1. Urinary System Chapter 25

2. Overview 1.Structures/Organs 2. Location (Kidneys) – T 12 to L 3 – 150 g

3. Kidney Structure 1. Renal hilum 2. Protective Tissue – Fibrous capsule; fat capsule 3. Internal Structure – Cortex – Medulla – Pelvis and Calyces

4. Blood Supply

5. Nephrons 1. Overview 2. Renal Corpuscle – Glomerulus – Bowman’s Capsule 3. Function of Renal Corpuscle 4. Tubules – PCT – Loop of Henle – DCT – Collecting Ducts

6. Tubule - Histology

7. Nephron Capillary Beds 1. Peritubular 2. Vasa Recta

8. Juxtaglomerular Apparatus 1. JGA – Granular cells – Juxtaglomerular cells – Macula densa 2. Filtration – Membrane – Process

9. How Urine is Formed Three Steps to forming Urine – 1. Glomerular Filtration Blood moved into glomerulus Forced Out: “Filtrate” – 2. Tubular reabsorption Glucose; Amino Acids; 99% Water; Salts, etc. reclaimed by kidneys – 3. Tubular secretion What is not needed -------  Urine

10. Glomerular Filtration 1. Passive Process 2. Glomerular Blood Pressure 3. Passage of Molecules 4. Pressures – Net Filtration Pressure – Glomerular Hydrostatic Pressure 5. Regulation – Intrinsic (in Kidney) – Extrinsic (Nervous and Endocrine)

11. Intrinsic and Extrinsic Controls

12. Tubular Reabsorption 1. Introduction – Filtrate enters PCT – “Transepithelial” process Transcellular or paracellular routes

13. 2. Reabsorption of Sodium – Active/Transcellular – Out of the Tubule: “Primary Active Transport” (Na-K pump) – Secondary Active Transport at Luminal face With glucose, amino acids

14. Tubular Reabsorption 3. Nutrients, Water and Ions – Reabsorption via secondary active transport (glucose, amino acids, ions, lactate, vitamins) Cotransport with sodium ions – Water follows Na + – Passive Tubular Reabsorption Aquaporins

15. Reabsorption – PCT

16. Reabsorption – Other Tubules and Collecting Ducts

17. Tubular Secretion 1. Some substances not reabsorbed. 2. Tubular Secretion: Reverse of reabsorption 3. Filtrate from Peritubular capillaries ------  filtrate in tubules – H + ; K + ; NH 4 + 4. Functions – Disposal of drugs – Urea – Excess K + – Blood pH

18. Osmotic Gradient (Regulating Urine Concentration and Volume) Osmolality: number of solute particles dissolved in one liter of water One function of the kidney’s is to keep the solute load of body fluids constant at 300mOsm (milliosmol = 1 osmol = 1 mole of nonionizing substance/1L) which is ‘isotonic’ This is done by regulating urine concentration and volume and is accomplished via countercurrent mechanism

19. Counter Current Mechanism Countercurrent means substances flowing in opposite directions Involves flow of filtrate through loops of Henle (Juxtamedullary nephrons) and blood flow in vasa recta PCT filtrate = 300mOsm (same as blood plasma). Increases to 1200 as goes to the deepest part of the medulla

20. Countercurrent Multiplier Establishes an osmotic gradient Descending Limb (LOH) – Impermeable to solutes and permeable to water Ascending Limb (LOH) – Permeable to solutes and impermeable to water – By time reaches DCT becomes very dilute (100) or hypotonic Collecting ducts become permeable to urea

21. Countercurrent Exchanger Maintains the osmotic gradient Blood flow is sluggish Permeable to water and NaCl – Allows blood to make passive exchanges with surrounding interstitial fluid and achieve equilibrium As blood flows deep into the medulla, it loses water and gains salts (hypertonic) As flow moves up to cortex the reverse occurs It helps to maintain the medullary osmotic gradient by removing salts

22. Formation of Dilute and Concentrated Urine If AHD hormone is not released, as filtrate flows through the ascending loop it is dilute; a hypo-osmotic filtrate will continue through the collecting duct – CT’s are impermeable to water (low aquaporins); no reabsorption of water occurs – Na and other ions can be removed from the DCT making the filtrate more dilute Concentrated Urine – ADH is released will increase the number of aquaporins in the CT’s – ADH release depends on the level of body hydration 99% of water in filtrate is reabsorbed into the blood and less than 1L/day of concentrated urine is excreted (ability to produce concentrated urine allows us to survive in times of low water availability) Diuretics: enhance output of urine

23. Summary of Nephron Function

24. Ureters

25. Bladder and Urethra

26. Animation Link

27. Control of Continence and Micturition