Anatomy and Phisology Exam 2 Chapters 5 and 6

List the three main layers of the integumentary system from superficial to deep ( Compare and contrast the dermis, epidermis, and hypodermis in terms of function, vascularity, innervation, and tissue type)

1. Epidermis - outermost protective shield of the body, a vascular no blood vessels, consist of mostly stratified squamous epithelial

2. Dermis- underlies the epidermis and makes the bulk of the skin, support, mostly dense connective tissue, vascular

3. Hypodermis - loosely anchors skin to underlying structures, mostly muscle, shock absorption and instillation, mostly adipose tissue with some areolar connective tissue, vascular

List and describe the function of each of the 4 cell types of the epidermis

Keratinocytes

– Produce keratin (protein that makes skin protective)

Melanocytes

– Produce pigment melanin, which is packaged into

melanin protects cell nucleus from UV damage

Dendritic cells, or Langerhans cells

– Ingest foreign substances (phagocytosis) and are key

activators of immune system

Tactile epithelial cells, or Merkel cells

– Sensory receptors for touch located at epidermal-

dermal junction

List the five strata of the epidermis from superficial to deep

o Compare and contrast these layers in terms of type of cells involved, number of layers of

cells, and function

Five layers (strata) of the epidermis

5. Stratum corneum (most superficial)- 20–30 rows of flat, anucleated, keratinized dead cells, Protect deeper cells from the environment, water loss, abrasion and penetration , Act as a barrier against biological, chemical, and physical assaults

4. Stratum lucidum (only in thick skin) of thin, translucent band of two to three rows of clear, flat, dead keratinocytes, extra protection

3. Stratum granulosum - cells are flattened, so layer is thin, Keratinization begins, 4-6 layers of cells,

2. Stratum spinosum- Scattered among keratinocytes are abundant melanosomes and dendritic cells, also called prickle cells, 8-10 layers, strength, flexibility, and immune defense

1. Stratum basale (deepest) - Single row of stem cells that divide (mitotic), produces new skin cells, pigmentation, and touch sensation

CHARILE LOVES GRANDMAS SOFT BROWNIES

Compare and contrast thick and thin skin in terms of strata, location on the body, and presnece of

hair and sebaceous glands

Thick skin contains all five layers (including stratum

lucidum) Located on palms, fingertips, and soles, no hair and no sebaceous glands

Thin skin- contains only four layers (no stratum

lucidum) everywhere but where thick skin is, has hair and sebaceous glands

Compare and contrast the papillary dermis and reticular dermis in terms of which is more

superficial or deep, what tissue type is involved, and what receptors are involved

BOTH LAYERS OF DERMIS

papillary dermiS- the thin, superficial layer of areolar Connective tissue, taticle corpuscle’s, detects light touch

reticular dermis- makes up ~80% of dermal thickness, Consists of dense irregular connective tissue, Many elastic fibers provide stretch-recoil properties, lamellar corpuscles, detects deep pressure and vibrations

Explain what causes friction ridges, what is the function of these ridges, and what type of skin

these friction ridges are located in

occur in thick skin, formed by dermal papillae in the papillary dermis that create raised ridges in the epidermis, exchange grip, exchange touch and sensitivity, create unique fingertips

Define the dermal vascular plexus

network of blood vessels between reticular layer and subcutaneous tissue

Define cleavage (tension) lines and explain their importance in wound healing

natural lines formed by collgean fibers in the dermis that determine how the skin streches and heals, located in the recticular layer of the dermis

• Important to surgeons because incisions parallel to

cleavage lines heal more readily

Define flexure lines and what causes them

of reticular layer are dermal folds at or

near joints, caused by repeated bending and folding of skin, and the dermis being tightly attached to deeper tissue

Describe what is happening at an anatomical/physiological level in stretch marks (striae) and

blisters

Extreme stretching of skin can cause dermal tears, Leaving silvery white scars called striae

Also known as “stretch marks”

• Acute, short-term traumas (e.g., burn or repeated friction)

to skin can cause blisters, fluid-filled pockets that

separate epidermal and dermal layers

List the three main skin pigments and compare and contrast where they are created/reside, what

color they are, and what their function is

Carotene- yellow to orange pigment, Accumulates in stratum corneum , Can be converted to vitamin A for vision and epidermal health, from carrots

Hemoglobin- Pinkish hue of fair skin is due to lower levels of, redish, red blood cells within blood cells, carries oxygen

Melanin- brown/black , produced by melanocytes in the epidermis, protects skin from UV radiation

List 6 different alterations in skin color and explain what physical or emotional states may cause

each

Yellowness , or jaundice

▪ Liver disorders

Red/purple/green/yellow marks, or bruises, or

ecchymoses, or hematomas

▪ Result of blood leakage from damaged blood

vessel beneath skin

– Brown or black patches

▪ Hyperpigmented, thickened skin in folds may be a

sign of endocrine disorder

Blueness, or cyanosis

▪ Low oxygenation of hemoglobin; sign of respiratory

or cardiovascular issues

– Pallor, or blanching

▪ Emotional stress, low blood pressure, anemia

(decreased ability of blood to carry oxygen),

– Redness, or erythema

▪ Embarrassment, fever, inflammation, allergy

Describe the functions of hair (pilli)

Sense insects on skin before bite or sting

– Hair on head guards against physical trauma

– Protect from heat loss

– Shield skin from sunlight

– Eyelashes shield eyes

– Nose hairs filter particles from inhaled air

Differentiate between hard and soft keratin in terms of its structure, function, and location in the

integumentary system

Hard keratin - tough rigid protein that is stronger and more durable, found in hairs and nails, function is to provides strength, protection, and resistance to damage.

Soft Keratin- softer more flexible protein, found in the epidermis, protects the skin while allowing flexibility and movement

root

portion within scalp, where keratinization is still

going on

Shaft

portion that extends above scalp, where

keratinization is complete

Hair follicle

from epidermal surface to dermis

Hair follicle receptor (or root hair plexus):

sensory

nerve endings that wrap around bulb

Arrector pili

small band of smooth muscle attached to

follicle

Describe the cause of different hair colors, and what causes hair to become gray/white

Hair pigments are made by melanocytes in hair follicles

– Combinations of different melanins (yellow, rust,

brown, black) create all the hair colors

▪ Red hair has additional pheomelanin pigment

▪ Gray/white hair results when melanin production

decreases and air bubbles replace melanin in shaft

• Compare and contrast vellus and terminal hair in terms of location, thickness, color, and length

Vellus hair: pale, fine body hair of children and adult Females and males

Terminal hair: coarse, long hair : Found on scalp and eyebrows, At puberty, Appear in axillary and pubic regions of both sexes, Also, on face and neck of males

List the two main factors that affect hair growth

Nutrition and hormones affect hair growth

Describe follicular growth cycles and relate these to why some hair on the body grows longer than

other hairs

Follicles go through growth cycles between active and

resting phases

– Average 2 m m growth per week

– Follicle life span varies

▪ Scalp is average of 4 years, so can grow long

▪ Eyebrows is only few months, so never grow long

Describe how/why hair loss can occur with age, physical/emotional stress & nutritional status

Balding with age, Hair grows fastest between teen and 40s, After 40s hair shed faster than replaced

Telogen effluvium (TE) is abrupt hair thinning caused by an abundance of hair follicles entering resting phase at

same time, Often caused by stress-induced factors such as: hormonal changes with childbirth, surgery, severe

emotional stress, or crash dieting

Other causes or thinning and/or texture change:

– Low thyroid hormone levels

– Drugs (ex: antidepressants, chemotherapeutic drugs)

– Severe dietary deficiencies of proteins or minerals

Root

Root embedded in skin

Nail plate

visible attached portion

Free edge

Part of nail that extends beyond the fingertip or toe

Nail bed

is epidermis underneath keratinized nail plate

Nail matrix

: thickened portion of bed responsible for nail

growth

Nail folds

skin folds that overlap border of nail

Cuticle, or eponychium

nail fold that projects onto

surface of nail body

Describe how nails may serve as an indicator of health (specifically, yellow-tinged nails,

thickened yellow nails, spoon-shaped nails, and horizontal lines on nails)

Yellow-tinged may indicate respiratory or thyroid

gland disorder

– Thickened yellow nails can be due to fungal infection

of nail

– Koilonchya, also called “spoon nail,” is an outward

concavity of nail may signal iron deficiency

– Beau’s lines are horizontal lines across nails may

indicate severe illnesses such as uncontrolled

diabetes, heart attack, or cancer chemotherapy

Compare and contrast eccrine and apocrine sweat glands in terms of location, function,

components of the secreted sweat, and which is more numerous

• Eccrine (merocrine) sweat glands are the most numerous, Abundant on palms, soles, and forehead, Function in thermoregulation, Secrete sweat

– 99% water, salts, metabolic wastes (urea, uric acid,And ammonia), and dermcidin (microbe-killing peptide)

• Apocrine sweat glands are merocrine glands, mostly Located axillary and anogenital areas, About 2000 large glands deep in the dermis and

subcutaneous tissue, Secrete viscous milky or yellowish sweat that contains fatty substances and proteins, Bacteria break down sweat, leading to body odor

, Begin functioning at puberty, Function unknown but may act as sexual scent gland

List and describe two types of modified apocrine sweat glands

Ceruminous glands: located in lining of external ear

canal; secrete cerumen (earwax)

– Mammary glands: secrete milk

• Describe the function and location of sebaceous glands

Produce sebum, found throughout the body usually attached to hair folliculies but not on thick skin

Describe cradle cap and its relation to sebaceous glands

Overactive sebaceous glands in infants can cause

seborrhea (cradle cap)

– Begins as pink, raised lesions on scalp that turn

yellow/brown and slough off

• List the functions of skin

Its main functions include:

– Protection

– Body temperature regulation

– Cutaneous sensations

– Metabolic functions

– Blood reservoir

– Excretion

Describe what the skin protects against in its role as a chemical, physical, and biological barrier

Chemical - sweat and sebum (oil) help provide an acidic environment to prevent bacterial growth. Antimicrobial substances help destroy harmful microorganisms. Low PH helps lessen mutiplication, melanain is a uv barrier agianst UV radiation damage

Physical barrier- protects against physical injury, harmful substances, and water loss\

Biological Barriers - dendritic cells help engulf foregin atigens, activate white blood cell response. Macrophages also help activate the immune system

• Explain how skin regulates body temperature

Sweating- sweat is produced when body gets too hot, cooling the body

Vasodilation- blood vessels in the skin widden allow more blood flow to the surface of the skin to release heat,

vasoconstriction- blood vessels in the skin narrow, reducing blood flow to the surface and conserve body heat.

• List receptors involved in cutaneous sensation, and describe what stimuli these receptors detect

Cutaneous sensory receptors are part of the nervous

system

• Exteroreceptors respond to stimuli outside body

– Touch: tactile (Meissner’s) corpuscle in dermal

papillae and tactile epithelial cells with associated

sensory nerve endings

– Deep pressure: lamellar (Pacinian) corpuscles in

deeper dermis or subcutaneous tissue

– Hair movement: hair follicle receptors

– Painful stimuli of the skin: free nerve endings

List some risk factors for skin cancer

Overexposure to UV radiation

– Frequent irritation of skin

Describe what each letter stands for in the ABCD(E) rule for recognizing skin cancer, and be able

to apply these to a case study

A: asymmetry; the two sides of the pigmented area do

not match

– B: border irregularity; exhibits indentations

– C: color; contains several colors (black, brown, tan,

sometimes red or blue)

– D: diameter; larger than 6 mm (size of pencil eraser)

– (E: evolution or evolving; changes over time)

• Describe what is happening at an anatomical and physiological level when a burn occurs, and list

some potential harmful side effects/outcomes

tissue damage caused by heat, electricity, radiation,

or certain chemicals

– Damage caused by denaturation of proteins, which

destroys cells

• Immediate threat is dehydration and electrolyte imbalance

– Leads to renal shutdown and circulatory shock

Describe the rule of nines and what this rule is used for in relation to burns

Body is broken into 11 sections, with each section

representing 9% of body surface (except genitals, which

account for 1%)

– Used to estimate volume of fluid loss

Describe the three degrees that burns can be classified as

First-degree

▪ Epidermal damage only

– Localized redness, edema (swelling), and pain

– Second-degree

▪ Epidermal and upper dermal damage

– Blisters appear

– First- and second-degree burns are referred to as partial-thickness

burns because only the epidermis and upper dermis are involved

– Third-degree

▪ Entire thickness of skin involved (referred to as full-thickness burns)

▪ Skin color turns gray-white, cherry red, or blackened

▪ Little or no edema, and area not painful because nerve endings are

destroyed

▪ Skin grafting usually necessary

• List the requirements for a burn to be considered critical

>25% of body has second-degree burns

– >10% of body has third-degree burns

– Face, hands, or feet bear third-degree burns

List different treatments for burns

Debridement (removal) of burned skin

– Antibiotics

– Temporary covering

– Skin grafts

Describe changes to the integumentary system that occur with aging

Epidermal replacement slows; skin becomes thin, dry,

and itchy (decreased sebaceous gland activity)

– Subcutaneous fat and elasticity decrease, leading to

cold intolerance and wrinkles

– Increased risk of cancer due to decreased numbers of

melanocytes and dendritic cells

– Hair thinning

Understand the skeleton initially consists of _____, which is replaced by bone in the _______

The skeleton initially consists of cartilage, which is

replaced by bone (except in areas requiring flexibility)

during embryonic development

Compare and contrast skeletal cartilage and perichondrium in terms of components, function,

vascularity, and innervation

Skeletal cartilage: highly resilient, molded cartilage that

consists primarily of water

– Contains no blood vessels or nerves

• Perichondrium: layer of dense connective

tissue surrounding cartilage

– Helps cartilage resist outward expansion

– Contains blood vessels for nutrient delivery

Compare and contrast hyaline, elastic, and fibrocartilage in terms of function, abundance, and

fiber types

HyalineProvides support, flexibility, and resilience

▪ Most abundant type

▪ Contains collagen fibers only

– Elastic cartilage

▪ Similar to hyaline cartilage, but contains both

collagen and elastic fibers

– Fibrocartilage

▪ Thick collagen fibers provides great tensile strength

• Describe two types of cartilage growth, including when in the lifetime cartilage growth occurs

Appositional growth—new matrix laid down on

surface of cartilage

▪ Cartilage-forming cells in perichondrium secrete

matrix against external face of existing cartilage

Durning childhood and adolesecne

– Interstitial growth—new matrix made within cartilage

▪ Chondrocytes within lacunae divide and secrete

new matrix, expanding cartilage from within

Childhood and adolescence

List and describe 7 different functions of bones

Support for body and soft organs

2. Protection of brain, spinal cord, and vital organs

3. Anchorage as levers for muscle action

4. Mineral storage of calcium and phosphorus

5. Blood cell formation, called hematopoiesis, in red

bone marrow of certain bones

6. Triglyceride (fat) storage used for an energy source;

in bone cavities

7. Hormone production of osteocalcin that helps to

regulate insulin secretion, glucose homeostasis, and

energy expenditure

Describe the four different shapes bones can be classified into, and provide examples of each

1. Long bones

▪ Longer than wide with a medullary cavity extending

the length of the shaft

▪ Ex. most limb (arm and leg) bones

2. Short bones

▪ Cube-shaped bones

▪ Ex. wrist and ankle bones

▪ Sesamoid bones form within tendons

– Ex. Patella (kneecap)

– Vary in size and number in different individualsCopyright

3. Flat bones

▪ Thin, flat, slightly curved

▪ Ex. sternum, ribs, most cranial bones

4. Irregular bones

▪ Complicated shapes

▪ Ex. vertebrae and hip bones

• Compare and contrast compact and spongy bone in terms of location and structure

Compact bone: dense outer layer on every bone that

appears smooth and solid

• Spongy bone: made up of a honeycomb of small, needle-

like or flat pieces of bone called trabeculae

– Open spaces between trabeculae are filled with red or

yellow bone marrow

i: shaft (diaphysis),

tubular shaft that forms long axis of bone

▪ Consists of compact bone surrounding central

medullary cavity that is filled with yellow bone

marrow in adults

(epiphyses

ends of long bones that consist of

compact bone externally and spongy bone internally

epiphyseal line

Between diaphysis and epiphysis

– Periosteum:membrane

white, double-layered membrane that

covers external surfaces except joints

Fibrous layer:membrane

outer layer consisting of dense

irregular connective tissue

Osteogenic layer: membrane

inner layer abutting bone and

contains primitive osteogenic stem cells that gives

rise to most all bone cells

Describe where periosteum and endosteum are located

periosteum- covers outer surface of bones expect joints

endosteum - lines inner surface of bones

• Understand that the red bone marrow is a

hematopoietic tissue (creates red blood cells)

• Understand that bones have many named markings that represent areas of passage or

attachment for other structures in the body

Sites of muscle, ligament, and tendon attachment on

external surfaces

– Areas involved in joint formation or conduits for blood

vessels and nerves

• Three categories of bone markings:

– Projections—sites of muscle and ligament

attachment

– Surfaces—form joints

– Depressions and openings—for blood vessels and

nerves

List the 5 types of bone cells and describe their functions

osteogenic cells

– Mitotically active stem cells that divide into osteoblasts

Bone growth and repair

Osteoblasts

Build new bone by producing bone matrix

Osteocytes

Maintain bone tissue and monitor bone health. Mature osteoblasts

Bone lining cavity

Cover inactive bones surfaces and help regulate mineral exchange and bone remodeling

Osteoclasts - break down bone , relasing calium into blood

• Describe the following components of compact bone: osteon, lamellae, lacunae, central canals,

perforating canals, and canaliculi

osteon- basic structural unit of compact bone, made of circualr layers of bone tissue surronding a centeral cannal

Lamellae- collagen fibers that run in different directions in adjacent rings, Withstands stress and resist twisting

Lacunae- small cavities that contain osteocytes

Centeral cannal - runs through core of osteon, Contains blood vessels and nerve fibers

Perforating cannal- canals lined with endosteum that occur at right angles to central canal, Connect blood vessels and nerves of periosteum,

medullary cavity, and central canal

Canaliculi- hairlike canals connect lacunae to each

other and to central canal

• Describe the creation, makeup, and function of osteoid; understand it is organic

Osteoid secreted by osteoblasts, Consists of ground substance and collagen Fibers, which contribute to high tensile strength

and flexibility of bone, it is organic

• Describe what anatomical component facilitates the resilience of bone

Resilience of bone is due to sacrificial bonds in

collagen molecules that stretch and break to

dissipate energy and prevent fractures

– If no additional trauma, bonds re-form

• Describe the makeup and function of hydroxyapatites (mineral salts); understand it is inorganic

Hydroxyapatites (mineral salts)

▪ Makeup 65% of bone by mass

▪ Tiny calcium phosphate crystals in and around

collagen fibers

▪ Responsible for hardness and resistance to

compression

INORGANIC

Describe two types of ossification, including when in the lifetime this occurs and ends

Ossification (osteogenesis) is the process of bone tissue

formation

Long bones grow lengthwise by interstitial (longitudinal)

growth of epiphyseal plate

• Bones increase thickness through appositional growth (through life)

Bones stop growing during adolescence

– Some facial bones continue to grow slowly through

life

• Describe how bone thickens/grows in width, and explain when this occurs

Growing bones widen as they lengthen through

appositional growth

– Can occur throughout life

• Bones thicken in response to increased stress from

muscle activity or added weight

List 4 different hormones that regulate bone growth, and identify which is the most important in

stimulating epiphyseal plate activity

Growth hormone: most important hormone in stimulating

epiphyseal plate activity in infancy and childhood

• Thyroid hormone

• Testosterone (males) and estrogens (females) at puberty:]

• Define bone remodeling, including the terms bone deposit and bone resorption

Bone remodeling- breaks down old bone tissue and replaces it with new bone tissue , osteoclasts- breakdown and remove old damgdged bone, osteoblasts- build new bone tissue

Bone reasorbtion- breaking down and removing old or damaged bone, osteoclasts

Bone deposit- forming new bone tissue, osteoblasts

• Describe how bone remodeling is regulated by hormones, identifying which hormones are

involved and describing what happens if hypocalcemia or hypercalcemia occurs

Remodeling occurs continuously but is regulated by two

control loops:

o Maintaining calcium homeostasis

▪ Hormonal negative feedback loop involving

parathyroid hormone maintains blood calcium

– Keeping bone strong

▪ Mechanical and gravitational forces acting on bone

drive remodeling to keep bone strong

– Calcitonin: produced in thyroid gland in response to

high levels of blood calcium levels

Hypocalcemia: low levels of calcium cause

hyperexcitablility

– Hypercalcemia: high levels of calcium cause

nonresponsiveness

• Describe how bone remodeling also can occur in response to mechanical stress, and explain

Wolff’s law in relation to this principlE

Bones reflect stresses they encounter

– Bones are stressed when weight bears on them or

muscles pull on them

• Wolf’s law states that bones grow or remodel in response

to demands placed

• Understand that hormones control whether/when remodeling occurs, and mechanical stress

determines where it occurs

Mechanical stress causes remodeling by producing

electrical signals when bone is deformed

– Compressed and stretched regions are oppositely

charged

– Compression/tension changes fluid flows within

canaliculi, which may also stimulate remodeling

Hormonal controls determine whether and when

remodeling occurs in response to changing blood

calcium levels, but mechanical stress determines

where it occurs

Define fractures, and describe the 3“either/or” fracture classifications

Three “either/or” fracture classifications

– Position of bone ends after fracture

▪ Nondisplaced: ends retain normal position

▪ Displaced: ends are out of normal alignment

– Completeness of break

▪ Complete: broken all the way through

▪ Incomplete: not broken all the way through

– Whether skin is penetrated

▪ Open (compound): skin is penetrated

▪ Closed (simple): skin is not penetrated

Describe comminuted, compression, spiral, epiphyseal, depressed, and greenstick fractures

Comminuted Bone fragments into

three or more pieces.

Particularly common

in older adults.

Compression Bone is crushed.

Common in porous

bones (i.e., osteoporotic

bones) subjected to

extreme trauma, as in a

fall.

Spiral Ragged break from

excessive twisting

forces.

Common sports

fracture.

Epiphyseal Epiphysis separates from

the diaphysis at epiphyseal

plate.

Occur where cartilage cells

are dying and calcification of

the matrix is occurring

Depressed Broken bone

portion is pressed

inward.

Typical of skull

fracture.

Greenstick Bone breaks incompletely.

Only one side of the shaft

breaks; the other side bends.

Common in children

• Describe the three different types of reduction of fractures

Closed reduction: physician manipulates to correct

position

– Open reduction: surgical pins or wires secure ends

– Immobilization of bone by cast or traction is needed

for healing

• List (in order) and describe the four major stages of fracture repair

Hematoma forms

– Torn blood vessels hemorrhage, forming mass of

clotted blood called a hematoma

– Site is swollen, painful, and inflamed

Fibrocartilaginous callus forms

– fibroblasts and chondroblasts produce collagen fibers and Cartilage

-soft callus forms

Bony Callus Forms

-osteoblasts replace the soft callus with spongy bone

Fracture comes stronger and more stable

Bone remodeling

Osteoclasts remove acess bone

Osteoblasts - deposit new bone

Bone restore to normal shape and strength

• Describe osteomalacia, rickets, osteoporosis, and Paget’s disease

o Identify various risk factors, treatments, and prevention methods for osteoporosis

Osteomalacia

– Results in soft, weak bones

– Pain upon bearing weight

• Rickets (osteomalacia of children)

– Results in bowed legs and other bone deformities

because bones ends are enlarged and long

– Cause: vitamin D deficiency or insufficient dietary

calcium

Excessive and haphazard bone deposit and resorption

cause bone to grow fast and develop poorly

– Called Pagetic bone

Osteoporosis is a group of diseases in which bone

resorption exceeds deposit

Most often aged, postmenopausal females

▪ Affects 30% of females aged 60–70 years and

70% by age 80

▪ Estrogen plays a role in bone density, so when

levels drop at menopause, females run higher

risk

– Males are less prone due to protection by the

effects of testosterone

Additional risk factors for osteoporosis:

– Insufficient exercise to stress bones

– Diet poor in calcium and protein

– Smoking

– Genetics

– Hormone-related conditions

▪ Hyperthyroidism

▪ Diabetes mellitus

– Consumption of alcohol or certain medications

Traditional treatments

▪ Calcium

▪ Vitamin D supplements

▪ Weight-bearing exercise

▪ Hormone replacement therapy

Plenty of calcium in diet in early adulthood

– Reduce consumption of carbonated beverages and

alcohol

▪ Leach minerals from bone, so decrease bone

density

– Plenty of weight-bearing exercise

▪ Increases bone mass above normal for buffer

against age-related bone loss

Describe how bone changes across the lifespan in terms of density, mass, mineralization, and

healing ability

In children and adolescents, bone formation exceeds

resorption

– Males tend to have greater mass than females

• In young adults, both are balanced

• In adults, bone resorption exceeds formation

Bone density changes over lifetime are largely

determined by genetics

– Gene for vitamin D’s cellular docking determines

mass early in life and osteoporosis risk at old age

• Bone mass, mineralization, and healing ability decrease

with age beginning in fourth decade

– Except bones of skull

– Bone loss is greater in whites and in females