Gland  =  Group of epithelial cells specialized for secretion. 
 

     Exocrine gland  =  Gland which secretes chemical substances into 
          a duct  (ex. sweat gland). 
 

     Endocrine gland  =  Gland which secretes chemical messengers 
          (hormones) into the blood (ex. thyroid gland). 
 

     Hormone  =  Chemical messenger which is secreted into the blood 
          by specialized cells and alters the activity of other cells in the body. 
 

     Target cell  =  Cell on which a hormone exerts its effect. 
 

     Receptor  =  Component of a cell with which a chemical messenger 
          (such as a hormone) combines to exert its effect. 
 

     1. Antidiuretic hormone (ADH).

          Permits reabsorption of water by the collecting ducts. 
 

     2. Oxytocin.

          Stimulates contraction of uterus. 

          Stimulates milk secretion. 
 

     Stimulate other glands: 

          1. Thyroid-stimulating hormone (TSH). 

               Stimulates the thyroid gland. 

          2. Adrenocorticotropic hormone (ACTH).

               Stimulates the adrenal cortex. 
 

     Stimulate the gonads (gonadotropins): 

          3. Follicle-stimulating hormone (FSH).

               Stimulates development of gametes (sperm and ova). 

          4. Luteinizing hormone (LH).

               Stimulates production of sex hormones. 
 

     Stimulate nonendocrine tissues: 

          5. Growth hormone.

               Stimulates growth and affects metabolism. 

          6. Prolactin.

               Stimulates milk production. 
 

     1. Stimulates growth of bone and cartilage.

          GH deficiency in childhood  ---->  dwarfism. 

          GH oversecretion in childhood  ---->  gigantism. 

          GH oversecretion in adult  ---->  acromegaly. 
 

     2. Stimulates protein synthesis.

          GH deficiency in late adulthood ----> may contribute to age-related 
               breakdown of body structure. 
 

     3. Increases blood glucose.
 

     1. Treatment of dwarfism.

          Replacement therapy with human growth hormone. 

          Replacement therapy  =  Administration of a hormone to a 
               person whose natural production of that hormone is deficient. 

          Manufactured by recombinant DNA technology. 

          Must be injected. 
 

     2. Treatment of gigantism or acromegaly.

          Surgical removal of the pituitary gland. 
 

          1. Required for growth and development. 

               a. Skeleton. 

               b. Brain. 
 

          2. Stimulates cell metabolism. 

               a. Increases basal metabolic rate (BMR). 
 

          1. Goiter.

               Enlarged thyroid gland. 

               Results from iodine deficiency. 

               Prevention -- iodized salt. 
 

          2. Hypothyroidism.

               Thyroxine deficiency. 

               Slowed physiologic function. 

                    Fatigue. 
                    Slowed speech and mental function. 
                    Inability to tolerate cold. 
                    Decreased BMR. 

             Treatment -- Thyroxine replacement therapy. 
 

          3. Hyperthyroidism.

               Thyroxine oversecretion. 

                    Thyroid gland is stimulated by substances not under 
                         feedback control. 

             Increased rate of physiological function. 

                    Insomnia, anxiety. 
                    Weight loss. 
                    Rapid heart rate. 
                    Excess heat production, skin is flushed. 
                    Increased BMR. 

             Exophthalmos -- protrusion of the eyeballs. 

             Treatment:

                    Antithyroid drugs. 

                    Surgical removal of thyroid. 

                    Radioactive iodine. 
 

          1. Four tiny glands lying behind the thyroid. 
 

          2. Secrete parathyroid hormone (PTH). 

               Important for regulation of blood calcium. 
 

          3. Effects of parathyroid hormone. 

               a. Promotes resorption of Ca⁺⁺ from bone. 

               b. Promotes renal tubular reabsorption of Ca⁺⁺. 

               c. Increases blood Ca⁺⁺ levels. 
 

          4. Feedback control. 

               When blood Ca⁺⁺ levels are low, secretion of PTH is 
                stimulated. 
 

          1. Cardiovascular. 

               Increases heart rate, stroke volume, and blood pressure. 
 

          2. Respiratory.

               Stimulates the respiratory center. 

               Bronchodilation. 
 

          3. Metabolic.

               Mobilizes energy stores for utilization. 

               Increases blood glucose and free fatty acids. 
 

          1. Mineralocorticoids (ex. aldosterone). 

               Regulate Na⁺ and K⁺ balance. 
 

          2. Glucocorticoids (ex. cortisol). 

               Regulate glucose metabolism -- increase blood glucose. 

               Anti-inflammatory effects at high doses. 
 

          3. Androgens. 

               Male sex hormones. 

               Produced in small amounts in both males and females. 
 

     1. Membrane transport.

          Promotes the uptake of glucose and amino acids into cells. 

          Exception:  Uptake of glucose into the brain is independent of 
               insulin. 
 

     2. Metabolism.

          Stimulates metabolic pathways which favor the storage of
             nutrients. 

          Increases formation and storage of glycogen in liver and muscle. 

          Increases formation and storage of triglycerides in adipose 
               tissue. 

          Increases protein synthesis. 

          Decreases blood glucose, fatty acids, and amino acids. 
 

          Testosterone is secreted during the prenatal period. 

           Very little is produced during childhood. 

          Large increase at the onset of puberty. 

          Testosterone secretion declines late in life. 
 

          1. Required for reproductive function.

               Differentiation of male reproductive tract and genitalia. 

               Growth of prostate gland and seminal vesicles.

               Spermatogenesis. 
 

          2. Stimulation of male secondary sex characteristics.

               Facial and body hair. 

               Balding. 

               Deepening of voice. 

               Antler growth (deer).
 

          3. Anabolic actions.

               Bone growth, followed by closure of epiphyseal discs. 

               Muscular development. 
 

          4. Brain and behavior.

               Libido. 

               Aggressive behavior. 
 

          A. Benefits.

               1. Increase muscle mass. 

                2. Probably improve performance. 
 

          B. Side Effects.

              1. Temporary sterility. 

              2. Liver damage (ex. hepatitis, liver cancer). 

              3. Heart disease. 

              4. Aggressive behavior. 

              5. Premature puberty. 

              6. Masculinization of women. 
 

          Secretion begins at puberty. 

          Secreted in a cyclic manner until menopause 
               (late 40's - early 50's).

          Elevated during pregnancy. 

          Very low levels after menopause. 
 

          1. Required for reproductive function.

               Maturation of the female reproductive tract. 

               Cyclic changes in the uterus. 

               Maturation of ovarian follicles. 
 

          2. Stimulation of female secondary sex characteristics.

               Distribution of fat. 

               Breast development . 
 

          3. Anabolic actions.

               Bone growth, followed by closure of epiphyseal discs. 
 

          4. Brain and behavior.
 

          1. Males.

             FSH is required for spermatogenesis.

             LH stimulates testosterone secretion.
 

          2. Females.

             FSH stimulates growth and maturation of ovarian follicles.

             Both FSH and LH are required for estrogen secretion.

               Midcycle LH surge triggers ovulation.
 

          Primary function -- To prepare the uterus for pregnancy
              and to maintain pregnancy.
 

          1. Changes in uterine lining.

               a. Thick, spongy, and full of blood vessels. 

               b. Prepared for implantation of the fertilized egg.

               c. Withdrawal of progesterone triggers menstruation.
 

          2. Development of mammary glands.
 

          3. Inhibits ovulation.