We have 2.2-2.4 million nephrons in both kidneys (1.1-1.2 in each).
 

Glomerulus:

(The functional filtration unit of the nephron) is a group of anastomosing capillaries in the kidney invested in two layers of epithelium making Bowman’s capsule, and imbedded in the mesangium.​

• Glomerular capillary tuft (imbedded in mesangium) is invested in two layers of epithelium:

  • Inner visceral epithelial cells with podocytes separated from the capillaries by basement membrane.

  • Outer parietal epithelial cells. 

  • The space between the two layers is called Bowman’s space.

  • Glomerular capillary tuft + the epithelial cells → glomerulus.

Holes are present in the endothelial cells called fenestrations, sized 70-100 nm, to enhance the filtration process. 

Basement Membrane:

• Negatively charged.

• Central area is dense, called lamina densa. The peripheral areas are less dense and called lamina rara, the one that’s toward the endothelial cells is called lamina rara interna, and the one toward the bowman capsule is called lamina rara externa.

• It is made up of collagen type IV with negatively charged molecules (3 alpha peptide chains, making a triple helix):

• The start of the peptide chain is called globular non-collagenous domain, which can be subject to antibodies, causing Anti-GBM-antibodies (Anti-GBM-glomeronephritis)→ presents with hematuria. The same antibodies may react with alveolar basement membrane in the lungs (being called Anti-ABM-antibodies), presenting with hematemesis.

• If the antibodies are attacking the kidneys and lungs, presenting with hematuria and hematemesis, they cause a syndrome called Goodpasture syndrome.​

• Mutations in the basement membrane cause hereditary nephritis.

 

​Visceral epithelium:

• The space between the visceral epithelium cells is 20-30 nm, covered with is a filtration diaphragm made of the protein nephrin, against which there may be antibodies causing proteinuria.

• They have finger like processes called podocytes.

Mesangial cells:

• Contractile, phagocytosis, proliferate, and they can produce pathologically active products.

Collagen:

• I→ bones.

• II → cartilage.

• III → many places.

• IV → basement membrane.

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Glomerular filtration barrier is a size and charge barrier (allowing only small and positively charged molecules to pass easily).

• Minimal change glomerulopathy → cytokine produced neutralizes the negatively charged basement membrane → albumin pass through the filtration barrier →​ albuminuria. 

  • Commonest cause of Nephrotic syndrome in children. 

  • Only seen in electronic microscope. 

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References:

• Dr. Najeeb Lectures. Dr. Najeeb Lectures - World's Most Popular Medical Lectures [Internet]. 2016 [cited 16 February 2016]. Available from: http://www.drnajeeblectures.com

• Hall J, Guyton A. Guyton and Hall textbook of medical physiology.

• Kumar P, Clark M. Kumar & Clark's clinical medicine.

• Le T, Krause K. First aid for the basic sciences. New York: McGraw-Hill Medical; 2012.

• Arias L. Histol glomérulo [Internet]. Kidneypathology.com. 2016 [cited 16 February 2016]. Available from: http://www.kidneypathology.com/English_version/Glomeruli_histology.html (Figure 1)

• 303. Jci.org. JCI -What determines glomerular capillary permeability? [Internet]. 2016 [cited 16 February 2016]. Available from: http://www.jci.org/articles/view/23577/figure/1 (Figure 2).

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Written by:         Lama Al Luhidan
Reviewed by:     Bassam AlGhamdi
                            Roaa Amer
Format editor:   Adel Yasky

Publisher:           Bader Altamimi