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The Endocrine System 13 Unit 1 Chapter 13 Endocrine 13 • to interstitial fluid circulation • exocrine- secreted to ducts lumen or outside the body • Endocrine glands: • Hormone secretion + other functions: Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue & placenta Unit 1 Pituitary, thyroid, parathyroid, adrenal & pineal Figure 13.1 Hormone Operation 13 Response determined by responding cell, i.e. different cells may respond differently to the same hormone • Cell may respond to more than one hormone, i.e. has more than one type receptor Unit 1 • General chemical signal in circulation • Slower than nerve responses • Target cells must have a specific receptor Hormone Chemistry 13 • Soluble in lipids = Hydrophobic steroids, e.g. testosterone, estrogens, etc. thyroid hormones, e.g. T3, T4 Nitric oxide (NO) Amino acid derivatives, e.g. epinephrine, norepinephrine Peptides, e.g. antidiuretic Hormone (ADH), oxytocin Proteins, e.g. insulin & growth hormone • General Action depends on chemistry Unit 1 • Water soluble= Hydrophillic • Hormone detaches from carrier in blood stream • Diffusion through interstitial fluid & cell membrane into cell • Binds to & activates receptor • Receptor-hormone complex alters gene expression • If new mRNA protein synthesis • New proteins alter cell activity 13 Unit 1 Lipid Soluble Action Figure 13.2 Water-Soluble Action 13 • Diffuses from blood and binds to receptor in plasma membrane • Starts reaction inside cell forming second messenger • Second messenger causes activation of several proteins (enzymes) • Activated proteins produce physiological responses • Second messenger is inactivated Unit 1 Cyclic AMP is a common one Figure 13.3 Control of Secretions 13 Signals from nervous system, e.g. adrenal medulla release of epinephrine Chemical changes in blood, e.g Blood Ca2+ affects parathyroid hormone Other hormones, e.g. ACTH from pituitary stimulates cortisol release from adrenal cortex Unit 1 • Release occurs in short bursts • Regulated by: • Major link between nervous & endocrine systems • Hypothalamic Cells synthesize at least 9 hormones • Pituitary synthesizes 7 • Regulate growth, development, metabolism & homeostasis 13 Unit 1 Hypothalamus & Pituitary Pituitary 13 • Two lobes; anterior & posterior • Hypophyseal portal veins Unit 1 Connect capillaries in hypothalamus to capillaries in anterior pituitary • Axons of hypothalamic neurons (neurosecretory cells) end near capillaries of hypothalamus • Secrete Releasing hormones or Inhibiting hormones portal veins • Regulate release of anterior pituitary hormones Unit 1 Hypothalamus Pituitary 13 Figure 13.4 Human Growth Hormone (hGH) 13 • Promotes synthesis of IGFs = somatomedins • Released in bursts (~2 hour intervals) • Hypothalamus Growth Hormone Releasing Hormone (GHRH) & Growth Hormone Inhibiting Hormone (GHIH ) Regulated by blood glucose levels Unit 1 in liver, muscle, cartilage & bone Thyroid Stimulating Hormone 13 Regulated by circulating thyroid hormone levels Unit 1 • Stimulates the formation & secretion of Thyroid hormones from thyroid gland • Hypothalamus Thyrotropin Releasing Hormone (TRH)- no TIH Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH) 13 • In females: FSH starts follicle development LH stimulates formation of corpus luteum & secretion of progesterone • In males: • Gonadotrophin releasing Hormone (GnRH) from hypothalamus is suppressed by high levels of estrogen in females and testosterone in males Unit 1 FSH stimulates sperm production in testes LH stimulates release of testosterone • Initiates & maintains milk production by mammary glands • Ejection of milk depends on oxytocin • Prolactin inhibiting hormone (PIH) suppresses prolactin release • High levels of Estrogens PRH prolactin release • Unknown function in males Hypersecretion impotence 13 Unit 1 Prolactin (PRL) • Controls production & secretion of glucocorticoids from adrenal cortex • Corticotrophin Releasing Hormone (CRH) from hypothalamus stimulates secretion of ACTH • Stress related stimuli can also stimulate ACTH release • Glucocorticoids inhibit CRH & ACTH release 13 Unit 1 Adrenocortcotrophic Hormone (ACTH) Melanocyte Stimulating Hormone (MSH) 13 Unit 1 • Small circulating amounts • Excess causes skin darkening Posterior Pituitary 13 • axon terminals from hypothalamus• Release hormones • Oxytocin- enhance smooth muscle contraction during birth & milk ejection may play role in emotional bonding Causes kidney to retain more water Vasoconstriction increase in blood pressure high blood osmotic pressure increase secretion Unit 1 • Antidiuretic Hormone (ADH) = vasopressin Figure 13.5 Figure 13.6 Thyroid Gland 13 • Below larynx- two lobes follicular cells surround follicles thyroxin (T4) & triiodothyronine (T3) Stored in follicle calcitonin Unit 1 • Parafollicular cells (C-cells) Figure 13.7a Figure 13.7b Thyroid Hormones 13 • T4 & T3 increase basal metabolic rate, protein synthesis & growth • Blood level is controlled via feedback through hypothalamus • Calcitonin inhibits osteoclasts decrease in blood Ca2+ Feedback control on blood levels Unit 1 Increased body ATP demand can also raise blood levels Figure 13.8 Parathyroid Glands 13 Increases number & activity of osteoblasts Slows loss of Ca2+ & Mg2+ in urine Promotes production of calcitriol increases rate of Ca2+, Mg2+ & HPO42- absorption in GI tract Unit 1 • Small round masses in posterior of thyroid gland • Chief cells release parathyroid hormone (PTH) • Regulator of Ca2+, Mg2+ & HPO42- Figure 13.9 Figure 13.10 Pancreas 13 • Fattened organ in curve of duodenum • Mostly an exocrine organ for digestion • Endocrine cells in pancreatic islets • alpha cells glucagon • beta cells insulin Unit 1 • Several cell types: Figure 13.11a Figure 13.11b Figure 13.11c • Low blood glucose stimulates glucagon release • Glucagon stimulates liver glucose release increased blood glucose • High glucose levels stimulate insulin release • Insulin increase glucose transport into skeletal muscle and adipose cells decreased blood glucose • Insulin promotes Amino Acid uptake, protein synthesis & lipid storage • ANS also modulates hormone release 13 Unit 1 Actions of Insulin & Glucagon Figure 13.12 Adrenal Gland Near kidneys Two separate gland structuresAdrenal cortex and adrenal medulla 3 zones in Cortex-3 steroid hormones Outer zone mineralocorticoids Middle zone glucocorticoids Inner Zone androgens Unit 1 • • • • 13 Figure 13.13a Figure 13.13b Mineralocorticoids 13 Decreased BP release of renin from kidney Renin causes angiotensinogen angiotensin I In lungs Angiotensin converting enzyme (ACE) causes Angiotensin I angiotensin II Angiotensin II causes Aldosterone release Unit 1 • Aldosterone is the major form • Stimulates Na+ reabsorption from urine to blood • Stimulates excretion of K + into urine • Part of renin-angiotensin-aldosterone pathway Figure 13.14 Glucocorticoid action • • • • 13 Increase rate of protein breakdown Stimulate liver formation of glucose Breakdown of triglycerides in adipose Anti-inflammatory effects- • Depresses immune system • Regulated by negative feedback through hypothalamus Unit 1 Inhibit white blood cells • Small amount secreted from adrenal cortex • Contribute to libido in females • Converted to estrogens by other body tissues • Stimulate axillary hair growth in both boys & girls • Contribute to adolescent growth spurt 13 Unit 1 Androgens • Consists of sympathetic post ganglionic cells • stimulated by preganglionic sympathetic neurons • Releases Epinephrine and norepinephrine • gives systemic sympathetic effects • occurs during strong physiological stress 13 Unit 1 Adrenal Medulla Gonads 13 • Produce gametes • Release sex steroids (testosterone or estrogen & progesterone) • Also hormone inhibin • hormones from pituitary (FSH & LH) • Ovaries also produce a hormone relaxin during pregnancy • details later in course Unit 1 Inhibits FSH release Pineal 13 • Small gland attached to roof of third ventricle of brain • Produces melatonin • Sets bodies biological clock Unit 1 More released in darkness • Prostaglandins (PG) & leukotrienes (LT) • Derived from fatty acids • Act locally in most tissues & released from most body cells • LTs stimulate white blood cells & mediate inflammation • PGs affect many visceral functions & also modulate inflammation, promote fever & intensify pain 13 Unit 1 Other hormones Stress Responses 13 Nerve mediated response-sympathetic Unit 1 • Part of homeostatic responses • When successful leads to extra physiological capacity and long term adaptation • Initial “fight-or-flight” response Stress- Resistance Reaction 13 Slower & longer Than initial response • CRHACTHCortisol mobilize metabolites (amino acids, glucose & fat) • GHRHhGH mobilize fats & glucose for energy and promote tissue growth & repair • TRHTSHthyroid hormones increased Metabolic capacity Unit 1 Hypothalamus Increased CRH, GHRH, TRH • Some decrease in function with aging • Loss of negative feedback sensitivity, e.g. decline in circulating thyroid hormones • PTH levels rise loss of bone mass • Less glucocorticoid production • Slower release of insulin • Thymus declines after puberty • Ovary response to gonadotrophins stops • Slow decline in testosterone production 13 Unit 1 Aging
