Anatomy and Physiology Chapter 6 - Bones

Major functions of the skeletal system

Major functions of the skeletal system

Protection, Mineral storage and acid-base homeostasis, blood cell formation (hematopoiesis in red bone marrow), fat storage (yellow bone marrow), movement, support

Hyaline cartilage in the skeletal system

Articular cartilage and the epiphyseal plate

Fibrocartilage in the skeletal system

Cushioning between bones, ex. intervertebral disc, menisci, etc.

Dense regular collagenous connective tissue in the skeletal system

Tendons and ligaments

Dense irregular connective tissue in the skeletal system

Periosteum

Long bone

longer than they are wide, the size of the bone doesn't matter. ex. humerus, metacarpal

Short bone

cube shaped, carpals and tarsals

Flat bone

broad, flat, and thin. ex. ribs, skull bones, sternum

Irregular bone

Not easily classifiable, ex. vertebra

Sesamoid bone

round and flat, found in tendon, ex. patella

Epiphysis

The end of a long bone, covered by articular cartilage

Diaphysis

middle of a long bone, covered by periosteum

Spongy bone

Made of trabeculae, found inside flat and long bones

Epiphyseal line

remnant of epiphyseal plate

Medullary cavity

cavity in bones containing bone marrow

Endosteum

membrane on the inner surface of bone that contains bone cells

Periosteum

layer of dense irregular connective tissue that is rich with blood supply and nerves, inner layer has different bone cells

Perforating fibers

collagen fibers that connect the periosteum to the bone tissue

Nutrient foramen

small opening in the outside of the bone for a nutrient artery and vein, and nerves

Red bone marrow

Hematopoietic, found everywhere in the fetal skeleton and only in the axial skeleton and the heads of the femur and humerus in adults

Yellow bone marrow

Stores fat as triglycerides, mostly blood vessels and adipocytes, appendicular skeleton in adults

Organic ECM

Osteoid, produced by osteoblasts, provides flexibility and tensile strength from collagen, contains GAG, proteoglycans, and glycoproteins

Inorganic ECM

Hydroxyapatite crystals (mostly calcium and phosphorus salts, includes other salts and ions). Harden the ECM and provide compression strength

Osteogenic cells

differentiate into different bone cells

Osteoblasts

deposit bone matrix until they completely surround and trap themselves

Osteocytes

mature bone cells trapped in the ECM, maintain the bone

Osteoclasts

large, multinucleated cells that break down the bone matrix

Osteon

Structural unit of compact bone

Concentric lamellae

circular rings of bone matrix, collagen runs in the same direction in one lamella and in the opposite direction in the next lamella, prevents twisting

Central canal

canal in the middle of the osteon, contains blood vessels and nerves

Lacunae

small cavities in bone that contain osteocytes

Canaliculi

hair like canals that connect lacunae to each other and to the central canal so all osteocytes get oxygen and nutrients

Interstitial lamellae

fill in spaces between osteons, remnants of old osteons that got resorbed

Circumferential lamellae

extend around the circumference of the diaphysis deep to the periosteum, resist twisting of the bone

Perforating canals

perpendicular canals that connect to the central canals of the osteons

Trabeculae

structural unit of spongy bone, concentric lamellae with osteocytes in lacunae, no central or perforating canals

Endochondral ossification

most bones use this, built on hyaline cartilage model

Intramembranous ossification

many flat bones, built on model of embryonic connective tissue

Ossification

process of bone formation, produces primary bone that is then remodeled into mature bone

Intramembranous ossification steps

1. osteoblasts develop in the primary ossification center from mesenchymal cells
2. osteoblasts secrete organic matrix, trap themselves and become osteocytes
3. osteoblasts lay down trabeculae of early spongy bone, some of the surrounding mesenchyme becomes periosteum
4. osteoblasts in the periosteum lay down early compact bone

Endochondral ossification steps

1. Hyaline cartilage model is made
2. Chondroblasts in the perichondrium differentiate into osteoblasts/periosteum
3. Osteoblasts build bone collar on the external surface + chondrocytes die and the cartilage calcifies
4. Primary and secondary ossification centers develop, osteoblasts build early spongy bone
5. Osteoclasts carve out medullary cavity, everything finishes ossifying

Epiphyseal plate

Hyaline cartilage plate in long bones that allow for longitudinal growth; if fractured, bones may not fully develop

Zone of reserve cartilage

zone of epiphyseal plate that is closest to the epiphysis, cartilage is just back up if more bone growth is needed

Zone of proliferation

zone where chondroblasts divide in the epiphyseal plate

Zone of hypertrophy and maturation

zone where chondroblasts mature into chondrocytes

Zone of calcification

zone where the chondrocytes die and the ECM calcifies

Zone of ossification

zone where osteoblasts build bone on the calcified cartilage, closest to diaphysis

Appositional growth

osteoblasts directly deep to the periosteum deposit bone, which makes the bone thicker; starts as circumferential lamellae but turns into osteons or breaks down as it gets deeper

Resorption

osteoclasts remove bone matter, releases calcium and decreases pH

Deposition

osteoblasts building bone matter, traps calcium

Blood calcium homeostasis

If blood calcium is too low, parathyroid hormone increases osteoclast activity, increases kidney retention of calcium, and intestinal absorption of calcium

Osteoporosis

inadequate inorganic matrix in ECM, bones become brittle and fracture more easily

Increased osteoblast activity

Increased bone deposition; caused by compressional load or exercise, tension placed on bone, testosterone, adequate dietary intake of calcium and vitamins C, D, & K

Decreased osteoclast activity

Increase bone deposition; estrogen, calcitonin, increase in blood calcium ion concentration

Decreased osteoblast activity

Increased bone resorption; inadequate exercise, inadequate dietary intake of calcium or vitamins C, D, & K

Increased osteoclast activity

Increased bone resorption; continuous pressure placed on bone, parathyroid hormone, decrease in blood calcium ion concentration

Bone repair steps

1. Hematoma fills the gap between bone fragments
2. Fibroblasts and chondroblasts build soft callus
3. Osteoblasts build bone callus
4. Bone callus is remodeled into secondary bone