Chapter 6: Osseous Tissue and Bone Structure 1

2

Cells of Bone Osteoprogenitor -precursor to osteoblast Osteoblasts -produce bone matrix Osteocytes -trapped osteoblast Osteoclasts -dissolve bone matrix 3

Compact Verses Spongy Bone 4

Long Bone Structure 5

Flat Bone Structure 6

Ossification Endochondrial Intramembranous 7

Intermembranous Typical of flat bones Ossification of mesenchymal cells 8

Endochondral Ossification Long bones Hyaline cartilage breaks down 9

Postnatal Bone Growth Interstitial growth: Increase bone length (adolescence) Appositional growth: Increase thickness and remodeling of all bones 10

Epiphysial Plate 11

12

Bone Growth Growth hormone stimulates cell division Thyroid hormone modulates growth hormone Testosterone and estrogens (at puberty) – Promote adolescent growth spurts – End growth by inducing epiphyseal plate closure 13

14

Bone Resorption Osteoclasts secrete – Lysosomal enzymes (digest organic matrix) – Acids (convert calcium salts into soluble forms) Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood 15

Control of Remodeling What controls continual remodeling of bone? – Hormonal mechanisms that maintain calcium homeostasis in the blood – Mechanical and gravitational forces 16

Bone Remodeling Balance between resorption and formation 17

Copyright © 2010 Pearson Education, Inc. Figure 6.11 Bone growth Bone remodeling Articular cartilage Epiphyseal plate Cartilage grows here. Cartilage is replaced by bone here. Cartilage grows here. Bone is resorbed here. Bone is resorbed here. Bone is added by appositional growth here. Cartilage is replaced by bone here.

Hormonal Control of Blood Ca 2+ Calcium is necessary for – Transmission of nerve impulses – Muscle contraction – Blood coagulation – Secretion by glands and nerve cells – Cell division 19

Hormonal Control of Blood Ca 2+ Primarily controlled by parathyroid hormone (PTH) Calcitonin has minor role Leptin influences bone remodeling 20

Exercise and Bones Builds stronger bone Inactivity leads to weak bones – Astronauts shrink as much as 4 inches 21

Bone Repair 22

Homeostatic Imbalances Heterotrophic Bones -abnormal bone formation – Tendons, joints, kidneys, testes, sclera of the eye – Fibrodysplasia Ossificans Progressiva Dwarfism -pituitary failure Acromegaly -bone/cartilage thickening along facial contours Gigantism -growth hormone overproduction Marfan Syndrome -excessive cartilage at epiphyseal plates Rickets -vitamin D deficiency Paget's disease Osteoporosis 23

Osteoporosis 24