Exam 2 Review:  Chapter 6:  Bone Homeostasis & Bone Disease

remodeling - The ongoing and continual activity of osteoclasts and osteoblast in the periosteum and endosteum of all bones in response to the variables affecting calcium homeostasis and the response to the mechanical forces of gravity and exercise and the necessity for repairs to any fractures, even of microscopic scale, that occur due to the minor traumas of ordinary physical activity in which old bone matrix is resorbed and replaced by new bone matrix.

hypercalcemia - An abnormally high concentration of calcium ions in the blood; at worst, cardiac arrest may occur.

hypocalcemia - An abnormally low concentration of calcium ions in the blood; at worst, respiratory failure may occur (skeletal muscles for breathing lose strength).

calcium homeostasis - The ability to maintain internal equilibrium of blood calcium and phosphate ion levels by adjusting the complex negative feedback processes regulating calcium absorption from the digestive tract (which is also stimulated by the activated form of Vitamin D = calcitriol), calcium deposition/dissolution in the skeletal system, and mineral excretion by the kidneys; the endocrine control of calcium homeostasis is achieved by the antagonistic interplay of parathyroid hormone (PTH) from the parathyroid glands which tends to increase blood calcium levels by stimulating osteoclasts and (thyro)calcitonin from the thyroid gland which tends to decrease blood calcium levels by inhibiting osteoclasts. [See fig. 6.12, p. 189]

parathyroid hormone (PTH) - A protein hormone produced by the parathyroid glands in response to a drop in blood calcium ions that will cause an elevation in the amount of calcium in the body in three ways: (1) increases osteoclast number and activity, thus increasing bone resorption, (2) decreases calcium excretion by the kidney while increasing phosphate excretion, and (3) increased calcitriol synthesis from Vitamin D -- calcitriol increases intestinal absorption of calcium; the net effect of  parathyroid hormone (PTH) = parathormone on phosphate ion levels is to decrease blood phosphate levels by increasing phosphate excretion into the urine.

calcitonin (CT) - A protein hormone produced by the thyroid gland in response to a rise in blood calcium ions that will cause a decrease in the amount of calcium in the body by inhibiting osteoclast activity, thus decreasing bone resorption.  [aka thyrocalcitonin]

human growth hormone (hGH) - A protein hormone produced by the anterioir pituitary gland which targets all body cells to encourage normal growth.

sex hormones - Steroid hormones produced by the gonads (androgens from the testes and estrogens from the ovaries) which regulate the various aspects of reproductive physiology and also play a role in bone growth and metabolism.

osteoporosis - A disease in which the bones become extremely porous, are subject to fracture, and heal slowly, occurring especially in women following menopause and often leading to curvature of the spine from vertebral collapse.

osteoarthritis - A form of arthritis (inflammation of the joints), occurring mainly in older persons, that is characterized by chronic degeneration of the cartilage of the joints. Also called [aka degenerative joint disease]

osteomyelitis - Any infection (usually bacterial) of bone and bone marrow in which the resulting inflammation can lead to a reduction of blood supply to the bone.

osteogenic sarcoma* - A serious malignant bone tumor; most common in children and young adults where it tends to affect the femur.

[*Note:  a sarcoma is a general term for any malignant cancer derived from a connective tissue cell type.]

List:

4.  four vitamins particularly important for healthy bones.

          A, B₁₂, C, D

Describe:

1. the endocrine regulation of bone (calcium/phosphate) homeostasis.

          The endocrine control of bone (mineral) homeostasis is achieved by the antagonistic interplay of two hormones:  (1) parathyroid hormone (PTH) = parathormone from the parathyroid glands which tends to increase blood calcium levels by three mechanisms:  (a) stimulating osteoclasts to dissolve bony matrix, (b) by targeting the kidneys to conserve/save calcium ions from the urine (while encouraging phosphate ion excretion) and (c) by targeting the intestines, in cooperation with activated Vitamin D = calcitriol, to encourage calcium abosrption from meals; and (thyro)calcitonin from the thyroid gland which tends to decrease blood calcium levels by inhibiting osteoclasts.  The net effect of  parathyroid hormone (PTH) = parathormone on phosphate ion levels is to decrease blood phosphate levels by increasing phosphate excretion into the urine.  See the Negative Feedback Regulation Diagram.
 
Sketch and Label

8. the negative feedback regulation of blood calcium concentration.

          See description above and the Negative Feedback Regulation Diagram.