Collecting duct

Definition

The collecting duct is a crucial component of the nephron in the kidney, responsible for the final concentration of urine. It plays a key role in regulating water and electrolyte balance by reabsorbing water and certain ions from the filtrate, ultimately influencing blood pressure and fluid homeostasis. The collecting duct connects the distal convoluted tubule to the renal pelvis, serving as a passage for urine before it enters the ureter.

5 Must Know Facts For Your Next Test

1. The collecting duct is primarily composed of two types of cells: principal cells, which are involved in water and sodium reabsorption, and intercalated cells, which help regulate acid-base balance.
2. The permeability of the collecting duct to water is controlled by ADH, which is released in response to increased plasma osmolality or decreased blood volume.
3. In addition to water, the collecting duct also plays a role in the reabsorption of electrolytes such as sodium and potassium, influencing overall electrolyte balance.
4. The collecting duct can also secrete certain ions like hydrogen and ammonium to help maintain acid-base homeostasis.
5. The function of the collecting duct is essential for concentrating urine, allowing the body to conserve water during dehydration and excrete excess fluid when hydration levels are adequate.

Review Questions

• How does the structure of the collecting duct contribute to its function in urine concentration?
  • The structure of the collecting duct, with its varying permeability to water and solutes, allows for effective regulation of urine concentration. Principal cells within the duct respond to ADH, increasing their permeability to water when needed. This means that when hydration levels are low, more water is reabsorbed back into circulation, resulting in concentrated urine. Conversely, when fluid levels are adequate, less water is reabsorbed, leading to more diluted urine.
• Discuss the role of ADH in regulating water reabsorption within the collecting duct and its impact on overall fluid balance.
  • ADH plays a pivotal role in regulating water reabsorption in the collecting duct by making it more permeable to water. When released from the posterior pituitary gland in response to increased plasma osmolality, ADH binds to receptors on principal cells. This triggers aquaporin channels to insert into their membranes, allowing more water to be reabsorbed into the bloodstream. As a result, this process directly influences fluid balance by concentrating urine and helping maintain blood pressure.
• Evaluate how disturbances in the function of the collecting duct can lead to clinical conditions related to fluid balance.
  • Disturbances in collecting duct function can lead to significant clinical conditions such as diabetes insipidus or hyponatremia. In diabetes insipidus, inadequate ADH production or receptor dysfunction prevents proper water reabsorption, resulting in excessive urination and dehydration. Conversely, if excessive ADH is produced, it can lead to water retention and hyponatremia, where sodium levels drop dangerously low due to diluted serum. Understanding these mechanisms is vital for managing fluid balance disorders effectively.

Related terms

nephron: The basic structural and functional unit of the kidney, consisting of a glomerulus and a series of tubules that filter blood and form urine.

ADH (Antidiuretic Hormone): A hormone that regulates water reabsorption in the collecting duct by increasing its permeability to water, thus concentrating urine.

renal pelvis: The funnel-shaped structure at the center of the kidney that collects urine from the collecting ducts and channels it into the ureter.