Pressure, flow and equilibrium

Question 1

What are the general properties of simple diffusion

Answer 1

1) uses kinetic energy - does not require ATP
2) diffuses from an area of higher conc. to lower conc.
3) diffusion continues until equilibrium is reached
4) diffusion is faster with higher conc. gradients, over shorter distances, at higher temps, for smaller molecules
5) diffusion can take place in an open system, or through a permeable partition.

Question 2

what affects the permeability of a molecule across a membrane?

Answer 2

• the molecule’s lipid solubility
• the molecule’s size
• the lipid composition of the membrane

Question 3

what affects the permeability of a molecule across a membrane?

Answer 3

• the molecule’s lipid solubility
• the molecule’s size
• the lipid composition of the membrane

Question 4

what is a pressure gradient in the body?

Answer 4

> blood vessels

• blood flows from highly pressurised in the aorta, down its pressure gradient from an area of high pressure to an area of low pressure in the veins = almost zero in the venae cavae
• This pressure drops over distance as energy is lost because of friction
• the amount of flow in and out is the same
• rapid drop in pressure in the capillaries

Question 5

how do valves work in the body?

Answer 5

• they allow for the build up of pressure in the heart to create that strong pressure that has to overcome the valve pressure to then be great enough to push around the body
• valves create the pressure differences

Question 6

how/ why does fluid flow through the body (pressure)?

Answer 6

• fluid flows only if there is a pressure gradient
• no pressure gradient = no flow
• flow rate depends on change in pressure, not absolute pressure value.

Question 7

describe poiseuille’s law in terms of flow rate

Answer 7

• poiseuille’s law is a way of calculating resistance in a vessicle.
• flow is the change is pressure over the resistance so resistance can have a major impact on flow rate.

> R = viscosity of fluid x length of tube divided by
N number of vessels in parallel, pi radius of vessel^4

therefore radius has a significant effect of resistance, as its to the power of 4. The greater the radius, the lower the resistance. Major influence as viscosity and length don’t change much.

> this is controlled via vasodilation and constriction, the radius hanging is what is allowing the change in flow to different areas of the body when needed

Question 8

what are the main factors in driving O2 into the body?

Answer 8

> small changes in alveolar pressure allow for large volumes of air to move into the lungs
the diaphragm contracting and increases the volume in the lungs, which causes a drop in pressure from inside to outside, causing air to rush in
Also the air pressure gradient for O2 means that there is also a partial pressure gradient driving O2 into the lungs as there is a lesser PP of O2 in lungs compared to air.

Question 9

Describe gas solubility in the body

Answer 9

> Haemoglobin in the RBC is what picks up O2 at the alveoli
at altitude, because there is less pO2 in the air, the carrying capacity of Haemoglobin goes down because there is a loss of he pressure gradient.