ENDOCRINE SYSTEM

· Functions: maintain homeostasis

· Types of messengers:

Hydrophobic- can pass through cell membrane

e.g. steroids

Hydrophilic- bind to cell-surface receptors and

trigger release of second messengers

see transparencies

· Types of molecular messengers: 412

1. Paracrine

2. Neurotransmitter

3. Neurohormones

4. True hormones

5. Pheromones

· General mechanism:

1. Initiating or inhibiting changes inside cells

2. Regulator cells detect changes; release

molecular messengers in response

3. Feedback control- negative and positive

· Main types of effects:

1. Kinetic- control secretion by exocrine and

endocrine gland; muscle contraction & pigment

e.g. epinephrine, melatonin, secretin, gastrin..

2. Metabolic- carbohydrate and protein balance;

electrolyte and water balance

e.g. thyroxine, insulin, growth hormone,ADH

aldosterone, calcitonin

3. Morphogenic- general growth, maturation..

e.g. growth hormone, thyroxine,FSH, LH

4. Behavioral- tropic effects

e.g. estrogen, progesterone, and androgens

· Hypothalamic control: 399-403

Posterior pituitary- stores oxytocin and ADH-

hormones made in hypothalamus

Anterior pituitary- produces 7 hormones

FSH, LH, TSH, ACTH, MSH, prolactin and growth

Hypothalamus controls(via portal blood vessels) the secretion of these hormones

· High levels of a particular polypeptide hormone in the blood may cause:

1. Loss of receptor proteins for that hormone in the target cells

2. Loss of target tissue sensitivity for that hormone

3. Decrease responsiveness of the target tissue for that hormone

· Endocrine glands:

1. Thyroid gland- thyroxine, and calcitonin

2. Parathyroid gland- parathyroid hormone

3. Adrenal gland- cortex- aldosterone and corticosterone

4. Pancreas- insulin and glucagons

5. Stomach- gastrin

6. Small intestine- CCK, secretin, GIP

7. Kidneys-erythropoietin

8. Gonads- estrogen, progesterone, testosterone

9. Prostaglandin- fatty acid- effects involve smooth muscle

· Mechanism of hormonal action:

Steroid hormone

The function of cyclic AMP as a second messenger-

see transparency