Renal Structure and Renal Structure and FunctionFunction

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KidneysKidneys

PairedPaired RetroperitonealRetroperitoneal Partially protected by the 11Partially protected by the 11thth and and

1212thth ribs ribs Right slightly lower due to liverRight slightly lower due to liver Surrounded by renal capsuleSurrounded by renal capsule Adipose capsuleAdipose capsule Renal fasciaRenal fascia

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AnatomyAnatomy

Hilum (hilus)Hilum (hilus) Renal artery and veinRenal artery and vein Cortex Cortex MedullaMedulla Renal pyramids and renal papillaeRenal pyramids and renal papillae Major and minor calycesMajor and minor calyces Renal PelvisRenal Pelvis UretersUreters

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Ureters connect kidneys to urinary Ureters connect kidneys to urinary bladderbladder

Urethra leads from bladder outside Urethra leads from bladder outside the bodythe body

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Kidneys make up 1 % of body mass, Kidneys make up 1 % of body mass, but receive about 25% of cardiac but receive about 25% of cardiac output.output.

Kidney has two major functions:Kidney has two major functions:1. Filtration of blood1. Filtration of blood

Removes metabolic wastes from the Removes metabolic wastes from the body, esp. those containing nitrogenbody, esp. those containing nitrogen

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2. Regulation:2. Regulation:

Blood volume and compositionBlood volume and composition

ElectrolytesElectrolytes

Blood pHBlood pH

Blood pressureBlood pressure

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NephronNephron

Functional unit of the kidneyFunctional unit of the kidney Filtration, tubular reabsorption, Filtration, tubular reabsorption,

tubular secretiontubular secretion Renal corpuscle:Renal corpuscle:

– Glomerulus – capillariesGlomerulus – capillaries– Glomerular or Bowman’s capsuleGlomerular or Bowman’s capsule

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Bowman’s capsuleBowman’s capsule– Receives filtrateReceives filtrate

Proximal convoluted tubuleProximal convoluted tubule– Reabsorption of water and solutesReabsorption of water and solutes

Nephron loop or Loop of HenleNephron loop or Loop of Henle– Regulates concentration of urineRegulates concentration of urine

Distal convoluted tubule and Distal convoluted tubule and Collecting ductCollecting duct

Reabsorption of water and Reabsorption of water and electrolyteselectrolytes– ADH, aldosterone, ANPADH, aldosterone, ANP

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FiltrationFiltration

Renal corpuscleRenal corpuscle Filtration membraneFiltration membrane

– Fenestrated endothelium of Fenestrated endothelium of capillariescapillaries

– Basement membrane of glomerulusBasement membrane of glomerulus– Slit membrane between pedicels of Slit membrane between pedicels of

podocytespodocytes

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Forces that influence Forces that influence filtrationfiltration Glomerular blood hydrostatic Glomerular blood hydrostatic

pressurepressure

Opposing forces:Opposing forces:– Plasma colloid osmotic pressurePlasma colloid osmotic pressure– Capsular hydrostatic pressureCapsular hydrostatic pressure

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Glomerular Filtration Glomerular Filtration RateRate Volume of plasma filtered / unit Volume of plasma filtered / unit

timetime Approx. 180 L /dayApprox. 180 L /day Urine output is about 1- 2 L /dayUrine output is about 1- 2 L /day About 99% of filtrate is About 99% of filtrate is

reabsorbedreabsorbed

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GFR influenced by:GFR influenced by:

Blood pressure and blood flowBlood pressure and blood flow Obstruction to urine outflowObstruction to urine outflow Loss of protein-free fluid Loss of protein-free fluid Hormonal regulation Hormonal regulation

– Renin – angiotensin Renin – angiotensin – AldosteroneAldosterone– ADHADH– ANPANP

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Juxtaglomerular Juxtaglomerular apparatusapparatus Juxtaglomerular cells lie in the wall Juxtaglomerular cells lie in the wall

of afferent arterioleof afferent arteriole Macula densa in final portion of Macula densa in final portion of

loop of Henle – monitor Naloop of Henle – monitor Na++ and Cl and Cl-- conc. and waterconc. and water

Control blood flow into the Control blood flow into the glomerulusglomerulus

Control glomerular filtrationControl glomerular filtration2323

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Tubular reabsorptionTubular reabsorption

Water, glucose, amino acids, Water, glucose, amino acids, urea, ionsurea, ions

Sodium diffuses into cell; actively Sodium diffuses into cell; actively pumped out – drawing water with pumped out – drawing water with itit

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In addition to reabsorption, also have In addition to reabsorption, also have tubular secretion – substances move tubular secretion – substances move from peritubular capillaries into from peritubular capillaries into tubules – a second chance to remove tubules – a second chance to remove substances from blood. substances from blood.

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By end of proximal tubule have By end of proximal tubule have reabsorbed:reabsorbed:

60- 70% of water and sodium60- 70% of water and sodium about 100% of glucose and amino about 100% of glucose and amino

acidsacids 90 % of K+, bicarb, Ca++, uric acid90 % of K+, bicarb, Ca++, uric acid Transport maximumTransport maximum – maximum – maximum

amount of a substance that can be amount of a substance that can be absorbed per unit timeabsorbed per unit time

Renal thresholdRenal threshold – plasma conc. of a – plasma conc. of a substance at which it exceeds Tm.substance at which it exceeds Tm.

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Loop of HenleLoop of Henle

Responsible for producing a Responsible for producing a concentrated urine by forming a concentrated urine by forming a concentration gradient within the concentration gradient within the medulla of kidney.medulla of kidney.

When ADH is present, water is When ADH is present, water is reabsorbed and urine is reabsorbed and urine is concentrated.concentrated.

Counter-current multiplierCounter-current multiplier3232

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Distal convoluted tubule Distal convoluted tubule and collecting ductsand collecting ducts

What happens here depends on What happens here depends on ADHADH

Aldosterone affects Na+ and K+Aldosterone affects Na+ and K+ ADH – facultative water ADH – facultative water

reabsorptionreabsorption Parathyroid hormone – increases Parathyroid hormone – increases

Ca++ reabsorptionCa++ reabsorption

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Distal convoluted tubule Distal convoluted tubule and collecting ductsand collecting ducts

Tubular secretion to rid body of Tubular secretion to rid body of substances: K+, H+, urea, substances: K+, H+, urea, ammonia, creatinine and certain ammonia, creatinine and certain drugsdrugs

Secretion of H+ helps maintain Secretion of H+ helps maintain blood pHblood pH

(can also reabsorb bicarb and (can also reabsorb bicarb and generate new bicarb)generate new bicarb)

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Renal diagnostic Renal diagnostic proceduresprocedures Urinalysis is non-invasive and Urinalysis is non-invasive and

inexpensiveinexpensive Normal properties are well known Normal properties are well known

and easily measuredand easily measured

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pHpH

Normally 4.8 – 8.0Normally 4.8 – 8.0 Higher in alkalosis, lower in Higher in alkalosis, lower in

acidosisacidosis Diabetes and starvation Diabetes and starvation ↓ ↓ pHpH Urinary infections ↑ pH Urinary infections ↑ pH

– Proteus and pseudomonas are urea Proteus and pseudomonas are urea splitterssplitters

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Specific gravitySpecific gravity

Normal values 1.025 -1.032Normal values 1.025 -1.032 High specific gravity can cause High specific gravity can cause

precipitation of solutes and precipitation of solutes and formation of kidney stonesformation of kidney stones

When tubules are damaged, urine When tubules are damaged, urine specific gravity approaches that of specific gravity approaches that of glomerular filtrate – 1.010 – remains glomerular filtrate – 1.010 – remains fixed = 2/3 of nephron mass has fixed = 2/3 of nephron mass has been lostbeen lost

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Diabetes insipidus = 1.003Diabetes insipidus = 1.003 Diabetes mellitus = 1. 030Diabetes mellitus = 1. 030 Emesis or fever = 1.040Emesis or fever = 1.040

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Microscopic analysisMicroscopic analysis

Red blood cells – should be few or Red blood cells – should be few or nonenone– Hematuria – large numbers of rbc’s Hematuria – large numbers of rbc’s

in urinein urine– CatheterizationCatheterization– MenstruationMenstruation– Inflamed prostate glandInflamed prostate gland– Cystitis or bladder stonesCystitis or bladder stones

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Casts – precipitate from cells lining Casts – precipitate from cells lining the renal tubulesthe renal tubules– Red cells – tubule bleedingRed cells – tubule bleeding– White cells – tubule inflammationWhite cells – tubule inflammation– Epithelial cells – degeneration, necrosis Epithelial cells – degeneration, necrosis

of tubule cellsof tubule cells

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Crystals –Crystals –– InfectionInfection– InflammationInflammation– stonesstones

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White blood cells White blood cells – PyuriaPyuria– Urinary tract infectionUrinary tract infection

BacteriaBacteria

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Substances not normally Substances not normally present in urinepresent in urine

AcetoneAcetone Bile, bilirubinBile, bilirubin GlucoseGlucose Protein – albuminProtein – albumin

– Renal disease involving Renal disease involving glomerulusglomerulus

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Blood Urea Nitrogen Blood Urea Nitrogen BUNBUN

Urea produced by breakdown of Urea produced by breakdown of amino acids - influenced by diet, amino acids - influenced by diet, dehydration, and hemolysisdehydration, and hemolysis

Normal range 10-20 mg/ dLNormal range 10-20 mg/ dL If the GFR decreases due to renal If the GFR decreases due to renal

disease or blockage, or decreased disease or blockage, or decreased blood flow to kidney - BUN increasesblood flow to kidney - BUN increases

General screen for abnormal renal General screen for abnormal renal functionfunction

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Creatinine clearanceCreatinine clearance

Creatinine is an end product of Creatinine is an end product of muscle metabolismmuscle metabolism

Muscle mass is constant; creatinine Muscle mass is constant; creatinine is constantis constant

Normal 0.7 – 1.5 mg/ dL in plasmaNormal 0.7 – 1.5 mg/ dL in plasma Can then be compared to Can then be compared to

creatinine in urine over 24 hour creatinine in urine over 24 hour period to determine clearanceperiod to determine clearance

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Creatinine clearance is an indirect Creatinine clearance is an indirect measure of GFR and renal blood flowmeasure of GFR and renal blood flow

Creatinine is neither reabsorbed nor Creatinine is neither reabsorbed nor secreted, just freely filtered.secreted, just freely filtered.

Amount excreted = amount filteredAmount excreted = amount filtered Useful to monitor changes in chronic Useful to monitor changes in chronic

renal functionrenal function Increases with trauma with massive Increases with trauma with massive

muscle breakdownmuscle breakdown

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Diagnostic testingDiagnostic testing

Inulin clearance - not absorbed or Inulin clearance - not absorbed or secreted = GFRsecreted = GFR

PAH – para-aminohippuric acid – PAH – para-aminohippuric acid – not absorbed ; actively secreted not absorbed ; actively secreted = renal plasma flow= renal plasma flow

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