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How do the kidneys filter blood in humans?

Class 10 ScienceNCERT chapter: Life Processesइसे हिंदी में पढ़ें

Exam-ready answer

Kidneys filter blood through tiny units called nephrons. Blood enters the glomerulus under pressure, forcing water, glucose, salts, and urea into Bowman's capsule. As this filtrate passes through the tubule, useful substances are reabsorbed into blood. The remaining fluid, urine, collects in the collecting duct and is carried to the bladder.

Explanation

The kidney contains about a million nephrons, the structural and functional units. Each nephron begins with a cup-shaped Bowman's capsule enclosing a bundle of capillaries called the glomerulus. Blood enters the glomerulus through the afferent arteriole and leaves through the efferent arteriole, which is narrower. This creates high pressure, forcing small molecules like water, glucose, amino acids, salts, and urea out of the blood into the Bowman's capsule. This process is called filtration.

The filtrate then flows through the long tubule of the nephron. As it passes, useful substances such as glucose, amino acids, most salts, and much of the water are selectively reabsorbed back into the blood capillaries surrounding the tubule. This reabsorption ensures that the body does not lose essential nutrients. The amount of water reabsorbed depends on the body's needs and is controlled by hormones.

What remains after reabsorption is urine, which contains excess water, urea, and other waste products. The urine collects in the collecting duct and then passes into the ureter. From the ureter, urine goes to the urinary bladder, where it is stored until it is expelled through the urethra. Thus, the kidneys filter blood and maintain the body's internal environment by removing harmful wastes.

Points to remember

  1. Nephron is the functional unit of the kidney; it filters blood and forms urine.
  2. Glomerular filtration: Blood pressure forces water, glucose, salts, and urea from the glomerulus into Bowman's capsule.
  3. Selective reabsorption: Useful substances like glucose, amino acids, and water are reabsorbed into blood in the tubule.
  4. Urine formation: The remaining fluid (urine) is collected and transported via ureters to the urinary bladder.
  5. The kidneys help in excretion and maintain water and salt balance in the body.

Exam tip

Draw a labelled diagram of a nephron showing Bowman's capsule, glomerulus, tubule, and collecting duct. Label the parts clearly and mention the steps of filtration and reabsorption in your answer.

Questions students also ask

What is the role of the glomerulus in the kidney?
The glomerulus is a network of capillaries inside Bowman's capsule. Its high blood pressure forces small molecules like water, glucose, salts, and urea out of the blood into the capsule, starting the filtration process.
Why is reabsorption important in the nephron?
Reabsorption prevents the loss of essential substances like glucose, amino acids, and water. These are taken back into the blood as the filtrate flows through the tubule, so only waste products remain in the urine.
What is the difference between filtration and reabsorption?
Filtration is the movement of water and small solutes from blood into Bowman's capsule due to pressure. Reabsorption is the selective movement of useful substances from the filtrate back into the blood in the tubule.

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