Urogenital Module BMS305: Kidney Histology

Kidney Structure

• The kidney is a compound tubular gland that performs many functions (see physiology).

Outer Cortex

• Reddish and granular in appearance
• Subdivided into three regions:
  • Cortex proper: Just under the capsule
  • Columns of Bertini: Extensions of the cortex between medullary pyramids
  • Labyrinth: Around medullary rays

Inner Medulla

• Greyish in appearance
• Contains medullary pyramids (up to 18) and medullary rays (represent collecting tubules)
• Medullary pyramids are formed of collecting tubules, loops of Henle, and straight blood vessels (vasa recta)

Renal Lobe and Lobule

• Renal lobe: Medullary pyramid + overlying cortex proper
• Renal lobule: Medullary ray + corresponding cortical tissue (cortical labyrinth)
• Lobules are demarcated by interlobular arteries

The Nephron

• Functional part of uriniferous tubules
• 1-4 million per kidney
• Types: cortical nephron (short loop of Henle) and juxta-medullary nephron (long loop of Henle)

Components of the Nephron

• Malpighian renal corpuscle
• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule

Malpighian Renal Corpuscle

• Rounded body in the cortex, 200 µm in diameter
• Has two poles: urinary pole (continuous with proximal convoluted tubule) and vascular pole (through which afferent arteriole enters and efferent arteriole leaves)

Components of the Malpighian Corpuscle

• Bowman's capsule
• Glomerulus (glomerular capillaries)
• Mesangial cells

Bowman's Capsule

• Double-walled cup-shaped epithelial capsule
• Formed of outer parietal layer and inner visceral layer (podocytes) adherent to capillaries
• Capsular space between the two layers

Podocytes

• Modified squamous cells in the visceral layer of Bowman's capsule
• Separated from glomerular capillaries by subpodocytic space containing glomerular filtrate
• Formed of cell body, major cytoplasmic processes, and minor processes that terminate in feet processes firmly implanted on the basement membrane of glomerular capillaries
• Filtration slits (40 nm in diameter) are closed by slit diaphragms
• Functions: filtration, formation of renal blood barrier, and renewal of glomerular basement membrane

Glomerulus (Glomerular Capillaries)

• 50 tufts of blood capillaries arising from the afferent arteriole and draining to the efferent arteriole
• Electron microscopy shows fenestrated glomerular endothelium and thick glomerular basement membrane

Mesangial Cells

• Branched cells between glomerular capillaries and attached to their walls by processes
• Functions: support (secrete collagen and matrix), renewal of glomerular basement membrane, and change to macrophages to phagocytose foreign bodies and old basement membrane

Renal Blood Barrier (RBB)

• Barrier between blood in glomerular capillaries and glomerular filtrate in capsular space
• Components:
  • Glomerular endothelium with pores (100 nm)
  • Fused basement membranes of glomerular endothelium and podocytes (most effective component)
  • Slit diaphragms between feet processes of podocytes
• Functions: blocks blood cells and platelets, blocks plasma proteins (mainly albumin), and blocks small proteins and organic anions

Study guide for the urogenital module, covering the histology of the kidney, including its structure and functions.