HBF 102: Passive Transport Quiz

Course Information

• Faculty: Medicine
• University: Helwan National University
• Academic Year: 2024-2025
• Year: 1
• Semester: 1
• Module: Human Body Function (HBF) 102

Passive Transport

• Lecturer: Ashraf Algendy, Professor
• Department: Medical Physiology
• Topic: Passive Transport

Objectives

• Clarify the importance of biological transport
• Identify biological membranes that enclose body fluid compartments
• Categorize different types of transport
• Describe different types of passive transport
• Outline the various types of passive transport

Importance of Transport

• Supplies tissues with oxygen and nutrients
• Removes waste products and carbon dioxide
• Facilitates communication between tissues
• Crucial for immunity
• Enables essential physiological function of secretory products

Transport in the Body

• Occurs through two types of membranes:
  • Capillary membrane (between plasma and tissue fluid (ISF))
  • Cell membrane (between intracellular fluid (ICF) and ISF)

Diagram of Alveolar and Capillary Structure

• Demonstrates the alveolar and capillary parts of the respiratory system, including:
  • Alveolar epithelial cells
  • Surfactant
  • Alveolar lumen
  • Basement membrane of alveolar epithelium
  • Interstitium
  • Basement membrane of capillary endothelium
  • Endothelial cells
  • Plasma
  • Red cell membrane
  • Intraerythrocyte fluid
  • Hb molecule

Types of Transport Mechanisms (Diagram)

• Passive diffusion (oxygen)
• Diffusion through aqueous channel (sodium)
• Facilitated diffusion with a carrier protein (glucose)
• Active transport against concentration gradient with input of energy (potassium)

Transport Summary

• Passive transport: Does not need energy; moves from high to low concentration (downhill).
  • Includes: Simple diffusion, Facilitated diffusion, Osmosis, Filtration (bulk flow), Solvent drag
• Active transport: Needs energy; moves from low to high concentration (uphill).

Diffusion

• The tendency of a substance to spread out to fill available space
• Materials move from high to low concentration
• Does not require energy

Simple Diffusion

• Driven by random thermal motion (kinetic energy)
• Transports:
  • Lipid-soluble substances through the lipid bilayer
  • Small, uncharged, lipid-insoluble substances through the lipid bilayer
  • Ions through channels

Facilitated Diffusion

• Uses carrier proteins or channels for substance passage.
• Transport of glucose across cell membranes using glucose transporters
• Amino acid transport across cell membranes using amino acid transporters.
• Urea transport across cell membranes using urea transporters

Criteria for Facilitated Diffusion

• Saturation: A transporter has a limited number of binding sites for a solute; reaches a maximum transport rate
• Stereospecificity: Each carrier is specific for certain substances, or even specific isomers
• Competition: A specific site of certain molecules (like D-glucose), on a carrier could be occupied by related compounds (like D-galactose), hindering transport of the original molecule

Factors affecting rate of diffusion (Formula)

• J = PA (CA-CB)
  • J: Net rate of diffusion
  • P: Permeability
  • A: Surface area
  • CA: Concentration in solution A
  • СB: Concentration in solution B

Factors affecting permeability

- Partition coefficient (K) - ratio of oil/water solubility; high K, high permeability
- Diffusion coefficient (D) - Stockes-Einstein equation (dependent on solute size and viscosity)

Filtration

• Passage of water from high to low concentration
• High hydrostatic pressure forces water through capillary membranes/renal tubules
• Facilitates water reabsorption due to osmosis

Starling Forces

• Critical for filtration
  • Capillary hydrostatic pressure
  • Tissue hydrostatic pressure
  • Tissue oncotic pressure
  • Capillary oncotic pressure

Transporter types

• Uniport
• Symport
• Antiport
• Cotransport

Solvent Drag

• Diffusion of solute following the diffusion of its solvent
• Solvent drags solute to be reabsorbed

Additional Question

• Question: Which of the following substances can pass through a cell membrane by simple diffusion?

  • Correct answer: CO2

• Question: Which substance has the highest partition coefficient?

  • Correct answer: CO2

• Question: What force is responsible for filtration?

• Correct Answer: Hydrostatic pressure

Test your knowledge on passive transport mechanisms as discussed in the Human Body Function module. This quiz covers the importance of biological transport, types of membranes involved, and the categories of passive transport. Prepare to explore the physiological significance of these processes in the human body.