Collecting ducts

Collecting Ducts

The collecting ducts are a series of tubules and ducts that connect the nephrons to the renal pelvis in the kidney. They play a crucial role in the regulation of water, electrolyte balance, and acid-base homeostasis in the body. The collecting ducts are the final component of the kidney's filtration system and are essential for the concentration of urine.

Structure

The collecting duct system is composed of several segments:

• Cortical collecting ducts: These are located in the renal cortex and receive filtrate from the distal convoluted tubules of the nephrons.
• Outer medullary collecting ducts: These ducts descend into the outer medulla of the kidney.
• Inner medullary collecting ducts: These are found in the inner medulla and eventually merge to form the papillary ducts, which empty into the renal pelvis.

The walls of the collecting ducts are lined with two main types of cells:

• Principal cells: These cells are involved in sodium reabsorption and potassium secretion, regulated by the hormone aldosterone.
• Intercalated cells: These cells play a role in acid-base balance by secreting hydrogen ions or bicarbonate.

Function

The primary functions of the collecting ducts include:

• Water Reabsorption: The collecting ducts are the site of action for the hormone antidiuretic hormone (ADH), which increases the permeability of the duct walls to water, allowing for water reabsorption and concentration of urine.
• Electrolyte Balance: The ducts help in the reabsorption of sodium and the secretion of potassium, which are crucial for maintaining electrolyte balance.
• Acid-Base Homeostasis: Intercalated cells in the collecting ducts secrete hydrogen ions or bicarbonate to help maintain the body's pH balance.

Clinical Significance

Disorders of the collecting ducts can lead to various medical conditions, such as:

• Diabetes Insipidus: A condition characterized by the inability to concentrate urine due to a lack of ADH or a response to it.
• Hyperkalemia: An elevated level of potassium in the blood, which can occur if the collecting ducts do not secrete enough potassium.
• Acidosis or Alkalosis: Imbalances in acid-base homeostasis can result from dysfunction in the intercalated cells of the collecting ducts.

Also see

• Nephron
• Renal cortex
• Renal medulla
• Antidiuretic hormone
• Aldosterone