Frog's three-chambered heart, portal systems and excretion, is my understanding of Rana tigrina correct?
Meera Patel11th Sample
1 Sept 2026 · 1 min read
I've been through the frog section of Structural Organisation in Animals twice and I want to verify the parts that need reasoning, not just terms. This is what I understood, please correct anything.
Digestion: short alimentary canal because frogs are carnivores. Food goes mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum and cloaca. Liver makes bile, stored in the gall bladder; pancreas also pours juice into the duodenum.
Circulation: closed system, heart with three chambers, two atria and a ventricle, plus a sinus venosus and a conus arteriosus. RBCs are nucleated. Blood goes through the hepatic portal and renal portal systems.
What I'm unsure about:
- If the ventricle is single, does that mean oxygenated and deoxygenated blood mix?
- Is the adult frog ammonotelic or ureotelic? I wrote both in two notebooks.
- In males, how do sperms leave the body? I know there are 10 to 12 vasa efferentia, but where do they go from there?
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[+][–]Tanvi Deshmukh12thSample· 1mo ago
Your digestive and circulation summary is right. On (1): yes, the ventricle receives oxygenated blood from the left atrium and deoxygenated blood from the right atrium (which got it from the sinus venosus), and so the blood gets mixed in the ventricle. Then it leaves via the conus arteriosus, which divides and sends blood on. That's why frogs are said to have an "incomplete double circulation" in many textbooks, but NCERT simply says that blood from the ventricle is pumped out and mixed blood goes to the body. Just know "mixing in ventricle" as the fact.
[+][–]Mehak AroraDropperSample· 1mo ago
Excretion in frog: the adult frog is ammonotelic, it just releases ammonia since it lives near water. The kidneys are bean-shaped, dark red, and there's a pair of ureters. Males: the ureter comes out of the kidney and it also carries sperms, so it's called urinogenital duct, opens into the cloaca. Females: ureter and oviduct open separately into the cloaca.
[+][–]Siddharth RaoDropperSample· 1mo ago
Small correction, mehak: adult frog is ureotelic, it excretes urea. Tadpoles are ammonotelic (aquatic larvae). NCERT says "frog excretes urea and thus is ureotelic". Ammonia is for fully aquatic animals like bony fishes, and tadpole.
[+][–]Mehak AroraDropperSample· 1mo ago
oh no, I mixed up the larva and the adult. Ureotelic for adult. Thanks!
[+][–]Meera Patel11thSample· 1mo agoAuthor
yes, that clears the two notebooks problem. Thank you siddharth bhaiya, and everyone else too. The Bidder's canal one is new to me, I'll add it.
[+][–]Nisha Verma12thSample· 1mo ago
Your sperm path question: testes (yellowish, ovoid, attached to the upper part of the kidneys by a double fold of peritoneum called mesorchium) give rise to vasa efferentia, 10-12 of them. They enter the kidneys on their side and open into Bidder's canal. Bidder's canal then communicates with the urinogenital duct, which comes out of the kidney and opens into the cloaca. So the kidney tubules and the reproductive path share the duct in male frogs.
Female: ovaries are a pair, near the kidneys, no connection to them, and the oviducts open into the cloaca separately. Fertilisation is external, in water, and a tadpole develops, then metamorphoses.
[+][–]Ishita GoyalDropperSample· 1mo ago
Portal system is a classic confusion. A portal system is a blood vessel pair that begins and ends in capillaries, with a vein in between. In frog the hepatic portal vein carries blood from the intestine to the liver, and the renal portal vein carries blood from the hind limbs/posterior body to the kidneys. In humans, we have only the hepatic portal one. That's a likely MCQ: "renal portal system is present in frog but not humans".
[+][–]Zoya Khan12thSample· 1mo ago
Respiration is one that connects well to the cloaca and the skin: in water the frog respires through the skin (cutaneous respiration, the skin is moist and thin and permeable), on land it uses lungs, skin and the buccal cavity. Tadpoles respire with gills. Frog also has a bilobed tongue used for catching food, and the stomach has HCl and gastric juice, so digestion is not only for the intestine. Hope the extra bits help in revision!
