URINARY SYSTEMURINARY SYSTEM

Overall FunctionOverall Function

Blood homeostasisExcretes wasteRegulates blood pressureErythropoeisisActivates Vitamin D

KidneysKidneys

Renal, Nephr-T12-L3 regionRetroperitonealProtective layers

– Renal capsule– Adipose capsule– Renal fascia

KidneyKidney

HilusCortexMedulla

– Renal pyramids (8-18)– Renal papilla

Pelvis– Minor calyx– Major calyx

Kidney MicrostructureKidney Microstructure

NephronFunctional unit of the kidneyGlomerulusNetwork of blood capillariesAfferent & Efferent arteriolesSlits & Pores

Nephron - TubulesNephron - Tubules

Glomerular capsule (Bowman’s capsule)– Renal corpuscle

Proximal convoluted tubule Descending limb of loop of nephron (Henle) Loop of nephron Ascending limb of loop of nephron Distal convoluted tubule Collecting tubule

Blood supplyBlood supply

1200 ml/minFilters blood volume 60 x/day1/5 CO

Nephron PhysiologyNephron Physiology

Controls blood concentration & volumeHelps regulate blood pHRemoves toxic waste from bloodUrine production (2-4 pts/day)

Glomerular filtrationGlomerular filtration

45 gallons of filtrate/day!Passive processGlomerulus to capsule

Glomerular filtrationGlomerular filtration

Net filtration pressure favors filtrationGlomerular blood pressure (60 mm Hg,

other caps are 10-30 mm Hg)Capsular pressure

– Opposes filtration

Colloid osmotic pressure– Opposes filtration

Arterial blood pressureArterial blood pressure

Stable glomerular filtration rateUrine output increases/decreases as blood

pressure increases/decreases

Sympathetic stimulationSympathetic stimulation

Tubular Reabsorption & Tubular Reabsorption & SecretionSecretion

Proximal convoluted tubulePermeable to solutes & they are actively

reabsorbedPermeable to water & it is passively

reabsorbedSome tubular secretion (H+ and K+)

Descending limbDescending limb

Relatively impermeable to solutesPermeable to water, it is reabsorbedInterstitial gradient promotes reabsorption

LoopLoop

Urea is recycled

Ascending limbAscending limb

Permeable to NaCl, it is reabsorbedImpermeable to water

Distal Convoluted TubuleDistal Convoluted Tubule

AldosteroneAnti-diuretic hormoneSecretion occurs (H+, NH3, drugs)Juxtaglomerular apparatus (where

precursors of erythropoeitin & renin are made)

Collecting tubule (ducts)Collecting tubule (ducts)

Aldosterone causes sodium reabsorptionADH causes water reabsorptionUrea to interstitial space

Vasa rectaVasa recta

Thin walled blood vessels serving tubulesCounter-currentMaintains interstitial concentrationsAids in concentrating urineSome water reabsorption

Other renal functionsOther renal functions

Vitamin D activationsErythropoietin precursorBlood pressure - renin

Minimum urine volumeMinimum urine volume

.5 liters/dayMaximum urine concentration is 1200

milliosmoles/literMake about 600 mosmol of waste/day600 mosmol waste/day / 1200 mosmol/liter

= .5 liters/day

UreterUreter

Kidney to bladderPeristalsis

Urinary BladderUrinary Bladder

Holds up to about 800 mls of urine in pelvic cavity

Internal & External sphinctersMicturition = UrinationMicturition reflexVoluntary urination

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UrethraUrethra

Urinary bladder to external urethral orificeLong in males, short in females