D3.3 Homeostasis PDF

# D3.3 Homeostasis: ## SL: * Homeostasis: Maintaining a constant internal body environment. * **Examples**: * Blood glucose concentration * Blood osmotic concentration * Blood pH * Body Temperature * Multicellular organisms have an advantage that the internal environment between cells ca...

# D3.3 Homeostasis: ## SL: * Homeostasis: Maintaining a constant internal body environment. * **Examples**: * Blood glucose concentration * Blood osmotic concentration * Blood pH * Body Temperature * Multicellular organisms have an advantage that the internal environment between cells can be regulated. * **Feedback**: Using information about the outcome of a process to make decisions about the future of that process. * **Positive feedback**: Increases the gap between the original and the new level. * **Negative feedback**: Decreases the gap, so the original level is restored. (achieve balance) * **Study figure 3 page 722** ## Negative feedback mechanisms form the basis of homeostasis control systems. (reach stability) ## Positive feedback is not common in the human body (promotes change rather than stability) # Regulation of Blood Glucose: * **Set point for glucose concentration is 5mmol/dm³** * **Homeostasis mechanisms are mediated by insulin and glucagon. (figure 5 page 723)** * **Pancreas is considered as both exocrine and endocrine gland** * **Exocrine**: Glands with ducts (digestive enzymes to the small intestine) * **Endocrine**: Ductless glands with special tissue called islets of Langerhans (secrete hormones directly to the bloodstream) # *There are 2 types of cells:* * **Alpha cells (α cells)**: Secrete glucagon when the blood glucose level falls below the set point. * **Glycogen Glucagon Glucose released into the blood from liver** * **Beta cells (B cells)**: Secrete insulin when blood glucose concentrations rise above the set point. * **Glucose Insulin Glygogen** * **Stimulates uptake of glucose by many target cells (muscles and liver).** # *Diabetes: The condition in which a person has consistently elevated blood glucose levels even during fasting.* * **Leads to presence of glucose in urine.** * **Causes damage to tissues.** * **Impairs water reabsorption during urine production in the kidney (greater loss of water in urine therefore dehydration)** * **If a person is constantly thirsty, needs to urinate more frequently, feels tired, and craves sugary drinks, test for glucose to check if they have developed diabetes.** # 2 types of diabetes: * **Type 1 diabetes (early onset diabetes):** Autoimmune disease arising from damage of B cells in the islets of Langerhans resulting in the inability to produce sufficient insulin. * **Type 2 diabetes (late onset diabetes):** Inability to process or respond to insulin due to deficiency of insulin receptors/glucose transporters on target cells. (slow onset) * **Causes: Not fully understood** * **Main risk factors: Sugary/fatty diets, obesity, lack of exercise, genetic factors** # Treatment for Diabetes: ## Type 1 Diabetes * Testing blood glucose concentration regularly. * Injecting insulin when it's too high (before a meal) - prevents a peak of blood glucose. * Timing is very important. * New implanted devices release insulin into the blood when necessary. * Permanent cure: Using stem cells that may become fully functional replacement of beta cells. ## Type 2 Diabetes * Adjusting the diet to reduce peaks of blood glucose. * Eating small amounts of food frequently. * Avoid eating foods with high sugar content. * High-fibre foods should be included to slow the digestion of other foods. * Exercise and weight loss are beneficial as they improve insulin uptake and action. # *Thermoregulation (example of negative feedback)* * Control of core temperature to keep it close to set point (human set point: 37°C) * **Negative feedback**: * If body temperature falls below set point - increase heat generation (reduce heat loss) * If body temperature rises above set point - increase heat loss. * Thermoreceptors: Nerve endings in specialized sensory neurons that monitor body temperature. * **Cold Thermoreceptors** * **Warm Thermoreceptors** * Thermoreceptors: * **Peripheral**: Located in the skin (external temperatures) * **Central**: Located in the core of the body (in the hypothalamus) * **Hypothalamus**: Part of the brain that monitors body temperatures using sensory inputs from both peripheral and central thermoreceptors, and initiates responses (hypothermia, hyperthermia) to bring back temperature to set point. # Heat (generated by metabolic reactions). * **Metabolic rate < increased/decreased** by either raising or lowering amount of heat generated. * **Increase Metabolic Rate**: Hypothalamus secretes thyrotropin releasing hormone (TRH) * **TRH** moves to pituitary gland causing release of thyroid stimulating hormone (TSH) * **TSH** stimulates thyroid gland (in neck) to secrete thyroxin. * **Thyroxin** increases metabolic rates, mostly in liver, muscles, brain cells. # *Thermoregulation mechanisms in humans:* * Humans can regulate their body temperatures (also birds, mammals (other than humans) ## Responses to cold * Vasoconstriction * Shivering * Uncoupled respiration * Hair erection ## Responses to heat * Vasodilation * Sweating * **Study in details table 1 page 727** * **Read (Modeling heat loss) page 728** # HL: # *Kidneys and Osmoregulation:* * Osmoregulation: Part of homeostasis that maintains osmotic (water) concentration of body fluids within normal limits. * **Osmotic concentration**: Overall concentration of the solutes in the fluid (controlling water content and pressure of cells). * **Kidneys carry out osmoregulation by controlling amounts of water and salts that are removed from the body in urine** * **Excretion**: Removal of toxic waste products from the body. * **Nitrogen-containing compounds (urea)** * **Kidneys also remove extra substances that were absorbed from food and are not used by the body -> drugs, pigments from food** # *Structure of the kidney: (figure 21 page 733)* * **renal artery** * **Cortex** * **Medulla** * **Pelvis** * **Ureter** * **Renal vein** * **Kidney is made up of basic functional units called nephrons.** # *Structure of a nephron: (figure 14 page 729)* * **Glomerulus** * **Afferent arteriole** * **Efferent arteriole** * **Bowman's capsule** * **Proximal convoluted tubule.** * **Loop of Henle** * **Vasa recta** * **Medulla** * **Cortex** * **Distal convoluted tubule** * **Collecting duct** * **Study the parts/functions of the nephron from figure 14 page 729** # *Kidneys work to clean blood from waste products, mainly Urea, by producing urine.* * **Urea** made in liver during a process called deamination (breaking down excess amino acids). **Ammonia (NH₃ ) converted to Urea** * **Ultrafiltration: (first step of producing urine)** * **Takes place in Bowman's capsule and glomerulus.** * **Glomerulus**: Ball shaped network of blood capillaries where blood flows into it by the afferent arteriole and leaves using efferent arteriole then continues on to other capillaries in the kidney. * **Fluid is filtered out of the blood capillaries to produce tissue fluid (which most of it passes back to the capillaries)** * **Blood pressure is high and walls of capillaries are permeable for that reason much larger proportion of the blood plasma is filtered out** * **Afferent arteriole is wider in diameter than the efferent arteriole.** * **Walls of capillaries are highly permeable due the presence of pores called fenestrations that help in the filtration process.** * **The filtered fluid is called glomerular filtrate. (most filtered molecules are small in seize and almost most proteins and blood cells remain in the blood).** * **Study figure 15 page 730.** * **Filter unit has 2 layers:** * **Basement membrane**: Non-cellular gel made of negatively charged glycoproteins that are cross-linked forming a mesh. It prevents plasma proteins from being filtered out. * **Inner wall of Bowman's capsule that consists of outgrowths branching cells called podocytes.** * **Podocytes**: Supportive, foot-shaped, modified cells of the capsule wall that form a network of slits, where filtrate passes through them to the capsule. * **Total volume of glomerular filtrate per day is 180 litres!! But the volume of urine produced per day is only about 1.5 litres.** # *Selective reabsorption: (second step of producing urine)* * **Most of the water and minerals in the filtrate will be reabsorbed to blood capillaries from the filtrate and all of the glucose and amino acids will be reabsorbed.** * **Proximal convoluted tubules is where most reabsorption takes place as follows:** * **Sodium ions**: By active transport/pump proteins. * **Chloride ions**: By charge gradient set up by active transport of sodium ions. * **Glucose**: By cotransporter proteins. * **Water**: By osmosis. * **See figure 17 page 731** * **See figure 19 page 732** # *Role of loop of Henle:* * **Loop of Henle is located in the medulla of the kidney.** * **In the medulla, the concentration gradient starts at 300 mOsm (milliosmoles) near the cortex and rises to 1200 mOsm near the centre of the kidney. See figure 22 page 733** * **The role of the loop of Henle is to maintain the osmotic concentration gradient in the medulla.** * **Filtrate enters the loop of Henle from the proximal convoluted tubule into the descending limb, water molecules leave the descending limb due to the walls being permeable to water (contain many aquaporins) resulting in a more hypertonic filtrate with higher solute concentration** * **As for the ascending limb solutes (Na+) ions start leaving through sodium pumps** * **The filtrate reaching distal convoluted tubules has solute concentration lower than the normal body fluids (hypotonic)** # *Osmoregulation:* * **Filtrate entering the distal convoluted tubules is hypotonic (100 mOsm), number of aquaporins in the distal convoluted tubules can differ (by removing them from the membranes) resulting in unusually low permeability of water** * **Hypothalamus monitors the osmotic concentration of the blood.** * **If osmotic concentration is too high**: * **Hypothalamus causes pituitary gland to secrete (ADH) antidiuretic hormone.** * **More aquaporins to be moved to the plasma membranes in the distal convoluted tubules and collecting duct** * **Increasing their water permeability** * **More reabsorption of water to blood/less water in urine** * **If osmotic concentration is too low**: * **Hypothalamus causes pituitary gland to stop secreting ADH.** * **Less aquaporins leading to less permeability of membranes to water** * **Less reabsorption of water to blood** * **More water in urine** * **At the end of collecting duct, the filtrate is now called urine and moves to pelvis of kidneys to move through the ureters to the urinary bladder.** * **Study table 4 page 736**