Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Endocrine System Types of Signaling Molecules • Hormones • Local Regulators - reach target cells solely by diffusion • Neurotransmitters/Neurohormones - utilize neurotransmitters • Pheromones - released into the external environment Hormones • Secreted into extracellular fluid, reach target cells through bloodstream • Secreted by endocrine glands Signaling Pathways • Endocrine Signaling – Secreted molecules diffuse into blood stream and trigger response in cells throughout the body • Paracrine Signaling (Local Regulators) – Molecules diffuse locally and trigger response in nearby cells • Synaptic Signaling – Neurotransmitters diffuse across a synapse and trigger response of target cell tissue Signaling Pathway Continued • Autocrine Signaling (Local Regulators) – Secreted molecules diffuse and trigger a response in the cells that secrete them • Neuroendocrine Signaling – Neurohormones diffuse into bloodstream and trigger responses in target cells throughout the body Chemical Classes of Hormones • Polypeptides - made up of polypeptide chains, formed by cleaving longer proteins, water-soluble • Steroid - fused lipid, non-polar, lipidsoluble • Amine - synthesized from a single amino Cellular Response Pathways • Receptor location differs between water-soluble and lipid-soluble • Water-soluble are secreted by exocytosis and bind to cell surface receptors • Lipid-soluble diffuse across the membrane Once Inside the Cell • Water-soluble hormones attach to the receptor which responds via signal transduction (G protein-coupled receptors, cAMP, second messenger) Lipid-Soluble Hormones • Intracellular receptors bind to the hormone, creating a hormone-receptor complex • HRC moves into the nucleus where it interacts with the DNA, stimulating transcription Multiple Effects of Hormones • effects by a certain hormone vary when target cells differ in the molecules that receive them •For example epinephrine can: - trigger glycogen breakdown in liver - increase blood flow to skeletal muscles - decrease blood flow to digestive tract •Tissues vary in their responses due to the different receptors or signal transduction pathways - epinephrine receptor of a liver cell is called a beta receptor, intestinal blood vessels have an alpha-type epinephrine receptor • Lipid soluble hormones have different effects, too - estrogen in birds stimulates the liver to synthesize the yolk protein but it also stimulates the reproductive system to synthesize proteins that make the egg white. • Sometimes a hormone has different effects in different species - thyroxine regulates metabolism in humans and other vertebrates (frogs) but it does extra in frogs: fuels resorption of the tadpole’s tail when morphing into an adult Signaling by Local Regulators • Act similarly to hormones • Chemical compounds function as local regulators: •Cytokines- role in immune responses •Growth factors- stimulate cell proliferation and differentiation, ensure normal cell development • Nitric oxide- both neurotransmitter and local regulator, allows for male erection • Prostaglandins- modified fatty acids, help sperm reach egg and help induce labor by stimulating smooth muscles of uterus •In immune system: promote fever and inflammation, intensify pain sensation • a loop where the response to stimuli is reduced •Prevents excessive pathway activity by getting rid of hormone signaling • important in maintaining homeostasis Some Results from the Hormone Pathways • signal transduction within target cells brings a physiological response • The response reduces the stimulus and the pathway will end • example: low pH in small intestine (duodenum) triggers endocrine cells to secrete secretin cells. They enter the bloodstream, go to pancreas, which releases bicarbonate therefore raising the pH this is self limiting because the response to secretin (bicarbonate) reduces the stimulus (pH) • blood glucose [ ] controls metabolic rate, it is critical to keep levels near set point • Hormones glucagon and insulin regulate [ ] of glucose in the blood • both produced in the pancreas • insulin released to trigger the uptake of glucose from the blood when blood glucose levels rise above normal level • glucagon promotes the release of glucose into the blood when blood glucose drops below set point • insulin lowers blood glucose levels by stimulating all cells outside of brain to take up glucose from the blood • also decreases rate of glycogen breakdown in the liver • glucagon influences levels b/c of effects on target cells in the liver • the liver, skeletal muscles, and adipose tissues store fuel , liver stores sugar as glycogen (only the liver is sensitive to glucagon) • when glucose set point is low, glucagon triggers liver cells to boost glycogen hydrolysis and convert a.a. and glycerol to glucose bloodstream back to normal level (see nest slide) Coordination of Endocrine and Nervous Systems • The hypothalamus receives messages received from the nervous system and responds • Sends excretory messages to posterior and anterior pituitary glands Posterior Pituitary • Grows as extension of the hypothalamus • Secretes oxytocin and antidiuretic hormone (ADH) – Oxytocin stimulates production of milk release – ADH promotes kidney water retention • Uses endocrine signaling Anterior Pituitary • Hormones released by hypothalomous regulate anterior pituitary secretions • Each hormone is either a releasing hormone or an inhibiting hormone • Secreted near capillaries at base of hypothalamus Tropic Hormones • Hormones that regulate the function of endocrine glands or cells Nontropic Hormones • Hormones that target nonendocrine tissues • Prolactin - stimulates mammary glands • Melanocyte Stimulating Hormone regulates pigment Thyroid Gland: Metabolism and Development • Thyroid Hormone- pair of similar hormones from amino acid tyrosine: Triidothyronine (T3) and thyroxine (T4) – Regulates bioenergetics, helps maintain normal blood pressure, heart rate, muscle tone, regulates digestive and reproductive functions • Thyroid gland- in mammals, two lobes on the ventral surface of the trachea • All vertebrates require thyroid hormones for normal functioning of bone-forming cells and branching of nerve cells during embryonic development of brain Parathyroid Glands: Control of Blood Calcium • Calcium essential to normal functioning of cells • Parathyroid glands- four small structures embedded in posterior surface of the thyroid – Release PTH (parathyroid hormone) when Ca2+ levels fall below set point of 10mg/100mL – PTH raises Ca2+ levels directly and indirectly – If Ca2+ rises above set point, calcitonin released from thyroid gland • Calcitonin is hormone that inhibits bone resorption and enhances Ca2+ release by kidney Adrenal Glands: Response to Stress • In mammals, two glands with different cell types, functions, embryonic origins: – Adrenal Medulla(central): “fight or flight” response, releases 2 hormones, epinephrine (adrenaline) and norephinephrine (noradrenaline) • both increase glycogen breakdown by liver cells and stimulate release of fatty acids from fat cells- increase available chemical energy • Catecholamines-class of amine hormones • Also increase blood supply to heart, brain, skeletal muscles – Adrenal Cortex(outer): responds to endocrine signals, stressful stimuli causes hypothalamus to release that stimulates anterior pituitary gland to release hormone ACTH • When ACTH reaches cortex, stimulates endocrine cells to secrete family of steroids called corticosteroids, 2 types in humans: – glucocorticoids- glucose metabolism, promote glucose synthesis from noncarbohydrate sources (ex. Proteins) – Mineralocorticoids- mainly work in maintaining salt and water balance Gonadal Sex Hormones • Most released from testes of males and ovaries of females (gonads) – Produce/secrete 3 major categories of steroid hormones: • Androgens- mainly testosterone, main role at puberty, responsible for development of human male secondary sex characteristics • Estrogens- most important is estradiol, maintenance of female reproductive system and development of female secondary sex characteristics • Progestins- include progesterone, mostly prepare and maintain tissues of the uterus Pineal Gland: Melatonin • Pineal Gland- small mass of tissue near the center of the mammalian brain – Synthesizes and secretes hormone melatonin, a modified amino acid • Primary function relates to biological rhythms associated with reproduction • Secreted at night, amount released depends on length Diseases • Hyperthyroidism: excessive secretion of thyroid hormone, most common form is Graves’ disease – Autoimmune, immune system produces antibodies that bind to the receptor for TSH and activate continued thyroid hormone production – Often proturding eyes from fluid accumulation behind eyes • Hypothyroidism: often weight gain, lethargy, intolerance to cold in adults – Congenital: inherited, results in retarded skeletal growth and poor mental development, can be prevented, if treated with thyroid hormones early in life • Tetany: calcium levels fall, potentially fatal, skeletal muscles begin to contract convulsively • a disruption of glucose homeostasis can lead to serious effects on the heart, blood vessels, eyes, and kidneys • Diabetes Mellitus can be a result -caused by a insulin deficiency or reduced response to insulin in target tissues - blood glucose levels rise, but cells unable to take up enough glucose to meet metabolic requirement -Fat becomes main substrate for cell resp., can form acidic metabolites that clump in the blood, lowering pH and killing Na and K ions life threatening - too much glucose in blood for kidneys to reabsorb, the glucose is excreted (way to test if one has it) • Type 1 Diabetes: -insulin-dependent - immune system destroys the beta cells of the pancreas -destroys persons ability to make insulin, therefore it needs to be injected, no cure yet (want to find replacement beta cells) • Type 2 Diabetes - non-insulin-dependent - insulin is produced but target cells fail to take up glucose from the blood so the levels remain high -genetic or if overweight • Growth Disorder: -there is growth hormone (GH) which is secreted by the anterior pituitary gland and it stimulates growth. -The liver responds to GH by letting go insulin-like growth factors that directly fuel bone and cartilage growth •An absence of GH: skeleton stops growing in immature animals. In humans, there can be too much GM or too little. -hypersecretion-too much, leads to gigantism, about 8 - hyposecretion- growth hormone deficiency, too little, properly proportioned but only about 4 feet tall, grow slower, pituitary dwarfism, treatment if diagnosed before puberty ("Endocrine System Diseases: Cushing's Syndrome, Addison's Disease and More.“, 1. ) • Osteoporosis: -a condition where bones become fragile and are likely to break very easily - due to lack of estrogen or testosterone (which increases bone absorption), malnutrition, but also… - inadequate intake of calcium and Vitamin D - not enough calcium from diet results in weak bones that are brittle -PTH is made when Ca+ in blood is too low. If too much PTH produced, bones continue to release calcium into blood, therefore they have will have too littleweak -low Vitamin D levels: it helps small intestine absorb calcium, without it they have a hard time doing so. (“Parathyroid Function: How Parathyroid Glands Work, HowParathyroids Make Parathyroid Hormone and Control Calcium in Bones and Blood.“, 1) • http://www.youtube.com/watch?v=rS7SM4 vzs18 • http://www.youtube.com/watch?v=eyO8Di m3T3U&NR=1