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Biology 220 Test 1 Chapter 7: Bone Tissue  Information in chapters 8 (bones of the skeletal system) and 9 (joints) will be covered in the laboratory. For your lecture test, familiarize yourself with purposes of the skeletal system, histology of spongy and compact bone, anatomy of long bones, endochondral and intramembranous bone, effects of vitamins, minerals and hormones on bone health and growth.  Functions of the Skeleton ● support ▪ bones of the lower limbs, pelvis, & vertebral column hold up the body ▪ nearly all bones provide support for the muscles & soft tissue  ▪ mandible & maxilla support the teeth ● protection ▪ bones enclose & protect the brain, spinal cord, heart, lungs, pelvic viscera, & bone marrow (protects the delicate structures ) ● movement ▪ bones allow mobility by serving as a lever ▪ limb movements, breathing, & other movements are produced by the action of muscle on the bones ● electrolyte balance ▪ skeleton s tores calcium,  phosphate  ions,  &  fat  (yellow  bone  marrow)  & releases them into the tissue fluid & blood according to the body’s physiological needs ● acid-base balance ▪ bone tissue buffers the blood against excessive pH changes by absorbing or releasing alkaline phosphate and carbonate salts ● blood formation ▪ red bone marrow is the major producer of blood cells, including cells of the immune system (hemopoiesis)   Bones by Shape ● long bones ▪ most important bones in body movement are the long bones of the  limbs because they  serve as rigidlevers thatareactedupon byskeletalmuscles to  produce the major body movements ▪ humerus, radius, & ulna of the arm & forearm ▪ femur, tibia, & fibula of the thigh & leg ▪ metacarpals, metatarsals, & phalanges of the hands & feet ● flat bones ▪ most of the c ranial  bones;  such  as  the  paired  parietal  bones  that  form  the  dome of the top of the head ▪ sternum (breastbone), scapula (shoulder blade), ribs & hip bones

● short bones ▪ wrists & ankles have a total of 30 short bones ( carpal & tarsal bones ) ▪ produce relatively limited gliding movements ● irregular bones ▪ bones that do not fit into any of the other categories ▪ vertebrae & the sphenoid & ethmoid bones of the skull (some facial bones) ● sesamoid bones ▪ bone embedded within a tendon ▪ kneecap  Typical Long Bone ● makes red blood cells ● composed of an outer shell of dense white osseous tissue called c ompact (dense or lamellar) b  one ● the shell encloses a space called the m  edullary cavity or marrow cavity, which contains yellow bone marrow & spicules of spongy bone  ▪ it is lined by a layer of cells at rest which are called  cytes ● at the end of the bone, the central space is occupied by a more loosely organized form of osseous tissue called spongy (cancellous)  bone by compact bone surrounded ▪ ▪ consists of slivers of bone called s picules & t rabeculae (thin plates) ▪ calcified & hard but named for its sponglike  appearance  ● principal  features  of  a  long bone  are  its  shaft, called the d  iaphysis  ( not solid  because of medullary cavity) and an expanded head at each end called the epiphysis ▪ the diaphysis provides leverage ▪ the epiphysis is e nlarged to strengthen the joint & provide added surface area for the attachment of ligaments and tendons ● the joint surface where one bone meets another is covered with a layer of  hyaline cartilage called the a  rticular cartilage ( participating in the joint for movement ) ● externally, a bone is covered with a sheath called the periosteum (  anchors a  tendon or ligament)  ▪ outer fibrous layer is made of fibrous connective tissue & collagen − contains  nerves and  blood vessels that take care of the needs  of bones − has osteoblasts & osteoclasts ▪ inner osteogenic layer is the layer of bone-forming cells − contains  osteoblasts (builds bone) and osteoclasts (destroys bone) ● thin layer of reticular tissue called the endosteum lines the internal marrow cavity, covers all the honeycombed surfaces of spongy bone, & lines the canal system ▪ contains osteoblasts and osteoclasts   ● in children & adolescents, an e piphyseal plate of hyaline cartilage separates the marrow spaces of the epiphysis & diaphysis

▪ zone where bones grow in length ● in adults, the epipyseal plate is depleted and the bones can no longer grow, but an epiphyseal line marks where the plate used to be     Bone Cells ● osteogenic (osteoprogenitor) cells ▪ stem cells that develop from mesenchymal cells then give rise to other bone cell ▪ found in endosteum, inner layer of periosteum, & central canals ▪ multiply continyally & some go on to become the osteoblasts ● osteoblasts ▪ bone-forming cells; cuboidal or angular ▪ line up in a single layer on bone surface under endosteum & periosteum ▪ new ones generated by mitosis & differenation of osteogenic cells ▪ secrete osteocalcin which stimulates insulin secretion by the pancrease, increases insulin sensitivity in adipocytes, & limit growth of adipose tissue − hormonal function ● osteocytes ▪ former osteoblasts (“adults ”) that are trapped in the matrix they deposited ▪ reside in the  lacunae (tiny cavities) which are interconnected by slender channels called canaliculi ▪ has delicate fingerlike processes that reach into the canalicule to contact the processes from neighboring osteocytes ▪ some also contact osteoblasts on the bone surface ▪ neighboring osteocytes are connected by gap junctions where processes meet, so they can pass their metabolic wastes to the nearest blood vessel for disposal ● osteoclasts ▪ bone-dissolving cells found on the bone surface ▪ formed by the fusion of several stem cells, therefore are unusually large  Compact Bone ● onionlike concentric lamellae, which are layers of matrix (lacunae & cells) concentrically arranged  around a c entral  (haversian  or o  steonic ) c anal (blood vessel) & connected with each other  by canaliculi  ( allow  cells  to communicate  with one another ) ● a central canal & its lamellae constitute an o  steon ( haversian system),  which  is  the basic structural unit of compact bone ● central canals  are joined by transverse or diagonal passages called Volkmann (perforating) c anals  ● osteon has lacunae (space) filled with an osteoblast; in between spaces is hard cement that makes bone tough because cells make collagen fibers

▪ space d  oes not mean empty ● blood brings minerals into the bones ▪ fiber is important in women along with Vitamin C & c alcium  − if you don’t get minerals you can get osteoporosis (estrogen drop) ● intrastructure is weaker bones  Bones Grow Longer ● during a child’s growthspurt (on-set of puberty) ● girls develop estrogen & boys develop testosterone which helps bone growth ▪ cartilage keeps hormones ● once done growing, the epiphyseal plate becomes the epiphyseal line  Bones Grow Wider ● in the endosteum ● estrogen tells osteoclasts to start breaking down the bone, which indicates the osteocytes from the inner estrogenic layer to turn into osteoblasts to make bone ▪ “widdle from the middle”  ● osteoblasts and osteoclasts are on the inside and outside layers ▪ more osteoclasts on the inside ▪ more osteoblasts on the outside ● if you break a bone, the body makes adjustments based on your needs  Intramembranous Ossification ● develop within a fibrous sheet as dense fibrous connective tissue ● produces flat bones of the skull & most of the clavicle (collarbone) ● stages: ▪ embryonic connective tissue (mesenchyme) condenses into a layer of soft tissue with a dense supply of blood capillaries;  mesenchymal cells enlarge  because the membrane take in water & differentiate into osteogenic cells, & regions of mesenchyme become a network of soft sheets called  trabeculae  ▪ osteogenic cells gather on trabeculae  &  differeniate into osteoblasts; cells deposit an organic matrix called osteoid  tissue  (soft collagenous tissue similar to bone except for a lack of minerals); as trabeculae grow thicker, calcium phosphate is deposited into the matrix; some osteoblasts are trapped in the matrix and become osteocytes; mesenchyme close to surface of a trabeculae remains uncalcified, but becomes denser & more fibrous, forming a periosteum ▪ osteoblasts continue to deposit minerals, producing a honeycomb of bony trabecular; some trabecular persist as permenant spongy bone, while osteoclasts resorb & remodel other to form a marrow cavity in the middle of the bone ▪ trabeculae at surface continue to calcify until the spaces between them are filled in, converting the spongy bone into compact bone; this process gives rise to the sandwichlike arrangement typical of mature flat bones 

Endochondral Ossification ● bone is preceded by a hyaline cartilage “model” that becomes replaced by osseous tissue ● begins around 6th week of fetal development & continues into a person’s 20s ● vertebrae, ribs, sternum, scapula, pelvic girdle, & bones of the limbs (most bones) ● stages: ▪ mesenchyme develops into hyaline cartilage; perichondrium produces chondrocytes & cartilage model grows in thickness ▪ perichondrium stops producing chondrocytes & starts producing osteoblasts, which deposit a thin collar of bone around the middle of the cartilage model;former perichondrium is now considered to be periosteum; chondrocytes enlarge because the membrane takes in water & matrix between lacunae is reduced to thin walls; region of chondrocyte formation is called primary ossification center;  walls of matrix between lacunae  calcify & block nutrients from reaching the chondrocytes; cells die & lacunae merge into a single cavity in the middle of the model ▪ blood vessels penetrate the bony collar & invade the primary ossification center; center is hallowed out & filled with blood & stem cells & becomes the primary  marrow  cavity;  stem  cells give rise to osteoblasts (line the cavity, begin depositing osteoid tissue, & calcify it to form a temporary network of bony trabeculae) & osteoclasts; as bony collar thickens & elongates, a wave of cartilage death progresses toward end of the bone; osteoclasts in marrow cavity, follow this wave, dissolving calcified cartilage remnants & enlarging marrow cavity of diaphysis; chondrocyte enlargement & death will occur creating a  secondary ossification center ▪ second center becomes hallowed out (same as first), producing a  second  marrow cavity in epiphysis, which expands outward from the center, in all directions; ▪ epiphysis fills with spongy bone; cartilage is limited to articular cartilage covering each joint surface, & to an  epiphyseal plate (thin wall of cartilage separating the primary & secondary marrow cavities) ▪ all remaining cartilage of the plate is consumed & the gap between the epipyhysis  & diaphysis closes; primary & secondary marrow cavities unite into a single cavity & bone can no longer grow in length  Minerals & Hormones ● Calcium & Phosphate ▪ mandatory in bone ▪ deposit into fibers to give strength ▪ drink a class of milk & get calcium & phosphate into intestine & blood, have to get it out if the lumen, doesn’t want to move on its own so it needs vitamin D ● Vitamin D ▪ Ca++ absorption in the intestine (phosphate along with it) ▪ used to take minerals out of the source (the lining) & put into the body

▪ can get from milk (added in, not naturally from cow) & the sun ● Vitamin A ▪ need for bones to grow to their potential ▪ osteoclasts won’t function so bone destruction slows, so slow bone growth ● Vitamin C ▪ adequate amounts are necessary to make enough collagen fibers ▪ if lacking, bones will be fragile (old people) ▪ can get from fruit ● Growth Hormone (GH) ▪ goes to the liver & makes chemicals (somatomedin), which encourages epiphyseal plate replacement ▪ too much GH = giant ▪ too little GH = dwarf ▪ get from a decent diet & appropriate amount of sleep ● Thyroid Hormone ▪ too much or too little = stunted growth ▪ example: Thyroxin hormone ▪ too little thyroxin = too little GH = stunted growth ▪ too much thyroxin = quick replacement of the epiphyseal plate = stunted growth ▪ you have to exercise ● Testosterone ( Sex Hormone) ▪ present at various stages of development in males ▪ around puberty, hormones become increased & are important in stimulating the epiphyseal plates to start growing ▪ hormone that says to stop growing & form epiphyseal line ▪ doesn’t shut down the growth factory for a long time ● Estrogen ( Sex Hormone) ▪ present at various stages of development in females ▪ around puberty, hormones become increased & are important in stimulating the epiphyseal plates to start growing ▪ hormone that says to stop growing & form epiphyseal line ▪ growth time is  less than males ● Parathormone (Parathyroid Hormone) ▪ raises calcium in blood (helping control levels of calcium & phosphate) ● Thyrocalcitomin ▪ lowers calcium in blood (helping control levels of calcium & phosphate)  For That To Work ● have an adequate diet ● get an appropriate amount of sleep ▪ hormones are released only during sleep ▪ if not sleeping properly, c ortisol (stress hormone) level will go up − can make you put on fat − affects metabolism

● exercise regularly ▪ helps deposit minerals correctly     ...