Ch. 17 (17.2 and 17.7)

17.7 Explain some general causes and examples of hormone hyposecretion and hypersecretion.

Hyposecretion: inadequate hormone release. It can result from tumors or lesions that destroy an endocrine gland or interfere with its ability to receive signals from another cell. For example, a fractured sphenoid bone can sever the hypothalamo-hypophyseal tract and prevent the transport of oxytocin and ADH to the posterior pituitary. The resulting ADH hyposecretion disables the water-conserving capability of the kidneys and leads to diabetes insipidus, an output of abundant but glucose-free urine. Autoimmune diseases can also lead to hormone hyposecretion when endocrine cells are attacked by autoantibodies--antibodies that fail to distinguish between foreign matter and one's own tissues. Hypersecretion: excessive hormone release. Some tumors result in the overgrowth of functional endocrine tissue. A Pheochromocytoma is a tumor of the adrenal medulla that secretes excessive amounts of epinephrine and norepinephrine. Additionally, some tumors in nonendocrine organs produce hormones. For example, some lung tumors secrete ACTH and overstimulate cortisol secretion by the adrenal gland. Certain autoimmune disorders can cause endocrine hyposecretion while others cause hypersecretion. Toxic Goiter is when antibodies mimic the effect of TSH on the thyroid, activating the TSH receptor and causing thyroid hypersecretion.

Explain how the pituitary is controlled by the hypothalamus and its target organs.

Pituitary hormones are not secreted at constant rates. The timing and amount of pituitary secretion are regulated by the hypothalamus, other brain centers, and feedback from the target organs. Hypothalamic control enables the brain to monitor conditions within and outside the body and to stimulate or inhibit the release of anterior lobe hormones in response. For example, in times of stress, the hypothalamus triggers ACTH secretion, which leads to cortisol secretion and mobilization of materials needed for tissue repair. The posterior pituitary is controlled by neuroendocrine reflexes--the release of hormones in response to nerve signals. Target organs also regulate the pituitary and hypothalamus through feedback loops. Negative feedback inhibition-- the pituitary stimulates another endocrine gland to secrete its hormone, and that hormone feeds back to the pituitary or hypothalamus and inhibits further secretion of the pituitary hormone.

17.2 Distinguish between the anterior and posterior lobes of the pituitary.

The anterior pituitary arises from a pouch that grows upward from the embryonic pharynx, while the posterior pituitary arises as a bud growing downward from the brain. The anterior pituitary, also called the anterior lobe or adenohypophysis, constitutes about three-quarters of the pituitary as a whole. It has no nervous connection to the hypothalamus, but is linked to it by a complex of blood vessels called the Hypophyseal Portal System. The hypothalamus controls the anterior pituitary by secreting hormones that enter the primary capillaries, travel down the venules, and diffuse out of the secondary capillaries into the pituitary tissue. The posterior pituitary, also called the posterior lobe, constitutes the posterior one-quarter of the pituitary. It is actually nervous tissue, not a true gland. Hormones of the posterior pituitary are made by certain neuroendocrine cells in the hypothalamus. Their axons pass down the stalk as a bundle called the Hypothalamo-Hypophyseal Tract and end in the posterior lobe. Hormones are then stored in the nerve endings of the posterior pituitary until a nerve signal coming down the same axons triggers their release.

17.2 Describe the anatomical relationships between the hypothalamus and the pituitary gland.

The hypothalamus forms the floor and walls of the third ventricle of the brain. It regulates primitive functions of the body ranging from water balance and thermoregulation to sex drive and childbirth. Many of its functions are carried out by way of the pituitary gland.

Describe the effects of growth hormone.

Unlike the other pituitary hormones, GH is not targeted to just one or a few organs but has widespread effects on the body. It also induces the liver and other tissues to secrete growth stimulants called insulin-like growth factors(IGF-I and IGF-II), which then stimulate other target cells. One effect of IGF is to prolong the action of GH. GH has a short half-life while IGFs have long half-lives. Mechanisms: 1. Protein synthesis: GH boosts the translation of existing mRNA(protein production); and the transcription of DNA and thus the production of more mRNA. 2. Lipid metabolism: To provide energy for growing tissues, GH stimulates adipocytes to catabolize fat and release fatty acids and glycerol into the blood. By providing these fuels, GH makes it unnecessary for cells to consume their own proteins. This is called the protein-sparing effect. 3. Carbohydrate metabolism: GH also has a glucose-sparing effect. Its role in mobilizing fatty acids reduces the dependence of most cells on glucose so they will not compete with the brain, which is highly glucose-dependent. 4. Electrolyte balance: GH makes electrolytes available to the growing tissues. It also influences bone, cartilage, and muscle growth, especially during childhood and adolescence.

Adrenocorticotropic hormone (ACTH) -- produced by? Target organ? Function?

anterior pituitary; adrenal cortex; growth of adrenal cortex, secretion of glucocorticoids

Growth hormone (GH) -- produced by? Target organ? Function?

anterior pituitary; liver, bone, cartilage, muscle, fat; widespread tissue growth

Prolactin (PRL) -- produced by? Target organ? Function?

anterior pituitary; mammary glands; milk synthesis

Follicle-stimulating hormone (FSH) -- produced by? Target Organ? Function?

anterior pituitary; ovaries, testes; Female-growth of ovarian follicles and secretion of estrogen; male-sperm production

Luteinizing hormone -- produced by? Target organ? Function?

anterior pituitary; ovaries, testes; Female-ovulation, maintenance of corpus luteum; male-testosterone secretion

Thyroid-stimulating hormone (TSH) -- produced by?Target organ? Function?

anterior pituitary; thyroid gland; growth of thyroid, secretion of thyroid hormone

Somatostatin -- produced by? Function?

hypothalamus; inhibits secretion of growth hormone (GH) and thyroid-stimulating hormone (TSH)

Prolactin-inhibiting hormone (PIH) -- produced by? Function?

hypothalamus; inhibits secretion of prolactin (PRL)

Corticotropin-releasing hormone (CRH) -- produced by ? Function?

hypothalamus; promotes secretion of adrenocorticotropic hormone (ACTH)

Gonadotropin-releasing hormone (GnRH) -- produced by? Function?

hypothalamus; promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Growth hormone-releasing hormone (GHRH) -- produced by? Function?

hypothalamus; promotes secretion of growth hormone (GH)

17.2 Thyrotropin-releasing hormone (TRH) -- produced by ? Function?

hypothalamus; promotes secretion of thyroid-stimulating hormone (TSH) and prolactin (PRL)

Antidiuretic hormone (ADH) -- produced by? Target organ? Function?

posterior pituitary; kidneys; water retention

Oxytocin (OT) -- produced by? Target organ? Function?

posterior pituitary; uterus, mammary glands; labor contractions, milk release, possibly involved in ejaculations, sperm transport, sexual affection, and mother-infant bonding