Osmosis and diffusion Flashcards
Extracellular fluid
fluid outside of the cell
Intracellular fluid
fluid inside of the cell
aka cytoplasm
Cytoplasm
Means ‘cell substance’.
Gel-like, fluid-matrix of cytosol containing organelles and molecules.
Eukaryotic animal cell - The plasma membrane
referred to simply as the cell membrane or cytoplasmic membrane.
- boundary of the cell, protecting the organelles; it holds the cell together.
- Regulates movement of material into and out of the cell.
- Important role in cell communication
It is a phospholipid bilayer.
- made up of lipids and proteins.
- Consists of a hydrophilic (water-loving) outer and hydrophobic (water-hating) core.
- Composition of the membrane can change as required.
Aspects of the structure can be removed as well as new/additional material added
Main composition of membrane
Lipids
– Phospholipids, glycolipids, sterols, amphipathic lipids.
• Amphipathic – has both hydrophilic and lipophilic (fat-loving) regions.
Proteins
– Integral (transmembrane) proteins, peripheral proteins, lipidanchored proteins.
Carbohydrates
– Glycoproteins, some glycolipids.
Transport processes - Simple diffusion
Movement of a substance from an area of high concentration to an area of low concentration,
e.g. Carbon dioxide leaving cells
Transport processes - Osmosis
Special form of diffusion which only applies to water. It is the movement of water from a region of high water potential to a region of low water potential across a semi-permeable membrane.
e.g. Movement of water into and out of cells
Transport processes - Channel-mediated passive transport (facilitated diffusion)
Diffusion of particles across a membrane via membrane-bound channel proteins (movement down a concentration gradient)
e.g. Movement of sodium ions into nerve cells
Transport processes - Carrier-mediated passive transport (facilitated diffusion)
Diffusion of particles across a membrane via membrane-bound carrier proteins (movement down a concentration gradient)
e.g. Movement of glucose into cells
Diffusion
The movement of a substance from an area of high concentration to an area of low concentration
- Particles diffuse as they make contact with other particles and are moved in different directions.
- Diffusion occurs down a concentration gradient
Simple diffusion
Where molecules pass through the plasma membrane directly
- Examples of molecules able to pass: O2, H2O, CO2, N2
- They move by dissolving into the fluid of the phospholipid layer and then diffusing across it.
- When molecules cross the membrane they have permeated the membrane.
What is Dialysis?
Artificial filtration/cleaning of the blood to remove waste products, toxins etc.
– Dialysis is a means of keeping someone suffering late - stage chronic kidney disease alive while a suitable kidney donor is located
– One of two methods:
• Pump passing blood via special membrane in place of kidneys to remove waste products
• Allowing waste products to diffuse directly into special dialysis fluid within the body
How does Dialysis work?
– Relies on diffusion.
– Two types haemodialysis and peritoneal dialysis
Haemodialysis
– Blood from radial artery passed through membrane which allows small waste particles such as urea to diffuse out into a special dialysis fluid; large particles (e.g. blood cells) are retained
– The filtered blood is then returned to the patient via a suitable vein in the leg or wrist
Peritoneal dialysis
– Sterilised dialysis fluid is introduced into the peritoneal cavity of the patient through the abdominal wall
– The membrane of the cavity allows waste products from the blood to pass through and into the dialysis fluid.
– After 2-3 hours the dialysis fluid is drained from the patient and replaced with fresh for another cycle.
Osmosis
The movement of water from a region of high water potential to a region of low water potential across a semi-permeable membrane
• Osmosis: special form of diffusion which only applies towater.
- Higher water potential = lower solute concentration.
- Lower water potential = higher solute concentration.
• Water potential has the symbol Ψ (psy).
Osmotic pressure
Movement of water either into or out of a cell will cause changes in the pressure both inside and outside of that cell.
Pressure within a solution which has been caused by osmosis is called osmotic pressure.
• Potential osmotic pressure
– The maximum pressure which could develop in a solution.
• Actual osmotic pressure
– The pressure which exists in the solution at that moment.
Homeostasis
“Maintenance of relatively constant states within the body”
- Homeostasis is essential for correct physiology: osmotic pressure, volume, ion concentrations, blood sugar, pH etc.
- Homeostasis of volume and pressure is particularly essential to healthy cellular function.
- Both tend to be maintained at a constant rate as intracellular fluid is maintained at the same potential osmotic pressure as the extracellular fluid
Isotonic
Where two regions of fluid have the same potential osmotic pressure as each other.
- Iso: meaning ‘same’.
- Tonic: meaning ‘pressure’.
• Isotonic solutions have the same potential osmotic pressure (and water potential) because they each contain the same concentration/s of solute/s.
Hypertonic
Higher pressure. Greater solute content (low water potential).
Hypotonic
Lower pressure. Lower solute content (high water potential).
Disorders of water balance
Extreme, prolonged shifts in water balance within the body and its cells has important consequences for physiology.
- Too much water is as bad for physiology as too little!
- Net effects on cells are similar.
Dehydration and water intoxication
Dehydration
Where you use/lose more fluid than you take in
Stages of dehydration can broadly be defined by the % loss of body weight as follows:
- 5% – Mild
- 10% – Moderate
- 15% – Severe
Changes the osmotic balance of the body.
- Balance of minerals in your body also changes.
- Turgidity of cells decreases as water leaves cells.
- Severe dehydration can result in rupture and death of cells (cell lysis).
Dehydration Symptoms
Dry and irritated skin, loose skin, bags under the eyes, headaches, general weakness, dizziness, confusion, dry mouth, difficulty swallowing, dry and tired feeling eyes
Water intoxication
Where you take in more water than you use, resulting in dilution of salts and other minerals
Results in hyponatremia – situation where sodium content of your blood is below normal.
- Changes the osmotic balance of the body.
- Balance of minerals in your body also changes, you risk dangerously diluting out your electrolytes.
- Turgidity of body cells increases as water enters cells.
- Severe water intoxication can result in death as cells of the body swell, rupture and die (cell lysis).
Water intoxication symptoms
Nausea, headaches, pressure in your head, altered vision (things moving or inability to see properly), feeling cold and confused; eventually leading to coma
Facilitated diffusion
The assisted transport of certain molecules across the plasma membrane using either protein channels or carriers
Channel-mediated passive transport
Cell membrane has specialised proteins called membrane-bound channel proteins.
• Channels allow specific ions or small, water-soluble molecules to cross the membrane.
– Channels allow these molecules to avoid the hydrophobic core of the plasma membrane.
gated channels
Able to open and close to the passing of molecules
Important role in pathology and homeostasis.
Several methods control channel access:
– Chemical signals.
– Mechanical signals.
– Electrical signals.
– Light signals.
aquaporins
- Specialised water-channels
* These allow water to move across quicker than by simple diffusion
Carrier-mediated passive transport
Cell membrane has specialised proteins called membrane-bound carrier proteins.
they actively change shape
- carrier proteins will typically only permit specific molecules to bind.
- They allow hydrophilic molecules to avoid the hydrophobic core of the plasma membrane.
Carrier proteins transport permitted molecules by
- Molecule within vicinity of the carrier protein is deemed permissible.
- Carrier protein undergoes conformational change to fit the shape of the molecule to be transported, allowing it to enter the carrier.
- Further change allows the molecule to be ejected from the carrier and either into or out of the cell.
