2. Chapter 11 Endocrine Glands
Secretion & Action of Hormones
(Pages )
Endocrine Glands & Hormones (Table 11.1)
Hormones are regulatory molecules secreted into the blood by endocrine glands.
Chemical categories of hormones include steroids (include testosterone, estradiol, progesterone and cortisol.), amines (such as thyroid hormones), polypeptides and proteins (such as insulin) , and glycoproteins (such as follicle stimulating hormone).
Interactions between the various hormones produce effects that may be:
1. Synergistic (when 2 or more hormones work together to produce a particular
result. Their effects may be additive as the action of epinephrine
and norepinephrine on the cardiac rate, or complementary as in
the action of estrogen, cortisol, prolactin and oxytocin on
mammary glands to produce and secrete milk in lactation.),
2. Permissive (when a hormone enhances the responsiveness of a target organ
to a second hormone, or when it increases the activity of the
second hormone as in the effect of estradiol on the
responsiveness of the uterus to progesterone.),
3. Antagonistic (when the actions of one hormone antagonize the effects
of another as in the action of insulin and glucagon on glucose
concentration in the blood).

3. Endocrine glands lack ducts that are present in exocrine glands.
Endocrine glands secrete hormone into the blood.
Blood carries hormones to target cells that contain specific receptor proteins for the hormone, and can respond in a specific fashion.
Endocrine glands can be:
1.A discrete organ whose primary functions are the production and
secretion of hormones, as pituitary gland.
2.A group of cells in an organ as pancreas, heart, liver, adipose
tissue and kidneys.
3.Specialized neurons secrete neurohormones as in hypothalamus.
Some chemicals are secreted both as NT and hormone as Norepinephrine.
Thus, the endocrine system and the nervous system are related and no sharp distinction can be drawn between them on the basis of the chemicals they release.
Hormones affect: 1. Regulation of the total body Metabolism.
2. Growth.
3. Reproduction

4. Fig. 11.1 The major endocrine glands.

7. Fig. 11.24 Endemic goiter is caused by insufficient iodine in the diet.
A lack of iodine causes hypothyroidism, and the resulting elevation in TSH secretion stimulates the excessive growth of the thyroid.

8. Fig. 11. 26 A symptom of hyperthyroidism
Fig A symptom of hyperthyroidism. Hyperthyroidism is characterized by an increased metabolic rate, weight loss, muscular weakness, and nervousness. The eyes may also protrude (exophthalmos) due to edema in the orbits.