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Histology; topic- Bones, Study notes of Histology

Georgetown University (GU)Histology

This a study sheet containing high yield material about bones

Typology: Study notes

2017/2018

Uploaded on 01/30/2018

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Bone Micro Anatomy
► Introduction
•Roles of Bone:
•Support body mass
•Facilitate Movement
•Protect vital organs
•Site of hematopoiesis
•Calcium reservoir
•Comparison Bone/Cartilage
•Similarities: Hard tissues
■Have LIVING CELLS in matrix
(Lacunae)
■Common mesenchymal progenitor
cells
•Differences: Bone heavily vascularized/
cartilage avascular
■Bone heavily vascularized/cartilage
avascular
■Cartilage less calcified, uses long
range diffusion
•Bone is a dynamic tissue: constant remodeling
•Movement required for proper bone
remodeling
•Placticity used in orthodontics
•Loss of bone mass during flight/
immobilization
•Piezoelectric potential ( (-) bone deposition;
(+) bone reabsorption
► Bone matrix
•Organic: 25% of total mass, mostly fibrous
•Fibers: Collagen type 1 (90%) provide
elasticity, tensile strength
•Ground substance
■Glycosaminoglycans
■Glycoproteins
•Osteonectin & Osteopontin
( anchor minerals & promote
crystal formation.
•Osteocalcin & Bone
Sialoprotein: Calcium
binding
•Osteoid- new organic matrix
•Inorganic
•Provide compressive strength
•Mostly salts of calcium phosphate
•Amorphous
•Crystals: Hydroxyapatite
•Hydration shell around hydroxyapatite
► Bone cells
•Mesenchymal osteoprogenitor: osteogenic cell stem
cells)
•Committed cells controlled by BMP
•Location: inner and outer lining of bone
•Self-renewal: PDGF, TGFB, IGF
•Differentiation: BMP, Vit D3
•Osteoblast: Bone forming cell
•Non-dividing cells
•Location: Bone matrix surface
•Secrete bone matrix (osteoid)
•High secretory activity shown abundant RER,
Golgi
•Secretion activated by GH sex steroids
•Bone apposition: deposit of osteoid between
osteoblast cell layer and existing bone.
•Secrete osteoclast stimulating factors
•Osteocyte: terminally differentiated cells
•Terminally differentiated cell
•Osteoblast that got trapped in its mineralized
matrix
•Location: Lacunae
•Connection to other cells: Extend filpodia (gap
junctions)
•Osteocytic osteolysis
■Calcium released inside lacunae
■PTH increase resorption ( chief cells
PThyroid)
■Calcitonin decrease resorption
(parafollicular cell of Thyroid)
•Osteoclast: macrophage/monocyte lineage- phagocytic.
•Multinucleated; critical for Ca2+ homeostasis
•Location: On bone resorptive surfaces-
Howship’s lacunae
•Ruffled border: indicates bone resorption.
Cytoplasmic process surrounded by a ring-
shape sealing zone= clear zone
•Regulated by:
■PTH (indirect from osteoblasts
increase resorption
■Calcitonin, estrogen decrease
resorption
•Function in osteoclastic osteolysis
■Focal decalcification: by acidification
•Cirtric acid release
•Carbonic anhydrase
■Extracellular digestion by hydrolytic
enzymes for Proteolysis
•Collagenase
•Acid phosphatase
•Sulfatase
► Bone organization & architecture
•Periosteum
•Tough connective tissue
•Location: cover bone surfaces. 2 types
■Fibrous periosteum: Outer fibrous
layer highly vascularized
■Osteogenic periosteum: inner cellular
layer (osteogenic cells, osteoblasts)
•Attachment: by Sharpey’s fibers
•Point of origin: Volkmann’s canal
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Bone Micro Anatomy

► Introduction

  • Roles of Bone:
    • Support body mass
    • Facilitate Movement
    • Protect vital organs
    • Site of hematopoiesis
    • (^) Calcium reservoir
  • Comparison Bone/Cartilage
    • Similarities: Hard tissues

■ Have LIVING CELLS in matrix

(Lacunae)

■ Common mesenchymal progenitor

cells

  • Differences: Bone heavily vascularized/ cartilage avascular

■ Bone heavily vascularized/cartilage

avascular

■ Cartilage less calcified, uses long

range diffusion

  • Bone is a dynamic tissue: constant remodeling
    • Movement required for proper bone remodeling
    • Placticity used in orthodontics
    • Loss of bone mass during flight/ immobilization
    • Piezoelectric potential ( (-) bone deposition; (+) bone reabsorption ► Bone matrix
  • Organic: 25% of total mass, mostly fibrous
  • Fibers: Collagen type 1 (90%) provide elasticity, tensile strength
  • Ground substance

■ Glycosaminoglycans

■ Glycoproteins

  • Osteonectin & Osteopontin ( anchor minerals & promote crystal formation.
  • Osteocalcin & Bone Sialoprotein: Calcium binding
  • Osteoid- new organic matrix
  • Inorganic
  • Provide compressive strength
  • Mostly salts of calcium phosphate
  • Amorphous
  • Crystals: Hydroxyapatite
  • Hydration shell around hydroxyapatite ► Bone cells
  • Mesenchymal osteoprogenitor: osteogenic cell stem cells)
  • Committed cells controlled by BMP
  • Location: inner and outer lining of bone
  • Self-renewal: PDGF, TGFB, IGF
  • Differentiation: BMP, Vit D
  • Osteoblast: Bone forming cell
  • Non-dividing cells
  • Location: Bone matrix surface
  • (^) Secrete bone matrix (osteoid)
  • High secretory activity shown abundant RER, Golgi
  • Secretion activated by GH sex steroids
  • Bone apposition: deposit of osteoid between osteoblast cell layer and existing bone.
  • Secrete osteoclast stimulating factors
  • Osteocyte: terminally differentiated cells
  • Terminally differentiated cell
  • Osteoblast that got trapped in its mineralized matrix
  • Location: Lacunae
  • Connection to other cells: Extend filpodia (gap junctions)
  • Osteocytic osteolysis

■ Calcium released inside lacunae

■ PTH increase resorption ( chief cells

PThyroid)

■ Calcitonin decrease resorption

(parafollicular cell of Thyroid)

  • Osteoclast: macrophage/monocyte lineage- phagocytic.
    • Multinucleated; critical for Ca2+ homeostasis
    • Location: On bone resorptive surfaces- Howship’s lacunae
    • Ruffled border: indicates bone resorption. Cytoplasmic process surrounded by a ring- shape sealing zone= clear zone
    • Regulated by:

■ PTH (indirect from osteoblasts

increase resorption

■ Calcitonin, estrogen decrease

resorption

  • Function in osteoclastic osteolysis

■ Focal decalcification: by acidification

  • Cirtric acid release
  • Carbonic anhydrase

■ Extracellular digestion by hydrolytic

enzymes for Proteolysis

  • Collagenase
  • Acid phosphatase
  • Sulfatase

► Bone organization & architecture

  • Periosteum
    • Tough connective tissue
    • Location: cover bone surfaces. 2 types

■ Fibrous periosteum: Outer fibrous

layer highly vascularized

■ Osteogenic periosteum: inner cellular

layer (osteogenic cells, osteoblasts)

  • Attachment: by Sharpey’s fibers
  • Point of origin: Volkmann’s canal

• Endosteum

• Thin single cell layer (progenitor cells,

osteoblasts & clasts)

• Function: Line bone internal surfaces

(trabeculae, Haversian canals)

■ Bone nutrition and maintenance

• Bone Proper

• Woven: Immature

■ Amorphous CaPO4, random

disposition of collagen

• Lamellar: mature adult bone

■ Organized disposition of collagen

with crystalline CaPO

• Cancellous (spongy)

• Irregular lamellae

(trabeculae)

• Space filled with marrow

• Most converted to

compact bone except

■ Flat bones

■ Alveolar bone

around teeth

■ Short bones

■ Epiphyses &

Diaphysis of long bones

• Anastomse: fused

trabeculae trap blood vessels and lymphatic inside canal

• Compact (cortical)

• Form diaphysis of long

bones

• Location: thin layers

around epiphyses

• Highly organized

■ Circumferential

(outer and inner)

■ Haversian system

(osteon) cylindrical columns of 4- concentric lamellae

■ Interstitial (space

between osteon)

• Endosteum and Periosteum role in bone growth, repair

and remodeling

• Both have osteogenic cell

■ Cells that divide

■ Cells that give rise to osteoblasts

(vascular environment) or Chondrocyte (in avascular environment) ► Mechanisms of Calcification

1. Osteoblasts secrete the new organic matrix, non-

mineralized – osteoid

2. Osteoblasts secrete factors (alk Phosphatase,

glycoproteins: osteonectin and osteocalcin ( high

affinity calcium binding proteins), calcium salts subsequent mineralization of matrix

2.a. Alk Phos: promotes accumulation of inorganic

phosphates in osteoid

2.b. Matrix vesicles contain

pyrophosphate= inhibits calcification and allows phosphate release

3. Osteoblasts become trapped in their mineral matrix-

lacunae and osteocytes

4. Osteocytes keep limited ability to secrete and reabsorb

bone into lacuna=bone turnover ► Bone Remodeling

• Balance between bone deposition and resorption allows

bone to repond to mechanical stress, adaptation to movement/strain

• Deposition ensures high vascularity- traps new vessels

during bone deposition and anastamose of trabeculae

• Resorption: allows formation of canals/ marrow cavity

• Osteons constantly remodel

• Helps maintain homeostasis

• Required to maintain shape in growing bones

► Nutritional factors

• Vit C

• Deficiency: Scurvy (Altered collagen

formation); fragile bones, fractures

• Excess: N/A

• Vit D

• Deficiency: impaired intestinal absorption of

calcium. Rickest, skeletal deformities (bowed legs), osteomalacia, weak bones

• Excess: abnormal calcification of soft tissue,

toxic

• Vit A

• Deficiency: skeletal deformity, slow bone

growth, small skull, CNS damage

• Excess: Slow cartilage growth and accelerated

ossification ► Hormonal factors

• Growth Hormone

• Deficiency: dwarfism

• Excess: gigantism; pituitary tumor

• Sex steroid: generally stimulatory for bone and

influence appearance of ossification enters. Early puberty short stature. Late puberty tall stature

• Hyperparathyroidism: excess PTH, too much Ca2+ in

blood, and deposits in kidney

Bone Development

► Introduction

• Mesenchymal uncommitted precursor

• OSteprogenitor Osteoblast Osteocyte

• Intramembranous endochondral

• Chondropogenitor Chondroblast Chondrocyte

• Appositional Interstitial

► Intramembranous ossification- DIRECT

• Mesenchymal condensation & Mineralization +

Osteoprogenitor differentiation

  • Epiphyseal plate provide growth in length. Epiphyseal spicules get incorporated into diaphysis ► Bone Repair
  • Unstable fracture repaired by endochondral ossification

•.3. Fracture, interuuption of blood

supply, necrosis + clot

•.4. Decrease 02, marcophages/

fibroblasts, fibrous tissue

•.5. Periosteal osteoprogenitors

chondrogenic

•.6. Cartilage bridge at callus (4 days

after)

•.7. Blood vessels reappearOsteogenic

•.8. Primary bone forms 2 weeks after break then

2ndary

•.9. Mechanical stress + muscular activity restore

shape

  • Fracture in non-weight bearing bone or hair line fracture repaired by intramembranous ossification.

Tissue Type Fibrous ECM

Hyaline Cartilage

Elastic Cartilage

Bone

Component Collagens Collagens Amorphous ECM

Elastin Fibrous ECM, Amorphous ECM ( hypoxyapatite

► Joints : arthroses

  • Synarthroses joints= no movement
    • Syndesmosis (fibrous joints): joined by dense connective tissue
    • Synostose: immobilized, fused bone (old skull bones)
    • Synchondrose (primary cartilaginous joint): bones joined by hyaline cartilage (rib.sternum)
    • Symphysis (2ndary cartilaginous joint): bones joined by fibrocartilage (pubic symphysis, intervertebral discs)
  • Diarthrose (synovial/articular) Moveable joints
    • Articular cartilage ( no perichondrium)
    • Synovial fluid
    • Reinforced by ligaments
    • Stabilized by luscles and tendons
    • Ligaments and tendons attached to bone by Sharpey’s fibers
    • Capsule (2 layers)

■ Outer membrane: fibrous

■ Inner membrane: synovial membrane

  • A cell: phagocytic
  • B cell: secrete synovial fluid Ligament= Bone to Bone Tendon= muscle to bone