Biology · Structural Organisation in Animals · NEET
The vena cava is the name given to the major veins of the frog. They collect deoxygenated (impure) blood from all parts of the body and carry it back towards the heart. Frogs have an anterior (precaval) and a posterior (postcaval) vena cava. In NEET, remember: 'vena cava' = the big body veins that bring blood IN to the heart.
The vena cava does not open straight into the atrium. First it pours blood into a triangular structure called the sinus venosus. The sinus venosus then joins the right atrium. So the correct path is: body -> vena cava -> sinus venosus -> right atrium. Skipping the sinus venosus is a common mistake.
Both are extra chambers linked to the heart, but they sit on opposite sides. The sinus venosus is on the venous (incoming) side: it receives blood from the vena cava and passes it to the right atrium. The conus arteriosus is a sac-like structure on the ventral side that comes off the ventricle and sends blood OUT into the arteries. Sinus = blood in, conus = blood out.
The vena cava carries deoxygenated (impure) blood collected from the body tissues back to the heart. This is different from the pulmonary vein, which brings oxygenated blood from the lungs to the left atrium. NEET 2025 asked exactly this, and the answer was vena cava.
Arteries form the arterial system: they carry blood AWAY from the heart to all parts of the body, starting from the conus arteriosus. Veins form the venous system: they collect blood FROM the body and bring it back to the heart, ending in the vena cava and sinus venosus. Simple rule: Arteries = Away, Veins = towards the heart.
Frogs have two special venous connections called portal systems. The hepatic portal system carries blood between the liver and intestine, and the renal portal system links the kidney with the lower body. These portal veins are part of the venous system that ultimately drains into the vena cava and back to the heart.
What is the name of the blood vessel that carries deoxygenated blood from the body to the heart in a frog?
Choose the correct statements regarding frog's anatomy: A. Hepatic portal system is the special venous connection between liver and intestine. B. There are twelve pairs of cranial nerves arising from the brain. C. The ureters and oviducts open separately into the cloaca in female frogs. D. Hind-brain consists of cerebellum, medulla oblongata and optic lobes. E. Sinus venosus joins the right atrium of heart.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Frogs have an anterior vena cava (precaval) that drains the front region and a posterior vena cava (postcaval) that drains the hind region. Both pour deoxygenated blood into the sinus venosus.
The sinus venosus is a triangular collecting chamber that receives blood from the vena cava and passes it into the right atrium of the heart. It acts as the entry gate on the venous side.
The conus arteriosus is a sac-like structure on the ventral side of the heart, arising from the ventricle. It carries blood out of the heart into the arteries that supply the body.
The pulmonary vein carries oxygenated blood from the lungs to the left atrium. This is the opposite of the vena cava, which brings deoxygenated blood to the right atrium via the sinus venosus.
NEET repeatedly asks about the exact blood path (vena cava, sinus venosus, conus arteriosus) and about the portal systems. Direct one-line questions like NEET 2025 and statement-based questions like NEET 2026 have both used these facts, so knowing the exact vessels earns easy marks.
