Lesson 28 - Excretion

28: excretion Thursday, April 4, 2024 nitrogenous waste 5:56 PM • type of metabolic waste to be excreted • waste product from breaking down proteins and nucleic acid • must balance toxicity of waste (amino groups) with cost of waste production (energy / water loss) • uric acid: ○ relatively non-toxic ○ doesn't dissolve in water § when the organism excretes, it does not also excrete water § reduces water loss (none) ○ VERY energetically costly ○ reptiles/birds, insects • urea: ○ low-moderate toxicity ○ moderate water loss ○ energetically costly § bond building § water conservation ○ many land animals § all mammals and some amphibians • ammonia: ○ toxic (goes into water) ○ no internal water loss, but must be diluted in water ○ little water loss ○ aquatic animals 4 basic steps to excretion 1. filtration ○ excretory tubule collects water and small solutes (extracellular matrix) from blood (called filtrate) 2. reabsorption ○ water and essential solutes recovered from filtrate to keep ○ nutrients, ions, etc. 3. secretion ○ solutes (toxins, excess ions, overconsumed vitamins) added by selective secretion 4. excretion ○ filtrate released as urine mammalian excretory system 1. 2. 3. 4. 5. • kidneys are paired organs excretory tubules (nephrons) in cortex and medulla filtrate produced from unfiltered blood in renal artery resorbed filtrate returns to blood via renal vein urine collects in renal pelvis, exits via ureter to bladder each nephron has a long tubule and a ball of capillaries (glomerulus) • filtrate formed when blood pressure forces solute into bowman's capsule • processing occurs along the nephron which of the following structures in the mammalian excretory is mismatched with its function? a. renal artery: delivers unfiltered blood b. renal vein: delivers filtered blood c. renal cortex: houses the nephrons d. renal pelvis: houses the bladder ○ where urine collects on the way to the urine, then bladder mammalian nephron • proximal tubule: ○ proximal to the glomerulus ○ RESORPTION of EVERYTHING - water, salt, ions, and nutrients ○ waste starts concentrating ○ toxins actively secreted into filtrate • descending limb of loop of henle: ○ more WATER RESORPTION § diffusing out of the renal medulla and into the bloodstream ○ epithelium only permeable to water • ascending limb of loop of henle: ○ no water removal; it RETAINS WATER ○ salt moves out to maintain osmolarity of interstitial fluid § salt concentration becomes higher in the medulla than ○ epithelium only permeable to water • ascending limb of loop of henle: ○ no water removal; it RETAINS WATER ○ salt moves out to maintain osmolarity of interstitial fluid § salt concentration becomes higher in the medulla than the filtrate throughout ascension § passive transport continues throughout the lower end § active transport is required on the higher end to remove it ○ waste low in volume but more dilute § losing solute but no water is being lost • distal tubule: ○ REGULATES SALT (and K+) ○ more WATER RESORBED and concentration of excretory product • collecting duct: ○ formation of urine which of the following statements about mammalian excretion is false? a. substances like solutes always diffuse across the nephron membrane, with the direction based on differences in concentration gradient ○ "always" ○ active transport takes place at some locations b. whenever water is diffusing out of the nephron, solutes are diffusing in gradient ○ "always" ○ active transport takes place at some locations b. whenever water is diffusing out of the nephron, solutes are diffusing in ○ in the descending limb of the loop of henle, water is moving in, but no solutes are diffusing c. water resorption happens at every stage of the process, concentrating waste ○ in the ascending limb of the loop of henle, water is retained in the filtrate d. all of the above water conservation • osmolarity in the filtrate and interstitial fluid are low in the cortex and high in the inner medulla • water moving out / solute moving in → water concentration is greater in the filtrate than the interstitial fluid • water moving in / solute moving out → water concentration is greater in the interstitial fluid than the filtrate • mammals produce hyperosmotic urine to reduce water loss ○ water in urine < water in environment ○ salt in urine > salt in environment ○ high solute concentration • maintaining the steep osmotic gradient requires active transport of NaCl into the cortex and medulla of the kidney ○ allows natural diffusion of water out of the filtrate to the cortex and medulla → water conservation ○ resorbed water eventually moves to bloodstream via veins in the cortex and medulla • reducing water loss is energetically costly • in the collecting duct, urine is highly concentrated with a great amount of urea and small amount of water water conservation on land • desert mammals ○ highly hyperosmotic urine § 8 times more concentrated than humans' ○ many long nephrons maintain steep osmotic gradients § the deeper the nephron goes into the increasingly concentrated medulla, the more water that is pulled out § more steep gradient • freshwater mammals ○ have more short nephron loops and lower urine concentration § filtrate spends less time in the concentrated area of the medulla § less steep gradient ○ lose more water because they are surrounded by it • birds ○ primarily produce uric acid, which is highly water efficient § non-toxic, highly energetically costly § not water soluble, so not much water is secreted ○ bladder is reduced, and less water is weighing them down in the air water conservation in water • freshwater fish ○ hyperosmotic ○ excrete large volumes of dilute urine § active regulatory process § compensates for constantly gaining water ○ conserve salts by resorbing ions from filtrate § compensates for constantly losing salt • marine fish ○ hypoosmotic ○ filtration rates low because little urine is produced § compensates for constantly gaining water ○ conserve salts by resorbing ions from filtrate § compensates for constantly losing salt • marine fish ○ hypoosmotic ○ filtration rates low because little urine is produced ○ little urine excreted, constantly drinking water § active regulatory process § compensates for constantly losing water ○ chloride cells in gills help maintain salt balance § compensates for constantly gaining salt § excess salt because they are drinking saltwater