anatomy and physiology chapter 6

Skeletal system

Bones, cartilages, and ligaments of the body.

Support

Hold up the body, support for muscles.

Movement

Muscles pull on bones to move the body.

Protection

enclose and protect delicate organs

Blood formation

Red bone marrow produces blood cells.

Electrolyte balance

Reservoir for calcium and phosphate.

Acid-base balance

Buffers pH changes by absorbing or releasing alkaline salts, e.g., calcium phosphate.

Hormone secretion

Bones secrete osteocalcin and lipocalcin 2, which stimulate insulin secretion, increase insulin sensitivity and aid in responding to stress.

Detoxification

Bones absorb heavy metals and other foreign elements, releasing them more slowly for excretion.

Bone (osseous tissue)

Connective tissue with matrix hardened by calcium phosphate deposition.

Osteology

Study of bone.

Mineralization or calcification

The hardening process of bone matrix.

Flat bones

Thin curved plates; most cranial bones, sternum, scapula, ribs & hip bones.

Long bones

Long with expanded ends; many bones of the limbs (humerus, ulna, femur, tibia, metacarpals, metatarsals, phalanges etc.).

Short bones

Carpal and tarsal bones of hands, feet.

Irregular bones

Vertebrae, some skull bones.

Diaphysis

Shaft of the bone; in long bone provides leverage.

Epiphysis

Expanded portion at each end; provides strength to the joint and increased surface area for attachment of tendons and ligaments.

Epiphyseal plate

Hyaline cartilage separating marrow cavities of epiphysis and diaphysis; present only in children and adolescents aka growth plate.

Periosteum

Outer sheath of dense irregular connective tissue; some of its collagen fibers penetrate into bone matrix as perforating fibers.

Nutrient foramina

Holes where blood vessels of periosteum penetrate into the bone.

Endosteum

Internal surface covering; composed of reticular connective tissue with cells that deposit osseous tissue and others that dissolve it.

Articular cartilage

Hyaline cartilage at the ends of most adjoining bones; enables joints to move more easily, with the aid of synovial fluid.

Flat bone features

Sandwichlike arrangement of inner and outer tables (layers) of compact bone; between compact bone is middle layer of spongy bone.

Osteogenic cells

Stem cells that give rise to osteoblasts. In endosteum and inner layer of periosteum.

Osteoblasts

Bone-forming cells that make the organic matter of bone and promote its mineralization.

Osteogenesis

Bone-building activity of osteoblasts.

Osteocytes

Former osteoblasts that became trapped in the matrix they deposited.

Lacunae

Cavities where osteocytes reside, interconnected by canaliculi.

Canaliculi

Channels that connect osteocytes and blood vessels.

Gap junctions

Connections that allow osteocytes to share nutrients and chemical signals.

Osteoclasts

Bone-dissolving macrophages present in endosteum and osteogenic layer of periosteum.

Osteolysis

Bone breakdown actions of osteoclasts (pathological).

Resorption

Breakdown of bone by osteoclast (normal process).

Hydrochloric acid (HCl)

Substance secreted by osteoclasts onto bone surface, dissolving minerals of bone matrix.

Lysosomal enzymes

Enzymes that digest organic components of bone matrix.

Matrix of osseous tissue

Stony material surrounding osteocytes and lacunae, giving bone flexibility and strength.

Organic components of bone

Primarily collagen, also includes glycosaminoglycans, proteoglycans, and glycoproteins.

Inorganic components of bone

Primarily hydroxyapatite (calcium phosphate salt), also includes calcium carbonate and small amounts of other minerals.

Concentric lamellae

Layers of matrix around a central (osteonic or haversian) canal, resembling tree rings.

Osteon

The basic structural unit of compact bone; comprised of a central canal and its lamellae.

Perforating canals

Transverse passages that connect central canals of adjacent osteons.

Circumferential lamellae

Layers of matrix around inner and outer boundaries of compact bone.

Interstitial lamellae

Irregular patches of lamellae; leftovers of old osteons that were remodeled.

Spongy bone

Bone with a lattice of slivers called spicules and trabeculae, with a porous appearance.

Trabeculae

Thin plates and beams arranged along bone's lines of stress.

Bone marrow

Soft material occupying marrow cavity of a long bone, spaces within spongy bone, and largest of central canals.

Red bone marrow

Myeloid or hematopoietic tissue that forms the cellular components of blood.

Yellow bone marrow

Adipose tissue that gradually replaces red marrow with age.

Red marrow in infants and children

Nearly every bone has red marrow.

Red marrow in adults

Limited to skull, vertebrae, sternum, ribs, part of pelvis, and proximal ends of humerus and femur; rest of the bones have yellow marrow.

Transformation of yellow marrow

In case of severe or chronic anemia, yellow marrow can transform back into red marrow.

Bone formation

Occurs in two ways—intramembranous and endochondral.

Mesenchyme

Embryonic connective tissue from which both intramembranous and endochondral ossification begin.

Intramembranous ossification

Produces flat bones of skull, part of mandible, and most of clavicle (collarbone).

Stages of intramembranous ossification

1. Mesenchyme condenses into sheet of tissue permeated by blood vessels; mesenchymal cells become osteoblasts that secrete osteoid tissue (prebone). 2. Minerals (primarily calcium phosphate) crystalize on collagen of osteoid; osteoblasts promote this mineralization and become trapped in the matrix to become osteocytes. 3. Spongy bone becomes a honeycomb of trabeculae; mesenchyme adjacent to developing bone condenses to form fibrous periosteum on each surface. 4. Osteoblasts beneath periosteum create zones of compact bone on each side of spongy bone.

Endochondral ossification

Produces most other bones, including vertebrae, ribs, scapulae, pelvic girdle, limb bones, and parts of skull.

Timing of endochondral ossification

Begins in sixth week of fetal development; continues into a person's 20s.

Chondrification

Embryonic mesenchyme becomes a hyaline cartilage model of the future bone.

Ossification

Cartilage broken down and replaced by bone.

Primary ossification center

Forms near the middle where chondrocytes enlarge, die, and walls around them calcify; osteoblasts deposit bone collar and perichondrium becomes a periosteum.

Metaphysis

A growth zone at the junction between the diaphysis and epiphysis of a long bone, where cartilage is replaced by osseous tissue and the bone grows in length.

Secondary marrow cavity

Forms at the end of bone during endochondral ossification.

Bone elongation

Occurs from changes within the metaphysis.

Zone of reserve cartilage

Typical resting hyaline cartilage.

Zone of cell proliferation

Chondrocytes multiply.

Zone of cell hypertrophy

Chondrocytes enlarge; walls of matrix between lacunae are very thin.

Zone of calcification

Minerals deposited in walls of matrix.

Zone of bone deposition

Chondrocytes die; blood vessels invade the spaces created; osteoblasts deposit concentric lamellae and osteocytes dissolve the temporary calcified cartilage.

Interstitial growth

Cartilage growth from within.

Achondroplastic dwarfism

Long bones of the limbs stop growing in childhood, while growth of other bones is unaffected.

Appositional growth

Deposition of new bone tissue at the surface.

Bone remodeling

The process where old bone is absorbed and new bone is deposited; 10% of skeleton replaced every year.

Wolff's law of bone

The structure of a bone is determined by the mechanical stresses placed upon it.

Nutritional factors in bone health

Calcium and phosphate are raw materials for mineralization.

Vitamin A

Promotes synthesis of glycosaminoglycans.

Vitamin C (ascorbic acid)

Promotes cross-linking of collagen.

Vitamin D (calcitriol)

Enables calcium absorption from diet.

Calcitonin

Hormone secreted by the thyroid gland that stimulates osteoblast activity.

Growth hormone

Promotes cartilage growth at epiphyseal plates.

Sex steroids

Estrogen and testosterone stimulate osteoblasts.

Parathyroid hormone (PTH)

Causes osteoblasts to release osteoclast-stimulating factor that stimulates osteoclasts to resorb bone.

Primary purpose of PTH

To maintain appropriate level of blood calcium.

Aging Skeletal System

Changes with age include loss of bone mass and strength, with osteoblasts becoming less active after age 35-40.

Osteopenia

A net loss of bone characterized by a measurable decline in bone density, especially affecting spongy bone.

Osteoporosis

A severe loss of bone that compromises physical activity and health, leading to easy fractures.

Stress Fracture

A break caused by abnormal trauma.

Pathological Fracture

A break resulting from a stress that normally wouldn't fracture a bone, often due to weakened bone from disease.

Closed Reduction

A procedure to fix a fracture where broken parts are aligned without surgery.

Open Reduction-Internal Fixation (ORIF)

A surgical repair of a fracture using plates, screws, or pins.

Closed Fracture

A fracture where the skin is not broken.

Open Fracture

A fracture where the skin is broken and the bone protrudes through the skin.

Complete Fracture

A fracture where the bone is broken into two or more pieces.

Incomplete Fracture

A partial fracture that extends only partway across the bone, with pieces remaining joined.

Nondisplaced Fracture

A fracture where the portions of bone are still in correct anatomical alignment.

Displaced Fracture

A fracture where the portions of bone are out of anatomical alignment.

Comminuted Fracture

A fracture where the bone is broken into three or more pieces.

Greenstick Fracture

A fracture where the bone is bent toward one side and has an incomplete fracture on the opposite side.

Hairline Fracture

A fine crack in which sections of bone remain aligned, common in the skull.

Impacted Fracture

A fracture where one bone fragment is driven into the marrow cavity or spongy bone of another.