Glomerular Histology

Overview
  • The glomerulusg is essentially a small tuft of capillaries, known as the glomerular capillaries, surrounded by a several layers of epithelial cells which provide a selective filtration barrier and direct filtered fluids into the remainder of the nephron.
Basic Structures
  • Renal Afferent Arteriole:
    • This is an arteriole through which blood enters the glomerular capillaries.
  • Glomerular Capillaries:
    • This is a small tuft of inter-connecting capillaries with a fenestrated endothelium and specialized basement membrane known as the glomerular basement membrane which is involved in selective filtration of blood
  • Podocytes
    • Podocytes are a specialized type of epithelial cell which directly invest the glomerular capillaries and are critical for the selectivity of glomerular filtration. Uniquely, podocytes contact the glomerular capillaries' basement membrane using thin outpouchings known as "Foot Processes" that are closely approximated with one another. The narrow area between adjacent foot processes forms an extremely thin slit which is sometimes termed the "Slit Diaphragm".
  • Renal Efferent Arterioles:
    • These are the vessels through which blood exits the glomerular capillaries. Although vasculature lying after a set of capillaries would be typically be considered a venule, the vasculature which drains the glomerular capillaries is histologically similar to arterioles and is thus termed a "Renal Efferent Arteriole".
  • Bowman's Capsule:
    • This is a layer of epithelial cells that surrounds the glomerular capillaries and is continuous with the epithelium of the proximal tubule. Fluid filtered through the Glomerular Capillaries is thus directed into the proximal tubule by the Bowman's Capsule.
  • Bowman's Space:
    • Simply refers to the histological space between the Bowman's Capsule and the glomerular tuft.
  • Mesangium:
    • The mesangium is a basement membrane-like matrix in which the glomerular capillaries are embeded and which provides them structural support. Mesangial cells live within the mesangium and maintain this matrix.