Question

Describe nitrogenous waste removal and salt and water balance (osmoregulation) of birds. Include in your answer: a. a comparison of avian and mammalian kidneys with special reference to the structures and functions of nephrons b. the blood circulatory pattern of the avian kidney and the function of the renal portal valves c. the structure and function of salt glands and the advantage for birds of a non-pressure based compared to a pressure-based osmoregulatory mechanism

Answer 1

Nitrogenous waste products are formed in all living organisma as a result of metabolism of the body. Excess nitrogen is eliminated from the body. Nitrogenous wastes are formed as ammonia, but ammonia is very toxic in nature. Ammonia cannot be stored in cells due to its toxicity . It requires large amount of water for its elimination. Aquatic organisms can easily eliminate ammonia but terrestial organisms need to convert it into other forms . The main nitrogenous waste products are

. Ammonia

. Uric acid

. Urea

Birds excrete nitrogenous waste in the form of uric acid. They convert toxic ammonia to uric acid. Mammals including humans convert ammonia into urea and excrete from the body. Conversion of ammonia to uric acid is more energy intensive process than conversion of ammonia to urea by mammals. But uric acid production have advantages too. Uric acid is less toxic when compared to urea and need only less water.

a.

Kidneys are the excretory organs in both birds and mammals. Birds have a pair of kidneys and ureters.Each kidney in birds is divided into 3 lobes

. Cranial lobe

. Middle lobe

. Caudal lobe

Avian kidney is divided into subunits called Lobules. Lobules have 2 parts

. Outer Cortex

. Inner Medulla

Mammals and Birds have Nephron as the functional unit of the kidney. There are two kindas of nephrons in birds

. Reptilian nephron

. Mammalian nephrion

In reptilian nephron loop of henle is absent. So they have less ability to concentrate the urine . In mammalian nephron loop of henle is present. Hence they can concentrate urine. This a difference from mammalian nephron. Renal portal system is aunique property present in avian kidney. When compared to mammals birds produce urine osmotically more concentrated than plasma . This is to conserve water.

b.

Avian circulatory system is very efficient . It not only transports oxygen and nutrients but help in maintainence of body temperature. The circulatory system ofbirds are similar to mammals, have a 4 chambered heart and vessels. There is no mixing of oxygenated and deoxygenated blood in heart. The walls of left ventricles are much more thicker in birds. When compared mammals birds have a larger heart . large heart is to meet high metabolic demands of flight. And also the cardiac output of birds is higher than that of mammals. Arteries,veins, capillaries, arterioles are present in the body. Renal portal system is aunique character of birds.

c.

Birds regulate water and electrolytr balance in the body. This called osmoregulation. Kidneys and salt glands play a major role in the osmoregulation of birds. Kidney play a major role in water conservation. Avian kidneys produce osmotically more concentrated than the plasma. But the ability to concentrate urine is less when compared to mammals. The salt glandsof birds lie under the skin in supraorbital depressions of the frontal bone. Salt gland help in the elimination of excess salts present in the body. They help in osmoregulation. The avian salt gland have 2 main ducts

. Medial

. Lateral

These salt glands excrete the hypertonic sodium chloride by the stimulus of central and peripheral osmoreceptors and volume receptors.