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Functions of the Excretory System Remove nitrogenous wastes caused by metabolism Protein amino acids Nucleic acids nitrogenous groups o Ammonia:* very toxic can be transported if very diluted Aquatic animals: excrete directly Terrestrial animals: make a less toxic form in the liver & concentrated in kidneys ▫ Urea:* nontoxic, water soluble. Mammals, amphibians & some marine ▫ Uric Acid:* nontoxic, water insoluble paste. Insects, bird & some reptiles Regulate water loss and gain Systems Flatworms: Protonephridia o Flame cells collect interstitial fluid of body, Cilia move fluid through the tube, Water and salt adjusted Earthworms: Metanephridia o Tubes with internal openings to collect fluids, Salts/water adjusted in capillary area, Urine is hypoosmotic to body fluid Insects: Malphighian tubules o Dead end tubes dangle in the hemolymph in body cavity, Salts, wastes pumped into tube, rectum restores salts to blood, Nitrogenous wastes are dry and excreted with feces Vertebrates: Kidney with Nephrons o Overviews: Filtration:* water and solutes enter nephron Reabsorption:* water and valuable solutes are reabsorbed into the blood Secretion:* substances in blood are transported to the filtrate Excretion:* urine leaves the body o Kidney:* excretory organ, basic unit is a nephron Filtrate:* water, urea & solute (glucose, AA, ions & vitamins), extracted by kidneys o Two parts: renal cortex & renal medulla o Renal artery & vein supply blood for cleaning o Nephron:* functional unit of kidney, starts & ends in the cortex Bowman’s Capsule:* cup shaped, receives the filtrate Glomerulus:* ball of capillaries Combined form a filtration unit st 1 – Blood pressure forces plasma out & into tube: all solutes 2nd – Glomerulus & Bowman’s capsule: filtrate is processed Out of blood salt sugar urea water 3rd – Proximal Tubule:* Secretion into & reabsorption out of tube through active & passive transport o 75% of salts, water, nutrients, glucose, AA are reabsorbed Out of blood ammonia drugs poison Into blood salts, water, nutrients, glucose, amino acids 4th – Descending Loop of Henle:* carries filtrate into the medulla, length varies in animals, depends on environment – dryer = longer Into blood/interstitial water 5th – Ascending Loop of Henle:* carries filtrate into the cortex. 6th – Distal tubule:* Cortex, pH regulation (helps buffer blood) by absorbing bicarbonate and secreting H+. Farthest away from Bowman’s capsule. Into tube K+, H+ Into blood/interstitial Na+, Cl-, bicarbonate 7th – Collecting Duct: in medulla. Urine is collected & disposed of. Water & salt is reabsorbed o Only 20% of nephrons go through the medulla, rest stay in cortex 8th – Urine travels to renal pelvis 9th – Ureters carry urine to bladder 10th – Bladder stores urine 11th – Urethra:* tube through which urine exits the body Into blood/interstitial salt Control Water intake sets off hormones o Lots of water: very dilute urine, remove water without losing salts o Little water: slightly hyperosmotic urine to remove wastes with as little water as possible Antidiuretic Hormone (ADH)* – need water/volume o Made in hypothalamus, released from pituitary o Receive impulses from osmoreceptor cells when osmolarity (solute concentration) increases o Increases permeability to water in distal convoluted tubule and collecting duct o Increase reabsorption of water decreases osmolarity and shuts off ADH = negative feedback Aldosterone – need water/volume and salt o Released by tissue near glomerulus o Causes the tubules to retain sodium and water, increases the volume of fluid in the body, and drives blood pressure up.