I am a medical student. I have one friend who is persuing his MBBS degree in Taishan Medical UNiversity. I got these notes from him. These notes are by Dr. Bikesh, He is a famous lecturer of TMU. These notes have helped me a lot and i also watch his lecture videos , which are great; highly simple and huge content. I am uploading with Renal physiology. If you want some other topics i would upload for you. "Let the Knowledge be spread" Dr. Bikesh

1. Renal Physiology 2Renal Physiology 2
Dr. Bikesh Pandey

2. Urine formation 1Urine formation 1

3. Renal Blood SupplyRenal Blood Supply

4. Renal Blood SupplyRenal Blood Supply

5. Renal blood flow (RBF)Renal blood flow (RBF)
• It is the volume of blood delivered to the kidneys per unit time.
• Kidneys receive roughly 22% of cardiac output.
• Thus, RBF = 1.1 L/min in a 70-kg adult male.
Renal plasma flow (RPF)Renal plasma flow (RPF)
• It is the volume of blood plasma delivered to the kidneys per
unit time.
• Since plasma in blood is about 55% , RPF = 605 ml/min

6. Urine FormationUrine Formation
• Results from :
– Glomerular Filtration
– Tubular Reabsorption
– Tubular Secretion

8. Excretion Rate ofExcretion Rate of
different Substancesdifferent Substances
Panel APanel A
• Substance is freely filtered by the
glomerular capillaries but is neither
reabsorbed nor secreted.
• Excretion rate = Filtration rate
• Eg: Creatinine
Panel BPanel B
• Substance is freely filtered but is
also partly reabsorbed from the
tubules
• Excretion rate < Filtration rate
• Eg: Most of the electrolytes

9. Excretion Rate ofExcretion Rate of
different Substancesdifferent Substances
Panel CPanel C
• Substance is freely filtered & is fully
reabsorbed thus is not excreted
• Excretion rate = 0
• Eg: AA and Glucose
Panel DPanel D
• Substance is freely filtered & is not
reabsorbed, but additional quantities of
this substance are secreted from the
peritubular capillary
• Excretion rate = Filtration rate +
Secretion rate
• Eg : Organic acids and Bases blood

10. Urinary space
Slit pores

11. Glomerular FiltrationGlomerular Filtration
• It is the “First Step” in Urine Formation.
• Blood is filtered through Filtration Barrier.Filtration Barrier.
Filtration BarrierFiltration Barrier
• Endothelium
• Basement Membrane
• Filtration slit

12. Glomerular FiltrationGlomerular Filtration
Glomerular filtration rate (GFR)Glomerular filtration rate (GFR)
• It is the volume of fluid filtered from the glomerular
capillaries into the Bowman's capsule per unit time.
• Normal GFR is about 125 ml/min, or 180 L/day
• RPF is 605 ml/min & GFR is 125 ml/min, thus it can be
said that GFR is 20% of RPF, suggesting 20% of the
plasma is filtered through glomerulus that reaches to
kidney.

13. Glomerular FiltrationGlomerular Filtration
Importance of High GFRImportance of High GFR
• We know that,
– Entire plasma volume is only about 3 L.
– GFR is about 180 L/day
This means : the entire plasma can be filtered and
processed about 60 times each day.
• This is necessary to be able to remove waste products

14. Glomerular FiltrationGlomerular Filtration
FilterabilityFilterability
• It is the “Degree of easiness for a substance to cross
the glomerulus”
• It is inversely propotional to Molecular weight (MW).
• Negative charged molecules cross less easily than
positive charged molecule for same MW, due to the
fact that basement membrane and podocytes are also
negatively charged.

15. <> A filterability of 1.0 means that the substance is filtered as freely as water;
<> A filterability of 0.75 means that the substance is filtered only 75 per cent as
rapidly as water

16. Glomerular FiltrationGlomerular Filtration
Composition of the Glomerular FiltrateComposition of the Glomerular Filtrate
• Glomerular filtrate is essentially:
– Devoid of cellular elements like RBC/WBC/PLT and
– Protein-free
• The concentrations of most salts and organic molecules, are similar to the
concentrations in the plasma.
– Exceptions include
• Calcium and fatty acids
• Because of the fact that, they are partially bound to the plasma proteins.
• Almost one half of the plasma calcium and most of the plasma fatty acids are bound to
proteins, and these bound portions are not filtered through the glomerular capillaries.

17. Glomerular FiltrationGlomerular Filtration
(1) Hydrostatic pressure of glomerular capillaries
- Promotes filtration
(2) Hydrostatic pressure of Bowman’s capsule
- Opposes filtration
Determinants of the GFRDeterminants of the GFR
(Fluid Dynamics)
The GFR is determined by “Net filtration pressure”
Which is determined by the the following forces:

18. Glomerular FiltrationGlomerular Filtration
(3) Osmotic pressure of glomerular capillary - Opposes filtration
(4) Osmotic pressure in Bowman’s capsule - Promotes filtration
– We know that, protein is not filtered through glomerulus.
– Concentration of protein in the glomerular filtrate is so low that the colloid
osmotic pressure of the Bowman’s capsule fluid is considered to be zero.
Determinants of the GFRDeterminants of the GFR
(Fluid Dynamics)
The GFR is determined by “Net filtration pressure”
Which is determined by the the following forces:

20. Glomerular FiltrationGlomerular Filtration
Calculation of GFRCalculation of GFR

21. Glomerular hydrostatic pressureGlomerular hydrostatic pressure
• It is determined by three variables:
(1) Arterial pressure
∞∞ GFRGFR
(1) Afferent arteriolar resistance
1/∞ GFR1/∞ GFR
(3) Efferent arteriolar resistance
∞∞ GFRGFR in the beginning; later onin the beginning; later on 1/∞ GFR1/∞ GFR
The initial increase causes blood to stay in glomerulus for longerThe initial increase causes blood to stay in glomerulus for longer
time thus GFR increases , but as soon as resistance increasestime thus GFR increases , but as soon as resistance increases
more than 3 folds in efferent arteriole the RPF decreases, So GFRmore than 3 folds in efferent arteriole the RPF decreases, So GFR

23. Filtration FractionFiltration Fraction ( FF = GFR / RPF )( FF = GFR / RPF )
• It is the ratio of the GFR to the RPF.
• Increasing the filtration fraction also concentrates the plasma
proteins and raises the glomerular colloid osmotic pressure.

24. Control of GFRControl of GFR

25. Control of GFRControl of GFR
• Norepinephrine & Epinephrine
– Released from the adrenal medulla.
– They constrict afferent and efferent arterioles, causing
reductions in RBF & thus GFR is reduced.
• EndothelinEndothelin
– Released by damaged vascular endothelial cells
– It is a powerful vasoconstrictor.

26. Control of GFRControl of GFR
• Endothelial-Derived Nitric OxideEndothelial-Derived Nitric Oxide
– Released by the endothelium.
– Decreases Renal Vascular Resistance and Increases GFR
• Prostaglandins and BradykininProstaglandins and Bradykinin
– It causes vasodilation & GFR is increased.
– These vasodilators are not of major importance in regulating GFR in
normal conditions, but Under stressful conditions, such as volume
depletion or after surgery, the administration of nonsteroidal anti-
inflammatory drugs (NSAID’s), such as aspirin, that inhibit prostaglandin
synthesis may cause significant reductions in GFR.

27. Control of GFRControl of GFR
• Angiotensin IIAngiotensin II
– It preferentially constricts efferent arterioles.
– It should be kept in mind that increased angiotensin II
formation usually occurs in circumstances associated with
volume depletion, which tend to decrease GFR.
– In these circumstances, angiotensin II, by constricting
efferent arterioles, helps prevent decreases in glomerular
hydrostatic pressure and GFR.
– Thus it is better to say “Angiotensin II prevents ↓in GFR due
to volume depletion”

29. Tubuloglomerular FeedbackTubuloglomerular Feedback
• This feedback autoregulates RBF and GFR.
• This mechanism is specifically directed toward stabilizing NaCl
delivery to the distal tubule.
• Has two components:
(1) An afferent arteriolar feedback mechanism
(2) An efferent arteriolar feedback mechanism.
• These feedback mechanisms depend on special anatomical
arrangements of the Juxtaglomerular apparatusJuxtaglomerular apparatus

30. Tubuloglomerular FeedbackTubuloglomerular Feedback
Juxtaglomerular apparatusJuxtaglomerular apparatus
(1) Macula densa(1) Macula densa
(2) Juxtaglomerular (JG) cells(2) Juxtaglomerular (JG) cells
(3) Extraglomerular mesangium(3) Extraglomerular mesangium

31. Tubuloglomerular FeedbackTubuloglomerular Feedback
• Not completely understood.
• Experiment suggests that decreased GFR
slows the flow rate in the loop of Henle,
causing increased reabsorption of sodium and
chloride ions in the ascending loop of Henle,
thereby reducing the concentration of sodium
chloride at the macula densa cells.

32. Tubuloglomerular FeedbackTubuloglomerular Feedback
• This decrease in sodium chloride concentration initiates a signal from the
macula densa that has two effects :
1. It decreases resistance to blood flow in the afferent arterioles
– Which raises glomerular hydrostatic pressure and helps return GFR toward
normal
2. It increases renin release from the juxtaglomerular cells
– Renin increases the formation of angiotensin I from angiotensinogen, which is
converted to angiotensin II.
– Finally, the angiotensin II constricts the efferent arterioles, thereby increasing
glomerular hydrostatic pressure and returning GFR toward normal.

33. TubuloglomerularTubuloglomerular
FeedbackFeedback

34. Myogenic Autoregulation of RenalMyogenic Autoregulation of Renal
Blood Flow and GFRBlood Flow and GFR
• Another mechanism that contributes to
maintenance of a relatively constant renal
blood flow and GFR.
• Ability of individual blood vessels to resist
stretching during increased arterial pressure, a
phenomenon referred to as the myogenic
mechanism.
• Muscles of small arterioles respond to
increased wall tension or wall stretch by
contraction of the vascular smooth muscle.

35. Myogenic Autoregulation of RenalMyogenic Autoregulation of Renal
Blood Flow and GFRBlood Flow and GFR (cont.)(cont.)
• Stretch of the vascular wall allows increased
movement of calcium ions from the
extracellular fluid into the cells, causing them to
contract.
• This contraction prevents over distention of the
vessel and at the same time, by raising
vascular resistance, helps prevent excessive
increases in renal blood flow and GFR when
arterial pressure increases.

36. Why increased protein intake causesWhy increased protein intake causes
increased GFR?increased GFR?
• GFR and renal blood flow increase 20 to 30 per cent within 1 or
2 hours after a person eats a high-protein meal.
Possible explanation is the following:
• Increased release of AA in blood, which are reabsorbed in the
PCT.
• AA and sodium are reabsorbed together by the proximal
tubules, increased amino acid reabsorption also stimulates
sodium reabsorption in PCT.
• This decreases sodium delivery to the macula densa, which
elicits a tubuloglomerular.
• Decreased afferent arteriolar resistance then raises renal blood

37. Why polyuria in Diabetes?Why polyuria in Diabetes?
• Large increases in blood glucose levels in
uncontrolled diabetes mellitus.
• Because glucose is also reabsorbed along with
sodium in PCT, increased glucose delivery to
the tubules causes them to reabsorb excess
sodium along with glucose.
• This, in turn, decreases delivery of sodium
chloride to the macula densa, activating a
tubuloglomerular feedback.

38. DM , HTNDM , HTN
Urinary tract obstruction (kidney stone)Urinary tract obstruction (kidney stone)
↑↑ plasma proteinsplasma proteins
↓↓Arterial pressure in fluid lossArterial pressure in fluid loss
↓↓Angiotensin IIAngiotensin II
↑↑Sympathetic activity, vasoconstrictorSympathetic activity, vasoconstrictor
hormones (NE, Endothelin)hormones (NE, Endothelin)

39. To be continued…To be continued…