Renal Blood Flow & JGA

Renal blood flow

-1200-1300 mL/min (400ml/100gm/min)

-Renal fraction 20-30% of CO, while two kidney make <.5% of total body wt.

-Increased in cortex than medulla.

- RBF shows remarkable constancy due to autoregulation.

-Renal artery….............. afferent arteriol….. glomerular capillaries….efferent arteriole .peritubular capillaries……venos system

RBF & O2 Consumption

• Renal O2 consumption (6ml/100gm/min) very high being only second to heart (8ml).

• A-V O2 difference- (approx 1.5 ml/dl) of blood is smallest of the major organ system.

• O2 consumption – directly proportional to bld flow. Unlike other organs where bld flow related to O2 requirements of the organ.

Renal capillariesGlomerular capillaries

high hydrostatic pressure- (45 mmHg) why??

Peritubular capillaries

low hydrostatic pressure – (8 mmhg) help reabsorption

Vasa recta

loop U shaped supplying juxtamedullary nephrons

blood flow is few and sluggish…………………

concentration of urine

3. Blood Supply to the Kidney

• The renal artery -- segmental arteries -- interlobar arteries that communicate with one another via arcuate arteries.

• The arcuate arteries give off branches called interlobular arteries that extend into the cortex.

• Venous return of blood is via similarly named veins.

Blood Supply to the Kidney

• The interlobular arteries --afferent arterioles -- glomerulus - efferent arterioles --capillary network surrounding the tubule system of the nephron.

• The interlobular veins are then the collecting vessel of the nephron capillary system.

Characteristics of the renal blood flow:

1, 94% to the cortex

2, Two capillary beds

High hydrostatic pressure in glomerular capillary (about 50 mmHg) and low hydrostatic pressure in peritubular capillaries (about 10 mmHg)

Vesa Recta

Blood flow in kidneys and other organs

Organ Approx. blood flow(ml/min/g of tissue)

A-V O2 difference(ml/L)

Kidney 4.00 12-15(depends on reabsorption of

Na+ )

Heart 0.80 -

Brain 0.50 -

Skeletal muscle (rest)

0.05 -

Skeletal muscle (max. exercise)

1.00 -

Auto regulation of renal blood flow• Constant renal blood flow despite wide changes

in arterial blood pressure• It is present in denervated kidney• MechanismAff arteriolar VD BP RBF GFR Nacl reabsorption

Nacl at macula densa aff art VD & eff art VC ( renin-AT) RBF &GFR

Myogenic mechanism BP stretch of art wall VC RBF

Blood Flow = Capillary Pressure / Flow resistance

1) Myogenic Mechanism of the autoregulation

Autoregulation of glomerular filtration rate

-Constant GFR despite changes in ABP

-Mechanism

Tubuloglomerular feed back• decrease GFR….. Nacl at macula densa……… afferent

arteriolar VD & efferent arteriolar VC ( renin- AT)• Increase GFR…..more Nacl at macula densa ……VC of

afferent arteriole • Myogenic autoregulation

Increase ABP…….stretch….aff art VC

2. Neural regulation of GFR

• Sympathetic nerve fibers innervate afferent and efferent arteriole

• Normally sympathetic stimulation is low but can increase during hemorrhage and exercise

• Vasoconstriction occurs as a result which conserves blood volume(hemorrhage)and permits greater blood flow to other body parts(exercise)

3. Hormonal regulation of GFR• Several hormones contribute to GFR regulation• Angiotensin II. Produced by Renin, released by

JGA cells is a potent vasoconstrictor. Reduces GFR- NE,&ENDOTHELIN

• ANP(released by atria when stretched) increases GFR by increasing capillary surface area available for filtration

• NO• ANP,Bradikinin &• Prostaglandin E2

Juxstaglomerular apparatusConsist of

1. Juxtaglomerular cells/Granular cells- specialized myoepithelial cells

- located in the media of aff. arterioles - Stimulated by blood pressure- Secret renin- Have well developed ER, Mito, Robosomes and Golgi app.- Act as a BARORECEPTERs and respond to change in pressure. - Also stimulated by hypovolaemia and sympathetic discharge

Juxstaglomerular apparatusConsists of2. Macula densa- specialised renal tubular epithelial cells cells lining early DCT between aff. & eff. arterioles- stimulated by Nacl- Imp in autoregulation- Act as a chemorecepter

3. Lacis cells- Between aff & eff arterioles- Contain renin and immune complexes- In contact with both MD cells and JG cells

2. The juxtaglomerular apparatusIncluding macula densa, extraglumerular mesangial cells, and juxtaglomerular (granular cells) cells

ProstaglandinsProstaglandins

• A prostaglandin is any member of a group of lipid compounds that are derived from fatty acids and have important functions in the animal body.

• Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring.

• Hormone-like substances• Function:

– Vasodilatation– Increase of perfusion– Decrease of water reabsorption– Decrease of active Na+ transport in tubules

Renin-angiotensin system Renin-angiotensin system

• A hormone system that helps regulate long-term blood pressure and blood volume in the body.

• The system can be activated when there is a loss of blood volume or a drop in blood pressure (such as in a hemorrhage).

• If the perfusion of the juxtaglomerular apparatus in the kidneys decreases, then the juxtaglomerular cells release the enzymatic hormone renin.

• Activation: – from VOLUME RECEPTORS in afferent arteriole → decrease in perfusion →

decrease in tonus of afferent arteriole– from CHEMORECEPTORS in macula densa → decrease of NaCl in macula

densa cells

Renin-angiotensin system Renin-angiotensin system

• Renin activates the renin-angiotensin system by cleaving angiotensinogen, produced in the liver, to yield angiotensin I, which is further converted into angiotensin II by specialized cells of the lung capillaries.

• Angiotensin II then constricts blood vessels, increases the secretion of ADH and aldosterone, and stimulates the hypothalamus to activate the thirst reflex, all these actions leading to increased blood pressure.

Rennin-Angiotensin-Aldosterone System

Fall in NaCl, extracellular fluid volume, arterial blood pressure

JuxtaglomerularApparatus

ReninLiver

Angiotensinogen

+

Angiotensin I Angiotensin II Aldosterone

Lungs

ConvertingEnzyme

AdrenalCortex

IncreasedSodiumReabsorption

HelpsCorrectAngiotens

inase A

Angiotension III

Renin Renin

• Also known as angiotensinogenase, is a circulating enzyme released mainly by juxtaglomerular cells of the kidneys in response to low blood volume or low body NaCl content.

• Actions of renin:– Vasoconstriction in efferent arteriole (increase of glomerular

filtration)– Peripheral vasoconstriction (increase in blood pressure)– Secretion of aldosterone (reabsorption of Na+ and water)

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2) Tubuloglomerular feedback

Is it Christmas yet. . .