G4iii: Define a portal system. Describe the anatomy & function of three portal systems in the body

  • Portal system = arrangement where blood is collected from one set of capillaries passes through another vessel (portal) to another set of capillaries before entering the systemic circulation

3 Portal Systems

1. Liver

  • Deoxygenated blood from: distal oesophagus, SB, colon, rectum, spleen

Drain into sup. mesenteric v., inf. Mesenteric v., splenic v.

All join to form PORTAL V (portal vessel)

Drains into HEPATIC SINUSOIDS (caps 2)

R), Middle, L) hepatic veins

Drain into IVC


  • Function:
    • Portal circulation carries nutrients, absorbed drugs, old RBCs to the liver
    • Liver as an immune organ filters for Ag removal & metabolises absorbed nutrients for synthesis/storage/presentation to systemic circulation

2. Renal

  • Kidneys receive 25% CO (600mL/min/kidney)
  • Function
    • 2 capillary beds

Glomerular caps → ↑hydrostatic P → promotes filtration (60mmHg)

Peritubular caps → ↓hydrostatic P → promotes reabsorption (15mmHg)

  • Peritubular capillaries surround nephron, along LoH & allow stronger reabsorption capacity

Hypothalamus & Pituitary Gland

  • Hypothalamus forms floor & walls of 3rd ventricle
  • It is the central relay station for the endocrine system
  • Gathers signals from environment → integrates → sends on info/commands via hormones + neurotransmitters
  • Pituitary gland lies directly under hypothalamus
    • ADENOHYPOPHYSIS (ant lobe) = APG
    • NEUROHYPOPHYSIS (post lobe) = PPG

NB: Independent origins & separate functions


  • No nervous connection to hypothalamus
  • Hypothalamus linked to APG via HYPOPHYSEAL PORTAL SYSTEM

Hypothalamus secretes hormones into PIRMARY CAPS (caps 1)

Hormones travel down HYPOPHYSEAL PORTAL SYSTEM (portal)

Hormones diffuse OUT of SECONDARY CAPS (caps 2) into pituitary tissue

Function: connects hypothalamus to APG, allows rapid exchange of hormones