Circulatory system
Last Updated on Friday, 3 February 2012 10:08 Written by Sandesh Wednesday, 7 April 2010 10:56
HEPATIC PORTAL SYSTEM
The portal system is a system of blood vessels which starts in capillaries in one organ and ends in capillaries in another organ before entering the heart.
In hepatic portal system, venous blood from stomach, intestine, pancreas and spleen are collected and forms hepatic portal vein which enter the liver.
Hepatic portal vein is formed by the union of following veins:
- Splenic vein: collects blood from spleen and pancreas.
- Superior mesenteric vein: collects blood from small intestine and some part of colon.
- Inferior mesenteric vein: collects blood from rest of colon and rectum.
- Gastric vein: collects blood from the stomach.
- Superior pancreatico-duodenale vein: collects blood from the pancreas and duodenum.
- Cystic vein: collects blood from gall bladder.
The portal vein divides into right and left branches before entering the liver. In liver they divide into capillaries which ultimately unite to form hepatic veins. Hepatic veins unite to the inferior venacava.
IMPORTANCE OF HEPATIC PORTAL SYSTEM:
Hepatic portal system collects blood from all parts of alimentary canal in to the liver. So, the nutrients absorbed from intestine passes through liver before entering the general blood circulation.
Importance of hepatic portal system are:
- Excess nutrients are stored in the liver which can be released slowly so that blood contains nutrients all the time. Excess glucose is stored in the form of glycogen produced by the process of glycogenesis.
- Toxins absorbed from intestine are detoxified by the Kupffer cell of liver. So, this protects the other organs from these toxins
Human Blood Group:
According to the presence and absence of certain protein molecules called antigen and antibody in blood, human blood can be divided into many groups. Presence of antigens attached to the surface of RBC determines the group of a blood. However, antibodies are present in plasma against to that of the present antigen.
There are more than 300 blood group systems, but only 2 systems are clinically important. These are ABO and Rh blood grouping systems.
ABO blood grouping system:
ABO blood grouping system was first discovered by Karl Landsteiner in 1901. He was awarded Novel prize in 1930. In this system, there are four blood groups in human viz. A, B, AB and O.
In a person with blood group A has antigen A in RBC and antibody B in plasma
In a person with blood group B has antigen B in RBC and antibody A in plasma
In a person with blood group AB has both antigens A and B in RBC and antibody absent in plasma
In a person with blood group O has no antigen in RBC and both antibodies A and B in plasma
Rhesus (Rh) blood grouping system:
This system of human blood grouping was discovered by Karl Landsteiner and Weiner in 1940. Rh (D) factor is an antigen found in surface of RBC which determines blood group to be positive (or negative if Rh factor absent). It was also found in the RBC of Rhesus monkey so named as Rh factor. 85% of people are Rh positive while remaining 15% are with Rh negative blood group. In a person with Rh negative blood group, Rh antibody doesn’t occur naturally in plasma. But it can be produced by body against the Rh antigen, if he or she receives blood with Rh antigen.
If a female with Rh negative becomes pregnant with a foetus having blood group of Rh positive then she may develop Rh antibody in her blood. Rh antibody is produced in her body when stimulated by Rh antigen of foetus blood. Amount of Rh antibody in first pregnancy is minimum, therefore pregnancy is normal this time. However, if mother again conceives foetus with Rh positive, then Rh antibody of mother blood enter placenta and start to destroy foetal RBCs. As a result, death of foetus takes place and miscarriage occurs. This clinical feature is known as erythroblastosis foetalis.
