Introduction
The excretory system in animals is responsible for the removal of metabolic wastes and the maintenance of homeostasis. This study note will cover the various excretory products, the organs involved in excretion, and the processes by which these products are eliminated from the body.
Excretory Products
Nitrogenous Wastes
Metabolism of proteins and nucleic acids results in the production of nitrogenous wastes. The primary nitrogenous wastes include:
- Ammonia (NH3)
- Urea
- Uric Acid
Ammonia
- Highly toxic and requires a large amount of water for excretion.
- Excreted by aquatic animals such as fish and amphibians.
- Ammonotelic organisms: Organisms that excrete ammonia.
Urea
- Less toxic than ammonia and requires less water for excretion.
- Produced in the liver through the urea cycle.
- Excreted by mammals, including humans, and some amphibians.
- Ureotelic organisms: Organisms that excrete urea.
Uric Acid
- Least toxic and requires minimal water for excretion.
- Excreted by birds, reptiles, and insects.
- Uricotelic organisms: Organisms that excrete uric acid.
Remember the differences in water requirements for excreting ammonia, urea, and uric acid when studying animal adaptations to their environments.
Other Excretory Products
- Carbon dioxide (CO2): Excreted through respiration.
- Water: Excreted through urine, sweat, and respiration.
- Salts and Ions: Excreted through urine and sweat.
Excretory Organs
Human Excretory System
Kidneys
- Structure: The kidneys are bean-shaped organs located on either side of the vertebral column.
- Nephrons: Functional units of the kidney, consisting of the glomerulus and renal tubule.
- Functions: Filtration, reabsorption, secretion, and excretion.
Ureters
- Tubes that transport urine from the kidneys to the urinary bladder.
Urinary Bladder
- A muscular sac that stores urine until it is excreted.
Urethra
- A tube that carries urine from the bladder to the outside of the body.
Other Excretory Organs
- Lungs: Excrete carbon dioxide and water vapor.
- Skin: Excretes sweat, which contains water, salts, and urea.
- Liver: Converts ammonia to urea and excretes bile pigments.
Processes of Excretion
Filtration
- Occurs in the glomerulus of the nephron.
- Blood pressure forces water, salts, glucose, amino acids, and urea into the Bowman's capsule.
- Glomerular Filtrate: The fluid that enters the Bowman's capsule.
Reabsorption
- Occurs in the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT).
- Essential substances like glucose, amino acids, and ions are reabsorbed into the blood.
- Water is reabsorbed by osmosis.
Secretion
- Occurs in the DCT and collecting duct.
- Additional wastes and excess ions are secreted into the tubule from the blood.
Excretion
- The final urine is collected in the collecting ducts and transported to the bladder via the ureters.
- Urine is excreted through the urethra.
Regulation of Kidney Function
Hormonal Control
- Antidiuretic Hormone (ADH): Increases water reabsorption in the kidneys.
- Aldosterone: Increases reabsorption of sodium and water.
- Atrial Natriuretic Peptide (ANP): Reduces reabsorption of sodium and water.
Osmoregulation
- The kidneys maintain the balance of water and electrolytes in the body.
- Counter-current mechanism in the loop of Henle helps in the concentration of urine.
Understanding the role of hormones in kidney function is crucial for NEET exams.
Disorders of the Excretory System
Kidney Stones
- Hard deposits of minerals and salts that form in the kidneys.
- Can cause severe pain and blockage of urine flow.
Uremia
- Accumulation of urea in the blood due to kidney failure.
- Requires dialysis or kidney transplant.
Glomerulonephritis
- Inflammation of the glomeruli in the kidneys.
- Can lead to kidney damage and impaired function.
Do not confuse glomerulonephritis with nephritis, which is a general term for kidney inflammation.
Conclusion
Understanding the excretory products and their elimination is essential for maintaining homeostasis in the body. The kidneys play a pivotal role in filtering blood, reabsorbing essential substances, and excreting wastes. Hormonal regulation ensures the proper functioning of the kidneys and the balance of fluids and electrolytes.
TipPractice diagram-based questions and understand the physiological processes to excel in NEET Zoology.
By mastering these concepts, you will be well-prepared for questions on the excretory system in the NEET exam.
