1. Renal blood flow is tightly regulated to maintain a constant rate of around 1200 mL/min despite wide changes in blood pressure, through mechanisms like autoregulation and tubuloglomerular feedback. 2. The kidneys receive a high blood flow of around 20-30% of cardiac output despite their small size, and oxygen consumption in the kidneys is very high, second only to the heart. 3. Blood enters the kidneys through the renal artery and is distributed through a branching network of arteries before entering the glomerular capillaries and surrounding the nephron tubules, with the renal veins collecting the blood and returning it to circulation.

1. Renal Blood Flow & JGA

2. 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

3. 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.

4. Renal capillaries
Glomerular 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

5. 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.

6. 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.

7. 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

8. 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 -

9. Auto regulation of renal blood flow
• Constant renal blood flow despite wide changes
in arterial blood pressure
• It is present in denervated kidney
• Mechanism
Aff 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

10. Blood Flow = Capillary
Pressure / Flow
resistance
1) Myogenic
Mechanism of the
autoregulation

11. 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

12. 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)

13. 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

15. Juxstaglomerular apparatus
Consist 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

16. Juxstaglomerular apparatus
Consists of
2. 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

17. 2. The juxtaglomerular apparatus
Including macula densa, extraglumerular mesangial cells, and juxtaglomerular (granular cells)
cells

20. 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

21. Renin-angiotensin systemRenin-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

22. Renin-angiotensin systemRenin-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.

23. Rennin-Angiotensin-Aldosterone System
Fall in NaCl, extracellular fluid volume, arterial blood pressure
Juxtaglomerular
Apparatus
ReninLiver
Angiotensinogen
+
Angiotensin I Angiotensin II Aldosterone
Lungs
Converting
Enzyme
Adrenal
Cortex
Increased
Sodium
Reabsorption
Helps
CorrectAngiotens
inase A
Angiotension III

24. ReninRenin
• 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)

25. 2934
2) Tubuloglomerular feedback

26. Is it Christmas yet...