Two antagonistic hormones regulate the homeostasis of calcium (Ca2+) in the blood of mammals
Parathyroid hormone (PTH) is released by the parathyroid glands
Calcitonin is released by the thyroid gland
Antagonistic Hormone Pairs control blood calcium levels
Parathyroid gland (behind thyroid)
Falling blood Ca2+ level
Blood Ca2+ level (about 10 mg/100 mL)
Blood Ca2+ level rises.
Stimulates Ca2+ uptake in kidneys
Stimulates Ca2+ release from bones
Increases Ca2+ uptake in intestines
Active vitamin D
PTH increases the level of blood Ca2+
It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys
It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food
Calcitonin decreases the level of blood Ca2+
It stimulates Ca2+ deposition in bones and secretion by kidneys
The adrenal glands are adjacent to the kidneys.
Each adrenal gland actually consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion).
The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline).
These hormones are members of a class of compounds called catecholamines.
They are secreted in response to stress-activated impulses from the nervous system.
They mediate various fight-or-flight responses.
Epinephrine and norepinephrine
Trigger the release of glucose and fatty acids into the blood
Increase oxygen delivery to body cells
Direct blood toward heart, brain, and skeletal muscles, and away from skin, digestive system, and kidneys.
The release of epinephrine and norepinephrine occurs in response to nerve signals from the hypothalamus.
Summary: Stress and the Adrenal Gland
(a) Short-term stress response
(b) Long-term stress response
Effects of epinephrine and norepinephrine:
2. Increased blood pressure 3. Increased breathing rate 4. Increased metabolic rate
1. Glycogen broken down to glucose; increased blood glucose