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Human Body - Excretory System (Kidneys, Nephron)

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Excretion is the process of removing metabolic waste products like CO2CO_2, H2OH_2O, and nitrogenous wastes such as urea from the body.

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The Human Urinary System consists of a pair of kidneys, two ureters, a urinary bladder, and a urethra.

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The kidney is divided into two main regions: the outer dark region called the Renal Cortex and the inner lighter region called the Renal Medulla.

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The Nephron is the structural and functional unit of the kidney. Each kidney contains approximately 11 to 1.21.2 million nephrons.

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A Nephron consists of two main parts: the Malpighian Corpuscle (comprising the Glomerulus and Bowman's capsule) and the Renal Tubule.

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Ultrafiltration occurs in the Glomerulus under high pressure, where water and small solutes are pushed into the Bowman's capsule to form glomerular filtrate.

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Selective Reabsorption occurs in the renal tubules, where useful substances like glucose, amino acids, and most of the H2OH_2O are taken back into the blood.

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Urine is the final fluid produced, containing 95%95\% water, 2.5%2.5\% urea, and 2.5%2.5\% other waste substances like uric acid and salts.

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Dialysis is an artificial method used to filter the blood when a person's kidneys fail to function correctly.

📐Formulae

Urea Formula: (NH2)2CO\text{Urea Formula: } (NH_2)_2CO

Excretion=Filtration−Reabsorption+Secretion\text{Excretion} = \text{Filtration} - \text{Reabsorption} + \text{Secretion}

Net Filtration Pressure=Glomerular Hydrostatic Pressure−(Colloid Osmotic Pressure+Capsular Hydrostatic Pressure)\text{Net Filtration Pressure} = \text{Glomerular Hydrostatic Pressure} - (\text{Colloid Osmotic Pressure} + \text{Capsular Hydrostatic Pressure})

💡Examples

Problem 1:

What is the composition of normal human urine in terms of water and urea percentages?

Solution:

Water: 95%95\%, Urea: 2.5%2.5\%.

Explanation:

Human urine is primarily composed of H2OH_2O. The remaining 5%5\% consists of organic and inorganic wastes, of which urea (NH2)2CO(NH_2)_2CO is the primary nitrogenous component.

Problem 2:

Identify the part of the nephron where the maximum reabsorption of water and glucose takes place.

Solution:

Proximal Convoluted Tubule (PCT).

Explanation:

The PCT is lined with microvilli that increase the surface area for the selective reabsorption of essential nutrients like glucose and nearly 65%65\% of filtered H2OH_2O back into the peritubular capillaries.

Problem 3:

Why is the diameter of the afferent arteriole wider than the efferent arteriole in the glomerulus?

Solution:

To create high hydrostatic pressure for Ultrafiltration.

Explanation:

The difference in diameter creates a pressure gradient (PhydrostaticP_{hydrostatic}) in the glomerulus, forcing liquid and small molecules through the semi-permeable walls into the Bowman's capsule.