Lecture Notes: Tissue Fluid in A-Level Biology

Overview

• Topic: Tissue Fluid
• Purpose: Understanding what tissue fluid is, how it is formed, and how water is reabsorbed.

What is Tissue Fluid?

• Definition: A liquid that surrounds the cells in the body.
• Components:
  • Water
  • Glucose
  • Amino acids
  • Fatty acids
  • Dissolved ions and minerals
  • Oxygen
• Function: Allows essential molecules like glucose and oxygen to diffuse into cells, aiding in survival and processes such as respiration.

Formation of Tissue Fluid

• Capillaries:
  • Only one cell thick with tiny gaps between cells.
  • Allows water and small molecules to be forced out.
• Blood flow:
  • Arterioles connected to capillaries have increased pressure.
  • High pressure causes ultrafiltration.
• Ultrafiltration: Acts like a sieve, allowing only small molecules to pass through.
• Substances forced out include:
  • Water
  • Dissolved minerals and salts
  • Glucose
  • Small proteins
  • Individual amino acids
  • Fatty acids
  • Oxygen
• Large molecules that remain in the blood:
  • Red blood cells
  • Platelets
  • Large proteins

Reabsorption of Tissue Fluid

• Necessity: Prevents running out of blood liquid and swelling of tissues.
• Process:
  • Occurs at the venule end of capillaries, nearer to the veins.
  • Low pressure in capillaries at this end.
  • Large molecules remain in the blood, creating a very negative water potential.
  • Osmosis: Water in tissue fluid moves back into capillaries via osmosis down the water potential gradient.
• Waste molecules in water:
  • Carbon dioxide
  • Urea
  • Reabsorbed with water back into the blood.

Lymphatic System

• Role: Absorbs excess tissue fluid not reabsorbed by capillaries to prevent equilibrium.
• Lymph vessels:
  • Similar to veins with valves.
  • Absorb remaining tissue fluid, referred to as lymph.
  • Returns it to blood near the heart.

Summary

• Importance of Tissue Fluid: Essential for delivering nutrients and oxygen to cells and removing waste.
• Mechanism: High hydrostatic pressure causes formation while low water potential and lymphatic system facilitate reabsorption.

Conclusion: This lecture explained tissue fluid's role, formation, and reabsorption mechanisms, stressing its importance in bodily function.

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