lecture 6

Question 1

body fluid compartments

Answer 1

The body fluids are in two compartments: the extracellular fluid (ECF)
and intracellular fluid (ICF). The ECF and ICF are in osmotic equilibrium
but have very different chemical composition.
Intracellular fluid is 2/3 of the
total body water volume. Material
moving into and out of the ICF
must cross the cell membrane.
KEY
Intracellular fluid
Interstitial fluid
Plasma
Extracellular fluid includes all
fluid outside the cells. The ECF is
1/3 of the body fluid volume.
The ECF consists of:
• Interstitial fluid (IF), which lies
between the circulatory system and
the cells, is 75% of the ECF volume.
• Plasma, the liquid matrix of blood, is 25%
of the ECF volume. Substances moving
between the plasma and interstitial fluid
must cross the leaky exchange epithelium
of the capillary wall.

Question 2

homeostasis vs. equilibrium

Answer 2

Homeostasis does not mean equilibrium
Homeostasis – the ability of the body to maintain a relatively constant internal environment.
Equilibrium – a state of balance due to the equal action of opposing forces.

Question 3

water and the body

Answer 3

Water is the most important molecule in the human body because it is the solvent for all living matter.
Water is the only molecule that can move freely between cells and the ECF.
Because of this free movement of water, the extracellular and intracellular fluid compartments reach a state of osmotic equilibrium, in which the fluid concentrations are equal on the two sides of the cell membrane.

Question 4

homeostasis and equilibrium

Answer 4

Even with osmotic equilibrium between the ECF and ICF, the concentration of solutes in the fluid can be more concentrated in one of the two body compartments. This means the body is in a state of chemical disequilibrium.

Question 5

know the chart on slide six

Answer 5

lawl

Question 6

homeostasis and equilibrium

Answer 6

Many body solutes mentioned so far are ions which carry electrical charges.
The body as a whole is electrically neutral, but a few extra negative ions are found in the ICF, while their matching positive ions are located in the ECF. As a result, the inside of cells is slightly negative relative to the extracellular fluid.
This ionic balance results in a state of electrical disequilibrium. Changes in this disequilibrium create electrical signals.

Question 7

osmosis

Answer 7

The movement of water across a selectively permeable membrane in response to its solute concentration gradient is called osmosis.
Water diffuses through plasma membranes through the lipid bilayer and through specific water channels called aquaporins.
In osmosis, water moves to dilute the more concentrated solution. Once concentrations are equal, net movement of water stops.

Question 8

osmolarity

Answer 8

Osmolarity - Measure of total concentration of solute particles
When solutions of different osmolarity are separated by membrane permeable to all molecules, both solutes and water cross membrane until equilibrium reached.
When solutions of different osmolarity are separated by membrane impermeable to solutes, osmosis occurs until equilibrium reached.

This applies to the cell membrane which is selectively permeable.

Question 9

osmotic pressure

Answer 9

Osmosis can be quantitatively measured using osmotic pressure.
The pressure that must be applied to exactly oppose the osmotic movement of water into another compartment is known as the osmotic pressure.
Osmotic pressure is measured in atmospheres (atm) or millimeters of mercury (mm Hg).
A pressure of 1 mm Hg is equivalent to the pressure exerted on a 1-cm2 area by a 1-mm-high column of mercury.