1. Human Anatomy & Physiology I
Skeletal System
Human Anatomy & Physiology I

2. Introduction Bone tissue is a complex and dynamic living tissue.
It continually engages in a process called remodeling – building new bone tissue and breaking down old bone tissue.
Bone is made up of several different tissues working together: bone, cartilage, dense connective tissues, epithelium, adipose tissue, and nervous tissue.

3. Support
The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles.

4. Protection
The skeleton protects many internal organs from injury. For example, cranial bones protect the brain, vertebrae protect the spinal cord, and the ribs protect the heart and lungs.

5. Movement
Because skeletal muscles attach to bones, when muscles contract, they pull on bones. Together, bones and muscles produce movement.

6. Mineral homeostasis
Bone tissue stores several minerals, especially calcium and phosphorus. On demand, bone releases minerals into the blood to maintain critical mineral balance (homeostasis) and to distribute the minerals to other parts of the body.

7. Blood cell production
Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis.

8. Triglyceride storage
Triglycerides stored in the adipose tissue of yellow bone marrow are an important chemical energy reserve.

9. Histology Compact and spongy bone Osteons
Bone cells: osteoblast, osteoclast, osteocytes
Hematopoetic Tissue
Chemical Composition of Bone

10. Compact bone tissue Contains few spaces!
It forms the external layer of bones and makes up the bulk of the diaphyses of long bones.
Provides protection and support and resist the stresses produced by weight and movement.

11. Osteon
Compact bone is arranged in units called osteons or Harvesian systems.
Osteons in compact bone tissue are aligned in the same direction along lines of stress.

12. Spongy bone Spongy bone does NOT contains osteons.
It consist of trabeculae, an irregular latticework of thin columns of bone.
The macroscopic spaces between the trabeculae of some bones are filled with red bone marrow.
Within each trabeculae are osteocytes that lie in lacunae.

13. Bone cells
Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts

14. Bone cells
Osteogenic cells: The only bone cell that undergo division; the resulting daughter cells develop into osteoblasts. They are going to be found along the inner portion of the periosteum, in the endosteum, and in the canals within the bone that contain blood vessels.

15. Bone cells
Osteoblasts: (buds or sprouts) are bone building cells. They synthesize and secrete collagen fibers and other organic components needed to build the matrix of bone tissue, and they initiate calcification. As osteoblasts surround themselves with matrix, they become trapped in their secretion and become osteocytes.

16. Bone cells
Osteocytes: mature bone cells, are the main cells in bone tissue and maintain its daily metabolism, such as exchange of nutrients and wastes with the blood. Like osteoblasts, osteocytes do not undergo cell division.

17. Bone cells
Osteoclasts: (clast = break) are huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell) and are connected to the endosteum. One the side of the cell that faces the bone surface, the osteoclast’s plasma membrane is deeply folded into a ruffled border.

18. Ruffled border
Here the cell releases powerful lysosomal enzymes and acids that digest protein and mineral components of the underlying bone matrix.
This breakdown of bone matrix, termed resorption, is part of the normal development, growth, maintenance, and repair of bone.

19. Bone cells

20. Hematopoetic Tissue
Red bone marrow is a highly vascularized tissue located in the microscopic spaces between the trabeculae of spongy bone.

21. Red bone marrow
Consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers.
It is present in developing bones of the fetus and in some adults bones (i.e. pelvis, ribs, skull, vertebras, epiphyses of long bones).

22. Red bone marrow

23. Bone markings: Projections & Depressions

24. Long & Short

25. Irregular & Flat

26. Sesamoid & Wormian

27. Typical Long Bone Epiphysis & Diaphysis Bone Marrow
Periosteum & endosteum
Articular cartilage
Medullary Cavity
Epiphyseal Plate or Line

28. Bone formation
The process by which bone forms is called ossification or osteogenesis.
Two (2) types:
Intramembranous
Endochondral

29. Bone formation
In the first type of ossification, called intramembranous ossification, bone forms directly on or within loose fibrous connective tissue membranes.
In the second type, endochondral ossification, bone forms within hyaline cartilage.

30. Intramembranous ossification
Development of the center of ossification
Calcification
Formation of trabeculae
Development of the periosteoum

31. Intramembranous Ossification
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Mesenchymal cell
Osteocyte
Osteoblasts
Sheet of condensing
mesenchyme
Trabecula
Calcified bone
Osteoid tissue
Blood capillary
Fibrous periosteum 1
Condensation of mesenchyme into soft sheet
permeated with blood capillaries 2
Deposition of osteoid tissue by osteoblasts
on mesenchymal surface; entrapment of first
osteocytes; formation of periosteum
Osteoblasts
Fibrous periosteum T
rabeculae
Osteoblasts
Osteocytes
Spongy bone
Marrow cavity
Compact bone
Figure 7.8 3
Honeycomb of bony trabeculae formed by
continued mineral deposition; creation of
spongy bone 4
Surface bone filled in by bone deposition,
converting spongy bone to compact bone.
Persistence of spongy bone in the middle layer.
produces flat bones of skull and clavicle
7-31

32. Intramembranous Ossification
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Periosteum:
Fibrous layer
Osteogenic
layer
Osteoid tissue
Osseous tissue
(bone)
Osteoblasts
Osteocytes
© Ken Saladin
Figure 7.9
note the periosteum and osteoblasts.
7-32

33. Endochondral ossification
Development of the cartilage model
Growth of the cartilage model
Development of the primary ossification center
Development of the secondary ossification centers
Formation of articular cartilage

34. Stages of Endochondral Ossification
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Articular
cartilage
Spongy bone
Epiphyseal
line
Perichondrium
Hyaline
cartilage
Secondary
marrow cavity
Periosteum
Epiphyseal
plate 1
Early cartilage model
Epiphysis
Nutrient
foramen
Secondary
ossification
center
Marrow cavity
Metaphysis
Compact bone
Enlarging
chondrocytes
Blood
vessel
Diaphysis
Bony collar
Primary
marrow
cavity
Primary
ossification
center
Metaphysis
Secondary
ossification
center
Periosteum
Cartilage 2
Formation of
primary
ossification center,
bony collar, and
periosteum 3
Vascular invasion,
formation of primary
marrow cavity, and
appearance of
secondary
ossification center 4
Bone at birth, with
enlarged primary
marrow cavity and
appearance of
secondary marrow
cavity in one epiphysis 5
Bone of child, with
epiphyseal plate at
distal end 6
Adult bone with a
single marrow
cavity and closed
epiphyseal plate
Figure 7.10
7-34

35. Bone homeostasis
Bone is the body’s major calcium reservoir, storing 99% of total body calcium.
The level of calcium in the blood can be regulated by controlling the rate of calcium resorption from the bone into the blood and the calcium deposition from blood into bone.

36. Calcium homeostasis Parathyroid hormone (PTH) Calcitriol
Calcitonin (CT)
Just a note: Miacalcin (calcitonin harvested from salmon) is an effective drug for the treatment of osteoporosis because it slows bone resorption!

37. © Robert Calentine/Visuals Unlimited
Design of Spongy Bone
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Greater trochanter
Head
Trabeculae of
spongy bone
Compact bone
Lines of stress
Shaft (diaphysis)
Figure 7.6
7-37
© Robert Calentine/Visuals Unlimited

38. Bone growth vs. bone loss

39. Fractures that involves the growth plate!