Maintaining a Stable Internal Environment

INTRODUCTION

Maintaining a stable internal environment, or homeostasis, is essential for the survival of complex animals. Living organisms must maintain a salt and water balance, and they must continually remove the toxic by-products generated by metabolism. Organisms have evolved a variety of strategies to maintain a more or less stable internal environment. In animals that have a circulatory system, the blood typically passes through excretory organs, commonly termed kidneys. In terrestrial animals, the kidneys not only play a major role in the removal of wastes, but are also the primary organs of osmoregulation. Kidneys are paired, bean-shaped structures which are present at the lumber region along the two sides of the vertebral column and are retroperitoneal in nature. Kidneys are covered over by a fibrous connective tissue capsule and are kept in position by renal fascia. Mammalian kidneys are metanephric in origin. Structural and functional units are known as nephrons, and there are one million in number per kidney. Kidneys receive blood through the renal artery, and the blood leaves the kidney through the renal vein. The blood entering the kidneys undergoes pressure filtration, ultra-filtration and reabsorption, leading to the formation of urine. Kidneys regulate internal homeostasis by regulating the fluid and electrolyte balance in the body. The major functions performed by the kidneys are filtration of blood, formation of urine, removal of non-gaseous N2 wastes in the form of urea, uric acid, and ammonia, regulation of fluid volume, and regulation of fluid and electrolyte volume leading to regulation of blood volume and blood pressure.

OBJECTIVES

• Study of anatomical regions of mammalian kidney (sheep kidney)

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... This pressure leads to filtration under pressure, which is known as ultra filtration. This filtration leads to filtration of the blood into blood filtrate and nephric filtrate. Larger diameter will allow the reduction in the pressure exerted by the blood on the renal blood vessels, leading to the proper filtration.

Q.2

a) With the rise in ADH concentration, the permeability of the collecting tubules to water

b) Retention of water leads to a rise in fluid volume and a corresponding rise in blood volume

c) Urine will be highly concentrated due to increased reabsorption of water

Q.3 In the following states, the secretion of the ADH will increase in the blood:

 Reduction in fluid volume in the body

 Decrease in the blood pressure of the body

 When the person drinks less water

 Hypovolemia, that is, the reduction in the fluid volume of the body