The Excretory System

ICSE Class 10 Biology • Chapter 07

1. Definition and Significance

Excretion: The process of removal of harmful nitrogenous metabolic wastes (like Urea, Uric Acid, Ammonia) from the body.

Why is it necessary?

To remove toxic wastes.
To maintain water balance (Osmoregulation).
To maintain pH of blood.

Practice Q1: Waste Products

CONCEPT CHECK Name the primary nitrogenous waste product in humans.

Ans: Urea (Produced in Liver, Excreted by Kidneys).

2. Human Urinary System

Organs:

Kidneys (2): Bean-shaped, located on either side of backbone. Right kidney is slightly lower than Left (due to Liver).
Ureters (2): Tubes carrying urine from Kidney to Urinary Bladder.
Urinary Bladder: Muscular sac that stores urine temporarily.
Urethra: Channel for expelling urine out.

[IMAGE PLACEHOLDER: HUMAN URINARY SYSTEM]

Diagram of Excretory System. Labels: Left/Right Kidney, Adrenal Glands, Ureters, Bladder, Sphincter, Urethra. Show Renal Artery and Renal Vein. (Invert for dark mode).

3. Internal Structure of Kidney

Cortex: Outer dark region (contains Malpighian corpuscles).
Medulla: Inner lighter region (contains Henle's loop). Formed of conical pyramids.
Pelvis: Funnel-shaped space where urine collects.

4. Structure of Nephron (Uriniferous Tubule)

Nephrons are the structural and functional units of the kidney.

Parts of Nephron:

Malpighian Body (Renal Corpuscle):
- Bowman's Capsule: Cup-shaped structure.
- Glomerulus: Tuft of capillaries formed by Afferent (wider) and Efferent (narrower) arterioles.
Renal Tubule:
- PCT (Proximal Convoluted Tubule): In Cortex.
- Loop of Henle: U-shaped hairpin loop (Descending & Ascending). In Medulla.
- DCT (Distal Convoluted Tubule): In Cortex. Opens into Collecting Duct.

[IMAGE PLACEHOLDER: STRUCTURE OF NEPHRON]

Detailed diagram of a Nephron. Labels: Afferent/Efferent Arteriole, Glomerulus, Bowman's Capsule, PCT, Loop of Henle, DCT, Collecting Duct. Show capillary network (Vasa Recta). (Invert for dark mode).

5. Urine Formation

3 Main Steps:

Ultrafiltration: Occurs in Glomerulus due to high pressure (Hydrostatic pressure). Blood filters out liquid part into Bowman's capsule (Glomerular Filtrate). Blood cells & proteins remain behind.
Selective Reabsorption: Useful substances (Glucose, Water, Salts) are reabsorbed back into blood capillaries from PCT and Loop of Henle.
Tubular Secretion: Distal tubule cells secrete K+, H+ ions into the urine (Active transport).

Exam Practice Questions

Practice Q3: Ultrafiltration

APPLICATION Why does blood in the Glomerulus flow under high pressure?

Ans: Because the Afferent arteriole (incoming) is strictly wider than the Efferent arteriole (outgoing), creating a hydrostatic pressure backlog.

Why is the Afferent arteriole wider than the Efferent arteriole?

Ans: To create a high hydrostatic pressure in the Glomerulus needed for Ultrafiltration.