THE URINARY SYSTEM– b III. Physiology … - Urine IV. Other Organs: THE URINARY SYSTEM– b III. Physiology … - Urine IV. Other Organs: Ureters, Bladder, & Urethra

B. Step 2: Tubular Reabsorption (figure 25.14) 1. Introduction Selective process moving substances from filtrate to blood; mostly via active transport & diffusion a. Nutrients & water: absorbed automatically b. Ions and 10% water: regulated; depends on body homeostasis c. Location: Primarily in PCT, DCT, Collect. Ducts Three major renal processes: Afferent arteriole Efferent arteriole Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary Tubule Cells 2. Tubular reabsorption Tubule Cells Interstial Fluid Lumen Peritubular Capillary

REVIEW SECONDARY ACTIVE TRANSPORT d. Methods: Primary & Secondary Active Transport Extracellular fluid Glucose Na+-glucose symport transporter loading glucose from ECF Na+-glucose symport transporter releasing glucose into the cytoplasm Na+-K+ pump Na diffuses Cytoplasm 1 The Primary Active Transport stores energy by creating a steep concentration gradient for Na+ . 2 As Na+ diffuses back using a cotransporter protein, the protein also moves glucose against its concentration gradient REVIEW SECONDARY ACTIVE TRANSPORT Figure 3.11 step 2

Peritubular Capillaries B. Step 2: Tubular Reasorption … 2. Sodium Reabsorption via active transport Importance: Its active transport provides energy to move other items by secondary active transport Peritubular Capillaries Lumen of Tube Interstial fluid Kidney Tube Cell 2

3. Reabsorption of Nutrients, Water, & ions Via Secondary Active Transport a. sodium diffuses in for step 2 and energy generated causes: Cotransport via Secondary Active Transport: Nutrients, Vitamins, some ions form Low to High Then diffuse to peritubular capillaries 3 Transport Maximum (Tm) = maximum transport capacity due to Limited number of protein carriers/channels When saturated, excess is excreted in urine Lumen of Tube Kidney Tube Cell Peritubular Capillaries 2 3 Glucose Amino A. Vitamins Ions (some) 1 sign of diabetes = glucose and ketones in urine

3. Reabsorption of Nutrients, Water, & Ions … Passive c. Osmosis of H2O, passively i) Most H2O diffuses out of Tubules: H2O diffusion gradient created by movement of Na+-- osmosis occurs from filtrate  peritubular capillaries ii) Collecting Duct: have control of remaining 25% water via ADH 4 Lumen of Tube Peritubular Capillaries Kidney Tube Cell 4

3. Reabsorption of H2O, Nutrients, & Ions … d. Passive Tubular Reabsorption 5 and 6 As water diffused out of filtrate, solute concen. Increases to create diffusion gradient Ions (Ca+,Mg+2, and Cl-) diffuse; filtrate   peritubular cap Lipid-soluble substances & urea diffuse out of filtrate to  peritubular capillaries Peritubular Capillaries Lumen of Tube Kidney Tube Cell 4 Lipids 5-6 Urea ions(some)

4. Reabsorptive Capabilities a. PCT - site of most reabsorption 65% of Na+ and water All nutrients &Small proteins b. Loop of Henle Descending limb: H2O Ascending limb: Na+, K+ c. DCT and collecting duct - hormonally regulated Water (ADH) in collecting duct Na+ (aldosterone) HCO3- (for blood pH)

ADH inserts aquaporins 4. Reabsorptive Capabilities of the Tubules and Collecting Ducts d. Mechanism of Aldosterone Na+ K+ Targets collecting ducts (principal cells) and distal DCT Promotes synthesis of Na+ and K+ channels and Pumps Result: Na+ reabsorbed, K+ secreted; water follows Na+ e) Mechanism of ADH ADH inserts aquaporins (H2O channels)  allows triggers H2O to diffuse out of the Collecting Ducts H2O DCT Regulated by aldosterone: Na+ aquaporin K+ H2O Collecting Duct

C. Step 3: Tubular Secretion Blood or Tubule cells → tubule lumen Functions: Disposes of drugs, metabolites Eliminates wastes (urea/uric acid) Rids body of excess K+ Helps Control blood pH (via H+ or HCO3–) Locations: Prox. CT mostly Collecting Duct Dist. CT Afferent arteriole Three major renal processes: Glomerular filtration Tubular reabsorption Tubular secretion Urine

D. Regulation of Urine Concentration and Volume 1. Basic Concepts Kidney must maintain constant solute concentration: of body fluids = 300 mOsmo How– Countercurrent mechanism: parallel portions of a tube connected by a hairpin turn  maximum transfer of substances c. Loop of Henle ascending and descending limbs create NaCl/H2O gradient in interstitial fluid Cortex Medulla

2. Mechanism: Countercurrent in Loop and Vasa Recta i) Descending Limb Permeable to H2O Not to NaCl ii) Ascending Limb Permeable to NaCl via active transport Not to H2O H2O H2O iii) Vasa Recta maintains medulla gradient while removing water and solutes to blood. NET RESULT: filtrate more dilute at Dist CT (100) than interstial fluid & blood (300) Interstial fluid

3. Formation of Dilute or Concentrated Urine a) DILUTE URINE Filtrate is already dilute at top of DCT Absence of ADH = no aquaporins then collecting tubule impermeable to H2O Medullary gradient not used Active transport Passive transport Collecting duct Descending limb of loop of Henle DCT Cortex NaCI H2O NaCI Outer medulla NaCI H2O Urea Inner medulla Large volume of dilute urine (a) Absence of ADH

b) Formation of Concentrated Urine ADH inserts aquaporins  triggers H2O diffusion out of collecting ducts (reabsorption) medullary osmotic gradient of loop creates the lower concentration for H2O diffusion Almost all the H2O reabsorbed (remaining 25%) Overall: then up to 99% of H2O in filtrate reabsorbed Active transport Passive transport Collecting duct H2O Descending limb of loop of Henle H2O DCT Cortex H2O NaCI H2O H2O NaCI Outer medulla H2O NaCI Urea H2O H2O Urea Inner medulla H2O Small volume of concentrated urine (b) Maximal ADH

E. Renal Clearance = volume of plasma cleared of a known substance (test substance like inulin) in a given time Used to identify kidney disease RC = GFR = 125 ml/min When substance is neither reabsorbed nor secreted If RC < 125 ml/min, the substance is being reabsorbed At RC = 0, substance is completely reabsorbed If RC > 125 ml/min, the substance is being secreted

III. Urine Color Odor pH Specific Gravity Chemical Composition Water Nitrogen Wastes: Urea, Solutes: Na+, K+, phosphate, sulfate Other Nitrogen Wastes: Uric Acid, Creatinine Variable: Ca+2, Mg+2, Bi-carbonate ABNORMAL SUBSTANCES

IV. The other Organs A. Ureters direct flow to Bladder B. Bladder emptied out by urethra Urination (micturition) is controlled by voluntary external sphincter This holds up to 1 liter! Figure 15.6 (a) Female.

Figure 25.21a Structure of the urinary bladder and Urethra. Peritoneum Ureter In males, urethra also part of reproductive system Urethra = passage for urine and semen in men Rugae Detrusor muscle Adventitia Ureteric orifices Trigone of bladder Bladder neck Internal urethral sphincter Prostate Prostatic urethra Urogenital diaphragm External urethral sphincter Urethra Spongy urethra Erectile tissue of penis External urethral orifice (b) Male. The long male urethra has three regions: prostatic, membranous and spongy.

END OF PPT Review Questions

Participating… The outermost layer of the kidney is known as the ________ while the core is called the ____________. Kidneys are considered _______________ because they are found on the dorsal wall of the abdominal cavity behind the peritoneum. What 2 hormones are secreted by the kidneys? cortex medulla retroperitoneal Renin and EPO

Participating… The functional unit of the kidney is known as the __________ . The three steps of urine formation are: 1. ______________, 2. ______________, and 3. ___________. What cells of the JG apparatus release renin? nephron filtration reabsorption secretion granular

Participating… What are 3 things that trigger renin release by the granular cells? Low levels of NaCl ions indicates ______ flow rates in the nephron and are detected by ______ _______ cells of the J-G apparatus which signal the _________ arteriole to _________. Very low b.p.; low filtrate flow; sympathetic stimulation low macula densa afferent dilate

Participating… The __________ _________ developed in the long loops of Henle allows the body to produce __________ urine. Aldosterone targets the collecting tubules and the ______ ; it promotes ____ (and thus H2O) reabsorption by stimulating the production of what? countercurrent multiplier concentrated DCT Na+ Na+ and K+ channels and Na-K pumps

peripheral resistance SYSTEMIC BLOOD PRESSURE (–) Granular cells of juxtaglomerular apparatus of kidney Baroreceptors in blood vessels of systemic circulation Release (+) (+) Renin (+) Sympathetic nervous system Catalyzes cascade resulting in conversion Angiotensinogen Angiotensin II (+) (+) (+) Adrenal cortex Systemic arterioles Releases Aldosterone Vasoconstriction; peripheral resistance Targets Kidney tubules Na+ reabsorption; water follows (+) Stimulates (–) Inhibits Increase Decrease Blood volume Systemic blood pressure Hormonal (renin-angiotensin) mechanism Neural controls Extrinsic mechanisms indirectly regulate GFR by maintaining systemic blood pressure, which drives filtration in the kidneys.