A&P CH 6 PDF

Chapter 6 A&P (bone function, compact vs spongy bone, long bone 4 cell types: periosteum, endosteum, intramembranous, exercise effect on bone, hormones, calcium, parathyroid hormone vs calcitonin) Bone function  Primary functions of the skeletal system –Support –Storage of...

Chapter 6 A&P (bone function, compact vs spongy bone, long bone 4 cell types: periosteum, endosteum, intramembranous, exercise effect on bone, hormones, calcium, parathyroid hormone vs calcitonin) Bone function  Primary functions of the skeletal system –Support –Storage of minerals and lipids –Blood cell production –Protection –Leverage Compact vs Spongy bone  Osteon—cylindrical functional unit of compact bone Compact bone is denser and stronger than spongy bone  Spongy bone lacks osteons Osteons- Osteons serve as the functional unit of bone. Their thick lamellar rings provide mechanical support and strength to bone –Red bone marrow ▪Forms blood cells ▪Contains blood vessels that supply nutrients to osteocytes by diffusion –Yellow bone marrow ▪Stores fat Long bone Mineral storage Long bones store minerals like calcium, phosphorus, sodium, and magnesium, which are essential for regulating physiological activities. Structure and support Long bones provide strength, structure, and stability to the skeleton. Periosteum  Periosteum—membrane that covers outside of bones –Except within joint cavities –Outer, fibrous layer and inner, cellular layer –Fibers are interwoven with those of tendons –Perforating fibers—fibers that become incorporated into bone tissue ▪Increase strength of attachments Endosteum  Endosteum—incomplete cellular layer that lines medullary cavity –Active during bone growth, repair, and remodeling –Covers trabeculae of spongy bone –Lines central canals of compact bone –Consists of flattened layer of osteogenic cells Intramembranous Intramembranous ossification is a process that develops bones from sheets of connective tissue membranes, and is involved in the formation of certain flat bones of the skull, the clavicles, and some irregular bones Exercise effect on bone  Effects of exercise on bone –Mineral recycling allows bones to adapt to stress –Heavily stressed bones become thicker and stronger –Exercise, particularly weight-bearing exercise, stimulates osteoblasts Bone degeneration –Bone degenerates quickly –Up to one-third of bone mass can be lost in a few weeks of inactivity Hormones 6.7 Exercise, Nutrition, and Hormones (4 of 4) Nutritional and hormonal effects on bone –Growth hormone and thyroxine stimulate bone growth –Sex hormones ▪Estrogen and testosterone stimulate osteoblasts –Parathyroid hormone and calcitonin maintain calcium ion homeostasis Parathyroid hormone and calcitonin maintain calcium ion homeostasis Parathyroid hormone (PTH) –Produced by parathyroid glands in neck –Increases blood calcium ion levels by ▪Stimulating osteoclast activity (indirectly) ▪Increasing intestinal absorption of calcium by enhancing calcitriol secretion by kidneys ▪Decreasing calcium excretion by kidneys Calcium  Characteristics of bone –Dense matrix due to deposits of calcium salts –Osteocytes (bone cells) within lacunae organized around blood vessel –Canaliculi ▪Narrow passageways that allow for exchange of nutrients, wastes, and gases –Periosteum ▪Covers outer surfaces of bones (except at joints) ▪Consists of outer fibrous and inner cellular layers Bone development –Ossification (osteogenesis)—bone formation –Calcification—deposition of calcium salts ▪Occurs during ossification –Two forms of ossification ▪Endochondral ossification ▪Intramembranous ossification –Some human bones grow until about age 25 Parathyroid hormone vs calcitonin Parathyroid hormone (PTH) and calcitonin are hormones that work together to regulate calcium levels in the blood Parathyroid hormone (PTH) Secreted by the parathyroid glands in the neck, PTH increases calcium levels in the blood by activating osteoclasts, which break down bone to release calcium. PTH also helps the kidneys absorb calcium Calcitonin Produced by the C-cells in the thyroid gland, calcitonin decreases calcium levels in the blood by inhibiting osteoclasts and increasing the amount of calcium excreted in urine The levels of both PTH and calcitonin are controlled by blood calcium levels: PTH: The parathyroid glands release PTH when blood calcium levels are low. Calcitonin: The thyroid gland releases calcitonin when blood calcium levels are high.