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Transcript
Endocrine System Topic 16 I. Endocrine System A. the endocrine system and nervous system work together to coordinate the activities of the body B. the endocrine system is a network of glands and tissues that secrete hormones which are chemical messengers that are made in one place and carried by the blood to act on another part of the body C. compared to the nervous system, the signals of the endocrine system take longer but will last longer D. two types of hormones – steroid and peptide hormones 1. peptide hormones are large, hydrophilic, charged and cannot diffuse across the plasma membrane – the receptors for these hormones are found on the surface of the target cell and causes it to transmit a signal into the cell’s interior – can be used to turn on a protein kinase that phosphorylates certain proteins and changes their activity – or they can be used to release secondary messengers in the cell that amplify the signal and alter cell activities – this type of indirect signaling is called signal transduction cascade 2. steroid hormones – small and hydrophobic – most come from cholesterol, including estrogen, progesterone, testosterone, and cortisol – they can diffuse through the cell membrane – these bind to steroid hormone receptors after they have diffused into the cell through the plasma membrane – the receptors and hormones enter the nucleus and bind to the target regions in genes that regulate transcription turning the genes on and off E. Endocrine glands 1. hypothalamus – section of the posterior forebrain – located above the pituitary gland - releases hormone-like substances called releasing factors into the anterior-pituitary hypothalamic portal circulatory system which triggers the anterior pituitary to secrete the hormone indicated by the releasing factor 2. pituitary gland – small gland with two lobes lying at the base of the brain – the two lobes (anterior and posterior) function as independent glands (a) anterior pituitary gland (1) Growth horomone – growth of long bones (2) thyroid stimulating hormone (TSH) – stimulates the thyroid to secrete thyroxine (3) adrenocorticotrophic hormone (ACTH) – stimulates the adrenal cortex to secrete corticoids (4) prolactin – responsible for milk production by the female mammary glands (5) follicle stimulating hormone – FSH – spurs the maturation of seminiferous tubules in males and encourages maturation of follicles in the ovaries (6) luteinizing hormone – LH – induces the cells of the testes to mature – in females, stimules ovulation (b) posterior pituitary (1) ADH – vasopressin – acts on the kidney to reduce water loss (2) oxytocin – acts on the uterus during birth to cause uterine contraction 3. thyroid gland – produces thyroxine ( a modified amino acid) which accelerates metabolism throughout the body – too little thyroxine (hypothyroidism) causes goiter, decreased heart rate, lethargy, obesity, and decreased mental alertness – too much thyroxine (hyperthyroidism) causes profuse sweating, high body temperature, increased metabolism, high blood pressure, loss of weight, and irritability 4. parathyroid glands – small – located on the posterior surface of the thyroid – secrete parathyroid hormone (parathormone) – regulates the calcium and phosphate balance between the blood, bone, and other tissues – increased parathyroid hormone increases bone formation 5. pancreas – has an exocrine and an endocrine function (a) exocrine – secretes enzymes through ducts into the small intestine (b) endocrine – secretes hormones into the blood stream – islets of Langerhans – secrete glucagon and insulin (1) insulin – stimulates cells to remove glucose from the blood (2) glucagon – stimulates the breakdown of glycogen into glucose 6. Adrenal glands – found on top of the kidneys – made of the adrenal cortex and the adrenal medulla (a) adrenal cortex – responds to stress – ACTH stimulates the adrenal cortex to synthesize and secrete the steroid hormones known as corticosteroids (1) glucocorticoids – cortisol and cortisone – involved in glucose regulation and protein metabolism, increase blood glucose levels, reduces the body’s inflammatory responses (2) mineralocorticoids – aldosterone – regulates plasma levels of sodium and potassium – water volume (3) androgens – male sex hormones (b) adrenal medulla – secret hormones into circulatory system – produces epinephrine (adrenaline) and norepinephrine (noradrenaline) – both come from a class of amino acids called catecholamines (1) epinephrine – increases glycogen to glucose in liver and muscle tissue which causes a rise in blood gluocse levels and an increase in metabolism (2) norepinephrine – along with epinephrine, increase the rate and strength of the heartbeat, and dilate and constrict blood vessels which increases the blood supply to skeletal muscle, the heart and brain – while decreasing the blood supply to the kidneys, skin, and digestive tract – this is the “fight or flight” response 7. ovaries and testes (a) testes – testosterone (b) ovaries – estrogen and progesterone How the endocrine system works endocrine system feedback mechanism pancreas, insulin, and glucagon