· Generally veins collect blood from different parts of the body to the heart.
· However, there are some veins that before reaching the heart carry blood to some other organs where they form a network of capillaries.
· These are portal veins.
· Organs that receive blood from portal veins are called portal organs.
· Examples: liver, kidneys etc.
· So, the portal system is a system of veins carrying blood from one organ to another instead of carrying it to the heart.
· There are two portal systems in the frog.
· They are the hepatic portal system and renal portal system.
A. HEPATIC PORTAL SYSTEM
· It consists of veins collecting blood from different parts of the alimentary canal and hind limbs to the liver.· It consists of the following veins.
(a) Anterior Abdominal Vein:
(a) Anterior Abdominal Vein:
· It is formed by the union of two pelvic veins and vesicular veins.
· Pelvic veins are the lateral branches of the femoral veins from the hind limbs which collect blood from the outer parts of the hind limbs.
· The vesicular vein collects the blood from the urinary bladder.
· At its anterior end, it divides into two branches, entering into the right and left lobes of the liver where it breaks up into capillaries inside it.
(b) Hepatic portal vein:
· It collects blood from different parts of the alimentary canal and spleen.
· It is formed by the union of the following veins.
(i) Gastric vein:
· The capillaries of the stomach join to form a gastric vein.
· It collects the blood from the stomach.
(ii) Duodenopancreatic vein:
· The capillaries from the duodenum and pancreas join to form the duodenopancreatic vein.
· It collects the blood from the duodenum and pancreas.
(iii) Intestinal vein:
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| Hepatic portal system |
(iii) Intestinal vein:
· The capillaries from the intestine join to form an intestinal vein.
· It collects the blood from the intestine.
(iv) Splenic vein:
(iv) Splenic vein:
· The capillaries from the spleen join to form a splenic vein.
· It collects the blood from the spleen.
(v) Rectal vein:
(v) Rectal vein:
· The capillaries of the rectum join to form the rectal vein.
· It collects the blood from the rectum.
· Hepatic portal veins also receive the oesophageal vein.
· The hepatic portal vein enters the liver after giving a small branch, which joins the anterior abdominal vein.
· The hepatic portal vein also breaks up into a network of capillaries into the liver.
· The capillaries formed by the anterior abdominal and hepatic portal vein in the liver join with the hepatic arterioles to form a pair of veins called hepatic veins one on each side. They open into sinus venosus.
· Large amount of glucose, amino acids and other digested nutrients are present in the hepatic portal vein and a large amount of urea is present in the anterior abdominal vein.
Significance of the Hepatic Portal System
· The hepatic portal system has the following significances:
(i) The blood which comes from the alimentary canal contains digested food like glucose and amino acids. The excess glucose is converted into glycogen which is stored in the liver for later use. When an individual feels a deficiency of energy, the glycogen is converted into glucose and transferred into the bloodstream through hepatic veins.
(ii) Harmful nitrogenous wastes like ammonia (also the extra amino acids) are converted into urea which is later removed by kidneys. Thus the blood is detoxified (purified) of harmful nitrogenous waste.
(iii) Liver produces blood proteins that are circulated into the bloodstream.
(iv) If solid particles like bacteria enter the blood, the liver cells engulf and destroy them.
(v) The liver also removes poisonous substances present in the blood coming from the gut such as carbolic acids, indol etc. These poisonous substances are produced in the large intestine due to the incomplete oxidation of proteins by bacteria.
· Large amount of glucose, amino acids and other digested nutrients are present in the hepatic portal vein and a large amount of urea is present in the anterior abdominal vein.
Significance of the Hepatic Portal System
· The hepatic portal system has the following significances:
(i) The blood which comes from the alimentary canal contains digested food like glucose and amino acids. The excess glucose is converted into glycogen which is stored in the liver for later use. When an individual feels a deficiency of energy, the glycogen is converted into glucose and transferred into the bloodstream through hepatic veins.
(ii) Harmful nitrogenous wastes like ammonia (also the extra amino acids) are converted into urea which is later removed by kidneys. Thus the blood is detoxified (purified) of harmful nitrogenous waste.
(iii) Liver produces blood proteins that are circulated into the bloodstream.
(iv) If solid particles like bacteria enter the blood, the liver cells engulf and destroy them.
(v) The liver also removes poisonous substances present in the blood coming from the gut such as carbolic acids, indol etc. These poisonous substances are produced in the large intestine due to the incomplete oxidation of proteins by bacteria.
B. RENAL PORTAL SYSTEM
· The veins which carry blood to a capillary system in the kidneys constitute a renal portal system.
· The deoxygenated blood from each of the hind limbs is collected by two veins.
(i) Femoral vein: It collects the blood from the outer side of the limb.
(ii) Sciatic vein: It collects the blood from the inner side of the limb.
· The femoral vein on entering the body cavity divides into dorsal and ventral branches.
(i) Femoral vein: It collects the blood from the outer side of the limb.
(ii) Sciatic vein: It collects the blood from the inner side of the limb.
· The femoral vein on entering the body cavity divides into dorsal and ventral branches.
· The dorsal femoral branch (iliac vein) joins with the sciatic vein in the pelvic region to form the renal portal vein.
· The renal portal vein then travels upwards and while running along the outer side of the kidney of its sides, it receives the dorsolumbar vein.
· The dorsolumbar vein receives blood from the lumbar region.
· The renal portal vein enters the kidney and breaks up into the capillaries.
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| Renal portal system |
Significance of renal portal system
· The renal portal system collects the blood from the hind limbs and another posterior region of the body.
· Urea and nitrogenous wastes contained in the venous blood is first filtered in the kidneys before the blood goes to the post-caval vein and then to the heart.
· Thus, the blood going to the heart contains comparatively fewer impurities after passing through the renal portal system.
· Starts from the truncus arteriosus which divides into right and left aortic trunks from each of which arise three arterial arches: Carotid arch, Systemic arch and Pulmocutaneous arch.
· Starts from the truncus arteriosus which divides into right and left aortic trunks from each of which arise three arterial arches: Carotid arch, Systemic arch and Pulmocutaneous arch.
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