November 30, 2016 & URINE FORMATION

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1 & URINE FORMATION REVIEW!

2 Urinary/Renal System 200 litres of blood are filtered daily by the kidneys Usable material: reabsorbed back into blood Waste: drained into the bladder away from the heart to the heart a filter to bladder kidneys

3 There are 2 kidneys in the human body Each kidney has three layers: The outer layer : cortex The inner layer : medulla Hollow chamber: renal pelvis The functional unit of the kidneys is called the nephrons (1 million per kidney) cortex renal pelvis nephron medulla renal artery renal vein ureter

4 Functions/Responsibilities The kidneys are responsible for: Ion regulation and osmoregulation: regulation of salt and water balance Waste management: excretion of metabolic wastes like urea, excess H+ ions and drugs Hormone production: function as an endocrine gland releasing hormones like Vitamin D Gluconeogensis: glucose production from noncarbohydrate sources Blood pressure regulation Blood ph

5 Nephron The unit of a kidney is the nephron it carries out the process of removing waste and saving certain molecules from excretion Flow of nephron: Glomerulus -> Bowman s Capsule -> Proximal Convoluted Tubule -> Descending Loop of Henle -> Ascending Loop of Henle -> Distal Convoluted Tubule -> Collecting Duct

6 Urine Formation Urine formation depends on three functions: i) filtration: the movement of fluids from the blood into the Bowman s capsule ii) reabsorption: the transfer of essential solutes and water from the nephron back into the blood iii) secretion: the movement of materials from the blood back into the nephron

7 vasa recta Filtration Afferent arteriole carries blood to a knot of capillaries called the glomerulus Efferent arteriole drains from each glomerulus into the vasa recta which wraps around the nephron for further reabsorption later Blood pressure forces water and small molecules that need to be filtered, out of the glomerulus and are collected by the Bowman's Capsule Blood cells and proteins behind in the efferent arteriole

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9 Reabsorption 600mL/min of fluid flows through the kidneys 120mL is filtered into the nephrons (Would produce 120mL of urine every minute) > In order to maintain homeostasis, you would have to consume 1L of fluid every 10 min of your day. Actually, 1mL of the 120mL forms urine. The other 119mL of fluids and solutes are reabsorbed. Reabsorption occurs until a threshold level is reached. Any excess NaCl is excreted with urine.

10 Secretion Nitrogen-containing wastes, excess H +, and even drugs like penicillin can be secreted (moved from blood into the nephron) ex. OAT (organic anion transporter)

11 Active transport Na+ ATP is used Flashback: Cellular Transport Passive transport Cl- through protein channel No energy needed Osmosis Movement of water down the concentration gradient

12 Proximal convoluted tubule Responsible for most of the reabsorption of water and solutes from the filtrate Na +, Cl -, glucose and amino acids are transported out of the filtrate Water will follow by osmosis These molecules are returned to the venous blood leaving the kidney

13 Loop of Henle The kidneys produce urine that is hypertonic to the blood plasma Loop of Henle functions as a countercurrent multiplier creating a concentration gradient in the medulla *Let s start in reverse to understand. Thick ascending Loop of Henle: Thick Loop is NOT permeable to water Water is forced to stay inside the tubule. This means that the medulla fluid has a higher concentration of Na + and Cl - than the cells of the tubule.

14 Descending Loop of Henle: *is permeable to water but not very permeable to Na + and Cl - Due to osmosis, water will move out of the tubule due to the medulla fluid being more concentrated in Na + because of the ascending loop Tubule fluid is less concentrated than the blood plasma, and solutes that have been left behind in the medulla create a concentration gradient Loop of Henle cont.

15 Distal convoluted tubule Fluid entering is less concentrated than the surrounding cortex fluid so the tubule will lose water by osmosis In presence of aldosterone (hormone), Na + will be reabsorbed while K + or H + will be secreted (secretion of H + important for acid-base balance)

16 Fluid entering the collecting duct is at the same concentration as blood plasma, but NaCL has been moved out of the tubule fluid so urea and other waste products make up the solute content The concentration gradient established by the Loop of Henle increases, so more and more water is absorbed from the tubule fluid and this leaves a very concentrated urine in the collecting duct. Collecting duct

17 Formation of Urea Excess amino acids cannot be stored in the body The liver breaks down nitrogenous compounds (amino acids mostly) This is called deamination This produces urea which must be removed from the body

18 Dehydration and Sweating A hormone called antidiuretic hormone (ADH) helps kidneys increase water reabsorption When ADH is released, more concentrated urine is produced so this conserves body water When you sweat, blood solutes become more concentrated and ADH (made by hypothalamus) is released from pituitary gland where it is stored Only happens in collecting duct!

19 Aldosterone and ADH November 30, 2016

20 Disease and Issues Diabetes Insipidus Destruction of ADH producing cells of the hypothalamus Urine output increases dramatically (up to 20L of dilute urine/day) = strong thirst response Must drink large quantities of water to replace what they were not able to reabsorb Diabetes Mellitus Inadequate amount of insulin so blood sugar levels rise. The proximal tubule can reabsorb 0.1% blood sugar, so all this excess sugar stays in the nephrons. Water remains in the nephron because osmotic pressures are altered due to the excess sugar. This water is lost as urine so these people are also excessively thirsty.

21 What is diabetes mellitus? November 30, 2016

22 Dialysis Kidneys are not able to do their work by themselves so the use of a machine is needed A unit called a dialyzer mimics the action of a nephron Kidney Transplant 85% effective in restoring function Issue: immune response of the recipient

23 Dialysis November 30, 2016