2. 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)
3. 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.
4. 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
5. 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
6. 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.
H2O
H2O
Water Molecule
Dissolved Molecule
7. 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
8. 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
9. 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
H2O
H2O
Water
Molecule
Dissolved
Molecule
10. 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
11. Passive Transport by proteins
Passive transport of materials across the membrane
using transport proteins is called facilitated diffusion.
Channel
proteins
Concentrati
on gradient
Plasma
membra
ne
12. Passive Transport by proteins
Some transport proteins, called channel proteins,
form channels that allow specific molecules to flow
through.
13. 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
15. 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.
16. Cell Membrane Transport
1- Factors affecting transport
- cell membrane
- Chemical gradient
- Electrical gradient
- Rate of transport
2- Passive transport
- Diffusion
- Osmosis
- Facilitated diffusion
3- Active transport
- Pumps
- phagocytosis
- Endocytosis/exocytosis
17. 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
18. 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
19. 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
20. 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 -)
21. 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.
Exocytose
Endocytosis
22. Dialysis
Definition
Artificial process that partially replaces renal
function
Removes 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
23. 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.
24. Ultrafiltration
Made possible by osmosis
Movement of water
Across semipermeable membrane
From low osmolality to high osmolality
Osmolality – number of osmotically active particles
in a unit (litre) of solvent
25. 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.
26. 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 .
27. 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
28. HD Access
2 types of access for HD:
Must provide good flow
Reliable access
A fistula: arterio-venous (AV)
Vascular Access Catheter
