Ch 7:8 + Some of 9 - Integumentary System PDF

BSC2085-0001 (9/17/24) 1 LESSON 7: Chapter 06 Integumentary System Introduction Inspection of the skin, hair, and nails is significant part of a physical exam Skin is the most vulnerable organ as it...

BSC2085-0001 (9/17/24) 1 LESSON 7: Chapter 06 Integumentary System Introduction Inspection of the skin, hair, and nails is significant part of a physical exam Skin is the most vulnerable organ as it acts as a barrier to the outside activity o exposed to radiation, trauma, infection, and chemicals § requires tactics to help repair it o receives more medical treatment than any other organ system dermatology: scientific study and medical treatment of integumentary system (skin) The Skin and Subcutaneous Tissue The integumentary system consists of the cutaneous membrane (skin) and accessory structures (hair, glands, nails) The skin (integument) is body’s largest and heaviest organ Consists of two layers: o epidermis: superior, outermost; composed of stratified squamous epithelium o dermis: deeper connective tissue layer (dense connective tissue – irregular) – accessory structures originate in the dermis § sweat glands § nails § hair o below the dermis is the hypodermis (superficial fascia/subcutaneous layer), NOT part of the skin but usually studied with it Thickness ranges from 0.5 to 6 mm o 0.5 mm: eyelids, thinness allows for quick movement o 6 mm: back, shoulder blades, scapula Thickness of skin ranges mainly due to variation in dermis thickness but skin is classified as thick or thin based on epidermis (thick skin ONLY has the layer stratum lucidum) thick skin covers palms, soles, and corresponding surfaces of fingers and toes o has sweat glands, but no hair follicles or sebaceous (oil glands) o epidermis about 0.5 mm thick, primarily due to thick stratum corneum thin skin covers rest of the body o has hair follicles, sebaceous glands, and sweat glands Functions of the Skin protection: resistance to trauma and infection o keratin: protein that provides physical protection § keratin fibers linked by desmosomes keeps cells linked to skin o dermcidin, defensin, and acid mantle protect against bacteria o barrier to water, ultraviolet (UV rays), harmful chemicals vitamin D synthesis o UV radiation causes epidermal cell to produce cholecalciferol (vitamin D3) – converted to calcitriol by the liver and kidneys sensation (tactile & thermal) o many nerve endings that react to various stimuli thermoregulation o alters blood flow to release or retain heat o cutaneous vasoconstriction, cutaneous vasodilation BSC2085-0001 (9/17/24) 2 § vasodilation: blood vessels dilate, making us look flush. as it cools off, it cools off the blood in the blood vessels as it circulates § vasoconstriction: look paler because the blood vessels constrict and shuts blood off and keeps it closer to core to keep you warmer nonverbal communication o facial expressions (raise eyebrows, frown, smile, etc.) Epidermis general features of the epidermis o keratinized stratified squamous epithelium § includes dead cells at skin surface packed with tough keratin protein gets further and further from dermis, more cut off from its blood supply and nutrients so they start to starve and die shields living cells o avascular (lacks blood vessels) § depends on the diffusion of nutrients from underlying connective tissue o contains sparse nerve endings for touch and pain Cells of the Epidermis Five epidermal cell types: o keratinocytes: § great majority of epidermal cells (found largely in stratum corneum, allows for skin to be pulled, moved, etc.) § synthesize keratin: give skin its strength o stem cells: can undergo mitosis § undifferentiated cells that give rise to keratinocytes § in deepest layer of epidermis, stratum basale o melanocytes § synthesize pigment melanin that shields DNA from ultraviolet radiation by absorbing the radiation get tan by an increased production of melanin § occur only in stratum basale but have branched processes that spread among keratinocytes and distribute melanin via melanosomes o tactile cells § touch receptor cells associated with dermal nerve fibers tactile/Merkel disc: collective term for tactile/Merkel cell and associated nerve fiber § in basal layer of epidermis o dendritic cells § phagocytic immune cells that guard against toxins, microbes § found in stratum spinosum and stratum granulosum Layers of the Epidermis Cells of epidermis arranged in four to five zones, or strata, listed here from deep to superficial: stratum basale (aka stratum germinativum because it is always germinating – producing – new cells) o single layer of stem cells and keratinocytes resting on the basement membrane o also contains scattered melanocytes and tactile cells BSC2085-0001 (9/17/24) 3 stratum spinosum o several layers of living keratinocytes joined by desmosomes and tight junctions o named for appearance of cells after histological preparation (with spines sticking out of it: spikey) o contains dendritic (Langerhans) cells that defend against invaders stratum granulosum o three to five layers of flat, living keratinocytes that start to dehydrate and die o cells containing dark-staining keratohyalin granules stratum lucidum o thin, pale layer found only in thick skin o keratinocytes packed with clear protein eleidin o cells here are dead and lack nucleus/organelles § can’t produce much protein without nucleus stratum corneum o up to 30 layers of dead, scaly, keratinized cells linked by desmosomes o resists abrasion, penetration, water loss § callus: due to an increase in mitosis of cells on palms (increase in keratinocytes due to an increase in abrasion) The Life History of a Keratinocyte Keratinocytes produced by mitosis in stratum basale or deepest part of stratum spinosum o mitosis requires abundant oxygen and nutrients o once cells migrate away from blood vessels of the dermis, mitosis cannot occur New keratinocytes push older ones toward the surface (stratum corneum) o over time, keratinocytes flatten, produce more keratin and lipid-filled lamellar granules o in 30 to 40 days, a keratinocyte makes its way to the skin surface and exfoliates (flakes off) as specks called dander (may combine with oil to become dandruff) § keratinocyte multiplication is slower in old age, faster in injured or stressed skin § calluses or corns are thick accumulations of dead keratinocytes on hands or feet epidermal water barrier: located in the stratum granulosum, it is formed from lipids from keratinocytes as well as tight junctions between them o helps prevent dehydration o does not prevent the absorption of water by the stratum corneum when we soak in a bath (“prune fingers) o Our fingers get wrinkles when submerged in water because of a nervous system reaction that contracts muscles and makes it easier to grab onto things The Dermis Beneath the epidermis is the dermis General features o connective tissue layer 0.2 mm to 4 mm thick o composed mainly of collagen (prevents overstretching); also contains elastic (allow stretching) and reticular fibers o well supplied with blood vessels (moves nutrients), sweat glands, sebaceous glands, and nerve endings BSC2085-0001 (9/17/24) 4 o houses hair follicles and nail roots o muscles of facial expression attach to dermis o wavy, bumpy, conspicuous boundary between dermis and epidermis (like two interconnected hands) that increase surface area (strength of diffusion) and strength of connection § dermal papillae: upward, finger-like extensions of dermis § epidermal ridges are downward waves of epidermis papillary layer o superior layer, thin zone of areolar tissue in and near the dermal papillae o allows for mobility of leukocytes and other defense cells o rich in small blood vessels reticular layer o deeper, thicker layer of dermis o composed of dense irregular connective tissue, allows for stretching in all directions o stretch marks (striae): tears in the collagen fibers caused by stretching of the skin due to pregnancy or obesity o damaged dermal blood vessels (burns, shoe friction) may cause serous fluid to seep out and form a blister between dermis and epidermis Two types of fibers found in the dermis o collagen fibers § strong, resists overstretching but can bend easily § flexibility o elastic fibers § permits stretching when pulled; when released, recoils back to original length § provides flexibility and stretching (though the stretching is dependent on the collagen fibers o skin turgor – caused by H2O content in skin (allows it to snap back to shape) § dehydrated skin shows loss of turgor (resilience and flexibility): pinched skin stays pinched after release. need to rehydrate dermatitis: inflammation of the papillary layer o characterized by pain/itchiness o inflammation can rapidly spread across the entire integument o caused by infection, radiation, mechanical, or chemical (ex. poison ivy) irritation decubitus ulcers: bedsores caused by problems with dermal circulation o caused by compression of superficial blood vessels o sores common on skin covering joints or bony prominences o kills epithelial cells, erodes dermal tissue Skin Color Variations in skin and hair color due primarily to type and amount of melanin pigment o melanin produced in melanocytes, stored in melanosomes (vesicles) o melanosomes transferred to keratinocytes where they cluster around the cell nucleus to absorb UV radiation (radiation can damage DNA) o dark eumelanin and reddish-yellow pheomelanin BSC2085-0001 (9/17/24) 5 § eumelanin varieties: brown and black eumelanin; responsible for tan, brown, and black skin § pheomelanin responsible for yellowish to reddish tones in some Asians and Native Americans, and pinkish tones of white skin Other contributing factors o UV radiation stimulates melanin synthesis: increase in melanocytes when tanning o Degree of show-through of dermal vessels and white collagen o diet can lead to possible accumulation of carotene pigment from yellow and orange vegetables (carrots, squash) § accumulates in epidermal cells and fatty tissues of the dermis § used to produce vitamin A – needed for epithelial maintenance and pigment for photoreceptors for vision § lack of vitamin A can cause night blindness (nyctalopia) Skin colors of diagnostic value: o cyanosis: blueness due to oxygen deficiency in blood o erythema: redness (flushness) due to increased blood flow to skin o pallor: paleness due to decreased blood flow to skin o albinism: white skin due to genetic lack of melanin (skin pale, hair white, and even some paleness in eyes) o vitiligo: loss of skin color in patches due to melanocytes, probably caused by autoimmune reaction to melanocytes (attack melanocytes, making them unable to produce melanin) o jaundice: yellowing due to bilirubin in blood (break down product of hemoglobin) § can be caused by compromised liver function (can’t filter out bilirubin) o hematoma: bruising, blood clotting under skin Skin Markings Skin has a variety of markings: o friction ridges: formed from dermal papillae § markings on the fingertips that leave oily fingerprints § everyone has a unique pattern formed during fetal development that remains unchanged throughout life; not even identical twins have identical fingerprints § enhance fingertip sensitivity; improve grip o flexion lines (flexion creases) § lines on the flexor surfaces of the digits, palms, wrists, elbows § mark sites where skin folds during flexion of joints o freckle § flat, melanized patch o mole (nevus) § elevated, melanized patch, often with hair § should be watched for changes in color, diameter, or contour that may suggest cancer o hemangiomas (birthmarks) § patches of discolored skin caused by benign tumors (overgrowth) of dermal capillaries BSC2085-0001 (9/17/24) 6 § some disappear in childhood, others last for life § examples: capillary hemangioma (strawberry birthmark), cavernous hemangioma, port-wine stain The Hypodermis hypodermis (subcutaneous tissue): layer of connective tissue beneath the skin o contains more areolar and adipose tissue than the dermis o pads body and binds skin to underlying tissues o common sites of drug injections (hypodermic needles) due to many blood vessels o subcutaneous fat: refers to subcutaneous tissue that is comprised predominantly of adipose tissue § energy reservoir § thermal insulation: keeps temperature stable § thicker in females; thinner in infants and elderly Hair & Nails Introduction hair, nails, & cutaneous glands are the accessory organs (appendages) of the skin hair & nails are composed of mostly dead, keratinized cells pliable soft keratin makes up stratum corneum of skin compact hard keratin makes up hair and nails o tougher and more compact due to numerous disulfide bridges between keratin molecules Functions of Skin hair function depends on body region and type of hair hair receptors alert us of parasites crawling on skin hair on trunk and limbs is mostly vestigial (not really needed) scalp hair retains heat and protects against sunburn pubic and axillary hair – signify sexual maturity and aid in transmission of sexual scents guard hairs (vibrissae) guard nostrils and ear canals (act as filters) eyelashes and eyebrows enhance facial expression and nonverbal communication o also prevents particles and sweat from getting in eyes Hair a hair is also called a pilus (plural: pili) slender filament of keratinized cells growing from a tube in the skin called a hair follicle hair covers most of the body o does NOT cover: palms, soles: palmar, planter; and lateral surfaces and distal segments of fingers & toes; lips, nipples, and parts of genitals limbs and trunk have 55 to 70 hairs per square cm; face has about 10 times as many; 100,000 hairs on an average person’s scalp à lose hair as you get older differences in hairiness across individuals is mainly due to differences in texture and pigment of hair types of hair: o downy hair (lanugo) § fine, downy, unpigmented hair that appears on the fetus in the last 3 months of development (fluffy, light, hard-to-see) o vellus hair BSC2085-0001 (9/17/24) 7 § fine, pale hair (not as fluffy as downy hair) that replaces lanugo by time of birth § two-thirds of the hair of females; one-tenth of the hair of males; all the hair of children except eyebrows, eyelashes, and scalp hair o terminal hair § longer, coarser, more heavily pigmented § eyebrows, eyelashes, and hair of the scalp § after puberty, forms axillary and pubic hair § male facial hair and some of the hair on the trunk and limbs Structure of the Hair and Follicle structure of a hair: o shaft is portion above skin surface, root is portion below skin surface o in dermis or hypodermis, hair root ends with dilated bulb § bulb grows around dermal papilla – bud of vascular connective tissue, provides nutrition to hair § hair matrix: mitotically active cells immediately above the papilla; growth center for the hair, pushes hair up o hair has up to three layers: § medulla: core of loosely arranged cells and air spaces § cortex: bulk of the hair; layers of elongated cells § cuticle: outermost region consisting of multiple layers of thin, scaly cells that overlap like roof shingles two principle layers o (external & internal) epithelial root sheath: extension of the epidermis lying adjacent to hair root; widens at deep end into bulge, a source of stem cells for follicle growth o connective tissue root sheath: derived from dermis but a bit denser; surrounds epithelial root sheath associated with the follicle o sensory nerve fibers entwine each follicle and respond to hair movements o (piloc) arrector muscle: bundle of smooth muscle attaching follicle to dermis; contracts (and pulls) to make hair stand on end (piloerection; from fear/cold) Hair Texture & Color Color due to pigment granules in the cells of the cortex o brown and black hair is rich in eumelanin o red hair has high concentration of pheomelanin o blond hair has an intermediate amount of pheomelanin and very little eumelanin o gray and white hair have little or no melanin; air present in medulla texture related to cross-sectional shape of hair o straight hair is round o wavy hair is oval o curly hair is relatively flat (squished) Nails fingernails and toenails o clear, hard derivatives of stratum corneum BSC2085-0001 (9/17/24) 8 o composed of thin, dead cells packed with hard keratin (has more disulfide bridges, stronger than hair) § heat from shower softens harder keratin o functions of nails § improve grooming, picking apart food, other manipulations § provide a counterforce to enhance sensitivity of fleshy fingertips of tiny objects (produces vibration) o structure of nail § nail plate: hard part of nail; includes overhanging free edge, nail body (visible attached part), and nail root (under overlying skin) § surrounding skin rises as a nail fold (on the side), separated from the nail plate by the nail groove § nail bed: skin underlying the nail plate § nail matrix: growth zone at proximal end of nail; its thickness obscures underlying vessels and appear as white lunule § cuticle (eponychium): narrow zone of dead skin that overhangs proximal end of nail o appearance of nails can be valuable in medical diagnosis § swollen, clubbed fingertips in oxygen deficiency § dietary deficiencies Cutaneous Glands Sweat Glands Two kinds of exocrine sweat glands: apocrine and eccrine o apocrine sweat glands § groin, anal region, axilla, areola, beard area in males § ducts lead to nearby hair follicles; produce sweat that is milky and contains fatty acids § inactive until puberty; respond to stress and sexual stimulation bromhidrosis: disagreeable body odor; usually inadequate hygiene; bacteria use fatty acids for energy o eccrine (merocrine) sweat glands § most numerous skin glands – 3 to 4 million in adult skin, especially dense on palms, soles, and forehead § simple tubular glands produce watery perspiration that helps cool the body o myoepithelial cells § found in both apocrine and eccrine glands § contract in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct production and composition o 99% water o pH range of 4 to 6 § acid mantle: inhibit bacterial growth o begins as a protein-free filtrate of blood plasma produced by deep secretory portion of gland, oozes out of capillary BSC2085-0001 (9/17/24) 9 § some sodium chloride reabsorbed by duct, but some sodium chloride and other small solutes (potassium, urea, lactic acid, ammonia) remain in the sweat o some drugs are excreted in sweat § ex. cocaine, heroin, barbiturates Types of perspiration o insensible perspiration: NOT noticed; does NOT produce visible wetness of skin. lose approximately 500 mL/day § cutaneous transpiration: water loss from skin not due to sweating. water diffuses between the keratinocytes and evaporates from the skin surface skin not completely waterproof, loses water & can gain water o diaphoresis: sensible perspiration; sweating with wetness of the skin, in response to heat, exercise, circulatory shock § 1 L or more of sweat per hour may be lost during exercise Sebaceous Glands sebaceous glands produce oily secretion called sebum gland structure o flask-shaped, short ducts open into hair follicles holocrine mode of secretion o fill, burst, & die; then coats hair follicle keeps skin and hair from becoming dry, brittle, and cracked Ceruminous Glands ceruminous glands: modified apocrine glands found only in external ear canal o coiled, simple tubular glands o produce cerumen (earwax) § yellow, waxy secretion combined with sebum and death epithelial cells; waterproofs the canal § keeps eardrum pliable § kills bacteria § makes guard hairs of ear sticky to help block foreign particles from entering auditory canal Mammary Glands mammary glands: milk-producing glands that develop in female during pregnancy & lactation o modified apocrine sweat glands, produce casein o rich secretion released through mammary ducts opening at nipple o mammary ridges or milk lines: two rows of mammary glands in most mammals § primates kept only two glands, but a few people have additional nipples along the milk line (polythelia) Skin Disorders Skin Cancer Most skin cancer is caused by exposure to UV rays of the sun most often on the head, neck, and hands most common in fair-skinned (little melanin) people and the elderly one of the most common, easily treated cancers highest survival rates if detected and treated early BSC2085-0001 (9/17/24) 10 Three types of skin cancer named for the epidermal cells in which they originate: o basal cell carcinoma (stratum basale) o squamous cell carcinoma (squamous cells) o malignant melanoma (toward base area as well) Basal Cell Carcinoma most common type least dangerous because it seldom metastasizes forms from cells in stratum basale small, shiny bump with central depression and beaded edges Squamous Cell Carcinoma arises from keratinocytes of stratum spinosum lesions usually on scalp, ears, lower lip, or back of the hand raised, reddened, scaly appearance later forming a concave ulcer chance of recovery good with early detection and removal tends to metastasize to lymph nodes and may become lethal Melanoma arises from melanocytes less than 5% of skin cancers can be successfully removed if caught early, but usually fatal if metastasizes greater risk factor is familial history highest incidence in males, redheads, people who had severe sunburn as a child ABCDE rule for detecting melanoma: o A: asymmetry (in shape) o B: border irregularity o C: color (mix of brown, black, tan, red/blue) o D: diameter (greater than 6 mm) o E: evolving (size, shape, color Burns burns can result in death due to fluid loss, infection, and toxic effects of eschar – the burned, dead tissue classified according to depth of tissue involvement: first-degree burn – only involves the epidermis o redness, slight edema, and pain o heals within days second-degree burn (partial-thickness burn) – involves part of dermis o may appear red, tan, or white; blistered and painful o two weeks to several months to heal and may leave scars third-degree burn (full thickness burn) – involves all of dermis and often some deeper tissues o often requires skin grafts; need fluid replacement, infection control, supplemental nutrition o may damage pain receptors so it may hurt less than second-degree or first Skin Grafts third-degree burns often require skin grafts o autograft: tissue from another location on the same person’s body BSC2085-0001 (9/17/24) 11 o allograft: tissue from unrelated person, usually deceased donors o artificial and lab-based approaches under development epidermal growth factor: peptide growth factor that o promote division of germinative cells o accelerates keratin production o stimulates epidermal repair o stimulates glandular secretions LESSON 8: Chapter 07 Bone (Osseous) Tissue Tissues & Organs of the Skeletal System – Introduction skeletal system: composed of bones, cartilages, and ligaments joined to form a framework for the body o osteology: study of bone; there are 206 major bones in the human body § cartilage is the forerunner of most bones and covers many joint surfaces cartilage begins as a cartilage matrix and later ossifies into bone § ligaments hold bones together at joints § tendons attach muscle to bone *Functions of the Skeleton* roles of the skeleton o support: limb bones & vertebrae support body; jaw bones support teeth; some bones support viscera o protection: of brain, spinal cord, heart, lungs, and more o movement: limb movements, breathing, and other movements depend on bone o electrolyte & acid-base balance: moderates calcium & phosphate levels and buffer blood against large pH changes by altering phosphate & carbonate salt levels o blood formation: red bone marrow is the chief producer of red & white blood cells o hormone secretion: bone cells secrete hormones that affect action of insulin and moderate the stress response Bones & Osseous Tissue bone (osseous tissue): connective tissue with the matrix (outside of cell) hardened by calcium phosphate & other minerals o mineralization or calcification: the hardening process of bone (aka osseous tissue) individual bones (each an organ) consist of bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue (broken bone hurts because of nerve stimulation), fibrous connective tissue (wrap around bone) o the word bone can refer to the organ or just the osseous tissue General Features of Bones variety of bone shapes o flat bones: thin, curved plates; protect soft organs § ex. parietal bones of skull, sternum, scapula, ribs, coxal “hip” bones o long bones: longer than wide; rigid levers acted upon by muscles; crucial for movement § ex. humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, phalanges BSC2085-0001 (9/17/24) 12 o short bones: approximately equal in length & width; bones of wrist (metacarpals) and ankle o irregular bones: elaborate shapes; vertebrae and some skull bones Bone Markings bone markings: surface features of a bone. They include: o depressions, grooves, tunnels along the bone surface § indicated where blood vessels and nerves run along the side of the bone or enter the bone o elevations of projections § indicates where tendons & ligaments attach onto bone § indicates where articulations (joints) occur with other bones General Features of Bones general anatomy of a long bone: o compact (dense or cortical) bone: dense outer shell of bone; enclosed the marrow (medullary) cavity – cavity contains yellow bone marrow o spongy (cancellous) bone: loosely organized bone tissue § found in center of ends and center of shafts of long bones & in middle of nearly all others, covered by more durable compact bone § skeleton is three-fourths compact and one-fourth spongy bone by weight o diaphysis: shaft that provides leverage o epiphysis: enlarged end of a long bone § strengthen joint and anchor ligaments & tendons o epiphyseal line – remnant of childhood growth zone, epiphyseal plate – children (epiphyseal plate is composed of cartilage) o articular cartilage: layer of hyaline cartilage that covers joint surface; allows joint to move more freely o periosteum: external sheath covering most of bone (separates & protects bone) § outer fibrous layer of collagen and inner osteogenic layer of bone- forming cells collagen can bend but cannot stretch much bone-forming cells: stem cells à osteocytes § perforating/Sharpey’s fibers of periosteum penetrate underlying bone matrix § periosteum functions to isolate bone, provide route for blood vessels & nerves, and participates in bone growth/repair o endosteum (endo – in): thin layer of reticular connective tissue lining marrow cavity and all internal bone surfaces. The endosteum: § is an incomplete cellular layer (not a continuous sheet) § covers the trabeculae of spongy bone § lines the central canals of osteons (aka Haversian systems) compact bone § contains osteogenic cells, osteoblasts, & osteoclasts osteogenic cells: undergo mitosis, some become osteoblasts osteoblasts: produce bone matrix; they can become trapped in lacunae and therefore become osteocytes o osteocytes: maintain the bone matrix BSC2085-0001 (9/17/24) 13 osteoclasts: remove bone matrix § active in bone growth/repair flat bones have a sandwich like structure: o inner & outer tables of compact bone enclosing layer of spongy bone in between (called diploë in cranium) Four Types of Bone Cells osteocytes: former osteoblasts that have become trapped in the matrix they deposited o lacunae: tiny cavities where osteocytes reside o canaliculi: little channels that connect lacunae o cytoplasmic processes of osteocytes reach into canaliculi and contact processes of neighboring cells; gap junctions allow for passage of nutrients, wastes, signals o some osteocytes reabsorb bone matrix while others deposit it o act as strain sensors: when stressed, produce biochemical signals that regulate bone modeling (shape & density changes that are adaptive) o maintains protein & mineral composition of the matrix; plays a role in the repair of damaged bone osteoblasts & osteocytes secrete hormone osteocalcin o part of body’s acute stress response (sympathetic NS), stimulates pancreatic secretion of insulin, increases insulin sensitivity, promotes energy availability osteoclasts: bone-dissolving cells found on bone surface o perform osteolysis/resorption: the breakdown of bone, as part of bone remodeling; important in releasing calcium & phosphate into body fluid o do NOT develop from osteogenic cells; they develop from same bone marrow stem cells that give rise macrophages (different origin from other bone cells) o very large cells formed from fusion of several stem cells; have multiple (usually 3-4, but up to 50) nuclei in each cell The Matrix composition of osseous tissue matrix o by dry weight, averages one-third organic and two-thirds inorganic matter organic matter – 1/3 of matrix, synthesized by osteoblasts o collagen & carbohydrate: protein complexes, such as glycosaminoglycans, proteoglycans, & glycoproteins inorganic matter – 2/3 of matrix, mineral component o 85% hydroxyapatite [(Ca10(PO4)6(OH)2], a crystallized calcium phosphate salt o 10% calcium carbonate, CaCO3 o Many inorganic magnesium, fluoride, sodium combination forms a composite material that provides flexibility & strength o without organic matter: brittle o without inorganic matter: bendy collagen & minerals of bone form a composite material, provides flexibility & strength o mineral portion allows the bone to support body weight without sagging § Rickets is a disease caused by mineral deficiency and resulting in soft, deformed bones – not enough calcium from diet (could be caused by not enough UV light exposure which is needed to produce vitamin D3) vitamin D3 helps absorb calcium BSC2085-0001 (9/17/24) 14 if blood calcium levels are low, bone tissue is broken down and bones become brittle o protein portion gives some flexibility § collagen molecules contain sacrificial bonds that break under stress and dissipate shock under load § osteogenesis imperfecta (brittle bone disease) results from a defect in collagen deposition à bones snap easily § analogy: collagen is like steel rebar in concrete – it provides extra strength and allows the concrete to bend & not shatter Compact Bone concentric lamellae: layers of matrix surrounding a central (Haversian) canal running longitudinally o a central canal & its lamellae constitute and osteon (Haversian system); central canals connected by transverse perforating/Volkmann’s canals o collagen corkscrews down each lamella; helical arrangement in one lamella is opposite of adjacent lamella – enhances strength (like a hashmark) o osteons separated by a cement line, which prevents spread of microfractures circumferential lamellae: found encircling inner outer region of dense bone o outside interstitial lamellae: fill irregular regions between osteons Spongy Bone spongy bone anatomy: o lattice of bone slivers (spicules) and plates (trabeculae) covered with endosteum, canaliculi of lacunae opens into the surface of the trabeculae o sponge-like appearance o spaces filled with red bone marrow (contains blood vessels). marrow used to produce blood cells o matrix arranged in lamellae, but few osteons & no central canals § all osteocytes close to bone marrow o provides strength with minimal weight (because of its gaps) § trabeculae develop along bone’s lines of stress o has a greater surface area than compact bone o it is the first to be broken down by osteoclasts Bone Marrow bone marrow: soft tissue occupying marrow cavities of long bones and small spaces of spongy bone o red bone marrow (myeloid tissue – involved in the production of blood cells) § contains multiple tissues, including hematopoietic tissue – tissue that 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 & femur o yellow bone marrow found in adults § contains adipose tissue, does NOT produce blood § can transform back to red marrow in event of chronic anemia Bone Remodeling BSC2085-0001 (9/17/24) 15 homeostasis: bone building (osteoblasts) & recycling (osteoclasts) must be balanced o if there is more bone breakdown than building, bone becomes weaker § osteopenia, osteoporosis o if there is more bone building than breakdown, bone becomes stronger § weight-bearing exercise cause osteoblasts to build bone faster than osteoclasts can break down bone tissue o if blood calcium levels are high: released in urine o if blood calcium levels are low: break down bone tissue Bone Loss Bone loss due to microgravity (decrease in gravity) o bone production can increase with an increase in gravity but to an extent LESSON 9: Chapter 07 Bone (Osseous Tissue) Bone Development human bones grow until approximately the age of 25 ossification or osteogenesis: the formation of bone calcification: the process of depositing calcium salts during bone ossification and in other tissues (ex. cartilage) bone develops by two methods, both beginning with embryonic mesenchyme o intramembranous ossification § bone tissue forms in dermis o endochondral ossification § replace cartilage with bone tissue Intramembranous Ossification intramembranous ossification: also called dermal ossification since it occurs in the dermis. important in lifelong thickening and remodeling of long bone. It produces the flat bones of the skull, most of the clavicle, and part of the mandible summary of stages: o production & deposition of osteoid tissue into embryonic mesenchyme à dermis o calcification (using calcium salts) of osteoid tissue and entrapment of osteoblasts, causing them to become osteocytes o honeycomb of spongy bone forms underneath the periosteum which is developing on the outside o osteoblasts under the periosteum fill in between the trabeculae, forming compact bone and leaving spongy bone underneath Endochondral Ossification bone develops from hyaline cartilage model; it produces most bones of body (bones of limbs, vertebrae, ribs, sternum, scapula, pelvic girdle) summary of stages (using the metacarpal as an example): o mesenchyme forms early hyaline cartilage model o formation of primary ossification center (at the center of the long bone – shaft), bony collar – under periosteum, and periosteum) o vascular (blood vessels) invasion (hollows it out) primary ossification center to form the primary marrow cavity – osteoblasts enter and line the cavity, formation of secondary ossification center [formed by osteoblasts] (at an epiphysis – one end of bone) BSC2085-0001 (9/17/24) 16 o bone at birth, the long bone contains an enlarged primary marrow cavity at the diaphysis, a secondary marrow cavity in one epiphysis, and a secondary ossification center in the other epiphysis o during infancy and childhood, the epiphyses fill with spongy bone, and a thin wall of cartilage (epiphyseal plate) separating the primary & secondary marrow cavities o Adult bone contains a single marrow cavity and close epiphyseal plate (the epiphyseal plate ossifies and becomes the epiphyseal line)