Lesson 11 of 11 · 12 min
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Frog anatomy and physiology walkthrough
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Must-know facts
19 facts
- 1Only four basic tissue types build all complex animals: epithelial, connective, muscular and neural; the heart contains all four.
- 2Organ system = two or more organs doing a common function by physical and/or chemical interaction; the sharing of work is division of labour.
- 3Frog: class Amphibia, phylum Chordata; common Indian species Rana tigrina; poikilotherm.
- 4Aestivation = summer sleep, hibernation = winter sleep, both in deep burrows; gas exchange is then only through the skin.
- 5The frog never drinks water; it absorbs water through its moist, mucus-covered skin.
- 6Body = head + trunk; no neck, no tail.
- 7Fore limb 4 digits, hind limb 5 digits (larger, muscular, webbed).
- 8Male frog: vocal sacs, and a copulatory pad on the first digit of each fore limb.
- 9Short alimentary canal because the frog is carnivorous; tongue bilobed; bile and pancreatic juice reach the duodenum through a common bile duct.
- 10In water: cutaneous respiration only. On land: buccal cavity, skin and lungs.
- 11Heart: three chambers (two atria, one ventricle), pericardium, sinus venosus joining the right atrium, conus arteriosus on the ventral side.
- 12Hepatic portal system (liver–intestine) and renal portal system (kidney–lower body) are both present in the frog.
- 13Frog RBCs are nucleated; lymph lacks some proteins and RBCs; circulation is closed, with a three-chambered heart in which blood mixes in the one ventricle.
- 14Frog is ureotelic; kidneys are made of uriniferous tubules (nephrons).
- 15Male ureter = urinogenital duct; in the female, ureters and oviducts open separately into the cloaca.
- 16Ten pairs of cranial nerves; optic lobes in the mid-brain; medulla leaves through the foramen magnum.
- 17Eyes and internal ears are the only well-organised sense organs; no external ear, only a tympanum; the ear also balances.
- 1810–12 vasa efferentia → Bidder's canal → urinogenital duct → cloaca; testes held by the mesorchium.
- 19A female lays 2500–3000 ova at a time; fertilisation external in water; tadpole larva metamorphoses into the adult.
Common traps
Where marks are lost
Giving the frog five digits on the fore limb and four on the hind limb.
It is the other way round: fore limb 4, hind limb 5. The hind limb is the bigger, muscular, webbed one used for leaping and swimming.
Saying the lungs are the frog's only respiratory organ on land, or that the lungs work during hibernation.
On land the buccal cavity, skin and lungs all work. In water, and during aestivation and hibernation, only the skin does.
Calling the frog heart four-chambered because it has a sinus venosus and a conus arteriosus.
The three chambers are two atria and one ventricle. The sinus venosus joins the right atrium and the conus arteriosus leaves the ventricle; neither is counted as a chamber.
Assuming frog RBCs lack a nucleus, like human RBCs.
Frog RBCs are nucleated and contain haemoglobin.
Giving the female frog a urinogenital duct.
Only in the male does the ureter carry sperms too. In the female the ureters and oviducts open separately into the cloaca, and the ovaries have no functional link with the kidneys.
Placing the optic lobes in the fore-brain.
The fore-brain has the olfactory lobes, cerebral hemispheres and diencephalon; the pair of optic lobes marks the mid-brain; the hind-brain has the cerebellum and medulla oblongata.
Thinking the frog has an external ear.
It has no external ear; only the tympanum is seen outside. The internal ear handles both hearing and balance.
Calling the frog uricotelic or ammonotelic.
The frog excretes urea, so it is ureotelic.
Key terms
20 terms
- Tissue
- A group of similar cells, with their intercellular substance, doing a particular job.
- Organ system
- Two or more organs that work together, physically and/or chemically, for one common function.
- Division of labour
- The sharing of the body's work among cells, tissues, organs and organ systems.
- Morphology
- Study of the form of an organism; in animals, the external appearance of its organs and parts.
- Anatomy
- In animals, the study of the form of the internal organs.
- Poikilotherm
- A cold-blooded animal whose body temperature follows that of its surroundings.
- Aestivation
- Summer sleep in a burrow to escape extreme heat.
- Hibernation
- Winter sleep in a burrow to escape extreme cold.
- Nictitating membrane
- A membrane covering the frog's eye that protects it in water.
- Tympanum
- The membrane beside the frog's eye that receives sound; the only visible part of its ear.
- Cutaneous respiration
- Gas exchange through the moist skin by diffusion.
- Pulmonary respiration
- Breathing with the lungs.
- Sinus venosus
- Triangular chamber that receives blood from the vena cava and joins the right atrium.
- Conus arteriosus
- Sac-like structure on the ventral side of the heart into which the ventricle opens.
- Portal system
- A special venous link between two organs: hepatic portal (intestine–liver) and renal portal (lower body–kidney).
- Ureotelic
- Excreting nitrogenous waste mainly as urea.
- Urinogenital duct
- The male frog's ureter, which carries both urine and sperms to the cloaca.
- Mesorchium
- Double fold of peritoneum holding each testis to the kidney.
- Bidder's canal
- Canal in the kidney into which the vasa efferentia open, linking them to the urinogenital duct.
- Metamorphosis
- The change of the tadpole larva into the adult frog.