Hormones and the Endocrine System

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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

Slide 60

Antagonistic Hormone Pairs control blood calcium levels

PTH

Parathyroid gland (behind thyroid)

STIMULUS:

Falling blood Ca2+ level

Homeostasis:

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

Slide 61

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

Slide 62

Adrenal Hormones: Response to Stress

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).

Slide 63

Catecholamines from the Adrenal Medulla

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.

Slide 64

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.

Slide 65

Summary: Stress and the Adrenal Gland

Stress

Adrenal gland

Nerve cell

Nerve signals

Releasing hormone

Hypothalamus

Anterior pituitary

Blood vessel

ACTH

Adrenal cortex

Spinal cord

Adrenal medulla

Kidney

(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