Proximal convoluted tubule

Definition

The proximal convoluted tubule (PCT) is a highly coiled section of the nephron in the kidney, situated between the Bowman’s capsule and the loop of Henle. It plays a crucial role in reabsorbing essential nutrients, ions, and water from the filtrate back into the bloodstream, making it vital for maintaining homeostasis and fluid balance.

5 Must Know Facts For Your Next Test

1. The proximal convoluted tubule is lined with microvilli, which increase the surface area for absorption and enhance its efficiency in reclaiming substances from filtrate.
2. About 65-70% of filtered water and a high percentage of glucose, amino acids, sodium, and bicarbonate are reabsorbed in the PCT.
3. The cells of the PCT actively transport sodium ions out of the tubule, which helps to drive the passive reabsorption of water through osmosis.
4. The PCT is also involved in secreting certain substances such as hydrogen ions and toxins, helping regulate pH and eliminate waste.
5. Disruptions in PCT function can lead to conditions like Fanconi syndrome, where reabsorption of substances like glucose is impaired, leading to their loss in urine.

Review Questions

• How does the structure of the proximal convoluted tubule facilitate its function in reabsorption?
  • The proximal convoluted tubule has a highly folded structure with microvilli on its epithelial cells, which significantly increases its surface area. This design allows for more efficient reabsorption of essential nutrients and water from the filtrate back into the bloodstream. Additionally, the presence of various transport proteins in its membrane helps facilitate the active transport of ions and nutrients, maximizing the amount that can be reabsorbed.
• What are the key physiological processes occurring within the proximal convoluted tubule that contribute to fluid balance?
  • In the proximal convoluted tubule, approximately 65-70% of filtered water is reabsorbed along with significant amounts of glucose, amino acids, and electrolytes. The active transport of sodium out of the PCT cells creates an osmotic gradient that promotes water reabsorption through osmosis. This process is crucial for maintaining fluid balance in the body and ensuring that essential nutrients are conserved while waste products continue toward excretion.
• Evaluate how dysfunctions in the proximal convoluted tubule impact overall kidney function and health.
  • Dysfunctions in the proximal convoluted tubule can severely impair kidney function by disrupting normal reabsorption processes. Conditions such as Fanconi syndrome highlight how issues can lead to excessive loss of vital substances like glucose and bicarbonate in urine. This impairment can result in metabolic imbalances, dehydration, and increased levels of waste products in the bloodstream, ultimately compromising renal health and overall physiological homeostasis.

Related terms

nephron: The basic structural and functional unit of the kidney, responsible for filtering blood and forming urine.

Bowman's capsule: The cup-like sac at the beginning of the nephron that encases the glomerulus and collects the filtrate.

loop of Henle:

A U-shaped section of the nephron that plays a significant role in concentrating urine by creating a concentration gradient in the renal medulla.