Homework Quiz Question 1

Homework Quiz Question 2 You are sick and take an antibiotic. Describe the pathway of the drug through the urinary system, starting from the aorta to the toilet!

Passive transport. Substances move spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. The rate of diffusion can be greatly increased by transport proteins in the membrane. Active transport. Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP. Diffusion. Hydrophobic molecules and (at a slow rate) very small uncharged polar molecules can diffuse through the lipid bilayer. Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins, either channel or carrier proteins. ATP

Three Functions of Urine Formation 1. Filtration – movement of fluids from the blood in the glomerulus to the Bowman’s capsule 2. Reabsorption – transfer of fluids from nephron into peritubular capillaries 3. Secretion – transfer of fluids from peritubular capillaries into nephron Filtration. Reabsorption. Secretion. Excretion. Capillary Excretory tubule Filtrate Urine interstitial fluid

Filtration Water and solutes flow from the glomerulus into Bowman’s capsule due to high blood pressure flow 65 mmHg vs. normall ~ 25 mmHg Semi-permeable membrane Red blood cells, platelettes and some blood proteins are too large to fit through the filtration slits and pores. Filtration. Reabsorption. Secretion. Excretion. Capillary Excretory tubule Filtrate Urine

Nutrient Flow SoluteGlomerulus  Bowman’s Capsule? wateryes NaClyes H + ionsyes amino acidsyes glucoseyes plasma proteinsno red blood cells (erythrocytes) no plateletsno

Reabsorption reclaims valuable substances from the filtrate and returns them to the body fluids. Water, salt and nutrients saves us from having to continuously replenish our body with fluid. Filtration. Reabsorption. Secretion. Excretion. Capillary Excretory tubule Filtrate Urine Reabsorption 20% of fluid flowing into kidney is filtered into nephrons; however less than 1% of the fluid in the nephron is used to make urine. A LOT OF REABSORPTION!

Secretion Other substances are extracted from body fluids and added to the contents of the nephron toxins and excess ions Filtration. Reabsorption. Secretion. Excretion. Capillary Excretory tubule Filtrate Urine

Reabsorption Secretion protein transporters move nutrients into interstitial fluid and blood kidney tissue will only reabsorb a certain level of nutrients – threshold level Filtration. Reabsorption. Secretion. Excretion. Capillary Excretory tubule Filtrate Urine Diffusion. Hydrophobic molecules and (at a slow rate) very small uncharged polar molecules can diffuse through the lipid bilayer. Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins, either channel or carrier proteins. ATP protein transporters move wastes from blood to interstitial fluid to nephron

The Details…

1. Bowman’s Capsule High pressure filter water and dissolved solutes leave glomerulus; enter Bowman’s capsule water Na + H + Cl - glucose amino acids vitamins minerals urea uric acid

2. Proximal Tubule Selective reabsorption of nutrients (need transporters) Secretion of H+ and ammonia pH determined by HCO 3 - reabsorption and H + secretion H + NH 3 HCO 3 -, K + Na +, Cl - H 2 O amino acids glucose vitamins

3. Loop of Henle – Descending Limb Nephron membrane only permeable to H 2 O (osmosis) and impermeable to salt Reabsorption of water As fluids travel down the loop of henle, the fluids within the tube become more concentrated. H2OH2O

4. Loop of Henle – Ascending Limb only permeable to salt (need ionic transporters) and not permeable to water Reabsorption of salt As fluids travel up the loop of henle the fluid is becoming less concentrated NaCl

5. Distal Tubule Selective reabsorption of nutrients (need transporters) Secretion of H+, ammonia and K+ pH determined by HCO 3 - reabsorption and H + secretion H + NH 3 K + HCO 3 - Na +, Cl - H 2 O

6. Collecting Duct Urine formation by concentration of nephron fluid Any urea and urine that is reabsorbed is less than that was filtered into nephron Why is some urea reabsorbed? Contributes to the formation of a hypertonic interstitial fluid causes water to be reabsorbed CONCENTRATING THE URINE NaCl urea water

Proximal tubule Filtrate H 2 O Salts (NaCl and others) HCO 3 – H + Urea Glucose; amino acids Some drugs Key Active transport Passive transport CORTEX OUTER MEDULLA INNER MEDULLA Descending limb of loop of Henle Thick segment of ascending limb Thin segment of ascending limb Collecting duct NaCl Distal tubule NaClNutrients Urea H2OH2O NaCl H2OH2O H2OH2O HCO 3  K+K+ H+H+ NH 3 HCO 3  K+K+ H+H+ H2OH2O

H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCl Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX H2OH2O Urea H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Osmolarity of interstitial fluid (mosm/L) 300 Osmolarity – concentration of solutes in a solution, the higher the Osmolarity, the more concentrated the solution, the better it is able to pull water towards it.

Diabetes (Type II) Not enough insulin released from pancrease High levels of glucose in the blood Why do you think that individuals with Type II Diabetes (untreated) (a) Excrete a large amount of gluose in the urine? (b) Excrete large amounts of urine?

Kidney Stones crystallization of some urine solutes a 2 – 3 mm stone can obstruct flow to the ureter Treatment: increased water consumption surgery