transepithelial water transport

Definition

Target type: biologicalprocess

The directed movement of water (H2O) from one side of an epithelium to the other. [GOC:yaf]

Transepithelial water transport is a crucial physiological process that involves the movement of water across epithelial cell layers, which line the surfaces of organs and cavities within the body. This process is essential for maintaining fluid balance, regulating blood pressure, and facilitating nutrient absorption. Here's a detailed breakdown of the process:

**1. Water Movement Across the Cell Membrane:**

* Water primarily moves across cell membranes through osmosis, a passive process driven by differences in water potential.
* Water potential is influenced by solute concentration, pressure, and gravitational forces.
* Water moves from areas of high water potential (low solute concentration) to areas of low water potential (high solute concentration) to achieve equilibrium.

**2. Aquaporins: The Water Channels:**

* Aquaporins are transmembrane proteins that form selective water channels in cell membranes, facilitating rapid water transport.
* These channels are highly regulated, allowing for precise control of water flow.

**3. Transcellular and Paracellular Pathways:**

* Water can move across epithelial cells via two main pathways:
* **Transcellular pathway:** Water moves through the cell, passing through both the apical (facing the lumen) and basolateral (facing the blood) membranes.
* **Paracellular pathway:** Water moves between adjacent cells through tight junctions, which are protein complexes that regulate intercellular permeability.

**4. Driving Forces for Water Transport:**

* **Osmotic pressure gradients:** The concentration difference of solutes between the lumen and the blood creates an osmotic pressure gradient, driving water movement.
* **Hydrostatic pressure gradients:** Pressure differences across the epithelium, such as blood pressure in capillaries, can also influence water transport.

**5. Regulation of Transepithelial Water Transport:**

* **Hormonal control:** Hormones like antidiuretic hormone (ADH) and aldosterone play crucial roles in regulating water reabsorption in the kidneys.
* **Neural regulation:** The nervous system can influence water transport by controlling the activity of aquaporins and other membrane transport proteins.

**6. Examples of Transepithelial Water Transport:**

* **Kidney:** Reabsorption of water from the filtrate in the nephron, contributing to urine formation.
* **Intestine:** Absorption of water from ingested food, facilitating nutrient digestion and absorption.
* **Lungs:** Transport of water vapor from the blood into the alveoli for gas exchange.
* **Salivary glands:** Secretion of saliva, containing water and electrolytes.
* **Sweat glands:** Secretion of sweat, primarily composed of water, for thermoregulation.

Transepithelial water transport is a complex process that involves intricate interplay between membrane transport, cell signaling, and hormonal regulation. It is essential for maintaining fluid balance, regulating blood pressure, and supporting various physiological processes within the body.'
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Compounds (29)