Ch. 16 The Endocrine System

List and describe the chief effects of anterior pituitary hormones.

- Growth hormone (GH): Stimulates somatic growth; mobilizes fats. -Thyroid-stimulating hormone (TSH): Stimulates thyroid gland to release thyroid hormones. -Adrenocorticotrpic hormone (ACTH): Promotes release of glucocorticoids and adrogens. -Follicle-stimulating hormone (FSH): IN females, stimulates ovarian follicle maturation and production of estrogens. In males, stimulates sperm production. -Luteinizing hormone (LH): In females, triggers ovulation and stimulates ovarian production of estrogens and progesterone. In males, promotes testosterone production. -Prolactin (PRL): Promotes lactation.

List the major endocrine organs, and describe their body locations.

- Pineal gland within the brain superior and posterior to the Hypothalamus. - Hypothalamus is within the brain anterior and inferior to the Pineal gland. -The Pituitary gland is connected to the Hypothalamus through the infindubulum and is inferior to the Hypothalamus. -The Thyroid gland is in the neck and anterior to the Parathyroid glands. -The Parathyroid glands are posterior to the Thyroid glands. -The Thymus is inferior to the Thyroid/ Parathyroid glands and is anterior to the heart. -The adrenal glands are superior to the kidneys. -The Ovaries/ Testis like medially within the body between each thigh. The testis are exterior to the body whereas the ovaries are internal and inferior to the belly button.

Describe the two major mechanisms by which hormones bring out their effects on their target tissues.

- The Cyclic AMP Signaling Mechanism: 1.) A hormone binds to a receptor. 2.) The receptor activates G protein. The G protein behaves like a light switch. 3.) G protein activates adenylate cyclase. 4.) Andeylate cyclase converts ATP to cyclic AMP. 5.) Cyclic AMP activates protein kinases. -The PIP2-Calcium Signlaing Mechanism: 1.) A hormone binds to a receptor. 2.) The receptor activates G protein. 3.) Phospholipase C splits a plasma membrane phospolipid called PIP2 into two second messangers: DAG and IP3. 4.) Dag activates a protein kinase enzyme which triggers responses within the target cell. IP3 releases Ca2+ from intracellular storage sites.

Describe the effects of the two groups of hormones produced by the thyroid gland.

- Thyroid Hormone (TH) : Increases basal metabolic rate and body heat production, by turning on transcription of genes concerned with glucose oxidation. Regulating tissue growth and development. Maintaining blood pressure by increasing the number of adrenergic receptors in blood vessels. - Calcitonin : Inhibits osteoclast activity, inhibiting bone resorption and release of Ca2+ from the body matrix, and stimulates Ca2+ uptake and incorporation into bone matrix.

Identify factors that influence activation of a target cell by a hormone.

-Blood levels of the hormone. -Relative number of receptors for that hormone on or in the target cells. -Affinity (strength) of the binding between the hormone and the receptor.

Distinguish between hormones, paracrines, and autocrines.

-Hormones are chemical messengers secreted by cells into the extracellular fluids. - Autocrines are a type of hormone that has its chemicals effects exerted onto the same cells that secrete them. -Paracrines are a type of hormone that acts locally (within the same tissue) but affect cell types other than those releasing the paracrine chemicals.

Follow the process of thyroxine formation and release.

1.) The import of iodine into the cells. 2.) Iodination of tyrosine. 3.) The release of the thyroid hormones.

Briefly describe the importance of melatonin.

An amine hormone derived from serotonin. Melatonin concentrates in the blood rise and fall in a daily cycle. Peak levels occur during the night and make us drowsy

Indicate important differences between hormonal and neural controls of body functioning.

Both are systems that regulate the functions of the body. Neural are almost instantaneous, short-lived and use cells to transmit impulses. Hormonal are delayed, longer-lasting, and use chemicals called HORMONES to influence metabolic activities. Hormones regulate metabolic functions.

Indicate the general functions of parathyroid hormone.

Controls calcium balance in the blood. - Stimulates osteaclasts (bone - resorbing cells) to digest some of the calcium - rich bony matrix and release ionic calcium and phosphates to the blood. - Enhances reabsorption of Ca2+ ( and excretion of phosphate PO4^3) by the kidneys. - Promotes activation of vitamin D, thereby increasing absorption of Ca2+ by intestinal mucosal cells. Vitamin D is required for absoption of Ca2+ from food, but first the kidneys must convert it to tis active vitamin D3 form, calcitriol. PTH stimulates this transformation.

State the location of enteroendocrine cells.

Enteroendocrine cells are hormone-secreting cells sprinkled in the mucosa of the gastrointestinal tract (GI)

Describe how hormones are classified chemcally.

Hormones are classified as amino acids or steroids and are classified as such through their water solubility. -Amino acid based hormones tend to be water soluble and so cannot cross the plasma membrane in order to enter a cell they would need a receptor. -Steroids are lipid soluble not water soluble and thus can cross the plasma membrane.

List hormones produced by the adrenal gland, and cite their physiological effects.

In the cortex: -Mineralocorticoids (aldosterone) -Glucocorticoids (cortisol) -Gonadocorticoids (sex hormones) In the Medulla: -Norepinephrine (20%) -Epinephrine (80%)

Describe structural and functional relationships between the hypothalamus and the pituitary gland.

It derives from a down growth of hypothalamic tissue and maintains its neural connection with the hypothalamus via a nerve bundle called the hypothalamic-hypophyseal tract, which runs through the infundibulum. This tract arises from neurons in the paraventricular and supraoptic nuclei of the hypothalamus. These neurosecretory cells synthesize one of two neurohormones and transport them along their axons to the posterior pituitary. When these phyothalamic neurons fire, they release the stored hormones into a capillary bed in the posterior pituitary for distribution throughout the body.

Antagonism

Occurs when one hormone opposes the action of another. For e.g. insulin which lowers blood glucose levels, is antagonized by glucagon, which raises blood glucose levels. How does antagonism occur? Antagonism may compete for the same receptors, act through different metabolic pathways, or even cause down-regulation of the receptors for the antagonistic hormone.

List three kinds of interactions of different hormones acting on the same target cell.

Permissiveness Synergism Antagonism

Permissiveness

Permissiveness - Is the situation in which one hormone can not exert its full effects without another hormone being present. For e.g. Reproductive system hormones largely regulate the development of the reproductive system.

Synergism

Synergism - Occurs when more than one hormone produces the same effects at the target cell and their combined effecs are amplified. For e.g. both glucagon and epinephrone cause the liver to release glucose to the blood. When they act together, the amount of glucose released is about 150% of what is released.

Discuss the structure of the posterior pituitary, and describe the effects of the two hormones it releases.

The posterior pituitary consists largely of axon terminals of hypothalamic neurons whose cell bodies are located in the supraoptic or paraventricular nuclei. The paraventricular neurons primarily make oxytocin, and the supraoptic neurons mainly produce antidiuretic hormone (ADH). Oxytocin stimulates the uterine contractions;initiates labor and initiates milk ejection. ADH stimulate kidney tubule cells to reabsorb water.

Explain how hormone release is regulated.

The synthesis and release of most hormones are regulated by some type of negative feedback mechanism. Some internal or external stimulus triggers hormone secretion. As levels of hormones rise, it causes target organ effects, which then feedback to inhibit further hormone release. As a result, blood levels of many hormones vary only within a narrow range

Define endocrinology

the scientific study of hormones and the endocrine organs.

Describe the functional roles of hormones of the testes, ovaries, and placenta.

• Estrogen is responsible for maturation of the reproductive organs and the appearance of the secondary sex characteristics of the female at puberty. Acting with progesterone promotes breast development and cyclic changes in the uterine mucosa • Testosterone initiates the maturation of the male reproductive organs and the appearance of secondary sex characteristics and sex drive. Also responsible for normal sperm production and maintains the reproductive organs in the mature functional state. • The placenta is a temporary endocrine organ that sustains the fetus during pregnancy. It also secrets several steroids and protein hormones that influence the course of pregnancy. These hormones incluse estrogen , progesterone and human chorionic gonadotropin (hCG)

Compare and contrast the effects of the two major pancreatic hormones.

• Glucagon - 29 amino acid polypeptide is a very potent hyperglycemic agent. The major target of glucagon is the liver o Breakdown of glycogen to glucose (glycogenolysis) o Synthesis of glucose from lactic acid and from noncarbohydrate molecules (gluconeogenesis) o Release of glucose to the blood by liver cells, causing blood glucose levels to rise. • Insulin - is a small 51 amino acid protein consisting of two amino acid chains linked by disulfide bonds. It synthesizes as part of a larger polypeptide chain called proinsulin. Enzymes then excise the middle portion of this chain releasing functional insulin. Effects are most obvious when we have just eaten. o Enhances membrane transport of glucose into most body cells (muscle and fat) o Inhibits the breakdown of glycogen to glucose. o Inhibits the conversion of amino acids or fats to glucose. These inhibiting effects counter any metabolic activity that would increase plasm levels of glucose

Briefly explain the hormonal functions of the heart, kidney, skin, adipose tissue, bone, and thymus.

• Kidneys - secrets erythropoietin is a glycoprotein hormone that signals bone marrow to increase production of red blood cells. • Skin - produces cholecalciferol and inactive form of vitamin D then becomes fully activated within the kidneys. The active form calcitriol is a regulator of the carrior system that intestinal cells use to absorb Ca2+ from food. • Adipose tissue - release leptin which serves to tell your body how much stores energy (as fat) you have. • Bone - osteoblast secrete osteocalcin prods pancreatic beta cells to divide and secrete more insulin. • Thymus - secrets several hormones including thymulin, thymopoietins and thymosins these hormones are involved in normal development of T lymphocytes and the immune response.