![]() The chemical coordination of various organs of the body is achieved by hormones which are secreted by the endocrine glands. ![]() It includes both neural system and endocrine glands. The system for control and coordination is highly evolved in the frog. Excretory wastes are carried by blood into the kidney where it is separated and excreted. The frog excretes urea and thus is a ureotelic animal. The thin-walled urinary bladder is present ventral to the rectum which also opens in the cloaca. In females the ureters and oviduct open seperately in the cloaca. The ureters act as urinogenital duct which opens into the cloaca. Two ureters emerge from the kidneys in the male frogs. Each kidney is composed of several structural and functional units called uriniferous tubules or nephrons. These are compact, dark red and bean like structures situated a little posteriorly in the body cavity on both sides of vertebral column. The excretory system consists of a pair of kidneys, ureters, cloaca and urinary bladder. The elimination of nitrogenous wastes is carried out by a well developed excretory system. The circulation of blood is achieved by the pumping action of the muscular heart. The blood carries nutrients, gases and water to the respective sites during the circulation. RBC’s are nucleated and contain red coloured pigment namely haemoglobin. The blood cells are RBC (red blood cells) or erythrocytes, WBC (white blood cells) or leucocytes and platelets. The blood is composed of plasma and cells. The former is called hepatic portal system and the latter is called renal portal system. Special venous connection between liver and intestine as well as the kidney and lower parts of the body are present in frogs. The veins collect blood from different parts of body to the heart and form the venous system. The blood from the heart is carried to all parts of the body by the arteries (arterial system). The ventricle opens into a sac-like conus arteriosus on the ventral side of the heart. It receives blood through the major veins called vena cava. A triangular structure called sinus venosus joins the right atrium. It has three chambers, two atria and one ventricle and is covered by a membrane called pericardium. Heart is a muscular structure situated in the upper part of the body cavity. The lymphatic system consists of lymph, lymph channels and lymph nodes. The blood vascular system involves heart, blood vessels and blood. The vascular system of frog is well-developed closed type. During aestivation and hibernation gaseous exchange takes place through skin. Air enters through the nostrils into the buccal cavity and then to lungs. The lungs are a pair of elongated, pink coloured sac-like structures present in the upper part of the trunk region (thorax). The respiration by lungs is called pulmonary respiration. On land, the buccal cavity, skin and lungs act as the respiratory organs. Dissolved oxygen in the water is exchanged through the skin by diffusion. In water, skin acts as aquatic respiratory organ (cutaneous respiration). The undigested solid waste moves into the rectum and passes out through cloaca.įrogs respire on land and in the water by two different methods. ![]() ![]() Digested food is absorbed by the numerous finger-like folds in the inner wall of intestine called villi and microvilli. Final digestion takes place in the intestine. Bile emulsifies fat and pancreatic juices digest carbohydrates and proteins. The duodenum receives bile from gall bladder and pancreatic juices from the pancreas through a common bile duct. ![]() Partially digested food called chyme is passed from stomach to the first part of the small intestine, the duodenum. Digestion of food takes place by the action of HCl and gastric juices secreted from the walls of the stomach. Pancreas, a digestive gland produces pancreatic juice containing digestive enzymes. Liver secretes bile that is stored in the gall bladder. Oesophagus is a short tube that opens into the stomach which in turn continues as the intestine, rectum and finally opens outside by the cloaca. The mouth opens into the buccal cavity that leads to the oesophagus through pharynx. The alimentary canal is short because frogs are carnivores and hence the length of intestine is reduced. The digestive system consists of alimentary canal and digestive glands. Figure 7.20 Diagrammatic representation of internal organs of frog showing complete digestive system ![]()
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