Homeostasis and Kidney

• The role of the loop of Henlé is to concentrate salt in the tissue fluid of the medulla.
• A low water potential in the medulla allows an osmotic flow of water out of the collecting duct and distal convoluted tubule, creating a concentrated urine for excretion.
• The loop of Henlé is a counter current multiplier; the longer the loop, the greater the concentration gradient between the filtrate and the tissue fluid of the medulla, meaning more water can be reabsorbed from the descending loop.
• Animals adapted to dry environments have longer loops of Henlé and reabsorb more water to the blood, for example, camels.
• Camels produce highly concentrated urine and lose less water when they excrete it.
• Mammals living in fresh water, such as otters, have short loops and less concentrated urine.
• A micrograph of the medulla shows the role of the loop of Henlé in concentrating salt in the tissue fluid of the medulla.
• Nitrogenous waste cannot be stored, excess amino acids are converted into nitrogenous waste.
• Mammals convert amino acids to urea in the liver.
• The filtrate becomes more concentrated as it descends and the water potential gets lower.
• The filtrate passes into the ascending limb of the loop of Henlé.
• Uric acid is insoluble and requires little water to excrete, making it light for flight and an adaptation for living in a terrestrial environment.
• The filtrate passes from the proximal convoluted tubule to the descending limb of the loop of Henlé, which carries it through the medulla towards the pelvis.
• Salts are actively transported out of the ascending limb of the loop of Henlé into the tissue fluid of the medulla, lowering the water potential in the medulla.
• Uric acid has a lower toxicity than urea, allowing young animals to excrete it at the egg stage of the life cycle.
• The high concentration of salt in the medulla means that the water potential is always lower in the medulla than the filtrate.
• The ascending limb of the loop of Henlé is impermeable to water.
• The descending limb of the loop of Henlé is permeable to water, allowing water to leave the filtrate by osmosis and be carried away by the vasa recta blood vessel.
• Urea has a medium toxicity and solubility.
• Urine can be concentrated or diluted according to the need to conserve or eliminate water.
• Fish convert excess amino acids to ammonia by deamination only, ammonia is highly toxic and highly soluble.
• Fish live in large volumes of water and ammonia is excreted easily.
• Insects, birds and reptiles use more ATP than it takes to make urea in order to make uric acid.
• Conditions that must be kept constant include blood glucose, core body temperature, and blood solute potential.
• Negative feedback is a system that restores conditions to a set point when it detects a deviation, resulting in narrow fluctuations around the set point.
• Homeostasis is important so that cells can function efficiently even if external conditions fluctuate or the body has different levels of activity.
• Homeostasis is the maintenance of a constant internal environment.
• Each condition has a set point.
• A control centre sends impulses to an effector (muscle or gland), which returns conditions to the set point – this is negative feedback.
• The renal artery supplies oxygen and glucose and has a high concentration of urea.
• The renal vein removes carbon dioxide and has a lower concentration of urea.
• The ureter transfers urine to the bladder.
• Urine is released through the urethra.
• Kidney dissection involves risk assessment, hazard, risk, and control measures.
• Cut away from the body onto a white tile during kidney dissection.
• The kidney can be divided into three visible regions: the cortex, the medulla, and the pelvis.
• The cortex is the outer region of the kidney.
• The medulla of the kidney is organised into triangular renal pyramids.
• The pyramids in the medulla of the kidney drain into the pelvis.
• The nephron is the functional unit of the kidney.