Chapter 15

Diabetes mellitus and diabetes insipidus are both due to lack of a hormone. Which hormone causes which? What symptom do they have in common? What would you find in the urine of a patient with one but not the other?

Diabetes mellitus is due to a lack of insulin production or action, whereas diabetes insipidus is due to a lack of ADH. Both conditions are characterized by production of copious amounts of urine. You would find glucose in the urine of a patient with diabetes mellitus, but not in the urine of a patient with diabetes insipidus.

Describe the direct gene activation mechanism of lipid-soluble hormones.

1. The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor 2. The receptor hormone complex enters the nucleus 3. The receptor-hormone complex binds a specific DNA region 4. Binding initiates transcription of the gene to mRNA 5. The mRNA directs protein synthesis

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

The two pancreatic hormones are glucagon (released by Alpha cells) and insulin (released by Beta cells). There effects on blood sugar are antagonistic: glucagon is a hyperglycemic hormone (increases blood glucose), whereas insulin is a hypoglycemic hormone (decreases blood glucose).

Since Cyclic AMP is a very common second messenger that has many different effects in many different cells, what determines the effect that cAMP has in a given cell?

This is determined by the specific protein kinases that cell contains, and the substrates within that cell available for phosphorylation.

Describe Calcitonin.

Calcitonin is a hormone released by the parafollucular cells of the thyroid gland in response to a rise in blood Ca2+ levels - is given to treat Paget's disease and sometimes osteoporosis. It inhibits osteoclast activity (inhibiting bone resorption and release of Ca2+ from bony matrix) and stimulates Ca2+ uptake and incorporation into bone matrix

APPLY Synthetic melatonin supplements are available, although their efficacy and long-term safety have not been proved. What do you think they might be used for?

Melatonin is used by some individuals as a sleep aid, particularly to counter jet lag.

Describe the regulation of secretion of Glucocorticoid (primarily Cortisol) secretion.

Negative feedback regulates glucocorticoid secretion - Cortisol release is promoted by ACTH , which is triggered in turn by the hypothalamic releasing hormone CRH. Rising cortisol levels prevent CRH release and shut off ACTH and thus cortisol secretion.

Why are receptors for water-soluble hormones in the plasma membrane? Why are receptors for lipid-soluble steroid and thyroid hormones inside the cell?

Receptors for water-soluble hormones must be in the plasma membrane since these hormones cannot diffuse across the plasma membrane. Receptors for lipid-soluble steroid and thyroid hormones are inside the cell because these hormones can diffuse across the plasma membrane into the cell.

Describe Prolactin (PRL).

Prolactin (PRL) is a protein hormone structurally similar to GH, produced by prolactin cells, and stimulates milk production by the breasts

Describe how a goiter is formed.

A goiter is an enlarged protruding thyroid gland that occurs if myxedema results from lack of iodine. The follicular cells produce colloid but cannot iodinate it and make functional hormones. The pituitary gland secretes increasing amounts of TSH in a futile attempt to stimulate the thyroid to produce TH, but the only result is that the follicles accumulate more and more unusable colloid.

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

All major hormones circulate to virtually all tissues, but a hormone influences the activity of only those tissue cells that have receptors for it - target cells. Hormones act at receptors in one of two ways: 1. Water-soluble hormones (amino acid-based hormones) act on receptors in the plasma membrane - use the GPCR cycle to bring about an effect 2. Lipid-soluble hormones (steroid) act on receptors inside the cell - change a gene

Describe the regulation of secretion of GH.

Secretion of GH is regulated chiefly by two hypothalamic hormones with antagonistic effects: 1. Growth hormone-releasing hormone (GHRH) - stimulates GH release 2. Growth hormone-inhibiting hormone (GHIH) (also called somatostatin) - inhibits GH release.

Describe the difference between the adrenal gland responding to short-term and long-term stress.

Short-term stress causes the hypothalamus to activate the adrenal medulla via neural stimuli. It uses action potentials triggered by the hypothalamus in response to stressors,which activates the sympathetic nervous system to stimulate the adrenal medulla to release epineprine (80%) and norepinephrine (20%) into the blood stream (fight-or-flight response) Long-term stress causes the hypothalamus to activate the adrenal cortex via hormonal stimuli. This makes sense because long-term stress requires long-term effects of the endocrine system (hormones), while a fast fight-or-flight response requires a fast neural stimulation to a short-term stressor.

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

In order for a target cell to respond to a hormone, the cell must have specific receptor proteins on its plasma membrane or in its interior to which that hormone can bind - receptors for adrenocorticotropic hormone (ACTH) are normally found only on certain cells of the adrenal cortex. The degree of target cell activation depends equally on three other factors: 1. Blood levels of hormone 2. Relative numbers of receptors for that hormone on or in the target cells 3. Affinity (strength) of the binding between the hormone and the receptor

Describe the three ways insulin lowers blood glucose levels.

It enhances membrane transport of glucose into most body cells, especially muscle and fat cells (stores it) It inhibits the breakdown of glycogen into glucose It inhibits the conversion of amino acids or fats to glucose (this counters any metabolic activity that would increase plasma levels of glucose)

List the four anterior pituitary hormones that are tropic hormones and name their target glands.

LH and FSH are tropic hormones that act on the gonads, TSH is a tropic hormone that acts on the thyroid, and ACTH is a tropic hormone that acts on the adrenal cortex. (If you said growth hormone, that's also a good answer, as GH causing the liver to release IGFs might also be considered a tropic effect.)

Which type of hormone generally stays in the blood longer following its secretion, lipid soluble or water soluble?

Lipid-soluble hormones have longer half-lives, meaning that they stay in the blood longer. (They are not as readily excreted by the kidneys because they are bound to plasma proteins, and most need to be metabolized by the liver before they can be excreted.)

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

NS regulates activity of muslces and glands via electrochemical impulses delivered by neurons and those organs respond within miliseconds. Endocrine system influences metabolic activity by means of hormones - takes a lot longer (and lasts a lot longer) and has a more general control than NS

Describe the layers of the cortical cells.

Superficial to deep: Zona glomerulosa - produce mineralocorticoids (such as aldosterone), hormones that help control balance of miners and water in blood Zona fasciculata - produce metabolic hormones called glucocorticoids (such as cortisol) Zona reticularis - produce small amounts of adrenal sex hormones, or gonadocorticoids

What is the difference between T3 and T4? Which one of these is referred to as thyroxine?

T4 has four bound iodine atoms, and T3 has three. T4 is the major hormone secreted, but T3 is more potent. T4 is referred to as thyroxine.

Describe Thyroid-stimulating hormone (TSH).

TSH is a tropic hormone that stimulates normal development and secretory activity of the thyroid gland

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. Endocrine Gland Stimuli: 1. Humoral stimuli - endocrine glands secrete hormones in direct response to changing blood levels of certain critical ions and nutrients - parathyroid hormone and blood Ca2+ levels 2. Neural stimuli - nerve fibers stimulate hormone release - response to stress, in which the sympathetic NS stimulates adrenal medulla to release norepinephrine and epinephrine 3. Hormonal stimuli - endocrine glands release their hormones in response to hormones produced by other endocrine organs - releasing and inhibiting hormones produced by the hypothalamus regulate the secretion of most anterior pituitary hormones, and many anterior pituitary hormones in turn stimulate other endocrine organs to release their hormones

Why does TH require plasma proteins in order to move through blood? Where are the receptors for TSH located?

Thyroid hormone must be carried through blood by plasma proteins because it is lipid soluble and so does not readily dissolve in blood, which is mostly water. The receptors for TSH (thyroid-stimulating hormone) are located on the plasma membrane of the thyroid follicular cells (on the sides facing away from the colloid). (Recall that TSH is a water-soluble hormone from the anterior pituitary.)

Describe the Cyclic AMP second-messenger mechanism of water-soluble hormones.

1. Hormone binds receptors 2. Receptor activates G protein 3. G protein activates adneylate cyclase 4. Adenylate cyclase converts ATP to cAMP 5. cAMP activates protein kinases - these trigger responses of target cells

Describe the four mechanisms that regulate aldosterone secretion.

1. The renin-angiotensin-aldosterone mechanism - influences both blood volume and blood pressure by regulating the release of aldosterone and therefore Na+ and water reabsorption by the kidneys 2. Plasma concentration of potassium - fluctuating blood levels of K+ directly influence the zona glomerulosa cells in the adrenal cortex (increased K+ stimulates aldosterone release and decreased K+ inhibits it) 3. ACTH - released by anterior pituitary has little or no effect on aldosterone release except when a person is severly stressed 4. Atrial natriuretic peptide (ANP) - a hormone secreted by the heart when blood pressure rises, fine-tunes blood pressure and sodium-water balance of the body

Describe Aldosterone.

Aldosterone reduces excretion of Na+ from the body - its primary target is the kidney tubules where it stimulates Na+ reabsorption (increasing blood volume and blood pressure) and causes K+ secretion into the tubules for elimination from the body

How does the rate of release differ between Amino Acid-based hormones and steroid hormones.

AA based hormones are synthesized and then stored within the cells, waiting to be secreted. Steroid hormones are not stored in cells and are secreted as soon as they are synthesized.

Desribe Adrenocorticotropic Hormone (ACTH).

ACTH is secreted by the corticotropic cells of the anterior pituitary - stimulates adrenal cortex to release corticosteroid hormones (most importantly glucocorticoids), that help the body resist stressors

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

Adipose tissue - releases leptin - serves to tell your body how much stored energy/fat you have and helps to control appetite - the more fat you have the more leptin will be in your blood Heart - atria (chambers of heart) contain specialized cardiac muscles cells that secrete atrial natriuretic peptide (ANP) - decreases amount of Na+ in the ECF, thereby reducing blood volume and blood pressure Kidneys - interstitial cells secrete erythropoietin - signals bone marrow to increase production of RBCs - kidneys also release renin - acts as an enzyme to initiate the renin-angiotensin-aldosterone mechanism of aldosterone release Skeleton - osteoblasts in bone secrete osteocalcin - a hormone that prods pancreatic beta cells to divide and secrete more insulin, it also restricts fat storage by adipocytes, and trigers the release of adiponectin - improves glucose handling and reduces body fat Skin - produces cholecalciferol (inactive form of vitamin D3) - calcitriol (activated form) regulates the carrier system that intestinal cells use to absorb Ca2+ from food - without this vitamin, bones would become soft and weak Thymus - thymic epithelial cells secrete several different families of peptide hormones, including thymosins, thymulin, and thymopoietins - involved in normal development of T lymphocytes (immune response)

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

Adrenal Cortex Hormones (Corticosteroids): Mineralcorticoids - made in Zona glomerulosa - regulate electrolyte concentrations in ECF (particularly Na+ and K+), most important mineralocorticoid is aldosterone (regulates Na+ and K+ and accounts for 95% of the mineralocorticoids produced). Glucocorticoids - made in zona fasciculata - influence the energy metabolism of most body cells and help us resist stressors, help body keep blood glucose levels constant, help maintain blood pressure Gonadocorticoids - made in Zona reticularis - contribute to axillary and pubic hair development, estrogen production - ACTH stimulates release but gonadocorticoids do not exert feedback inhibition Adrenal medulla: Cells synthesize the catecholamines - epinephrine and norepinephrine via a molecular sequence from tyrosine to dopamine to NE to epinephrine

List and describe the chief effects of anterior pituitary hormones.

Anterior pituitary releases six hormones, all of them peptides or proteins - growth hormone (GH), thryroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone, and prolactin. Tropic hormones regulate the secretory action of other endocrine glands (TSH, ACTH, FSH, and luteinizing hormone are all tropic). All anterior pituitary hormones except growth hormone affect their target cells via a cyclic AMP second-messenger system.

Which class of hormones consists entirely of lipid-soluble hormones? Name the only hormone in the other chemical class that is lipid soluble.

Steroids are all lipid soluble. Thyroid hormones are the only amino acid-based hormones that are lipid soluble.

Why is regulation of Na+ and K+ so crucial to the body?

Changes in Na+ concentration lead to changes in blood volume and blood pressure - where Na+ goes, water follows. K+ sets resting membrane potential of all cells and determines how easily action potentials are generated in nerve and muscle. Their regulation is the primary job of aldosterone, a potent mineralocorticoid.

Zoe drank too much alcohol one night and suffered from a headache and nausea the next morning. What caused these "hangover" effects?

Drinking alcoholic beverages inhibits ADH secretion from the posterior pituitary and causes copious urine output and dehydration. The dehydration causes the hangover effects.

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

Endocrine glands include the pituitary, thyroid, parathyroid, adrenal, and pineal glands. The hypothalamus is considered a neuroendocrine organ because it has neural functions and it produces and releases hormones.

State the location of enteroendocrine cells.

Enteroendocrine cells are hormone-secreting cells sprinkled in the mucosa of the gastrointestinal tract (GI) These hormones help regulate a wide variety of digestive function.

Describe the negative feedback loop for TH release.

Falling TH blood levels trigger release of TSH, and ultimately of more TH. Rising TH levels feed back to inhibit the hypothalamic-anterior pituitary axis, temporarily shutting off the stimulus for TSH release

Describe Gonadotropins (FSH and LH).

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are referred to collectively as gonadotropins - they regulate the function of the gonads.

What are the two forms a hormone can circulate in the blood as?

Free or bound to a protein carrier. Lipid-soluble (steroids and thyroid hormone) are not water soluble so they must travel in blood attached to proteins of the blood plasma.

List the three classes of hormones released from the adrenal cortex and briefly state the major effect(s) of each.

Glucocorticoids are stress hormones that, among many effects, increase blood glucose. Mineralocorticoids increase blood Na+ (and blood pressure) and decrease blood K+. Gonadocorticoids are male and female sex hormones that are thought to have a variety of effects (for example, contribute to onset of puberty, sex drive in women, pubic and axillary hair development in women).

What are the three types of stimuli that control hormone release?

Hormone release can be triggered by humoral, neural, or hormonal stimuli.

Distinguish between hormones, paracrines, and autocrines.

Hormones - long-distance chemical signals that travel in blood or lymph throughout the body (in blood/ other cell) Paracrines - short-distance chemical signals (act locally) (in ECF / other cells) Autocrines - short-distance chemical signals that exert their effects on the same cells that secrete them (in ECF / themselves)

What is the difference between a hormone and a paracrine?

Hormones are released into the blood and transported throughout the body, whereas paracrines act locally, generally within the same tissue.

Describe how hormones are classified chemically

Hormones chemical structure determines one of its critical properties: solubility in water - nearly all hormones can be classified chemically either as based on amino acids or as steroids. Amino acid based - water soluble and cannot cross the plasma membrane Steroids - lipid soluble and can cross the plasma membrane

What kind of stimuli causes the pancrease to respond to a rise or fall in blood sugar?

Humoral stimuli - blood sugar falls and alpha cells secrete glucagon to raise it / blood sugar rises and beta cells secrete insulin to lower it

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

Hypothalamus has neural connection with posterior lobe of pituitary gland via a bundle of axons called the hypothalamic-hypophyseal tract. There is a vascular connection between hypothalamus and anterior lobe of pituitary gland - primary capillary plexus communicates inferiorly via the small hypophyseal portal veins with a secondary capillary plexus (this makes up the hypophyseal portal system).

Indicate the general functions of parathyroid hormone.

Parathyroid hormone (PTH) is the single most important hormone controlling calcium balance in the blood - falling blood Ca2+ levels trigger PTH release, and rising blood Ca2+ levels inhibit release. PTH increases Ca2+ levels in blood by stimulating three target organs: the skeleton, the kidneys, and the intestine. PTH release: 1. Stimulates osetoclasts to digest bony matrix and release ionic Ca and P into blood 2. Enhances the kidneys reabsorption of Ca2+ from the forming urine into the blood 3. Promotes activation of vitamin D, thereby increasing absorption of Ca2+ by intestinal mucosal cells

MAKE CONNECTIONS Where in the cell are steroid hormones synthesized? (Hint: Recall cell components from Chapter 3.) Where are peptide hormones synthesized? Which of these two types of hormone could be stored in vesicles and released by exocytosis?

Steroid hormones are synthesized on the membrane of the smooth endoplasmic reticulum. Peptide hormones are synthesized on rough endoplasmic reticulum. Peptide hormones can be stored in vesicles and released by exocytosis.

Describe Growth Hormone (GH).

Somatotropic cells of anterior lobe produce GH - an anabolic hormone that has both metabolic and growth-promoting actions. Metabolic effects - GH mobilizes fats from fat depots for transport to cells, icnreasing blood levels of fatty acids and encouraging their use for fuel GH mediates most of its growth-enhancing effects indirectly via a family of growth-promoting proteins called insulin-like growth factors (IGFs).

What kind of hormone (steroid or AA) is released by the adrenal cortex, adrenal medulla, anterior pituitary, and posterior pituitary.

The adrenal cortex (a) releases steroid hormones. The adrenal medulla (b) and anterior pituitary (c) and posterior pituitary (d) all release amino acid-based hormones. ACTH from the anterior pituitary acts to cause release of steroid hormones from the adrenal cortex. Both the adrenal medulla (b) and posterior pituitary (d) are composed of nervous tissue rather than the glandular tissue (a type of epithelial tissue) that other glands are made of.

Describe the factors that influence insulin release.

The blood glucose levels represent a balance of humoral, neural, and hormonal influences - insulin is the major hypoglycemic factor that counterbalances the many hyperglycemic hormones. Elevated blood glucose levels (primary factor) Rising blood levels of amino acids and fatty acids Acetylcholine released by parasympathetic nerve fibers Hyperglycemic hormones - indirect effect

For each of the following statements, indicate whether it applies more to the endocrine system or the nervous system: rapid; discrete responses; controls growth and development; long-lasting responses.

The endocrine system is more closely associated with growth and development, and its responses tend to be long-lasting, whereas nervous system responses tend to be rapid and discrete.

Which of the two chemical classes of hormones introduced at the beginning of this chapter do the gonadal hormones belong to? Which major endocrine gland secretes hormones of this same chemical class?

The gonadal hormones are steroid hormones. A major endocrine gland that also secretes steroid hormones is the adrenal cortex.

Which hormone does the heart produce and what is its function?

The heart produces atrial natriuretic peptide (ANP). ANP decreases blood volume and blood pressure by increasing the kidneys' production of salty urine.

Which feedback loop lies at the very core of endocrinology?

The hypothalamic-pituitary-target endocrine organ feedback loop.

What is the key difference between the way the hypothalamus communicates with the anterior pituitary and the way it communicates with the posterior pituitary?

The hypothalamus communicates with the anterior pituitary via hormones released into a special portal system of blood vessels. In contrast, it communicates with the posterior pituitary via action potentials traveling down axons that connect the hypothalamus to the posterior pituitary.

Describe the adrenal glands.

The paired adrenal (suprarenal) glands, each lying just superior to each kidney, are structurally and functionally divided into two separate glands: the adrenal cortex and the adrenal medulla. Each region produces its own set of hormones.

What is the main function of the hormone produced by the skin?

The major function of vitamin D3, produced in inactive form by the skin, is to increase intestinal absorption of calcium.

What is the major target of glucagon and what are the promoted actions at this target?

The major target of glucagon is the liver, where it promotes the following actions: Breakdown of glycogen to glucose Synthesis of glucose from lactic acid and noncarbohydrate molecules Release of glucose to the blood by liver cells, causing blood glucose levels to rise

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

The male and female gonads produce steroid sex hormones identical to those produced by adrenal cortical cells - the difference is the source and relative amounts produced. Ovaries produce estrogens and progesterone - responsible for maturation of the reproductive organs and the appearance of the secondary sex characteristics of females at puberty. Testes produce sperm and male sex hormones, primarily testosterone, which is activated during puberty and initiates the maturation of the male reproductive organs and the appearance of secondary sex characteristics and sex drive. The placenta is a temporary endocrine organ - it sustains the fetus during pregnancy and it secretes several steroid and protein hormones that influence the course of pregnancy.

Describe nervous system modulation.

The nervous system can both modify both "turn-on" factors and "turn-off" factors that affect the endocrine system - the action of insulin and several other hormones normally keeps blood glucose levels in the range of 90-110mg/100ml of blood, however, when body is under stress, blood glucose levels rise because hypothalamus and sympathetic NS centers are strongly activated to ensure that body cells have sufficient fuel in case vigorous activity is required.

Briefly describe the importance of melatonin.

The pineal gland secretes melatonin, an AA hormone derived from serotonin. Melatonin levels rise during night and lowest levels occur around noon. Suprachiasmatic nucleus (biological clock) of hypothalamus richly supplied with melatonin receptors and when exposed to bright light, can suppress melatonin secretion by resetting clock timing.

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 - strong stimulant of uterine contraction released in significantly higher amounts during childbirth and in nursing women - stretching of cervix of uterus as birth nears dispatches afferent impulses to the hypothalamus, which responds by synthesizing oxytocin and triggering its release from the posterior pituitary - acts via the PIP2-Ca2+ second-messenger system to mobilize Ca2+. Oxytocin also acts at the hormonal trigger for milk ejection (via positive feedback mechanisms) and as a neurotransmitter in the brain where it is involved in sexual and affectionate behavior. Antidiuretic Hormone (ADH) - prevents wide swings in water balance, helping the body avoid dehydration and water overload - hypothalamic neurons called osmoreceptors continually monitor the solute concentration of blood, when solutes threaten to become too concentrated, osmoreceptors transmit excitatory impulses to the hyplothalamic neurons, which release ADH. ADH targets kidney tubules which respond by reabsorbing more water from the forming urine and returning it to bloodstream (concentration of blood declines)

Which two endocrine glands are found in the neck?

The thyroid and parathyroid glands are found in the neck.

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

The two major hormones produced by the thyroid are the two iodine-containing amine hormones, thyroxine (T4) and triiodothyronine (T3), which ultimately make up thyroid hormone (TH). TH enters a target cell (like a steroid) and binds to intracellular receptors within the cell's nucleus and initiates transcription of mRNA for protein synthesis. Effects of thyroid hormone/TH: 1. Increasing basal metabolic rate and body heat production 2. Regulating tissue growth and development 3. Maintaining blood pressure by increasing the number of adrenergic receptors in blood vessels

What are the two major stimuli for aldosterone release? What is the major stimulus for cortisol release?

The two major stimuli for aldosterone release are (1) a decrease in blood volume or blood pressure, which triggers the renin-angiotensin-aldosterone mechanism, and (2) an increase in plasma K+ levels. The major stimulus for cortisol secretion is ACTH from the anterior pituitary. ACTH release, in turn, is controlled by CRH from the hypothalamus. CRH release follows a diurnal (day-night) rhythm and is increased in response to various stressors, as well as by hypoglycemia and fever.

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

Three types of hormone interaction: 1. Permissiveness - one hormone cannot exert its full effects without another hormone being present - reproductive system hormones largely regulate the development of the reproductive system, however, thyroid hormone is also necessary for normal timely development of reproductive structures 2. Synergism - more than one hormone produces the same effects at the target cell and their combined effects are amplified - both glucagon and epinephrine cause the liver to release glucose to the blood, when they act together, the amount of glucose released is about 150% of what would be released if each hormone acts independently 3. Antagonism - one hormone opposes the action of another - insulin (lowers blood glucose levels) is antagonized by glucagon (raises blood glucose levels)

Name the cells that release each of the thyroid hormone, parathyroid hormone, and Calcitonin.

Thyroid follicular cells release thyroid hormone, parathyroid cells in the parathyroid gland release parathyroid hormone, and parafollicular (C) cells in the thyroid gland release calcitonin.

What is the major effect of thyroid hormone? Parathyroid hormone? Calcitonin?

Thyroid hormone increases basal metabolic rate (and heat production) in the body. Parathyroid hormone increases blood Ca2+ levels in a variety of ways. Calcitonin at high (pharmacological) levels has a Ca2+-lowering, bone-sparing effect. (At normal blood levels its effects in humans are negligible.)

What is the difference between type 1 and type 2 diabetes? Which has more insulin present in the bloodstream?

Type 1 - insulin is absent Type 2 - insulin is present but its effects are deficient People with type 2 diabetes tend to have elevated levels of circulating insulin

Describe up-regulation and down-regulation.

Up-regulation is the absence of a hormone increases the number of receptors. The cells become more sensitive to low levels of a hormone and they are looking for a hormone in this process. Down-regulation is the presence of a hormone decreases the number of hormone receptors and the cells become less sensitive. During this process they become used to the hormones. Up-regulation - persistently low levels of hormone cause target cells to form additional receptors for that hormone Down-regulation - persistently high levels of hormone concentrations can decrease the number of receptors for that hormone

Follow the process of thyroxine formation and release.

When thyroid-stimulating hormone/TSH from the anterior pituitary binds to receptors on follicular cells, their first response is to secrete store thyroid hormone and their second response is to begin synthesizing more colloid to "restock" the follicle lumen. Follicular cells synthesize thyroid hormone: 1. Thyroglobulin is synthesized and discharged into the follicle lumen 2. Iodide is trapped - actively transported in 3. Iodide is oxidized to iodine 4. Iodine is attached to tyrosine - in colloid, forming DIT and MIT 5. Iodinated tyrosines are linked together to form T3 and T4 6. Thyroglobulin colloid is endocytosed - combined with a lysosome 7. Lysosomal enzymes split T4 and T3 from thyroglobulin and the hormones diffuse from the follicular cell into the bloodstream