The venous system includes veins or those blood vessels which carry blood from different parts of body towards the heart. In frog it consists of three type of veins:
(1) Pulmonary veins, (2) Caval veins and (3) portal veins.
1. Pulmonary veins: Oxygenated blood from two lungs is collected by right and left pulmonary veins which unite to form a common pulmonary vein opening directly into the left auricle on the dorsal side.
2. Caval veins: Deoxygenated blood from rest of the body travels towards heart in three large vessels, two anterior precavals and single posterior postcaval, all the three opening into sinus venosus.
a. Anterior venacava or precavals: The right and left precavls or anterior venacava collect venous blood from the anterior part of body. Each precaval is formed by the union of 3 major veins which are:
i. External jugular: It is formed by the union of lingual form tongue and mandibular from outer margin of lower jaw.
ii. Innominate: It is formed by the union of internal jugular from cranial cavity and orbit and subscapular from shoulder and back of arm.
iii. Subclavian: It is formed by the union of brachial from forelimb and the musculo-cutaneous from muscles & skin of side of body and head.
b. Posterior venacava or postcaval: The single postcaval is a large, dark-coloured vein lying ventral to dorsal aorta. Its posterior end is formed between the two kidneys by the union of 5-6 pairs of renal veins collecting blood from kidneys. It also receives a pair of genital veins (spermatic in male and ovarian in female) from gonads. The postcaval then runs forwards, dorsally to the liver and receiving from it a pair of short hepatic veins, before opening into the posterior part of sinus venosus.
3. Portal Veins: A vein which collects blood from one organ of body and supplies blood to another organ instead of going to heart is called as portal vein. Thus, a portal vein is bicapillary vein, it is formed by the union of capillaries and terminates into capillaries. All veins associated with a portal vein forms portal system. Frog consists of two portal systems.
a. Renal Portal system: The veins which carry blood to a capillary system in kidneys constitute the renal portal system. Blood of each hind leg is collected by two veins, an outer fermoral and an inner sciatic. On entering the abdominal cavity the femoral divides into a dorsal renal portal and a ventral pelvic vein. The sciatic unites with the renal portal of its own side and while running along there outer border of kidney of its side it receives blood from lumbar region by a dorso-lumbar vein. Renal portal vein enters the kidney by several branches which break up into capillaries.
The importance of renal portal system is that kidney filters the blood and removes nitrogenous metabolic wastages from blood.
b. Hepatic portal system: It consists of hepatic portal vein and anterior abdominal vein.
A large hepatic portal vein is formed by the union of several branches from stomach, intestine, spleen, and pancreas. The veins which unite to form hepatic portal vein are:
• Gastric from stomach.
• Pancreatic from pancreas.
• Duodenal from duodenum.
• Anterior mesenteric from small intestine.
• Spleenic from spleen.
It carries blood of alimentary canal, laden with digested foodstuffs, to the liver into which it breaks up into capillaries. The liver converts excess glucose into glycogen and stores it as reserve food.
Anterior abdominal vein : The pelvic veins of both sides unite to form a median ventral or anterior abdominal vein. It receives blood from urinary bladder and ventral abdominal wall and runs forwards to enter liver into which it breaks up into capillaries. Before entering liver the anterior abdominal and hepatic portal veins are connected by a small loop.
(1) Pulmonary veins, (2) Caval veins and (3) portal veins.
1. Pulmonary veins: Oxygenated blood from two lungs is collected by right and left pulmonary veins which unite to form a common pulmonary vein opening directly into the left auricle on the dorsal side.
2. Caval veins: Deoxygenated blood from rest of the body travels towards heart in three large vessels, two anterior precavals and single posterior postcaval, all the three opening into sinus venosus.
a. Anterior venacava or precavals: The right and left precavls or anterior venacava collect venous blood from the anterior part of body. Each precaval is formed by the union of 3 major veins which are:
i. External jugular: It is formed by the union of lingual form tongue and mandibular from outer margin of lower jaw.
ii. Innominate: It is formed by the union of internal jugular from cranial cavity and orbit and subscapular from shoulder and back of arm.
iii. Subclavian: It is formed by the union of brachial from forelimb and the musculo-cutaneous from muscles & skin of side of body and head.
b. Posterior venacava or postcaval: The single postcaval is a large, dark-coloured vein lying ventral to dorsal aorta. Its posterior end is formed between the two kidneys by the union of 5-6 pairs of renal veins collecting blood from kidneys. It also receives a pair of genital veins (spermatic in male and ovarian in female) from gonads. The postcaval then runs forwards, dorsally to the liver and receiving from it a pair of short hepatic veins, before opening into the posterior part of sinus venosus.
3. Portal Veins: A vein which collects blood from one organ of body and supplies blood to another organ instead of going to heart is called as portal vein. Thus, a portal vein is bicapillary vein, it is formed by the union of capillaries and terminates into capillaries. All veins associated with a portal vein forms portal system. Frog consists of two portal systems.
a. Renal Portal system: The veins which carry blood to a capillary system in kidneys constitute the renal portal system. Blood of each hind leg is collected by two veins, an outer fermoral and an inner sciatic. On entering the abdominal cavity the femoral divides into a dorsal renal portal and a ventral pelvic vein. The sciatic unites with the renal portal of its own side and while running along there outer border of kidney of its side it receives blood from lumbar region by a dorso-lumbar vein. Renal portal vein enters the kidney by several branches which break up into capillaries.
The importance of renal portal system is that kidney filters the blood and removes nitrogenous metabolic wastages from blood.
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| FROG: PORTAL SYSTEM |
b. Hepatic portal system: It consists of hepatic portal vein and anterior abdominal vein.
A large hepatic portal vein is formed by the union of several branches from stomach, intestine, spleen, and pancreas. The veins which unite to form hepatic portal vein are:
• Gastric from stomach.
• Pancreatic from pancreas.
• Duodenal from duodenum.
• Anterior mesenteric from small intestine.
• Spleenic from spleen.
It carries blood of alimentary canal, laden with digested foodstuffs, to the liver into which it breaks up into capillaries. The liver converts excess glucose into glycogen and stores it as reserve food.
Anterior abdominal vein : The pelvic veins of both sides unite to form a median ventral or anterior abdominal vein. It receives blood from urinary bladder and ventral abdominal wall and runs forwards to enter liver into which it breaks up into capillaries. Before entering liver the anterior abdominal and hepatic portal veins are connected by a small loop.