Collecting ducts

Definition

Collecting ducts are a series of tubules in the kidney that collect urine from the nephrons and transport it to the renal pelvis. They play a crucial role in the regulation of water and electrolyte balance, influenced by hormones like antidiuretic hormone (ADH) and aldosterone, which adjust the permeability of the ducts to water and sodium, respectively.

5 Must Know Facts For Your Next Test

1. Collecting ducts can reabsorb water from urine, which is controlled by ADH levels in the body; higher ADH means more water reabsorption.
2. The structure of collecting ducts includes principal cells and intercalated cells, each with specific functions related to ion balance and acid-base regulation.
3. When aldosterone is present, sodium reabsorption in collecting ducts increases, which can lead to increased blood volume and blood pressure.
4. Collecting ducts are located in the renal medulla and are responsible for concentrating urine before it enters the renal pelvis.
5. Disruption in the function of collecting ducts can lead to conditions like diabetes insipidus, where there is excessive urine production due to lack of ADH action.

Review Questions

• How do collecting ducts regulate water reabsorption in response to changes in ADH levels?
  • Collecting ducts regulate water reabsorption by adjusting their permeability to water based on ADH levels. When ADH is secreted in response to dehydration or high plasma osmolality, it binds to receptors on the principal cells of the collecting ducts, prompting the insertion of aquaporin-2 channels into the cell membrane. This allows more water to be reabsorbed from the urine back into the bloodstream, thereby concentrating the urine and reducing water loss.
• Discuss how aldosterone affects sodium reabsorption in collecting ducts and its overall impact on fluid balance.
  • Aldosterone acts on the principal cells of the collecting ducts, enhancing sodium reabsorption. When aldosterone levels are high, sodium channels and sodium-potassium pumps are activated, leading to increased reabsorption of sodium from the urine. This not only retains sodium in the body but also draws water back into circulation due to osmosis, ultimately increasing blood volume and maintaining blood pressure.
• Evaluate the implications of dysfunctional collecting ducts on homeostasis within the body.
  • Dysfunctional collecting ducts can significantly disrupt homeostasis by affecting water and electrolyte balance. For example, conditions like nephrogenic diabetes insipidus arise when there is a lack of response to ADH, leading to excessive urine output and dehydration. This imbalance can trigger compensatory mechanisms such as increased thirst or hormonal adjustments, but if unregulated, it can result in severe dehydration, electrolyte imbalances, and potentially life-threatening consequences if not addressed promptly.

Related terms

nephron:

The functional unit of the kidney responsible for filtering blood and forming urine.

antidiuretic hormone (ADH):

A hormone that regulates water retention in the body by increasing the permeability of the collecting ducts to water.

aldosterone:

A hormone produced by the adrenal glands that promotes sodium reabsorption in the kidneys, affecting fluid balance and blood pressure.