Skeletal System - Bone Tissue (235 #6) Flashcards
Skeletal System Functions
1) Support - soft tissue and attachments for muscles
2) Protection - internal organs
3) Assistance in Movement - with muscles
4) Mineral Homeostasis - storage & release
5) Blood Cell Production - red bone marrow = homeopoiesis
6) Triglyceride Storage - yellow bone marrow
Diaphysis
the bone’s shaft or body
Epiphyses
the proximal and distal ends of the bone
Metaphyses
the regions between the diaphysis and epiphyses. Contains Epiphyseal Growth Plate = hyaline cartilage that allows the diaphysis of the bone to grow in length. Replaced by Epiphyseal Line = bone.
Articular Cartilage
thin layer of hyaline cartilage covering part of epiphyses where bone forms articulation (joint) with other bone. Reduces friction and absorbs shock. repair is limited due to lack of perichondrium.
Periosteum
tough connective tissue sheath, associated blood supply surrounds bone where there is no articular cartilage. Outer fibrous layer is dense irregular connective tissue, inner osteogenic layer is cells for growing in thickness. Nourishes, protects, repairs, attachment point. Connected to bone by perforating (Sharpey’s) fibres - collagen bundles extending into bone ECM.
Medullary/Marrow Cavity
hollow cylindrical space in diaphysis that contains fatty yellow blood marrow and numerous blood vessels. Reduces weight of bone.
Endosteum
thin membrane that lines the medullary cavity. Small amount of connective tissue plus a single layer of bone-forming cells.
Osseous Tissue / Bone
abundant ECM with widely-separated cells. ECM is 15% water, 30% collagen and 55% crystallized mineral salts - calcium phosphate, calcium hydroxide, hydroxyapatite, CaCO3, Fl, Mg, K, S. Undergo CALCIFICATION, initiated by osteoblasts, requires presence of collagen.
hardness = mineral salts
flexibility = collagen
Cells in Bone
1) osteogenic cells
2) osteoblasts
3) osteocytes
4) osteoclasts
osteogenic cells
unspecialized bone stem cells derived from mesenchyme - only bone cells to undergo cell division, resulting in osteoblasts. Found along inner surface of periosteum, the endosteum and the canals within bones that contain blood vessels.
osteoblasts
bone-building cells. Synthesize and secrete collagen and other stuff for ECM. As they are surrounded by ECM, they become osteocytes.
osteocytes
mature cone cells - the main cells in bone tissue and maintain metabolism, waste removal, etc.
osteoclasts
huge cells derived from the fusion of up to 50 monocytes (WBC) concentrated in the endosteum. Facing bone surface, cell has ruffly border and releases lysosomal enzymes/acids to break down ECM - RESORPTION. Minerals enter osteoclasts by endocytosis, then exit on the other side by exocytosis and into the interstitial fluid, then blood capillaries. In response to hormones, they help regulate blood Ca2+ levels and are target cells for osteoporosis drug therapy.
COMPACT bone
1) few spaces
2) strongest form of bone tissue
3) beneath periosteum of all bones
4) bulk of diaphyses of long bones
5) protection, support, resists stresses
6) 80% of skeleton
COMPACT tissue histology
made of repeating osteons (haversian systems) with little space btwn them:
1) central (haversian) canal - blood vessels, nerves, lymphatics
2) concentric lamellae - mineralized ECM
3) lacunae - btwn CL, contain osteocytes
4) canaliculi - tiny channels radiate from lacunae with ECF and fingerlike processes of osteocytes, which talk using gap junctions.
5) interstitial lamellae - btwn neighbouring osteons, actually older partially-destroyed osteons
6) perforating (Volkmann’s) canals penetrate compact bone and bring blood vessels, nerves, lymphatic vessels from periosteum.
7) circumferential lamellae - around entire inner & outer circumference of long bone from initial bone formation. Outer is attached to periosteum by perforating (Sharpey’s) fibers. Inner lines medullary cavity.
SPONGY BONE (trabecular/cancellous)
1) no osteons
2) located in interior of bone
3) lamellae in irregular pattern called trabeculae.
4) spaces are filled with red bone marrow in RBC-producing bones, or yellow bone marrow (adipose tissue) in others.
5) many small blood vessels that nourish osteocytes.
6) short, flat, sesamoid and irregular bones.
7) core of the epiphyses and narrow rim of medullary cavity in long bones
SPONGY tissue histology
1) concentric lamellae - mineralized ECM
3) lacunae - btwn CL, contain osteocytes
4) canaliculi - tiny channels radiate from lacunae with ECF and fingerlike processes of osteocytes, which talk using gap junctions.
SPONGY vs. COMPACT
1) spongy is lighter
2) spongy supports and protects red bone marrow
3) spongy trabeculae are arranged along lines of stress. Typically found where stresses are low or from many directions
4) compact bone osteons are parallel to diaphysis.
5) compact bone is thickest where stress is applied in relatively few directions.
Blood & Nerve Supply
1) periosteal arteries & veins - small vessels + nerves make periosteum VERY sensitive to tearing or tension.
2) nutrient arteries & veins (large) - centre of diaphysis, through nutrient foramen, divides into proximal and distal inside medullary cavity.
3) metaphyseal arteries & veins - enter the metaphyses and supply RBM and bone tissue.
4) epiphyseal arteries & veins
Intramembranous Ossification
Simpler method - bone forms directly in mesenchyme.
1) Dvlp Ossification Centre - chemical changes cause mesenchymal cells to cluster and differentiate into osteogenic cells and then osteoblasts - secrete ECM.
2) Calcification - ECM secretion stops, osteocytes in lacunae. In days, Ca2+ and other mineral salts are deposited and ECM hardens
3) formation of trabeculae - bone ECM develops into trabeculae that fuse together to form spongy bone. Connective tissue associated with RB vessels differentiates into RBM
4) Dvlp Periosteum - mesenchyme condenses at bone periphery and turns into periosteum. Thin layer of compact bone replaces spongy bone.
Much of newly formed bone is remodeled as bone is transformed into adult size/shape.
Endochondral Ossification
1) Dvlp Cartilage Model - chemical changes => mesenchymal cells to cluster and differentiate into chondroblasts - secrete ECM, producing cartilage model of hyaline plus covering called perichondrium.
2) Growth of Model - chondroblasts are buried in ECM, now called chondrocytes - undergo cell division and more ECM secretion to grow the model - INTERSTITIAL & APOSITIONAL growth. Chondrocytes in the mid-region hypertrophy and the ECM calcifies. Others die due to lack of nutrients in calcified ECM, forming lacunae
3) Dvlp Primary Ossification Centre - inward from external surface of bone. Mid-region of cartilage model, nutrient artery penetrates the perichondrium, goes through a nutrient foramen. Osteogenic cells in perichondrium are stimulated to differentiate into osteoblasts as a result. Perichondrium develops into periosteum once it starts to form bone. Osteoblasts deposit bone ECM over calcified cartilage, forms spongy bone. Ossification spreads toward ends of model
4) Dvlp Medullary Cabity - osteoclasts break down some of new spongy, leaving a cavity.
5) Dvlp Secondary Ossification Centre - epiphyseal arteries enter epiphyses, secondary OC starts. No Medullary cavities form in epiphyses. Proceeds OUTWARD from centre of epiphyses.
6) Dvlp Articular Cartilage and Epiphyseal Growth Plate - hyaline over epiphyses becomes articular. Hyaline remains btwn diaphysis and epiphyses.
Epiphyseal Growth Plate
later of hyaline cartilage in the metaphysis of a growing bone - 4 zones:
1) resting cartilage - nearest epiphysis, small scattered chondrocytes. anchor plate to epiphysis, don’t take part in growth.
2) proliferating cartilage - slightly larger chondrocytes stacked like coins, divide and secrete ECM, replacing dead chondrocytes at diaphyseal side.
3) hypertrophic cartilage - large maturing chondrocytes in columns
4) calicified cartilage - few cells thick, dead chondrocytes with calcified ECM. Osteoclasts dissolve calcified cartilage and osteoblasts replace with bone ECM -> endochondral ossification (replacement of cartilage with bone). Becomes new diaphysis!
If a bone fracture damages EGP, bone may be shorter than normal in adult size, since damage to cartilage (avascular) accelerates closure of EGP due to cessation of chondrocyte division.
Epiphyseal Line
in adults, EGP closes due to cartilage cells no longer dividing. EGP fades, leaving bony structure called Epiphyseal LINE.
