PHGY 216 Module 1 Exam | Complete Solutions (Verified)

PHGY 216 Module 1 Exam | Complete Solutions (Verified) What are the six main functions of the endocrine system? - Maintain constant internal environment via the regulation of metabolism and H2O/electrolyte balance - Adaptive stress response - Growth and development - Reproduction - Red blood cell production - Integration with the autonomic nervous system and regulation of both the circulation and digestive functions What are the two major categories of the classification of hormones? - Hydrophilic - Lipophilic What are hydrophilic hormones? - Hormones that are highly water-soluble and have low lipid solubility Where are hydrophilic hormones found? - Unbound to carrier molecules within the plasma What are peptide hormones? - Hydrophilic hormones are composed of peptides (short amino acid chains) or proteins (longer amino acid chains) What are amines? - A major group of hydrophilic hormones - Hormones based on single amino acid residues - E.g. Catecholamines (norepinephrine and epinephrine), thyroid hormones What makes thyroid hormones different from other amines? - They are not hydrophilic What makes catecholamines different from other amines? - They are found both free and bound to carrier molecules What are lipophilic hormones? - Hormones that are highly soluble in lipids and are poorly soluble in water - Generally require carrier molecules for transport throughout the body - Lipophilic hormones include the amine thyroid hormones and the steroid hormones What are the steps of peptide hormone synthesis? - Synthesis - Packaging - Storage - Secretion Describe the synthesis step of peptide hormone synthesis. - Large precursor proteins called preprophormones are synthesized by endoplasmic reticulum ribosomes Describe the packaging step of peptide hormone synthesis. - Preprohormones travel through the ER and Golgi complex, are processed into active hormones, and packaged into secretory vesicles Describe the storage step of peptide hormone synthesis. - Hormone-containing secretory vesicles can be stored until the cell receives the appropriate signal Describe the secretion step of peptide hormone synthesis. - The appropriate signal initiates exocytosis of the vesicles and the hormones are released into the blood From which molecule are steroid hormones synthesized? - Cholesterol How is the type of steroid hormone produced controlled? - The hormone produced by a tissue is dependent on the specific enzymes within the cells of that tissue - E.g. The enzyme associated with cortisol synthesis is found only in the adrenal cortex Why can't steroid hormones be stored? - Due to their lipophilicity - Must be released as they are synthesized In what state must lipophilic hormones be in to enter their target cell? - The hormone must be unbound from its carrier protein How many hormones are bound to their carriers? - At any given time not 100% of a steroid hormone in the blood is bound to its carrier molecule - Hormones are constantly binding and unbinding dynamically in an equilibrium In which state are hormones active? - When they are unbound Where are the peptide hormones and catecholamine receptors found? - On the outer surface of the plasma membrane of their target cells Where are the steroid, and thyroid hormone receptors found? - Inside their target cells What are the effects of peptide hormones and catecholamines binding to their receptors? - Produces effects within the cells by activating second messenger systems (cAMP and Ca2+) - The pathways amplify the initial signal Describe the cAMP second messenger system. - Extracellular messengers bind to a receptor and activated g proteins which shuttles to and activate several adenylyl cyclase molecules - Activated proteins convert ATP into cAMP which then activates protein kinase A - The activated protein kinase A enzymes then phosphorylate and activate target proteins Describe the Calcium second messenger system. - An extracellular messenger binds to a receptor activating a g protein - The g protein shuttles to activate several phospholipase C enzymes - These proteins convert PIP2 to IP3 and dAG - IP3 mobilizes intracellular ca2+ which activates calmodulin - The Ca2+-calmodulin complexes then activate Ca2+-calmodulin-dependent protein kinase (CaM kinase) which phosphorylates and activates target proteins How do steroid and thyroid hormones produce their effects? - They can pass through the plasma membrane and the nuclear membranes of the cell - Binding to their receptors inside target cells produces effects by regulating gene transcription and protein synthesis Describe the steps of lipophilic hormone-induced protein synthesis. - Free lipophilic hormones diffuse across the plasma membrane and/or the nuclear membrane to interact with intracellular receptors - The hormone-receptor complex (H-R) binds to the hormone response element within the DNA - DNA binding activates specific genes and produces mRNA - mRNA leaves the nucleus - The mRNA binds to a ribosome and proteins are synthesized - The newly synthesized proteins ultimately lead to the cellular responses of the hormone What are the key differences between hormones and neurotransmitters? - Neurotransmitters belong to the nervous system and hormones are a central component of the endocrine system - Neurotransmitters are transmitted across a synaptic cleft hormones are transported by the blood - The endocrine glands produce hormones while neurotransmitters are produced by neurons - Neurotransmitters must travel a short distance to their target while hormones may travel a great distance Compare and contrast the response time for nervous control and endocrine control. - Nervous: Rapid responses (milliseconds) - Endocrine: Slow response (minutes to hours) Compare and contrast the duration of effects for nervous control and endocrine control. - Nervous: Brief in duration (ends when the stimulus stops) - Endocrine: Long in duration (effects persist after stimulus stops) Compare and contrast the number of targets for nervous control and endocrine control. - Nervous: Hard-wired to one specific target (muscle or gland) - Endocrine: Many different targets in the body (blood circulates) What are the two lobes of the pituitary gland? - Posterior - Anterior Describe the posterior pituitary gland. - Comprised of neural-like tissues and is sometimes called the neuropophysis Describe the anterior pituitary gland. - Comprised of glandular epithelial tissues and is also called adenohypophysis How does the hypothalamus stimulate hormone release in the posterior pituitary lobe? - The hypothalamus is connected to the posterior pituitary by neural pathways - There are two well-defined clusters of neurons called the supraoptic nucleus and the paraventricular nucleus - Axons from the nuclei project down the pituitary stalk and terminate on blood vessels in the posterior pituitary How does the hypothalamus stimulate hormone release in the anterior pituitary lobe? - The hypothalamus is connected to the anterior pituitary by the hypothalamic-hypophyseal portal system - The hypothalamus secretes hormones into the portal system and they are carried directly to the anterior pituitary - These hormones either inhibit or promote the release of anterior pituitary hormones Which hormones are released from the posterior pituitary gland? - Vasopressin - Oxytocin What is vasopressin? - Antidiuretic hormone (ADH) - Enhances water retention by the kidneys - Causes contraction of arteriolar smooth muscle What is oxytocin? - A hormone that stimulates the contraction of uterine smooth muscle cells during childbirth - Promotes milk ejection during breastfeeding What are tropic hormones? - Hormones that stimulate other endocrine glands to release their hormones What are the six hormones released by the anterior pituitary gland? - Growth hormone - Adrenocorticotropic hormone - Thyroid-stimulating hormone - Follicle-stimulating hormone - Luteinizing hormones - Prolactin What is growth hormone? - The primary hormone for regulating overall body growth What is adrenocorticotropic hormone? - A hormone that stimulates the secretion of cortisol by the adrenal cortex What is the luteinizing hormone? - The hormone in females responsible for ovulation and formation of the corpus luteum - Stimulates the secretion of estrogen and progesterone from the ovaries - In males, LH stimulates the release of testosterone from the interstitial cells of Leydig What is thyroid-stimulation hormone? - Hormone that stimulates the release of thyroid hormones from the thyroid gland What is follicle-stimulation hormone? - In females, FSH stimulates the growth and development of ovarian follicles and promotes secretion of estrogen by the ovaries - In males, FSH is required for sperm production What is prolactin? - The only anterior pituitary hormone that is not tropic - In females, it enhances breast development and milk production Describe the pathway of the hypothalamic-hypophyseal portal system. - Hypophysiotropic hormones produced by neurosecretory neurons in the hypothalamus enter the hypothalamic capillaries - The hypothalamic capillaries rejoin to form the hypothalamic-hypophyseal portal system - The portal system branches into the capillaries of the anterior pituitary - The hypophysiotropic hormones which leave the blood across the anterior pituitary capillaries control the release of anterior pituitary hormones - When stimulated by the appropriate hypothalamic-releasing hormone the anterior pituitary secreted a given hormone into these capillaries - The anterior pituitary capillaries rejoin to form a vein through which the anterior pituitary hormone leaves for ultimate distribution throughout the body by the systemic circulation What are the hypothalamic hormones? - Hormones released by the hypothalamus that influence the release of hormones by the anterior pituitary - Thyrotropin-releasing hormone - Gonadotropic releasing hormone - Growth hormone inhibiting hormone - Corticotropin-releasing hormone - Growth hormone-releasing hormone - Prolactin-releasing hormone - Prolactin-inhibiting hormone What is thyrotropin-releasing hormone? - Hormone that stimulates the release of TSH and prolactin What is gonadotropin-releasing hormone? - Hormone that stimulates the release of FSH and LH What is growth hormone inhibiting hormone? - Hormone that inhibits the release of growth hormone and TSH What is corticotropin-releasing hormone? - The hormone that stimulates the release of ACTH What is growth hormone releasing hormone? - Hormone that stimulates the release of growth hormone What is prolactin releasing hormone? - Hormone that stimulates the release of prolactin What is prolactin-inhibiting hormone? - Hormone that inhibits the release of prolactin Why don't certain sections of the hypothalamus have a blood-brain barrier? - To allow the hypothalamus to monitor the blood and response to circulating chemicals or even changes of plasma composition such as osmolarity Describe the three-hormone hierarchic chain of command of hypothalamic hormones. - The hypothalamic hormone is released into the portal system before travelling to the pituitary gland to regulate the output of a tropic hormone - The tropic hormone is then transported by the systemic circulation to its target endocrine gland - There, the third hormone is regulated and a physiological effect is produced How is the secretion of regulatory hormones controlled? - The hormone ultimately secreted by the target gland acts in a negative feedback fashion to reduce the secretion of the regulatory hormones Where is the thyroid gland located? - Over the trachea just below the larynx Describe the structure of the thyroid gland. - Two lobes connected by the isthmus Describe the cellular structure of the thyroid gland. - Follicular cells are arranged to form hollow spheres throughout the gland - Appear as ring structures - Contain C cells that secrete calcitonin - The centre of each ring is filled with colloid What are the components of colloid? - Made up of large protein molecules called thyroglobulin Where thyroid hormones are synthesized and stored What is tetraiodothyronine? - A thyroid hormone that contains four iodine molecules and represents about 90% of the thyroid hormones secreted What is triiodothyronine? - Thyroid hormone that contains three iodine molecules and represents the remaining 10% of secreted hormone How do thyroid hormones differ from other lipophilic hormones? - They can be stored bound to thyroglobulin in the colloid of the thyroid gland Describe the steps of thyroid hormone synthesis. - Tyrosine-containing thyroglobulin is produced within the follicular cells by the endoplasmic reticulum-Golgi complex - It is then transported to the colloid by exocytosis - iodine is taken up by follicular cells through iodide trapping - Iodide is driven against its concentration gradient by using an Na+ cotransporter that moves Na+ down its concentration gradient - Iodide is then transferred into the colloid of the follicular lumen - Iodide organification - As iodide moves into the colloid, thyroperoxidase converts into a highly reactive state - Iodine immediately attached to a tyrosine residue on a thyroglobulin molecule producing monoiodotyrosine (two iodines → diiodotyrosine) - A coupling process occurs that combines MITs and DITs to form the thyroid hormones - One MIT and one DIT make T3 - Two DITs make T4 Describe the steps of thyroid hormone release. - The follicular cells engulf a portion of the thyroglobulin-containing colloid by phagocytosis - Creates hormone-filled vesicles - Once inside the follicular cell, lysosomes fuse with the vesicle and digestive enzymes release all of the MIT, DIT, T3, and T4 from the thyroglobulin - Due to their lipophilicity T3 and T4 immediately cross the plasma membrane to the blood where they bind to plasma proteins mainly thyroid-binding globulin Describe the effects of thyroid hormones on metabolic rate and heat production. - Increase the overall basal metabolic rate by increasing oxygen consumption and energy expenditure - Increasing metabolic rate also increases heat production Describe the effects of thyroid hormones on intermediary metabolism. - Thyroid hormone influences the enzymes involved in fuel metabolism - Effects differ depending on the amount of thyroid hormone present Describe the sympathomimetic effects of thyroid hormones. - Thyroid hormone can increase a target cell's response to catecholamines by increasing the number of catecholamine receptors Describe the effects of thyroid hormones on the cardiovascular system. - Can increase heart rate and the strength of contraction through its sympathomimetic effects - Increase in blood volume and flow Describe the effects of thyroid hormones on growth. - Stimulates the release of both growth hormone and insulin-like growth factor - Promotes their actions to stimulate the synthesis of new structural proteins and skeletal growth What effects do TSH have? - Influences most of the stages of thyroid hormone synthesis and release - Affects the size of the thyroid gland (shrinks with a lack of TSH, and swells with an increase of TSH) How is the release of TSH and TRH controlled? - Negative feedback What is hypothyroidism? - Occurs when the thyroid gland does not secrete enough thyroid hormone into the blood What is primary failure of the thyroid gland? - An impairment in the thyroid gland's ability to produce thyroid hormones - Characterized by low levels of T3 and T4 but elevated levels of TSH since no T3 or T4 are being produced to provide negative feedback - E.g. Hashimoto's thyroiditis What is secondary failure of the thyroid gland? - Occurs when the hypothalamus and/or the pituitary fail to secrete adequate TRH and/or TSH respectively - Characterized by low T3 and/or T4 What is the most common cause of hypothyroidism? - Inadequate dietary supplements of iodine - Characterized by low T3 and T4 and elevated TSH What are the symptoms of hypothyroidism? - Coll intolerance - Slower reflexes - Reduced mental alertness - Easy to fatigue - A slow, weak heart rate - Weight gain due to decreased basal metabolic rate What is cretinism? - Congenital hypothyroidism - Characterized by dwarfism and intellectual disability What are the results of secondary to excess hypothalamic or anterior pituitary secretions? - Hyperthyroidism - Observed when there is a tumour in either the hypothalamus (secrete excess TTRH) or in the anterior pituitary (secrete excess TSH) - Characterized by T3 and T4 elevation, and TRH and/or TSH elevation What is the result of a thyroid tumour? - Causes hyperthyroidism - A tumour on the thyroid gland results in an increased secretion of thyroid hormone - Characterized by elevated T3 and T4 and decreased TSH What is graves disease? - The most common cause of hyperthyroidism - An autoimmune disease in which the body produces a long-acting thyroid stimulator (LATS) - The LATS antibody, targets and activates TSH receptors on follicular cells causing them to grow larger and increase in number - Characterized by high levels of T3 and T4 and low levels of TSH What are the symptoms of hyperthyroidism? - Increased heart rate - Excessive heat production - Muscle weakness due to skeletal muscle protein degradation - Mood swings due to increased CNS mental alertness - Elevated basal metabolic rate that causes weight loss even with increased caloric intake What is a goiter? - A symptom that can arise from both hypothyroidism and hyperthyroidism - An enlarged thyroid gland that is usually quite visible - Can result from any condition that leads to increased TSH Where are the adrenal glands located? - At the top of the kidneys What are the two layers of the adrenal glands? - Adrenal cortex - Adrenal medulla What are the three zones of the adrenal cortex? - Zona glomerulosa - Zona fasciculata - Zona reticularis What are the three main categories of adrenal cortex hormones? - Mineralocorticoids - Glucocorticoids - Sex hormones What is the purpose of mineralocorticoids? - Influence mineral (electrolyte) balance Where are mineralocorticoids produced? - In the zona glomerulosa What is the purpose of glucocorticoids? - Play a role in glucose, lipid and protein metabolism Where are glucocorticoids produced? - Zona fasciculata - Zona reticularis What is the importance of mineralocorticoids? - Influencing salt and water balances - The absence of mineralocorticoids would cause a person to die in a matter of days due to circulatory shock What is the major mineralocorticoid produced? - Aldosterone What occurs in the absence of aldosterone? - ECF volume drops - Blood pressure decreases - Circulatory shock What are the two stimuli for the secretion of aldosterone? - Activation of the renin-angiotensin-aldosterone system in response to reduced Na+ and a fall in blood pressure - Direct stimulation of the adrenal cortex by increased K+ concentration What are the metabolic effects of glucocorticoids, specifically cortisol? - Stimulates gluconeogenesis in the liver - Produces glucose from non-carbohydrate precursors like Amino acids - Induces protein degradation in muscle to obtain amino acids - Inhibits glucose uptake by most tissues, except the brain) - Breaks down lipid stores to mobilize free fatty acids for fuel What is the role of cortisol in stress adaptation? - Cortisol causes a shift away from proteins and fat stores and increases carbohydrate stores - Increases the availability of glucose to ensure adequate brain function - Increased levels of amino acids, free fatty acids and glucose provide building blocks for wound repair How is the secretion of cortisol controlled? - Negative feedback control - The hypothalamus releases CRH to stimulate the anterior pituitary gland to release ACTH