Hormonal Control of Metabolism

Thyroid & Parathyroid Glands

Thyroid Hormones released by thyroid Thyroxine (T4) - peptide hormone made from aa

tyrosine receptors on most body cells increases basal metabolic rate & O2 consumption

especially in liver, kidneys & heart people with higher thyroxine can oxidize sugars

faster

T4’s neg. feedback pathway:

•if the metabolic rate decreases, receptors in the hypothalamus are activated.

•the hypothalamus secretes Thyroid releasing hormone (TRH), which stimulates the release of Thyroic stimulating hormone (TSH),

•TSH travels in the bloodstream to the thyroid gland and initiates the release of thyroxine.

•thyroxine increases metabolism by stimulating increased oxidation of glucose by somatic cells.

•the higher levels of of thyroxine feed back to inhibit the release of TRH and TSH from the pituitary.

Goiters

A goiter is a pronounced swelling of the thyroid gland in the neck caused by insufficient iodine intake in the diet.

The main source of iodine in your diet is iodized salt.

Hypothyroidism(“Hypo” means less)

Underactive Thyroid Gland

Occurs when the thyroid doesn’t produce enough hormones.

Hypothyroidism decreases metabolism.

Hyperthyroidism(“Hyper” means more)

Overactive Thyroid Gland

Occurs when the thyroid produces excess hormones.

Hyperthyroidism increases metabolism.

Thyroid Disorders

The parathyroid glands help regulate calcium levels in the blood and lower

phosphate levels.

Calcium is used for development and maintenance of strong bones and teeth. It is also works in the heart, nerves, and muscles.

When the level of calcium in the blood is too low, the parathyroid glands

release parathyroid hormone (PTH).

A rise in PTH causes calcium levels in the blood to increase and phosphate levels to decrease by influencing the kidneys, intestines, and bones.

The Parathyroid Glands and Homeostasis

Bone contains calcium phosphate. Calcium ion goes to the blood and the phosphate ions out via the urine. Calcium levels in the blood return to normal, so PTH secretion stops.

Kidneys reabsorb Ca2+ Intestines absorb Ca2+ Bones release Ca2+

PTH causes:• the kidneys to reabsorb more calcium• The intestines absorb and retain more calcium from food. • Calcium release from the bones. (98% of calcium is stored in the skeletal system.)

Parathyroid Hormones