#28-46 CHAPTER 6: OSSEOUS TISSUE AND BONE STRUCTURE

STUDY
PLAY
skeletal system and functions
--Skeletal system includes:
-bones of the skeleton
-cartilages, ligaments, and connective tissues

Functions:
1. Support
2. Storage of minerals (calcium)
3. Storage of lipids (yellow marrow)
4. Blood cell production (red marrow)
5. Protection
6. Leverage (force of motion)
Long bones
(bone shape)
-Are long and thin
-Are found in arms, legs, hands, feet, fingers, and toes
Ex: Humerus
Flat bones
(bone shape)
-Are thin with parallel surfaces
-Are found in the skull, sternum, ribs, and scapula
ex: parietal bone
Sutural bones
(bone shape)
-Are small, irregular bones
-Are found between the flat bones of the skull
irregular bones
(bone shape)
-Have complex shapes
-Examples:
-spinal vertebrae
-pelvic bones
short bones
(bone shape)
-Are small and thick
-Examples:
-ankle
-wrist bones
sesamoid bones
(bone shape)
-Are small and flat
-Develop inside tendons near joints of knees, hands, and feet
Diaphysis
(bone markings)
-Diaphysis - the shaft
A heavy wall of compact bone, or dense bone
A central space called marrow cavity
Epiphysis
(bone markings)
-Epiphysis-wide part at each end & articulation with other bones
-Mostly spongy (cancellous) bone
-Covered with compact bone (cortex)
Metaphysis
(bone markings)
Metaphysis:
where diaphysis and epiphysis meet
Osteocytes
(bone cells)
-Mature bone cells that maintain the bone matrix
-Live in lacunae
-Are between layers (lamellae) of matrix
-Connect by cytoplasmic extensions through canaliculi in lamellae
Do not divide
-Maintains protein and mineral content of matrix
-Helps repair damaged bone
DO NOT DIVIDE THERFORE THERE ARE STEM CELLS
Osteoblasts
(bone cells)
-Immature bone cells that secrete matrix compounds (osteogenesis)
-Osteoid - Matrix produced by osteoblasts, but not yet calcified to form bone
-Osteoblasts surrounded by bone become osteocytes
Osteoprogenitor Cells
(bone cells)
-Mesenchymal stem cells that divide to produce osteoblasts
-Are located in inner, cellular layer of periosteum (endosteum)
-Assist in fracture repair
Osteoclasts
(bone cells)
-Secrete acids and protein-digesting enzymes
-Giant, mutlinucleate cells
-Dissolve bone matrix and release stored minerals (osteolysis)
-Are derived from stem cells that produce macrophages
compact bone
...
osteon
-The basic unit of mature compact bone
-Osteocytes are arranged in concentric lamellae
-Around a central canal containing blood vessels
perforating canals
-Perpendicular to the central canal
-Carry blood vessels into bone and marrow
circumferential lamelle
-Lamellae wrapped around the long bone
-Binds osteons together
periosteum
-Covers all bones except parts enclosed in joint capsules
-It is made up of an outer, fibrous layer and an inner, cellular layer

Functions:
1. Isolate bone from surrounding tissues
2. Provide a route for circulatory and nervous supply
3. Participate in bone growth and repair
endosteum
--An incomplete cellular layer:
-lines the marrow cavity
-covers trabeculae of spongy bone
-lines central canals
-Contains osteoblasts, osteoprogenitor cells, and osteoclasts
-Is active in bone growth and repair

Very inside of the bone interact with marrow, lines the marrow cavity
spongy bone
-Does not have osteons
-The matrix forms an open network of trabeculae
-Trabeculae have no blood vessels
-The space between trabeculae is filled with red bone marrow:
-which has blood vessels
-forms red blood cells
-and supplies nutrients to osteocytes
-In some bones, spongy bone holds yellow bone marrow:
-is yellow because it stores fat
bone development
-Human bones grow until about age 25
-Osteogenesis:
bone formation
-Ossification:
-the process of replacing other tissues with bone
-Calcification is the process of depositing calcium salts and occurs here
-The 2 main forms of ossification are:
-intramembranous ossification aka - dermal ossification:occurs in the dermis and produces dermal bones such as mandible and clavicle
-endochondral ossification
intramembraneous
(dermal) ossification
1. Mesenchymal cells aggregate and cluster together, differentiate into osteoblasts, begin to secrete organic components of matrix= ostiod which then becomes mineralized with Ca salts forming---> BONE MATRIX
ossification at ossification center,
2. as ossification proceeds, osteoblasts are trapped inside boney pockets where differentiate into osteocytes... developing bone grows outward from ossificationn center in small struts called ** spicules
3. Blood vessels begin to branch and grow into the area between spicules.... rate of bone growth accelerates with oxygen and nutrients.. as spicules interconnect they trap blood vessels within bone tas
4. cont. deposition of bone by osteoblasts located lose to blood vessels results in plate of spongy bone with blood vessels weaving throughout
5. subsequent remodeling around blood vessels produces osteons typical of compact bone (osteoblasts on bone surface and connective tissue around bone-----> form periosteum)
endochondrial
Ossifies bones that originate as hyaline cartilage (most bones originate as hyaline cartilage).
1. Chondrocytes in the center of hyaline cartilage:
-Enlarge, form struts and calcify, and die, leaving cavities in cartilage
2. Blood vessels grow around the edges of the cartilage and cells in the perichondrium change to osteoblasts:
-Produces layer of superficial bone around shaft which continues to grow & become compact bone
3. Blood vessels enter the cartilage bringing fibroblasts that become osteoblasts and spongy bone develops at the primary ossification center
4. Remodeling creates a marrow cavity:
-bone replaces cartilage at the metaphyses
5.Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers
6. Epiphyses fill with spongy bone:
-cartilage within the joint cavity is articulation cartilage
-cartilage at the metaphysis is epiphyseal cartilage
epiphyseal lines
-When long bone stops growing, after puberty epiphyseal cartilage disappears and are visible on X-rays as an epiphyseal line
mature bone blood supply
1. Nutrient artery & vein:
a single pair of large blood vessels
enter the diaphysis through the nutrient foramen
femur has more than 1 pair
2. Metaphyseal vessels:
supply the epiphyseal cartilage
where bone growth occurs
3. Periosteal vessels provide:
blood to superficial osteons
secondary ossification centers
bone remodeling
-The adult skeleton maintains itself and replaces mineral reserves by remodeling
-Remodeling - recycles and renews bone matrix
-involves osteocytes, osteoblasts, and osteoclasts

-Effects of exercise on bone: heavily stressed bones become thicker and stronger
-mineral recycling allows bone to adapt to stress

-Bone degeneration: Bone degenerates quickly - Up to 1/3 of bone mass can be lost in a few weeks of inactivity
nutrition and hormones effects on bones
-Normal bone growth and maintenance requires nutritional and hormonal factors
-Minerals - A dietary source of calcium and phosphate salts:
plus small amounts of magnesium, fluoride, iron, and manganese
-Vitamins
Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation
Vitamin A stimulates osteoblast activity
Vitamins K and B12 help synthesize bone proteins
hormones
-Calcitriol:
-made in kidneys & helps absorb calcium & phosphorus from digestive tract
-synthesis requires vitamin D3 (cholecalciferol)
-Growth hormone & thyroxine stimulate bone growth
-Estrogens & androgens stimulate osteoblasts
-Calcitonin & parathyroid hormone regulate calcium & phosphate levels
PTH
-Produced by parathyroid glands in neck
-Increases calcium ion levels by:
-stimulating osteoclasts
-increasing intestinal absorption of calcium
-decreases calcium excretion at kidneys
calcitonin
-Secreted by C cells (parafollicular cells) in thyroid
-Decreases calcium ion levels by:
-inhibiting osteoclast activity
-increasing calcium excretion at kidneys
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