Flow and Pressure

Flow must remain the same in both pulmonary circulation and systemic circulation because they are in series.

Which division of circulation exists at high resistance and high pressure with several vascular beds in parallel to one another?

Which division of circulation exists at low resistance and low pressure?

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

What is the definition of stroke volume?

What is the definition of cardiac output?

How do we calculate cardiac output?

What is the correct healthy range for stroke volume?

What is the correct healthy range for cardiac output?

What is the correct definition of venous return?

Venous return must be equal to cardiac output

What is the definition of central venous pressure?

What is the definition of preload?

The unit of preload is mmHg

What is the correct definition of total peripheral resistance?

Ventricular filling is not related to preload

What is the correct definition of afterload?

Afterload is proportional to average arterial blood pressure

The equation below represents rate of diffusion according to Fick's law. Label it.

What does Darcy's law of flow tell us?

What is the correct equation for flow?

If pressure or flow changes, resistance will change.

What does Poiseuille's law tell us?

The equation below shows us how resistance changes according to Poiseuille's law.

Blood is a non-Newtonian fluid. What does this mean?

Laminar flow is the flow of a fluid when each particle follows a [blank_start]smooth[blank_end] path which does not [blank_start]interfere[blank_end] with others. This results in a [blank_start]constant[blank_end] velocity of fluid throughout. [blank_start]Viscous[blank_end] drag at the sides of a vessel will slow blood. This becomes more apparent as the radius of the vessel [blank_start]decreases[blank_end]. The cells in the blood therefore align in the [blank_start]fastest[blank_end] moving portion of the fluid. This is known as [blank_start]axial streaming[blank_end]. This [blank_start]reduces[blank_end] 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 [blank_start]fluctuate[blank_end] in a chaotic fashion. This means that blood will flow in several [blank_start]directions[blank_end] with the [blank_start]mixing[blank_end] of layers. This occurs in large arteries at [blank_start]branch[blank_end] points and partially [blank_start]obstructed[blank_end] arteries (e.g. partially opened valves). This [blank_start]increases[blank_end] resistance and causes vibrations. In the heart, high velocity blood flow vibrations can be detected as [blank_start]murmurs[blank_end]. In the airways, high velocity air flow vibrations can be detected as [blank_start]wheezes[blank_end]. Turbulent flow [blank_start]increases[blank_end] the energy required to drive blood flow and increases loss of energy through [blank_start]friction[blank_end] generating heat.

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

What is the correct equation for total resistance of tubes in series?

What is the correct equation for total resistance of tubes in parallel with one another?

Total resistance increases with more resistances in systems in both series and parallel

What is another way of expressing the inverse of resistance, given as gtotal, g1, g2 etc?

We can regulate blood flow through an organ or tissue independent of MABP

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

What is the correct equation for mean arterial blood pressure?

If mean arterial blood pressure is equal to cardiac output multiplied by total peripheral resistance, what does this tell us?

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 [blank_start]oscillates[blank_end]. Blood flows into the large arteries and is still oscillatory between [blank_start]systolic[blank_end] and diastolic pressure. This pressure is the [blank_start]mean arterial[blank_end] blood pressure. Blood flows into the smaller arteries with a large [blank_start]decrease[blank_end] in pressure. This is therefore the main site for control of [blank_start]total peripheral resistance[blank_end]. A small change in the [blank_start]radii[blank_end] of these vessels will have a profound effect on resistance. Blood flows into the capillaries with an additional pressure [blank_start]decrease[blank_end]. Although we have a smaller [blank_start]diameter[blank_end] in the capillaries, they are more highly [blank_start]branched[blank_end] than the arterioles. Therefore, we have more tubes in [blank_start]parallel[blank_end] so total resistance is [blank_start]lower[blank_end] 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 [blank_start]low[blank_end].

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 [blank_start]oscillates[blank_end]. The maximum pressure is [blank_start]lower[blank_end] 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 [blank_start]diameter[blank_end] they are more highly [blank_start]branched[blank_end] than the arterioles. This means we have more tubes in series and thus total resistance is [blank_start]lower.[blank_end] 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 [blank_start]low[blank_end] because there are few of them and they have wide [blank_start]diameters[blank_end]. There is a dramatic increase in the systemic arteries due to their [blank_start]smaller[blank_end] diameters. However, as branching increases across the capillaries, resistance [blank_start]decreases[blank_end] as there are more highly branches tubes in [blank_start]parallel[blank_end]. As blood drains into the venules, resistance [blank_start]increases[blank_end] due to fewer tubes occurring in [blank_start]parallel[blank_end]. Resistance decreases again in the great veins due to their wide [blank_start]diameter[blank_end].