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The Endocrine System. Chapter 13. Endocrine. to interstitial fluid circulation exocrine- secreted to ducts lumen or outside the body Endocrine glands: Pituitary, thyroid, parathyroid, adrenal & pineal Hormone secretion + other functions:
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The Endocrine System Chapter 13
Endocrine • to interstitial fluid circulation • exocrine- secreted to ducts lumen or outside the body • Endocrine glands: • Pituitary, thyroid, parathyroid, adrenal & pineal • Hormone secretion + other functions: • Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue & placenta
Hormone Operation • General chemical signal in circulation • Slower than nerve responses • Target cells must have a specific receptor • 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
Hormone Chemistry • Soluble in lipids = Hydrophobic • steroids, e.g. testosterone, estrogens, etc. • thyroid hormones, e.g. T3, T4 • Nitric oxide (NO) • Water soluble= Hydrophillic • 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
Lipid Soluble Action • 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
Water-Soluble Action • Diffuses from blood and binds to receptor in plasma membrane • Starts reaction inside cell forming second messenger • Cyclic AMP is a common one • Second messenger causes activation of several proteins (enzymes) • Activated proteins produce physiological responses • Second messenger is inactivated
Control of Secretions • Release occurs in short bursts • Regulated by: • 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
Hypothalamus & Pituitary • Major link between nervous & endocrine systems • Hypothalamic Cells synthesize at least 9 hormones • Pituitary synthesizes 7 • Regulate growth, development, metabolism & homeostasis
Pituitary • Two lobes; anterior & posterior • Hypophyseal portal veins • Connect capillaries in hypothalamus to capillaries in anterior pituitary
Hypothalamus 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
Human Growth Hormone (hGH) • Promotes synthesis of IGFs = somatomedins • in liver, muscle, cartilage & bone • Released in bursts (~2 hour intervals) • Hypothalamus Growth Hormone Releasing Hormone (GHRH) & Growth Hormone Inhibiting Hormone (GHIH ) • Regulated by blood glucose levels
Thyroid Stimulating Hormone • Stimulates the formation & secretion of Thyroid hormones from thyroid gland • Hypothalamus Thyrotropin Releasing Hormone (TRH)- no TIH • Regulated by circulating thyroid hormone levels
Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH) • In females: • FSH starts follicle development • LH stimulates formation of corpus luteum & secretion of progesterone • In males: • FSH stimulates sperm production in testes • LH stimulates release of testosterone • Gonadotrophin releasing Hormone (GnRH) from hypothalamus is suppressed by high levels of estrogen in females and testosterone in males
Prolactin (PRL) • 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
Adrenocortcotrophic Hormone (ACTH) • 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
Melanocyte Stimulating Hormone (MSH) • Small circulating amounts • Excess causes skin darkening
Posterior Pituitary • axon terminals from hypothalamus- • Release hormones • Oxytocin- enhance smooth muscle contraction during birth & milk ejection • may play role in emotional bonding • Antidiuretic Hormone (ADH) = vasopressin • Causes kidney to retain more water • Vasoconstriction increase in blood pressure • high blood osmotic pressure increase secretion
Thyroid Gland • Below larynx- two lobes • follicular cells surround follicles • thyroxin (T4) & triiodothyronine (T3) • Stored in follicle • Parafollicular cells (C-cells) • calcitonin
Thyroid Hormones • T4 & T3 increase basal metabolic rate, protein synthesis & growth • Blood level is controlled via feedback through hypothalamus • Increased body ATP demand can also raise blood levels • Calcitonin inhibits osteoclasts decrease in blood Ca2+ • Feedback control on blood levels
Parathyroid Glands • Small round masses in posterior of thyroid gland • Chief cells release parathyroid hormone (PTH) • Regulator of Ca2+, Mg2+ & HPO42- • 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
Pancreas • Fattened organ in curve of duodenum • Mostly an exocrine organ for digestion • Endocrine cells in pancreatic islets • Several cell types: • alpha cells glucagon • beta cells insulin
Actions of Insulin & Glucagon • 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
Adrenal Gland • Near kidneys • Two separate gland structures- • Adrenal cortex and adrenal medulla • 3 zones in Cortex-3 steroid hormones • Outer zone mineralocorticoids • Middle zone glucocorticoids • Inner Zone androgens
Mineralocorticoids • Aldosterone is the major form • Stimulates Na+ reabsorption from urine to blood • Stimulates excretion of K + into urine • Part of renin-angiotensin-aldosterone pathway • 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
Glucocorticoid action • Increase rate of protein breakdown • Stimulate liver formation of glucose • Breakdown of triglycerides in adipose • Anti-inflammatory effects- • Inhibit white blood cells • Depresses immune system • Regulated by negative feedback through hypothalamus
Androgens • 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
Adrenal Medulla • Consists of sympathetic post ganglionic cells • stimulated by preganglionic sympathetic neurons • Releases Epinephrine and norepinephrine • gives systemic sympathetic effects • occurs during strong physiological stress
Gonads • Produce gametes • Release sex steroids (testosterone or estrogen & progesterone) • Also hormone inhibin • Inhibits FSH release • hormones from pituitary (FSH & LH) • Ovaries also produce a hormone relaxin during pregnancy • details later in course
Pineal • Small gland attached to roof of third ventricle of brain • Produces melatonin • Sets bodies biological clock • More released in darkness
Other hormones • 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
Stress Responses • Part of homeostatic responses • When successful leads to extra physiological capacity and long term adaptation • Initial “fight-or-flight” response • Nerve mediated response-sympathetic
Stress- Resistance Reaction Slower & longer Than initial response • Hypothalamus Increased CRH, GHRH, TRH • CRHACTHCortisol mobilize metabolites (amino acids, glucose & fat) • GHRHhGH mobilize fats & glucose for energy and promote tissue growth & repair • TRHTSHthyroid hormones increased Metabolic capacity