Important Diagrams: Excretory Products and their Elimination | Biology Class 11 - NEET PDF Download

Excretion is the biological process through which organisms remove waste products generated by their metabolic activities. These waste products include substances like carbon dioxide, urea, ammonia, excess salts, and water. Excretion is crucial for maintaining the internal environment of an organism within optimal conditions for cellular function, a concept known as homeostasis.

1. Human Excretory System

(a) Introduction to Excretion: Excretion is the process of removing metabolic wastes from the body to maintain internal balance and health.

(b) Types of Metabolic Wastes in Humans: Metabolic wastes in humans include carbon dioxide, water, urea, ammonia, uric acid, and other toxic compounds.

(c) Importance of Complex Excretion Processes: While diffusion plays a role in excretion for lower organisms, the human body's complexity requires more specific processes to eliminate diverse waste products effectively.

(d) The Role of Kidneys in Excretion: Kidneys are vital organs responsible for filtering blood and producing urine, thereby eliminating waste products from the body.

(e) Structure and Function of Nephrons: Nephrons are the functional units of the kidneys, comprising a complex structure involved in filtration, reabsorption, and secretion.

(f) Filtration and Reabsorption in the Kidneys: Blood is filtered in the kidneys, where essential substances such as glucose, amino acids, salts, and water are reabsorbed, while waste products remain in the filtrate.

(g) Formation of Urine: Excess water and nitrogenous waste are converted into urine within the kidneys before being passed to the urinary bladder.

(h) Urinary Tract and Bladder Control: Urine travels from the kidneys to the urinary bladder through the ureters. The urinary bladder, controlled by the Central Nervous System, stores urine until it is expelled.

(i) Brain Signaling and Urine Excretion via Urethra: The brain signals the urinary bladder to contract when it's time to urinate. Urine is then expelled from the body through the urethra, completing the excretion process.

2. Structure of Kidney

Human kidneys are bean-shaped organs situated beneath the rib cage, roughly the size of a fist.

• They play a crucial role in the excretory system by filtering blood to produce urine.
• External features include a convex and concave border, with a hilum on the inner concave side for entry and exit of blood vessels and ureter.
• The outer layer is encased by a tough capsule.
• Internally, the kidney consists of a renal cortex and a renal medulla, with the hilum extending into the renal pelvis.
• The renal pelvis contains calyces, and medullary pyramids project into these calyces.
• Renal columns known as Columns of Bertini extend between the medullary pyramids.
• Nephrons, the functional units, make up the kidney.

3. Structure of Nephron

Nephrons are vital for maintaining fluid balance, blood pressure regulation, and waste elimination in the body.

• They consist of two main components: the renal corpuscle and the renal tubule.
• The renal corpuscle, comprising the glomerulus and Bowman’s capsule, filters blood, allowing small molecules to pass through while retaining larger ones.
• The renal tubule, including segments like the proximal and distal convoluted tubules, facilitates processes like reabsorption, secretion, and excretion.
• Functions of nephrons include filtration (in the renal corpuscle), reabsorption (primarily in the renal tubule), secretion (transferring additional substances into the tubule), and excretion (formation of urine).
• There are two types of nephrons: cortical nephrons, which are abundant and maintain overall fluid balance, and juxtamedullary nephrons, which produce concentrated urine and aid in water conservation.

4. Functions of the Tubules: Tubular Secreation

Tubular reabsorption is the crucial second step in urine formation, ensuring essential substances are retained while excess waste is eliminated. It involves active transport for absorbing glucose and ions, and passive transport for water absorption.

Key tubules involved:

• Proximal Convoluted Tubule (PCT): Reabsorbs ions, water, and nutrients, while eliminating toxins and regulating pH.
• Ascending Loop of Henle: Reabsorbs sodium and chloride ions.
• Descending Loop of Henle: Allows water reabsorption by creating a concentration gradient.
• Distal Tubule (including DCT): Selectively reabsorbs ions and aids in pH balance maintenance.
• Collecting Duct: Reabsorbs solutes and water.
• Secretion involves expelling waste ions like hydrogen, potassium, and ammonia into urine.
• The bladder fills with urine, then empties through micturition upon brain signal.

5. Counter-Current Mechanism

The kidney uses counter current mechanisms like Henle's loop and vasa recta to conserve water. These mechanisms involve blood flowing in opposite directions in adjacent tubules or vessels, creating a concentration gradient in the inner medulla. This gradient aids in water reabsorption from collecting tubules by facilitating the movement of substances like NaCl and urea.

6. Haemodialysis

Hemodialysis is a procedure where a dialysis machine and a special filter called an artificial kidney, or a dialyzer, are used to clean your blood. To get your blood into the dialyzer, the doctor needs to make an access, or entrance, into your blood vessels. This is done with minor surgery, usually to your arm.