BSCI201: LEx2

Goytia

The epidermis is composed of what?

keratinized stratified squamous epithelium

What are the five strata (deep to superficial) of the epidermis?

stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and stratum corneum

What mnemonic is this? “Come Let’s Get Sun Burned”

Corneum, Lucidum, Granulosum, Spinosum, Basale

What is the prickly appearance of cells in the stratum spinosum is due to strong intercellular attachments provided by?

desmosomes

Keratinocytes

Produces keratin and is the precursor for vitamin D. Function is protection and waterproofing skin.

Melanocytes

Produces melanin. Found in the keratinocytes in the stratum spinosum to protect mitotic basal stem cells from UV rays

Dendritic cells (Langerhans cells)

provide immune surveillance in the epidermis through phagocytes

Merkel cells (Tactile cells)

sensory receptors located in the stratum basale and linked to sensory nerve fibers

What is the dermis composed of?

Fibrous CT

What layers are found in the Dermis?

Papillary layer and Reticular layer

Papillary layer

Composed of areolar CT, contains capillaries, sensory receptors like Tactile corpuscles and free nerve endings

Reticular layer

Composed of Dense Irregular CT, provides strength (collagen fibers) and stretch-recoil properties (elastic fibers). Contains pacinian (lamellar) corpuscles (vibration/pressure sensation)

Pacinian (lamellar) corpuscles

These sensory receptors for pressure and vibration are located in the reticular layer of the dermis, not the epidermis

What is the hypodermis composed of?

adipose tissue

Merocrine secretion

Products are secreted by exocytosis, substances released by cell

What are glands that are merocrine?

eccrine sweat glands and apocrine sweat glands

Holocrine secretion

Products secreted by rupture of the entire gland cell

What gland is of holocrine secretion?

Sebaceous glands

What are the sweat (sudoriferous) glands?

eccrine glands, apocrine glands, sebaceous (oil) glands

Eccrine glands

Uses merocrine secretion via duct to the skin surface. Used for thermoregulation

Apocrine glands

Uses merocrine secretion via duct to the hair follicle. Found in axilla and groin.

What are some modified apocrine glands?

ceruminous glands (ear wax) and mammary glands (milk)

Sebaceous glands

Uses holocrine secretion, producing an oily substance (sebum) that lubricates skin and hair - not associated with thermoregulation

Hair

The cells of the hair matrix, which undergo cell division, come from the epidermal stratum basale

Healing involves what?

regeneration and fibrosis

What is regeneration?

replacement of original tissue

What is fibrosis?

Formation of scar tissue, typical in the dermis

What is the first type of tissue to fill a large gap during healing?

granulation tissue (new CT and blood vessels)

Where does scar tissue result from?

Fibrosis, where fibroblasts proliferate and deposit collagen fibers. Scar tissue has decreased elasticity and fewer blood vessels.

First degree burn

Only epidermis is damaged, characterized by localized redness, edema, and pain

Superficial Second degree burn

Damage to the epidermis and superficial dermis. Characterized by blisters and extreme pain. Adnexa (Hair follicles and glands) remain and healing usually occurs by re-epithelialization with no scar.

Deep Second degree burn

Damage to deeper dermis. Less moist and pain. Heal by scar deposition, contraction, and limited re-epithelialization.

Third degree burn

Damage to the entire thickness of the skin. Permanent loss of adnexa. Often less painful because nerve endings are destroyed. Requires skin grafting.

When are burns critical?

Over 25% of the body has second degree burns, over 10% of the body has third degree burns, or the third degree burns are on the face, genitalia, hands, or feet.

Fill in the blanks

Osteogenic cells (Mesenchymal Stem Cells)

differentiate into osteoblasts

Osteoblasts

deposits osteoid (organic matrix) and produce the hormone Osteocalcin

Osteocytes

Mature bone cells trapped in lacunae. Communicates with each other via gap junctions through extensions that travel in canaliculi

Osteoclasts

resorb (break down) bone matrix by secreting lysosomal enzymes and acid

Compact bone is organized into repeating structural units called what?

Osteons

Osteons consist of what?

Lamellae surrounding a central (haversian) canal containing blood vessels and nerves.

Adjacent osteons connect via what?

Perforating (volkmann’s) canals

Compact bones has high or low porosity?

low porosity

Spongy bone is composed of what?

taberculae

Spongy bone lacks what?

Osteons, central canals, and perforating canals

Spongy bones has high or low porosity?

high porosity

Hematopoiesis (blood cell formation)

occurs in the red bone marrow, which is found in the spongy bone throughout life

Intramembranous ossification

forms bone from fibrous membranes, forming flat bones

Endochondral ossification

forms bone by replacing a hyaline cartilage, forming all long bones, short bones, and irregular bones

Longitudinal Growth

Increases in length, occurs at the epiphyseal plate (metaphysis) throughout endochondral processes

What are the 4 zones of the epiphyseal plate?

Proliferation Zone, Hypertrophic Zone, Calcification Zone, and Ossification Zone

Proliferation Zone

Chondroblasts divide via mitosis (hyperplasia), pushing the epiphysis away from the diaphysis

Hypertrophic Zone

Older chondrocytes enlarge (hypertrophy)

Calcification Zone

Cartilage matrix calcifies, and chondrocytes die

Ossification Zone

Calcified cartilage is replaced by bone tissue, forming spongy bone

Appositional Growth

Increase in width/diameter, occurs in all bones. Involves addition of external bone layers by osteoblasts in the periosteum and the resorption of internal layers by osteoclasts in the endosteum

What are the hormones that help regulate bone growth?

Growth Hormone (GH), Thyroid hormone, Testosterone, and Estrogen

What does growth hormone and thyroid hormone do for bone growth?

stimulate epiphyseal plate activity

What does testosterone and estrogen do for bone growth?

promote osteoblast activity, inhibit osteoclast activity, promote calcification, and ultimately induce epiphyseal plate closure

What does menopause/estrogen cause for the bone?

Loss of estrogen in early menopause leads to the lifting of osteoclast inhibition, resulting in increased osteoclast activity and subsequent bone resorption, leading to bone mass reduction (osteoporosis). Woman likely to show hypocalcemia

Parathyroid hormone (PTH)

Released during hypocalcemia (low blood Ca2+). Promotes bone resorption (activates osteoclasts), increases Ca2+ reabsorption in the kidneys and stimulates calcitriol synthesis. Reduces calcium loss in urine

Calcitriol (active vitamin D3)

Expressed during hypocalcemia. Essential for Ca2+ homeostasis as it increases Ca2+ absorption in the gut (small intestine), increases Ca2+ reabsorption from kidneys and activates osteoclasts to resorb bone

Calcitonin

Expressed during hypercalcemia. Decreases osteoclast activity, promoting bone deposition

Osteomalacia

“bending” bones, softening of the bone is caused by decreased mineralization of the osteoid matrix

What is the purpose bone remodeling?

maintain Ca2+ homeostasis and adapt bone structure too mechanical stress

Wolff’s law

states that bone tissue adapts its structure and shape in response to the mechanical stresses placed upon it

Where do bones become thicker at?

attachment sites for active skeletal muscles

Lack of mechanical stress leads to what?

rapid loss of bone density (resorption exceeds deposition)

What are the stages of bone healing?

Hematoma forms, fibrocartilaginous callus forms, bony callus formation, bone remodeling

Hematoma forms

Torn vessels hemorrhages, and a clot forms

Fibrocartilaginous callus forms

fibroblasts secrete collagen and chondroblasts produce fibrocartilage to “glue” the sections (internal callus)

Boney callus formation

Osteoprogenitor cells differentiate into osteoblasts to produce new spongy bone (hard callus)

Bone remodeling

The bony callus is remodeled in response to mechanical stressors; compact bone replaces spongy bone, and the final structure resembles the original

What are the functional classifications for joints?

Synarthroses, Amphiarthroses, and Diarthroses

Synarthroses

Immovable joints, Synostoses (fused bone) are considered synarthrotic joints

Ampiarthroses

Slightly movable joints

Diarthroses

Freely movable joints

What are the structural classifications?

Fibrous joints, Cartilaginous joints, and Synovial joints

Fibrous joints

Bones united by fibrous CT

Cartilaginous joints

Bones united by cartilage, lacking a joint cavity

Synovial joints

Possess a joint cavity

Articular Cartilage

Hyaline cartilage covering the articulating surfaces of the bones.

Joint Cavity

Contains synovial fluid, which acts as a lubricant (reduces friction), provides nutrients to the cartilage, and absorbs shock (due to hyaluronic acid).

Articular Capsule

Double-layered structure forming the boundary of the synovial joint. It consists of an outer fibrous capsule and an inner synovial membrane which produces the synovial fluid

Ligament

A strong band of fibrous connective tissue (dense regular CT) that holds bones together

Tendon

Attaches muscle to bone; made of dense regular connective tissue

Bursa

A flattened, fibrous sac containing synovial fluid that prevents friction between skin/bone, or tendon/bone. Made of dense regular connective tissue

Sheath

An elongated bursa that wraps around a tendon

Plane Joint

Nonaxial, allows gliding, ie. intercarpals

Hinge Joint

Uniaxial, allows flexion/extension, ie. elbow, knee

Pivot Joint

Uniaxial, allows rotation, ie. Radioulnar joint, atlanto-axial joint (allows us to move head side to side, motion NO)

Condyloid Joint

Biaxial, allows flexion/extension, ab/adduction, circumduction, ie. knuckes

Saddle Joint

Biaxial, allows opposition, ie. thumb

Ball-and-socket Joint

multiaxial, allows flexion/extension, ab/adduction, rotation, circumduction, ie. shoulder, hip

Flexion

Decreases the angle of the joint

Extension

Increases the angle of the joint

Hyperextension

Excessive extension beyond the normal range of motion

ABduction

Movement away from the midline

ADduction

Movement toward the midline

Circumduction

Describes a cone in space (combination of F/E, Ab/Adduction)