Unit O: Excretory System Unit O: Excretory System Chapter 25

Standards CORE: I can explain the overall function of the urinary system I can outline the major organs and their function in the urinary system I can explain how urine production contributes to homeostasis NO ADVANCED!

Excretory system AKA: the urinary system (how you make pee!) HANK: https://www.youtube.com/watch?v=WtrYotjYvtU TWO FUNCTIONS OF THE EXCRETORY SYSTEM: Osmoregulation: the control of the gain and loss of water and dissolved solutes Excretion: the disposal of metabolic wastes

Osmoregulation Compared to our aquatic relatives, land animals need to be very aware of our water intake/output Land animals Gain water by drinking and eating Lose water by evaporation and waste disposal Their kidneys, behavioral adaptations, and waterproof skin help to conserve water (VERY important!)

CONNECTION 25.5 Do we need to drink eight glasses of water each day? Water lost in thermoregulation can cause osmoregulatory problems Is it true you can “drown” from drinking too much water?? YES!! BUT…its very very rare – you’d need to drink many many litres of water in a very short amount of time. Its called HYPONATREMIA: too much water in our blood, dilutes the salts/solutes to the point where the blood becomes hypotonic to the body’s cell causing them to swell (NOT good – especially in the brain!!) can be fatal!!

Thirst is usually an adequate guide to water intake – usually by the time you’re thirsty you are already dehydrated! Figure 25.5

25.6 Animals must dispose of nitrogenous wastes Nitrogenous wastes are the toxic byproducts from the breakdown of protein Ammonia is poisonous but soluble and is easily disposed of by animals Urea is less toxic and easier to store Some land animals save water by excreting uric acid - virtually dry waste Urea and uric acid take energy to produce Proteins Nucleic acids Amino acids Nitrogenous bases — NH2 Amino groups Most aquatic animals, including most fishes Mammals, amphibians, sharks, some bony fishes Birds and many other reptiles, insects, land snails NH3 O C NH2 N H HN Uric acid Urea Ammonia Figure 25.6

25.7 The liver has 6 main functions: Produces urea from ammonia Detoxification: converts alcohol  fats (which are stored in the liver leads to a fatty liver – NOT good!) Produces bile: emulsifier of fats, stored in the gall bladder Produces blood plasma proteins and lipoproteins (EX. Albumin- regulating osmotic pressure; fibrinogen/prothrombin – clotting) Adjusts the blood sugar level: glucose  glycogen based on pancreatic hormones (insulin & glucagon) Removes dead red blood cells from the blood, send the hemoglobin to the bone marrow and the rest is converted into bile

25.8 Alcohol consumption can damage the liver The liver has a strategic location in the body between the intestines and the hear t 25.8 Alcohol consumption can damage the liver Liver function can be impaired by excessive alcohol consumption (converts alcohol  fats creating a fatty liver) or hepatitis (inflammation of parts of liver can lead to liver chirrosis: parts or all of liver stop working) Liver Intestines Kidneys Hepatic Por tal vein Figure 25.7

25.9 The excretory system plays several major roles in homeostasis The excretory system expels wastes and regulates water and ion balance Nephrons, the functional units of the kidneys extract a filtrate from the blood and refine it to urine Urine leaves the kidneys via ureters is stored in the urinary bladder, and is expelled through the urethra

Anatomy of the human excretory system Aorta Inferior vena cava Renal artery and vein Ureter Urinary bladder Urethra A The excretory system Kidney Renal cortex Renal medulla Renal pelvis B The kidney Bowman’s capsule C Orientation of a nephron within the kidney Renal artery Renal vein Nephron tubule Collecting duct To renal pelvis Glomerulus 1 Proximal tubule 3 Distal tubule Capillaries From another nephron Arteriole from renal artery Arteriole from glomerulus Branch of renal vein 2 Loop of Henle with capillary network D Detailed structure of a nephron Figure 25.9A–D

25.10 Overview: The key processes of the excretory system are filtration, reabsorption, secretion, and excretion In filtration blood pressure forces water and many small solutes into the nephron (occurs in Bowmen’s Capsule in the glomerulus)

The product of all of the above processes is urine which is excreted In reabsorption valuable solutes are reclaimed from the filtrate (occurs through the rest of the nephron: in the PCT, LoH, DCT & CD) In secretion excess H+ and toxins are added to the filtrate (occurs in PCT & DCT) The product of all of the above processes is urine which is excreted H2O, other small molecules Urine Excretion Secretion Reabsorption Filtration Capillary Interstitial fluid Nephron tubule

25.11 From blood to filtrate to urine: A closer look Nutrients, salt, and water are reabsorbed from the proximal and distal tubules

Blood pH is regulated by the secretion of H+ and reabsorption of HCO3– There is a network of blood capillaries (vasa recta) that are located over the Loop of Henle which reabsorb many nutrients and salts High NaCl concentration in the medulla promotes reabsorption of water in the Loop of Henle

Loop of henle details Descending loop is only permeable to water (osmosis) Ascending loop in only permeable to salt (actively pumped) Best to think of it backwards with ascending first (pump out salt) and then descending (water follows passively by osmosis)

Overview: reabsorption and secretion in a nephron Blood Bowman’s capsule Proximal tubule Distal tubule NaCI – HCO3 Nutrients H2O Some drugs and poisons + H Cortex H2O K Collecting duct Loop of Henle Urea Urine (to renal pelvis) Medulla Filtrate composition Glucose Amino acids Some drugs Reabsorption Secretion Figure 25.11

Collecting Duct: reabsorbs water under hormonal control; regulates how concentrated the urine in response to blood osmolarity HORMONE: Antidiuretic hormone (ADH): regulates the amount of water the kidneys excrete by controlling the # of aquaporins in the collecting duct ADH production is inhibited by alcohol consumption

CONNECTION 25.12 Kidney dialysis can be a lifesaver Compensating for kidney failure A dialysis machine removes wastes from the blood and maintains its solute concentration Line from artery to apparatus Tubing made of a selectively permeable membrane Pump Dialyzing solution Line from apparatus to vein Figure 25.12 Fresh dialyzing solution Used dialyzing solution (with urea and excess ions)