On the land and in dry atmosphere excess water in the body is removed by

On the land and in dry atmosphere excess water in the

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On the land and in dry atmosphere, excess water in the body is removed by evaporation through the skin. Greater percentage of the carbon IV oxide is excreted by diffusion through the skin; the rest is removed through expiration through the mouth and the lungs.
Page | 69 [ BIO NOTE- SS2 ] The kidneys are located on the dorsal wall of the amphibian body. The urinary bladder found as a ventral outgrowth from the cloaca is not truly a urinary bladder as the Wolfian ducts do not open into it. The fluid in the bladder is believed to be secreted by the blood vessels in the bladder and the opening and closing of the bladder is controlled by a sphincter. The bladder in essence acts as a reservoir holding water for use during dry periods. The nitrogenous waste in amphibians is urea extracted from the blood by ultra filtration. The Wolfian duct passes through the outer side of the kidneys and opens into the cloaca. Excretion in fish Excretion in fish is by the kidneys and gills. The kidneys lie along either side of the dorsal aorta. Each kidney is long and extends a reasonable length of the body, tapering anteriorly. In the anterior part of the kidney called the leyding’s gland, the vas deferens is found. The posterior part is truly the urinary part and from it, ducts lead into the ureter. The ureter runs into the small urino-genital sinus that opens into the cloaca. Carbon IV oxide is excreted through the gills. The main nitrogenous waste is urea and is excreted by the kidneys. Fish in an effort to maintain the osmotic pressure of its body retains much of its urea in the body fluid and in some tissues. Most tissues of fish except the brain the blood produce urea while a portion of the kidney tubules absorb urea from the glomerular filtrate. The resulting urine consists mainly of water and excess salt. Excess urea is excreted through the gills.
Page | 70 [ BIO NOTE- SS2 ] Excretion in other vertebrates All vertebrates have a pair of kidneys which are generally similar in structure and functions as those of mammals. Structure of the mammalian kidney There is a pair of kidneys in each vertebrate. The kidneys form the urinary part. In mammals, the kidneys are bean-shaped and dark-red in colour. They are surrounded by fat deposits which hold the kidneys in position in the abdominal cavity. In man, the right kidney is slightly lower than the left kidney. The longitudinal section of the kidney shows that it consists of two main regions: a. An outer cortex b. Inner medulla An expanded tube at the depression on one side of the kidney where the ureter enters the kidney is called the pelvis, and these projections are known as pyramids . Two branches of the dorsal aorta called the renal arteries carry blood to the kidneys. Two renal veins carry blood from the kidneys into the inferior vena cava. Actual excretion is carried out by the uniferous tubules . Each tubule ends as a small rounded funnel called the Bowman’s capsule located in the cortex. A knot of blood capillaries fits into the bowman’s capsule. This knot is called the glomerulus.

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