Renal Physiology and Function

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Renal Physiology and Function
Ricki Otten MT(ASCP)SC uotten_at_unmc.edu
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Objectives

• Please review the objectives located on page 1 of
  the lecture handout

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Kidney Function

• Form urine (excretory function)
• Maintain acid-base balance
• Regulates body water balance
• Maintain electrolyte balance
• Aids in maintaining BP
• Excrete toxic (and) waste products
• Reabsorb essential substances
• Hormonal function
• Target organ for aldosterone, ADH
• Secretes renin (an enzyme)
• Erythropoietin, vitamin D

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Kidney Function

• Depends upon proper
• Renal blood flow (20-25 cardiac output)
• Glomerular filtration
• Tubular absorption
• Tubular secretion

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Urinary System

• Each kidney about the
• size of your fist

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Inflammation/Infection
Pyelonephritis
Cystitis
Urethritis
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Nephron

• Functional unit of kidney
• 1.5 million per kidney
• Components
• Glomerulus
• Tubules
• (PCT, Loop of Henle, DCT)
• Collecting ducts/tubules
• Functions to form urine
• Filtration
• Reabsorption
• Secretion

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Glomerulus

• Capillary tuft
• Bowmans space
• Bowmans Capsule
• Afferent arteriole
• Efferent arteriole
• Empties into PCT

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Glomerulus

• Function Filtration of blood
• Allows passage of water, electrolytes and low
  molecular weight substances (lt70,000)
• Filtration based on solutes size and charge
• Difference between glomerular filtrate and blood
  is absence of
• Protein
• Protein-bound substances bilirubin, drugs
• Cells (RBC, WBC)

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Glomerular Filtrate

• Specific Gravity
• 1.010
• Ultrafiltrate volume
• 120 ml/min

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Glomerular Filtration

• Dependent upon
• Basement membrane
• cell structure
• Hydrostatic pressure
• Oncotic pressure
• RAA system

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Glomerular Filtration

• Dependent upon
• Basement membrane
• cell structure
• Hydrostatic pressure
• Oncotic pressure
• RAA system

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Renin-Angiotensin-Aldosterone
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Renal Tubules

• PCT
• Loop of Henle
• Descending limb
• Ascending limb
• Not permeable to water
• DCT
• ADH (controls water)
• Aldosterone (controls Na)
• Collecting ducts/tubules
• ADH (controls water)

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Renal Tubules

• Functions
• Reabsorption of essential substances
• Secretion of waste, toxins, metabolites, drugs,
  protein-bound substances, etc
• Final urine output 1 ml/min
• Range 0.3 15 ml/min (dependent on hydration
  status)

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Tubular Transport Mechanisms

• Active transport energy is required
• Passive transport simple diffusion
• Renal Threshold
• Glucose 160-180 mg/dl (plasma)

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Normal Urine Composition

• Water 94
• Solutes 6
• Urea
• Sodium
• Chloride

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Normal Urine Composition

• Water 94
• Solutes 6
• Urea
• Sodium
• Chloride

Urea end product of protein metabolism Creatinin
e end product of muscle metabolism Uric acid
end product of purine metabolism
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Factors Influencing Concentration of Substances

• Dietary intake
• Physical activity
• Body metabolism
• Endocrine function (ADH, Aldosterone)
• Body position (orthostatic proteinuria)

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Urine Output

• Average 24 hour volume
• Normal 1500 2000 ml/24 hour
• Extreme 600 2500 ml/24 hours
• Factors that influence urine output (volume)
• Fluid intake
• Non-renal loss (vomiting, diarrhea, sweating)
• Secretion of ADH (too little, too much)
• Bodys need to excrete solutes (glucose)

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Abnormal Urine Output

• Polyuria gt2500 ml/24 hr
• Artificially induced by suppression of ADH
• (diuretics, caffeine, alcohol)
• Diabetes mellitus plasma glucose exceeds renal
  threshold
• Diabetes insipidus
• Neurogenic DI lack of ADH
• Nephrogenic DI tubules unable to respond to ADH

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Abnormal Urine Output

• Oliguria (low)
• Anuria (absence)
• Nocturia

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Renal Function Tests

• Tubular Reabsorption
• Glomerular Filtration
• Renal Blood Flow
• Tubular Secretion

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Tubular Reabsorption Tests

• Can the kidneys concentrate urine
• Concentration Tests control of fluid intake
  important in interpretation of test
• Fluid deprivation
• Free water clearance

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Tubular Reabsorption Tests

• Laboratory
• Specific gravity (number and density)
• Refractometer
• Reagent strip
• Osmolality (number of particles in solution)
• Better test
• More accurate

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Glomerular Filtration Tests

• Assess filtering ability of glomerulus
• Clearance tests
• Measures the RATE at which kidneys can clear a
  filterable substance from the blood
• This substance must not be reabsorbed or secreted
  by the tubules
• GFR glomerular filtration rate

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Glomerular Filtration Tests

• Specimen requirements
• Timed urine specimen 24 hour collection
• Plasma sample
• Clearance calculation UV ml/min
• P

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Glomerular Filtration Tests

• Endogenous
• Creatinine (most common)
• Exogenous
• Inulin (considered the standard)

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Glomerular Filtration Tests

• Creatinine clearance test
• Endogenous substance (found in the body)
• Produced at a steady rate
• Dependent on muscle mass (male, female, child,
  adult)
• Thus normalized to body surface area using a
  nomogram
• Children
• Obese

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Glomerular Filtration Tests

• Calculate creatinine clearance UV
• P
• Urine creatinine (U) 185 mg/dl
• Plasma creatinine (P) 0.9 mg/dl
• Urine volume (V) 1250 ml/24 hr
• Height 60
• Weight 260 lb

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Calculate Creatinine Clearance

• CrCl UV
• P

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Calculate Creatinine Clearance

• UV 185 mg/dl x 1250 ml x 1 hour
  178.4
• P 0.9 mg/dl 24 hours 60 min
• CrCl 178 ml/min

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Calculate Creatinine Clearance

• UV 185 mg/dl x 1250 ml x 1 hour
  178.4
• P 0.9 mg/dl 24 hours 60 min
• CrCl 178 ml/min
• Is this normal for a 20 year old male?

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Calculate Creatinine Clearance

• UV 185 mg/dl x 1250 ml x 1 hour
  178.4
• P 0.9 mg/dl 24 hours 60 min
• CrCl 178 ml/min
• Is this normal for a 20 year old male?
• No, it is increased
• Correct value for body surface area

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Corrected Creatinine Clearance

• CrCl 178 ml/min
• Corrected CrCl
• CrCl x 1.73m2 178 ml/min x 1.73
• BSA 2.39
• 128.8 129 ml/min

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Corrected Creatinine Clearance

• CrCl 178 ml/min
• Corrected CrCl 129 ml/min
• Is this normal for a 20 year old male?

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Corrected Creatinine Clearance

• CrCl 178 ml/min
• Corrected CrCl 129 ml/min
• Is this normal for a 20 year old male? Yes

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Renal Reserve

• Large margin of reserve in renal function
• Greater than 50 of kidney function must be lost
  before
• Clinical symptoms apparent
• Biochemical abnormalities evident
• Thus, not useful for screening for early renal
  disease

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• Renal Blood Flow
• Tubular Secretion

No objectives
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