Renal Physiology and Function Part I
Function, Physiology & Urine
Ricki Otten MT(ASCP)[email protected]
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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’
• Bowman’s space
• Bowman’s 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 (<70,000)
– Filtration based on solute’s 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
Creatinine: 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)– Body’s need to excrete solutes (glucose)
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Abnormal Urine Output
• Polyuria: >2500 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