![Physiological importance of diffusion
• When two substances, come in contact, directly or
through a permeable membrane, diffusion will take
place, when the molecular concentration of a
substance in solution is higher in one part of a liquid
than in another & when any absolute barrier does
not intervene.
• E.g 1] Admixture of foodstuffs with digestive juices.
• 2] Absorption from the intestine
• 3] Exchange between plasma & red cells](https://image.slidesharecdn.com/diffusion-230529141711-ac146762/85/diffusion-pptx-9-320.jpg)
![• 4]Exchange in the capillary bed e.g food stuffs,
O2 etc. pass out from blood stream (higher
conc.) to the tissue fluid (lower conc)& then to
the tissue cells (lowest conc.) where they are
used up. The metabolites including Co2, on the
otherhand, come out of cells( higher conc) where
they are produced, to the tissue fluid (lower
conc) & then to the blood stream (lowest conc)
• 5] Exchange in the lung capillaries e.g O2 from air
(higher conc) enters the venous blood (lower
conc) while Co2 from venous blood (higher conc)
diffuses out into air (lower conc).
• 6] Admixture of gases in the lungs.](https://image.slidesharecdn.com/diffusion-230529141711-ac146762/85/diffusion-pptx-10-320.jpg)
diffusion.pptx
- 1. DIFFUSION
- 2. Passive Transport Mechanism Diffusion • Passive Transport Mechanism • The passive transport mechanisms are diffusion and osmosis. • Diffusion: It is a passive process by which molecules moves from area of higher concentration gradient to that of lower concentration gradient and does not require energy for the process.or spontaneous admixture of the molecules of the two substances in contact is called diffusion. • The molecules are in constant motion. Motion is least in solids, maximum in gases & intermediate in liquids. • When a solid & liquid/two miscible liquids/ a liquid & gas/ two gases, are in contact,molecules of two substances will pass into each other until an uniform admixture is obtained.
- 3. • The diffusion is of two types: Simple diffusion and facilitated diffusion. • . • Simple diffusion : The movements of molecules from area of higher concentration to that of lower concentration due to kinetic motion of the ions or molecules through the intermolecular spaces or membrane openings without the aid of any carrier protein is known as simple diffusion. It does not require any energy (ATP) for transport
- 4. Examples: The lipidsoluble compounds (alcohol, oxygen, nitrogen) diffuse through the lipid bilayer; while water-soluble substances pass through the aqueous channel ( urea, glucose and ions). Diffusion also occurs through leak channel and gated channels. The leak channels are open always, e.g. K+ channels. Gated channels are voltage gated, ligand- gated, mechanical-gated and temperature gated as explained earlier.
- 5. • The main factors affecting diffusion are the concentration gradients of the substances, number of channels and opening in the membrane and kinetic motion of the molecule. • The factors that affect the diffusion rate across the cell membrane are enlisted below: • 1. Thickness: Greater the thickness of cell membrane • slower will be the diffusion. • 2. Temperature: The higher the body temperature • faster is the diffusion. • 3. Size of the molecule: Smaller the molecular size • of substance rapid is the diffusion. • 4. Concentration gradient difference: Larger the • concentration gradient faster is the diffusion. • 5. Cross-sectional area of membrane: Diffusion is • directly proportional to the available cross sectional area
- 6. • 6. Diffusion coefficient (D) of the substance: D: • Permeability X area of cross section available for transport. • Facilitated diffusion : Carrier protein mediated • transport of substance across cell membrane • is known as facilitated diffusion. • Characteristic Features • 1. The substance to be transported binds to the carrier • protein. The binding causes confirmational change • in carrier protein molecule and this aid in the • transport and release of the substance to the other • side of the membrane . • 2. The energy for transport is provided by the concentration gradient of the substance transported.
- 7. • No energy source (ATP) is required. This carrier mediated transport of ions and organic substrates into or out of the cell down their concentration gradient passively is also called passive carrier mediated transport. • 3. The facilitated diffusion occurs faster than simple diffusion. • 4. When concentration of the transported substance becomes high enough the facilitated transporter gets saturated and this limits the rate of transport
- 8. • 5. If more than one substance competes to bind with • common transporter, it leads to competitive inhibition. • Examples of Facilitated Diffusion • 1. Insulin-mediated transport of glucose in muscle cells. When more insulin is present, more of these glucose transporters (GLUT) ( Glucose transporter (GLUT) is a facilitative transport protein involved in glucose translocation across the cell membrane). are added to the membrane of cells of such muscle and glucose moves into the muscle cells. • 2. Transport of glucose along intestinal epithelium by • glucose transporter.
- 9. Physiological importance of diffusion • When two substances, come in contact, directly or through a permeable membrane, diffusion will take place, when the molecular concentration of a substance in solution is higher in one part of a liquid than in another & when any absolute barrier does not intervene. • E.g 1] Admixture of foodstuffs with digestive juices. • 2] Absorption from the intestine • 3] Exchange between plasma & red cells
- 10. • 4]Exchange in the capillary bed e.g food stuffs, O2 etc. pass out from blood stream (higher conc.) to the tissue fluid (lower conc)& then to the tissue cells (lowest conc.) where they are used up. The metabolites including Co2, on the otherhand, come out of cells( higher conc) where they are produced, to the tissue fluid (lower conc) & then to the blood stream (lowest conc) • 5] Exchange in the lung capillaries e.g O2 from air (higher conc) enters the venous blood (lower conc) while Co2 from venous blood (higher conc) diffuses out into air (lower conc). • 6] Admixture of gases in the lungs.