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Bones and Skeletal Tissues

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1 Bones and Skeletal Tissues
Dr. Anderson GCIT

2 Cartilage Skeletal Cartilage – softer than bone, precedes bones in human embryos Surrounded by perichondrium, which: resists expansion of the cartilage and feeds the cells in the cartilage matrix via its blood vessels

3 Cartilage Growth Appositional Growth – new tissue is laid down on the outside of the existing structure Cartilage grows from the outside Interstitial Growth – new tissue is created within the matrix of existing cartilage Cartilage grows from within

4 Bones! 206 in humans Axial Skeleton – skull, vertebral column and ribcage Appendicular skeleton – long bones in limbs, shoulder and pelvic girdles, and digits

5 General Bone Classification
Long Bones – longer than wide All limb bones sans the patella Short Bones – a roughly cubic or rounded Carpals and tarsals Flat Bones – Thin, flattened, sometimes curved Ribs, sternum, etc. Irregular Bones Vertebrae, hip bones, etc.

6 Bone Function Support Protection Movement
Mineral and growth factor storage Blood cell formation (marrow) Fat storage

7 Gross Anatomy of Bones Bone markings Textures (in cross section)
Bulges (heads, trochanters, etc.) Depressions (fossae, sinuses, foramina, grooves) Textures (in cross section) Compact bone Spongy bone

8 Example - Long Bone Structure
Diaphysis (shaft) Medullary cavity (contains marrow) Epiphyses (ends) Immediately preceded by epiphyseal line Periosteum – surrounds the bone and contains bone-building cells (osteoblasts) and bone-destroying cells (osteoclasts)

9 Spongy bone present interior to compact bone
Epiphyses often lined with hyaline cartilage at articulation points

10 Periosteum & Endosteum
Periosteum - Double-layered membrane that surrounds bone Richly supplied with blood vessels and nerves that enter the bone itself through the nutrient foramina Endosteum – covers internal bone surfaces (trabeculae in spongy bone and canals through compact bone)

11 Other Bones Short, Flat & Irregular Bones
No epiphyses or diaphyses Do contain spongy bone, compact bone and marrow In flat bones, spongy bone is called the diploe

12 Red vs. Yellow Marrow Yellow marrow = stored fat
Red Marrow = hematopoetic (blood producing) tissue Located in most bones in children In adults, most active areas are in the head of the humerus and femur, and in the flat bones

13 Microscopic Anatomy Four Cell Types
Osteogenic Cells – Stem cells that form osteoblasts Osteoclasts – bone-destroying cells Osteocytes -

14 Structural Unit of Bone
Osteon (Haversian System) – a tube or cylinder of bone matrix Detailed structure can be found on pg. 181 in the text

15 Osteon Made of concentric rings of bone surrounding a Haversian Canal (contains blood vessels) Between each layer (lamella) are the osteocytes (in lacunae) Connecting adjacent osteocytes are canaliculi

16 Interstitial Lamellae
Lie between proper osteons to fill gaps May have been an osteon that was “remodeled” during growth from injury Circumferential Lamellae Form the outer layers of the diaphyses of long bones

17 Spongy Bone No osteons, however still provide support against stress
Nutrients arrive from blood in the endosteum

18 Chemical Composition of Bone
Organic Components – cells and osteoid, the organic part of the bone matrix Osteoid is composed of collagen and glycoproteins, which are made by osteoblasts Collagen fibers can form sacrificial bonds – weak bonds that break easily under stress and prevent the entire bone from fracturing Bones also made of salts (CaPO4 crystals) which are the inorganic component of bones that provide hardness

19 Bone Development (Ossification)
Occurs during: Initial Growth (child to adult size) Video Repair (Broken Bones)

20 Ossification Types Intramembranous Ossification – (flat bones) when bone develops from a fibrous membrane Pg. 182 in textbook Endochondrial Ossification – Hyaline cartilage is replaced with bone by osteocytes Pg. 183 in text

21 Bone Development (Intramembranous Ossification)

22 Bone Development (Endochondrial Ossification)

23 Class Assignment How do bones become ossified from birth?
Make sure to include Important structures Prenatal to adult (stable) bone

24 Post-natal Bone Growth
Chondrocytes proximal to the epiphyses grow fast, and away from the diaphysis Chondrocytes die, and the matrix is eventually replaced by new bone by invading osteocytes and calcified (the calcification zone) In adulthood, the diaphysis and epiphyses fuse, largely ending longitudinal growth

25 Growth in Diameter (Thickness)
To deal with the increased forces from lengthening, bones need to gain thickness Bones change in length to thickness ratio as they grow Osteoclasts break down bone to remodel the shape, while osteoblasts add to bone thickness (appositional growth)


27 Hormonal Regulation of Bone Growth
Growth Hormone (HGH) released by pituitary gland Increase growth rate of long bones Thyroid Hormone (TH) Increase long bone growth rate Androgens (Testosterone, Estrogen Progesterone) Cause sex-specific changes to skeleton

28 Bone Remodeling and Repair
Bone remodeling occurs under the periosteum or endosteum 5-7% of our bone mass is replaced every week! Factors affecting how bone is remodeled include Stress Nutrition Age Trauma

29 Bone Deposit and Resorption
Deposit – (by osteoblasts) occurs wherever bone is injured and extra strength is required Resorption – osteoclasts “dissolve” bone by the release of enzymes and hydrochloric acid Once liberated, these substances enter the blood stream where they can either be used (Ca) or eliminated (dead cell fragments)

30 Response to Mechanical Stress
Bones will adapt to the stress placed upon them (Wolff’s Law), E.g. -Handedness : larger bones in dominant limbs Trochanters – form where the largest muscles attach Bone mass is also loss when physical stresses are absent, e.g. astronauts in space, the disabled, tooth loss

31 Bone Repair Because of the crystalline nature of the inorganic matrix of bone, bones are subject to fractures

32 Terms to Describe Fractures
Displaced/non-displaced – epiphyses are either aligned or unaligned Non-displaced Displaced

33 Terms to Describe Fractures
Complete fracture – bone not broken through Incomplete – bone broken through completely Complete Incomplete

34 Terms to Describe Fractures
Linear – break is parallel to the long axis of the bone Transverse – bone breaks across short axis Linear Transverse

35 Terms to Describe Fractures
Compound (Open) – bone penetrates the skin Simple (Closed)- bone does not penetrate the skin Compound (Open) Simple (Closed)

36 Bone Repair – The Break Almost immediately after injury, a hematoma forms from broken blood vessels in the periosteum, endosteum and Haversian canals. Bone cells die and pain ensues.

37 Bone Repair – Callus (Soft) Formation
The broken area is perfused with newly synthesized capillaries and WBC’s clean up dead cellular debris. Bone reconstruction occurs via osteoblast and osteoclast migration to the area of damage.

38 Bone Repair – Callus (Hard) Formation
New scaffold of bone (trabeculae) form at the site This continues until a bony callus is formed roughly two months later

39 Bone Repair - Bone Remodeling
Bony callus is remodeled (osteoclasts and osteoblasts) and eventually converted into compact bone on the outside surfaces

40 Bone Diseases Osteomalacia – bones not sufficiently mineralized
Poor nutrition leads to limited mineralization “Rickets” in children – can lead to deformities in growing bone

41 Osteoporosis When bone resorption outpaces bone deposit
Most common in post-menopausal women, as estrogen suppresses osteoclast activity May be combated with Hormone replacement Exercise Good nutrition

42 Paget’s Disease Haphazard bone formation
Osteoblast outpaces osteoclast activity Bone is deposited where is should not be

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