Chapter 39.3, Problem 9SAQ

Summary Introduction

To draw:

A mammalian nephron, label and describe the primary function of each part, and also show the direction of water and electrolyte in each part.

Introduction:

Nephron is the basic functional unit of kidneys. It helps in removal of metabolic wastes from the body. In addition to this, it also helps in maintaining the water and electrolytes balance in the body.

Explanation of Solution

Pictorial representation:

Fig.1: A mammalian nephron.

A mammalian nephron consists of three parts, namely proximal convoluted tubules (PCT), loop of Henle and distal convoluted tubules (DCT). The proximal convoluted tubule is the most proximal part of the nephron that functions to reabsorb water, glucose, amino acids, and ions such as sodium and chloride from the filtrate produced in the glomerular capsule.

The loop of Henle is the next part of the nephron that lies between the proximal convoluted tubule and distal convoluted tubule. It can be divided into two parts, descending and ascending loop of Henle. The descending loop of Henle is permeable to water but impermeable to ions. On the other hand, the ascending loop of Henle is permeable to ions but impermeable to water. The loop of Henle creates an increasing concentration gradient from cortex to medulla of the kidneys to produce concentrated urine.

The third and last part of the nephron is the distal convoluted tubules. This part is associated with the active secretion of wastes such as ions ( ${\text{K}}^{\text{+}}$ and ${\text{HCO}}_{\text{3}}{}^{\text{-}}$), acids, drugs and toxins. Variable reabsorption of water and some ions also occur in this part under the influence of hormones.

Conclusion

A mammalian nephron comprises three parts, namely PCT, loop of Henle and DCT.