5.2.4

• the three are :

  • the outer region is called the cortex
  • the inner region is called the medulla
  • the centre is the pelvis, which leads into ureter

  In a longitudinal section you can see that the kidney contains 3 regions surrounded by a tough capsule

  A) cortex

  B) medulla

  C) pelvis

  D) ureter

  
• Fine structure of kidney

  bulk of each kidney consists of tiny tubules called nephrons

  • each nephron starts in the cortex at a cup-shaped structure called the Bowman’s capsule
  • the remainder of the nephron is a coiled tubule that passes through cortex, before joining a collecting duct that passed back down into medulla

  you can tell which tubules are proximal by the microvilli on the inner surface of wall ; distal tubers are smoother

  A) glomerulus

  
• Blood supply and filtering

  renal artery splits to form many afferent arterioles, which each lead to a knot of capillaries called glomerulus

  • blood from glomerulus continues into an efferent arteriole which carries the blood to more capillaries surrounding the rest of the tubule

  → these capillaries eventually flow together into renal vein

  • each glomerulus is surrounded by Bowman’s capsule
  • fluid from the blood is pushed into Bowman’s by process of ultrafiltration
• Blood supply and filtering 2

  • filter is the barrier between blood in capillary + lumen of the Bowman’s capsule
  • barrier consists of three layers, adapted to enable ultrafiltration :
  • endothelium of capillary

  narrow gaps between cells of endothelium of the capillary wall

  cells of the endothelium also contains pores, called fenestration

  these gaps allow blood plasma + substances dissolved in it to pass out capillary

  A) afferent

  B) efferent

  C) podocytes

  D) basement

  E) foot

  
• Blood supply and filtering 3

  the basement membrane

  consists of fine mesh of collagen fibres glycoproteins

  → mesh acts as a filter to prevent passage of molecules with a relative molecular mass of greater than 69000

  → most proteins and all red blood cells are held in capillaries of glomerulus
• Blood supply and filtering 4

  Bowman’s capsule epithelial cells

  podocytes

  • they have many finger-like projections called major processes

  → each major process are minor processes or foot processes that hold cells away from endothelium of capillary

  these projections ensure that there are gaps between cells

  fluid enters into lumen of Bowman campsule

  3 parts of Bowman capsule leading to enter collecting ducts

  • proximal convoluted tubule
  • loop of Henle
  • distal convoluted tubule
• a nephron

  A) loop of Henle

  B) renal

  C) proximal

  D) distal

  E) peritubular

  
• Filtrate moves through the structures in a nephron in the following order:

  • Bowman's capsule (renal capsule) - This surrounds a capillary ball known as the glomerulus, from which filtrate is formed, and contains cells called podocytes in its inner layer.
  • Proximal convoluted tubule (PCT) - This section reabsorbs useful substances, including water, glucose, and salts, into surrounding capillaries and the epithelial cells in its wall have microvilli to increase their surface area.