Endocrine System Answers

Endocrine System Endocrine System: The endocrine system is made up of the cells, tissues, and organs that secrete hormones into body fluids such as the blood stream. What is its function? To control certain physiological activities and help maintain homeostasis What is the difference between an endocrine gland and an exocrine gland? Endocrine glands secrete hormones into the body fluids, while exocrine glands secrete substances into ducts leading to a body surface Each hormone acts only on specific cells in the body; these are called __target_ cells. Hormone Action: __Steroid___ hormones are lipid-soluble and can pass through cell membranes. Their receptors are located in the target cell's __nucleus__. The hormone-receptor complex binds with the _DNA__ and activates specific _genes__. Transcription of a specific gene results in the synthesis of a molecule of _mRNA_, which in turn, directs the synthesis of a specific _protein_. _Non-steroid_ hormones combine with receptors on target cell __membranes__; the receptors have a __binding__ site and a/an _activity__ site. The hormone-receptor complex (as first messenger) triggers a cascade of biological activity. The complex activates a protein in the cell membrane, called a _G-protein_. What is the name of a common second messenger? The most common second messenger is cAMP Prostaglandins are locally-produced lipids that affect the organ in which they are produced, with a variety of effects. What are some of these effects? Relax or contract smooth muscle, stimulate secretion, influence blood pressure, affect reproductive physiology Control of Hormone Secretion: There are several ways in which hormone release is very closely regulated. All of these mechanisms use _negative_ _feedback_. The hypothalamus regulates the _anterior_ _pituitary_ gland’s release of hormones. The __nervous__ system influences certain endocrine glands directly with impulses. Other glands respond directly to changes in the composition of the _internal_ environment. Explain in general how negative feedback works. When the concentration of a regulated substance reaches a certain level, the gland is inhibited from secreting more hormone. Pituitary Gland: The pituitary gland is attached to the base of the brain and has a front lobe called the __anterior pituitary__ and a rear lobe called the ___posterior pituitary___. The brain controls the activity of the pituitary gland in two ways: Releasing hormones from the _hypothalamus____ control the secretions of the anterior pituitary and are carried in the bloodstream by __hypophyseal portal____ veins. The posterior pituitary releases hormones into the bloodstream in response to nerve impulses from the __hypothalamus__. Anterior Pituitary: The anterior pituitary consists mostly of __epithelial __ tissue arranged around blood vessels and enclosed in a capsule of collagenous __connective_ tissue. How many hormones does it secrete? Six What function do most of them have in common? Several stimulate other endocrine glands Growth Hormone (GH): What is the function of GH? It stimulates body cells to grow and reproduce What factors influence growth besides GH? Nutritional status, genetics Which hormones from the hypothalamus control the levels of GH? GH-Releasing Hormone and GH_Release-Inhibiting Hormone What disorders may result from a lack of or too much GH? Too little: pituitary dwarfism. Too much: gigantism, acromegaly Prolactin (PRL): What is the function of PRL? Promotes milk production in lactating women What is its target tissue? The breasts Which hormones of the hypothalamus control the secretion of PRL? Prolactin release-inhibiting hormone, and prolactin releasing factor Thyroid Stimulating Hormone (TSH): What is the function of TSH? To stimulate the thyroid gland to secrete thyroid hormones What is its target organ? The thyroid gland What hypothalamic hormones affect its release? Thyrotropin-Releasing Hormone (TRH) How are these hormones from the hypothalamus regulated? As the level of circulating thyroid hormones fall, the hypothalamus secretes TRH. When the levels of circulating thyroid hormones are at a rising level, the hypothalamus stops secreting TRH. Adrenocorticotropic Hormone (ACTH): What is the target organ for ACTH? Adrenal Cortex What hormone does it affect the release of? Cortisol What is the name of the hormone from the hypothalamus that controls the release of ACTH? Corticotropinreleasing Hormone (CRH) Follicle Stimulating Hormone (FSH): What are the target organs for FSH? Gonads (testes or ovaries) What effect does it have on males? Stimulates sperm production in the testes On females? Stimulates development of ovarian follicles, secretion of estrogens Which hormone from the hypothalamus affects its release? Gonadotropin-Releasing Hormone Luteinizing hormone (LH): What does it do? Causes ovulation and formation of corpus luteum in the ovary How is it different in males than in females? In males it stimulates the testes to release testosterone What is its controlling hormone from the hypothalamus called? Gonadotropin-releasing hormone Posterior pituitary: The posterior lobe consists of __nerve__ fibers and supporting _neuroglial cells arising in the hypothalamus. What structure actually produces the hormones released by the posterior pituitary? The hypothalamus Antidiuretic Hormone (ADH): What is the function of this hormone? It causes the kidneys to conserve water What disorder may result if ADH is not secreted in sufficient quantities? Diabetes insipidus Oxytocin: What are the functions of this hormone ? It causes contraction of the uterine walls during childbirth, and milk letdown during breast feeding Thyroid Gland: The thyroid gland is located below the _larynx___ and consists of two broad __lobes__ connected by an ___isthmus__. The thyroid consists of secretory parts called _follicles___, filled with hormone-storing __colloid__. Thyroxine (T4): How many iodine atoms does it contain? Four Triiodothyronine (T3): How many iodine atoms does it contain? Three cells What is the function of these two hormones? They increase metabolic rate in many Which of these hormones is more potent? T3 How does TSH affect their release? TSH stimulates the thyroid to release T3 and T4 How do they affect the release of TSH? When these hormones reach a high level, the release of TSH is inhibited What is a goiter and what may cause one? A goiter is an enlarged thyroid gland that is usually caused by lack of iodine. Without iodine, the thyroid cannot make T3 and T4, and thus nothing inhibits the release of TSH. The excess TSH continues to over- stimulate the thyroid, causing it to grow abnormally and produce a goiter. ions Calcitonin: What is the function of this hormone? It lowers blood levels of calcium and phosphate What part of the thyroid secretes it? It is secreted by the extrafollicular cells of the thyroid Parathyroid Glands: How many are there and where are they found? Four: located on the back of the thyroid gland Parathyroid hormone PTH: What is the function of this hormone? To increase blood calcium levels How does it achieve this function? Stimulates osteoclasts in bone which break down bone tissue and release calcium into the blood; it also influences the kidneys to conserve calcium How is it related to calcitonin from the thyroid? PTH and Calcitonin have opposite effects and work together to maintain the correct levels of calcium ions in the blood Adrenal Gland: The adrenal glands sit atop the _kidneys_, enclosed in a layer of __fat__. Adrenal medulla: The adrenal medulla is made up of modified __post-ganglionic neurons__ that are connected to the _sympathetic__ nervous system. The hormones secreted are the same as neurotransmitters of this system, but are called hormones because they are secreted into the blood _. Epinephrine & Norepinephrine: What effects do these have on the body? Similar effects to those of the sympathetic division of the autonomic nervous system: increase in heart rate & breathing rate, decrease in digestive activities What are they secreted in response to? Stress and “fight or flight” situations Adrenal cortex: The adrenal cortex makes up most of the adrenal glands and consists of __epithelial__ cells in three layers— an outer, middle, and an inner zone. Several groups of steroid hormones are secreted by the cortex. Mineralocorticoids: The hormone aldosterone controls the levels of _sodium__ ions by conserving them in the __kidneys__. It also causes the excretion of _potassium_ ions. Why is this important? Important in homeostasis of the body, maintaining electrolyte and water balance, and maintaining normal blood volume and pressure Which zone secretes mineralocorticoids? Outer zone Glucocorticoids: These hormones influence the metabolism of glucose, protein, and fat in response to conditions that __stress__ the body and require a greater supply of __glucose___ in the bloodstream. How does negative feedback control the release of these hormones? CRH from the hypothalamus causes the pituitary to release ACTH. ACTH in turn stimulates release of glucocorticoids. When a high level of glucocorticoids is present, they inhibit further release of CRH, and slow down or stop their own synthetic pathway. What else can trigger their release? Stress , injury, or disease Name an important Glucocorticoid. Cortisol Which zone secretes these hormones? Middle zone Adrenal sex hormones: Sex hormones, produced in the __inner_ zone, are mostly of the _male_ type, called _androgens_, but can be converted to __female___ hormones, called _estrogens_, in the skin, liver, and adipose tissues. These hormones supplement those released by the gonads, and may stimulate early development of reproductive organs. Pancreas: The pancreas secretes hormones as an _endocrine__ gland, and digestive juices into the digestive tract as an __exocrine__ gland. Where is the pancreas located? Behind and beneath the stomach Its endocrine portions are the pancreatic _islets_ that include two cell types--_alpha__ cells that secrete glucagon, and __beta___ cells that secrete insulin. Glucagon __increases__ the blood levels of glucose by stimulating the breakdown of _glycogen_ and the conversion of noncarbohydrates into ___glucose___. What controls the levels of glucagon in the blood? A negative feedback system; low blood glucose level stimulates glucagon secretion Insulin __decreases___ the blood levels of glucose by stimulating the liver to form __glycogen___, increasing __protein__ synthesis, and stimulating adipose cells to store _fat_. What controls the blood level of insulin? High blood glucose level Pineal gland: The pineal gland, near the upper portion of the thalamus, secretes _melatonin__, which is involved in the regulation of __circadian__ rhythms of the body. Thymus gland: The thymus gland, lying between the lungs under the __sternum____, secretes _thymosins_, which affect production and differentiation of T lymphocytes that are important in _immunity__. Reproductive Glands: The ovaries produce what two hormones? Estrogen and progesterone What hormones does the placenta produce? Estrogen, progesterone, and gonadotropin The testes produce __testosterone____. Digestive Glands and Other Hormone Producing Organs: The digestive glands secrete hormones associated with the processes of digestion. The __heart___ secretes atrial natriuretic peptide, which affects sodium excretion, and the kidneys secrete __erythropoietin___ for red blood cell production. Stress: Factors that serve as stressors to the body produce stress and threaten ___homeostasis_______________. Stress may be physical, psychological, or some combination of the two. What effects does physical stress have on the body? Threatens the survival of tissues and life What does psychological stress result from? Real or perceived dangers, anger, fear, anxiety, personal loss Responses to stress are designed to maintain homeostasis. The _hypothalamus__ controls the general stress syndrome, which involves increased sympathetic activity and increased secretion of which hormones? Epinephrine, cortisol, glucagon, growth hormone, and antidiuretic hormone.