Unit Five: The Body Fluids and Kidneys Chapter 27: Urine Formation By the Kidneys. II. Tubular Reabsorption and Secretion Guyton and Hall, Textbook of Medical Physiology, 12 th edition
Dec 29, 2015
Unit One: Introduction to Physiology: The Cell and General Physiology
Unit Five: The Body Fluids and KidneysChapter 27: Urine Formation By the Kidneys. II. Tubular Reabsorption and SecretionGuyton and Hall, Textbook of Medical Physiology, 12th editionRenal Tubular Reabsorption and Secretion
Tubular Reabsorption is Quantitatively Large andHighly Selective
Amount FilteredAmount ReabsorbedAmount Excreted% Filtered ReabsorbedGlucose g/day1801800100Bicarbonate mEq/day432043182>99.9Sodium mEq/day255602541015099.4Chloride mEq/day194401926018099.1Potassium mEq/day7566649287.8Urea g/day46.823.423.450Creatinine g/day1.801.80Table 27.1 Filtration, Excretion, and Reabsorption Rates of Different Substances by the KidneyTubular Reabsorption
Fig. 27.1Tubular Reabsorption (cont.) Active Transport
Solutes transported through epithelial cells orbetween cells
Primary active transport (i.e. Na+ and K+)
Secondary active transport
Fig. 27.2 Basic mechanism for transport of sodium through the tubular epithelial cell
Fig. 27.3 Mechanisms of secondary active transportTubular Reabsorption (cont.)Secondary active secretion into the tubules (i.e.counter-transport)
Pinocytosis-active reabsorption of proteins
Transport maximum-limit to the rate at whicha solute can be transported in secretion or reabsorption
Fig. 27.4 Relations among the filtered load of glucose, the rate of glucose reabsorption by the renal tubules, and the rate of glucose excretion in the urine.SubstanceTransport MaximumGlucose375 mg/minPhosphate0.10 mM/minSulfate.06 mM/minAmino Acids1.5 mM/minUrate15 mg/minLactate75 mg/minPlasma protein30 mg/minTransport Maximums for Substances Actively Reabsorbed by the TubulesSubstanceTransport MaximumCreatinine16 mg/minPara-aminohippuric acid80 mg/minTransport Maximums for Substances Actively SecretedSubstances that are actively transported but do notexhibit a transport maximum (i.e. Na in the proximaltubule
h. Passive reabsorption coupled to sodium reabsorption
Fig. 27.5 Mechanisms by which water, chloride, and urea reabsorption are coupled with sodium reabsorptionReabsorption and Secretion Along Different Parts of the Nephron Proximal Tubular Reabsorption - normally about 65% offiltered load of Na and water and slightly lower percentof chloride is reabsorbed before the loop of Henle
Have a high capacity for both active and passivereabsorption
b.Co-transport and counter-transport occurs
Fig. 27.6 Cellular ultrastructure and primary transport characteristics of the proximal tubule.Reabsorption and Secretion (cont.) Concentrations of Solutes Along the Proximal Tubule
Fig. 27.7Reabsorption and Secretion (cont.) Secretion of Organic Acids and Bases
End products of metabolism
Harmful drugs and toxins
PAH (para-aminohippuric acid) clearance: used toestimate renal plasma flowReabsorption and Secretion (cont.) Solute and Water Transport in the Loop of Henle
Fig. 27.8Reabsorption and Secretion (cont.) Solute and Water Transport in the Loop of Henle
Fig. 27.9
Reabsorption and Secretion (cont.) Distal Tubule - Macula densa of the juxtaglomerular complexprovides feedback control for GFR
Fig. 27.11Reabsorption and Secretion (cont.) Late Distal Tubule and Cortical Collecting Tubule
Principal cells reabsorb sodium and secrete potassium
Fig. 27.12Reabsorption and Secretion (cont.) Late Distal Tubule and Cortical Collecting Tubule (cont.)
Intercalated cells secrete hydrogen and reabsorbbicarbonate and potassium ions
c.Permeability is controlled by concentrations of ADH
Reabsorption and Secretion (cont.) Medullary Collecting Duct - absorb less than 10% of thefiltered water and sodium; final site for processingurine
Permeability controlled by ADH
Permeable to urea
Can secrete H+ against a concentration gradient (helpsregulate acid-base balance
Fig. 27.13Summary of Concentrations of Different Solutesin the Different Tubular Segments
Fig. 27.14Regulation of Tubular Reabsorption
Glomerulotubular Balance- ability of the tubules toincrease reabsorption rate in response to increasedtubular load
Peritubular Capillary and Renal Interstitial FluidPhysical Forces - hydrostatic and colloid osmotic forces govern the rate of reabsorption acrossthe peritubular capillariesRegulation of Tubular Reabsorption (cont.)
Fig. 27.15Regulation (cont.) Regulation of Peritubular Capillary Physical Forces
Peritubular capillary hydrostatic pressure is influencedby arterial pressure and resistance of the afferent andefferent arterioles
Increases in these pressures tend to raise peritubularhydrostatic pressure and decrease reabsorption rate
Increases in the resistance of the arterioles reduces thehydrostatic pressure and increases the reabsorption rateRegulation (cont.) Regulation of Peritubular Capillary Physical Forces
Raising the colloid osmotic pressure increases peritubularcapillary reabsorption
Colloid osmotic pressure is determined by
Systemic plasma colloid osmotic pressure
Filtration fractionRegulation (cont.) Renal Interstitial Hydrostatic and Colloid Osmotic Pressures
Fig. 27.16
Regulation (cont.) Hormonal Control of Tubular Reabsorption
Aldosterone increases Na reabsorption and stimulatesK secretion
Site of action is on the principal cells of the corticalcollecting tubule
Most important stimuli for aldosterone are increasedK and angiotensin II levels
Regulation (cont.) Angiotensin II Increases Na and Water Reabsorption
Angiotensin II stimulates aldosterone secretion
Angiotensin II constricts the efferent arterioles
Angiotensin II directly stimulates Na reabsorption inthe proximal tubules, the loops of Henle, the distaltubules, and the collecting tubules
Fig. 27.17 Direct effects of angiotensin II to increase proximal tubular sodium reabsorptionRegulation (cont.) ADH Increases Water Reabsorption
Fig. 27.18Regulation (cont.) ANP Decreases Na and Water Reabsorption
PTH Increases Ca Reabsorption
Sympathetic Nervous System Activation IncreasesNa Reabsorption
Quantifying Kidney Function Inulin Clearance
Creatinine Clearance
PAH (para-aminohippuric acid) Clearance
Fig. 27.19 Measurement of the GFR from the renal clearance of inulin
Fig. 27.20 Effect of reducing GFR by 50% on serum creatinine concentration and on creatinine excretion rate when the production rate of creatinine remains constant
Fig. 27.21 Approximate relationship between GFR and plasma creatinine concentration under steady-state conditions
Fig. 27.22 Measurement of renal plasma flow from the renal clearance of PAGSubstanceClearance Rate (ml/min)Glucose0Sodium0.9Chloride1.3Potassium12.0Phosphate25.0Inulin125.0Creatinine140.0
Approximate Clearance Rates for Some of the Substances Normally Handled by the Kidneys