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Transcript
Endocrine System Part 2 Thyroid • The thyroid is a gland in your neck, stimulated by the anterior pituitary’s release of TSH • The thyroid releases thyroxine which stimulates cells to increase metabolism • Thyroxine’s key ingredient is iodine, which is required in small doses for life – Hypothyroidism (less thyroxine) causes exhaustion and weight gain – Lack of iodine can cause hypothyroidism and a swelling of the thyroid (goiter) Protip: do NOT OD on iodine • Common reaction to discovery of metabolic properties of iodine: “Wow awesome I can take iodine and it will make me burn more calories!” – Yes, but… • Excessive intake of iodine can result in a thyroid storm, where all the internal organs are also in overdrive – Diet-based hyperthyroidism – Results in severe illness and possible death (and yes, weight loss) Calcium Management • The thyroid releases calcitonin, ostensibly to decrease calcium levels – Not clear whether its action is important • The thyroid also has small glands attached called the parathyroid glands – Four or eight small dots on the back • The parathyroid glands release parathyroid hormone or PTH PTH • PTH is released when blood calcium is low – Stimulates digestive system to absorb calcium – Stimulates kidneys to reabsorb calcium from urine – Stimulates osteoclasts to release calcium from bone • This is a big part of why calcium intake should be ongoing and not just once a week Glucose Management • Long-term metabolism is controlled by the pituitary gland (GH) • Medium-term metabolism is controlled by the thyroid (thyroxine) • Short-term metabolism is controlled by the pancreas – Releases hormones that manage glucose levels in the blood Why Glucose? • Recall that glucose is the energy source for all cells in the body – Neurons in particular absolutely must be nourished by glucose • Also recall that glucose is a polar (hydrophilic) molecule and so is “sticky” – No one wants to have their heart pump syrup through their arteries Insulin • The pancreas releases insulin whenever blood glucose gets high – Signals all cells to absorb additional glucose • This helps cells use and store energy – The liver produces more glycogen – Fat cells convert sugar to fat • If cells cannot absorb sugar then they cannot produce ATP and make things/move things – What do we call it when there is not an insulin signal to the cell? Insulin and Diabetes • Failure to release or receive insulin is called diabetes - Excessive sugar in the blood is called hyperglycemia and often results from diabetes • Type I diabetes results from a lack of insulin (usually damage to the pancreas by the immune system) • Type II diabetes results from excessive sugar intake, where cells become resistant to insulin signals via overuse Glucagon • The pancreas releases glucagon whenever blood sugar gets low – Stimulates fat and liver to release glucose into bloodstream • A deficiency of glucagon or excess of insulin can cause hypoglycemia – Critically low blood sugar causes crankiness followed by coma and death Gonads • The testes in men and ovaries in women are collectively referred to as gonads – AKA “the ‘nads” – Produce gametes (sperm & eggs) for babymaking • Produce sex hormones testosterone, estrogen and progesterone – Stimulated to do so by FSH and LH from the anterior pituitary Effects of Sex Hormones • Sex hormones promote production of gametes and development of gonads • Sex hormones also promote secondary sexual characteristics, especially after puberty – Men: facial/chest hair, Adam’s apple – Women: Breast development, wider hips – Men and women: pubic and axillary hair, production of sebum, actual interest in sex • What part of the brain do you think the sex hormones affect? Bonus Hormones • Erythropoietin (EPO) is a hormone released by the kidneys in response to low blood oxygen – Increases production of red blood cells • Two hunger hormones act against each other: – Leptin is produced by fat cells and lowers hunger – Ghrelin is produced by the intestines that stimulates hunger (mimicked by marijuana) • Human Chorionic Gonadotropin (hCG): Pregnancy hormone produced by the placenta that blocks menstruation – Tested for in pregnancy test Negative Feedback Loops! • Body temperature falls: TSH increased, thyroxine increased, body temperature increases, TSH inhibited • Glucose goes high: insulin released, glucose goes down, insulin inhibited • Glucose goes down: glucagon released, glucose goes up, glucagon inhibited • Calcium goes down: PTH released, calcium goes up, PTH inhibited • Also note that injecting steroids into the body will register as testosterone levels, causing an excess to cause the testes to shrivel in response