Anatomy and Physiology Anusha Murali Membrane Transport Anatomy and Physiology Anusha Murali
Membrane Transport Cell membrane is a barrier that controls which substances enter and leave the cell. Oxygen and water enter the cell. Co2 and waste leave the cell. Membrane Transport is the movement of these substances across the plasma membrane.
Membrane Transport Different types of membrane transport, depending: Characteristics of the substance being transported. Direction of transport. Occurs in two ways 1. Passive transport- Diffusion, facilitated diffusion, Osmosis and filtration. 2. Active Transport- Endocytosis, exocytosis.
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Passive Transport Does not require any extra energy. Example: Diffusion Tendency of atoms, molecules and ions in a liquid or air to move from areas of higher concentration to lower concentration, thus becoming more evenly distributed. The difference in the concentration is known as Concentration Gradient.
Sugar and water: Sugar is a solute and water is solvent. Diffusion can occur only 1. cell membrane is permeable to that substance 2. The concentration gradient exist such as substances is at a higher concentration on one side of the membrane or the other.
Cell membrane permeability is selective in nature. Lipid soluble substance such as oxygen, carbon dioxide and steroids freely cross the membrane by simple diffusion. Small solutes that are not lipid soluble such as ions of sodium, potassium and chloride may diffuse through the protein channels.
SIMPLE DIFFUSION In simple diffusion, small non charged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient). Oxygen and carbon dioxide and most lipids enter and leave cells by simple diffusion.
Note that the arrows indicate that the substance is moving from where there is more of that substance to where there is less of it, and that the substances are passing between the phospholipids of the membrane.
Osmosis Osmosis is a type of simple diffusion in which water molecules diffuse through a selectively permeable membrane from areas of high water concentration to areas of lower water concentration.
Note that the more particles dissolved in a solution, the less water there is in it, so osmosis is sometimes described as the diffusion of water from areas of low solute concentration to areas of high solute concentration
In each of the examples shown below, which of the solutions is hypertonic?
Hypertonic and Hypotonic Solutions A hypertonic solution has more solutes and less water than a hypotonic solution. During osmosis, water moves from the hypotonic solution (more water, less solutes) to the hypertonic solution (less water, more solutes).
Any solution that has the same osmotic pressure as the body fluids are said to be ISOTONIC.
Hypertonic Solutions that have higher osmotic pressure than body fluids are HYPERTONIC. If the cells are put into a hypertonic solution there will be a net movement of water by osmosis out of cells into the surrounding solution . Cells Shrink
Hypotonic Cells put into a hypotonic solution which has lower osmotic pressure than the body fluids, tend to gain water by osmosis. Cells Swell.
RBC RBC in distilled water: Hypotonic Situation: water will diffuse into the cell and cell bursts (hemolysis) RBC exposed to 0.9% NaCl solution: Normal Saline. Cells remain unchanged as this is a isotonic solution. Equal volumes of water enter and leave the cell.
RBC
More water enters than leaves and cell swell and bursts. Hypertonic: Hypotonic solution: More water enters than leaves and cell swell and bursts. Hypertonic: More water leaves than enters so cells shrink. http://www.youtube.com/watch?v=7-QJ-UUX0iY
Facilitated Diffusion http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html