• Endocrine Glands – lack the ducts that are present in exocrine glands. The endocrine glands secrete their products, which are biologically active molecules called hormones, into the blood. The blood carries the hormones to target cells that contain specific receptor proteins for the hormones, and which therefore can respond in a specific fashion to them.

• Amines – These are hormones derived from the amino acids tyrosine and tryptophan. They include the hormones secreted by the adrenal medulla, thyroid, and pineal glands. Some are polar (most) and some are nonpolar.
  
• Polypeptides and Proteins – Polypeptide hormones generally contain less than 100 amino acids; an example is antidiuretic hormone. These are always polar (a chain of amino acids)
• Glycoproteins – These molecules consist of a long polypeptide bound to one or more carbohydrate groups. Examples are follicle-stimulating hormone and luteinizing hormone.
  • Amines, Polypeptides and Glycoproteins will utilize a secondary messenger system. a secondary messenger system is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change
• Steroids – These are lipids derived from cholesterol. They include the hormones testosterone, estradiol, progesterone, and cortisol. (non polar, they pass through the cell membrane and meet up with a receptor in the nucleus or just outside in the cytoplasm)

• Thyroid hormones attach to chromatin-bound receptors located in the nucleus.

• Steroid hormones bind to cytoplasmic receptor proteins and translocate to the nucleus.

• Attachment of the hormone receptor protein complex to the cromatin activates genes and thereby stimulates RNA and protein synthesis.

• In the case of some hormones, activation of adrenylate cyclase occurs, resulting in the intracellular production of cyclic AMP.

• Cyclic AMP activates a cytoplasmic enzyme called protein kinase. Protein kinase phosphorylates specific enzyme protein and thereby changes the metabolism of the target cell for those hormones that use cAMP as a second messenger.

• In the case of other hormone actions, the enzyme phospholipase C is activated in the cell membrane, causing the release of inositol triphosphate into the cell.

• Inositol triphosphate stimulates the release of Ca++ from the endoplasmic reticulum of the target cell.

• Ca++ binds to regulatory proteins, such as calmodulin, that can influence the metabolism of the target cell.

PITUITARY GLAND

Hormones of the Posterior Pituitary Gland:

• Increases water reabsorption by the kidney tubules (water returns to the blood)
• Decreases sweating
• Causes vasoconstriction (in large amounts)

• Decreased water content in the body (alcohol inhibits secretion)

• Promotes contraction of myometrium of uterus (labor)
• Promotes release of of milk from mammary glands

• Nerve impulses from hypothalamus, the result of stretching of cervix or stimulation of nipple
• Secretion from placenta at end of gestation--- the stimulus is unknown

Hormones of the Anterior Pituitary Gland:

• Increases rate of mitosis
• Increases amino acid transport in to cells
• Increases rate of protein synthesis
• Increases use of fats for energy

• GHRH (hypothalamus) stimulates secretion
• GHIH---somatostatin (hypothalamus) inhibits secretion

• Increases secretion of thyroxine and T3 by thyroid gland

• TRH (hypothalamus)

• Increases secretion of cortisol by the adrenal cortex

• CRH (Hypothalamus)

• Stimulates milk production by the mammary glands

• PRH (hypothalamus) stimulates secretion
• PIH (hypothalamus) inhibits secretion

• Initiates growth of ova in ovarian follicles
• Increases secretion of estrogen by follicle cells

• Initiates sperm production in the testes

• GnRH (hypothalamus) stimulates secretion
• Inhibin (ovaries or testes) inhibits secretion

• Causes ovulation
• Causes the ruptured ovarian follicle to become the corpus luteum
• Increases secretion of progesterone by the corpus luteum

• Increases secretion of testosterone by the interstitial cells of the testes

• GnRH (hypothalamus)

Diseases of the Thyroid

Pancreas and Other Endocrine Glands

1. Insulin lowers blood glucose and stimulates the production of glycogen, fat, and protein.
2. Glucagon raises blood glucose by stimulating the breakdown of liver glycogen. It also promotes lipolysis and the formation of keytone bodies.
3. The secretion of insulin is stimulated by a rise in blood glucose following meals. The secretion of glucagon is stimulated by a fall in blood glucose during periods of fasting.

1. Melatonin secretion is regulated by the suprachiasmatic nucleus of the hypothalamus, which is is the major center for the control of circadian rhythms.
2. Melatonin secretion is highest at night, and this hormone has a sleep-promoting effect. In many species, it also has an antigonadotropic effect and may play a role in timing the onset of puberty in humans although this is as yet unproven.

1. Leydig cells in the interstitial tissue of the testes secrete testosterone and other androgens.
2. Granulosa cells of the ovarian follicles secrete estrogen.
3. The corpus luteum of the ovaries secretes progesterone, as well as estrogen.

• Did you know that almost all the research on stress has been conducted with men and that recent studies have found that women respond to stress in fundamentally different ways than men? Rather than simply "fight or flight," a woman's stress response may be to "tend and befriend." Read more about it here.