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

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

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All join to form PORTAL V (portal vessel)

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Drains into HEPATIC SINUSOIDS (caps 2)

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R), Middle, L) hepatic veins

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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)
Renal
  • 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

APG

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

Hypothalamus secretes hormones into PIRMARY CAPS (caps 1)

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Hormones travel down HYPOPHYSEAL PORTAL SYSTEM (portal)

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

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

  • GnRH, CRH, GHRH, TRH