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Endocrine System for AP Biology

By — McGraw-Hill Professional
Updated on Oct 24, 2011

Practice problems for these concepts can be found at: Human Physiology Review Questions for AP Biology

Endocrine signaling occurs when cells dump hormones into the bloodstream to affect cells in other parts of the body. Hormones are chemicals produced by glands such as the pituitary and distributed by the circulatory system to signal far-away target cells. Here we are at the pituitary gland. As you can see, it is not very big at all—it is the size of a pea and is divided into an anterior and a posterior division. The anterior pituitary gland is also called the adenohypophysis, and it produces six hormones: TSH, STH, ACTH, LH, FSH, and prolactin; the posterior pituitary gland, also known as the neurohypophysis, releases only two hormones: ADH and oxytocin (see definitions of these acronyms in the Glossary at the end of the book).

The two lobes of the pituitary gland differ in the way they deliver their hormones. If you look closely, you will see that there is a short stalk that connects the anterior portion of the pituitary gland to the brain. This stalk, called the hypothalamus, controls the output of hormones by the pituitary gland. The anterior pituitary is linked to the hypothalamus via the bloodstream. When the concentration of a particular anterior pituitary hormone is too low in the circulation, the hypothalamus will send releasing factors via the bloodstream that stimulate the production of the needed hormone. The posterior lobe of the pituitary gland is different—it is derived from neural tissue. Because of this, its connection to the hypothalamus is neural. ADH and oxytocin are produced by the nerve cell bodies that are located in the hypothalamus, where they are packaged into secretory granules and sent down the axons to be stored in the posterior pituitary. The posterior pituitary gland releases the hormones when appropriately stimulated by a nervous impulse from the hypothalamus. The following is a breakdown of the hormones you should be familiar with for the exam:

Hormones of the anterior pituitary are

FSH   Follicle-stimulating hormone. A gonadotropin—stimulates activities of the testes and ovaries. In females, it induces the development of the ovarian follicle, which leads to the production and secretion of estrogen.

LH   Luteinizing hormone. A gonadotropin—stimulates ovulation and formation of corpus luteum. Stimulates synthesis of estrogen and progesterone.

TSH   Thyroid-stimulating hormone. Works to stimulate the synthesis and secretion of thyroid hormones, which in turn regulate the rate of metabolism in the body.

STH (or HGH)   Somatotropic hormone (or human growth hormone). Stimulates protein synthesis and general growth in the body.

ACTH   Stimulates the secretion of adrenal cortical hormones, which work to maintain electrolytic homeostasis in the body.

Prolactin   Controls lactogenesis—production of milk by the breasts. Decreases the synthesis and release of GnRH (gonadotropin-releasing hormone), inhibiting ovulation.

CT teacher: "Have a good general understanding of these hormones and their functions."

Hormones of the posterior pituitary are

ADH   Stimulates reabsorption of water by the collecting ducts of the nephron.

Oxytocin   Stimulates uterine contraction and milk ejection for breastfeeding.

Hormones of the adrenal gland are

Cortisol   Stress hormone released in response to physiological challenges.

Aldosterone   Regulates sodium concentration of body.

Epinephrine   Raises blood glucose level, increases metabolic activity—"fight or flight" hormone. Also known as adrenaline.

Pancreatic hormones are

Insulin   Secreted in response to high blood glucose levels to promote glycogen formation. Lowers blood sugar.

Glucagon   Stimulates conversion of glycogen into glucose. Raises blood sugar.

The parathyroid hormone (PTH): Increases serum concentration of Ca2+, assisting in process of bone maintenance.

Sex hormones are

Progesterone   Regulates menstrual cycle and pregnancy.

Estrogen   Stimulates development of sex characteristics in women. Secreted in ovaries. Induces the release of LH, including the LH surge of the menstrual cycle. With progesterone, helps maintain the endometrium during pregnancy.

Testosterone   Stimulates sex characteristics in men. Secreted in testes.

Thyroid hormones are

Calcitonin   Lowers blood calcium. Works antagonistically to PTH.

Thyroxine   Stimulates metabolic activities.

The thymus hormone is thymosin, a hormone involved in the development of the T cells of the immune system.

The pineal gland hormone is melatonin, a hormone that is known to be involved in our biological rhythms (circadian). It is released at night.

How is the hormone secretion process of the body regulated? The two main types of regulation with which you should be familiar are negative feedback and positive feedback. Negative feedback occurs when a hormone acts to directly or indirectly inhibit further secretion of the hormone of interest. A good example of negative feedback involves insulin, which is secreted by the pancreas. When the blood glucose gets too high, the pancreas is stimulated to produce insulin, which causes cells to use more glucose. As a result of this activity, the blood glucose level declines, halting the production of insulin by the pancreas. Positive feedback occurs when a hormone acts to directly or indirectly cause increased secretion of the hormone. An example of this feedback mechanism is the LH surge that occurs prior to ovulation in females. Estrogen is released as a result of the action of FSH, and travels to the anterior pituitary to stimulate the release of LH, which acts on the ovaries to stimulate further secretion of estrogen.

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