Shared Flashcard Set

Details

Ch.11
The Endocrine System
32
Physiology
03/26/2009

Additional Physiology Flashcards

 


 

Cards

Term
Describe the chemical nature of hormones:
Definition

1) Amines: Derived from the amino acids tyrosine and tryptophan. Includes the water soluble hormones derived from the adrenal medulla, lipophilic thyroid and pineal glands.

2) Polypeptides and proteins: Proteins are large polypeptides. ADH is an 8 amino acid polypeptide, too small to be considered a hormone. Growth hormone (GH) has 191 amino acids, so it is a protein. Insulin is composed of 2 polypeptide chains derived from a single, larger molecule. Water soluble.

3)Glycoproteins: Consist of a protein bound to one or more carbohydrate groups. ex. FSH and LH. water soluble.

4)Steroids: Lipids derived from cholesterol. Includes testosterones, estradiol, progesterone and cortisol. Lipophilic.

Term
Define prehormone:
Definition
Molecule secreted by endocrine glands that are inactive until changed by their target cells. Also indicates a precursor of a prehormone. ex. preproinsulin.
Term
Define prohormone:
Definition
A precursor molecule that affects the metabolism of target cells; in the case of polypeptide hormones, it may be a longer chained prohormone cut and spliced together to make a hormone. ex. proinsulin.
Term
Describe the different types of hormone interactions (synergistic):
Definition
Synergistic- When two or more hormones work together to produce a particular result. May be complimentary or additive. ex. additive: epinephrine and norepinephrine seperately produces an increase in heart rate, when acting together in same concentrations stimulates an even greater cardiac rate. ex. complimentary: estrogen, cortisol, prolactin and oxytocin work together to enable the mammary gland to secrete milk.
Term
Describe the different types of hormone interactions (permissive):
Definition
Permissive: When the action of a second hormone enhances the responsiveness of a target organ to the second hormone, or when it increases the activity of the second hormone. ex. prior exposure of the uterus to estrogen induces the receptor hormones for progesterone, which improves the response of the uterus when it is subsequently exposed to progesterone. Estrogen thus has a permissive effect on the uterus to progesterone.
Term
Describe the different types of hormone interactions (Antagonistic):
Definition
The actions of one hormone antagonize the effects of another. ex. Lactation during pregnancy is inhibited because the high concentration of estrogen in the blood inhibits the sectretion and action of prolactin.
Term
Describe the significance of hormone concentrations:
Definition
Normal tissue responses are only produced when the hormones are present within their normal range of concentrations. When they are taken in pharmacological concentrations, they can cause the hormone to bind to receptors of different, but closely related hormones, producing abnormal effects. Sometimes there are harmful side effects. ex. high doses of cortisone for long periods can cause osteoperosis.
Term
Describe the significance of hormone cencentration in terms of priming, and downregulation:
Definition
Sometimes priming effects (caused by the upregulation of receptors) can cause sensitivity of a gland to cause further stimulation of hormone production. ex. small amounts of GnRH secreted by the hypothalamus increases the sensitivity of anterior pituitary cells to further increase GnRH stimulation. In priming, increased numbers of receptor proteins for the hormone being primed are inserted in the plasma membrane. Sometimes prolonged exposure to high concentrations of polypeptide hormones can desensitize the target cells, and subsequent exposure to the same concentrations of the same hormone produces less of a target tissue response. This is partly due to the fact that high concentrations of hormones can cause a decrease in the number of receptor proteins in their target cells- a phenomenon known as downregulation.
Term
Explain the mechanisms of action of steroid hormones:
Definition

1) Steroid hormones, transported bound to plasma carrier proteins, dissociate from their plasma carriers and pass through the plasma membrane of their target cell, because they are lipophilic.

2) the steroid hormone binds to receptors, which may be in the cytoplasm. 3) The hormone bound receptor translocates to the nucleus, where it binds to DNA.

4) This stimulates genetic transcription, resulting in new mRNA synthesis.

5) The newly formed mRNA codes for production of new proeins, which

6) produce the hormonal effects in the target cell.

Term
Explain the mechanisms of action of thyroid hormones:
Definition

1) Thyroxine (T4) carried to the target cell bound to its plasma carrier protein, dissociates from its carrier and passes through the plasma membrane of its target cell, because it is lipophilic. 2) In the cytoplasm, T4 is converted into T3 which

3) uses binding proteins to enter the nucleus.

4) The hormone-receptor complex binds to DNA,

5) stimulating the synthesis of new mRNA.

6) The newly formed mRNA codes for synthesis of new proteins, which

7) produce the hormonal effects in the target cell.

Term
Describe the Adenylate Cyclase-Cyclic AMP second messenger system:
Definition

1)The hormone binds to its receptor on the outer surface of the target cell's plasma membrane, because it is water-soluble.

2) G-proteins stimulate the activity of adenylate cyclase on the cytoplasmic side of the plasma membrane (due to the dissociation of the a subunit).

3) This enzyme catalyzes the production of cAMP, which

4) removes the inhibitory subunit from protein kinase.

5) Active protein kinase phosphotylates other enzyme proteins, activating or inactivating specific enzymes and therefore producing the hormonal effects of the target cell.

Term
Describe the phospholipase C-Ca2+ second messenger system:
Definition

1) The hormone binds to its receptor in the plasma membrane of its target cell,

2) causing the dissociation of G-proteins.

3) A G-protein subunit travels through the plasma membrane and activates phospholipase C, which catalyzes the breakdown of a particular membrane phospholipid into diacylglycerol and IP3.

4) IP3 enters the cytoplasm and binds to receptors in the smooth ER, causing the release of stored Ca2+. The Ca2+ then diffuses into the cytoplasm, where it  acts a a second messenger to promote the hormonal effects in the target cell.

Term
Describe how epinephrine uses two second messenger systems (shown by the action of epinephrine on a liver cell):
Definition

1) Binding of epinephrine to beta-adrenergic receptors activates adenylate cyclase and leads to the production of cAMP, which

2) activates protein kinase.

3) Binding of epinephrine to alpha-adrenergic receptors leads to a rise in the cytoplasmic Ca2+ concentration, which

4) activates calmodulin. Calmodulin then activates a protein kinase, which, like the protein kinase activated by cAMP,

5) alters the enzyme activity so that glycogen is converted into glucose 6-phosphate.

6) The phosphate group is removed by another enzyme, so that the liver cell secretes free glucose into the blood in response to epinephrine.

Term
Distinguish betwen the parts of the pituitary gland, and identify the hormones secreted by each part:
Definition

The pituitary gland is divided into two parts- the anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). The anterior lobe consits of two parts, the 1) pars distalis (anterior pituitary) and 2) the pars tuberalis- thin extension in contact with the infundibulum. The anterior pituitary secretes trophic hormones (trophic = "feed") which are 1) Growth hormone (GH) 2) Thyroid-stimulating hormone (TSH) 3) Adrenocorticotropic hormone (ACTH) 4) Follicle-stimulating hormone (FSH) 5) Luteinizing hormone (LH) 6) Prolactin (PRL).

The posterior pituitary (pars nervosa) stores and secretes two hormones, both of which are produced in the hypothalamus: 1) Antidiuretic hormone (ADH) and 2) Oxytocin.

Term
Explain how the hypothalamus regulates the anterior pituitary gland:
Definition

Anterior- Hypothalamic control of the anterior pituitary is acheived through hormonal regulation rather than neural regulation. Releasing and inhibiting hormones are produced by neurons in the hypothalamus, and transported to axon endings in the basal portyion of the hypothalamus (median eminence). Venules that drain the median eminence form a hypothalamo-hypophyseal portal system to the anterior pituitary, and the regulatory hormones secreted by the hypothalamus regulate the secretions of the anterior pituitary. Thyrotropin-releasing hormone (TRH) stimulates secretion of TSH, corticotropin-releasing hormone (CRH) stimulates secretion of ACTH, gonadotropin-releasing hormone (GnRH) stimulates sectretion of FSH and LH, prolactin-inhibiting horrmone (PIH) stimulates secretion of prolactin, and somatostatin stimulates secretion of growth hormone (GH).

Term
Explain how the hypothalamus regulates the posterior pituitary gland:
Definition

Posterior- ADH and oxytocin are produced in neuron cell bodies of the supraoptic nuclei and paraventricular nuclei of the hypothalamus. This means these nuclei are thus endocrine glands, and the hormones they produce are transported along axons of the hypothalamo-hypophyseal tract to the posterior pituitary, where they are stored and later released.

Term
Describe negative feedback inhibition in the regulation of hypothalamic and anterior pituitary hormones:
Definition
The hypothalamus and anterior pituitary are controlled by the effects of their own actions; their secretions are controlled by the target glands they regulate. Under normal conditions, target glands exert an inhibitory effect on the anterior pituitary. This effect can occur at two levels: 1) The target gland hormones can act on the hypothalamus and inhibit the secretion of releasing hormones, and 2) The target gland hormones can act on the anterior pituitary and inhibit its response to the releasing hormones.
Term
Identify the hormones of the adrenal medulla:
Definition
Epinephrine (80%) and norepinephrine (20%). The effects of these catecholamine hormones are similar to those caused by the stimulation of the sympathetic nervouse system, except the hormonal effects last about 10 times longer.
Term
Identify the categories of the corticosteroid hormones, and their specific origin:
Definition
They originate from the adrenal cortex, and they consist of 3 functional categories: mineralcorticoids from the zona glomerulosa, and glucocorticoids and sex steroids from the zona fasciculata, and zona reticularis.
Term
Describe the regulation of adrenal cortex secretion:
Definition

Mineralcorticoids (ex. aldosterone) regulate K+ and Na+ balance by stimulating the kidneys to retain Na+ and water, while excreting K+ in the urine. This increases blood volume and pressure and regulates electrolyte balance. Glucocorticoids- regulate balance of metabolism and glucose; stimulates gluconeogenesis and inhibits glucose utilization which helps raise blood glucose level and promotes lipolysis. Sex steroids- supplement the sex steroids secreted by the gonads; weak androgens.

Term
Describe the regulation of adrenal medulla secretion:
Definition

Secretion of epinephrine and norepinephrine increases cardiac output and heart rate, dilate coronary blood vessels, increase mental alertness, increase respiratory rate and elevates metabolic rate. It is activated durin "fight or flight" and its effects are supported by metabolic actions of epinephrine and norepinephrine. A rise in blood glucose due to hepatic glycogenolysis and rise in blood fatty acids due to stimulation of lipolysis.

Term
Describe the role of stress in adrenal gland function and secretion:
Definition

Sympathoadrenal system becomes activated with increased secretion of epinephrine and norepinephrine in response to stressors that cause the fight or flight rection.

A major function of the adrenal cortex in response to stress is the rise in glucocorticoid levels. Stress causes a response in the higher brain centers  which causes the hypothalamus to secrete increased amounts of CRH (corticotropin-releasing hormone) which cause the anterior pituitary to secrete higher levels of ACTH (adrenocortico-tropic hormone) which stimulates the adrenal cortex to secrete cortisol. High levels of glucocorticoids supress the immune system, cause atrophy of the hippocampus, catabolizes muscle protein and fat, and stimulates gluconeogenesis, raising blood glucose levels. This antagonizes the actions of anabolic hormones, incuding GH and insulin.

Term
Describe the structure of the thyroid gland:
Definition
Located just below the larynx, its two lobes are positioned on either side of the trachea and are connected anteriorly by a medial mass of thyroid tissue called the isthmus. It consists of numerous spherical hollow sacs called thyroid follicles, which contain a protein-rich fluid called colloid. The follicles are lined with follicular cells that synthesize the hormone thyroxine,and there are also parafollicular cells, which secrete the hormone calcitonin.
Term
Describe the production and action of the thyroid hormones:
Definition
The thyroid follicles accumulate iodide from the blood and secrete it into the colloid. Once in the colloid it is oxidized to iodine, and attached to tyrosine (within the polypeptide chain of the protein thyroglobulin). The attachment of 1 iodine to tyrosine forms MIT and 2 iodines forms DIT. When 2 DIT are coupled, T4 (thyroxine) is formed. When 1 MIT and 1 DIT are coupled, T3 is formed. Upon stimulation of TSH T3 and T4 is secreted into the blood as free hormones which stimulate protein synthesis, promote maturation of the nervous system, increase cell respiration rate and elevates the BMR (basal metabolic rate). The parafolliclar cells secrete calcitonin, which regulate calcium levels in the blood by causing decreased blood Ca2+ and mineralization of bone and stimulates secretion of calcium in urine by the kidneys. Works antagonistically with the parathyroid gland.
Term
Describe hypothyroidism (a disorder of thyroid function):
Definition
Hypothyroidism- Caused by inadequate secretion of thyroid hormones (thyroxine); it can result from a thyroid gland defect, insufficient TRH secretion from the hypothalamus, insufficient TSH from the anterior pituitary, or insufficient iodine in the diet. If iodine is inadequate, low T3 and T4 (thyroxine) would cause the anterior pituitary to secrete excess TSH, which would cause the thyroid to swell (hypertrophy). This produces a goiter.
Term
Describe hyperthyroidism (a disorder of thyroid function):
Definition
Hyperthyroididm- Caused by excessive thyroid hormones (thyroxine). In Graves disease, autoantibodies exert TSH-like effects on the thyroid. Since production of these antibodies aren't inhibited by negative feedback, the high secretion of thyroxine that results cannot turn off the excessive stimulation of the thyroid, producing a goiter.
Term
Describe cretinism (a disorder of hyroid function):
Definition
Cretinism- Due to hyperthyroidism during prenatal development and the first 6 months of life; since thyroxine stimulates protein synthesis and nervous sytem development, inadequate thyroxine during the critical time when the body is undergoing development can cause mental retardation.
Term
Identifty the locations of the parathyroid gland:
Definition
They are imbedded in the posterior surfaces of the lateral lobes of the thyroid gland. There are usually four pairs: left and right superior and inferior (this precise number can vary).
Term
Describe the actions of the parathyroid hormone:
Definition
It is the single most important hormone in the control of the Ca2+ levels in the blood. It promotes a rise in blood calcium levels by acting on the bones, kidneys and intestine and acts in response to decresed blood Ca2+ levels.
Term
Identify the insulin-secreting endocrine cells of the pancreas, and describe the actions of this hormone:
Definition
The endocrine cells are the islets of Langerhans. The beta cells secrete insulin. Insulin regulates plasma glucose concentration; after a sugary meal or drink, increased glucose stimulates the beta cells to secrete increased amounts of insulin. This causes insulin to bind to its receptors in the plasma membrane of its target cells, and through signalling molecules, causes intracellular vesicles containing GLUT4 carrier proteins to translocate to the plasma membrane. These proteins cause facilitated diffusion of glucose into the cells of insulin's target organs (primarily skeletal muscles, liver and adipose tissue). Insulin also indirectly stimulates activity of glycogen synthetase to promote conversion of glucose into glycogen for storage. This lowers blood glucose concentration.
Term
Identify the glucagon-secreting endocrine cells of the pancreas, and describe the actions of this hormone:
Definition
The endocrine cells are the islets of Langerhans. The alpha cells secrete glucagon. Glucagon acts antagonistically to insulin- glucagon is stimulated by a fall in plasma glucose concentration and insulin secretion that occurs when a person is fasting. Glucagon stimulates the liver to hydrolyze glycogen into glucose, allowing the liver to secrete glucose into the blood (glycogenolysis). Glucagon, along with the glucocorticoids, also stimulates gluconeogenesis- conversion of noncarbohydrates into glucose which raises plasma glucose concentration during fasting. Glucagon also promotes lipolyisis (hydrolyisis of stored fat) and ketogenesis (formation of ketone bodies from free fatty acids).
Term

Explain the nature and actions of the receptor proteins for insulin and the growth factors:

Definition
Insulin's mechanism of action bears similarities to the mechanisms of actions of other regulatory molecules known as growyth factors. 1) Insulin binds to two units of its receptor proteins. 2) This causes dimerization of the two units on the plasma membrane. 3) This causes phosphorylation of the receptor, and causes the activation of the tyrosine kinase portion of the receptor. 4) As a result, the receptor phosphorylates itself, thereby making the receptor even more active. The receptor then phosphorylates a number of cytoplasmic "signal molecules" that exerts a cascade of effects of the target cell, inluding gluycose reuptake and anabolic reactions.