Renal Physiology and Function Part I

Function, Physiology & Urine

Ricki Otten MT(ASCP)SCuotten@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’

• 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