Regional Circulations

Master answer

Portal System

• System where two separate capillary beds are supplied in consecutive series, before blood returns to the heart

Hepatic portal system

• Anatomy
  • Arterial blood perfuses the GI tract (from stomach to proximal rectum) via the Coeliac trunk, superior mesenteric arteries and inferior mesenteric arteries.
  • Capillary blood from GI tract drain to superior mesenteric and inferior mesenteric veins which converge to form the portal vein
  • Portal vein perfuses the liver as part of the portal triad
  • Hepatic venous blood drains into the inferior vena cava before returning to the heart
• Function
  • Protects systemic circulation from blood from portal venous blood
    • Toxins absorbed from GI tract (ammonia) metabolized by liver before reaching systemic circulation
    • Pathogens encounter leukocytes (e.g. macrophages) in space of Disse in liver
    • Fluctuation in blood constituents due to GI absorptions buffered by liver (e.g. glucose)

Renal portal system

• Anatomy
  • Renal arterial blood perfuses the renal cortex via afferent arterioles à glomeruli
  • Glomeruli drain blood into efferent arterioles
  • Efferent arteriolar vessels drain into peritubular capillary network
  • Proportion of efferent arteriolar vessels form vasa recta which supply blood to renal medullary interstitium via vasa recta à drains to renal venules and veins before returning to heart
• Function
  • As peritubular capillary network has lost Na and H₂O to glomerular filtrate à increases reabsorptive capacity of renal tubules due to concentration gradients

Hypothalamic-Pituitary Axis

• Anatomy
  • Arterioles from superior hypophysial artery (branch of circle of willis) supply hypothalamus via primary plexus à drains to portal hypophysial vessels
  • Portal veins supply anterior pituitary
  • Blood returns to heart via internal jugular vein
• Function
  • Delivery of tropic hormones to anterior pituitary for signalling
    • CRH
    • TRH
    • GnRH
    • GRH
    • PRH

Sakurai 2016

Answer by Sakurai