unit 5
TRANSCRIPT
Diffusion
Compounds move toward the area of lower concentration
Compounds permeable to the cell membrane will move through diffusion. (Compounds unable to pass through the membrane will only pass if membrane channels open)
Osmosis: Diffusion of Water
The diffusion of water across a selectively permeable membrane is called osmosis.
Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.
Osmosis
Each compound obeys the law of diffusion
However, some compounds are unable to cross the cell membrane (glucose, electrolytes…)
Water can cross will enter or exit the cell depending its concentration gradient
Note: the cell membrane is a semipermeable membrane
What controls osmosis?
Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis.
Before
Osmosis
After
Osmosis
Selectively permeable membrane
Water molecule
Sugar molecule
Cells in an isotonic solution
isotonic solution- (= concentrations)the concentration of
dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.
H2OH2O
Water Molecule
Dissolved Molecule
Cells in an isotonic solution
water molecules move into and out of the cell at the same rate, and cells retain their normal shape.
H2O
H2O
Water Molecule
Dissolved Molecule
Cells in a hypotonic solution
hypotonic solution: dilute solution thus low solute concentration
In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.
H2O
H2O
Water Molecule
Dissolved Molecule
Cells in a hypertonic solution
hypertonic solution:
concentrated solution, thus a high solute concentration
In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink
H2OH2O
Water Molecule
Dissolved Molecule
Passive Transport
When a cell uses no energy to move particles across a membrane passive transport occurs
Particles go DOWN their concentration gradient.
Diffusion & osmosis are passive transport.
Concentration gradientPlasma membrane
Passive Transport by proteins
Passive transport of materials across the membrane using transport proteins is called facilitated diffusion.
Channel proteins
Concentration gradient
Plasma membrane
Passive Transport by proteins
Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.
Active Transport
active transport :Movement of materials through a membrane against a concentration gradient and requires energy from the cell.
Concentration gradient
Plasma membrane
Carrier proteins
Cellular energy
Cellular energy
How active transport occurs
a transport protein called a carrier protein first binds with a particle of the substance to be transported.
Each type of carrier protein has a shape that fits a specific molecule or ion.
Endocytosis is an energy-using process by which cells absorb molecules (such as proteins) by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane. The opposite process is exocytosis.
Cell Membrane Transport
1- Factors affecting transport - cell membrane - Chemical gradient - Electrical gradient - Rate of transport2- Passive transport - Diffusion - Osmosis - Facilitated diffusion3- Active transport - Pumps - phagocytosis - Endocytosis/exocytosis
Factors affecting transport: cell membrane
The cell needs to absorb and excrete various compounds throughout its life.
These compounds need to pass through the membrane which is made from a phospholipid bilayer
The phospholipid bilayer is formed by phospholipid molecules bipolar molecule: the fatty acid side is hydrophobic, the phosphoric side is hydrophilic
The membrane is permeable to:
- H2O- Gases (O2, CO2, N2)- Lipids- Small, neutral
molecules (such as urea)
The membrane is impermeable to:
- Small, charged molecules
- “large molecules” such as amino acids, glucose and larger
these compounds must go through channels present in the membrane in order to enter or exit the cell
Factors affecting transport: Chemical gradient
Compound moves from an area of high concentration to low concentration (or concentration gradient)
All compounds permeable to the phospholipid bilayer will move this way
Factors affecting transport: Electrical force
Positive ions are attracted to negative ions and vice versa
Ions are repelled by ions of the same charge (+ against + and – against -)
Transport of Large Particles
Endocytosis is a process by which a cell surrounds and takes in material from its environment. The material is engulfed and enclosed by a portion of the cell’s
plasma membrane. resulting vacuole with its contents moves to the inside of the cell
Exocytosis is the expulsion or secretion of materials from a cell.
ExocytoseEndocytosis
Dialysis
DefinitionArtificial process that partially replaces
renal functionRemoves waste products from blood by
diffusion (toxin clearance)Removes excess water by ultrafiltration
(maintenance of fluid balance)Wastes and water pass into a special liquid –
dialysis fluid or dialysate
Types
Haemodialysis (HD)Peritoneal Dialysis (PD)They work on similar principles: Movement of
solute or water across a semi permeable membrane (dialysis membrane)
Peritoneal dialysis (PD) is a treatment for patients with severe chronic kidney disease. The process uses the patient's peritoneum in the abdomen as a membrane across which fluids and dissolved substances (electrolytes, urea, glucose, albumin and other small molecules) are exchanged from the blood.
Ultrafiltration
Made possible by osmosisMovement of waterAcross semipermeable membraneFrom low osmolality to high osmolalityOsmolality – number of osmotically active
particles in a unit (litre) of solvent
The process of diffusion
1.
2.
Blood cells are too big to pass through the dialysis membrane, but body wastes begin to diffuse (pass) into the dialysis solution.
3.
Diffusion is complete. Body wastes have diffused through the membrane, and now there are equal amounts of waste in both the blood and the dialysis solution.
The process of ultra filtration in PD 11.
2.
Blood cells are too big to pass through the semi-permeable membrane, but water in the blood is drawn into the dialysis fluid by the glucose.
3.
Ultra filtration is complete. Water has been drawn through the peritoneum by the glucose in the dialysis fluid by the glucose in the dialysis fluid. There is now extra water in the dialysis .
Haemodialysis
Dialysis process occurs outside the body in a machine
The dialysis membrane is an artificial one: Dialyser
The dialyser removes the excess fluid and wastes from the blood and returns the filtered blood to the body
Haemodialysis needs to be performed three times a week
Each session lasts 3-6 hrs
HD Access
2 types of access for HD: Must provide good flow Reliable access
A fistula: arterio-venous (AV)Vascular Access Catheter
Addendum to Principles (PD)Standard dialysis solution contains:
Na+ – 132 mEq/l Cl- – 96 -102 mEq/l Ca2+ – 2.5 – 3.5 mEq/l Mg2+ – 0.5 -1.5 mEq/l
Dialysis solution buffer: Sodium lactate Pure HCo3
-
HCo3- /Lactate combinations
Lactate is absorbed and converted to HCo3- by
the liverDextrose solution strengths: 1.5%, 2.5%,
4.25%