The Skeletal System: Bone Tissue Chapter 6

1. The Skeletal System: Bone TissueChapter 6

3. The Skeletal System: Bone Tissue • Functions of Bone and Skeletal System • Structure of Bone • Histology of Bone Tissue • Blood and Nerve Supply of Bone • Bone Formation • Bone’s Role in Calcium Homeostasis • Exercise and Bone Tissue • Aging and Bone Tissue

4. Functions of Bone and Skeletal System • Support • Protection • Assistance in Movement • Mineral Homeostasis • Blood Cell Production • Triglyceride Storage

5. Functions of Bone and Skeletal System • Support • Structural framework of the body • Supports soft tissues • Provides attachment points for tendons of skeletal muscle • Protection • Protects important internal organs • Cranium protects brain • Vertebrae protects spinal cord • Ribs protect lungs and heart

6. Functions of Bone and Skeletal System • Assistance in Movement • Skeletal muscle attaches to bone • Skeletal muscle contraction pulls on bone producing movement • Mineral Homeostasis • Bone tissue stores several minerals • Acts to serve as a reservoir of critical minerals • Calcium (99% of body’s content) • Phosphorus

7. Functions of Bone and Skeletal System • Blood Cell Production • Red bone marrow produces (Hemopoiesis) • Red blood cells • White blood cells • Platelets • Triglyceride Storage • Yellow bone marrow • Triglycerides stored in adipose cells • Serves as a potential chemical energy reserve

8. Structure of Bone • Long Bone Anatomy (Humerus) • Diaphysis • Epiphysis • Metaphysis • Epiphyseal growth plate • Articular cartilage • Perforating fibers • Periosteum • Medullary cavity • Endosteum

11. Histology of Bone Tissue • Extracellular matrix surrounding widely separated cells • Matrix • 15% water • 30% collagen fibers • 55% crystallized mineral salts • The most abundant mineral salt is calcium phosphate

12. Histology of Bone Tissue • A process called calcification is initiated by bone-building cells called osteoblasts • Mineral salts are deposited and crystallize in the framework formed by the collagen fibers of the extracellular matrix • Bone’s flexibilitydepends on collagen fibers

13. Histology of Bone Tissue • Four types of cells are present in bone tissue • Osteogenic cells • Undergo cell division (stem cells); the resulting cells develop into osteoblasts • Osteoblasts • Bone-building cells • Synthesize extracellular matrix of bone tissue • Osteocytes • Mature bone cells • Exchange nutrients and wastes with the blood

14. Histology of Bone Tissue • Osteoclasts • Release enzymes that digest the mineral components of bone matrix (resorption) • Regulate blood calcium level

15. Histology of Bone Tissue • Bone may be categorized as: • Compact • Spongy

16. Histology of Bone Tissue • Compact Bone • Resists the stresses produced by weight and movement • Components of compact bone are arranged into repeating structural units called osteons or Haversian systems • Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, - lacunae, osteocytes, and canaliculi

20. Histology of Bone Tissue • Osteon • Central canals run longitudinally through bone • Around the central canals are concentric lamellae • Rings of calcified matrix (like the rings of a tree trunk) • Between the lamellae are small spaces called lacunae which contain osteocytes • Radiating in all directions from the lacunae are tiny canaliculi filled with extracellular fluid and the plasma membrane extensions of the osteocyte

21. Histology of Bone Tissue • Osteon • Canaliculi connect lacunae, forming a system of interconnected canals • Providing routes for nutrients and oxygen to reach the osteocytes • The organization of osteons changes in response to the physical demands placed on the skeleton

22. Histology of Bone Tissue • Spongy Bone • Lacks osteons • Lamellae are arranged in a lattice of thin columns called trabeculae • Spaces between the trabeculae make bones lighter • Trabeculae of spongy bone support and protect the red bone marrow • Hemopoiesis (blood cell production) occurs in red bone marrow of spongy bone

23. Histology of Bone Tissue • Spongy Bone • Within each trabecula are lacunae that contain osteocytes • Osteocytes are nourished from the blood circulating through the trabeculae within the red bone marrow. • Interior bone tissue is made up primarily of spongy bone • The trabeculae of spongy bone are oriented along lines of stress • helps bones resist stresses without breaking while keeping them light.

25. Blood and Nerve Supply of Bone • Bone is richly supplied with blood • Periosteal arteries accompanied by nerves supply the periosteum and compact bone • Epiphyseal veins carry blood away from long bones • Nerves accompany the blood vessels that supply bones • The periosteum is rich in sensory nerves sensitive to tearing or tension

26. Bone Formation • The process by which bone forms is called ossification • Bone formation occurs in four situations: • 1) Formation of bone in an embryo • 2) Growth of bones until adulthood • 3) Remodeling of bone • 4) Repair of fractures

27. Bone Formation • Formation of Bone in an Embryo • Bone formation follows one of two patterns • Intramembranous ossification • Flat bones of the skull and mandible are formed in this way • “Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skull • Endochondral ossification • The replacement of cartilage by bone • Most bones of the body are formed in this way including long bones

28. Bone Formation • Formation of Bone in an Embryo • Cartilage formation and ossification occurs during the sixth week of embryonic development

29. Bone Formation - Intramembranous ossification

30. Bone Formation - Intramembranous ossification

31. Bone Formation - Intramembranous ossification

32. Bone Formation - Intramembranous ossification

33. Bone Formation - Endochondral ossification

34. Bone Formation - Endochondral ossification

35. Bone Formation - Endochondral ossification

36. Bone Formation - Endochondral ossification

37. Bone Formation - Endochondral ossification

38. Bone Formation - Endochondral ossification

40. Bone Growth During Infancy, Childhood and Adolescence • Growth in Length • The growth in length of long bones involves two major events: • 1) Growth of cartilage on the epiphyseal plate • 2) Replacement of cartilage by bone tissue in the epiphyseal plate

41. Bone Growth During Infancy, Childhood and Adolescence • Osteoclasts dissolve the calcified cartilage, and osteoblasts invade the area laying down bone matrix • The activity of the epiphyseal plate is the way bone can increase in length • At adulthood, the epiphyseal plates close and bone replaces all the cartilage leaving a bony structure called the epiphyseal line

43. Bone Growth During Infancy, Childhood and Adolescence • Growth in Thickness • Bones grow in thickness at the outer surface • Remodeling of Bone • Bone forms before birth and continually renews itself • The ongoing replacement of old bone tissue by new bone tissue • Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life

44. Bone Growth During Infancy, Childhood and Adolescence • A balance must exist between the actions of osteoclasts and osteoblasts • If too much new tissue is formed, the bones become abnormally thick and heavy • Excessive loss of calcium weakens the bones, as occurs in osteoporosis • Or they may become too flexible, as in rickets and osteomalacia

45. Factors Affecting Bone Growth and Bone Remodeling • Normal bone metabolism depends on several factors • Minerals • Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling • Vitamins • Vitamin A stimulates activity of osteoblasts • Vitamin C is needed for synthesis of collagen • Vitamin D helps build bone by increasing the absorption of calcium from foods in the gastrointestinal tract into the blood • Vitamins K and B12 are also needed for synthesis of bone proteins

46. Factors Affecting Bone Growth and Bone Remodeling • Hormones • During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the liver and bone tissue (under influence of hGH) • IGFs stimulate osteoblasts, promote cell division at the epiphyseal plate, and enhance protein synthesis • Thyroid hormones (T3 and T4) also promote bone growth by stimulating osteoblasts • Insulin promotes bone growth by increasing the synthesis of bone proteins

47. Factors Affecting Bone Growth and Bone Remodeling • Hormones • Estrogen and testosterone cause a dramatic effect on bone growth • Cause of the sudden “growth spurt” that occurs during the teenage year • Promote changes in females, such as widening of the pelvis • Ultimately-Shut down growth at epiphyseal plates • Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling

48. Bone’s Role in Calcium Homeostasis • Bone is the body’s major calcium reservoir • Levels of calcium in the blood are maintained by controlling the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone • Both nerve and muscle cells depend on calcium ions (Ca2+) to function properly • Blood clotting also requires Ca2+ • Many enzymes require Ca2+ as a cofactor

49. Bone’s Role in Calcium Homeostasis • Actions that help elevate blood Ca2+ level • Parathyroid hormone (PTH) regulatesCa2+ exchange between blood and bone tissue • PTH increases the number and activity of osteoclasts (i.e., resorption) • PTH acts on the kidneys to decrease loss of Ca2+ in the urine • PTH stimulates formation of calcitriol (active form of Vitamin D) a hormone that promotes absorption of calcium from foods in the gastrointestinal tract

50. Bone’s Role in Calcium Homeostasis