Anatomy and Physiology Chapter 1 - The Human Body: An Orientation Anatomy: the study of the body’s structures structures and their relationships to one another Physiology: the study of the body’s function.
Topics of o f Anatomy Gross/macroscopic anatomy: the study of large body structures (ex. kidneys, lungs) egional anatomy: all the structures of the body (muscles, bones, blood, etc.) in a particular region (legs, abdomen, etc.) are studied at one time !ystemic anatomy: body structure is studied system by system. !urface anatomy: the study of internal structures as they relate to the overlying skin surface. "icroscopic anatomy: the study of structures structures too small to be seen with the naked eye (ex. cells). Subdivisions include cytology cytology (cells (cells of the body) and histology (study histology (study of tissues) #e$elopmental anatomy: studies changes in the body throughout the life span, a subdivision being embryology embryology,, the study of developmental changes before birth.
Topics of Physiology as many di!erent subdivisions, mostly concerning speci"c body systems. #or example, renal physiology concerns kidney function and urine production. $ften focuses on events at cellular or molecular level.
Complementarity of !tructure and %unction #e&nition: %he principle of complementarity of structure and function states that what a structure can do depends on its speci"c form. #unction always re&ects structure and anatomy and physiology is inseparable.
'e$els of !tructural Organi(ation Chemical le$el: atoms combine to form molecules such as water and proteins. 'olecules associate to form organelles, the basic components of living cells. %his is the cellular cellular level. Tissue le$el: groups of similar cells that have a common function. #our basic types: epithelium, muscle, connective tissue, and nervous tissue. Organ: a discrete discrete structure composed of at least two tissue types that perform a speci"c function for the body. t the organ level, extremely complex functions functions become possible. Organ system le$el : organs that work together to accomplish a common purpose make up an organ system. %he organismal organismal level represents represents the sum total of all structural structural levels working working together to keep us alive.
"aintaining 'ife "aintaining )oundaries: an organism must keep its internal environment distinct from its external environment. ll the cells of our body are surrounded surrounded by a selectively permeable membrane. %he body as a whole is protected by the intergumentary system or skin. "o$ement : the activities promoted by the muscular system, such as propelling ourselves from one place to another such as running or swimming. s well, movement also occurs when substances are propelled through the internal organs. organs. %his is called contractility, the ability to move by shortening. esponsi$eness : the ability to sense changes in the environment and then respond to them. %he nervous system is most involved with responsiveness. #igestion: the breaking down of ingested food to simple molecules that can be absorbed by the blood, then distributed by the cardiovascular cardiovascular system. "eta)olism : a broad term that includes all chemical reactions that occur within our body cells. Cata)olism: breaking down substances Ana)olism: synthesiing more complex cellular structures *+cretion: the process of removing wastes (excreta) from the body. eproduction : occurs at cellular and organismal level Cellular reproduction reproduction: the original cell divides producing two identical daughter cells that may e used for body growth and repair. *eproduction of the human organism is the ma+or task of the reproductive system, Gro,th: an increase of the sie of a body part or the organism. !ur$i$al eeds utrients: chemical substances used for energy and cell building. %aken in via the diet. O+ygen and ,ater : molecules reuired for most chemical reaction in the body. ormal )ody temperature temperature: needed for continued chemical reactions (- degrees /elcius) Atmospheric pressure : the force that air exerts on the surface of the body. 0reathing and gas exchange rely on appropriate atmospheric pressure.
Homeostasis #e&nition: %he body’s ability to maintain a relatively stable internal internal condition even though the outside world is changing constantly. 1ynamic state of euilibrium refers to the fact that internal conditions conditions vary but always within relatively narrow limits. 2irtually every organ system plays a role in maintaining homeostasis. Homeostatic control /ommunication is essential for homeostasis. homeostasis. ll homeostatic control mechanisms involve at least three components that work together. %he receptor receptor is some type of of sensor that that monitors the environment environment and responds to changes called stimuli by sending information to the control centre along the a!erent pathway. %he control control centre determines determines the the set point (the (the level or range range at which a variable is to be maintained). 3t also analyes the input it receives and
determines the appropriate response. 3nformation then goes to the e!ector along the e!erent pathway. %he e!ector provides the means for the control centre’s response to the stimulus. %he results of the response then feed back to in&uence the e!ects of the stimulus. 3n negative feedback, the response is reduced. 3n positive feedback the response is increased.
egati$e feed)ac. mechanisms : in these systems, the output shuts o! the original e!ect of the stimulus or otherwise reduces its intensity. Positi$e feed)ac. mechanisms : in these systems the result or response enhances the original stimulus so that the result is accelerated. $ften referred to as cascades. Homeostatic im)alance: most diseases can be regarded as a result of homeostatic disturbance. Sometimes occurs when negative feedback cycles are overwhelmed.
The 'anguage of Anatomy !uperior: towards the head end, or upper part of a body structure4 above nferior: towards the lower end (away from the head end) of a body structure4 below 0entral: towards or at the front of the body4 in front of #orsal: towards or at the back of the body4 behind "edial : towards or at the midline of the body4 on the inner side of 'ateral: away from the midline of the body4 on the outer side of ntermediate: between a more medial and lateral structure Pro+imal: closer to the origin of the body part or to the point of attachment of a limb to the body trunk #istal: farther away from the origin of the body part !uper&cial e+ternal2 : towards or at the body surface #eep internal2: away from the body surface, more internal Anatomical position: the body is erect with feet slightly apart. 5alms face forward and the thumbs point away from the body. #irectional terms: allow us to explain where one body structure is in relation to another egional terms A+ial part: includes the head, neck, and trunk. ppendicular part: consist of appendages, or limbs, which are attached to the body’s axis. egional terms: used to designate speci"c areas within these division. Body Planes and !ections #or anatomical studies, the body is often sectioned along a plane. !agittal plane: a vertical plane that divided the body into its right and left parts.
%rontal plane: divide the body into anterior and posterior (front and back) parts Trans$erse plane : runs horiontally from right to left, divided body into superior and inferior parts O)li3ue sections : cuts made diagonally between horiontal and vertical planes
Body Ca$ities and "em)ranes #orsal )ody ca$ity: two subdivisions, cranial cavity (in the skull encasing the brain) and vertebral or spinal cavity (enclosing the spinal cord) 0entral )ody ca$ity: the more anterior and closer body cavities. ouses internal organs collectively called the viscera or visceral organs %wo ma+or subdivisions, the thoracic cavity and the abdominopelvic cavity %he thoracic cavity is superior to the abdominopelvic cavity. 3t is surrounded by the ribs and muscles on the chest. 3t is further subdivided into lateral pleural cavities, each enveloping a lung, and the medial mediastinum. %he mediastinum contains the pericardial cavity which encloses the heart and it also surrounds the remaining thoracic organ (esophagus, trachea, etc.) %he abdominopelvic cavity is inferior to the thoracic cavity, separated by the diaphragm %he abdominal cavity contains the stomach, intestines, spleen, and other organs. %he pelvic cavity (inferior) lies in the pelvis and contains the urinary bladder, some reproductive organs, and the rectum. "em)ranes in the 0entral Body Ca$ity %he walls of the ventral body cavity and the outer surfaces of the organs it contains are covered by a thin, double6layered membrane called the serosa or the serous membrane. %he part lining the cavity walls is the parietal serosa and it folds in on itself to form the visceral serosa. Separated by a thin layer of lubricating &uid: the serous &uid %his &uid allows the organs to slide without friction across other surfaces %he parietal pericardium lines the pericardial cavity and folds back as the visceral pericardium. %he parietal pleurae line the walls of the thoracic cavity and the visceral pleurae cover the lungs. %he parietal peritoneum is associated with the walls of the abdominopelvic cavity while the visceral peritoneum covers most of the organs within that cavity.
Chapter 4 - Tissue: The 'i$ing %a)ric Preparing Human Tissue for "icroscopy ll specimens must be "xed (preserved), cut into thin sections and stained %he stains used in light microscopy are dyes4 the stains in electron microscopy are heavy metal salts rtifacts: minor distortions that alter the tissue’s original condition
*pithelial Tissue
#e&nition: a sheet of cells that cover a body surface or line a body cavity /overing and lining epithelium: forms the outer layer of the skin, lines the open cavities of many systems and covers the walls of the closed ventral cavity Glandular epithelium: fashions the glands of the body !pecial Characteristics of *pithelium 7. Polarity: all epithelia contain an apical surface and a basal surface. ll epithelia exhibit apical6basal polarity, i.e. the cell regions near the apical surface di!er from those near the basal surface in structure and function 'ost apical surfaces have microvilli (for absorption) and some have cilia (to propel substances along their free surface) 0asal lamina: noncellular, adhesive sheet consisting largely of glycoproteins plus some "ne collagen "bres lying ad+acent to the basal surface. cts as a selective "lter or as a sca!olding along which epithelial cells can migrate to repair a wound 8. !peciali(ed contacts : epithelial cells "t close together by tight +unctions and desmosomes to form continuous sheets. %hese tight +unctions help keep proteins in the apical layer from migrating to the basal layer and thus help to maintain epithelial polarity -. !upported )y connecti$e tissue : all epithelial sheets rest upon and are supported by connective tissue. %he basal lamina and the reticular lamina form the basement membrane which helps the epithelia resist stretching and de"nes its boundaries 9. A$ascular )ut inner$ated: epithelia have nerve "bres but no blood vessels. %hey are nourished by substances di!using from the blood in the underlying connective tissue . egeneration : epithelium has a high regenerative capacity. s long as epithelia receive adeuate nutrition, they can replace lost cells by cell division
Classi&cation of *pithelia T,o names: the "rst indicates the number of cell layers and the second describes the shape of its cells Simple epithelia has one layer of cells, strati"ed has two or more ll epithelia have six sides which allows the cells to be closely packed. 0ut they do vary in height: Suamous cells are &attened and scale like, cuboidal cells are box6like and as tall as they are wide, and columnar cells are tall and rectangle shaped Strati"ed cells are named according to the cell shape in the apical layer !imple *pithelia 'ost concerned with absorption, secretion and "ltration ;$% protection !imple !3uamous *pithelium #lattened laterally, cytoplasm is sparse
%hin and permeable, found where "ltration or rapid di!usion is a priority (ex. the kidneys) *ndothelium: slick, friction reducing simple suamous epithelium lining found in lymphatic vessels and in all the hollow organs of the cardiovascular system (blood vessels and heart) "esothelium : found in serous membranes lining the ventral body cavity
!imple Cu)oidal *pithelium /onsists of a single layer of cells as tall as they are wide #unctions to secrete and absorb, forms the walls of the smallest duct glands and kidney tubules !imple Columnar *pithelium single layer of tall, closely packed cells
Glandular *pithelia Gland: one or more cells that make and secrete a particular product (secretion) *ndocrine: internally secreting *+ocrine: externally secreting =nicellular (scattered within epithelial sheets) or multicellular (have ducts at least initially) *ndocrine Glands /alled ductless glands and produce hormones Hormones: regulatory chemicals secreted into the extracellular space that act to stimulate some speci"c target organ in a characteristic way *+ocrine Glands Secrete their products onto body surfaces or into body cavities 5nicellular *+ocrine Glands /onsist of mucous cells and goblet cells sprinkled in the epithelial linings of the intestinal or respiratory tract amid columnar cells with other functions 5roduce mucin that dissolves in water to form mucus 3n goblet cells, the cuplike accumulation of mucin distends the top of the cell so it looks like a goblet "ulticellular *+ocrine Glands T,o )asic parts : a duct and a secretory unit (acinus) Supportive connective tissue surrounds the secretory unit to supply it with blood vessels and nerves #orms a "brous capsule that extends into the gland to divide the gland into lobes !tructural classi&cation: either simple (unbranched duct) or compound (branched duct). %ubular if the secretory cells form tubes or alveolar if the secretory cells form small &ask6like sacs. /alled tubuloalveolar if they have both secretory units "odes of secretion : merocrine secrete their products by exocytosis while holocrine glands accumulate their products within themselves until they rupture. pocrine cells pinch o! a part of their apex releasing the secretion as well as a small amount of cytoplasm. 1ebate as to whether this is found in humans •
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Connecti$e Tissue #ound everywhere, most abundant and widely distributed primary tissue type
Common Characteristics of Connecti$e Tissue 7. Common origin: all connective tissue arises from mesenchyme 8. #egrees of $ascularity : wide variety, from avascular cartilage to poorly vascularied dense connective tissue to well vascularied bone
-. *+tracellular matri+: connective tissue is composed mostly of extracellular matrix which allows it to bear weight, withstand great tension, and so on and so forth.
!tructural *lements of Connecti$e Tissue Three main elements : ground substance, "bres, and cells >round substance and "bres make up the extracellular matrix reolar connective tissue is used as a model for this group of tissues Ground !u)stance #e&nition: unstructured material that "lls the space between the cells and contains the "bres /omposed of interstitial (tissue) &uid, cell adhesion proteins, and proteoglycans /ell adhesion proteins serve as connective tissue ?glue@ that allows the connective tissue cells to attach themselves to matrix elements 5roteoglycans consist of a protein core to which glycosaminoglycans (>>s) are attached >>s (chondroitin sulphate and hyaluronic acid) are large negatively charged polysaccharides that make the ground substance viscous %he ground substance holds large amounts of water and functions as a molecular sieve %i)ers 5rovide support: three types are collagen, elastic, and reticular "bers Collagen &)ers : most abundant, extremely tough and provide high tensile strength *lastic &)ers: long, thin "bers that form a branching network in the extracellular matrix. /an stretch and recoil, snap connective tissue back into normal length and shape after stretching eticular &)ers: short, "ne, collagenous "bers continuous with collagen "bers. 0ranch extensively and form delicate networks around small blood vessels and support the soft tissue of organs Cells Blast cells: undi!erentiated, actively mitotic calls that secrete the ground substance and "bers characteristic of their particular matrix /onnective tissue proper has "broblasts, cartilage has chondroblasts, and bone has osteoblasts $nce they have synthesied the matrix, they become ?cyte@ cells /onnective tissue also contains fat cells, immune cells (like white blood cells and macrophages) "ast cells: cluster along blood vessels to detect foreign microorganisms and initiate the in&ammatory response against them "acrophages : large irregular cells that phagocytie foreign material from bacteria to dust particles
Types of Connecti$e Tissue
Connecti$e Tissue Proper 6 'oose Connecti$e Tissue Areolar Connecti$e Tissue Supports and binds other tissue ("bers), holds body &uids (ground substance), defends against infection (white blood cells and macrophages), and stores nutrients as fat (fat cells) #ibroblasts predominate but other cell types are also present 'ost obvious characteristic is the loose arrangement of its "bers 0ecause of its loose nature, it provides a reservoir of water and salts yaluronic acid makes its ground substance uite viscous and when a body region is in&amed the areolar tissue in the area soaks up excess &uid, so the area become pu!y (edema) 'ost widely distributed, serves as packing material between other tissues 5resent in all mucous membranes as lamina propria Adipose %at2 Tissue Stores nutrients in adipocytes, cells are packed close together and there is little matrix =sually accumulates in subcutaneous tissue to act as a shock absorber, as insulation, and as an energy storage site. elps prevent heat loss from the body eticular Connecti$e Tissue *esembles areolar connective tissue but the only "bers in its matrix are reticular "bers *eticular cells are scattered throughout the reticular "ber network, supports other cell types #ound only in lymph nodes, the spleen, and in bone marrow Connecti$e Tissue Proper 6 #ense Connecti$e Tissues $ften referred to as "brous connective tissues #ense egular Connecti$e Tissue /ontains closely packed bundles of collagen "bers running parallel to the direction of pull *esults in white, &exible structures with great resistance to tension where the tension is exerted in a single direction /ollagen "bers are slightly wavy allowing the tissue to stretch a little %his tissue has few cells other than "broblasts and is poorly vascularied #orms tendons that attach muscle to bone and aponeuroses which attach muscle to muscle 3t also forms fascia and ligaments #ense rregular Connecti$e Tissue Same structural elements as the regular variety except the bundles of collagen "bres are much thicker and run in more than one direction %his type of tissue forms sheets in body areas where tension is exerted in many directions like in the dermis or in "brous +oint capsules *lastic Connecti$e Tissue
few ligaments connecting ad+acent vertebrae are very elastic so that the dense connective tissue found in those structures is referred to as elastic connective tissue
Cartilage Stands up to both tension and compression, has ualities intermediate between dense connective tissue and bone %ough but &exible and provides a resilient rigidity
round substance contains large amounts of >>s, hyaluronic acid, and "rmly bound collagen "bers /artilage is ABC water which allows it to rebound when compressed and helps nourish the cartilage cells Chondro)lasts: predominant cell type in growing cartilage produces new matrix until skeleton stops growing. 'ature chondrocytes are usually found in lacunae %hree types of cartilage: 7. Hyaline Cartilage: most abundant cartilage type, contains large numbers of collagen "bers. 5rovides "rm support with some pliability, covers ends of long bones as articular cartilage 8. *lastic Cartilage: nearly identical to hyaline cartilage but with many more elastic "bers. #ound where strength and stretchability is needed: in the external ear and epiglottis -. %i)rocartilage: rows of chondrocytes alternate with rows of collagen "bers. /ompressible and resists tension well, found where strong support and the ability to withstand heavy pressure is needed: in the intervertebral discs and in the menisci of the knee
"uscle Tissue ighly cellular, well6vascularied tissues that are responsible for body movement "yo&laments: bring about movement or contraction in all cell types !.eletal muscle: these muscles form the &esh of the body and as they contract, they pull on bones or skin to cause body movement. Skeletal muscle cells (muscle "bers) are long cylindrical cells that contain many nuclei. %heir striation re&ects the precise alignment of their micro"laments Cardiac muscle: only found in the wall of the heart and help propel blood throughout the body. re striated but uninucleate and are branching cells that "t together tightly at uniue +unctions called intercalated discs !mooth muscle: have no visible striations, spindle shaped, and only have one nucleus. 'ainly found in the walls on hollow organs except the heart and acts to sueee substances through these organs (peristalsis and such)
Co$ering and 'ining "em)ranes %hree types, all are continuous multicellular sheets with an epithelium bound to an underlying layer of connective tissue proper
Cutaneous "em)rane %he skin: see chapter notes "ucous "em)ranes
resembles that of the ad+acent skin. %he end result is fully regenerated epithelium and an underlying area of scar tissue which may be visible or not
%his repair process follows healing of a wound. 3n simple infection, healing is by regeneration only
egenerati$e Capacity of #i8erent Tissues Dpithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, and blood6forming tissue regenerate extremely well Smooth muscle and dense regular connective tissue regenerate moderately well but skeletal muscle and cartilages have a weak regenerative capacity /ardiac muscle and the nervous tissue of the brain and spinal cord have virtually no functional regenerative capacity 3n nonregenerative tissues and in exceptionally severe wounds, "brosis totally replaces lost tissue
#e$elopmental Aspects of Tissues %he "rst events of embryonic development is the formation of three primary germ layers: the ectoderm , mesoderm , and endoderm %hese primary germ layers then specialie to form the four primary tissues: epithelium, nervous tissue, muscle, and connective tissue 3n adults, only epithelia and blood6forming tissues are highly mitotic
Chapter 9 - The ntegumentary !ystem T,o distinct regions : the epidermis and the dermis *pidermis: composed of epithelial cells, outermost protective shield of the body %he underlying dermis makes up the bulk of the skin and is a tough, leathery layer composed mostly of "brous connective tissue. 2ascularied ;utrients reach the epidermis by di!using through the tissue &uid from blood vessels in the dermis Hypodermis : the subcutaneous tissue +ust deep to the skin, is not part of the skin but shares some protective functions. lso called the super"cial fascia, it is super"cial to the skeletal muscles and is composed mostly of adipose tissue %he hypodermis anchors the skin to the underlying structures but loose enough so it can still slide freely (this ensures that many blows +ust glance o! our body). lso acts as a shock absorber and an insulator
*pidermis
#e&nition: keratinied strati"ed suamous epithelium consisting of four distinct cell types and four or "ve distinct layers Cells of the *pidermis eratinocytes : chief role is to produce keratin, are tightly connected by desmosomes and arise in the deepest cell layer known as the stratum basale. %hese cells undergo almost continuous mitosis4 as the cells are pushed upwards by the new cells being produced beneath them, they make the keratin that eventually dominates their cell contents. 0y the time the keratinocytes reach the free surface of the skin, they are little more than keratin "lled plasma membranes. 'illions of these dead cells rub o! every day "elanocytes : spider6shaped epithelial cells that synthesie the pigment melanin. #ound in the deepest layer of the epidermis and melanin accumulates in melanosomes that are moved along to the ends of the melanocyte’s process. #rom there, they are taken up by the keratinocytes %he melanin granules accumulate on the super"cial side of the keratinocytes and form a pigment shield to protect against =2 rays *pidermal dendritic cells 'angerhans cells2 : arise from bone marrow and migrate to the epidermis. %hey ingest foreign substances and are key activators of our immune system. Tactile "er.el2 cells : present at the epidermal6dermal +unction and function as a sensory receptor for touch 'ayers of the *pidermis Thic. $s; thin s.in : "ve layers in thick skin (extra stratum lucidum) and only four in thin skin (layers are also signi"cantly thinner) !tratum Basale Basal 'ayer2 1eepest epidermal layer, attached to the underlying dermis along a wavy borderline, consisting of a single layer of stem cells representing the youngest keratinocytes. lso called the stratum germinativum because of the rapid division of cells. Dach time one basal cell divides, one daughter cell is pushed into the cell layer above to begin the process of becoming a mature keratinocyte while the other stays behind to continue the process of producing new keratinocytes Some melanocytes present in the stratum basale and occasional tactile cells !tratum !pinosum Pric.ly 'ayer2 Several cell layers thick4 cells contain intermediate "laments (mainly tension6 resistant bundles of pre6keratin "laments) which span their cytosol to attach to desmosomes
s well as keratinocytes, there are melanin granules and epidermal dendritic cells (most abundant here)
!tratum Granulosum Granular 'ayer2 %hree to "ve cell layers in which keratiniation begins. Eeratinocytes &atten, their nuclei and organelles begin to disintegrate, and they accumulate two types of granules. eratohyaline granules: help to form keratin in the upper layers 'amellated granules: contain a water6resistant glycolipid that is spewed into the extracellular space that helps slow water loss across the epidermis Eeratinocytes become more resistant to destruction as their plasma membranes thicken and lipids released by the lamellated granules coat their external surface ote: above the stratum granulosum, the epidermal cells are too far from the dermal capillaries and get cut o! from nutrients and so they die !tratum 'ucidum Clear 'ayer2 %wo or three rows of clear, &at, dead keratinocytes with indistinct boundaries4 visible only in thick skin ere, the gummy substance of the keratohyaline granules clings to the keratin "laments in the cells, causing them to integrate into cable6like, parallel arrays !tratum Corneum Horny 'ayer2 $utermost layer and is a broad one of 8B to -B cell layers. ccounts for up to three uarters of the thickness of the epidermis Eeratin and the thick plasma membranes of the cells in this layer protect the skin against abrasion and penetration. %he glycolipid between its cells waterproofs this layer %he cell remnants of the stratum corneum are referred to as corni"ed or horny cells
#ermis #e&nition: Second ma+or skin region, is made up of strong, &exible connective tissue 3ts cells are typical of any connective tissue proper and include: "broblasts, macrophages, and occasional mast cells and white blood cells *ichly supplied with nerve cells, blood vessels, and lymphatic vessels air follicles, oil, and sweat glands are derived from the epidermis but reside in the dermis T,o layers: the papillary layer and the reticular layer The thin super&cial papillary layer is areolar connective tissue in which "ne, interlacing collagen and elastic "bres are mixed with small blood
vessels. 5hagocytes and other defensive cells wander freely through this layer looking for bacteria and other foreign substances #ermal papillae: peg like pro+ections on the superior surface of the papillary layer that indent the overlying dermis. 'ost contain capillary loops but some house free nerve endings and touch receptors ( 'eissner’s corpuscles) $n the palms of the hands and soles of the feet, these papillae lie atop dermal ridges, causing the epidermis to form epidermal ridges. /alled friction ridges, these increase gripping ability Sweat pores open along their crests (this is what creates "ngerprints) The deeper reticular layer is coarse, irregularly arranged, dense "brous connective tissue Cutaneous ple+us: the network of blood vessels, lying between the reticular layer and the hypodermis, which nourishes the reticular layer %he extracellular matrix of the reticular layer contains pockets of adipose cells and thick bundles of collagen "bres, mostly running parallel to the skin’s surface. Separations between these bundles form cleavage, or tension, lines in the skin. n incision is usually made parallel to these externally invisible cleavage lines %he collagen "bres of the dermis give skin strength and prevent most scrapes and +abs from penetrating the dermis. /ollagen also binds water and elastic "bres provide the stretch6recoil properties of the skin %le+ure lines : dermal folds that occur at or near +oints where the dermis is tightly secured to deeper structures and so cannot slide easily, causing deep skin creases to form
!.in Colour "elanin: a polymer made of tyrosine amino acids, ranges in colour from yellow to tan to reddish brown to black. 'ade by melanocytes and based on to the keratinocytes. Dventually, the melanosomes are broken down by lysosomes so it can only be found in the deeper layers of the epidermis. 5rotects 1; against the damaging e!ects of =2 radiation Carotene: a yellow to orange pigment found in certain plant products (such as carrots), tends to accumulate in the stratum corneum and in the fatty tissue of the hypodermis. 'ay pigment skin %he pinkish hue of fair skin is due to the colour of haemoglobin. /aucasian skin does not contain much melanin pigment and so allows haemoglobin’s crimson colour to show through
Appendages of the !.in key step in forming a skin appendage is the formation of an epithelial bud. %he process is stimulated by reduced production of cell adhesion factor (cadherin). $nce the cell6to6cell attractions are broken, the cells can move about and rearrange themselves, allowing an epithelial bud to form.
!,eat !udoriferous2 Glands T,o types: eccrine and apocrine 0oth types are associated with myoepithelial cells: specialied cells that contract when stimulated by the nervous system to force sweat to the skin surface *ccrine or merocrine2 s,eat glands : numerous simple, coiled, tubular glands. %he secretory part lies coiled in the dermis and the duct opens in a funnel shaped pore at the skin surface *ccrine gland secretion : a hypotonic "ltrate of the blood that is released through exocytosis by the secretory cells of the sweat glands Sweating is regulated by the sympathetic division of the autonomic nervous system. 3ts ma+or role is to prevent overheating of the body. Apocrine s,eat glands : found on axillary and anogenital regions and secretes a thick, milky or yellowish version of sweat. /ontains all the components of regular sweat plus some fatty substances and proteins Ceruminous glands: modi"ed apocrine glands whose product mixes with sebum to produce earwax
!e)aceous Oil2 Glands #e&nition: Simple, branched alveolar glands that secrete sebum (an oily substance) Holocrine glands: the central cells accumulate sebum until they burst and these lipids and cell fragments constitute sebum. Sebum is usually secreted into a hair follicle Sebum softens and lubricates hair and skin, prevents hair from becoming brittle, and slows water loss in skin. lso, has bactericidal properties %he arrector pili contractions force sebum out of the hair follicles to the skin surface
Hairs and Hair %ollicles #e&nition: airs or pili are &exible strands produced by hair follicles and consist largely of dead, keratinied cells air senses insects on the skin before they bite or sting us, hair on the scalp guards against trauma, heat loss, and sunlight. Dyelashes shield the eyes, and nose hairs "lter large particles from the air we inhale !tructure of a Hair Hard .eratin: dominated hair and nails (vs. soft keratin found in skin cells) and is tougher and more durable and does not &ake !haft: portion of hair where keratiniation is complete oot: portion of hair where keratiniation is still ongoing %hree concentric layers of keratinied cells:
"edulla : the central core consists of large cells and air spaces. $nly part of hair with soft keratin Corte+: the bulky layer surrounding the medulla, consists of several layers of &attened cells Cuticle: outermost layer, formed from a single layer of &attened cells that overlap like shingles on a roof. 3t is the most keratinied part of the hair and provides strength and keeps the inner layers compacted air pigment is made by melanocytes at the base of the hair follicle and transferred to the cortical cells !tructure of a Hair %ollicle air follicles fold down from the epidermis into the dermis Hair )ul): the deep end of the follicle4 is extended. hair follicle receptor or root hair plexus wraps around the hair bulb so it serves a sensitive touch receptor Hair papilla: contains a knot of capillaries that supply nutrients to the hair and signal it to grow %he wall of a hair follicle is composed of an outer connective root sheath, a thickened basement membrane called the glassy membrane, and an inner epithelial root sheath Hair matri+: actively dividing area of hair bulb that produces the hair, originates in the hair bulge (located close to the hair bulb) %he arrector pili is attached so that its contraction pulls the hair upwards and dimples the skin Types and Gro,th of Hair 0ellus: pale, "ne body hair of females and children Terminal: coarse, long hair of eyebrows, scalp, axillary and pubic regions Dach follicle goes through a growth cycle, in each cycle an active phase is followed by a regressive phase 1uring the regressive phase, the hair matrix cells die and the follicle base and hair bulb shrivel somewhat and the follicle enters a resting phase of one to three months fter the resting phase, the follicle regenerates and new hair growth starts
ails #e&nition: a scalelike modi"cation of the epidermis that forms a protective layer over the dorsal surface of the distal part of a "nger or toe. ;ails contain hard keratin Dach nail has a free edge and a body (the visibly attached portion) and a proximal root (within the skin) %he nail matrix is the thickened proximal position of the nail bed (the deeper layers of epidermis that extend beneath the nail) that is responsible for nail growth
%he hyponychium is the region below the free edge, informally called the uick
%unctions of the ntegumentary !ystem Protection %he skin constitutes three types of barriers: chemical , physical , and )iological Chemical 3nclude skin secretions and melanin, the acid mantel stops bacteria multiplication, and many bacteria are killed by dermcidin in sweat and bactericidal substances in sebum 1efensins are natural antibiotics secreted by the skin /athelicidins are protective peptides that prevent infection by >roup streptococcus bacteria 'elanin shields skin cells from =2 rays Physical/"echanical Barriers 5rovided by the continuity of the skin and the hardness of its keratinied cells and the water resistant glycolipids of the epidermis block most di!usion of water and water soluble substances between cells Some things do penetrate skin cells though (ex. #at soluble substances) Biological Barriers 3nclude the dendritic cells of the epidermis, macrophages within the dermis, and 1; itself %he dendritic cells activate the immune system by presenting antigens to the lymphocytes %he dermal macrophages are the second line of defense and they too act as antigen ?presenters@ 1; converts potentially destructive radiation into harmless heat
Body Temperature egulation Sweat glands secrete insensible perspiration daily to maintain body temperature homeostasis Sensible perspiration is activated in response to vigorous physical activity or high heat levels Fhen the external environment is cold, dermal blood vessels constrict to allow blood to bypass the skin surface temporarily thus slowing passive heat loss
Cutaneous !ensation /utaneous sensory receptors are found throughout the skin and they respond to stimuli outside the body (exteroceptors)
'eissner’s corpuscles in the dermal papillae and tactile discs allow us to feel something like a caress, while 5acinian corpuscles in the deeper dermis or hypodermis alert us to contact with deeper pressure air follicle receptors report on things like wind blowing though our hair #ree nerve endings sense painful stimuli
"eta)olic %unctions Skin modi"es cholesterol in the blood to a vitamin 1 precursor when hit by sunlight %he precursor is then transported to other body systems which activate it. 2itamin 1 plays a role in calcium metabolism and absorption Skin cells also activate some steroid hormones and make several biologically important enymes
Blood eser$oir %he dermal vascular supply is extensive and can hold large volumes of blood Fhen other body organs reuire a greater blood supply, the dermal blood vessels constrict to shunt more blood into the general circulation
*+cretion
Chapter < - Bones and !.eletal Tissues !.eletal Cartilages Bone !tructure= Types= and 'ocations !.eletal cartilage: made up of some variety of cartilage tissue consisting primarily of water. %he high water content of cartilage accounts for its resilience %he cartilage contains no nerves or blood vessels. 3t is surrounded by perichondrium, a layer of dense irregular connective tissue. %he perichondrium acts as to resist outward expansion of the cartilage and it contains the blood vessels from which nutrients di!use to reach the cartilage %here are three types of cartilage in the body. ll contain chondrocytes encased in lacunae with an extracellular matrix containing ground substance and "bers. Hyaline cartilages: provide support with &exibility and resistance, most abundant skeletal cartilage. $nly have "ne collagen "bers. Skeletal hyaline includes articular cartilages (covering ends of most bones and +oints), costal cartilages (connecting the ribs to the sternum), respiratory cartilages (forming the skeleton of the larynx and reinforcing other respiratory passageways), and nasal cartilages (supporting the nose) *lastic cartilages: contain more stretchy elastic "bers and are better able to stand up to repeated bending. %hey are found in the external ear and in the epiglottis
%i)rocartilages: highly compressible and have great tensile strength. /onsist of parallel rows of chondrocytes alternating with thick collagen "bers. #ound in sites sub+ected to heavy pressure and stretch, like the knee and the disks between the vertebrae
Gro,th of Cartilage #lexible matrix can accommodate mitosis. >rows in two ways: Appositional gro,th: cartilage6forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage nterstitial gro,th: the lacunae6bound chondrocytes divide and secrete new matrix, expanding the cartilage from within /artilage growth usually ends during adolescence
Classi&cation of Bones %he axial skeleton forms the long axis of the body and includes the skull, vertebral column, and rib cage. 3nvolved in protecting, supporting, or carrying other body parts %he appendicular skeleton consists of the bones of the upper and lower limbs and the bones that attach the limbs to the axial skeleton (shoulder and hip bones). %hese bones help us move and manipulate our environment.
'ong )ones: considerably longer than they are wide. as a shaft plus two ends. ll the limb bones except the wrist and ankle bones are long bones. !hort )ones: roughly cube shaped. 3nclude the bones of the wrist and ankle. !esamoid )ones: a special type of short bone found in a tendon %lat )ones: thin, &attened, usually a bit curved. %he sternum, scalpulae, ribs, and skull bones are &at bones. rregular )ones: have complicated shapes that "t none of the other classes. 3nclude vertebrae and hip bones.
%unctions of Bones !upport: bones provide a framework that supports the body and cradles its soft organs Protection: the fused bones of the skull protect the brain, the vertebrae surround the spinal column, the rib cage protects the vital organs of the thorax, etc. "o$ement : skeletal muscles use the bones as levers to move the body and its parts. Goints determine the range of movement possible "ineral and gro,th factor storage: bone is a reservoir for minerals, esp. calcium and phosphate. %he stored minerals are released into the bloodstream as needed. dditionally, bone matrix stores important growth factors Blood cell formation: most hematopoiesis (blood cell formation) occurs in the marrow cavities of certain bones Triglyceride fat2 storage : fat is stored in bone cavities as a source of stored energy
Bone !tructure
Gross Anatomy Bone "ar.ings 0ones display pro+ections, depressions, and openings that serve as the site of muscle, ligament, and tendon attachment, or as conduits for blood vessels and nerves Pro>ections: grow outward from the bone surface, and are usually an indication of the stresses created by muscles attached and pulling on them or are modi"ed surfaces where bones meet and form +oints
Pro>ections That Are !ites of "uscle and 'igament Attachment Tu)erosity: large rounded pro+ection, may be roughened Crest: narrow ridge of bone, usually prominent Trochanter: very large, blunt, irregularly shaped process (only found on femur) 'ine: narrow ridge of bone, less prominent than a crest Tu)ercule : small rounded pro+ection or process *picondyle : raised area on or above a condyle !pine: sharp, slender, often pointed pro+ection Process : any bony prominence Pro>ections That Help to %rom ?oints Head: bony expansion carried on a narrow neck %acet: smooth, nearly &at articular surface Condyle: rounded articular pro+ection amus: armlike bar of bone #epressions and openings : usually serve to allow passage of nerves and blood vessels #epressions %or Passage of Blood 0essels and er$es Groo$e: furrow %issure: narrow, slitlike opening %oramen: round or oval opening through a bone otch: indentation at the edge of a structure Others "eatus : canal6like passageway !inus: cavity within a bone, "lled with air and lined with mucous membrane %ossa: shallow, basinlike depression in a bone, often serving as an articular surface
Bone Te+tures: Compact or !pongy Bone %he external layer is compact bone and internal to this is spongy bone Spongy bone is a honeycomb of small needle6like or &at pieces of trabeculae %he open spaces between trabeculae are "lled with yellow or red bone marrow
!tructure of a Typical 'ong Bone Same general structure: shaft, bone ends, and membranes #iaphysis: shaft, forms the long axis of the bone. /onstructed of a relatively thick collar of compact bone that surrounds a central medullary cavity or
marrow cavity (in adults, this contains fat and is called the yellow marrow cavity) *piphysis: bone ends. /ompact bone forms the exterior and the interior contains spongy bone. %he +oint end is covered by a thin layer of articular (hyaline) cartilage. 0etween the diaphysis and the epiphysis of an adult long bone in an epiphyseal line (a remnant of the epiphyseal plate, a disk of hyaline cartilage that grows during childhood to lengthen the bone) "etaphysis : the region where the diaphysis and epiphysis meet
"em)ranes %he external surface of the bone (except the +oint surface) is covered by a glistening white, double6layered membrane called the periosteum Periosteum: has two layers, the outer "brous layer (dense irregular connective tissue) and the inner osteogenic layer, abutting the bone surface (consists primarily of bone forming cells called osteoblasts and bone destroying cells called osteoclasts). 3n addition, there are primitive stem cells called osteogenic cells that give rise to osteoblasts %he periosteum is supplied with nerve endings, lymphatic vessels, and blood vessels entering through the nutrient foramina Perforating !harpey@s2 &)ers: secure the periosteum to the underlying bone. /onsist of tufts of collegen "bers that extend from its "brous layer into the one matrix *ndosteum: delicate connective tissue covering the internal bone surfaces. /overs the trabeculae of spongy bone and lines the canals that pass through compact bone. /ontains both bone6forming and bone6destroying cells
!tructure of !hort= rregular= and %lat )ones ll share a simple design: consist of thin plates of periosteum6covered compact bone on the outside and endosteum6covered spongy bone on the inside. 1o not have a shaft or epiphysis. %hey contain bone marrow, but no marrow cavity is present 3n &at bones, the spongy bone is called the diploH
'ocation of Hematopoietic Tissue in Bones ematopoietic tissue (red marrow) is typically found in the trabecular cavities of spongy bone in long bones and in the diploH of &at bones 0oth cavities are often referred to as red marrow cavities 3n newborns, the medullar cavity of the diaphysis and all areas of spongy bone contain red bone marrow. 3n adult long bones, however, the fat6 containing medullary cavity extends well into the epiphysis and little red marrow is present in spongy bone cavities 'ost blood cell production in adult long bones occurs only in the head of the femur and humerus %he red marrow found in the diploH of &at bones and in some irregular bones is much more active in hematopoiesis
"icroscopic Anatomy of Bone
#our main cell types populate bone: osteogenic cells, osteoblasts, osteocytes, and osteoclasts. %hese are surrounded by an extracellular matrix of their own making
Compact Bone Osteon or Ha$ersian system2 : the structural unit of compact bone. Dach osteon is an elongated cylinder oriented parallel to the long axis of the bone. #unctions as a weight6bearing pillar n osteon is a group of hollow tubes of bone matrix, each one placed outside the next Dach matrix tube is called a lamella (compact bone is often called lamellar bone) 3n each lamella, the collagen "bers fun in a single direction, opposite to the direction of the ad+acent lamella. %his helps reduce torsion stress %iny crystals of bone slats also align with the collagen "bers and thus also alternate their direction in the ad+acent lamella Central canal or Ha$ersian canal2: a canal running through the core of each osteon, containing small blood vessels and nerves Perforating canals or 0ol.mann@s canals2 lie at right angles to the long axis of the bone and connect the blood supply of the periosteum to those of the central canal and medullary cavity %hese canals are lined with endosteum $steocytes occupy lacunae at the +unctions of lamellae. /analiculi connect the lacunae to one another and to the central canal /analiculi form when bone matrix hardens and the osteocytes become trapped within it. %iny canals, formerly tentacle6like extensions containing gap +unctions of the osteocytes, are thusly formed %he canaliculi tie all the osteocytes in an osteon together, permitting nutrient and wastes to be relayed from one osteocyte to the next throughout the osteon. 3t also permits cell6to6cell relays through its gap +unctions to allow bone cells to be well6nourished $steocytes maintain the bone matrix and act as stress or strain sensors in cases of bone deformation or other damaging stimuli. %hey also communicate with osteoblasts and osteoclasts nterstitial lamellae: incomplete lamellae lying between intact osteons. %hey either "ll gaps between forming osteons or are remnants of osteons cut through by bone remodeling Circumferential lamellae: extend around the entire surface of the diaphysis and resist twisting of the long bone
!pongy Bone %he trabeculae in spongy bone align to resist stress as much as possible %rabeculae contain irregularly arranged lamellae and osteocytes interconnected by canaliculi. ;o osteons are present. ;utrients reach the osteocytes by di!usion
Chemical Composition of Bone $rganic compounds include the cells and osteoid (the organic part of the matrix) $steoid includes ground substance and collagen made by the osteoblasts
!acri&cial )onds: between collagen molecules, break easily on impact to dissipate energy and prevent the bone from fracturing Hydro+yapatites mineral salts2: largely calcium phosphates present in the form of tiny crystals in and around collagen "bers in the extracellular matrix. ccount for the bone’s exceptional hardness which allows it to resist compression
Bone #e$elopment Ossi&cation osteogenesis2 : the process of bone formation %ormation of the Bony !.eleton %he skeleton of a human embryo before week A is constructed entirely from "brous membrane and hyaline cartilage 0one tissue eventually replaces most of the "brous or cartilage structures Structure (membranes and cartilage) that are &exible and resilient are able to accommodate mitosis so make growth easier ntramem)ranous Ossi&cation 1eveloped from a "brous membrane and results in the formation of the skull and the clavicles (membrane bones)4 most bones formed by this process are &at bones %our steps: 7. Ossi&cation centers appear in the &)rous connecti$e tissue mem)rane. Selected mesenchymal cells cluster and di!erentiate into osteoblasts, forming and ossi"cation center 8. Bone matri+ osteoid2 is secreted )y osteo)lasts ,ithin the &)rous mem)rane and calci&es; %rapped osteoblasts become osteocytes -. o$en )one and periosteum form. ccumulating osteoid is laid down in a random manner between embryonic blood vessels, forming a network of trabeculae called woven bone. 2ascularied mesenchymal condenses on the external face of the woven bone and becomes periosteum 9. 'amellar )one replaces ,o$en )one= >ust deep to the periosteum . *ed marrow appears. %rabeculae +ust deep to the periosteum thicken and are later replaced with mature lamellar bone, forming compact bone plates. Spongy bone (diploH), consisting of distinct trabeculae, persist internally and its vascular tissue becomes red marrow
*ndochondral Ossi&cation 0one development by replacing hyaline cartilage4 essentially all bones of the skeleton below the base of the skull are formed like this. 0egins in the centre of the hyaline cartilage at a region called the primary ossi"cation centre #irst, the perichondrium covering the hyaline cartilage ?bone@ in in"ltrated with blood vessels, converting in into a vascularied periosteum. s a result of this, the underlying mesenchyme cells specialie into osteoblasts. ;ow ossi"cation can begin.
1; A )one collar is laid do,n around the diaphysis of the hyaline cartilage model. $steoclasts secrete osteoid against the hyaline cartilage diaphysis, encasing it with bone. %his is called the periosteal )one collar. ; Cartilage in the centre of the diaphysis calci&es and then de$elops ca$ities . s the bone collar forms, chondrocytes within the shaft enlarge and signal the surrounding cartilage matrix to calcify. %he chondrocytes deteriorate due to lack of nutrients di!using from the blood and this deterioration opens up cavities. Dlsewhere, the cartilage grows briskly, causing the cartilage model to elongate ; The periosteal )ud in$ades the internal ca$ities and spongy )one forms. %he periosteal )ud contains a nutrient vein and artery, lymphatic vessels, nerve "bers, red marrow elements, osteoblasts, and osteoclasts. %he osteoclasts partially erode the calci"ed cartilage matrix and the osteoblasts secrete osteoid around the remaining fragments of hyaline cartilage, forming bone6covered cartilage trabeculae (the earliest version of spongy bone) 4; The diaphysis enlarged and a medullar ca$ity forms . s the primary ossi"cation enlarges, osteoclasts break down the newly formed spongy bone and open up a medullar cavity in the centre of the diaphysis. %he rapidly growing epiphysis still contains only cartilage, and the hyaline cartilage models continue to elongate by the division of viable cartilage cells at the epiphysis. $ssi"cation ?chases@ cartilage formation along the length of the shaft as cartilage calci"es, is eroded, and then is replaced by bony spicules on the epiphyseal surfaces facing the medullar cavity. 9; The epiphysis ossi&es . fter birth, secondary ossi"cation centers appear in one or both epiphyses and the epiphyses gain bony tissue. %he cartilage in the centre of the epiphysis calci"es, opening up cavities that allow a periosteal bud to enter. %he bony trabeculae form, +ust like in the diaphysis. Secondary ossi"cation is almost the exact same as primary ossi"cation, except the spongy tissue is retained and no medullar cavity is formed in the epiphysis. fter secondary ossi"cation, hyaline cartilage remains only on the epiphyseal surfaces as articular cartilage and at the +unction between the epiphysis and the diaphysis (the epiphyseal plate)
Postnatal Bone Gro,th
Gro,th in 'ength of 'ong Bones
Proliferation or gro,th (one: cells abutting the diaphysis, dividing rapidly, pushing the diaphysis way from the epiphysis thus allowing the whole bone to lengthen. Hypertrophic (one: older chondrocytes close to the diaphysis hypertrophy, leaving large interconnecting spaces. Calci&cation (one: area where the cartilage surrounding the hypertrophic one calcify so the chondrocytes die and deteriorate
Gro,th in idth Thic.ness2 >rowing bones widen as they lengthen by appositional growth $steoblasts beneath the periosteum secrete bone matrix while osteoclasts on the endosteal surface of the diaphysis remove bone %here is slightly less breaking down than building up, creating a thicker, stronger bone
Hormone egulation of Bone Gro,th *egulated by growth hormone released by the anterior pituitary gland, by thyroid hormones, and by male and female sex hormones (in puberty, leading to a growth spurt and masculiniationIfemininiation of certain parts of the skeleton)
Bone Homeostasis: emodeling and epair Bone emodeling 0one depositing and bone resorption occurs at the surface of the periosteum and the endosteum. %he two processes constitute bone remodeling. emodeling units: packets of ad+acent osteoblasts and osteoclasts that couple and coordinate bone remodeling Bone deposit: occurs wherever bone is in+ured or added bone strength is reuired Osteoid seam: an unmineralied band of gauy looking bone matrix, marking the presence of new matrix deposits by osteoblasts Calci&cation front: an abrupt transition between the osteoid seam and the older mineralied bone %he trigger for calci"cation of the osteoid seam is the local concentrations of phosphate ions and calcium ions and the presence of the enyme alkaline phosphatase Bone resorption: accomplished by osteoclasts as they digest the bone’s surface
$steoclasts secrete lysomal enymes to digest the organic matrix and hydrochloric acid to convert calcium salts into soluble forms %he dissolved matrix end products, growth hormones, and dissolved minerals are endocytosed, transported across the osteoclasts by transcytosis, and released into the blood by way of the interstitial &uid
Control of emodeling *egulated by two control loops: a negative feedback hormonal loop that maintains /a8J levels in the blood and another that involves responses to mechanical and gravitational forces acting upon the skeleton
Hormonal Controls 5arathyroid hormone (5%) and calcitonin regulate the amount of calcium in the blood 5% secretion is stimulated by decreased calcium levels in the blood to cause osteoclasts to resorb bone and boost blood calcium levels 3ncreased blood calcium causes 5% to stop being secreted in a negative feedback cycle esponse to "echanical !tress ol8@s la,: a bone grows strong or remodels in response to the demands placed upon it. bone’s anatomy re&ects the common stresses in encounters s a result of bending caused by weight bearing down on a bone, long bones are thickest midway along the diaphysis where the stress is the greatest. 0oth compression and tension are minimal towards the center of the bone so a bone can hollow out for lightness Bone epair 0ones are susceptible to fractures. They may )e classi&ed )y: 5osition of the bone ends after fracture : nondisplaced fractures vs. displaced fracture: whether bones are in their original alignment or not /ompleteness of the break: complete vs. incomplete: whether the bone is broken through or not $rientation of the break relative to the long axis of the bone : linear fractures run parallel to the long axis, transverse run perpendicular to it. Fhether the bone end penetrates the skin : open (compound) fractures vs. closed (simple) fractures eduction: realignment of the broken ends of a bone. 3n a closed (external) reduction, the physician coaxes it into position with his hands. 3n an open (internal) reduction, the bone ends are secured together surgically with pins or wires. 3t is then immobilied by a cast epair in a simple fracture in$ol$es four main stages: 7. A hematoma a mass of clotted )lood2 forms at the fracture site. Soon, bone cells deprived of nutrition die and the area becomes swollen, painful, and in&amed 8. %i)rocartilaginous callus forms. /apillaries grow into the hematoma and phagocytic cells invade the area begin cleaning up debris. 'eanwhile, "broblasts and osteoblasts invade the fracture site
and begin reconstructing the bone. %he "broblasts create collagen "bers that connect the broken bone ends. Some di!erentiate into chondroblasts and begin secreting cartilage matrix. %his entire mass of repair tissue, now called the "brocartilaginous callus , splint the bone -. Bony callus (the new bone trabeculae that appear in the "brocartilaginous callus to convert it to spongy bone) forms. 9. Bone remodeling occurs . %he bony callus is remodeled so the excess material on the diaphysis exterior is removed and compact bone is laid down to reconstruct the shaft walls. %he "nal structure of the remodeled area looks like the original unbroken bone because it withstands the same mechanical stressors
Homeostatic m)alances of Bone Osteomalacia and ic.ets $steomalacia includes a variety of disorders in which the bones are inadeuately mineralied. 0ones are soft and weak because calcium salts are not deposited in the osteoid *ickets is the analogous disease in children 0oth are caused by insuKcient calcium in the diet or by a vitamin 1 de"ciency Osteoporosis *efers to a group of diseases in which bone resorption outpaces bone deposit. %he bones become excessively fragile and break very easily. %he composition of the bone matrix is reduced and the bones become porous and light. $ccurs most often in the aged, especially women %reated by calcium and vitamin 1 supplements, weight6bearing exercise, and certain drugs that mimic estrogen or otherwise decrease osteoclasts activity Paget@s #isease /haracteried by excessive and haphaard bone deposit and resorption. %he newly formed 5agetic bone is hastily made and has an abnormally high ratio of spongy bone to compact bone. 1rug therapies have shown success in preventing bone breakdown.
