I/GCSE Biology Chapter Analysis - Chapter 2: Structure and Function of Living Organisms - Excretion (Part 2)
Let's explore the last part of IGCSE Biology's Chapter 2 sub-topic on excretion.
Ultrafiltration in the Bowman's Capsule and Glomerular Filtrate:
The process of filtration in the kidneys begins in the Bowman's capsule, where the glomerulus (a network of blood vessels) is located. Here, the blood is subjected to ultrafiltration, a process in which small molecules and water are forced out of the glomerular capillaries and into the Bowman's capsule, forming the glomerular filtrate. This filtrate contains water, glucose, amino acids, vitamins, and other small molecules, but it does not contain large molecules like proteins or blood cells.
Reabsorption of Water in the Collecting Duct:
As the glomerular filtrate passes through the tubular system of the nephron, the majority of the water is reabsorbed back into the bloodstream. This reabsorption occurs primarily in the collecting duct, where the hormone antidiuretic hormone (ADH) plays a crucial role. ADH promotes the insertion of water channels (aquaporins) in the collecting duct, allowing water to be reabsorbed and returned to the blood.
Selective Reabsorption of Glucose in the Proximal Convoluted Tubule:
In the proximal convoluted tubule, the glomerular filtrate undergoes selective reabsorption, where certain substances are actively transported back into the blood. One of the substances selectively reabsorbed is glucose. The proximal convoluted tubule has specialized transport proteins that actively pump glucose from the filtrate back into the bloodstream, ensuring that glucose is not lost in the urine.
Role of ADH in Regulating Water Content:
The hormone ADH, produced by the hypothalamus and released by the pituitary gland, plays a crucial role in regulating the water content of the blood. When the body's water levels are low, the hypothalamus detects this and stimulates the release of ADH, which then travels to the kidneys and promotes the reabsorption of water in the collecting ducts, ultimately helping to maintain the body's water balance.
Composition of Urine:
The final product of the excretory system is urine, which contains:
- Water: The main component of urine, with varying concentrations depending on the body's water balance.
- Urea: A waste product formed from the breakdown of excess amino acids in the liver.
- Ions: such as sodium, potassium, and chloride, which are also excreted in the urine.
Through the coordinated processes of ultrafiltration, selective reabsorption, and the regulation of water balance by ADH, the kidneys are able to maintain the body's homeostasis and excrete the waste products of metabolism.
Work hard for your I/GCSE Biology examination!
End of analysis. Great!
