IGCSE Biology Kidneys

Summary:

The kidneys are excretory organs that remove waste products like urea, ions, and water from the blood, which are then eliminated in urine. They also play a role in osmoregulation, controlling the water content in the blood. Nephrons in the kidneys filter the blood, allowing small molecules like water, glucose, urea, and ions to pass into the Bowman’s capsule, forming the glomerular filtrate. Useful substances like glucose and some ions are reabsorbed into the blood along the nephron, while water is reabsorbed in the collecting duct. Urea, excess ions, and some water are left behind, forming urine. This process is regulated by the hormone ADH, which stimulates water reabsorption based on blood concentration levels. When blood is more concentrated, more water is reabsorbed, leading to a smaller volume of concentrated urine. Conversely, less water is reabsorbed when blood is more dilute, resulting in a larger volume of dilute urine. The kidneys’ intricate processes ensure that waste products are efficiently removed, and the body’s water balance is well-maintained.

Excerpt:

IGCSE Biology Kidneys

The Kidneys:

Excretory products:
– Urea is a waste product from excess amino acids. It is produced in the liver and then transported to the kidneys in the plasma in the blood. The kidneys are the excretory organ for urea (ions and water), all removed in the urine.
– Carbon dioxide is an excretory product from respiration. This is produced in cells and is transported back to the lungs in the plasma in the blood. The lungs are the excretory organ responsible for removing carbon dioxide from the body.
– The skin is also an excretory organ, which removes products when we sweat, mainly water, and contains some waste products such as urea. Sweat also helps cool us down when we are hot, and we sweat more which evaporates from the skin, transferring heat energy away from the body.
– Plant waste from respiration and photosynthesis is removed through the stomata.