Basic Processes Of Kidney

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THREE BASIC RENAL PROCESSES

Glomerular Filtration: Filtering of blood into tubule forming the primitive urine

Tubular Reabsorption: Absorption of substances needed by body from tubule to blood

Tubular Secretion: Secretion of substances to be eliminated from the body into the tubule from the blood

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04/12/23

BASIC RENAL PROCESSES

GF

TR

TA

Urine Excreted

Efferent ArterioleAfferentArteriole

Glomerulus

KidneyTubule

Peritubular Capillary


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Glomerular Filtration

First step in urine formation180 liters/day filteredEntire plasma volume filtered 65

times/dayProteins not filtered


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Forces Involved inGlomerular Filtration

Glomerular CapillaryBlood Pressure + 55

Plasma Colloid Osmotic Pressure

-30

15

10

Bowman’s CapsuleHydrostatic Pressure

-

Net Filtration Pressure +


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Tubular Reabsorption

Water: 99% reabsorbed

Sodium: 99.5% reabsorbed

Urea: 50% reabsobed

Phenol: 0% reabsorbed


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Tubular Reabsorption

By passive diffusion

By primary active transport: Sodium

By secondary active transport: Sugars and Amino Acids


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Tubular Reabsorption is a Function of the Epithelial Cells Making up the Tubule

Lumen

Plasma

Cells


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Sodium Reabsorption

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water


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Rennin-Angiotensin-Aldosterone System

Stimulates Sodium Reabsorption in distal and collecting tubules

Naturetic peptide inhibitsIn absence of Aldosterone, 20mg of

sodium/day may be excretedAldosterone can cause 99.5%

retention


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Rennin-Angiotensin-Aldosterone System

Fall in NaCl, extracellular fluid volume, arterial blood pressure

JuxtaglomerularApparatus

ReninLiver

Angiotensin

+

Angiotensin Angiotensin Aldosterone

Lungs

ConvertingEnzyme

AdrenalCortex

IncreasedSodiumReabsorption

HelpsCorrect


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DIURETICS

ACE Inhibitors (Angiotensin Converting Enzyme): Cause loss of salt---> water follows

Atrial Naturetic Peptide (ANP) also inhibits sodium reabsorption

Osmotic diuretics: Are not reabsorbed


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Glucose and Amino Acids are reabsorbed by secondary active transport

They are actively transported across the apical cell membranes of the epithelial cells

Their active transport depends on the sodium gradient across this membrane

All other steps are passive


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GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM

Renal threshold (300mg/100 ml)

Plasma Concentration of Glucose

GlucoseReabsorbedmg/min

Filtered Excreted

Reabsorbed


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Tubular Secretion

Protons (acid/base balance)

Potassium

Organic ions


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Potassium Secretion

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water


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DUAL CONTROL OF ALDOSTERONE SECRETION

Fall in sodium

ECF Volume

Blood Pressure

Increased PlasmaPotassium

Increased Aldosterone secretion

Increased TubularPotassium Secretion

Increased UrinaryPotassium Secretion

Increased TubularSodium Reabsorption

Fall in Urinary

Sodium Excretion


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Reabsorption in Proximal Tubule (Summary)

Glucose and Amino Acids67% of Filtered SodiumOther Electrolytes65% of Filtered Water50% of Filtered UreaAll Filtered Potassium


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Secretion in Proximal Tubule (Summary)

Variable Proton secretion for acid/base regulation

Organic Ion secretion


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Reabsorption in Distal Tubule (Summary)

Variable Sodium controlled by Aldosterone

Chloride follows passively

Variable water controlled by vasopressin


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Secretion in Distal Tubule (Summary)

Variable Proton for acid/base regulation

Variable Potassium controlled by aldosterone


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Collecting Duct (Summary)

Variable water reabsorption controlled by vasopressin

Variable Proton secretion for acid/base balance


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REGULATION OF URINE CONCENTRATION

Medullary countercurrent system

Vasopressin


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Medullary countercurrent system

Osmotic gradient established by long loops of Henle

Descending limb

Ascending limb


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Descending limb

Highly permeable to water

No active sodium transport


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Ascending limb

Actively pumps sodium out of tubule to surrounding interstitial fluid

Impermeable to water


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COUNTERCURRENT MAKESTHE OSMOTIC GRADIENT

300

450

600

750

900

1050

1200

1200

From ProximalTubule

To DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

100

250

400

550

700

850

1000

1000

ActiveSodiumTransport

PassiveWaterTransport

Long Loopof Henle


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THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS PRESENT

From DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

300

400

550

700

850

1000

1100

1200

Interstitial Fluid

CollectingDuct

PoresOpen

Passive Water Flow


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WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS ABSENT A DILUTE URINE IS PRODUCE

From DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

100

100

100

100

100

100

100

100

Interstitial Fluid

CollectingDuct

PoresClosed

No Water FlowOut of Duct


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Renal Failure

Acute: Sudden onset, rapid reduction in urine output - usually reversible

Chronic: Progressive, not reversible

Up to 75% function can be lost before it is noticeable


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THE URINARY BLADDER STORES THE URINE

Gravity and peristaltic contractions propel the urine along the ureter

Parasympathetic stimulation contracts the bladder and micturition results if the sphincters (internal and external urethral sphincters) relax

The external sphincter is under voluntary control


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Reflex and Voluntary Control of Micturition

Bladder filling reflexively contracts the bladder

Internal Sphincter mechanically opens

Stretch receptors in bladder send inhibitory impulses to external sphincter

Voluntary signals from cortex can override the reflex or allow it to take place


Basic Processes Of Kidney

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