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Business Homework due in lab TASS W/F 12pm Contact the Tutoring Center for more details BI 233 Tutors Schedule an appointment 541-917-4697 More Tips for Success Study groups!!! Form one Join one Invite someone to join yours Review Name the 4 regions of the renal tubules 2. The structural and functional regions that form urine are the __________. 3. Micturition is controlled by the ____________ nervous system. 4. How is filtrate different that urine? (2 sentences) 1. Part 2 Urine Formation Filtrate Blood plasma minus most proteins Urine <1% of total filtrate Contains metabolic wastes and unneeded substances Urine Formation Glomerular filtration Tubular reabsorption 1. 2. Returns components to blood 3. Glucose amino acids, water and salt Tubular secretion Reverse of reabsorption Selective addition to urine 4. Water conservation Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary Three major renal processes: Glomerular filtration Tubular reabsorption Tubular secretion To cortical radiate vein Urine Figure 25.10 Glomerular Filtration Occurs at renal corpuscle Passive process driven by hydrostatic pressure Glomerulus is a very efficient filter Permeable membrane Water and small solutes pushed through filter Large surface area Higher blood pressure Efferent arteriole Glomerular capsule Glomerulus Afferent arteriole Parietal layer of glomerular capsule Capsular space Foot processes of podocytes Podocyte cell body (visceral layer) Red blood cell Proximal tubule cell Efferent arteriole Juxtaglomerular apparatus • Macula densa cells of the ascending limb of loop of Henle • Extraglomerular mesangial cells • Granular cells Afferent arteriole Juxtaglomerular apparatus Lumens of glomerular capillaries Endothelial cell of glomerular capillary Mesangial cells between capillaries Renal corpuscle Figure 25.8 Capillary Plasma Fenestration (pore) Filtration membrane • Capillary endothelium • Basement membrane • Foot processes of podocyte of glomerular capsule Filtration slit Slit Filtrate in diaphragm capsular space Foot processes of podocyte (c) Three parts of the filtration membrane Filtration slits Podocyte cell body Foot processes (b) Filtration slits between the podocyte foot processes Efferent arteriole Glomerular capsular space Proximal convoluted tubule Afferent arteriole Glomerular capillary covered by podocytecontaining visceral layer of glomerular capsule Cytoplasmic extensions of podocytes Filtration slits Parietal layer of glomerular capsule (a) Glomerular capillaries and the visceral layer of the glomerular capsule Podocyte cell body Fenestrations (pores) Glomerular capillary endothelium (podocyte covering and basement membrane removed) Foot processes of podocyte Figure 25.9a Glomerular Filtration Filtration membrane Allows passage of water and small solutes Fenestrations prevent filtration of blood cells Negatively charged basement membrane repels large anions Glomerular Filtration Net Filtration Pressure (NFP) Glomerular hydrostatic pressure (HPg) Capsular hydrostatic pressure (HPc) Blood osmotic pressure (OPg) Glomerular Filtration Net Filtration Pressure (NFP) The pressure responsible for filtrate formation NFP = HPg – (OPg + HPc) Afferent arteriole Glomerular capsule 10 mm Hg Net filtration pressure Glomerular (blood) hydrostatic pressure (HPg = 55 mm Hg) Blood colloid osmotic pressure (Opg = 30 mm Hg) Capsular hydrostatic pressure (HPc = 15 mm Hg) Figure 25.11 Net Filtration Pressure NFP = HPG – (OPG + HPC) = 55 mm Hg – (30 mmHg + 15 mmHg) = 10 mmHg Glomerular Filtration Glomerular Filtration Rate (GFR) 125 ml/min 1800 liters of blood through kidneys/day = 1200 ml/min = about 180 liters filtrate/day Glomerular Filtration Factors affecting GFR Kidney disease ↓ blood osmotic pressure, ↑ capsular osmotic pressure Hemorrhage ↓ glomerular blood hydrostatic pressure Hypotension Glomerular blood hydrostatic pressure = capsule hydrostatic and blood osmotic pressure = filtration stops! Renal suppression Glomerular Filtration GFR is tightly controlled by two types of mechanisms Intrinsic controls (renal autoregulation) Act locally within the kidney Extrinsic controls Nervous and endocrine mechanisms that maintain blood pressure and affect kidneys Glomerular Filtration Intrinsic controls Maintain a nearly constant GFR when MAP is in the range of 80–180 mm Hg Renal autoregulation Mechanisms that cause vasoconstriction of afferent arterioles in response to increased BP Extrinsic Controls Sympathetic nervous system At rest Renal blood vessels are dilated Renal autoregulation mechanisms prevail GFR maintained Extreme stress Norepinephrine and epinephrine released Both cause constriction of afferent arterioles Inhibits filtration Shunts blood to other vital organs Tubular Reabsorption 125 ml/min of filtrate produced Most of this fluid is reabsorbed A selective transepithelial process Includes active and passive process Most occurs in PCT Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary Three major renal processes: Glomerular filtration Tubular reabsorption Tubular secretion To cortical radiate vein Urine Figure 25.10 Tubular Reabsorption PCT Site of most reabsorption 65% of Na+ and water All nutrients Ions Small proteins Tubular Reabsorption Transcellular route Luminal membranes of tubule cells → cytosol of tubule cells → basolateral membranes of tubule cells → endothelium of peritubular capillaries Movement via the transcellular route involves: 1 Transport across the luminal membrane. 2 Diffusion through the cytosol. 3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.) 4 Movement through the interstitial fluid and into the capillary. Lateral intercellular space Tight junction Filtrate in tubule lumen The paracellular route involves: • Movement through leaky tight junctions, particularly in the PCT. Interstitial fluid Capillary endothelial cell Tubule cell Peritubular capillary Paracellular H2O 1 2 3 4 Transcellular Luminal membrane 1 Transcellular 3 4 2 Solutes 3 Paracellular 4 Basolateral membranes Active transport Passive transport Figure 25.13 Tubular Reabsorption Paracellular route Between cells Limited to water movement and reabsorption of Ca2+, Mg2+, K+, and some Na+ in the PCT where tight junctions are leaky Movement via the transcellular route involves: 1 Transport across the luminal membrane. 2 Diffusion through the cytosol. 3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.) 4 Movement through the interstitial fluid and into the capillary. Lateral intercellular space Tight junction Filtrate in tubule lumen The paracellular route involves: • Movement through leaky tight junctions, particularly in the PCT. Interstitial fluid Capillary endothelial cell Tubule cell Peritubular capillary Paracellular H2O 1 2 3 4 Transcellular Luminal membrane 1 Transcellular 3 4 2 Solutes 3 Paracellular 4 Basolateral membranes Active transport Passive transport Figure 25.13 Tubular Reabsorption Sodium Most abundant cation in filtrate Primary active transport out of the tubule cell by Na+-K+ ATPase in the basolateral membrane Na+ passes in through the luminal membrane by secondary active transport or facilitated diffusion mechanisms 1 At the basolateral membrane, Nucleus Filtrate in tubule lumen Na+ Tubule cell 3Na+ 1 2K+ 2K+ 3 K+ 4 Lipid-soluble 5 substances Cl–, Ca2+, K+ and other ions, urea Peritubular capillary 3 Reabsorption of organic 2 3Na+ Glucose Amino acids Some ions Vitamins H2O Interstitial fluid Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the luminal membrane. 6 Tight junction Primary active transport Secondary active transport Passive transport (diffusion) Cl– Paracellular route Transport protein Ion channel or aquaporin nutrients and certain ions by cotransport at the luminal membrane. 4 Reabsorption of water by osmosis. Water reabsorption increases the concentration of the solutes that are left behind. These solutes can then be reabsorbed as they move down their concentration gradients: 5 Lipid-soluble substances diffuse by the transcellular route. 6 Cl– (and other anions), K+, and urea diffuse by the paracellular route. Figure 25.14 Tubular Reabsorption Sodium Low hydrostatic pressure and high osmotic pressure in the peritubular capillaries Promotes bulk flow of water and solutes (including Na+) Tubular Maximum Transport maximum (Tm) reflects the number of carriers in the renal tubules available When the carriers are saturated, excess of that substance is excreted Example: too much glucose in the blood entering glomerulus will cause glucosuria Tubular Reabsorption Reabsorption of nutrients, water, and ions Blood becomes hypertonic to filtrate Water is reabsorbed by osmosis Cations and fat-soluble substances follow by diffusion 1 At the basolateral membrane, Nucleus Filtrate in tubule lumen Na+ Tubule cell 3Na+ 1 2K+ 2K+ 3 K+ 4 Lipid-soluble 5 substances Cl–, Ca2+, K+ and other ions, urea Peritubular capillary 3 Reabsorption of organic 2 3Na+ Glucose Amino acids Some ions Vitamins H2O Interstitial fluid Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the luminal membrane. 6 Tight junction Primary active transport Secondary active transport Passive transport (diffusion) Cl– Paracellular route Transport protein Ion channel or aquaporin nutrients and certain ions by cotransport at the luminal membrane. 4 Reabsorption of water by osmosis. Water reabsorption increases the concentration of the solutes that are left behind. These solutes can then be reabsorbed as they move down their concentration gradients: 5 Lipid-soluble substances diffuse by the transcellular route. 6 Cl– (and other anions), K+, and urea diffuse by the paracellular route. Figure 25.14 Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary Three major renal processes: Glomerular filtration Tubular reabsorption To cortical radiate vein Tubular secretion Urine Figure 25.10 Tubular Secretion Reabsorption in reverse K+, H+, NH4+, creatinine, and organic acids move from peritubular capillaries or tubule cells into filtrate Involves active transport since no concentration gradients in this case Na+ (65%) Glucose Amino acids H2O (65%) and many ions (e.g. Cl– and K+) Milliosmols Cortex (d) (a) 300 (e) Outer medulla (b) (c) 600 Some drugs – H+, HCO3 NH4+ Inner medulla Blood pH regulation 1200 (a) Proximal convoluted tubule: • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively transported; H2O and many ions follow passively • H+ and NH4+ secretion and HCO3– reabsorption to maintain blood pH (see Chapter 26) • Some drugs are secreted Active transport (primary or secondary) Passive transport Figure 25.18a Tubular Secretion Principle effects Rids body of Foreign substances (penicillin and other drugs) Nitrogenous wastes Excess K+ Controls blood pH: Altering amounts of H+ or HCO3– in urine Review continued… 5. Name the 4 steps to urine formation 6. 7. Dilute urine = _________ urine Concentrated urine = ___________ urine Questions?