1. Bones are alive Living bones: Form Grow Repair Remodel
Move at joints (with help from muscles)

2. Skeletal System – Normal Function
Movement
Protection
Normal Function
Support
Mineral Storage
Blood Cell Production

3. Bone Types

4. Long Bone – Macroscopic Anatomy
Epiphysis (end)
covered with hyaline cartilage
compact bone forms exterior
spongy bone forms interior
contains epiphyseal line/plate
Diaphysis (middle)
center composed of the medullary cavity containing yellow or red marrow. Marrow helps produce red blood cells.
Fig 7.1

5. Long Bone – Macroscopic Anatomy
Fig 7.2

6. Microscopic Anatomy
Osteon = circular structure organized around blood vessels
Osteocyte = bone cells
Bone matrix = hard calcium-based material between cells
Fig 7.3

7. Tissue Types – Compact Bone
Functions
Hard and provides stability, framework, protection
Structure
Matrix has hard mineral structure, based on calcium
Cells and matrix are arranged in regular, concentric pattern
Compact Bone

8. Tissue Types – Spongy Bone
Functions
Lightens total bone weight and provides space for bone marrow
Structure
Matrix is softer mineral, less organized and less of it
Empty spaces between matrix structure are filled with bone marrow
Spongy (cancellous) Bone

9. Spongy Bone

10. Tissue Types – Hyaline Cartilage
Functions
Provides soft and smooth covering to end of bone (articular surface)
Helps provide smooth and easy movement between bones (at joints)
Provides the starting material for new bone growth
Structure
Matrix is gelatinous with fibers and is evenly distributed between the cells
Cells (chrondocytes) are found in pairs within capsules called lacunae
Hyaline Cartilage

11. Bone Cells OSTEOCYTES = “bone” “cells” BONE IS NEVER AT REST =
OSTEOBLASTS
“bone builders” which deposit
calcium into bones
OSTEOCLASTS
“bone crushers” which break
down bone to release calcium when
Needed
BONE IS NEVER AT REST =
homeostasis!!!

12. Bone Physiology Living bones perform the following processes:
Formation
Starts as an embryo, continues through fetal development and after birth
Growth
Occurs from before birth through maturity
Remodel
Old matrix is removed and replaced with new matrix
Repair
Damaged bones will heal and return to normal structure

13. Bone Physiology – Formation

14. Bone Physiology – Formation
Fetal bones are made of hyaline cartilage
As cartilage cells die, they are replaced with spongy bone in diaphysis
After birth, spongy bone invades diaphysis
Compact bone replaces spongy bone in diaphysis
Hyaline cartilage remains on epiphyseal surface and in growth plate
Fig 7.5

15. Epiphyseal plate -cartilage band indicates ossification is occurring and spongy bone is being deposited

16. X Ray in Newborn

17. Bone Physiology - Repair
Hemotoma, a mass of clotted blood, forms at the fracture site.
A fibrous callus forms, and cartilage matrix is secreted.
Spongy bone forms to replace cartilage.
Bone remodeling occurs to remove excess material and replace compact bone.

18. Bone Physiology - Remodeling
Bone matrix is inorganic and breaks down over time
Specific bone cells (osteoclasts) remove old, broken matrix
Other bone cells (osteoblasts) re-make/deposit new matrix
The entire skeleton is re-modeled every 7-10 years
Remodeling slows with age, elderly people have thinner bones and are more susceptible to broken bones as a result

19. Aging and Bone Tissue
There are two principal effects of aging on bone tissue:
1) Loss of bone mass
Results from the loss of calcium from bone matrix
The loss of calcium from bones is one of the symptoms in osteoporosis
2) Brittleness
Results from a decreased rate of protein synthesis
Collagen fibers gives bone its tensile strength
The loss of tensile strength causes the bones to become very brittle and susceptible to fracture

20. Osteoporosis

21. Calcitonin
Released by cells of the thyroid gland in response to high blood [Ca2+].
Calcitonin acts to “tone down” blood calcium levels.
Calcitonin causes decreased osteoclast activity which results in decreased break down of bone matrix and decreased calcium being released into the blood.
Calcitonin also stimulates osteoblast activity which means calcium will be taken from the blood and deposited as bone matrix.
Notice the thyroid follicles on the right. The arrow indicates a C cell

22. Parathyroid Hormone
Released by the cells of the parathyroid gland in response to low blood [Ca2+].Causes blood [Ca2+] to increase.
PTH will bind to osteoblasts and this will cause 2 things to occur:
The osteoblasts will decrease their activity and they will release a chemical known as osteoclast-stimulating factor.
Osteoclast-stimulating factor will increase osteoclast activity.
Osteoclasts will begin breaking down bone in order to increase Ca 2+ into the blood.