Bone & Skeletal Tissue Chapter 6

Functions of the Skeletal system Support Protection Movement Mineral storage Hematopoiesis (blood cell formation)

Skeletal Cartilages

Cartilages of the respiratory tract

Classification of Bones Bone are identified by: shape internal tissues bone markings

Bone Shapes Long bones Flat bones Sutural bones Irregular bones Short bones Sesamoid bones

Long Bones Figure 6–1a

Long Bones Are long and thin Are found in arms, legs, hands, feet, fingers, and toes

Flat Bones Figure 6–1b

Flat Bones Are thin with parallel surfaces Are found in the skull, sternum, ribs, and scapula

Sutural Bones Figure 6–1c

Sutural Bones Are small, irregular bones Are found between the flat bones of the skull

Irregular Bones Figure 6–1d

Irregular Bones Have complex shapes Examples: spinal vertebrae pelvic bones

Short Bones Figure 6–1e

Short Bones Are small and thick Examples: ankle wrist bones

Sesamoid Bones Figure 6–1f

Sesamoid Bones Are small and flat Develop inside tendons near joints of knees, hands, and feet

Bone Markings Depressions or grooves: Projections: Tunnels: along bone surface Projections: where tendons and ligaments attach at articulations with other bones Tunnels: where blood and nerves enter bone

Bone Markings

Bone Markings Table 6–1 (2 of 2)

The femur Long Bones Figure 6–2a

Structure of a long bone The Humerus

Long Bones Diaphysis: Epiphysis: Metaphysis: the shaft wide part at each end articulation with other bones Metaphysis: where diaphysis and epiphysis meet

Flat Bones The parietal bone of the skull Figure 6–2b

Compact Bone Structure

Spongy Bone Figure 6–6

Spongy Bone Structure

Bone Cells Make up only 2% of bone mass: osteocytes osteoblasts osteoprogenitor cells osteoclasts

Bone Cells: Osteoblasts, Osteocytes & Osteoclasts

Periosteum Figure 6–8a

Endosteum Figure 6–8b

Bone Development Human bones grow until about age 25 Osteogenesis: bone formation Ossification: the process of replacing other tissues with bone

Intramembranous Ossification Also called dermal ossification: because it occurs in the dermis produces dermal bones such as mandible and clavicle There are 3 main steps in intramembranous ossification

Intramembranous Ossification: Step 1 Figure 6–11 (Step 1)

Intramembranous Ossification: Step 1 Mesenchymal cells aggregate: differentiate into osteoblasts begin ossification at the ossification center develop projections called spicules

Step 2

Intramembranous Ossification: Step 2 Blood vessels grow into the area: to supply the osteoblasts Spicules connect: trapping blood vessels inside bone

Step 3 Figure 6–11 (Step 3)

Intramembranous Ossification: Step 3 Spongy bone develops and is remodeled into: osteons of compact bone periosteum or marrow cavities

Endochondral Ossification Ossifies bones that originate as hyaline cartilage Most bones originate as hyaline cartilage

Endochondral Ossification: Step 1 Chondrocytes in the center of hyaline cartilage: enlarge form struts and calcify die, leaving cavities in cartilage Figure 6–9 (Step 1)

Step 2

Endochondral Ossification: Step 2 Blood vessels grow around the edges of the cartilage Cells in the perichondrium change to osteoblasts: producing a layer of superficial bone around the shaft which will continue to grow and become compact bone (appositional growth)

Step 3 Blood vessels enter the cartilage: bringing fibroblasts that become osteoblasts spongy bone develops at the primary ossification center

Step 4 Remodeling creates a marrow cavity: bone replaces cartilage at the metaphyses

Step 5 Capillaries and osteoblasts enter the epiphyses: creating secondary ossification centers

Step 6

Endochondral Ossification: Step 6 Epiphyses fill with spongy bone: cartilage within the joint cavity is articulation cartilage cartilage at the metaphysis is epiphyseal cartilage

Endochondral Ossification Appositional growth: compact bone thickens and strengthens long bone with layers of circumferential lamellae PLAY Endochondral Ossification Figure 6–9 (Step 2)

Appostional Growth

Blood Supply of Mature Bones 3 major sets of blood vessels develop Figure 6–12

Blood Vessels of Mature Bones Nutrient artery and vein: a single pair of large blood vessels enter the diaphysis through the nutrient foramen femur has more than 1 pair Metaphyseal vessels: supply the epiphyseal cartilage where bone growth occurs

Blood Vessels of Mature Bones Periosteal vessels provide: blood to superficial osteons secondary ossification centers

Mature Bones As long bone matures: osteoclasts enlarge marrow cavity osteons form around blood vessels in compact bone

Effects of Exercise on Bone Mineral recycling allows bones to adapt to stress Heavily stressed bones become thicker and stronger

Bone Degeneration Bone degenerates quickly Up to 1/3 of bone mass can be lost in a few weeks of inactivity

Wolff’s Law Tension and compression cycles create a small electrical potential that stimulates bone deposition and increased density at points of stress.

Effects of Hormones and Nutrition on Bone Normal bone growth and maintenance requires nutritional and hormonal factors

Minerals A dietary source of calcium and phosphate salts: plus small amounts of magnesium, fluoride, iron, and manganese

Calcitriol The hormone calcitriol: is made in the kidneys helps absorb calcium and phosphorus from digestive tract synthesis requires vitamin D3 (cholecalciferol)

Vitamins Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation Vitamin A stimulates osteoblast activity Vitamins K and B12 help synthesize bone proteins

Other Hormones Growth hormone and thyroxine stimulate bone growth Estrogens and androgens stimulate osteoblasts Calcitonin and parathyroid hormone regulate calcium and phosphate levels

Hormones for Bone Growth and Maintenance

Chemical Composition of Bone Figure 6–13

Bone homeostasis

Calcitonin and Parathyroid Hormone Control Bones: where calcium is stored Digestive tract: where calcium is absorbed Kidneys: where calcium is excreted

Parathyroid Hormone (PTH) Produced by parathyroid glands in neck Increases calcium ion levels by: stimulating osteoclasts increasing intestinal absorption of calcium decreases calcium excretion at kidneys

Parathyroid Hormone (PTH) Figure 6–14a

Calcitonin Figure 6–14b

Calcitonin Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by: inhibiting osteoclast activity increasing calcium excretion at kidneys

A misleading view of bone homeostasis Calcitonin does not play a central role in maintaining blood plasma Ca++ levels in adults. It is important to maintaining bone density, though.

Fracture Repair: Step 1 Figure 6–15 (Step 1)

Fracture Repair: Step 1 Bleeding: Bone cells in the area die produces a clot (fracture hematoma) establishes a fibrous network Bone cells in the area die

Fracture Repair: Step 2 Figure 6–15 (Step 2)

Fracture Repair: Step 2 Cells of the endosteum and periosteum: Divide and migrate into fracture zone Calluses stabilize the break: external callus of cartilage and bone surrounds break internal callus develops in marrow cavity

Fracture Repair: Step 3 Figure 6–15 (Step 3)

Fracture Repair: Step 3 Osteoblasts: replace central cartilage of external callus with spongy bone

Fracture Repair: Step 4 Figure 6–15 (Step 4)

Fracture Repair: Step 4 Osteoblasts and osteocytes remodel the fracture for up to a year: reducing bone calluses

Common fracture types

The Major Types of Fractures Pott’s fracture Figure 6–16 (1 of 9)

Comminuted fractures

Transverse fractures Figure 6–16 (3 of 9)

Spiral fractures Figure 6–16 (4 of 9)

Displaced fractures Figure 6–16 (5 of 9)

Colles’ fracture Figure 6–16 (6 of 9)

Greenstick fracture Figure 6–16 (7 of 9)

Epiphyseal fractures

Compression fractures Figure 6–16 (9 of 9)

Depression fracture of the skull

Age and Bones Bones become thinner and weaker with age Osteopenia begins between ages 30 and 40 Women lose 8% of bone mass per decade, men 3%

Effects of Bone Loss The epiphyses, vertebrae, and jaws are most affected: resulting in fragile limbs reduction in height tooth loss

Osteoporosis Severe bone loss Affects normal function Over age 45, occurs in: 29% of women 18% of men

Hormones and Bone Loss Estrogens and androgens help maintain bone mass Bone loss in women accelerates after menopause

Cancer and Bone Loss Cancerous tissues release osteoclast-activating factor: that stimulates osteoclasts and produces severe osteoporosis

Some decorative arrangements

I dare not Jim!