Blood Vessels and Tissue fluid
Circulatory System and Blood Vessels
Mass Flow/Mass transport
the bulk movement of substances down a pressure gradient.
A circulatory system is an example of mass transport as large amounts of substances are moved
from a high pressure to a low pressure.
Diffusion of for example oxygen from the gas exchange surface of the alveoli to all the respiring
tissues would be too slow to meet metabolic requirements (i.e. the rate of respiration required to
release enough energy) as the diffusion pathways are too slow and diffusion only moves small
numbers of molecules.
Role of the heart
to create the pressure gradient for the flow to occur. Ventricular contraction creates a high
pressure and blood returns into the relaxed atria that have a low pressure.
Structure and Adaptations of Blood Vessels
Arteries
Arteries transport blood away from the heart
Ventricular contraction creates a high pressure, so the arteries have thick walls to withstand the
pressure
The wall has a greater proportion of elastic tissue compared to muscle tissue
When ventricular contraction (systole) occurs, the blood enters the arteries under high pressure
So the elastic tissue stretches leading to smoothing out of the surge in blood pressure
When the ventricles relax the blood pressure falls and the elastic tissue recoils
This maintains the blood pressure and flow of the blood
The endothelial tissue lining the blood vessel gives a smooth surface reducing friction and giving
less resistance to flow
It also prevents blood from being trapped and therefore prevents blood clotting
Circulatory System and Blood Vessels
Mass Flow/Mass transport
the bulk movement of substances down a pressure gradient.
A circulatory system is an example of mass transport as large amounts of substances are moved
from a high pressure to a low pressure.
Diffusion of for example oxygen from the gas exchange surface of the alveoli to all the respiring
tissues would be too slow to meet metabolic requirements (i.e. the rate of respiration required to
release enough energy) as the diffusion pathways are too slow and diffusion only moves small
numbers of molecules.
Role of the heart
to create the pressure gradient for the flow to occur. Ventricular contraction creates a high
pressure and blood returns into the relaxed atria that have a low pressure.
Structure and Adaptations of Blood Vessels
Arteries
Arteries transport blood away from the heart
Ventricular contraction creates a high pressure, so the arteries have thick walls to withstand the
pressure
The wall has a greater proportion of elastic tissue compared to muscle tissue
When ventricular contraction (systole) occurs, the blood enters the arteries under high pressure
So the elastic tissue stretches leading to smoothing out of the surge in blood pressure
When the ventricles relax the blood pressure falls and the elastic tissue recoils
This maintains the blood pressure and flow of the blood
The endothelial tissue lining the blood vessel gives a smooth surface reducing friction and giving
less resistance to flow
It also prevents blood from being trapped and therefore prevents blood clotting
