Flow and Pressure

The bronchial circulation is a branch of the circulation. It supplies oxygenated blood to the tissues of the . It doesn't drain via a venous system, instead it drains into the . This causes mixing of deoxygenated and oxygenated blood.

Laminar flow is the flow of a fluid when each particle follows a path which does not with others. This results in a velocity of fluid throughout. drag at the sides of a vessel will slow blood. This becomes more apparent as the radius of the vessel . The cells in the blood therefore align in the moving portion of the fluid. This is known as . This viscosity because only the plasma is left at the walls of the vessel.

Turbulent flow is the flow of a fluid when velocity components randomly in a chaotic fashion. This means that blood will flow in several with the of layers. This occurs in large arteries at points and partially arteries (e.g. partially opened valves). This resistance and causes vibrations. In the heart, high velocity blood flow vibrations can be detected as . In the airways, high velocity air flow vibrations can be detected as . Turbulent flow the energy required to drive blood flow and increases loss of energy through generating heat.

This graph shows how flow changes with pressure in different types of tubes.
An example of a distensible vessel is the . When cardiac output increases, the to keep flow constant by reducing . However, it can only stretch so much, so flow does eventually .
In a rigid tube, blood flow and pressure are to one another. The lower the resistance, the the gradient.
A myogenic vessel is one with the ability to . These vessels in response to increased pressure in order to maintain constant flow. Flow increases to a point with increasing pressure until prevents flow from increasing further.

This diagram shows the blood flow through different tissues in systemic circulation. The vascular beds in each tissue are to one another. Therefore, when resistance in the arteries of tissue 1 as shown by the red squiggle, flow in the capillaries of tissue one . However, flow in tissues 2 and 3 remains .

This diagram shows changes in segment pressure and resistance in systemic circulation and pulmonary circulation. The red line shows changes in segment pressure in systemic circulation.
As the heart beats, pressure in the left ventricle .
Blood flows into the large arteries and is still oscillatory between and diastolic pressure. This pressure is the blood pressure.
Blood flows into the smaller arteries with a large in pressure. This is therefore the main site for control of . A small change in the of these vessels will have a profound effect on resistance.
Blood flows into the capillaries with an additional pressure . Although we have a smaller in the capillaries, they are more highly than the arterioles. Therefore, we have more tubes in so total resistance is and pressure does not decrease as much.
Blood flows into the veins and pressure decreases once more. When blood returns to the heart via the great veins the pressure is extremely .

This diagram shows changes in segment pressure and resistance across systemic circulation and pulmonary circulation. The green line shows changes in segment pressure in the pulmonary circulation.
As the heart beats, pressure in the right ventricle . The maximum pressure is than in the left ventricle because the blood only has to reach the lungs.
Blood pressure decreases across the arteries and arterioles.
Blood pressure doesn't decrease as harshly across the capillaries because whilst they have a smaller they are more highly than the arterioles. This means we have more tubes in series and thus total resistance is Pressure decreases further in the veins.

This diagram shows changes in segment pressure and segment resistance across systemic circulation and pulmonary circulation. The blue line shows the changes in resistance occurring across both circulations.
In the systemic large arteries, resistance is because there are few of them and they have wide .
There is a dramatic increase in the systemic arteries due to their diameters.
However, as branching increases across the capillaries, resistance as there are more highly branches tubes in .
As blood drains into the venules, resistance due to fewer tubes occurring in .
Resistance decreases again in the great veins due to their wide .