Endocrine System Wrap-up Lecture PDF

1 College of Medicine and Dentistry Endocrine system Wrap-up lecture Dr Doris Pierce 2 Endocrine pancreas 3 Endocrine pancreas – Cells and secretions • Pancreatic islets (previously islets of Langerhans) secrete glucagon, insulin, somatostatin, and pancreatic polypeptide (PP) • Alpha cells –...

1 College of Medicine and Dentistry Endocrine system Wrap-up lecture Dr Doris Pierce 2 Endocrine pancreas 3 Endocrine pancreas – Cells and secretions • Pancreatic islets (previously islets of Langerhans) secrete glucagon, insulin, somatostatin, and pancreatic polypeptide (PP) • Alpha cells – release glucagon in response to low blood glucose • Beta cells – release insulin in response to high blood glucose • Delta cells – release somatostatin which inhibits glucagon and insulin release OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/17-9-the-endocrine-pancreas. Creative Commons Attribution 4.0 International License. • PP cells – release PP which plays a role in appetite and regulation of pancreatic secretions 4 Endocrine pancreas – Regulation of blood glucose Insulin • Release triggered by gastrointestinal tract hormones in the presence of food and further stimulated by rising blood glucose levels • Primary targets are skeletal muscle and adipose tissue cells – require insulin for glucose uptake • No insulin receptors on red blood cells and cells of brain, liver, kidneys, and lining of the small intestine – do not require insulin for glucose uptake Luuis12321. https://commons.wikimedia.org/wiki/File:Signal_Transduction_Diagram-_Insulin.svg. This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. • Appears to trigger multiple biochemical reactions that result in rapid movement of glucose transporter vesicles to cell membrane, where they facilitate glucose into cell 5 Endocrine pancreas – Regulation of blood glucose • Facilitates uptake of glucose from the blood and stimulates glycolysis, lowering blood glucose levels • Stimulates glycogenesis in liver and skeletal muscle and inhibits enzymes involved in glycogenolysis and gluconeogenesis • Promotes triglyceride and protein synthesis Insulin Glycolysis - the metabolic pathway that converts glucose into pyruvate in the cytosol Glycogenesis - the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage; opposite of glycogenolysis 6 Endocrine pancreas – Regulation of blood glucose Glucagon • Release triggered by falling blood glucose levels • Stimulates gluconeogenesis, glycogenolysis, and the release of glucose into the circulation, raising blood glucose levels Gluconeogenesis • Stimulates fat catabolism and release of free fatty acids from adipose tissue (lipolysis) – glycerol converted to glucose in liver • Stimulates the liver to take up amino acids from the blood and convert them into glucose Glycogenolysis • Stimulates the liver to convert its stores of glycogen back into glucose and release glucose into blood Gluconeogenesis - The process of making glucose from its own breakdown products or from the breakdown products of lipids or proteins. Glycogenolysis - the release of glucose 6-phosphate from glycogen stores; can occur in both liver and skeletal muscle but under two different conditions 7 Glucagon and insulin feedback loop (Bich et al., 2020) 8 Other glands 9 Pineal gland • Functions not entirely clear • Pinealocytes produce and secrete the amine hormone melatonin (derived from serotonin) • Melatonin secretion dependent on light level • Daylight - production is inhibited – low blood melatonin levels promote wakefulness • Declining light levels - production increases, boosting blood levels and causing drowsiness 黄雨伞. https://commons.wikimedia.org/wiki/File:Suprachiasmatic_Nucleus.jpg. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. 10 Gonadal hormones - Males • Primary hormone produced by testes is testosterone • Important in development of reproductive system, maturation of sperm, and development of secondary sex characteristics e. g. deepened voice, body hair, and increased muscle mass • Anabolic steroid use can have feminising effect in males, including shrivelled testicles and enlarged breast tissue and masculinising effects such as growth of facial hair. • Testes also produce the peptide hormone inhibin - inhibiting FSH Artoria2e5. https://commons.wikimedia.org/wiki/File:Hypothalamic%E2%80%93pituitary%E2% 80%93gonadal_axis.svg. This file is licensed under the Creative Commons Attribution 3.0 Unported license. 11 Gonadal hormones - Females • Primary ovarian hormones are oestrogens (oestradiol, oestriol, and oestrone) • Oestrogens important in development of female reproductive system and secondary sex characteristics, regulation of menstrual cycle, and development and maintenance of pregnancy • Progesterone - contributes to regulation of menstrual cycle and important in preparing for and maintaining pregnancy • Also, low levels of testosterone Artoria2e5. https://commons.wikimedia.org/wiki/File:Hypothalamic%E2%80%93pituitary%E2% 80%93gonadal_axis.svg. This file is licensed under the Creative Commons Attribution 3.0 Unported license. • Ovarian follicles produce inhibin – inhibiting FSH secretion 12 Placental hormones • Oestrogens and progesterone • Human chorionic gonadotropin (hCG) - promotes progesterone synthesis and reduces mother’s immune function to protect the fetus from immune rejection • Human placental lactogen (hPL) plays a role in preparing the breasts for lactation • Relaxin – though to help soften and widen the pubic symphysis in preparation for childbirth Osmosis. https://commons.wikimedia.org/wiki/File:Pregnancy_hormone_graph.png. This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. 13 Organs with endocrine function 14 Organs with endocrine function GI system Heart • • Increase in blood volume or pressure triggers stretch in heart’s atrial wall cells → specialised atrial wall cells produce and secrete atrial natriuretic peptide (ANP) aids in decreasing blood pressure, blood volume, and blood sodium levels Fruehaufsteher2. https://commons.wikimedia.org/w/index.php?search=heart+gif&title=Special:MediaSearch&go=Go&type=ima ge. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. • • Gastrin - secreted in response to stomach distention - stimulates release of hydrochloric acid Secretin - stimulates release of bicarbonate from pancreas - buffers acidic chyme and inhibits further hydrochloric acid secretion by stomach Cholescystokinin (CKK) - promotes secretion of pancreatic enzymes and release of bile from gallbladder, facilitating digestion McortNGHH. https://commons.wikimedia.org/wiki/File:Effects_of_CCK_on_the_gastrointestinal_tract.svg. This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. 15 Organs with endocrine function cont. Kidneys • Play a role in regulating blood calcium levels via calcitriol production from vitamin D3, released in response to PTH secretion (PTH) • Produce erythropoietin (EPO) in response to low oxygen levels - stimulates production of red blood cells in bone marrow, thereby increasing oxygen delivery to tissues Roxbury-de. https://commons.wikimedia.org/wiki/File:Gray1120-kidneys.png. ublic domain. This applies worldwide. Adipose tissue • Leptin - produces feeling of satiety after a meal, thereby reducing appetite - also appears to trigger increasing deposition of cortical bone • Adiponectin - appears to reduce insulin resistance and protect blood vessels from inflammation and atherosclerosis - lower in obese people and rise following weight loss FatTeen97. https://commons.wikimedia.org/wiki/File:Excess_adipose_tissue.jpg. Public domain. This applies worldwide. 16 Organs with endocrine function cont. • Skeleton - bone produces at least two hormones - fibroblast growth factor 23 and osteocalcin • Skin - produces the inactive form of vitamin D3, cholecalciferol • Thymus - larger and more active during infancy and early childhood and begins to atrophy as we age; produces thymosins that contribute to development and differentiation of T lymphocytes • Liver - secretes at least four important hormones or hormone precursors: insulin-like growth factor (somatomedin), angiotensinogen, thrombopoietin, and hepcidin 17 Endocrine system aging May affect production, secretion, and catabolism of hormones • e. g. decreased vascularisation and increased connective tissue in anterior pituitary gland affects hormone production such as GH → declines with age, resulting in reduced muscle mass (atrophy) common in elderly • Reduced oestrogens and progesterone in women (menopause) and testosterone in men (andropause) • Increased parathyroid hormone combined with decreased levels of calcitonin (and oestrogens in women) → osteoporosis as PTH stimulates demineralisation of bones to increase blood calcium • Reduced production of thyroid hormones, causing a gradual decrease in the basal metabolic rate → reduced production of body heat and increased levels of body fat 18 Practice Questions 19 References • Bich, L., Mossio, M., & Soto, A. M. (2020). Glycemia regulation: From feedback loops to organizational closure [Conceptual Analysis]. Frontiers in Physiology, 11. https://doi.org/10.3389/fphys.2020.00069 • Anatomy & Physiology. Provided by: OpenStax CNX. Located at: http://cnx.org/contents/[email protected]. License: CC BY: Attribution.