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Biology - The Excretory System

Grade 10ICSE

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

🔑Concepts

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Excretion is the process of eliminating metabolic waste products, especially nitrogenous wastes like urea (NH2CONH2NH_2CONH_2), from the body to maintain homeostasis.

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The human urinary system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

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The Nephron is the structural and functional unit of the kidney, consisting of the Malpighian corpuscle (Glomerulus and Bowman's capsule) and the Renal Tubule (Proximal Convoluted Tubule, Loop of Henle, and Distal Convoluted Tubule).

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Ultrafiltration occurs in the Malpighian capsule due to high hydrostatic pressure in the glomerulus. The liquid that filters into the capsule is called the glomerular filtrate, which contains water, glucose, salts, and urea, but no blood cells or large proteins.

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Selective Reabsorption happens primarily in the Proximal Convoluted Tubule (PCTPCT), where useful substances like glucose, amino acids, and a large amount of H2OH_2O are taken back into the blood.

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Tubular Secretion occurs in the Distal Convoluted Tubule (DCTDCT), where certain ions (K+K^+, H+H^+) and foreign substances (drugs/penicillin) are actively secreted from the blood into the forming urine.

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Osmoregulation is the regulation of the osmotic pressure of body fluids by controlling the amount of water and salts. This is primarily controlled by the Antidiuretic Hormone (ADHADH), also known as Vasopressin.

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Urine typically contains approximately 95%95\% water and 5%5\% solid wastes (including 2.5%2.5\% urea and 2.5%2.5\% other salts and toxins).

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Abnormal constituents of urine include Glucose (indicating Diabetes Mellitus), Albumin (indicating kidney inflammation), and Bile pigments (indicating Jaundice).

📐Formulae

Peff=PG−(POP+PC)P_{eff} = P_G - (P_{OP} + P_C) where PeffP_{eff} is Effective Filtration Pressure, PGP_G is Glomerular Hydrostatic Pressure, POPP_{OP} is Colloid Osmotic Pressure, and PCP_C is Capsular Hydrostatic Pressure.

NH2CONH2NH_2CONH_2 (Chemical formula for Urea)

C6H12O6→MetabolismCO2+H2O+EnergyC_6H_{12}O_6 \xrightarrow{Metabolism} CO_2 + H_2O + Energy (Excretion removes the CO2CO_2 and excess H2OH_2O produced during cellular respiration.)

💡Examples

Problem 1:

Calculate the Effective Filtration Pressure (PeffP_{eff}) if the Glomerular Hydrostatic Pressure is 60 mmHg60\text{ mmHg}, the Blood Colloid Osmotic Pressure is 32 mmHg32\text{ mmHg}, and the Capsular Hydrostatic Pressure is 18 mmHg18\text{ mmHg}.

Solution:

Peff=60−(32+18)=10 mmHgP_{eff} = 60 - (32 + 18) = 10\text{ mmHg}

Explanation:

The net pressure responsible for ultrafiltration is the difference between the outward hydrostatic pressure and the opposing inward pressures (osmotic and capsular).

Problem 2:

What happens to the concentration of urine when a person is dehydrated?

Solution:

When dehydrated, the pituitary gland releases more ADHADH (Antidiuretic Hormone). This increases the permeability of the DCTDCT and collecting ducts to water, leading to increased water reabsorption. As a result, the urine becomes hypertonic (concentrated) and decreases in volume.

Explanation:

This is a classic example of negative feedback in osmoregulation to conserve H2OH_2O.

Problem 3:

Explain why the diameter of the afferent arteriole is wider than the efferent arteriole.

Solution:

The difference in diameter (Dafferent>DefferentD_{afferent} > D_{efferent}) creates high hydrostatic pressure in the glomerulus.

Explanation:

This pressure is essential for the process of ultrafiltration, forcing small molecules out of the blood and into the Bowman's capsule.