A&P-Chapter: 6

diaphysis.

The shaft of a long bone is the

Which two minerals are stored in major quantities in bone tissue?

calcium and phosphorus

Describe the process involved in bone remodeling

• Osteoclasts break down bone matrix by bone resorption; these cells attach to the bone surface and release enzymes and acids that digest/dissolve bone substances • The degraded bone materials pass through the osteoclasts and into the bloodstream • Osteoblasts move into the remodeling site and begin producing bone matrix by bone deposition • The action of osteoclasts and osteoblasts should balance one another • If osteoclast action is greater than that of osteoblasts, bones lose calcium and become weak (as in osteoporosis) • If osteoblast action is greater than that of osteoclasts, bones become abnormally thick and heavy and bone spurs are more likely to form • The sex hormones estrogens and androgens slow bone resorption and promote bone synthesis; estrogen is produced by the ovaries in females; testosterone, an androgen, is produced by the testes in males • Human growth hormone (hGH), produced by the anterior pituitary gland, also promotes bone growth

Compare the structural and functional differences between compact and spongy bone tissue

*Compact bone—has few spaces between the cells and the matrix; 80% of the skeleton is compact bone; strongest form of bone; forms the outer layer of all bones and most of the diaphysis of long bones *Spongy bone—has many spaces between the cells and the matrix; lightweight; 20% of the skeleton is spongy bone; makes up most of the bone tissue of short, flat, and irregular bones and most of the epiphyses of long bones; contains red bone marrow

Describe the structure and functions of each part of a typical long bone

*Diaphysis-is the bone's shaft or body, the long, cylindrical, main portion of the bone. *Epiphysis-are the proximal and distal ends of the bone. *Metaphyses- between; regions between the diaphysis and the epiphyses (growing bone contains epiphyseal plate/layer of hyaline cartilage once the bone stops growing it is replaced with epiphyseal line). *Articular cartilage-is a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms and articulation with another bone (helps reduce friction and absorbs shock at freely movable joints). *Periosteum-is a tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage (attached to underlying bone by perforating fibers). *Medullary cavity/Marrow cavity-is a hallow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults. *Endosteum- a thin membrane that lines the marrow cavity; also contains bone-forming cells

Describe the cellular composition of bone tissue and the functions of each type of cell

1. Osteogenic cells-unspecialized stem cells derived from mesenchyme, tissue from which all connective tissues are formed; ONLY bone cells that divide; found in periosteum and endosteum 2. Osteoblasts- bone building cells that produce the matrix; do not divide; found in the periosteum and endosteum 3. Osteocytes-mature bone cells; the main type of cell found in bone; carry out daily activities needed to maintain the tissue; do not divide 4. Osteoclasts-huge cells located mainly in the endosteum; break down bone matrix during process called resorption; release enzymes and acids that digest bone; do not divide; derived from monocytes, a type of WBC *Osteogenic cells divide and produce osteoblasts; osteoblasts surround themselves with matrix and become osteocytes

trabeculae

Compact bone is composed of units called osteons. In contrast, spongy bone is composed of _____.

red bone marrow

Hematopoiesis takes place in the ________ of some adult bones.

metaphysis

In which region of a long bone, such as the humerus, would you find the epiphyseal plate (growth plate)?

intramembranous ossification

Most of the bones of the skull are formed by this process.

epiphyseal plate

The ______ is composed of hyaline cartilage and allows the diaphysis to grow in length.

articular cartilage

The ______ is composed of hyaline cartilage and reduces friction between bones involved in a joint.

Describe the main functions of the skeletal system

The skeleton serves six major functions: support, , protection, movement, mineral homeostasis, storage of fat, and blood cell production

osteocytes

This cell is active once the matrix of bone calcifies. The cells sits in a lacunae.

canaliculi

What are the extracellular fluid filled extensions of the lacunae called?

Describe how exercise and mechanical stress affect bone tissue

When subjected to the stress of weight-bearing exercise (ex. walking, jogging, weightlifting), bone tissue strengthens as bone mass increases

epiphysis

Which region of a long bone articulates with other bones?

calcium and phosphorous

Which two minerals are needed in large quantities when bones are growing?

Explain why bone tissue is classified at a connective tissue

because of the matrix-the material between the cells; 15% water, 30% collagen fibers/protein, 55% crystallized mineral salts (mainly hydroxyapatite-calcium and phosphorus)

PTH will increase _______ activity while Calcitonin will decrease __________ activity.

osteoclast; osteoclast

Describe the importance of calcium in the body and explain how the blood calcium level is regulated

• 99% of the total body calcium is stored in the bones • The level of calcium in the bloodstream can be regulated by controlling the rate of calcium resorption from bone into blood and calcium deposition from blood into bone • Calcium ions (Ca2+) are needed for proper nerve cell function, muscle cell function, and blood clotting • Several hormones are involved in calcium homeostasis: PTH and calcitriol

Describe the steps of intramembranous ossification

• A connective tissue membrane is replaced by bone • The flat bones of the skull, most facial bones, the mandible, and part of the clavicle are formed this way • Fontanels (soft spots) in an infant's skull harden into bone by this process • Mesenchyme cells cluster together and form a center of ossification • These cells differentiate into osteogenic cells, and then into osteoblasts • The osteoblasts secrete bone matrix until they are surrounded by it • Matrix secretion stops, and the osteoblasts become osteocytes • The matrix hardens during calcification • Spongy bone is formed first, followed by periosteum, and then compact bone (Mesenchyme cells→osteogenic cells → osteoblasts→osteocytes)

Describe the effects of aging on bone tissue

• Aging causes the demineralization of bones; this is the loss of calcium and other minerals from the bone matrix • Aging also causes a decrease in the production of proteins in the body, such as collagen • Collagen gives bones their elasticity and flexibility

Explain how bone grows in length and thickness

• Bone growth in length is related to the activity of the epiphyseal plate • The epiphyseal plate contains chondrocytes that are constantly dividing (remember that osteocytes do NOT divide) • New chondrocytes are formed on the epiphyseal (end) side of the epiphyseal plate, and older chondrocytes are replaced by bone on the diaphysis (shaft) side of the plate • The thickness of the plate remains the same, but the bone length increases • At about age 18 in females and 21 in males (in the range of ages 18-25, on average), the epiphyseal plates close; this occurs as bone replaces all of the cartilage in the area • The epiphyseal line, made of bone, replaces the epiphyseal plate once a long bone stops growing in length • The clavicle is the last bone to stop growing • If a fracture damages the epiphyseal plate, the bone may never grow to adult length • Bones also grow in thickness (appositional growth) • Cells in the perichondrium differentiate into osteoblasts, which secrete matrix • These cells eventually surround themselves with layers of matrix and become osteocytes • At this same time, cells in the endosteum destroy bone that lines the marrow cavity

describe the steps of endochondral ossification

• Mesenchyme cells arrange themselves into the shape of the bone to be formed • These cells develop into chondroblasts, which produce cartilage matrix until they are surrounded by it • The chondroblasts become chondrocytes, mature cartilage cells • Eventually, a "cartilage model" of the bone is formed, complete with a perichondrium around it • The cartilage matrix hardens during calcification • Chondrocytes begin to die, and the cartilage matrix begins to disintegrate • Osteogenic cells found in the perichondrium differentiate into osteoblasts, which begin secreting bone matrix over the cartilage the length of the bone; the perichondrium is now called periosteum • Osteoblasts become osteocytes once they are surrounded by bone matrix • A layer of cartilage remains until adulthood in the region between the diaphysis and epiphysis of long bones; this is called the epiphyseal plate, or growth plate; it allows for continued ossification and lengthening of the bones in children (Mesenchyme cells→chondroblasts→chondrocytes→ osteogenic cells→osteoblasts →osteocytes)