Biology · Structural Organisation in Animals · NEET
The frog heart is myogenic. This means the heartbeat begins inside the cardiac muscle itself, not from an outside nerve. Because of this, a frog heart taken out of the body keeps beating for some time. This is the same type of heart found in all vertebrates, including humans. (Insect hearts, like the cockroach, are neurogenic.)
Because it is myogenic and autoexcitable. The signal to contract is made by the heart muscle on its own, so it does not need the brain or nerves to keep going. As long as the tissue stays alive, it contracts in a rhythm by itself. This is a favourite NEET point (asked in 2017).
Three chambers: two atria (upper) and one ventricle (lower). The single ventricle mixes some oxygenated and deoxygenated blood. Do not confuse this with the four-chambered human or mammalian heart. Amphibians and most reptiles have three chambers; crocodiles, birds and mammals have four.
The sinus venosus is a triangular structure that joins the right atrium of the frog heart. It collects deoxygenated blood coming in through the vena cava and passes it into the right atrium. NEET 2026 tested exactly this: 'Sinus venosus joins the right atrium' is a correct statement.
They sit at opposite ends. The sinus venosus is where blood ENTERS the heart (it joins the right atrium and receives blood from vena cava). The conus arteriosus is a sac on the ventral side where the ventricle sends blood OUT. Simple memory: venosus = veins in, conus (arterio) = arteries out.
It is a closed type. NCERT states the vascular system of frog is well-developed and closed, meaning blood always stays inside the heart and blood vessels. This is different from the cockroach (and other insects), which has an open circulatory system where blood flows freely in body spaces (haemocoel).
Frog's heart when taken out of the body continues to beat for some time. Select the best option from the following statements: (a) Frog is a poikilotherm (b) Frog does not have any coronary circulation (c) Heart is 'myogenic' in nature (d) Heart is autoexcitable
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.
Three: two atria and one ventricle. This mixes some oxygenated and deoxygenated blood in the single ventricle.
Myogenic means the heartbeat is generated by the heart muscle itself. The frog (and human) heart is myogenic, so it can beat without a nerve signal.
Yes. It has a hepatic portal system (liver and intestine) and a renal portal system (kidney and lower body). These are covered in the next concept.
The vena cava. It empties into the sinus venosus, which then joins the right atrium.
Yes. Besides the blood vascular system, the frog has a lymphatic system made of lymph, lymph channels and lymph nodes.
