A-Level Biology: Tissue Fluid

Introduction

• Topic: Tissue fluid
• Importance: Understanding what tissue fluid is, how it's formed, and how water is reabsorbed.

What is Tissue Fluid?

• Definition: Liquid surrounding cells in the body.
• Composition: Contains water, glucose, amino acids, fatty acids, dissolved ions, minerals, and oxygen.
• Function: Allows diffusion of essential molecules like glucose and oxygen into cells for survival and respiration.

Formation of Tissue Fluid

• Capillaries: One cell thick with tiny gaps.
  • Allows water and small molecules to be forced out.
• Blood flow: Arteries → Arterioles → Capillaries.
• High Pressure: When blood flows into capillaries, pressure increases causing ultrafiltration.
  • Acts like a sieve, forcing out water and small molecules, while larger molecules remain behind.
• Key Molecules Forced Out:
  • Water
  • Dissolved minerals and salts
  • Glucose
  • Small proteins
  • Amino acids
  • Fatty acids
  • Oxygen
• Large Molecules Remaining:
  • Red blood cells
  • Platelets
  • Large proteins

Reabsorption of Tissue Fluid

• Necessity: Prevents swelling and maintains blood volume.
• Process:
  • Occurs at the venule end of capillaries.
  • Large molecules remaining create a negative water potential.
  • Water moves back into capillaries by osmosis.
  • Low hydrostatic pressure at this end, facilitating osmosis.

Waste Removal

• Dissolved Wastes:
  • Carbon dioxide
  • Urea
• Osmosis: Water with dissolved waste moves back into blood.

Role of the Lymphatic System

• Lymphatic System: Absorbs remaining tissue fluid not reabsorbed by capillaries.
• Lymph Vessels: Similar to veins, have valves.
• Lymph: The absorbed liquid.
• Function: Returns lymph to the blood near the heart.

Summary

• Tissue fluid is crucial for nutrient and waste exchange.
• Formed through ultrafiltration due to high pressure in capillaries.
• Reabsorbed by osmosis at the venule end, with excess handled by the lymphatic system.

• Action Items: Review blood vessels video to understand the blood flow better.
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