Chapter 11 Endocrine Glands Secretion & Action of Hormones (Pages 317-318) 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).

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

Fig. 11.1 The major endocrine glands.

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.

Fig. 11. 26 A symptom of hyperthyroidism Fig. 11.26 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.