Homeostatic Regulation A hormone is :a Water-soluble hormones: Composed of amino acids and bind a receptor protein on the of the target cell. This starts a signal cascade inside the cell and the signal is amplified. A single molecule of epinephrine can cause conversion of glycogen into about one million molecules of glucose. WS hormones can travel freely in the blood because they "like" water. However, they are repelled by lipid or fatty structures Examples include : Steroid hormones Receptors are located within the cytoplasm of the target cell. To bind their receptors, these hormones must cross the cell membrane. They can do so because they are lipid-soluble. Generally synthesized from cholesterol. Example Hormonal Regulation Design a negative feedback loop Page 1 of 7
For Thyroxin: Thyrotropin-releasing hormone (TRH) stimulates the release of TSH (thyroid-stimulating hormone) and prolactin from the anterior pituitary. Thyroid-stimulating hormone is a hormone that stimulates the thyroid gland to produce thyroxine (T 4 ), and then triiodothyronine (T 3 ) which stimulates the metabolism of almost every tissue in the body. For Cortisol Stress Adrenaline (Epinephrine) stress hormones secreted from the adrenal glands, which sit above the kidneys. Adrenaline primarily binds to receptors on the heart and heart vessels. This increases heart rate, force of muscle contraction and respiration. (Short term response) Page 2 of 7
Cortisol binds to receptors on the fat cells, liver and pancreas, which increases glucose levels available for muscles to use. It also temporarily inhibits other systems of the body, including : Stress response Water Regulation How do you detect a need for fluids?? Page 3 of 7
Osmotic pressure builds up in Osmoreceptors in sense increased osmotic pressure and send signals to the pituitary gland to release into blood stream ADH affects distal tubule and collecting duct allowing more water to be reabsorbed into blood DIAGRAM OF THE NEPHRON: The Nephron: Primary functional unit of the kidney. Its microscopic tubular structure is responsible for the filtration of wasteful substances and reabsorption of valuable substances in the blood to create urine. Steps necessary to create URINE: 1. Glomerular Filtration 2. Tubular reabsorption 3. Tubular secretion 4. Water reabsorption Glomerular Filtration: Takes place in renal corpuscle Glomerulus Bowman s Capsule Water and other small substances are forced into the Bowman s Capsule Water Salts/ions (Na + & K + ) Glucose Waste product: Urea Page 4 of 7
Factors affecting Glomerular Filtration Permeability of the glomerulus Blood Pressure 4 times higher blood pressure than any other capillary - source of the force used for filtration. 2. Tubular reabsorption Takes place in the Proximal Tubule Between Bowman s Capsule and Distal Tubule Many of the substances filtered into the nephron are removed during tubular reabsorption Accounts for 65% of filtrate Substances can exit in 3 ways: 1. Passive transport Diffusion 2. Active Transport 3. Osmosis Active transport Salts (Na + & K + ) Glucose Amino acids Passive Transport Negatively charged ions (Cl - & HCO 3 - ) a. Electrical attraction with cations Osmosis Water is reabsorbed The proximal tubule reabsorbs: between 40 and 60% of the glomerular ultrafiltrate. Glucose and amino acids 70% of the filtered potassium (K) and 75% of the bicarbonate (HCO3). The cytoplasm of the cells that make up the proximal tubule is densely packed with mitochondria necessary to supply the energy for the active transport of sodium ions out of the proximal tubule. Water passively follows the sodium out of the cell along its concentration gradient. Reabsorption in The Loop of Henle Loop of Henle Thinner, U shaped portion of the proximal tubule that extends into the renal medulla Descending limb Permeable to water Enters into the salty medulla H 2 O exits into the capillaries along its gradient - Osmosis Consequently, the concentration of Na + inside increases Page 5 of 7
Ascending limb Impermeable to water Thin portion - Chloride ions are actively transported out Sodium cations diffuse out of nephrons due to attractive forces Thick portion Sodium cations are actively transported out into the medulla 3. Tubular Secretion - Takes place in the Distal Tubule Immediately prior to collecting duct Two primary secretions: Potassium ions (K + ) Hydrogen ions (H + ) Regulate blood ph by the removal of H + 4. Reabsorption of Collecting Duct As in the proximal tubule, water exits the filtrate via osmosis High concentration of salt in the medulla Permeability of collecting duct can alter based on water levels in blood: Enough water: less permeable less H 2 O returns to blood Dehydration: more permeable more H 2 O returns to blood Reabsorption & secretion: As the filtrate passes down the nephron most of it is reabsorbed into the blood A few substances are secreted from the blood to the nephron Reabsorption and secretion are energy intensive- the kidney is one of the most metabolically active organs in the body Filtering substances into the tubules and then reabsorbing nearly 100% of them, using energy, may seem to be a very wastefull process, but it allows the body to quickly remove many toxic substances from the blood (they are usually not reabsorbed) Net Process: Amt in Urine = Amt Filtered - Amt Reabsorbed + Amt Secreted Glomerular Filtration is Easy to Measure From Inulin or Creatinine Clearance Page 6 of 7
Water Regulation Water is expelled during respiration and is continually being moved through the skin to moderate temperature and flush the tissues of the skin Water is used for metabolic processes Lack of water = decreased organ function and toxin build up Common signs of dehydration: dark urine, afternoon fatigue, heartburn, dry skin, acne, headaches and constipation Effects on concentration and mood Blood sugar regulation If blood sugar is too HIGH: Insulin secreted from β cells in the Islet Langerhan Liver stores glucose as glycogen Muscles cells store glycogen and build protein Adipose tissue uses glucose to build fat IF TOO LOW: α cells found in the Islets of Langerhan Liver breaks down glycogen to glucose Adipose tissue breaks down fat Page 7 of 7