Biology XI: 7 Stru Orgn in Animals(9 Anatomy of the Frog)

Anatomy of the Frog Digestive System The mouth opens into the buccal cavity; food is captured by the tongue. Leads into the oesophagus, through the pharynx Oesophagus is short and opens into the stomach. Liver secretes bile, and pancreas secretes digestive juice containing digestive enzymes. Digestion starts in the stomach by the action of HCl. Partially digested food is passed on to the duodenum where it is acted upon by bile juices and pancreatic enzymes, and further broken down into simpler substances. Digested food is absorbed by the numerous finger-like folds called villi and microvilli on the inner walls of the intestine. The undigested food moves into the rectum, and passes out through the cloaca. Respiratory System Frogs can respire on land as well as in water. In water, they respire through the skin by diffusion (cutaneous respiration) On land, the buccal cavity, skin and lungs act as respiratory organs. (pulmonary respiration) The lungs are a pair of pink-coloured, sac-like organs present in the trunk region. Air enters through the nostrils, passes into the buccal cavity, and then into the lungs.     During aestivation or hibernation, respiration is cutaneous. Circulatory System Closed and well developed It has a lymphatic system also; consisting of lymphatic vessels and lymph nodes The heart is three-chambered (2 atria and 1 ventricle). It is covered by pericardium. Sinus venosis:Triangular structure that joins the right atrium and receives the major vein called the vena cava Conus arteriosus: Sac-like structure in which ventricles open Circulatory system consists of separate arterial system and venous system. Special venous connections are also present between different parts of the body: Hepatic portal system − connects liver and intestine Renal portal system − connects kidney and lower parts of the body The blood is composed of RBCs, plasma and WBCs Circulation is achieved by the pumping action of the heart. Excretory System Consists of: A pair of kidneys; composed of uriniferous tubules Ureters arise from the kidneys; in males ureters acts as urinogenital ducts, opening into the cloaca Urinary bladder In females, the ureters and oviduct open separately into the cloaca Frogs are ureotelic since they excrete urea. Nervous System Nervous system is organised into: Central nervous system (brain and spinal cord) Peripheral nervous system (cranial and spinal nerves) Autonomic nervous system (sympathetic and parasympathetic) There are 10 pairs of cranial nerves arising from the brain; enclosed in the cranium. Brain is enclosed in the brain box. Brain is divided into: Forebrain − Olfactory lobes, cerebral hemispheres and unpaired diencephalon Mid brain − A pair of optic lobes Hind brain − Cerebellum and medulla oblongata (continues into the spinal cord; enclosed in the vertebral column.) Reproductive System Have well-organised male and female reproductive systems Male Reproductive System Consists of a pair of yellowish, ovoid testes Testes adhered to the kidneys by mesorchium (double fold of peritoneum) Vasa efferentia (10−12) arise from the testis, enter the kidney on their sides, and open into bidder’s canal. Bidder’s canal opens into the cloaca; passes out faecal matter, urine and sperms to the exterior Female Reproductive System Includes a pair of ovaries, situated near the kidneys A pair of oviduct arises from the ovaries and opens into the cloaca separately. A mature female produces 2500−3000 ova at a time. Fertilisation is external and takes place in water. Development is indirect (passes through the larval stage called the tadpole)