Loop of Henle Function and Osmoregulation

Overview

This lecture explains the structure and function of the Loop of Henle in the kidney, focusing on its role in osmoregulation and how it controls water and salt balance in the body.

The Nephron and Loop of Henle Overview

• The nephron is the functional unit of the kidney responsible for filtering blood and forming urine.
• The Loop of Henle is a section of the nephron involved in osmoregulation (water and salt balance).
• The Loop of Henle consists of two parts: the descending limb (downward) and the ascending limb (upward).

Osmolarity and Osmosis Basics

• Osmolarity refers to the concentration of solutes (like salts) in a liquid.
• High osmolarity means high solute concentration; low osmolarity means low solute concentration.
• Diffusion is the movement of substances from high to low concentration.
• Osmosis is the passive movement of water from areas of low solute concentration to high solute concentration.

Tonicity Terms

• Hypertonic solutions have high solute and low water content (high osmolarity).
• Hypotonic solutions have low solute and high water content (low osmolarity).

Function of the Descending Limb

• The descending limb is permeable to water but not to salts.
• As filtrate moves down the descending limb, water leaves the tube, increasing osmolarity of the filtrate.
• The surrounding tissue is hypertonic, attracting water out of the descending limb.

Function of the Ascending Limb

• The ascending limb is permeable to salts (solutes) but not to water.
• Salts (like sodium, chloride, potassium) are actively transported out of the ascending limb.
• The surrounding tissue near the ascending limb is hypotonic due to lower salt concentration.

Importance of Permeability

• The arrangement ensures a concentration gradient is maintained for continuous water and salt reabsorption.
• Salt leaving the ascending limb makes surrounding tissue salty, which helps draw water from the descending limb.

Summary of Osmoregulation in the Loop of Henle

• Osmoregulation involves controlling both water and salt levels in the blood.
• The unique permeability of each limb allows for efficient water and salt reabsorption.
• The process helps maintain homeostasis of body fluids.

Key Terms & Definitions

• Nephron — the kidney's functional unit responsible for filtering blood and forming urine.
• Loop of Henle — part of the nephron that regulates water and salt balance.
• Descending limb — allows water to exit, impermeable to salts.
• Ascending limb — allows salts to exit, impermeable to water.
• Osmolarity — concentration of solutes (like salts) in a liquid.
• Osmosis — passive movement of water from low to high solute concentration.
• Permeable — allows substances to pass through.
• Hypotonic — low solute, high water concentration.
• Hypertonic — high solute, low water concentration.
• Osmoregulation — process of controlling water and salt levels in the body.

Action Items / Next Steps

• Watch the separate video on the sodium-potassium pump for details on active salt transport.
• Review videos on ADH and aldosterone for hormone regulation of water and salt.
• Create flashcards for the key terms listed above.