Endocrine System Lecture # 3

Transcription

1 Endocrine System Lecture # 3 Prof Kumlesh K. Dev Department of Physiology Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning Endocrine Lectures Thu 16th Apr hr Hormones basics on hormone signaling Fri 17th Apr hr Hormones II hypothalamus, pituitary, adrenal glands Mon 20th Apr hr Cancelled no lecture Thu 23rd Apr hr Hormones III thyroid, parathyroid, pineal glands Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning 1

2 What we cover? The 6 Glands Summary What we cover? The Hormones Summary regulating hormones Calcitonin Parathyroid hormone (PTH) Vitamin D Thyroid Gland Thyroid gland homones (T 3 /T 4 ) Calcitonin Pineal Gland Melatonin Androgens Testosterone Pancreas Insulin Glucagon Gastrointestine Serotonin many more 2

3 What we cover? The 6 Glands Summary Thyroid Gland Thyroid Thyroid Gland: front of upper part of trachea encapsulaed by a fiborous capsule develops from epithelial outgrowth of tongue TRACHEA Hormones Produced: Thyroxine (T 4 ) Triiodotyronine (T 3 ) Calcitonin in follicles in follicles by C cells Thyroxine (T 4 ) 3

4 T 3 and T 4 Hormones (1) Thyroid T4 & T3 are tyrosine-based hormones they control break down of carbohydrates & fats, synthesize proteins T4 contains 4 iodine atoms; T3 has one less T3 more effective, but T4 more abundant get carried by proteins in blood levels controlled by anterior pituitary lobe TSH (see later) only made by follicular cells when iodide available iodide actively absorbed from blood into thyroid follicles deficiency dietary iodine, thyroid enlarges to trap more iodine, i.e. goitre Goiter no T3/T4 made because not enough iodides ingested Hashimoto s disease autoimmune (autoantibodies destroy follicular cells) Hypothyroidism Symptoms of hypothyrodism Adults: low metabolic rate, cold sensitivity to, sluggishness Infants: stunted growth & bone formation, mental retardation Thyroid 4

5 Hyperthyroidism Thyroid high metabolic rate, hyperactivity, heat sensitivity, protruding eyes Grave s disease: when hyperthyroidism is due to an autoimmune problem (TSH is mimicked by autoantibodies) Treatments Beta blockers help some symptoms Anti-thyroid medications Radioactive iodine treatment destroys overactive thyroid cells Surgery thyroidectomy Which hormones alter Ca2+ levels? Three hormones regulate plasma concentration of Ca 2+ (and PO 4 3- ) Calcitonin (Thyroid gland) Parathyroid hormone (PTH) (Parathyroid gland) Vitamin D (cholecalciferol) Regulation of plasma Ca 2+ depends on hormonal control of exchange between ECF and Bone (most important in short-term) Kidneys Intestine 5

6 Physiological role of Muscle contraction Neurotransmitter release Blood clotting Intracellular signaling Proliferation Secretion Fertilization Cell motility Maintenance of tight junctions Structural integrity of bones and teeth Endocrine Control of Approx 1 kg in adult human 99% crystalline in bones and teeth 0.9% intracellular in soft tissues 0.1% in ECF bound to plasma proteins complexed with PO 4 3- freely diffusible: biologically active Plasma Ca 2+ : approx mmol/L Intracellular Ca 2+ : approx 100nmol/L 6

7 Why regulate plasma Ca2+? - to prevent aberrant neuromuscular excitability - Hypocalcemia overexcitability of nerves and muscles decreased free Ca 2+ causes increased Na permeability of cells severe overexcitability can cause fatal contractions of respiratory muscles - Hypercalcemia reduces excitability increased free Ca 2+ causes reduced Na permeability cardiac arrhythmia Calcitonin (2) calcitonin produced by C cells of thyroid gland negative-feedback fashion controlled by blood calcium levels and digested chemicals secreted in response to increase in plasma Ca 2+ concentration lowers plasma Ca 2+ and phosphate levels by inhibiting activity of bone osteoclasts stimulates secretion via kidneys unimportant except during hypercalcemia 7

8 Vitamin D (3) source of Vit D synthesized from cholesterol derivative when exposed to sun (inadequate source) amount supplemented by dietary intake activation of Vit D activated by liver and then by kidneys before it can exert its effect on intestines function of Vit D stimulates Ca 2+ and PO 4 3- absorption from intestine Parathyroid hormone (PTH) (4) small oval glands associated with thyroid embedded in thyroid capsule or thyroid normally 2 on each side (some have 5-6) PTH major controller of Ca2+ levels Calcitonin for fine adjustments trachea Principle cells secrete PTH in response thyroid to low blood Ca2+ PTH increases serum Ca2+ levels increases bone calcium release promotes kidney renal tubule reabsorption increases absorption from small intestine (involves Vitamin D parathyroid activation) essential for life: prevents fatal consequences of hypocalcemia 8

9 Feedback: PTH & Calcitonin Secretion Negative Feedback Disorders PTH hypersecretion hyper-parathyroidism characterized by hypercalcemia & hypophosphatemia PTH hyposecretion hypo-parathyroidism characterized by hypocalcemia & hyperphosphatemia Vitamin D deficiency Children rickets Adults osteomalacia 9

10 What we cover? The 6 Glands Summary Pineal Gland Melatonin (5) tiny, pinecone-shaped structure (~ 7 mm long) located in center of brain connected to hypothalamus by nerve fibers Melatonin produces Melatonin synthesised from serotonin (tryptophan) chief cells (modified neurons) secrete melatonin and serotonin pigments melanocytes regulates circadian rhythms (sleep) next slide plays a role in puberty & ageing acts as antioxidant to remove free radicals enhances immunity aged pineal has calcium and magnesium deposits maybe involved in schizophrenia (controversial) PINEAL GLAND 10

11 Circadian Rhythms Melatonin Suprachiasmatic nucleus (SCN) is body s master clock cyclic variations in protein concentrations in SCN causes cyclical neural discharge SCN set daily by activity levels driven by environment photoreceptors in retina transmit signals directly to SCN SCN relays message regarding light status to pineal gland this regulates Melatonin levels synthesis induced by darkness levels fall during daylight regulates circadian rhythms induces sleep (disrupted in jetlag) Anabolic Steroids Testosterone (6) Testosterone is best known anabolic steroid anabolic steroids: promote cell growth & division increase protein synthesis increase muscle mass and strength increase appetite increase bone remodeling and growth stimulate production of red blood cells Testosterone side effects of estrogen receptor activation: accelerated bone maturation in children elevated blood pressure & cholesterol levels mood change, acne, reduced sexual function, infertility, testicular atrophy, baldness 11

12 Pancreas Insulin & Glucagon (7-8) Insulin/Glucagon Pancreas has endocrine and exocrine functions! Islet of Langerhans rich blood supply for hormone drainage composed of ~3000 secretory cells surrounded by capsule scattered throughout pancreas β cells - insulin - promotes glucose uptake α cells - glucagon - opposite effect to insulin energy metabolism, growth and development Insulin is stored in granules in cytoplasm until secretion is triggered Endocrine Gastrointestine G.I.T. GIT neuroendocrine cells secrete many peptide & amine hormones Gastrin Secretin CCK Serotonin Somatostatin substance P vasoactive intestinal peptide (VIP) Bombesin Motilin Pancreatic polypeptide 12

13 What we cover? The Hormones Summary regulating hormones Calcitonin Parathyroid hormone (PTH) Vitamin D Thyroid Gland Thyroid gland homones (T 3 /T 4 ) Calcitonin Pineal Gland Melatonin Androgens Testosterone Pancreas Insulin Glucagon Gastrointestine Serotonin many more 13