Question

What happens to glucose which enters nephron along with filtrate during excretion in human beings? State two vital functions of the kidney.

Answer 1

Hint: Nephron is a basic unit of kidney. In urine formation there are three main processes namely, glomerular filtration, reabsorption and secretion, that take place in different parts of the nephron.

Complete Answer:
The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. On an average 1100-1200 ml of blood is filtered by the kidney per minute which constitutes roughly ${\dfrac{1}{5}}^{th}$ of the blood pumped out by each ventricle of the heart in a minute.

Tubular Reabsorption: A comparison of the volume of the filtrate formed per day(180 litres per day) with that of the urine released (1.5 litres), suggest that nearly 99 percent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption. The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. For example, substances like glucose, amino acids, $Na^+$, etc, in the filtrate are reabsorbed actively, whereas the nitrogenous wastes are absorbed by passive transport. Reabsorption of water also occurs passively in the initial segments of the nephron.

Tubular secretion: The phenomenon of secretion of metabolic wastes by tubular cells into the filtrate is known as tubular secretion. It includes secretion of $K^+$, $H^+$, ammonia and some wastes like hippuric acid, creatinine, drugs, pigments, toxins etc. It is the only mode of excretion in animals which do not have glomeruli, e.g., desert amphibians, marine fishes. Tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid -basic balance of body fluids.
From the above information it is clear that glucose is reabsorbed by nephrons by active transport.

Two vital function of kidney:
- Urine formation is the important function of the kidney.
- It helps in controlling body temperature by maintaining balance of minerals and water.

Note: Each nephron consists of two parts – the glomerulus and the renal tubule.
- Glomerulus: It is a tuft of capillaries formed by the branching of afferent arteriole which is a fine branch of renal artery. Glomerular capillaries join to form different arterioles.
- Renal tubule: It begins with Bowman's capsule which encloses glomerulus.