Endocrine System Test 2 - 2025 PDF

The Endocrine System  Objectives Describe the mechanisms of hormone action Identify the major glands & hormones of the body Discuss the functions and interactions of the hormones Describe the feedback mechanisms & antagonistic actions of various hormones in the body ...

The Endocrine System  Objectives Describe the mechanisms of hormone action Identify the major glands & hormones of the body Discuss the functions and interactions of the hormones Describe the feedback mechanisms & antagonistic actions of various hormones in the body  Endocrine System Major regulating system to maintain body functions & homeostasis Endocrine glands Ductless  secrete hormones into the circulation Hormones Amines Thyroxine, epinephrine and norepinephrine Proteins Insulin, growth hormone, calcitonin, antidiuretic hormone, oxytocin Steroids Cortisol, aldosterone, estrogen, progesterone, testosterone  Primarily via negative feedback Info about the effects of the Regulation of hormone is “fed back” to the gland  decreases hormone Hormone secretion when appropriate Secretion Effects of the hormone reverse the stimulus & decrease secretion of the hormone  Pituitary Gland Aka hypophysis Plays a role in the regulation of several body functions Hangs from hypothalamus by short stalk (infundibulum) Posterior pituitary gland (neurohypophysis) Extension of hypothalamus Anterior pituitary gland (adenohypophysis) Separate glandular tissue  Anterior Pituitary Posterior pituitary stores hormones produced in Releasing hormones of the hypothalamus circulate the hypothalamus. Release is stimulated by directly to the anterior pituitary and influence its neural impulses from hypothalamus secretions. Pituitary Gland Posterior Pituitary Gland Hormones ADH & oxytocin Produced by hypothalamus & stored in post. pituitary gland Hormone Functions Antidiuretic Increases water reabsorption by the kidney tubules Hormone (ADH) (water returns to the blood) Decreases sweating Causes vasoconstriction (in large amounts) Oxytocin Promotes contraction of myometrium of uterus (labor) Promotes release of milk from mammary glands  Functions to conserve water for regulation of blood pressure (BP) Stimulated by decreased water content in body (dehydration) Osmoreceptors in hypothalamus detect increased concentration of salts in body fluids Specific effects: Increases reabsorption of water by the kidneys  decreases amount of urine formed Water reabsorbs into blood, increasing blood volume and maintaining BP Inhibits sweating In large amounts  causes vasoconstriction  raises or at least maintains BP Alcohol inhibits ADH secretion  increases urinary output Excessive intake w/o fluid replenishment  feel thirsty & dizzy the next morning Thirst is due to loss of body water Dizziness results from low BP Posterior Pituitary Gland: ADH  Functions: stimulates contractions of uterus at end of pregnancy & stimulates release of milk when baby is nursing Contraction of uterus stimulated by stretching of cervix Generates sensory impulses to hypothalamus, which in turn stimulates pituitary to release oxytocin Continues until baby is delivered (stopping the positive feedback mechanism) In breastfeeding, stimulation of nipple triggers nerve impulses from hypothalamus to cause the release of oxytocin Stimulates contraction of the smooth muscle cells around the mammary ducts Posterior Pituitary Gland: Oxytocin  Hormones of anterior pituitary are regulated by releasing hormones from hypothalamus Hormones Growth hormone (GH) Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Prolactin Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Anterior Pituitary Gland  Aka somatotropin Functions to promote growth & protein repair/replacement Secretion regulated by hormones from hypothalamus: Growth hormone releasing hormone (GHRH) - stimulates secretion Produced during hypoglycemia and during exercise Growth hormone inhibiting hormone (GHIH) - inhibits secretion Produced in periods of hyperglycemia Specific effects: Increases rate of mitosis Increases amino acid transport into cells Increases rate of protein synthesis Increases use of fats for energy during hyperglycemis- not enough glucose Anterior Pituitary Gland: Growth Hormone  aka thyrotropin Increases secretion of thyroxine (T4) & triiodothyronine (T3) by thyroid Secretion is stimulated by thyrotropin-releasing hormone (TRH) from the hypothalamus TRH is produced when metabolic rate (energy production) decreases TSH release causes thyroxine to be produced/released  increases energy production & raises metabolic rate Anterior Pituitary Gland: TSH  Anterior Pituitary Gland: ACTH ACTH secretion is increased by corticotropin-releasing hormone (CRH) CRH is produced in any type of physiological stress situation Injury, disease, exercise, hypoglycemia, etc Increases secretion of cortisol by the adrenal cortex  Function: Initiates & maintains milk production by mammary glands Secretion of prolactin regulated by prolactin-releasing hormone (PRH) & prolactin-inhibiting hormone (PIH) from hypothalamus Mammary glands must first be acted on by estrogen & progesterone, during pregnancy After delivery of baby, prolactin secretion increases & milk is produced If the mother continues to breastfeed, prolactin levels remain high Anterior Pituitary Gland: Prolactin  Follicle stimulating hormone In women: stimulates the growth of ovarian follicles (egg development) In men: initiates sperm production within the testes Secretion stimulated by gonadotropin-releasing hormone (GnRH) from hypothalamus FSH secretion is decreased by inhibin (hormone produced by ovaries or testes) Luteinizing hormone In women: responsible for ovulation (release of mature ovum from ovarian follicle) & development of corpus luteum In men: stimulates interstitial cells of testes to secrete testosterone Secretion also regulated by GnRH from the hypothalamus Anterior Pituitary Gland: FSH & LH Thyroid Gland Located on the front & sides of trachea, just below the larynx Structural units are thyroid follicles made of cuboidal epithelium Follicles produce thyroxine (T4) & triiodothyronine (T3) Iodine is needed for synthesis of these hormones Thyroid also produces calcitonin  T4 & T3 Secretion is stimulated by TSH from the anterior pituitary Thyroxine (T4) & T3 have the same functions Regulate energy production & protein synthesis Contribute to growth & normal body functioning t/o lifespan Activity reflected in functioning of brain, muscles, heart, & nearly all other organs Specific effects: Increase cell respiration & metabolism of carbohydrates, fats, & excess amino acids  increases energy & heat production Increase the rate of protein synthesis w/in cells Thyroid Functions (T3 & T4)  Decreased Metabolic Rate (Energy Production) Stimulates hypothalamus Increased Metabolic Rate (Energy Production) Hypothalamus Thyrotropin-releasing hormone (TRH) Anterior Pituitary T3 & T4 TSH thyroid stim hormone Thyroid  Thyroid Gland: Calcitonin Function: Plays role in maintaining normal blood levels of Ca2+ & phosphate Assists in maintaining stable, strong bone matrix Decreases reabsorption of Ca2+ & phosphate from bones to the blood (reduces blood levels) Stimulus for secretion: hypercalcemia (high blood calcium) Parathyroid Glands 4 glands 2 on the back of each lobe of thyroid gland Secrete parathyroid hormone Antagonist to calcitonin Important for maintenance of normal blood levels of Ca2+ & phosphate  Parathyroid Glands Parathyroid hormone Raises blood Ca2+ level & lowers the blood phosphate level Secretion is stimulated by hypocalcemia Target organs: the bones, small intestine, and kidneys Specific effects Increases reabsorption of Ca2+ & phosphate from bones to the blood Increases absorption of Ca2+ & phosphate in the small intestine (requires vitamin D) Stimulates activation of vitamin D in kidneys Increases reabsorption of calcium by kidneys and excretion of phosphate (more than is obtained from bones) cilia detects Interaction of Calcitonin & PTH in Regulating Blood Calcium Level Pancreas Glucagon Alpha cells Release/Secretion Stimulated by hypoglycemia (low blood sugar) Can occur during physiological stress or when food is needed Functions: Stimulates liver to convert glycogen to glucose (glycogenolysis) Increases use of fats & excess amino acids for gluconeogenesis Gluconeogenesis: conversion of non-carbohydrate molecules to glucose for cell respiration Overall effect: Raise blood glucose level & increase available molecules for energy production Insulin Bets cells Release/Secretion Stimulated by hyperglycemia Occurs after eating Functions Increases cell permeability to glucose Increases glucose transport into cells for energy production Increases conversion of excess glucose to glycogen in the liver & skeletal muscles (glycogenesis) Increases amino acid & fatty acid transport into cells, and their use in synthesis rxns Insulin & Glucagon  Adrenal Glands 2 adrenal glands (suprarenal glands) Each located on top of a kidney 2 parts Inner: adrenal medulla Outer: adrenal cortex  Adrenal Medulla Innermost cavity Secrete epinephrine & norepinephrine Catecholamines Sympathomimetic Secretion of both is stimulated by sympathetic impulses from hypothalamus Functions duplicate & prolong those of sympathetic division of the ANS  Adrenal Medulla Epinephrine & norepinephrine Secreted in stressful situations Norepinephrine: secreted in small amounts Most significant function is to cause vasoconstriction in the skin, viscera, & skeletal muscles  raises BP Epinephrine: secreted in larger amounts Increases the heart rate (HR) & force of cardiac contraction Stimulates vasoconstriction in skin & viscera and vasodilation in skeletal muscles Dilates bronchioles, decreases peristalsis, stimulates glycogenolysis, increases the use of fats for energy, & increases rate of cell respiration Adrenal Cortex Secretes 3 types of steroid hormones: Mineralocorticoids - secreted in stressful situations Aldosterone Glucocorticoids - secreted in stressful situations Cortisol Sex hormones (estrogen and androgens)  Aldosterone Release is stimulated by: Low blood Na+ level Low blood volume or blood pressure High blood K+ level Functions: Increases reabsorption of Na+ ions by the kidneys to the blood Increases excretion of K+ ions by the kidneys in urine Overall effects  directly maintains normal blood levels of Na+ & K+ Indirectly, contributes to maintenance of normal blood pH, blood volume, & blood pressure  Cortisol Release is stimulated by ACTH (anterior pituitary) during physiological stress Disease, physical injury, severe hemorrhage, fear or anger, exercise, and hunger Functions: Increases use of fats & excess amino acids for energy (gluconeogenesis) Decreases use of glucose for energy (glucose-sparing) Increases conversion of glucose to glycogen in the liver Anti-inflammatory effect: stabilizes lysosomes & blocks effects of histamine  Ovaries Estrogen Secreted by the follicle cells of the ovary Stimulated by FSH from the anterior pituitary gland Functions: Promotes maturation of the ovum in the ovarian follicle Stimulates growth of blood vessels in endometrium (lining) of uterus in preparation for a possible fertilized egg Development of secondary sex characteristics Closure of growth plates Lower blood levels of cholesterol & triglyceride  Ovaries Progesterone Mature ovarian follicle becomes corpus luteum & begins to secrete progesterone in addition to estrogen Release stimulated by LH from anterior pituitary gland Needed for successful implantation of very early embryo in endometrium Promotes storage of glycogen & further growth of blood vessels in endometrium for the placenta Secretory cells of the mammary glands also develop under the influence of progesterone Inhibin Secreted by corpus luteum Decreases secretion of FSH by anterior pituitary gland, and GnRH by the hypothalamus  Testes Testosterone Steroid hormone secreted by interstitial cells of the testes LH stimulates secretion luetinizing hormone Promotes maturation of sperm At puberty, stimulates development of male secondary sex characteristics Brings about closure of epiphyseal plates of the long bones Inhibin Secreted by sustentacular cells of testes in response to increased testosterone Decreases secretion of FSH by the anterior pituitary gland Interaction of inhibin, testosterone, & anterior pituitary hormones maintains spermatogenesis at a constant rate  Mechanisms of Hormone Action The two-messenger mechanism: Protein hormone (1st messenger) bonds to membrane receptor; this rxn stimulates formation of cyclic AMP (2nd messenger) inside the cell; cyclic AMP activates the cell’s enzymes to bring about the cell’s characteristic response to the hormone Steroid hormones diffuse easily through cell membranes & bond to cytoplasmic receptors Steroid-protein complex enters the nucleus and activates certain genes, which initiate protein synthesis to bring about the cell’s characteristic response to the hormone  A. Two-messenger mechanism  Protein hormone (1st messenger) bonds to a membrane receptor  Stimulates formation of cyclic AMP (2nd messenger) inside cell  Cyclic AMP activates cell’s enzymes to bring about the cell’s characteristic response to the hormone Hormone receptors: proteins found in cell membrane, or w/in the cytoplasm or nucleus of the target cell  B. Steroid hormones diffuse easily through cell membranes & bond to cytoplasmic receptors  Steroid-protein complex enters the nucleus & activates certain genes  Initiates protein synthesis, bringing about cell’s characteristic response to the hormone Hormone receptors: proteins found in cell membrane, or w/in the cytoplasm or nucleus of the target cell Questions?