1. The document discusses various mechanisms of transport across cell membranes including diffusion, osmosis, and carrier-mediated transport. 2. Diffusion is the random movement of molecules across membranes down their concentration gradients. Osmosis describes the net diffusion of water across semipermeable membranes. 3. Carrier-mediated transport involves protein carriers and may be active transport, requiring ATP, or facilitated diffusion, using the molecule's own kinetic energy.

1. CHAPTER 6
Body Fluids and Membrane Transport
In Lecture Today:
- Body Water
- Fluid Compartments
- Cell membrane
- Mechanisms of transport across the cell membrane:
• Diffusion, and rate of diffusion
- Osmosis
- Molarity and Molality
- Osmolality
- Tonicity
- Carrier-mediated transport

2. Body Water
About 60% of the adult human body is composed of water. In this water
there are ions and substances essential for life either dissolved or floating.
The water is inside of the cells as well as outside:
Water inside the cells : Intracellular Fluid (ICF) ICF
Water outside the cells : Extracellular Fluid (ECF) ECF
CELL
- Claude Bernard, 19th century French physiologist:
“milieu interieur ”

3. Total Body Water
In a normal adult male, total body water (TBW) is 60% of body weight.
For example in a 70 Kg man TBW is 0.6 x 70 = 42 Kg or 42 L
In an Adult Male 70 Kg Body Weight:
Tissue % water Liters of water
Skin 72 9.07
Muscle 75 22.1
Skeleton 22 2.45
Blood 83 4.65
Fat 10 0.70
All others - 3.03
Total Body Water(TBW) 42

4. Percentage Body Water
The fraction of body weight that is water varies with both the age and
gender (male & female).
Female usually have more body fat which contains less water than other
body tissues. The % water content of the body also decreases with age.

5. Body Fluid Compartments
The fluids in the body are compartmentalized. Body fluids can be either
inside (ICF) or outside (ECF):
1- Intracellular Fluid (ICF) Compartment:
- About 40% of total body weight is ICF. There are
more than 75 trillions of cell in human body. Each ICF
cell-type has its own unique structure. But
concentration of most substances in the cell are
similar from one cell to another. That is why the fluid
inside all the cells of the body is considered as one
compartment.

6. Body Fluid Compartments
2- Extracellular Fluid (ECF) Compartment: All the fluids outside of the cells are
collectively called ECF, which is about 20% of total body weight.
- ECF is composed of :
1- Interstitial fluid (ISF) = ECF fluid between the cells.
2- Plasma = ECF of blood.
3- Transcellular fluid* =
synovial = in joints
peritoneal = visceral fluid
pericaridal = around the heart
intraocular = in the eyes
cerebrospinal fluid = within the brain
* Trancellular fluid can be considered as separate compartment.

7. Cell Membrane
• Separates intracellular fluid from extracellular fluid.
• Composed primarily of phospholipids and proteins.
• Proteins may serve as carriers, channels and receptors.

8. Mechanisms of Transport
Across Cell Membrane
• According to the means of transport there are two
categories:
1- Non-carrier-mediated transport
- Simple diffusion
2- Carrier-mediated transport
- Facilitated diffusion
- Active transport

9. Diffusion
• Random motion of molecules due to their thermal energy
is called diffusion.
• Molecules in a solution tend to reach a uniform state. For
example a drop of ink in a water container spreads
uniformly.

10. Diffusion

11. Diffusion Through the Cell Membrane
• Two major groups of molecules can pass the phospholipid
bilayer of cell membrane by simple diffusion:
1- Molecules that can dissolve in the lipid bilayer membrane,
non-polar molecules such as:
Lipid Soluble O2, Hormones (Steroids)
2- Small polar molecules which are uncharged
such as:
Small uncharged CO2, alcohol, and urea

12. Diffusion Through Protein Channels
• Small ions can use ion channels in the membrane:
Charged

13. Rate of Diffusion
• Rate of diffusion = number of diffusing molecules passing through the
membrane per unit time.
• Rate of diffusion depends on:
1- Concentration difference across the membrane.
2- Permeability of the membrane to the diffusing molecule.
3- Surface area of the membrane.
4- Molecular weight of the diffusing molecule.
5- Distance.
6- Temperature.
Concentration gradient x Surface area x Temperature
Rate of diffusion α
MW x distance

14. Osmosis
• The net diffusion of water across the
membrane is called osmosis.
• Osmosis can occur only if the membrane
is semipermeable.
• Semipermeable means that the membrane
must be more permeable to water than the
solute dissolved in water.

15. Osmotic Pressure
• What is osmotic pressure?
The force needed to prevent osmotic movement of water from one area to
another across a semipermeable membrane.

16. Molarity and Molality
• Equivalent of one molecular weight (g) of a substance dissolved in water to
make a total one liter solution is called a Molar solution (1 M).
• When equivalent of one molecular weight (g) of a substance is added to
one liter (Kg) of water, this solution is called Molal solution (1 m).
Molal solution is a better indication of solute to solvent ratio, therefore it is a
better indicator of osmosis. However, in the body since the differences between
Molal and Molar concentration of solutes is very small, Molarity is often used.

17. Molarity and Molality

18. Osmolarity
• Total molality of substances in a solution is called osmolality (Osm).
Our body fluids contain a mixture of various substances. Each
substance
has a certain molar concentration. The total sum of these concentration is
measured in Osmolar (Osmoles/Liter)
e.g A solution containing 1 m glucose and 2 m fructose has osmolality
of 3 osmol/L (3 Osm).
• Electrolytes such as NaCl are ionized when in solution, therefore one
molecule of NaCl in solution yields two ions. So 1 m of NaCl has
osmolality of 2 Osm.

19. Tonicity
• Solutions that have the same total concentration of solutes and the
same osmotic pressure as plasma* are said to be isotonic.
• Solutions that have a lower total concentration of solutes and a lower
osmotic pressure than plasma are said to be hypotonic.
• Solutions that have a higher total concentration of solutes and a higher
osmotic pressure than plasma are said to be hypertonic.
* In the body plasma has osmolarity of 0.28 Osm (280 mOsm).

20. Tonicity

21. Regulation of Blood Osmolarity
• Blood osmolarity is maintained within a narrow range and when this
osmolarity changes several regulatory mechanisms come into action.

22. Carrier-Mediated transport
• Unlike the simple diffusion, carrier-mediated transport shows:
1- Specificity
2- Competition
3- Saturation

23. Carrier-Mediated transport
• There are two major types of carrier-mediated transport:
a) Facilitated diffusion:
like simple diffusion facilitated diffusion is powered by thermal
energy of the diffusing molecules. But the transport of molecules
across the membrane is helped by a carrier protein. For example
glucose is transported to the cells of the body by faciliteted difussion.
the net transport is along the concentration gradient.
b) Active transport:
Movement of molecules against their concentration gradient which
requires energy (ATP). For example movement of calcium from
inside to outside of the cell.

24. Facilitated Diffusion

25. Active Transport
a) Primary active transport:
ATP is directly needed for the carrier
protein in the following sequences:
1- Binding of molecule to the carrier protein
2- ATP is hydrolysed to provide energy for transport.
3- Carrier changes its shape and moves the molecule across the membrane.

26. a) Primary active transport:
e.g Transport of Ca++ from inside to outside of the cell. Example 1

27. a) Primary active transport:
e.g Na/K pump.
Example 2

28. Active Transport
b) Secondary active transport (Co-transport):
The energy required is obtained from downhill
transport of Na+ into cell:
Na
ECF ICF Na
Na Na Na Na
Glucose Glucose
K K
CELL

29. b) Secondary active transport (Co-transport):
e.g Transport of glucose in kidney.

30. b) Secondary active transport (Co-transport):
e.g Co-transport of Na+ and glucose.