Regional Circulations — Portal Systems

Historical · V4 (2023) → G4.ii 1 exam appearance

2011B Q09

Exam question

Define a Portal System. Describe the anatomy and function of three portal systems in the body.

CICMWrecks answer

Master answer

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

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)

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

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

Past papers

1 appearance

Exam	Exact exam wording	Candidate success
2011B Q09	Define a Portal System. Describe the anatomy and function of three portal systems in the body.	32%