Define a Portal System. Describe the anatomy and function of three portal systems in the body.
A portal system is an arrangement by which blood collected from one set of capillaries passes
through a large vessel or vessels, to another set of capillaries before returning to the systemic
circulation. The three portal systems are the -
1) system of blood vessels that link the hypothalamus and the anterior
pituitary in the brain, which allows endocrine communication between the two structures.
2) within the liver, whereby venous blood from the GI tract drains into the superior and
inferior mesenteric veins; these two vessels are then joined by the splenic vein to form the
portal vein which enters the liver, drains into the hepatic sinusoids and then eventually
into the hepatic veins which join the inferior vena cava, with the purpose of defending
against by breaking down and metabolising most of what has been absorbed from the
gastrointestinal tract (including an immunoprotective action).
3) within the kidney, whereby blood from the afferent arterioles enters the glomerulus (first
capillary network), followed by the efferent arterioles, then the peritubular network
(second capillary network) and eventually the venous system, with the purpose of
stronger re-absorptive capacity for water from within long Loops of Henle that go deep
within the renal medulla
Recommended sources: Ganong Review of Medical Physiology Chps 18, 38, 29
Definition of a portal circulation:
Feeding artery: SMA, IMA, coeliac trunk
Primary capillary bed: intestinal capillaries
Portal vessel: the portal vein
Secondary capillary bed: hepatic sinusoids
Draining vein: hepatic veins
|Portal blood undergoes metabolic and immune modifications in the hepatic sinusoid, which allow for the biotranformation of drugs or metabolic substrates and the clearance of pathogens.|
Feeding artery: superior and inferior hypophyseal arteries
Primary capillary beds:
Portal vessel: the long portal vessels and short portal vessels
Secondary capillary bed: capillaries of the anterior pituitary
Draining vein: hypophyseal veins, which variably drain into the cavernous sinuses
To efficiently present hypothalamic regulatory hormones to the pituitary gland in high concentration (rather than releasing them into the systemic circulation)
Feeding artery: afferent arteriole
Primary capillary bed: glomerular capillaries
Portal vessel: efferent arterioles
Secondary capillary beds:
Draining vein: Renal vein
To reclaim solutes from the glomerular ultrafiltrate fluid.
To deliver solutes fr active excretion by the proximal tubule
To maintain concentration gradients in the renal medulla, (to reabsorb water).
Feeding artery: umbilical arteries
Primary capillary bed: foetal placental capillaries
Portal vessel: umbilical vein
Secondary capillary beds: foetal hepatic capillaries
Draining vein: foetal hepatic vein
|To allow the exchange of nutrients and gases between the mother and the foetus|
Henderson, J. R., and P. M. Daniel. "Portal circulations and their relation to countercurrent systems." Quarterly Journal of Experimental Physiology and Cognate Medical Sciences: Translation and Integration 63.4 (1978): 355-369.
Page, R. B. "The pituitary portal system." Morphology of Hypothalamus and its Connections. Springer, Berlin, Heidelberg, 1986. 1-47.
Daniel, Peter M. "The blood supply of the hypothalamus and pituitary gland." British medical bulletin 22.3 (1966): 202-208.