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 1. 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) Part 2 Urine Formation Filtrate Blood plasma minus most proteins Urine <1% of total filtrate Contains metabolic wastes and unneeded substances Urine Formation 1. Glomerular filtration 2. Tubular reabsorption Returns components to blood Glucose amino acids, water and salt 3. 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 To cortical radiate vein Tubular reabsorption Tubular secretion 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 Glomerular capsule arteriole Glomerulus
Afferent arteriole Foot processes Parietal layer of podocytes of glomerular Podocyte cell capsule body (visceral Capsular layer) space Red blood cell Efferent Proximal arteriole tubule cell
Juxtaglomerular apparatus • Macula densa cells of the ascending limb Lumens of of loop of Henle glomerular • Extraglomerular capillaries mesangial cells Endothelial cell • Granular cells of glomerular capillary Afferent arteriole Mesangial cells between capillaries
Juxtaglomerular Renal corpuscle apparatus
Figure 25.8 Filtration membrane • Capillary endothelium Capillary • Basement membrane • Foot processes of podocyte of glomerular capsule
Filtration slit Slit Plasma Filtrate in diaphragm capsular space Foot processes Fenestration of podocyte (pore) (c) Three parts of the filtration membrane Filtration slits
Podocyte cell body
Foot processes
(b) Filtration slits between the podocyte foot processes Glomerular capsular space Efferent arteriole Proximal convoluted tubule Afferent arteriole Cytoplasmic extensions Glomerular capillary Parietal layer of podocytes covered by podocyte- of glomerular Filtration slits containing visceral capsule layer of glomerular Podocyte capsule cell body (a) Glomerular capillaries and the visceral layer of the glomerular capsule Fenestrations (pores)
Glomerular capillary endothelium (podocyte covering and basement Foot processes membrane removed) 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
Glomerular (blood) hydrostatic pressure 10 (HPg = 55 mm Hg) mm Hg Blood colloid osmotic pressure (Opg = 30 mm Hg) Net filtration Capsular hydrostatic pressure 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 To cortical radiate vein Tubular reabsorption Tubular secretion 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 3 Transport across the basolateral The paracellular route transcellular route involves: involves: membrane. (Often involves the lateral intercellular spaces because • Movement through 1 Transport across the membrane transporters transport ions leaky tight junctions, luminal membrane. into these spaces.) particularly in the PCT. 2 Diffusion through the 4 Movement through the interstitial cytosol. fluid and into the capillary. Tight junction Lateral intercellular space Filtrate Tubule cell Interstitial in tubule fluid Peri- lumen Capillary tubular endothelial capillary cell Paracellular H2O 1 2 3 4 Luminal Transcellular membrane 1 Transcellular 3 4 2 Solutes 3 4 Active transport Paracellular Basolateral membranes 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 3 Transport across the basolateral The paracellular route transcellular route involves: involves: membrane. (Often involves the lateral intercellular spaces because • Movement through 1 Transport across the membrane transporters transport ions leaky tight junctions, luminal membrane. into these spaces.) particularly in the PCT. 2 Diffusion through the 4 Movement through the interstitial cytosol. fluid and into the capillary. Tight junction Lateral intercellular space Filtrate Tubule cell Interstitial in tubule fluid Peri- lumen Capillary tubular endothelial capillary cell Paracellular H2O 1 2 3 4 Luminal Transcellular membrane 1 Transcellular 3 4 2 Solutes 3 4 Active transport Paracellular Basolateral membranes 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, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport Nucleus creates concentration gradients Filtrate Interstitial Peri- that drive: in tubule Tubule cell fluid tubular 2 “Downhill” Na+ entry at the lumen capillary luminal membrane. 3 Reabsorption of organic + Na 2 nutrients and certain ions by + + 3Na 3Na cotransport at the luminal
Glucose 1 membrane. 2K+ 2K+ Amino 3 4 Reabsorption of water by acids K+ osmosis. Water reabsorption Some increases the concentration of ions the solutes that are left 4 Vitamins behind. These solutes can H2O then be reabsorbed as they move down their
Lipid-soluble 5 concentration gradients: substances 5 Lipid-soluble – 2+ + 6 Cl , Ca , K Cl– substances diffuse by the and other transcellular route. Tight junction Paracellular ions, urea route 6 Cl– (and other anions), + Primary active transport Transport protein K , and urea diffuse by the Secondary active transport Ion channel or aquaporin paracellular route. Passive transport (diffusion)
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, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport Nucleus creates concentration gradients Filtrate Interstitial Peri- that drive: in tubule Tubule cell fluid tubular 2 “Downhill” Na+ entry at the lumen capillary luminal membrane. 3 Reabsorption of organic + Na 2 nutrients and certain ions by + + 3Na 3Na cotransport at the luminal
Glucose 1 membrane. 2K+ 2K+ Amino 3 4 Reabsorption of water by acids K+ osmosis. Water reabsorption Some increases the concentration of ions the solutes that are left 4 Vitamins behind. These solutes can H2O then be reabsorbed as they move down their
Lipid-soluble 5 concentration gradients: substances 5 Lipid-soluble – 2+ + 6 Cl , Ca , K Cl– substances diffuse by the and other transcellular route. Tight junction Paracellular ions, urea route 6 Cl– (and other anions), + Primary active transport Transport protein K , and urea diffuse by the Secondary active transport Ion channel or aquaporin paracellular route. Passive transport (diffusion)
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 To cortical radiate vein Tubular reabsorption 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 Milliosmols + Cortex Na (65%) H2O (65%) and Glucose many ions (e.g. – + (d) Amino acids Cl and K ) (a)
300
(e) Outer
medulla (b)
(c) 600 Some + HCO – drugs H , 3 NH + 4 Inner medulla Blood pH regulation (a) Proximal convoluted tubule: 1200 • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively
transported; H2O and many ions follow passively + + – Active transport • H and NH4 secretion and HCO3 reabsorption to (primary or maintain blood pH (see Chapter 26) secondary) • Some drugs are secreted 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. Dilute urine = ______urine 7. Concentrated urine = ______urine
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