Lecture 4: The Endocrine System PDF

Lecture 4: The Endocrine System Ba-Etilayoo Atinga UENR ANATOMY.. Nervous and Endocrine Systems ◼ Act together to coordinate functions of all body systems ◼ Nervous system ❑ Nerve impulses/ Neurotransmitters ❑ Faster responses, briefer effects, acts on speci...

Lecture 4: The Endocrine System Ba-Etilayoo Atinga UENR ANATOMY.. Nervous and Endocrine Systems ◼ Act together to coordinate functions of all body systems ◼ Nervous system ❑ Nerve impulses/ Neurotransmitters ❑ Faster responses, briefer effects, acts on specific target ◼ Endocrine system ❑ Hormone – mediator molecule released in 1 part of the body but regulates activity of cells in other parts ❑ Slower responses, effects last longer, broader influence UENR ANATOMY.. Endocrine Glands ◼ 2 kinds of glands ❑ Exocrine – ducted ❑ Endocrine – ductless ◼ Secrete products into interstitial fluid, diffuse into blood ◼ Endocrine glands include ❑ Pituitary, thyroid, parathyroid, adrenal and pineal glands ❑ Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta not exclusively endocrine glands UENR ANATOMY.. UENR ANATOMY.. Hormone Activity ◼ Hormones affect only specific target tissues with specific receptors ◼ Receptors constantly synthesized and broken down ❑ Down-regulation ❑ Up-regulation ❑ Blocking hormone receptors e.g. RU486(Mifepristone) UENR ANATOMY.. Circulating and Local Hormones ◼ Hormone types ❑ Circulating – circulate in blood throughout body ❑ Local hormones – act locally ◼ Paracrine – act on neighboring cells eg IL-2 ◼ Autocrine – act on the same cell that secreted them e.g. NO(Viagra) UENR ANATOMY.. Chemical classes of hormones ❑ Lipid-soluble – use transport proteins ◼ Steroid-mainly of cholesterol ◼ Thyroid-T3&4,Iodine attaches to tyrosine ◼ Nitric oxide (NO)-Both neuroT & Hormone ❑ Water-soluble – circulate in “free” form ◼ Amine ◼ Peptide/ protein ◼ Eicosanoid UENR ANATOMY.. Mechanisms of Hormone Action ◼ Response depends on both hormone and target cell ◼ Lipid-soluble hormones bind to receptors inside target cells ◼ Water-soluble hormones bind to receptors on the plasma membrane ❑ Activates second messenger system ❑ Amplification of original small signal ◼ Responsiveness of target cell depends on ❑ Hormone’s concentration ❑ Abundance of target cell receptors ❑ Influence exerted by other hormones ◼ Permissive, synergistic and antagonistic effects UENR ANATOMY.. Lipid-soluble and Water-soluble Hormones UENR ANATOMY..  Free hormone Blood capillary 1 Lipid-soluble Transport hormone protein diffuses into cell 2 Activated Nucleus receptor-hormone Receptor complex alters gene expression DNA Cytosol mRNA 3 Newly formed mRNA directs Ribosome synthesis of specific proteins New on ribosomes protein 4 New proteins alter cell's activity Target cell  Blood capillary 1 Binding of hormone (first messenger) to its receptor activates G protein, Water-soluble which activates adenylate cyclase hormone Receptor Adenylate cyclase Second messenger G protein ATP cAMP 2 Activated adenylate cyclase converts ATP to cAMP Protein kinases 6 Phosphodiesterase inactivates cAMP 3 cAMP serves as a Activated second messenger protein to activate protein kinases kinases 4 Activated protein Protein kinases phosphorylate ATP cellular proteins ADP Protein— P 5 Millions of phosphorylated proteins cause reactions that produce physiological responses Target cell Control of Hormone Secretion ◼ Regulated by ❑ Signals from nervous system ❑ Chemical changes in the blood ❑ Other hormones ◼ Most hormonal regulation by negative feedback ❑ Few examples of positive feedback UENR ANATOMY.. Hypothalamus and Pituitary Gland ◼ Hypothalamus is a major link between nervous and endocrine system ◼ Pituitary attached to hypothalamus by infundibulum ❑ Anterior pituitary or adenohypophysis ❑ Posterior pituitary or neurohypophysis UENR ANATOMY.. Hypothalamus and Pituitary Gland UENR ANATOMY.. Anterior pituitary ❑ Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus ❑ Also regulated by negative feedback ❑ Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system ❑ Anterior pituitary hormones that act on other endocrine systems called tropic hormones UENR ANATOMY.. Hormones of the Anterior Pituitary ◼ Human growth hormone (hGH) or somatostatin ❑ Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis ◼ Thyroid-stimulating hormone (TSH) or thyrotropin ❑ Stimulates synthesis and secretion of thyroid hormones by thyroid ◼ Follicle-stimulating hormone (FSH) ❑ Ovaries initiates development of oocytes, testes stimulates testosterone production ◼ Luteinizing hormone (LH) ❑ Ovaries stimulates ovulation, testes stimulates testosterone production UENR ANATOMY.. Hormones of the Anterior Pituitary ◼ Prolactin (PRL) ❑ Promotes milk secretion by mammary glands ◼ Adrenocorticotropic hormone (ACTH) or corticotropin ❑ Stimulates glucocorticoid secretion by adrenal cortex ◼ Melanocyte-stimulating Hormone (MSH) ❑ Unknown role in humans UENR ANATOMY.. Negative Feedback Regulation UENR ANATOMY.. Effects of hGH and IGFs UENR ANATOMY.. 1 Low blood glucose 6 High blood glucose (hypoglycemia) (hyperglycemia) stimulates release of stimulates release of GHRH GHIH 2 GHRH stimulates 7 GHIH inhibits secretion secretion of of hGH by hGH by somatotrophs somatotrophs hGH Anterior pituitary 3 hGH and IGFs speed 8 A low level of hGH and up breakdown of liver IGFs decreases the rate glycogen into glucose, of glycogen breakdown which enters the blood in the liver and glucose more rapidly enters the blood more slowly 4 Blood glucose level 9 Blood glucose level rises to normal falls to normal (about 90 mg/100 mL) (about 90 mg/100 mL) 5 If blood glucose 10 If blood glucose continues to increase, continues to decrease, hyperglycemia inhibits hypoglycemia inhibits release of GHRH release of GHIH Posterior pituitary ❑ Does not synthesize hormones ❑ Stores and releases hormones made by the hypothalamus ◼ Transported along hypothalamohypophyseal tract ❑ Oxytocin (OT) ❑ Antidiuretic hormone (ADH) or vasopressin UENR ANATOMY.. Hypothalamohypophyseal tract UENR ANATOMY.. Oxytocin (OT) ❑ During and after delivery of baby affects uterus and breasts ❑ Enhances smooth muscle contraction in wall of uterus ❑ Stimulates milk ejection from mammary glands UENR ANATOMY.. Antidiuretic Hormone (ADH) ❑ Decreases urine production by causing the kindeys to return more water to the blood ❑ Also decreases water lost through sweating and constriction of arterioles which increases blood pressure (vasopressin) UENR ANATOMY..  1 High blood osmotic 5 Low blood osmotic pressure stimulates pressure inhibits hypothalamic hypothalamic osmoreceptors osmoreceptors Osmoreceptors 2 Osmoreceptors activate the 6 Inhibition of osmo- neurosecretory cells receptors reduces or that synthesize and stops ADH secretion release ADH Hypothalamus 3 Nerve impulses liberate ADH from axon terminals in the posterior pituitary into the bloodstream ADH Target tissues 4 Kidneys retain Sudoriferous Arterioles constrict, more water, (sweat) glands which increases which decreases decrease water blood pressure urine output loss by perspiration from the skin Thyroid Gland ◼ Located inferior to larynx ◼ 2 lobes connected by isthmus ◼ Thyroid follicles produce thyroid hormones ❑ Thyroxine or tetraiodothyronine (T4) ❑ Triiodothyronine (T3) ◼ Both increase BMR, stimulate protein synthesis, increase use of glucose and fatty acids for ATP production ◼ Parafollicular cells or C cells produce calcitonin ❑ Lowers blood Ca2+ by inhibiting bone resorption UENR ANATOMY.. Thyroid Gland UENR ANATOMY.. Control of thyroid hormone secretion ❑ Thyrotropin-releasing hormone (TRH) from hypothalamus ❑ Thyroid-stimulating hormone (TSH) from anterior pituitary ❑ Situations that increase ATP demand also increase secretion of thyroid hormones UENR ANATOMY..  1 Low blood levels of T3 and T3 or low metabolic rate stimulate release of Hypothalamus TRH 2 TRH, carried by hypophyseal portal veins to anterior pituitary, 5 Elevated stimulates T3inhibits release of TSH release of by thyrotrophs TRH and TSH TSH (negative feedback) Anterior 3 TSH released into blood stimulates pituitary thyroid follicular cells 4 T3 and T4 released into Thyroid blood by follicle follicular cells Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones Parathyroid Glands ◼ Embedded in lobes of thyroid gland ◼ Usually 4 ◼ Parathyroid hormone (PTH) or parathormone ❑ Major regulator of calcium, magnesium, and phosphate ions in the blood ❑ Increases number and activity of osteoclasts ❑ Elevates bone resorption ◼ Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback UENR ANATOMY.. Parathyroid Glands UENR ANATOMY.. Roles of Calcitonin, Parathyroid hormone, Calcitrol in Calcium Homeostasis UENR ANATOMY..  1 High level of Ca2+ in blood 3 Low level of Ca2+ in blood stimulates thyroid gland stimulates parathyroid parafollicular cells to gland chief cells to release release more CT. more PTH. 6 CALCITRIOL stimulates increased absorption of Ca2+ from foods, which increases blood Ca2+ level. 5 PTH also stimulates the kidneys to release 4 PARATHYROID HORMONE (PTH) 2 CALCITONIN inhibits CALCITRIOL. promotes release of Ca2+ from osteoclasts, thus decreasing bone extracellular matrix into blood Ca2+ level. blood and slows loss of Ca2+ in urine, thus increasing blood Ca2+ level. Adrenal Glands ◼ 2 structurally and functionally distinct regions ❑ Adrenal cortex ◼ Mineralocorticoids affect mineral homeostasis ◼ Glucocorticoids affect glucose homeostasis ❑ cortisol ◼ Androgens have masculinzing effects ❑ Dehydroepiandrosterone (DHEA) only important in females ❑ Adrenal medulla ◼ Modified sympathetic ganglion of autonomic nervous system ◼ Intensifies sympathetic responses ◼ Epinephrine and norepinephrine UENR ANATOMY.. Adrenal Glands UENR ANATOMY.. Pancreatic Islets ◼ Both exocrine and endocrine gland ◼ Roughly 99% of cells produce digestive enzymes ◼ Pancreatic islets or islets of Langerhans ❑ Alpha or A cells secrete glucagon – raises blood sugar ❑ Beta or B cells secrete insulin – lowers blood sugar ❑ Delta or D cells secrete somatostatin – inhibits both insulin and glucagon ❑ F cells secrete pancreatic polypeptide – inhibits somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes UENR ANATOMY.. Pancreas UENR ANATOMY.. Negative Feedback Regulation of Glucagon and Insulin UENR ANATOMY.. 1 Low blood glucose 5 High blood glucose (hypoglycemia) (hyperglycemia) stimulates alpha stimulates beta cells cells to secrete to secrete GLUCAGON INSULIN 2 Glucagon acts on 6 Insulin acts on various hepatocytes body cells to: (liver cells) to: accelerate facilitated convert glycogen diffusion of glucose into glucose into cells (glycogenolysis) speed conversion of form glucose from glucose into glycogen lactic acid and (glycogenesis) certain amino acids increase uptake of (gluconeogenesis) amino acids and increase protein synthesis speed synthesis of fatty acids (lipogenesis) 3 Glucose released slow glycogenolysis by hepatocytes slow gluconeogenesis raises blood glucose level to normal 7 Blood glucose level falls 4 If blood glucose 8 If blood glucose continues continues to rise, to fall, hypoglycemia hyperglycemia inhibits inhibits release of release of glucagon insulin Ovaries and Testes ◼ Gonads – produce gametes and hormones ◼ Ovaries produce 2 estrogens (estradiol and estrone) and progesterone ❑ With FSH and LH regulate menstrual cycle, maintain pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics ❑ Inhibin inhibits FSH ❑ Relaxin produced during pregnancy ◼ Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics ❑ Inhibin inhibits FSH UENR ANATOMY.. Pineal Gland ◼ Attached to roof of 3rd ventricle of brain at midline ◼ Masses of neuroglia and pinealocytes ◼ Melatonin – amine hormone derived from serotonin ◼ Appears to contribute to setting biological clock ◼ More melatonin liberated during darkness than light UENR ANATOMY.. Thymus and Other Endocrine Tissues ◼ Thymus ❑ Located behind sternum between the lungs ❑ Produces thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin ❑ All involved in T cell maturation UENR ANATOMY.. UENR ANATOMY.. The Stress Response ◼ Eustress in helpful stress / Distress is harmful ◼ Body’s homeostatic mechanisms attempt to counteract stress ◼ Stressful conditions can result in stress response or general adaptation syndrome (GAS) ❑ 3 stages – initial flight-or-fight, slower resistance reaction, eventually exhaustion ❑ Prolonged exposure to cortisol can result in wasting of muscles, suppression of immune system, ulceration of GI tract, and failure of pancreatic beta cells UENR ANATOMY.. Stress Response UENR ANATOMY.. Bibliography Tortora, Principles of Anatomy & Physiology, 14th edition, 2014, Wiley, ISBN 9781118345009 (hardback w/brief atlas), 9781118344392 (looseleaf pages w/brief atlas). Marieb, E.N.(2015.). Human Anatomy and Physiology. California: The Benjamin/Cummings Publishing Company Inc. McMinn, R. (1990). Last’s Anatomy: Regional and Applied. London: Churchill Livingstone. McMinn, R. M. & Hutchings, R. T. (2005). A Colour Atlas of Human Anatomy. London: Wolfe Medical Publishing. Ross, J. S., & Wilson, K. J. W.(2008) Foundations of Anatomy and Phsiology. (4th ed). Edinburgh: Churchill Livingstone. UENR ANATOMY..