Now that you are familiar with the overall organization of the kidney, let’s study the structures of the cortex in more detail.

• Using these sections of human kidney (sample 1, sample 2), examine the structures in the cortex at higher magnification. Note the presence of renal corpuscles and their associated convoluted tubules, as well as the straight tubules constituting the medullary rays, as seen in the image at the right.

• Study figure 19-5 in Junqueira’s Histology 14e and the image at the right of renal corpuscles. Examine renal corpuscles on the slides at higher magnification, and identify the simple squamous epithelium of Bowman's capsule, urinary space, glomeruli, and the large, pale podocytes. Mesangial cells that have a variety of functions (e.g. phagocytic and immune functions) are also present among the podocytes, but they are difficult to identify.
• Try to find examples of renal corpuscles that are cut to show the afferent or efferent arterioles, macula densa, and juxtaglomerular apparatus. It can be difficult to find these structures. The juxtaglomerular apparatus contains specialized smooth muscle juxtaglomerular cells and lacis cells (extraglomerular mesangial cells). Juxtaglomerular cells secrete renin, a protease that activates the renin-angiotensin-aldosterone system involved in blood pressure regulation. The macula densa regulates filtration rates in response to glomerular pressure and tubular fluid composition. The extraglomerular mesangial cells have functions similar to the mesangial cells associated with the podocytes and glomeruli.

Study the diagram and electron micrograph of glomeruli and their associated podocytes below and identify:

• Podocytes and their pedicels (foot processes)
• Fenestrated capillary endothelial cells
• Glomerular basement membrane
• Urinary (Bowman's) space

Note the organization of the podocyte pedicels and the endothelial cell fenestrations in close association with their shared basement membrane. These structures constitute the apparatus where blood is filtered to produce the initial urine that collects in the urinary space before it enters into the proximal convoluted tubule.

Clinical note: The inflammatory condition known as glomerulonephritis results from an autoimmune cross reaction on the part of the host against streptococcal antigens. Infections triggering this reaction can occur in either the skin or throat. The inflammatory response is largely confined to the glomeruli, damaging the capillaries and basement membrane to the extent that proteins and erythrocytes may appear in the urine. The injury results from antigen-antibody complexes getting stuck in the glomerular filter.


Next let's consider kidney infections and look at examples of the nephron.