• ossification is the detailed mineralization process that occurs in all bone tissue formation in which hydroxyapatite (calcium phosphate) and other ions are taken from the blood plasma and deposited in osteoid tissue as crystallized salts

• begins in fetal ossification and continues throughout life

1. osteoblasts produce collagen fibers (collagenous template) that spiral the longitudinal length of the osteon and form osteoid tissue (precursor to mineralized tissue)

2. osteoblasts then absorb calcium and phosphate from the blood to synthesize hydroxyapatite

3. osteoblasts export hydroxyapatite minerals into the matrix when accumulation exceeds solubility limits (levels reach the solubility product and minerals precipitate out of solution)

4. minerals accumulate and cause crystals to precipitate from solution and encrust collagen fibers and serves as seed crystals for the continuing deposition of more inbound calcium phosphate crystals

• this causes a brief positive feedback loop of crystallization that occurs until the bone tissue matrix is stuffed with dense mineral lattices and no more blood or other fluid can flow through the tissue

• abnormal bone tissue ossification is referred to as ectopic ossification and occurs in other organs (eg. lungs, brain, eyes, muscles, tendons, arteries) which creates calculi or hardened mineral masses in an otherwise soft organ

types of osseous tissue

compact (dense or cortical) bone

• dense outer shell of bone

• covers cancellous bone

cancellous (spongy) bone

• loosely organized bone tissue

• found in the center of epiphyses and center of diaphyses of long bones and in the middle of nearly all others

• called diploe in flat bones

• covered by durable compact bone

are cancellous and compact bone really that different?

• compact and cancellous bone are composed of the same osseous tissue cells in similar arrangements but cancellous bone has more surrounding space which decreases strength

• osteocytes do not need central canals of regular osteons

• mineral spines or spiculus join to form trabeculae (thin plates of osseous tissue) meshwork deep to compact bone

• this porous cancellous bone structure lightens the load and increases mobility for survival, houses red bone marrow, increases surface area that is lined with endosteum and contributes a rich blood supply for easy access to donate and accept minerals from the blood for bone remodeling

• trabecular plates are adaptive and develop greater densities along lines of mechanical stress (referred to as wolffs law)

composition and function of osseous tissue

• osseous tissue in compact bone is organized into units called osteons (haversian systems)

• osteons (haversian systems) consist of a central (haversian) canal that contains nerves and vasculature

• central (haversian) canals (lined with endosteum) are surrounded by rings of matrix called concentric lamellae

• perforating canals (lined with endosteum) pass between adjacent osteons and provide entry points for small blood vessels from the bone surface

• young osteoblasts form the osseous matrix then become osteocytes that maintain the tissue in lamellae and survive by gap junctions and the canaliculi network

types and functions of bone marrow

• bone marrow is soft tissue that occupies the marrow cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger central canals

red marrow (myeloid tissue) - 50%

• in nearly every bone in children

• remains in the skull, vertebrae, ribs, sternum, os coxae, proximal heads of humerus, and femur in adulthood (axial skeleton)

• composed of hematopoietic tissue which produces blood cells from stem cells 

• important for erythrocyte turnover

• the transition from fetal to adult hemoglobin can cause jaundice as bilirubin is a byproduct of hemoglobin breakdown 

yellow marrow (adipose tissue) - 50%

• found in adults

• long bone shafts contain yellow marrow

• no longer produces blood cells

• mainly used for energy reserves

• yellow can revert to red to severe states of blood loss )eg. severe or chronic anemia)

intramembranous ossification

• development of bones from an embryonic template

• happens quickly and early in development

• occurs in the axial skeleton and most flat bones (eg. skull, ribs, sternum)

• does not require a cartilage template

• forms in fibrous connective tissues

• occurs directly in the mesenchyme

• develops inside to out

1. mesenchyme condenses into a soft sheet of tissue that is permeated with blood vessels and capillaries

• mesenchymal cells align with the blood vessels and become osteoblasts then secrete soft collagenous osteoid tissue away from the vessels

2. osteoblasts deposit hydroxyapatite and other minerals on the osteoid tissue to harden the matrix

• blood vessels and capillaries are compressed by minerals and osteoblasts become osteocytes in lacunae as cell bodies are surrounded by calcified matrix and periosteum begins to form

3. mesenchyme adjacent of the developing bone condenses and forms a fibrous periosteum on each surface and the cancellous bone becomes a honeycomb of trabeculae

4. osteoblasts beneath the periosteum deposit layers of bone and fill in the spaces between trabeculae

• osteoblasts create a zone of compact bone on each side and thicken the bone overall while maintaining cancellous bone in the middle layer

EVERY - EMBRYONIC TEMPLATE

CHILD - CONDENSED MESENCHYME

OFTEN - OSTEOBLASTS DEPOSIT MINERALS

THROWS - TRABECULAE FORM

FITS - FILL IN TRABECULAE

endochondral ossification

• development of bones from a cartilage template

• begins during fetal development and continues throughout life

• requires cartilaginous model

• occurs in the appendicular skeleton and most long bones (eg. limbs)

• hyaline cartilage template is calcified into osseous tissue

• is an interrupted procedure with a long delay

1. mesenchyme differentiates into a template of hyaline cartilage with a perichondrium that produces chondrocytes 

2. the primary ossification center in the middle of the cartilage forms (diaphysis) and the perichondrium begins to produce osteoblasts (chondrocytes become osteoblasts through differentiation)

• osteoblasts deposit a thin of bone around the middle of the cartilage model and the perichondrium is considered periosteum

3. primary ossification center is invaded with vasculature and turns into the primary marrow cavity and the secondary ossification center appears at the end of the cartilage model (epiphysis)

• the marrow cavity is created by osteoclasts from blood vessels that digest calcified tissue and osteoblasts continue to thicken the bony collar as osteoclasts dissolve calcified cartilage

4. (at birth) secondary ossification center turns into the secondary marrow cavity that expands outward

• primary marrow cavity continues to enlarge

5. (childhood) epiphyses fill with cancellous bone and ossification is suspended until puberty as an epiphyseal plate is formed

• the epiphyseal plate is a thin wall of cartilage that separates the primary and secondary marrow cavities (metaphysis) which persists through childhood and serves as a growth zone for bone elongation during puberty (eventually turn into epiphyseal lines in adults which mark where the plates used to be)

6. (adulthood) cartilage in the epiphyseal plate is consumed to form the epiphyseal line (the bone can no longer grow in length) and primary and secondary marrow cavities unite 

• the gap between the epiphysis and diaphysis closes

• remnant cartilage at the ends of formed bones become the articular cartilages covering each joint surface

CHILDREN - CARTILAGE TEMPLATE

HAVE - HYALINE CARTILAGE MODEL

PROBLEMS - PRIMARY OSSIFICATION CENTER

PRESENTING - PRIMARY OSSIFICATION CAVITY

SOME - SECONDARY OSSIFICATION CENTER

SAVINGS - SECONDARY OSSIFICATION CAVITY

EACH - EPIPHYSEAL PLATE

EVENING - EPIPHYSEAL LINE

interstitial growth or bone elongation

• occurs during young life (early twenties)

• due to cartilage hyperplasia and hypertrophy within the epiphyseal plate

• epiphyseal plates close when the cartilage is exhausted and lengthwise growth is finished

1. zone of reserve cartilage

• region farthest from the marrow cavity

• consists of typical hyaline cartilage with resting chondrocytes

2. zone of cell proliferation (hyperplasia)

• chondrocytes multiply

• consists of longitudinal columns of flattened lacunae

3. zone of cell hypertrophy (hypertrophy)

• chondrocytes stop multiplying and begin to enlarge

• walls of the lacunae thin

4. zone of calcification

• minerals are deposited in the matrix between the columns of lacunae

• cartilage calcifies

5. zone of bone deposition

• lacunae break down and chondrocytes die by apoptosis

• chondrocyte death converts columns into longitudinal channels which are invaded by blood vessels and marrow from the marrow cavity

• osteoblasts line up along the walls of the channels and deposit concentric lamellae of matrix while the osteoclasts dissolve the temporary calcified cartilage

• this creates a region of cancellous bone at the end of the marrow cavity facing the metaphysis and this bone remains for life 

• around the perimeter of the marrow cavity continual ossification converts the cancellous bone to compact bone (osteoblasts deposit bone matrix layers that become concentric lamellae of an osteon)

RONALD - RESERVE CARTILAGE

PUSHED - PROLIFERATION

HIS - HYPERTROPHY

CHILD - CALCIFICATION

BACK - BONE DEPOSITION

appositional growth or bone thickening

• increase in width throughout life

• occurs by deposition of new bone at the surface

• osteoblasts on the deep osteogenic layer of periosteum undergo intramembranous ossification depositing osteoid tissue against compact bone

• tissue calcifies and osteoblasts become osteocytes

• if this occurs in parallel layers to the surface then circumferential lamellae are formed

• if adjacent blood vessels in the periosteum are enveloped by a ring of new osteoid tissue then new osteons with concentric lamellae can form

1. osteoblasts beneath the periosteum deposit bone to form ridges around a blood vessel

• the blood vessel lays in a groove between the ridges

2. the groove is transformed into a tunnel when the bone built on the adjacent ridges meet

• the periosteum of the groove becomes the endosteum of the tunnel

3. osteoblasts from the endosteum deposit bone to form new concentric lamellae

• the production of additional concentric lamellae fills in the tunnel and completes the formation of a new osteon

bone remodeling and mineral homeostasis

• bone remodeling functions to repair microfractures, release minerals into the blood when needed, and reshape bone in response to use and disuse

wolffs law of bone : architecture of the bone is determined by the mechanical stresses placed on it

• remodeling is a collaborative and precise action of osteoblasts and osteoclasts that are controlled by hormones

• bony processes grow larger in response to mechanical stress

• if more blood cells are needed then osteoclasts can dissolve trabeculae to widen the marrow cavity

• pagets disease is caused by abnormal bone remodeling

• a mature bone remains a metabolically active organ as it is involved in own maintenance of growth and remodeling

• mature bone exerts a profound influence over the rest of the body by exchanging minerals with tissue fluid (eg. abnormal blood calcium disrupts the function of other organ systems especially the nervous and muscular tissues)

mineral resorption mechanism by osteoclasts

• mineral resorption involves the dissolving of bone minerals for release into the bloodstream

• hydrogen pumps in osteoclast membranes secrete hydrogen ions into the space between the cell and the bone surface which decreases the pH (< 4)

• mineral crystals dissolve at a low and acidic pH

• acid phosphatase is an enzyme that digests collagen when activated

importance of body calcium outside of bones in other systems

• calcium imbalances are much more common than conditions related to phosphate although they are both vital and essential elements in living organisms

• calcium is needed in neuron communication, muscle contraction, blood clotting, and exocytosis

• there is approximately one kilogram of calcium in the adult body (99% in the skeleton)

• there should be a normal calcium concentration in blood plasma (45% is ionized calcium which readily diffuses across capillary walls to affect other tissues while 55% is reserved calcium that is bound to plasma proteins and is electrically neutral)

• calcium minerals are deposited into the skeleton and withdrawn when needed for other purposes

importance of body phosphate outside of bones in other systems

• phosphate is a component of DNA, RNA, ATP, phospholipids, and biological pH buffers

• the average adult has 500 to 800 g of phosphorus (85 to 90% is in the bones)

calcium homeostasis and hormonal regulation of bone mineral density

• calcium homeostasis depends on a balance between intake, urinary and fecal losses, and exchanges between osseous tissue

• calcium homeostasis is regulated by three hormones including (1) calcitriol or vitamin D₃, (2) calcitonin, and (3) parathyroid hormone

• these three hormones maintain normocalcemia

hypocalcemia (low calcium in the blood)

• has a wide variety of common causes but body calcium deficiency is not one of them

• causes include vitamin d deficiency, diarrhea (inability to absorb calcium because movement through the digestive tract is too quick), thyroid tumors, underactive parathyroids (hypoparathyroidism), pregnancy and lactation (second demand for calcium usage causes gestational or maternal hypocalcemia), and accidental removal of parathyroid glands during thyroidectomy surgery

calcitonin (an off switch for blood calcium)

• has regular effects but appears to have become unnecessary in adult humans for normocalcemia

• can be beneficial in children (high osteoclast activity) and pregnant of lactating women

• can also treat pagets disease (aberrant bone remodeling)

• secreted by cells of the thyroid gland and is released in response to hypercalcemia (high calcium in the blood)

• lowers blood calcium concentration by (1) osteoclast inhibition (reduces osteoclast activity by as much as 70% and reduces the amount of calcium liberated from the bones) and (2) osteoblast stimulation (increases the number and activity of osteoblasts and increases calcium deposition into the skeleton)

parathyroid hormone (an on switch for blood calcium)

• secreted by the parathyroid glands and is released in response to hypocalcemia

• raises calcium blood level through various mechanisms such as (1) increasing osteoclast population, (2) decreasing osteoblast activity, (3) promoting calcium reabsorption from filtrate in the kidneys which prevents loss of calcium in the urine and reintroduces calcium to blood, and (4) promoting the synthesis of calcitriol

calcitriol (1,25 dihydroxyvitamin d₃)

• an activated form of vitamin d produced by the sequential action of the skin, liver, and kidneys

• raises blood calcium concentration

• greatly enhances calcium absorption in small intestines

• increases calcium resorption from bone

• promotes kidney reabsorption of calcium

• without calcitriol children develop rickettsia and adults develop osteomalacia as vitamin d is essential for the adequate retrieval of dietary calcium and phosphate

osteoporosis

• the most common bone disease cause by severe loss of bone mineral density (particularly in the cancellous bone since it remodels frequently)

• bones lose mass and become brittle due to loss of organic matrix and minerals

• pathological fractures of the hip, wrist, and vertebral column are common

• often causes immobility which can lead to thrombosis and/or pneumonia

• estrogen maintains bone density in both sexes and inhibits osteoclast activity

• in men the adrenal glands produce the most estrogen

• in postmenopausal women rapid bone loss occurs since the ovaries cease to secrete estrogen (more dangerous for women sooner than men because of this) 

• young female athletes with low body fat become amenorrheic due to low ovarian estrogen secretion and this loss of estrogen can lead to osteoporosis and the high mechanical stress placed on the body can lead to fractures and incapacitation

• there are various clinical treatments include estrogen replacement therapy (slows bone resorption but increases risk of breast cancer, stroke, and heart disease) and forteo (parathyroid hormone derivative that slows bone loss and builds new bone but promotes bone cancer) as well as safer therapeutics including fosamax and actonel (destroy osteoclasts)

• the best treatment for osteoporosis is prevention which starts with a good bone-building diet during the early years and between ages 25 and 40

other bone disorders

osteitis deformans or pagets disease

• excessive proliferation of osteoclasts and resorption of excess bone with osteoblasts attempting to compensate by depositing extra bone

• results in rapid and disorderly bone remodeling and weak or deformed bones

• usually passes unnoticed by can sometimes cause pain and disfiguration as well as fractures

• most common in males over the age of fifty

osteomyelitis

• inflammation of osseous tissue and bone marrow as a result of bacterial infection

• often fatal and is very difficult to treat

osteogenesis imperfecta or brittle bone disease

• defect in collagen deposition that renders bones exceptionally brittle

• results in fractures present at birth or occurring with extraordinary frequency during childhood

• can cause tooth deformity and hearing loss due to deformity of the middle ear bones

• results from mutation of any several of the collagen genes

osteosarcoma or osteogenic sarcoma

• most common and deadly form of bone cancer

• occurs most often in the tibia. femur, and humerus of males between the ages of 10 and 25

• can metastasize to the lungs or other organs (in 10% of cases)

• death typically occurs within one year if left untreated

achondroplastic dwarfism

• condition in which the long bones of the limbs stop growing in childhood while the growth of other bones are unaffected

• results in short stature but normal sized head and trunk

• results from a failure of cartilage growth (failure of metaphysis chondrocytes in the zones of cell proliferation and hypertrophy to multiply and enlarge)

• results from a spontaneous mutation that can arise anytime that DNA is replicated

the integument

• the integumentary system consists of the skin and accessory organs including the hair, nails, and cutaneous glands

• the integument is the largest and heaviest organ 

• skin can be thick or thin

• thin skin covers most of the body and contains hair follicles (regardless of hair growth), sebaceous glands, and two types of sudoriferous glands (merocrine and apocrine) as well as some specialized glands

• thick skin is rarer and only found in the palms, soles, palmar side (hand), and plantar side (foot) of digits as it lacks hair follicles and sebaceous glands while only containing one type of sudoriferous gland (merocrine)

• serves as a barrier of resistance against trauma and infection by keratin (tough and fibrous protein that aggregates in most skin cells as keratinocytes in order to provide an anti-abrasive physical layer) and an acid mantle (sebaceous glands release sebum into the lumen of hair follicles and sudoriferous glands release moisture through the follicles or pores; the sebum and moisture combine to produce an acidic and oily mixture that traps and kills most pathogens) but the skin also has epidermal tight junctions that prevent crossing of pathogens and the dermis is an immune system surveillance region that can contain pathogens

• doubly waterproofed as glycolipids on the surface of the skin form a two-way barrier preventing dehydration and dilutional hypervolemia or water intoxication

• mitigates damage and protects the skin from ultraviolet radiation (melanin pigments migrate apically to disperse UV light away from living cells; melanin synthesis in basal melanocytes is a homeostatic response to UV exposure; darker skin indicates higher melanocyte activity and thus protects more effectively)

• performs vitamin d synthesis (UV radiation catalyzes a critical step in the synthesis of vitamin d within the epidermis)

• allows for sensation (largest sense organ that constantly informs the conscious mind of environmental conditions)

• allows for thermoregulation (thermoreceptors in the skin control local changes such as hair position, blood flow changes, and perspiration control to regulate heat preservation or dissipation)

the makeup of the skin

• composed of two layers including the (1) epidermis (keratinized stratified squamous epithelium) and the (2) dermis (broad connective tissue layer with areolar and dense irregular layers)

• the hypodermis (adipose connective tissue) is found below the dermis and is not considered a part of the integument

epidermis

• most superficial layer of skin

• composed of keratinized stratified squamous epithelium

dermis

• middle layer of skin

• composed of collagen with some elastic and reticular fibers as produced by fibroblasts

hypodermis

• mostly adipose tissue and blood vessels

• thin wisps of collagen are present as they loosely tether adipocyte clusters together

• function to pad the body (absorb shock and protect large resident blood vessels) and serve as an energy reservoir while also providing for thermoregulation and insulation

• drugs are introduced into the hypodermis by injection as the layer is thick and highly vascular for effective systemic absorption

the epidermis

composition

• composed of keratinized stratified squamous epithelium

• the apical dead cells are packed with keratin and held together by glycolipid layers and desmosomes that formed while living

• the living portions are avascular and rely on diffusion from vasculature beneath the basal lamina

• epidermal (rete) pegs interdigitate with dermal papillae to increase nourishment and sanitation effectiveness

layers of the epidermis

1. stratum corneum

• most superficial or apical stratum (dead keratinocytes)

• contains up to thirty rows of dead, scaly, keratinized cells (keratinocytes)

• resistant to abrasion, penetration, and water loss

• forms a durable, disposable surface layer

• cells are joined by corneodesmosomes that formed while living

• apical cells exfoliate as dander and are replaced from below

2. stratum lucidum

• present in both thin and thick skin but only visible in thick skin

• thin translucent zone superficial to the stratum granulosum

• zone of incomplete keratinization as partially keratinized dead keratinocytes appear translucent just deep to the stratum corneum

3. stratum granulosum

• first living layer (oldest keratinocytes)

• consists of three to five rows of flattened but living keratinocytes

• apical most living cells in epidermis that synthesize and secret glycolipid water barrier

• keratin filaments are crosslinked to increase cell rigidity and durability

• easily visibly by dark keratohyalin granules

4. stratum spinosum

• thickest living later (second thickest in thick skin but first thickest in thin skin)

• migratory layer of living keratinocytes and dendritic cells

• as keratinocytes migrate apically more keratin filaments aggregate and cause progressive flattening toward the surface (loss of cytoplasm and long filaments lead to spiny appearance)

• deepest cuboidal keratinocytes remain capable of mitosis

5. stratum basale

• deepest stratum (youngest keratinocytes)

• single row of basal and mostly columnar cells

• most diverse layer of epidermal strata containing stem cells, tactile or merkel cells, melanocytes, and living keratinocytes resting on the basal lamina and anchored by hemidesmosomes (adjacent cells adhere tightly together with desmosomes)

• melanogenesis and deposition occurs

• keratinocytes receive migratory orders

• tactile cells are stimulated

cells of the epidermis

precursor or stem cells

• perpetually dividing cells that differentiate into keratinocytes

• reside and remain in the stratum basale

• replenish lost keratinocytes on a continuous basis

keratinocytes

• great majority of epidermal cells

• synthesize keratin for barrier protection

• migrate apically and die for the greater good

melanocytes

• synthesize melanin to shield DNA from damaging ultraviolet light

• remain in stratum basale and secrete melanin in melanosomes for deposition in nearby keratinocytes

• do not migrate and divide slower (live longer) than keratinocytes

tactile or merkel cells

• basal cells that transduce fine touch stimulation to dermal nerve fibers residing in the stratum basale

dendritic or langerhans cells

• immune surveillance cells with phagocytic activity

• interspersed with living keratinocytes in the stratum spinosum

the dermis

composition

• composed mainly of collagen with some elastic fibers and reticular fibers all produced by fibroblasts

• well supplied with microvasculature or small blood vessels

• contain resident sweat glands, sebaceous glands, and touch receptors

• dermal papillae interdigitate with epidermal (rete) pegs to increase nourishment and sanitation effectiveness

• contains hair follicles and nail roots

• hair follicles are invaginated epidermis and small smooth muscles called arrector pili are associated with each hair follicle which allows for contraction in response to the cold, fear, or tactile stimulation

• sudoriferous (sweat) gland bodies reside in deep reticular dermis

• sebaceous glands reside in dermis and empty into hair follicles

layers of the dermis

1. papillary layer

• superficial zone of the dermis

• thinner zone of loose areolar connective tissue with papillae

• allows for mobility of immune cells in case of invasion

• provides papillary capillary network to nourish epidermis

• houses papillary touch receptors called tactile (meissners) corpuscles that reside in papillae and sense light touch (using tactile merkel cells)

2. reticular layer

• deeper and much thicker layer of dermis

• consists of dense irregular connective tissue characterized by thick and wavy collagen bundles in multiple directions

• provides tensile strength in any direction which is good for unpredictable stress

• stretch marks are caused by tearing in the reticular dermis

• contains pacinian (lamellar) corpuscles which are deep touch and pressure receptors

dermal features

• the integument has three major types of glands including (1) merocrine or eccrine sudoriferous (sweat) glands, (2) apocrine sudoriferous glands, and (3) sebaceous glands

• all glands are made mostly of epithelial tissues

merocrine (eccrine) sudoriferous (sweat) glands

• common and simple glands that are coiled and tubular

• found throughout the body

• utilize merocrine secretion (vesicular exocrine secretion mechanism)

• functions to produce watery perspiration that helps cool the body

• produce sweat that is slightly acidic with some ions but most ions are reabsorbed in the gland before sweat is released into the duct

apocrine sweat glands

• occur only in the inguinal, anal, axillary, pectoral, and bearded area in males

• utilize merocrine secretion

• ducts empty into nearby hair follicles rather than the skin surface

• function as scent glands that respond to stress and sexual stimulation

• produce thick and milky sweat with fatty acids

• develop at puberty and release pheromones (humans produce pheromones but lack the organ to detect them)

sebaceous (oil) glands

• flask shaped glands with short ducts that open into a hair follicle

• found throughout the body

• composed of stratified cuboidal epithelium

• utilize holocrine secretion

• the cell is replaced by mitosis at the base of the gland

• produces oily sebum 

• function to keep skin and hair from becoming dry and brittle

ceruminous glands

• simple and coiled tubular glands that exist only in the external ear canal

• true apocrine gland

• combines sebum and exfoliated cells to form cerumen (earwax)

• function to keep the eardrum pliant, waterproof the ear canal, kill bacteria, and hinder foreign particle entry

mammary glands

• milk producing glands that develop only during pregnancy and lactation

• found in the breasts

• true apocrine gland

• rich secretions released by ducts that open into the nipple

• mammary ridges or milk lines are two rows of mammary glands found in most mammals

the hypodermis

• mostly adipose tissue and blood vessels

• thin wisps of collagen are present as they loosely tether adipocyte clusters together

• function to pad the body (absorb shock and protect large resident blood vessels) and serve as an energy reservoir while also providing for thermoregulation and insulation

• drugs are introduced into the hypodermis by injection as the layer is thick and highly vascular for effective systemic absorption

life cycle of a keratinocyte

• keratinocytes are produced deep in the epidermis by the mitosis of stem cells in the stratum basale

• some of the deepest keratinocytes in the stratum spinosum also continue dividing 

• mitosis ceases once epidermal cells migrate two to three cells away from the dermis as mitosis requires an abundant supply of oxygen and nutrients which are acquired from blood vessels in the nearby dermis

• as new keratinocytes form the older ones are pushed toward the apical surface of the epidermis

• in 30 to 40 days keratinocytes make way to the surface and exfoliate or flake off

• keratinocyte migration is slower in old age and faster in skin that has been injured or stressed (accelerates keratinocyte multiplication and can result in calluses or corns which are accumulations of dead keratinocytes)

• as keratinocytes are pushed upwards by dividing cells below they flatten and produce more keratin filaments and lipid filled lamellar granules

• in the stratum granulosum these granules (1) release a protein called filaggrin which binds the cytoskeletal keratin filaments together into coarse and tough bundles, then (2) cells produce a tough layer of envelope protein beneath the plasma membrane which creates a nearly indestructible protein sac around keratin bundles and (3) lamellar granules release a lipid mixture that spreads out over the cell surface to waterproof it which creates a (4) barrier that cuts keratinocytes off from the supply of nutrients below which causes cell death and leaves the tough waterproof sac with bundles of keratin that creates the epidermal water barrier

• the stratum corneum contains compact layers of dead keratinocytes and keratinocyte fragments

• dead cells exfoliate off as dander which can accumulate

• dandruff is composed of clumps of dander stuck together by sebum

skin discoloration as diagnostic observations

cyanosis

• blue or grey hue of the skin and mucous membranes

• caused by oxygen deficiency in circulating blood

• most visible in the lips and oral mucosa as well as the tongue but also be seen in the palms and under the fingernails

• can result from conditions that prevent blood from picking up a normal load of oxygen in the lungs such as airway obstructions, drowning, choking, lung diseases including emphysema and respiratory arrest, cold weather, and cardiac arrest

erythema

• abnormal redness of the skin

• common sign of infection and inflammation

• results from increased blood flow in dilated cutaneous vessels or by dermal pooling of red blood cells that have escaped abnormally permeable capillaries

• can be narrowly circumscribed (around a mosquito or tick bite) or spread more broadly

pallor

• pale or ashen color

• occurs when there is little blood flow through the skin or when the blood has low oxygen levels

• reveals dermal collagen

• noticeable in face and palms

• can result from emotional stress, low blood pressure, circulatory shock, cold temperatures, or severe anemia

albinism

• genetic lack of melanin

• results in milky white hair and skin and blue grey eyes

• caused by a recessive, nonfunctional tyrosinase allele that prevents the synthesis of melanin from the amino acid tyrosine

jaundice

• yellowing of the skin and whites of eyes

• cause by high levels of bilirubin (hemoglobin breakdown product) in the blood

• the liver and spleen convert hemoglobin to bilirubin which the liver excretes in the bile

• when the liver is not developed enough (such as with cancer, hepatitis, cirrhosis, and prematurity) bilirubin cannot be disposed of efficiently and it accumulates

hematoma

• otherwise known as a bruise

• mass of clotted blood showing through the skin

• typically caused by accidental trauma or blows to the skin

• can be indicative of hemophilia, metabolic or nutritional disorders, and physical abuse

tissue growth and developmental mechanisms

1. hyperplasia

• tissue growth through cell multiplication (division)

• primary form of tissue growth during gestation, infancy, and childhood (also important in adolescence)

2. hypertrophy

• enlargement of preexisting cells

• characterizes muscle growth through exercise and the accumulation of body fat

3. neoplasia

• development of a tumor (neoplasm)

• can be benign and stop growing

• can be malignant and continue growing (forms cancer)

• both benign and malignant neoplasms are composed of abnormal and dysfunctional tissue

• benign neoplasms include skin moles, cysts, scars and keloids, as well as static organ tumors

• malignant neoplasms become carcinomas of various organs

4. metaplasia

• changing from one type of mature tissue to another

• an example is that of pseudostratified columnar epithelium in the bronchi of smokers which converts to stratified squamous epithelium (allows for greater protection from damage but reduces mucus production and movement)

classification of tissues

epithelial tissue

• all epithelia are avascular and depend on diffusion from deeper tissues with a blood supply for nutrition and sanitation

• consist of a layer or layers of densely packed and adherent cells with little room for extracellular matrix

• high cells to matrix ratio (lots of cells and little matrix)

• contains a basal lamina (basement membrane) which is the only visible matrix found in epithelial tissues

• the basal lamina is a protein sheet (containing collagen, laminin, and fibronectin) attached to the basal surface of the epithelium and functions to anchor the epithelium to underlying (connective) tissues

• cover internal and external surfaces and usually lie superficial to connective tissues

• line the internal lumen of hollow organs as part of the mucous membranes or mucosa

• line internal body cavities and resident organs as part of serous membranes or serosa

• form most glands and ducts (single or multiple layers of tissue can develop as a circular tube with an epithelial layer lining the tube)

• apical or outermost surfaces of epithelial tissues are exposed to the environment or an internal space

• serve as selective exchange membranes and as barriers

• adhere tightly to one another and to their basement membrane which prevents free and unwanted passage and protects underlying tissue

• tend to be more resilient than deeper tissues

shapes

1. squamous

• thin and flat (plate like)

• wider than they are tall

2. cuboidal

• square or rounded (cube like)

• as tall as they are wide

3. columnar

• tall and narrow (stalk like)

• taller than they are wide

types

1. simple epithelia

• single layer of cells

• consist of four types including (1) simple squamous, (2) simple cuboidal, (3) simple columnar, and (4) pseudostratified columnar

2. stratified epithelia

• multiple layers of cells

• consists of four types (omit two) including (1) stratified squamous and (2) transitional or urothelium

---

connective tissue

• tissues in which cells usually occupy less space than the extracellular matrix

• low cells to matrix ratio (little cells and lots of matrix) compared to epithelium

• most connective tissue cells are not directly adjacent as cells are separated by substantial matrix (including ground substance and fibers)

• some are highly vascular while others are avascular

types

1. connective tissue proper (lamina propria)

• include two dense or fibrous subtypes and three loose subtypes

2. supportive connective tissues

• three cartilage and three bone types

3. fluidic connective tissues

• blood

epithelial tissue

simple epithelia

simple squamous epithelium

characteristics

• single layer of thin and flat cells

• bulges where the nucleus is located

function

• thin layer permits rapid diffusion or selective transport

• can secrete lubricating substances

locations

• mesothelia of pleura

• serosa or serous membranes of stomach and intestines

• endothelium (luminal lining of blood vessels and heart)

• glomerular capsule (inner layer of filtration structure in the kidneys)

• kidney tubules

• alveoli (air sacs in the lungs)

• pericardium

• peritoneum

• mesenteries

simple cuboidal epithelium

characteristics

• single layer of square or rounded cells

• spherical and centrally placed nuclei

function

• absorption and secretion

• production of protective mucous coat

• movement of respiratory mucus

locations

• renal (kidney) ducts and tubules

• hepatic (liver) ductules for bile secretion

• thyroid follicles

• pancreatic ducts

• mammary gland ducts

• salivary gland ducts

• bronchioles

simple columnar epithelium

characteristics

• single layer of tall and narrow cells

• can have goblet cells and microvilli brush border (goblet cells are bulbous clear cells involved in the bulk secretion of mucus that produce an aqueous mixture containing mucin proteins and ions as well as acids and bases)

function

• bulk absorption and bulk secretion

• secretions usually contain a very high mucus content

locations

• luminal lining of the gastrointestinal tract

• gastric mucosa

• small intestine mucosa

• colonic mucosa

• rectal mucosa

• gallbladder tubules

• uterus and uterine tubes

pseudostratified ciliated columnar epithelium

characteristics

• single layer of cells that appears multilayered

• all cells touch the basement membrane

• ciliated on apical surface with a few interspersed goblet cells

function

• secrete and propel mucus 

locations

• respiratory mucosa

• nasal to bronchial mucosa

• portions of the male urethra

---

stratified epithelia

keratinized stratified squamous epithelium

characteristics

• multiple cell layers with dead compact cells 

• keratin filled flat cells on the surface that are dead and lack a nucleus

• can exfoliate and be replaced by deeper layers

function

• resist abrasion and penetration

• prevent infections as a barrier pathogens

• minimize fluid loss

locations

• found only in the epidermis

• particularly in the palms and soles

nonkeratinized stratified squamous epithelium

characteristics

• multiple cell layers that lack dead surface cells

• cells do not exfoliate

function

• mildly resist abrasion and penetration

• prevent infections as a barrier to pathogens

• must be constantly moistened

locations

• oral mucosa

• esophageal mucosa

• anal mucosa

• vaginal mucosa

• tongue

transitional epithelium or urothelium

characteristics

• round surface cells of different shapes and sizes

• can be binucleated

• can possess umbrella cells that cover more than one cell

• thick when relaxed and thin when stretched

function

• stretches to allow filling of urinary bladder

• protect underlying tissues from osmotic damage by urine

locations

• localized to urinary system

• ureters

• urinary bladder

• proximal urethral mucosa

• renal canal

types of body membranes

• membranes line external and luminal surfaces as well as body cavities and their resident viscera

cutaneous (external) membrane or the skin

• largest membrane in the body

• utilized for protection

• the superficial portion contains keratinized stratified squamous epithelium (epidermis) while the deep portion contains areolar connective tissue (papillary dermis)

mucous (luminal) membranes

• mucous membranes (mucosa) line the surface of hollow organs that open into an internal lumen

• the superficial portion contains an epithelial tissue layer (simple or pseudostratified columnar with goblet cells or nonkeratinized stratified squamous) that often has cilia or microvilli while the deep portion contains the lamina propria (usually areolar connective tissue) and muscularis mucosa (smooth muscle that moves the mucosa)

serous (cavity) membranes

• serous membranes (serosa) line the surfaces of body cavities and resident organs

• produce serous fluid obtained from blood plasma to lubricate organs and cavity walls

• thin membrane consisting of a simple squamous epithelium (mesothelium) and a slight layer of areolar connective tissue

intercellular junctions

• cells must cooperate to form a healthy barrier tissue

• most cells of a barrier tissue share via intercellular junctions

• intercellular junctions exist between neighboring cells and maintain the tissue layer so the tissues can live long and prosper

tight (occluding) junctions - create a seal

• a region of plasma membrane from two adjacent cells fused by adhesion proteins

• form a zone that completely seals off lateral intercellular spaces near the apical side of the membrane which makes it impossible for most substances to pass between cells

• most but not all epithelia have tight junctions

desmosomes (anchoring junctions) - provide structural support

• patches that hold cells together

• resist mechanical stress and keep cells from pulling apart

• hooklike and j shaped proteins arise from cytoskeleton traverse transmembrane grooves and latch on to one another

hemidesmosomes (half desmosomes) - anchor cells to basal lamina

• latch the basal surface of epithelium to the basal lamina and functions to resist epithelial layer delamination from underlying tissues

gap (communicating) junctions - allow direct communication and substance exchange

• pores that equilibrate internal conditions between cells of an epithelial tissue

• allow for free diffusion of ions, glucose, amino acids, and other small solutes through the cytoplasm of adjacent cells

• a ring like connexon arranged in segments (like that of an orange) forms a water filled pore with size exclusion properties

glands and modes of secretion

• glands are mostly made of epithelial tissue and function to secrete substances for use elsewhere in the body or for release and elimination from the body

exocrine glands (excreting)

• maintain contact with the internal and external body cavities via a duct or epithelial tube that conveys products to the surface

• external exocrine glands include sudoriferous, mammary, ceruminous, sebaceous, and lacrimal glands

• internal exocrine glands include goblet cells, mucus glands, digestive glands, and renal tubules

endocrine glands (secreting)

• ductless glands that do not reach the surface of the body

• examples include the thyroid, adrenal, thymus, and pituitary glands

merocrine (eccrine) secretion

• most common form of secretion

• vesicular exocytosis deposits endocrine or exocrine products into a duct, vessel, or other fluidic space

• include tear, sweat, and pancreatic glands, goblet cells, melanocytes, and all endocrine glands

apocrine secretion

• decapitation secretion

• apical surface fragments release membrane bound chunks of exocrine product into a duct

• include ceruminous and mammary glands

• not apocrine sudoriferous glands (perform merocrine secretion)

holocrine secretion

• suicide secretion

• exocrine gland cells accumulate a product and the entire cell breaks away to disintegrate in the duct

• the secretion is a mixture of cell fragments and synthesized substance

• include sebaceous and tarsal or oil glands of the eyelids

connective tissue

—

connective tissue proper (lamina propria)

cellular makeup

• fibroblasts are the most abundant cells that function to produce structural protein fibers such as collagen and elastin as well as the ground substance of the extracellular matrix

• resident immune cells protect the tissue from infection

• macrophages phagocytize pathogens and debris and trigger immune responses recruiting leukocytes from the blood

• mast cells secrete heparin to inhibit clotting and histamine to dilate blood vessels and increase blood flow which leads to swelling and inflammation

extracellular makeup

• fibers are made by fibroblasts

• type one collagenous fibers are made of collagen and are the tough, thick, slightly flexible and stretch resistant fibers of tendons, ligaments, and the deep dermis of skin

• elastic fibers are made of elastin and are thin, highly flexible, and branched to allow for stretch and elastic recoil

• reticular fibers are made of thin, type three collagen strands that compose a thin branching collagen network with glycoproteins and forms a framework for immune cells to reside upon

• ground substance is a gelatinous to rubbery consistency and contains glycosaminoglycans (GAGs; polysaccharides of amino sugars that draw in water to provide gelatinous consistency to ground substance), proteoglycans (PGs; large molecules incorporating GAGs that create strong structural bonds between cell membrane proteins, cell cytoskeletons, and extracellular matrix fibers to support tissue integrity), and adhesive glycoproteins (membrane bound proteins that bind cells to fibers and/or PGs to support tissue integrity)

subtypes of connective tissue proper

• these subtypes include dense or loosely organized fibers made up of mostly collagen, abundant vasculature, and seemingly empty space (ground substance appears empty)

• dense subtypes have a lot of type one collagen and less ground substance visible than loose subtypes

• dense subtypes vary in orientation of fibers

1. dense regular connective tissue

• all tendons and ligaments

• tendons attach muscle to bone and transfer muscular tension to bones

• ligaments bind bones together and resist stress

• densely packed and parallel

• often wavy with slender fibroblast nuclei

• avascular

2. dense irregular connective tissue

• lower (reticular) dermis

• capsules around the liver, kidney, and spleen viscera

• fibrous sheaths around cartilage and bones

• microvasculature

• densely packed but running in random directions

• withstand stress applied in unpredictable directions and imparts durability to tissues

—-

• loose subtypes have less collagen with other fibers mixed in and more ground substance or empty space between cells

• loose subtypes vary in types of fibers

1. areolar connective tissue 

• upper (papillary) dermis

• underlying epithelia, surrounding blood vessels, nerves, esophagus, trachea, fascia, mesenteries, visceral pericardium, and pleura

• made of elastic fibers (thin strands) and type one collagen (thick strands)

• contain fibroblasts and a lot of ground substance

• loosely organized fibers with abundant blood vessels

• nearly epithelial layer rests on a layer of areolar tissue (extensive vasculature in areolar tissue brings fresh blood to nourish and filter avascular epithelia by diffusion)

• contains a ready supply of infection fighting leukocytes that move about freely in areolar tissue

2. reticular connective tissue

• spleen, lymph nodes, thymus, and bone marrow

• made of type three collagen reticular fibers

—

cartilaginous connective tissue

• more rubbery and flexible than bone but more rigid than other connective tissues

• avascular with uniform cellular makeup

• cells begin as chondroblasts that produce a matrix of type two collagen and chondroitin

• chondroblasts become chondrocytes as they mature and trap themselves in lacunae

• all cartilage begins as hyaline cartilage (smooth and glassy and uniform appearance of a type two collagen matrix) but few locations are later modified into elastic cartilage or fibrocartilage

• perichondrium is a sheath of collagen fibers, fibroblasts, and chondroblasts that surrounds most hyaline and elastic cartilage (but not fibrocartilage and articular hyaline cartilage)

• perichondrium contains a reserve population of cells that contribute to cartilage growth and repair throughout life

1. hyaline cartilage

• smooth and glassy appearance due to fineness of type two collagen fibers relative to type one fibers

• flexibility eases joint movement and allows for some expansion or constriction while rigidity maintains a patent airway and gives shape to facial features

• articular cartilages are hyaline cartilage (joint surfaces at the ends of long bone)

• costal cartilage and the respiratory tract (tracheal rings, bronchial plates, laryngeal and nasal cartilages)

• the most abundant form of cartilage

2. elastic cartilage

• modified hyaline cartilage with additional elastin secreted into the cartilage matrix

• more flexible cartilage that is able to stretch and recoil to original shape due to elastic fibers

• limited to the external ear and the epiglottis of the larynx

• special stain for elastic fibers turns them deep purple

3. fibrocartilage

• modified hyaline with coarse bundles of type one collagen secreted into cartilage matrix

• more fibrous appearance in which chondrocytes form linearized rows

• resist compression and absorb shock but has limited flexibility

• does not regenerate due to a lack of perichondrium

• limited to the interpubic disc, knee menisci, articular disc of the jaw, and intervertebral discs

tissue injury and repair

• tissue regeneration is the replacement of dead or damaged cells by the same type of cells as before

• regeneration restores normal organ function

• fibrosis is the replacement of damaged tissue with scar tissue

• fibrosis does not restore normal function

basic understanding of stem cells

• tissues can change types within certain limits 

• stem cells exist but are not equal

• member cell differentiation occurs when unspecialized tissues of an embryonic, stem, or precursor cell become specialized and mature cell types

• differentiation is the specialization of a cell into one of a specific type which reduces flexibility in what the cell can do

• an example of this include embryonic mesenchymal cells which differentiate into muscle, bone, and cartilage

• differentiation is most prominent in youth but occurs in adults as well

• embryonic stem cells (ESCs) are totipotent in early stages because of unlimited developmental plasticity but the inner cells become pluripotent and cannot become accessory or pregnancy organs but can become anything else

• adult stem cells (ASCs) are multipotent cells that can develop into multiple cell lines but some are unipotent and can produce one mature cell type

relationship between surface area and volume

• when cells grow the volume increases more than the surface area

• surface area is proportional to the square of cell diameter

• volume is proportional to the cube of a cell diameter

• interaction with the extracellular environment occurs on the cell surface and allows for processes such as oxygen absorption, glucose uptake, and carbon dioxide efflux

• matters as organelle viability is at risk in a larger cell (if a cell grows too large the surface area becomes insufficient to support the cell machinery through inadequate environmental interaction)

• matters also because structural integrity is at risk in a rapidly growing and larger cell (if the volume of a cell increases abruptly before the membrane can grow to compensate the cell may rupture)

functions of different organelles

nucleus

• largest organelle that is visible with a microscope

• enclosed in a double membrane called the nuclear envelope which is perforated with nuclear pores

• the nuclear lamina is inside the nuclear envelope and is a densely fibrous but narrow zone composed of intermediate filaments

• contains nucleoplasm which has chromatin (genetic material) and nucleoli (produce ribosomes)

endoplasmic reticulum

• system of interconnected channels called cisterns enclosed by a membrane

• the rough endoplasmic reticulum is covered in ribosomes and functions to synthesize and fold proteins that are secreted from the cell or packaged in organelles

• the smooth endoplasmic reticulum lacks ribosomes and perform detoxification as well as steroid production and lipid manufacture

ribosomes

• small granules of protein that read messenger RNA and assemble amino acids into proteins specified by the code

golgi complex

• small system of cisterns that synthesize carbohydrates and finish protein and glycoprotein synthesis

lysosomes

• package of enzymes that hydrolyze macromolecules and substrates

peroxisomes

• contain different enzymes that use molecular oxygen to oxidize organic molecules and neutralize free radicals

proteasomes

• hollow cylindrical complexes of proteins that destroy unwanted proteins

mitochondria

• organelles specialized for the synthesis of ATP

centrioles

• short cylindrical assembly of microtubules that contribute to cell division

functions of different membrane proteins

• transmembrane proteins pass completely through the phospholipid bilayer and protrude from it on both sides

• peripheral proteins do not protrude into the phospholipid bilayer but adhere to either the inner and outer face of the membrane

receptor

• binds to chemical messengers and transport them into the cell

• usually specific for one particular messenger

enzyme

• breaks down a chemical messenger and terminates the effects

• carries out final stages of starch and protein digestion

• prevents excessive stimulation of a cell

carrier

• transmembrane protein that binds to solutes and transfers them to the other side of the membrane

• some carriers are pumps as ATP is consumed in the process

ion channel

• constantly open and allows ions to pass into and out of the cell

• passages that allow water and hydrophilic solutes to move through the membrane

• leak channels are always open and allow materials to pass through continually

gated ion channel

• opens and closes to allow ions through only at certain times

• ligand gated channels respond to chemical messengers

• voltage gated channels respond to changes in electrical potential or voltage across a plasma membrane

• mechanically gated channels respond to physical stress on a cell

cell identity marker

• a glycoprotein acting as a cell identity marker that distinguishes the cells of the body from foreign cells

• enables the immune system to tell which cells belong to the body and which are foreign invaders

cell adhesion molecule (CAM)

• binds one cell to another

• cells adhere to one another and to extracellular material

surface extensions of the membrane

microvilli

• extensions of the plasma membrane that primarily serve to increase surface area

• best developed in cells specialized for absorption (eg. simple columnar epithelial cells of the intestines and kidneys)

• can be dense and appear as fringe brush border on the apical cell surface

cilia

• hairlike processes (eg. ciliated pseudostratified columnar epithelia) that primarily serve to propel substances especially mucus

• nonmotile cilia adopt sensory roles

• nonmotile cilia are found in the inner ear, retina of the eye, the kidney, and the plasma membrane

• motile cilia are numerous but less widespread than nonmotile cilia

• motile cilia are found in the respiratory tract, uterine (fallopian) tubes, internal cavities (ventricles) of the brain, and short ducts (efferent ductules) associated with the testes

active versus passive transport

active transport

• mechanisms that consume adenosine triphosphate (ATP) for energy

• include active transport and vesicular transport

• active transport has a slower rate than passive

• active transport is more saturable than passive transport

• primary active transport is the process in which a carrier moves a substance up the concentration gradient using energy from ATP (eg. sodium potassium pump which outputs three sodium ions and intakes two potassium ions upon consumption of one ATP)

passive transport

• mechanisms that do not require adenosine triphosphate (ATP) expenditure by the cell

• include filtration and (simple and facilitated) diffusion as well as osmosis

simple versus facilitated transport

simple (direct) diffusion

• net movement of particles from a place of high concentration to a place of lower concentration as a result of constant and spontaneous motion

• nonpolar and hydrophobic (lipid soluble) substances and gases can diffuse directly through the lipid bilayer of the cell membrane

• the cell cannot control permeability of simple diffusing substances as the limiting factor is the availability of nonpolar surface area

facilitated diffusion (carrier mediated) transport

• diffusion through protein channels or pumps

• carrier mediated transport of a solute down the concentration gradient

• use membrane proteins to transport substances from one side of the membrane to the other

• includes passive facilitated diffusion as well as active transport

• cells control permeability by regulating channel protein abundance (expression) or by opening and closing channels (gating)

• solutes that use this form of transport include water and charged, hydrophilic solutes

• carriers exhibit specificity as transport proteins are specific for a class of certain ligands and the solute binds to a specific receptor site on the carrier protein

• carriers exhibit saturation and as the solute concentration rises the rate of transport increases but only to an extent or the transport maximum (more solute does not increase rate)

transport maximum and saturation

• the transport maximum (saturation point) is the point in which carriers are saturated and excess solute does not increase the rate of transport

• otherwise referred to as the maximum biological diffusion rate

• all carriers and channels or pumps for solute transport are occupied simultaneously and further increases in the concentration gradient to do not increase the rate of transport

• simple diffusion is the least saturable (greatest transport maximum)

• ungated and passive facilitated diffusion is the second saturable

• gated and passive facilitated diffusion is the third saturable

• active transport is the most saturable (lowest transport maximum)

factors affecting the rate of diffusion and transport

1. temperature

• an increase in temperature results in an increase in kinetic energy and an increase in diffusion and transport rate

2. molecular weight

• an increase in size results in a decrease in kinetic energy and a decrease in diffusion and transport rate

• larger molecules move slowly through a medium

3. steepness of concentration gradients

• the greater the difference between the two concentrations the greater the rate of diffusion and transport

4. membrane permeability

• an increase in permeability results in an increase in diffusion and transport rate

• cells can adjust permeability by adding or removing channel proteins and by opening or closing membrane gates

5. membrane surface area

• an increase in surface area makes more membrane available for the diffusion of particles

• in simple diffusion an increase in the lipid bilayer surface area increases the diffusion and transport rate

• in facilitated diffusion an increase in expressed and open channel proteins increases the diffusion and transport rate

types of transporters

• uniport transporters carry only one type of solute

• symport transporters perform cotransport and move two or more solutes through a membrane simultaneously and in the same direction

• antiport transporters perform countertransport and move two or more solutes through a membrane in the opposite direction

secondary active transport

• requires an energy input to move a solute up the concentration gradient

• depends indirectly on adenosine triphosphate (ATP)

• uses energy stored in an electrochemical gradient to move a different molecule against the gradient

• fueled by primary transport

osmosis and tonicity

osmosis

• net flow of water from one side of a selectively permeable membrane to another

• crucial to water distribution or fluid balance in the body

• the usual direction of net movement is from the watery side with a lower solute concentration to the less watery side with a higher solute concentration

• aquaporins are channel proteins specialized for water and can increase the rate of osmosis

• reverse osmosis is a process in which a mechanical pressure applied to one side of the system can override osmotic pressure and drive water through a membrane against the concentration gradient

tonicity

• the ability of.a solution to affect the fluid volume and pressure a cell

• a hypotonic solution has a lower concentration of nonpermeating solutes than the intracellular fluid which causes cells to swell and burst (lyse)

• a hypertonic solution has a higher concentration of nonpermeating solutes than the intracellular fluid which causes cells to lose water and shrivel (crenate)

• an isotonic solution has an equal solute concentration to that of the intracellular fluid which prevents changes. incell volume or shape

bulk transport

vesicular transport

• move large particles and droplets of fluid or numerous molecules at once through the membrane in bubble like vesicles

endocytosis

• vesicles bring matter into a cell

exocytosis

• vesicles release matter from the cell

phagocytosis

• referred to as cell eating

• process of engulfing particles such as bacteria and dust and cellular debris

• vesicles are called phagosomes

pinocytosis

• referred to as cell drinking

• process of taking in droplets of extracellular fluid containing molecules of some use to the cell

• vesicles are called pinocytotic vesicles

receptor mediated endocytosis

• more selective form of phagocytosis or pinocytosis

• enables a cell to take in specific molecules from the extracellular fluid with a minimum of unnecessary matter

• particles in the extracellular fluid bind to specific receptors on the plasma membrane

• the receptors cluster and the membrane sinks in to create a pit coated with a peripheral membrane protein called clathrin

• the pit pinches off to form a clathrin coated vesicle in the cytoplasm

• clathrin serves as an address label on the coated vesicle that directs it to an appropriate destination in the cell and informs other structures in the cell what to do with the vesicle

receptor mediated exocytosis

• process of discharging material from a cell

• a secretory vesicle in the cell migrates to the surface and docks on the peripheral proteins of the plasma membrane

• these proteins pull the membrane inward and create a dimple that eventually fuses with the vesicle and allows it to release the contents

transcytosis

• material is capture on one side of the cell and released on the other

diffusion by filtration through a tissue membrane

• passive movement of smaller and dissolved particles across the tissue layers by physiological forces or physical pressure in a selectively permeable fashion

• examples include the filtration of nutrients through gaps in the blood capillary walls and the filtration of wastes from the blood in the kidneys while holding back blood cells and large proteins

• typically occurs in a simple squamous tissue

hierarchy of life

atoms (smallest unit of life; small particles with unique chemical identities)

molecules

macromolecules

organelles (microscopic structures of a cell that carry out individual functions)

cells (smallest units that carry out all basic functions of life)

tissues (masses of similar cells and cell products that form a discrete region of an organ and performs a specific function)

organs (structures composed of two or more tissue types that work together to carry out a particular function)

organ systems (group of organs with unique collective functions)

organisms (most complex; single and complete individual)

homeostasis

• homeostasis refers to the ability to maintain internal stability

• involves the physiological ability to detect change and activate mechanisms that oppose it to maintain relatively stable internal conditions

• the state of the body fluctuates (dynamic equilibrium) within a limited range around a set point

negative feedback

• negates and reverse change to keep variable close to set point

• maintains or restores steady state

• activate mechanisms to reverse or mitigate change

• receptor cells respond to a stimulus and the integrating or control center makes decision on how to respond to the stimulus

• the effector organ is activated and restores conditions to the set point

example - brain regulation of body temperature

• if too warm the blood vessels dilate (vasodilation) in the skin and sweating begins (heat losing mechanism)

• if too cold the blood vessels constrict (vasoconstriction) and shivering begins (heat gaining mechanism)

positive feedback

• repeated feedback loop in which change produces more of the change until the stimulus goes away

• disrupt steady state or alter the set point

• produces rapid changes in appropriately healthy situations (eg. childbirth; blood clotting; fever)

• opposes the inertial qualities of homeostasis

example - childbirth

• fetal propulsion to the cervix stimulates nerve endings

• stimulated nerves trigger release of oxytocin

• oxytocin stimulates stronger uterine contraction to propel fetus towards the birth canal

• increases stimulation of cervical nerve endings

• increases surge of oxytocin causing the positive feedback loop to be repeated until child is born

example - blood clotting

• platelets adhere to injured area

• activated platelets release chemicals that activate and attract more platelets

• initiates cascade of enzymatic reactions to form a clot

• clot forms and seals the wound

• releases more chemicals that further activate platelets and enhance the clotting process

gradients and flow

• a gradient is a difference in chemical concentration, electrical charge, physical pressure, temperature, or another variable between one point and another

• if matter moves from a high to low point it flows down the gradient

• if matter moves from a low to high point it flows up the gradient

• chemicals flow down concentration gradients

• charged particles flow down electrical gradients

• ions governed by a combination of concentration and electrical charge flow down electrochemical gradients

• heat flows down a thermal gradient