7.4 Physiology of Osseous Tissue

Calcium and phosphate have many roles in human physiology

- Phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers. - Calcium is needed in neuron communication, muscle contraction, blood clotting, and exocytosis

Two mechanisms that Calcitonin uses to lower the concentration of blood calcium

1. Calcitonin reduces osteoclast activity 2. Calcitonin increases the number and activity of osteoblasts Calcitonin plays an important role in children where osteoclast are highly active, but has only a weak effect in adults.

PTH raises calcium blood level by four mechanisms

1. Increased osteoclast activity (more bone resorption) 2. Reduced osteoblast activity (less bone deposition) 3. More urinary phosphate excretion (prevention of hydroxyapatite formation) 4. Less urinary calcium excretion (conservation of calcium)

calculus

A calcified mass in an otherwise soft organ is called a

hypocalcemia

A calcium deficiency; it may cause excessive excitability of the nervous system and leads to muscle tumors, spasms, or tetany.

hypercalcemia

A calcium excess; it can cause nerve and muscle cells to become less excitable than normal. Symptoms may include emotional disturbances, muscles weakness, sluggish reflexes, and sometimes cardiac arrest.

helps provide adequate calcium and phosphate; without it, bones become soft, as in rickets in children and osteomalacia in adults

Calcitriol

ectopic ossification

Osseous tissue sometimes forms in other organs, resulting in abnormal calcification called

Calcium homeostasis is regulated by three hormones

calcitriol, calcitonin, and parathyroid hormone

Mineral Deposition (mineralization)

is a crystallization process in which calcium, phosphate, & other ions are taken from the blood plasma and deposited in bone tissue, mainly as crystals of hydroxyapatite.

Calcitriol

is a form of vitamin D, a hormone that raises blood calcium levels, is also necessary for bone deposition

Arteriosclerosis

is one example of ectopic ossification and results from calcification of the arterial walls

Parathyroid Hormone (PTH)

is secreted by the parathyroid gland when blood calcium levels are low

Mineral Resorption

is the process of dissolving bone, releasing minerals into the blood

Calcium

must be kept in a state of homeostasis between the bones and the blood

Calcitonin

secreted when the blood calcium concentration rises too high

calcium homeostasis

the disturbance of ____ in the skeleton disrupts function of other organ systems (especially nervous and muscular).