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Functional Anatomy of Kidney

Nephron = Renal tubule + glomerulus
Glomerulus + Bowman’s capsule = malphigion corpuscle.


Note that there are 2 ‘routes’ through which a substance can enter the renal tubule Viz ‘(A)’ and ‘(B)’ [A – By Glomerular filtration, B – By peritubular capillary exchange]

Glomerular Membrane

The barriers through which filtration has to take place

  • Glomerular endothelial cell layer : The glomerular capillaries are fenestrated (most permeable capillaries), the pore size of the fenestrae is 70 – 90 nm.
  • Basement membrane: Permeability of basement membrane depends on:

a. Size of particle

Neutral substances which are < 4nm are freely filtered; > 8nm are not filtered

Between 4 nm and 8nm, the permeability is inversely proportional to the diameter

b. Charge of the particle

Since the sialoprotein in the glomerular capillary wall are negatively charged, filtration of positively charged particles is facilitated whereas negatively charged particles are repelled. That why there is only 0.2% filterability of albumin(negatively charged) although it is filterable by size( effective diameter of ~ 7 nm.)

c. Visceral epithelial layer of Bowman’s capsule
. The visceral epithelial cell is called a podocyte; each podocyte has many foot processes, which inter digitate to form filtration slits:

The size of filtration slits = 25 nm.

Difference between Proximal Tubular Cell and Distal Tubular Cell




1. Brush border present

No brush border

2. Carbonic anhydrase present in luminal membrane

No carbonic anhydrase in luminal membrane

3. Has ‘leaky’ tight junctions

Has ‘tight’ tight junction

Difference between Cortical and Juxtamedullary Nephron


Cortical nephron

Juxtamedullary nephron

Form 85% of the nephrons

Form 15% of the nephrons

Short loop of Henle

Long loop of Henle

Peritubular capillary network is short

Form vasa recta

Blood flow is large

Blood flow is less

O2 extraction is very less

O2 extraction is large

PO2 is 50mmHg

PO2 is 15mmHg

Role in excretion of waste products in urine Involved in counter current system far formation of concentrated urine.

Special Cells in Collecting Tubule

  1. P (Principal) cell: For Na+ reabsorption
  2. I (Intercalated) cell: They are present in Cortical Collecting Duct.

Intercalated cells come in α and β varieties and participate in acid-base homeostasis.


Type of cell



α-intercalated cells

acid (via an apical H+-ATPase and H+/K+ exchanger) in the form of hydrogen ions

bicarbonate (via band 3, a basolateral Cl-/HCO3- exchanger)

β-intercalated cells

bicarbonate (via Pendrin a specialised apical Cl-/HCO3-)

acid (via a basal H+-ATPase)

Mesangial Cells

1. Intraglomerular mesangial cells (Lying between glomerular capillary loops)

These are contractile cells and play a role in regulation of glomerular filtration (Note: When these contract, the GFR decreases because the effective area of filtration is reduced) Agents causing their




Angiotensin II



Platelet activating factor

Platelet derived growth factor


Thromboxane A2

Leukotrienes C4 and D4









2.  Extra glomerular mesangial cells (Lacis cells)

These form part of the juxta – glomerular apparatus.

Secrete mesangial matrix,  phagocytic, inflammatory.

Juxtaglomerular Apparatus

Components are:

  • Juxtaglomerular cells These are modified smooth muscle cells in the tunica media of the afferent arteriole. The cells have renin containing granules. Stimulated by low Blood vol., Low BP, Low Na+, Sympathetic stimulation, Thromboxane A2.
  • Macula densa This is the modified region of the tubular epithelium; it marks the beginning of DCT. Act as sensor for Na Lacis cells

Mineralocorticoid receptor are not present on : (AIIMS Nov 08)
a. Distal nephron
b. Colon
c. Liver
d. Hippocampus


C. Liver

Renal Vessels / Renal Nerves

Renal vasodilation: Dopamine, prostaglandins, acetyl choline, high protein diet.

Renal vasoconstriction:

  1.  Angiotensin II Constricts efferent arteriole more than afferent arteriole so RBF GFR
  2. Norepinephrine Constricts afferent arteriole more than efferent arteriole so RBF GFR
Effect of stimulation of sympathetic nerves to kidney
  1. Vasoconstriction (Which decrease renal blood flow and GFR)
  2. Increases renin output Increases Na+ reabsorption
  3. Peritubular capillaries secrete Erythropoietin (85%) rest from liver etc

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