podocyte). The capillary tuft will invaginate and occupy the
Bowman's capsule to form the renal corpuscle.
Figure 1.3 shows a cross section of the glomerulus which is
composed of:- Bowman's capsule with its outer (parietal) layer lined by flat
epithelial cells, and inner visceral layer in contact with capillary tuft
lined with visceral epithelial cells (podocytes). Between the two
layers there is a space called urinary space. - Glomerular capillaries are lined by basement membrane which is
covered from inside with endothelial cells and from outside by
epithelial cells (podocytes). - Mesangium is composed of special cells and matrix. It is located
mainly at the hilum of the glomerulus, and extends between capillary
loops. Its main function is to support the capillary tuft, also, it may
have a phagocytic function and contractile function.
Phagocytic property of the mesangium helps in clearing the
glomerulus from any circulating immune complexes or antigens. The
contractile function may help in modulating the renal blood flow and
the capillary wall filtration surface.
Juxta-glomerular apparatus:
Juxta-glomerular apparatus is a specialized structure which is
present at the hilum (vascular pole) of the glomerulus (Figure 1.4). It is
composed of four groups of cells which contain granules in their cytoplasm
(most probably renin). These cells are:
- The macula densa cells which are modified cells in distal
convoluted tubules. - The epithelioid cells which are modified cells in the wall of the
afferent and-to less extent-efferent arterioles.