The fimbriae of the uterine tube, also known as fimbriae tubae, are small, fingerlike projections at the end of the fallopian tubes, through which…. Health Conditions Discover Plan Connect. Common hepatic duct.
Intermediate branch of hepatic artery. Hepatic artery proper. Read this next. Medically reviewed by Alana Biggers, M. Common hepatic duct Medically reviewed by the Healthline Medical Network. Intermediate branch of hepatic artery Medically reviewed by the Healthline Medical Network. Hepatic artery proper Medically reviewed by the Healthline Medical Network. Hepatic veins Medically reviewed by the Healthline Medical Network.
Jejunum Overview. What is the Vagus Nerve? Medically reviewed by Seunggu Han, M. Fimbriae Medically reviewed by the Healthline Medical Network. Page and Daniel give good overviews of this strange little circulatory system. In effect, there are two portal circulations here, which both drain into the same secondary capillary bed.
So instead you get this:. The function of the pituitary portal circulation is to act as a conduit for the quick transport of hypothalamic hormones into the anterior pituitary gland. The capillaries in the portal system are fenestrated, which means that relatively large substances can get through with relative ease. This is important, as may of the hypothalamic hormones are quite large - as an example, GHRH is a amino-acid peptide and CRH is a amino-acid peptide.
The use of a portal system here makes perfect sense for a number of reasons. In order to diffuse effectively into the anterior pituitary cells, these signalling peptides need to be present in relatively high concentration as without a decent concentration gradient these substances would never cross the membranes.
However, the hypothalamus is just a minuscule lump of neuroendocrine tissue, and would be incapable of pumping out the vast quantities of hormone molecules which would be required to achieve a high systemic blood concentration.
In any case, that would be highly wasteful, as there are no systemic targets for these substances. Ergo, having these portal vessels allows the efficient delivery of concentrated hormones directly to the pituitary. The renal portal system appears in the examiners' comments for Question 9 from the second paper of , but its position in the list of portal systems appears to be contested. This is probably because the mammalian kidney lacks a "proper" portal venous circulation which is seen in fish birds and reptiles.
Those guys get a portal vein which arises from other veins in the back half of the body draining the tail, lower abdomen, sex organs, etc. That vein connects directly to the peritubular capillaries to the kidney, which gives rise to fascinating pharmacological phenomena. For example, when injecting drugs into the posterior bodyparts of a reptile, portal venous drainage may result in much of the substance being cleared by the kidney before reaching the systemic circulation , which may lead to a life-threatening standoff with an incompletely sedated crocodile.
The point of this portal venous system in the lower vertebrates appears to be to make available an alternative low-pressure blood supply system for the kidney, which increases the capacity of the kidney to reabsorb water and electrolytes. It is well-developed in fish and amphibians, diminished in significance in birds and reptiles, and abandoned entirely in mammals. Anyway: this arrangement has still left mammals with a "portal system" of sorts, though it is not included in every list of portal systems whereas for the splanchnic and pituitary circulations there is no controversy.
It consists of the glomerulotubular circulation as the primary capillary bed, which forks into secondary capillary beds vasa recta and peritubular via afferent arterioles which act as the portal system:. The functional purpose of this portal circulation is to reclaim water and solutes from the glomerular ultrafiltrate fluid.
The peritubular capillaries do most of the solute reabsorption also supply actively excreted solutes to the proximal tubule. The function of this portal system is to carry nutrients from the digestive tract to the liver after a meal to store and metabolize.
What is a portal system? What is the purpose of the hepatic portal? Saikat R. Mar 7, Explanation: Portal system can be defined as a part of the systemic circulation, in which blood draining from the capillary bed of one structure flows through larger vessels to supply the capillary bed of another structure, before returning to the heart.
Diagram of hepatic portal system :. Related questions In what organ is the waste from the digestion process collected for eventual disposal? What organs are affected by diverticulitis? What are the names of the tissue layers of the stomach?
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