Chapter 07: Bone Tissue and Its Functions

What is the living skeleton made of?

Dynamic tissues and cells are permeated with nerves and blood vessels. It continuously remodels itself and interacts with other organ systems.

What is the study of bone known as?

Osteology

What are some unique features of the bone?

It is vascular and stores all minerals in bone; if the bone does not work, the organs will not work properly—stress on bone= more dense bone.

Skeletal system

Composed of bones, cartilages, and ligaments.

What does cartilage do?

Forerunner of most bones, covers joint surfaces. Body starts off cartilage, then Calcium and Phosphate harden it

CHONDRO= CARTILAGE asvascular

What do ligaments do?

Connective tissues that hold bones together.

What do Tendons do?

Attach muscles to bones for movement.

What are the 6 functions of the skeleton

Support

Protection

Movement

Electrolyte balance

Acid- base balance

Blood formation

"Strong People Move Every Active Bone."

How does the skeleton provide SUPPORT the body?

Limb bones and vertebrae support body, jaw bones, support teeth, some bones support viscera.

How does the skeleton provide PROTECTION for the body?

•Protects the brain, spinal cord, heart, lungs, and more

How does the skeleton provide MOVEMENT the body?

limb movements, breathing, and other movements depend on bone

How does the skeleton provide ELECTROLYTE BALANCE for the body?

Regulates calcium and phosphate levels

How does the skeleton provide ACID-BASE BALANCE for the body?

Buffers blood pH via phosphate and carbonate.

How does the skeleton provide BLOOD FORMATION for the body?

Red bone marrow produces blood cells.

What are some extra information about the functions of the skeleton?

Calcium activates nuerons

Long bones mainly have red bone marrow

Parathyroid gland - cant regulate calcium without it ->die

Red marrow growing

yellow marrow puberty

What is Bone (Osseous tissue)?

Connective tissue with matrix hardened by calcium phosphate.

What is Mineralization/Calcification?

Process of hardening bone tissue.

Extra notes about bones and Osseous tissue?

Infant =less bone more cartilage, highest cartilage = growth

more flexible to come out of womb

What are Flat bones? Examples ?

Thin, curved plates protecting soft organs.

-Ex. roof of the skull, the sternum (breastbone), the ribs, and scapulae (shoulder blades)

What are Long bones? Examples?

Longer than wide, crucial for movement. ; Rigid levers acted upon by muscles

-Located in the arm and forearm, thigh and leg, palms, soles, fingers, and toes

What are Short bones? Examples?

Equal length and width, allow gliding movements. -Glide across one another in multiple directions

-Ex. the carpal bones (wrists) and tarsal bones (ankles)

What are Irregular bones? Examples?

Complex shapes, do not fit other categories.

-Ex. vertebrae that form the spinal column, the bones of the pelvis, and several bones in the skull

What are Sutural bones? Examples?

Small, flat bones between skull flat bones. (joints)

What are Sesamoid bones? Examples?

Small, round bones developed inside tendons.

Patella

What are Dynamic tissues

Living tissues that interact with organ systems.

What is Compact bone

Dense outer shell providing strength.

What is Spongy bone

Loosely organized bone tissue, lighter.

-Found in center of ends and center of shafts of long bones and in middle of nearly all others

-Covered by more durable compact bone

What are long bone features?

-Diaphysis — shaft that provides leverage

•Medullary cavity (marrow cavity)—space in the diaphysis of a long bone that contains bone marrow

-Epiphyses — enlarged ends of a long bone

•Strengthen joint and anchor ligaments and tendons

Extra info about General features of Bones?

Spongy bone= a lot of red marrow

skeleton = 3/4 compact 1/4spongy bone

compact= does not break easily

What is the Articular cartilage

layer of hyaline cartilage that covers the joint surface; allows joint to move more freely, friction-free

EX.N=

articulation= touch

damage to cartilage= arthritis

No articular cartilage in head bc don't want brain moving

hyaline cartilage = take abuse

What is the Nutrient foramina

Minute holes allowing blood vessel penetration.

EX. N.=

foramina=holes, deliver nutrients break down nutrient to put in bloodstream

What is the Periosteum

external sheath covering most of bone

-Outer fibrous layer of collagen

•Some fibers continuous with tendons

•Perforating (Sharpey) fibers — outer fibers penetrate into bone matrix

-Inner osteogenic layer of bone-forming cells

•Important to bone growth and healing of fractures

Extra notes: damage = slowed growth

What is the Endosteum?

Thin layer of reticular connective tissue lining marrow cavity

-Has cells that dissolve osseous tissue and others that deposit it

Epiphyseal plate

Area of hyaline cartilage that separates epiphyses and diaphyses of children's bones

-Enables growth in length

-Epiphyseal line — in adults, a bony scar that marks where the growth plate used to be

Extra Notes : You can grow bc of chondrocyte

bone growth via hyaline cartilage

Ca + phosphate harden= done growing.

Features of long bone

Epiphyses and diaphysis

Compact and Spongy

Marrow cavity

Articular Cartilage

Periosteum

General features of Flat bone?

-Sandwich-like construction

Two layers of compact bone enclosing a middle layer of spongy bone

Both surfaces covered with periosteum

Diploe — spongy middle layer

•Absorbs shock

Marrow spaces lined with endosteum

What are the four principal types of bone cells?

Osteogenic cells- bone stem cell

Osteoblasts- building

Osteocytes- Mature bone cell=solidify= calcium + phosphate--> remodels based on needs

Osteoclasts- bone dissolving cells

What are osteogenic cells and function?

stem cells found in endosteum and inner layer of periosteum

-Arise from embryonic mesenchyme

Multiply continuously and give rise to most other bone cell types

What are Osteoblasts

Bone building cells

-Form single layer of cells under endosteum and periosteum

-Nonmitotic (no mitosis)

-Synthesize soft organic matter of matrix which then hardens by mineral deposition

-Stress stimulates osteogenic cells to multiply rapidly and increase the number of osteoblasts which reinforce bone

-Secrete hormone osteocalcin

•Stimulates insulin secretion of pancreas

•Increases insulin sensitivity in adipocytes which limits the growth of adipose tissue

EX.N=

stressing body through HIIT--> Ca+ Phosphate deposited --> prevent osteoporosis

What are Osteocytes

former osteoblasts that have become trapped in the matrix they deposited

-Lacunae — tiny cavities where osteocytes reside

-Canaliculi — little channels that connect lacunae

-Cytoplasmic processes of osteocytes reach into canaliculi and contact processes of neighboring cells

•Gap junctions allow for passage of nutrients, wastes, signals

-Some osteocytes reabsorb bone matrix while others deposit it

-Contribute to homeostatic mechanism of bone density and calcium and phosphate ions

-Act as strain sensors — when stressed, produce biochemical signals that regulate bone remodeling (shape and density changes that are adaptive) EX: bump on head bc of phone (evolution)

What are Osteoclasts?

bone-dissolving cells found on bone surface

-Osteoclasts develop from same bone marrow stem cells that give rise to blood cells (different origin from other bone cells)

-Very large cells formed from fusion of several stem cells

•Have multiple nuclei in each cell (3-4 nuclei, up to 50)

-Ruffled border (large surface area) faces bone - Several deep infoldings of the plasma membrane which increases surface area and resorption efficiency

-Cells often reside in resorption bays (pits in bone surface)

-Dissolving bone is part of bone remodeling

What is the Matrix of osseous tissue and function?

dry weight, about one-third organic and two-thirds inorganic matter

•Organic matter — synthesized by osteoblasts

-Collagen, carbohydrate - protein complexes, such as glycosaminoglycans, proteoglycans, and glycoproteins

•Inorganic matter

-85% hydroxyapatite (crystallized calcium phosphate salt)

-10% calcium carbonate

-Other minerals (fluoride, sodium, potassium, magnesium)

What makes bone a composite material?

a combination of a ceramic and a polymer

-Hydroxyapatite and other minerals are the ceramic and collagen (protein) is the polymer

-Ceramic portion allows the bone to support body weight without sagging

-Polymer (protein) gives some flexibility

What is rickets?

disease caused by mineral deficiency and resulting in soft, deformed bones (malleable bones)

Osteogenesis imperfecta

Brittle bone disease due to collagen defect.

What are Osteons?

Haversian systems in compact bone structure.

what are Perforating canals

Transverse passages connecting central canals.

what are circumferential lamellae?

fill outer region of dense bone

What are interstitial lamellae?

fill irregular regions between osteons

What does spongy bone consist of?

-Lattice of bone covered with endosteum

•Slivers of bone called spicules

•Thin plates of bone called trabeculae

-Spaces filled with red bone marrow

•Few osteons and no central canals

-All osteocytes are close to bone marrow

•Provides strength with minimal weight

Trabeculae

develop along bone's lines of stress

Gives strength in endosteum

what is Bone marrow?

soft tissue occupying marrow cavities of long bones and small spaces (trabeculae) of spongy bone

Red marrow (myeloid tissue)

-Contains hemopoietic tissue—produces blood cells

-In nearly every bone in a child

-In adults, found in skull, vertebrae, ribs, sternum, part of pelvic girdle, and proximal heads of humerus and femur

Yellow marrow found in adults

-Most red marrow turns into fatty yellow marrow

-Fatty marrow that does not produce blood

Can transform back to red marrow in the event of chronic anemia

Ex N-

children reb bone marrow --> more blood--> more o2 ---> more energy

anemic conditions can turn yellow back to red.

What is ossification or osteogenesis

Formation of bone

What are the two methods that bone develops in human fetus and infants?

-Intramembranous ossification

•Produces flat bones of skull and clavicle in fetus

•Thickens long bones throughout life

-Endochondral ossification

What are the 4 steps of intermembranous ossification

1)Deposition of osteoid tissue into embryonic mesenchyme

2)Calcification of osteoid tissue and entrapment of osteocytes

3)Honeycomb of spongy bone with developing periosteum

4)Filling of space to form compact bone at surfaces, leaving spongy bone in middle

Dogs Can Have Fun

What is Endochondral ossification?

During infancy and childhood, the epiphyses fill with spongy bone

•Cartilage is limited to the articular cartilage covering each joint surface and to the epiphyseal plate

-A thin wall of cartilage separating the primary and secondary marrow cavities

-Epiphyseal plate persists through childhood and adolescence

-Serves as a growth zone for bone elongation

By late teens to early 20s, all remaining cartilage in the epiphyseal plate is generally consumed

-Gap between epiphyses and diaphysis closes (metaphysis - epiphyseal line)

-Primary and secondary marrow cavities unite into a single cavity

-Bone can no longer grow in length

EX. N

line = done growing

gap= growth opportunities

chondrocytes= bone growth

What does ossification continue to do throughout life?

growth and remodeling of bones

length and width

What are the zones of the Metaphysis (5)

The region between diaphysis and epiphysis in growing bones.

1)Zone of reserve cartilage Typical histology of resting hyaline cartilage

(RESTING)

2)Zone of cell proliferation Chondrocytes multiplying and lining up in rows of small flattened lacunae

MORE OF ITS MULTIPLY CHONDROCYTES

3)Zone of cell hypertrophy Cessation of mitosis; enlargement of chondrocytes and thinning of lacuna walls

(GROW IN SIZE)

4)Zone of calcification Temporary calcification of cartilage matrix between columns of lacunae

(SOLIDIFYING)

5)Zone of bone deposition Breakdown of lacuna walls, leaving open channels; death of chondrocytes; bone deposition by osteoblasts, forming trabeculae of spongy bone

( MATURE BONE)

What is appositional growth ?

occurs at bone surface

-Continual growth in diameter and thickness

-Intramembranous ossification

-Osteoblasts of inner periosteum deposit osteoid tissue

•Become trapped as tissue calcifies

-Lay down matrix in layers parallel to surface

•Forms circumferential lamellae

•Osteoclasts of endosteum enlarge marrow cavity

With bone enlongation what happens to the Epiphyseal plate?

cartilage transitions to bone

-Functions as growth zone where bone elongates

-Has typical hyaline cartilage in the middle with transition zones on each side where cartilage is replaced by bone

What is Interstitial Growth

Growth from within the epiphyseal plate.

-Bone elongation is a result of cartilage growth within the epiphyseal plate

Epiphyses close when cartilage is gone — epiphyseal line of spongy bone marks site of former epiphyseal plate

•Lengthwise growth is finished

•Occurs at different ages in different bones

Ex.N

Toddler=megamind to protect the brain

what happens with Bone Remodeling

Absorption and deposition throughout life.

-Repairs microfractures, releases minerals into blood, reshapes bones in response to use and disuse

•Remodeling is a collaborative and precise action of osteoblasts and osteoclasts

•Bony processes grow larger in response to mechanical stress

what is Wolff's Law

Bone architecture determined by mechanical stresses.

osteoclasts breaks to allow shifting (braces)

what is Dwarfism, and the 2 types?

Abnormal short stature due to growth issues.

Achondroplastic Dwarfism

Pituitary Dwarfism

what is Achondroplastic Dwarfism

Long bones stop growing; normal torso.

•Normal torso, short limbs

-Failure of cartilage growth in metaphysis

-Spontaneous mutation produces mutant dominant allele

Pituitary Dwarfism

Lack of growth hormone; normal proportions with short

stature

what is the physiology of osseous tissue?

A mature bone remains a metabolically active organ

-Involved in its own maintenance of growth and remodeling

-Exerts a profound influence over the rest of the body by exchanging minerals with tissue fluid

What happens if there is a disturbance of calcium homeostasis in the skeleton?

• disrupts function of other organ systems

-Especially nervous and muscular

What is Mineral deposition (mineralization)?

process in which calcium, phosphate, and other ions are taken from blood and deposited in bone

-Osteoblasts produce collagen fibers that spiral the length of the osteon

-Fibers become encrusted with minerals that harden the matrix

•Hydroxyapatite crystals form at solubility product — critical level of calcium times phosphate concentration

•First few crystals act as seed crystals that attract more calcium and phosphate from solution

What is Abnormal calcification (ectopic ossification)?

formation of a calculus (calcified mass) in another soft organ such as a lung, brain, eye, muscle, tendon, or

artery (arteriosclerosis)

caused by injury usually

EX.N

elastic cartilage hardens- cauliflower ear

ateriosclerosis= less blood flow , stretched more than usual, calcium+phospahte to fill tear= plaque, can lead to death.

lung solidifying= cant get o2--> no energy= death.

What is Mineral resorption

process of dissolving bone and releasing minerals into blood

-Performed by osteoclasts at ruffled border

-Hydrogen pumps in membranes secrete hydrogen into space between osteoclast and bone surface

-Chloride ions follow by electrical attraction

-Hydrochloric acid (pH 4) dissolves bone minerals

-Acid protease enzyme digests collagen

ex.N braces = -Tooth moves because osteoclasts dissolve bone ahead of tooth; osteoblasts deposit bone behind the tooth

Why is calcium homeostasis important?

•Calcium and phosphate are used for much more than bone structure

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

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

•Minerals are deposited in the skeleton and withdrawn when they are needed for other purposes

•Total of about 1,100 g of calcium in adult body with 99% of it in bones

-Most exists as part of hydroxyapatite, but a little is in a form that is easily exchanged with the blood

-About 18% of skeletal calcium is exchanged with blood each year

•Normal calcium concentration in blood plasma is 9.2 to 10.4 mg/dL

-45% as Ca^(2+) that can diffuse across capillary walls and affect other tissues

-Rest in reserve, bound to plasma proteins

What is Hypocalcemia?

Deficient calcium levels causing nervous system excitability.

-Changes membrane potentials and causes overly excitable nervous system and tetany (muscle spasms)

•Laryngospasm can cause suffocation

-Caused by vitamin D deficiency, diarrhea, thyroid tumors, underactive parathyroid glands

-Pregnancy and lactation increase risk of hypocalcemia

-Accidental removal of parathyroid glands during thyroid surgery ( losing parathyroid gland = cant regulate calcium level--> death)

Ex. N

can't absorb calcium without vitamin D

What is Hypercalcemia?

Excessive calcium levels leading to reduced nerve excitability.

-Makes ion channels less responsive and thus nerve and muscle are less excitable

•Can cause emotional disturbance, muscle weakness, sluggish reflexes, cardiac arrest

-Hypercalcemia rarely occurs

What things does calcium homeostasis depend on?

Dietary intake

uniary and fecal losses

exchanges between osseous tissue

What three hormones regulate calcium homeostasis?

-Calcitriol, calcitonin, and parathyroid hormone

What is Calcitriol

Hormone that raises blood calcium levels.

•most active form of vitamin D

•Produced by actions of skin, liver, and kidneys

-Epidermal keratinocytes use UV radiation to convert

7-dehydrocholesterol to previtamin D_3; warm sun on skin converts this to vitamin D_3

-Liver adds hydroxyl group converting that to calcidiol

-Kidney adds hydroxyl group converting that to calcitriol

it increases calcium absorption by small intestine

-It also increases calcium resorption from the skeleton

•Stimulates osteoblasts to release RANKL, a chemical that stimulates production of more osteoclasts

-It weakly promotes kidney reabsorption of calcium ions, so less lost in urine

-Calcitriol is also necessary for bone deposition—helping provide adequate calcium and phosphate

-Inadequate calcitriol results in abnormal softness of bones in children (rickets) and in adults (osteomalacia)

What does calcitriol synthesis and action look like

Skin --> blood-->liver add OH di ---> Kidney add another OH ---> tri---> absorb calcium.

What is Calcitonin?

Hormone lowering blood calcium by inhibiting osteoclasts.

— secreted by C cells (clear cells) of thyroid gland when blood calcium levels rise too high

•Lowers blood calcium concentration in two ways:

-Inhibits osteoclasts thereby reducing bone resorption

-Stimulates osteoblasts to deposit calcium into bone

•Important in children, weak effect in adults

-Osteoclasts more active in children due to faster remodeling

May inhibit bone loss in pregnant and lactating women

What is Parathyroid Hormone (PTH)

•secreted by parathyroid glands on posterior surface of thyroid

•PTH released when calcium levels low in blood

PTH raises calcium blood level by four mechanisms

-Stimulates osteoblasts to secrete RANKL, thereby increasing osteoclast population and bone resorption

-Promotes calcium reabsorption by kidneys, so less lost in urine

-Promotes the final step of calcitriol synthesis in the kidneys, enhancing calcium-raising effect of calcitriol

-Inhibits collagen synthesis by osteoblasts, inhibiting bone deposition

Negative Feedback Loop

Mechanism correcting calcium level imbalances. for both hypecalcemia and hypocalcemia

Why is phosphate homeostasis important ?

•Average adult has 500 to 800 g phosphorus with 85% to 90% of it in the bones

•Normal plasma concentration is 3.5 to 4.0 mg/dL

•Occurs in two main forms

-HPO_4^(2-) and 〖H_2 PO〗_4^- (monohydrogen and dihydrogen phosphate ions)

•Phosphate levels are not regulated as tightly as calcium levels

•Calcitriol raises phosphate levels by promoting its absorption by small intestine

•PTH lowers blood phosphate levels by promoting its urinary excretion

What other factors affect Bone Growth?

Hormones and vitamins influencing bone development.

•Bone growth especially rapid in puberty and adolescence

-Surges of growth hormone, estrogen, and testosterone occur and promote ossification

-These hormones stimulate multiplication of osteogenic cells, matrix deposition by osteoblasts, and chondrocyte

multiplication and hypertrophy in metaphyses

EX.N

estrogen =more growth

Extra Notes abt bone growth

Bone growth especially rapid in puberty and adolescence (Continued)

-Girls grow faster than boys and reach full height earlier

•Estrogen has stronger effect than testosterone on bone

growth

-Males grow for a longer time and also taller

•Anabolic steroids cause growth to stop

-Epiphyseal plate "closes" prematurely

-Results in abnormally short adult stature

what is orthopedics?

branch of medicine dealing with prevention and correction of injuries and disorders of bones, joints, and muscles

•Includes the design of artificial joints and limbs and the treatment of athletic injuries

what is a Fracture?

Breaks in bone due to stress or trauma.

what is a pathological fracture?

break in a bone weakened by disease (such as bone cancer or osteoporosis)

-Usually caused by a stress that would not break a healthy bone

What are the classifications of fractures based on structural characteristics 3

-Direction of fracture line

-Break in the skin

-Multiple pieces

•Example: comminuted—three or more pieces

What are the 9 major factures types

•Transverse fractures

•Displaced fractures

•Compression fractures

•Spiral fractures

•Epiphyseal fractures

•Comminuted fractures

•Greenstick fractures

•Colles fractures

•Pott's fractures

"The Doctor Can Spot Every Crack, Gap, Chip, Problem."

what ate the general categories of fractures?

Closed or simple

•Completely internal (no break in skin)

•Only seen on x-rays

Open or compound

Project through the skin

•More dangerous due to:

•Infection

•Uncontrolled bleeding

What is a transverse fractures ?

•Break shaft across long axis

What is a Spiral fractures

•Produced by twisting stresses

Spread along length of bone

What is a Displaced fracture

•Produce new and abnormal bone arrangements

•Nondisplaced fractures retain normal alignment

what is a Compression fracture

Occurs in vertebrae under extreme stress.

Often associated with osteoporosis

What is a Greenstick fracture

One side broken, one side bent; common in children.

•Long bones have yet to fully ossify

What is a Comminuted fractures

Shatter affected area producing fragments

What is a Epiphyseal fracture

•Occur where bone matrix is calcifying

•A clean transverse fracture of this type heals well

•If not monitored, breaks between epiphyseal plate and cartilage can stop growth at site

Fix quickly*

What is a Pott's fracture

Bimalleolar fracture at the ankle.

•Occurs at ankle and affects both medial malleolus and lateral malleolus

What is a Colles fracture

Break in the distal radius.

What is the healing process of fractures

1)The Hematoma formation

hematoma is converted to granulation tissue by invasion of cells and blood capillaries.

2)Soft callus formation

Deposition of collagen and fibrocartilage converts granulation tissue to a soft callus.

3)Hard callus formation-

Osteoblasts deposit a temporary bony collar around the fracture to unite the broken pieces while ossification occurs.

4)Bone remodeling-

Small bone fragments are removed by osteoclasts, while osteoblasts deposit spongy bone and then convert it to compact bone.

bone wont break in same spot