INTEGRATED SCIENCE IIYEAR I SEMESTER II

Unit v

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

Cell Membrane Transport

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

AV Fistula

AV Fistula

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%

PD Access

Done under LA or GA

LAB MONITORING

HaemoglobinAlbuminCalciumPhosphorusGFR(24 hour urine)

SodiumPotassium UreaCreatinine