Chapter 17 .pdf
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The Endocrine System Chapter 17 17.1 - Overview Long distance communication to maintain homeostasis Chemical Primarily secretion (hormone) to travel throughout the body travel in blood and bind to receptors Hormones can be quick (seconds) or slow (days) and may involve many systems...
The Endocrine System Chapter 17 17.1 - Overview Long distance communication to maintain homeostasis Chemical Primarily secretion (hormone) to travel throughout the body travel in blood and bind to receptors Hormones can be quick (seconds) or slow (days) and may involve many systems Hormones are secreted from organs, glands, adipose tissue, and even bone Do not confuse this with the exocrine system (ducts) 17.1 – Other types of chemical signaling Autocrine – a chemical that elicits a response in the same cell (Interleukin) Paracrine – a chemical that communicates to other local cells (histamine and neurotransmitters) 17.2 – Types of Hormones Either from amino acids or lipids Amine – derived from modified amino acids tryptophan and tyrosine Peptide and protein – chains of amino acids transcribed from DNA Steroid – derived from the lipid cholesterol, hydrophobic, travel bound to a transport protein which extends half-life 17.2 – Pathways of Action Hormone receptor – a protein in or on the cell that binds to the hormone and initiates cellular mechanisms Receptor binds only to a certain shape hormone Response depends on the hormone and the target cell Hormone is considered a first messenger Hydrophilic hormones need a second messenger system, cAMP is most common and sometimes CA++ is used too 17.2 Intracellular hormone receptors – for lipid soluble hormones, binding inside the plasma membrane and moves toward the chromatin or binds in the nucleus, triggers transcription to mRNA and protein synthesis 17.2 Cell membrane receptors – hydrophilic hormones pass on message to a receptor on plasma membrane, G protein activates adenylyl cyclase enzyme which turns ATP into cAMP cAMP is the second messenger which activates protein kinase in cytosol which initiates a phosphorylation cascade to activate proteins cAMP deactivates quickly 17.2 – Factors Affecting Cell Response Downregulation – cells decrease receptors and become less reactive to excessive hormone levels Upregulation – cells increase their receptors and become more sensitive to hormones Permissive effect – 1 hormone enables another to act Synergistic effect – 2 hormones with similar effects amplify the cell’s response Antagonistic effect – hormones have opposing effects 17.2 – Regulation of Hormone Secretion Feed back loops – negative is more common then positive Chemical and neural stimuli can result in hormone secretion or inhibition 17.3 – The Pituitary Gland and Hypothalamus Command Receives center of the endocrine system info from endocrine and neural systems Part of the brain in the diencephalon, connects to pituitary through the infundibulum Posterior Anterior pituitary – neural tissue pituitary – glandular tissue 17.3 – Posterior pituitary Stores and secretes 2 hormones produced by the hypothalamus Oxytocin – stimulates uterine contraction and dilation of the cervix, receptors upregulate at the end of pregnancy Antidiuretic Hormone (ADH) – released due to high osmolarity, causes water reabsorption in the kidneys, can constrict blood vessels in very high concentrations 17.3 – Anterior Pituitary Does produce hormones, but only releases them in response to inhibiting or releasing hormones from the hypothalamus Hypophyseal portal system – connects anterior pituitary and hypothalamus through the infundibulum Responsible for 7 hormones 17.3 – Anterior Pituitary – Growth Hormone Anabolic, promotes protein synthesis and tissue building Stimulates lipolysis – more fatty acid in the blood for energy Stimulates liver to break down glycogen, more glucose in Stimulates liver to release insulin like growth factors (IGFs) the blood IGF – inhibits apoptosis, enhances cellular proliferation, and increases AA uptake for protein synthesis Gigantism, acromegaly, and pituitary dwarfism 17.3 – Anterior Pituitary Adrenocorticotropic Hormone (ACTH) – stimulates the adrenal cortex to secrete hormone (cortisol) Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) – regulate function of gonads FSH – stimulate production and maturation of sperm and ova, stimulate follicular growth in women LH – start ovulation and production of estrogen and progesterone, stimulates testosterone in males Prolactin – stimulate lactation, only during pregnancy 17.3 – Anterior Pituitary Thyroid-Stimulating secretion Hormone (TSH) – regulates thyroid gland 17.3 – Intermediate Pituitary Zone Melanocyte-Stimulating Hormone (MSH) – responsible for melanin production in response to UV light or pregnancy 17.4 – The Thyroid Gland Butterfly shaped organ anterior to the trachea Filled with sticky fluid called colloid – center of hormone production, needs iodine TSH causes cells to pull in iodide ions, the ions undergo oxidation (extra electrons are removed), iodine is linked to tyrosine (AA) Tyrosine attaches to 1 or 2 iodines, tyrosine then covalently bonds to form triiodothyronine (T3) or thyroxin (T4), we have more T4 17.4 – Thyroid Gland Less than 1% of T3 and T4 is free to cross into cells, the rest is bound to albumin or other plasma proteins and will be released as blood levels decline T3 is more potent than T4 Thyroid hormone influences metabolic rate, cause nutrient breakdown to produce ATP, increases body temperature, required for protein synthesis, development and growth, support neurological function, and increases sensitivity to epinephrine and norepinephrine High levels increase HR, BP, and contractility, 17.4 – Thyroid Gland Calcitonin – released by the thyroid to decrease blood calcium levels, functions are usually not significant in maintaining homeostasis Inhibits osteoclasts Increase osteoblast activity Decrease calcium absorption in intestines Increases calcium loss in urine 17.5 – Parathyroid Glands Normally gland 4 small round structures on the back of the thyroid Chief Cells – the functional cells that secrete parathyroid hormone (PTH) PTH will raise blood calcium levels by releasing calcium from bones, inhibits osteoblasts, increases Ca++ reabsorption in kidneys Stimulates production of calcitriol in kidneys – increases Ca++ absorption in intestines, antagonist to calcitonin 17.5 - PTH Hyperparathyroidism – weakens bones leading to fx and deformity, decreases response to nervous system due to cell membrane permeability to Na+ Hypoparathyroidism – increase permeability to Na+ leads to twitching, cramping, spasm, or convulsions. Can be fatal 17.6 – The Adrenal Glands Found on the superior kidney, a rich blood supply, 2 regions Adrenal cortex – outer aspect Adrenal medulla – inside region, extension of ANS Adrenal gland responds to physiological and psychological stress, 3 stages of stress reaction Alarm reaction – fight or flight, short term Stage of resistance – increase ability to respond to stressor Stage of exhaustion – depression, poor immune response, fatigue 17.6 – Adrenal Cortex 3 layers of lipid storing cells each producing a hormone Zona Glomerulosa – most superficial, produce mineralocorticoids like aldosterone (increase Na+, BP, and blood flow) Zona Fasciculata – middle region, produce glucocorticoids like cortisol (inhibit anabolism, break down stored nutrients to maintain fuel supplies, down regulate the immune system, agonist to aldosterone) the hippocampus has many glucocorticoid receptors Zona Reticularis – deepest, produces small amount of androgens, but most come from gonads 17.6 – Adrenal Medulla Produces epinephrine and norepinephrine (catecholamines) due to an acute response, fight or flight Converts glycogen to glucose Increase HR, BP, and pulse Dilates airways and prompts vasodilation to essential organs and vasoconstriction to other organs Down Dry regulates some aspects of immune system mouth, loss of appetite, pupil dilation, and loss of peripheral vision 17.6 – Adrenal Gland Disorders Cushing’s disease – hypersecretion of cortisol, high blood glucose with lipid deposits on face and neck (moon face, buffalo hump on back of neck, rapid weight gain, and hair loss) immunity and memory are impaired Addison’s disease – hyposecretion, low blood glucose and Na+ levels (general weakness, abdominal pain, weight loss, nausea, vomiting, sweating, and craving salty food) 17.7 – The Pineal Gland Inferior and posterior to thalamus Produces and secretes melatonin, derived from serotonin Production increases due to low light levels and melatonin causes drowsiness, influences circadian rhythms Circadian rhythm – sleepiness, wakefulness, appetite, and body temperature 17.8 – Gonadal and Placental hormones Testosterone – develop male reproductive system, mature sperm cells, and male secondary sex characteristics. Produced in testes and ovaries at a smaller level. Inhibin – inhibits secretion of FSH Estrogens – development of female reproductive system, regulate menstrual cycle, female secondary sex characteristics, and maintains pregnancy Progesterone pregnancy Placenta – regulates menstrual cycle and important in produces and secretes estrogens, progesterone, relaxin, human chorionic gonadotropin (hCG), and human placental lactogen (hPL) 17.8 Relaxin hCG hPL – softens the pubic symphysis to get ready for birth – protects the fetus from immune rejection – prepares breasts for lactation 17.9 – The Endocrine Pancreas Glucagon – from alpha cells, raise blood glucose levels (stimulates lipolysis, glycogenolysis, and gluconeogenesis) Insulin – from beta cells, decrease blood glucose levels, decrease lipolysis Somatostatin release Pancreatic – from delta cell, inhibits glucagon and insulin polypeptide hormone – from PP cell, plays a role in appetite and is also released while fasting 17.9 Glycolysis – break down of glucose to get ATP Glycogenolysis glucose for fuel – break down of glycogen to produce Gluconeogenesis Lipolysis acids – the liver converts AA to glucose for fuel – break down of stored triglycerides into free fatty Glycogenesis- storing glucose as glycogen 17.10 – Organs with Secondary Endocrine Functions Heart – atrial natriuretic peptide (ANP) decreases BP, blood volume, and blood Na+ levels GI Tract Gastrin - secreted by the stomach and stimulates the release of hydrochloric acid Secretin – from the small intestine which stimulates the release of bicarbonate from the pancreas Cholecystokinin (CCK) – from small intestine to stimulate pancreatic enzyme and gallbladder bile release Ghrelin – produced in the stomach to increase hunger Kidneys Renin – triggers the Renin-Angiotensin-Aldosterone system which will retain Na+ and water to increase BP and blood volume EPO – stimulates erythrocyte production in the bone marrow Calcitriol – regulates blood calcium levels, active form of vitamin D Adipose Tissue Leptin - binds to brain neurons to promote satiety after a meal and increase hunger (ghrelin) if levels are low, responds best to carbohydrate intake, affects TSH, FSH, and LH. Less leptin results in less dopamine (happy), exercise increases leptin sensitivity Skeleton Fibroblast Growth Factor 23 (FGF23) - will inhibit calcitriol formation and increase phosphorus excretion Osteocalcin – increases insulin production and increases sensitivity to glucose 17.10 Skin – cholecalciferol is the inactive form of vitamin D produced by cholesterol exposed to UV radiation Thymus – thymosins contribute to maturation and differentiation of T lymphocytes, thymus atrophies as we age Liver Hepcidin – blocks the release of iron from cells Insulin-like Growth Factor-1- immediate stimulus for growth especially bones Angiotensinogen Thrombopoietin – reacts with Renin to form angiotensin 1 – stimulates platelet production 17.11 – Development and Aging of the Endocrine System Comes from all 3 germ layers Human Growth Hormone, cortisol, and aldosterone production decline with age Menopause is associated with the decline of ovarian function and decrease of hormone levels Testosterone also decreases with age, but it rarely affects sperm production until very old age Thyroid gland decreases with age lowering metabolic rate Parathyroid increases with age which may contribute to osteoporosis 17.11 Insulin resistance seems to increase with age as 27% of Americans 65 and older have diabetes
