Continuous and intermittent flow Flashcards
What do elastic arteries do?
Convert the intermittent pumping of the heart into continuous blood flow
What are the elastic arteries?
The aorta, and main arteries supplying the heart and the legs
What is the composition of the elastic arteries?
Endothelium
Elastin
Smooth muscle
Collagen
What is the function of the elastic arteries?
Distribution of blood
dampening of pressure changes
conversion of intermittent pumping of the heart to continuous blood flow
What happens to energy during the cardiac cycle of the elastic arteries?
Mid systole - Energy used to stretch elastin
End systole - elastic energy stored in elastin
Mid diastole - elastin recoils and energy transferred to blood
End diastole - elastin returns to original shape
What happens to the pressure in the elastic arteries during the cardiac cycle?
Aortic pressure (systole) = 120mmHg (diastole) = 80mmHg
Left ventricular pressure (systole) = 120mmHg
(diastole) = 5mmHg
what determines the arterial blood pressure?
Elastic arteries which is also the driving force for flow
How do you calculate the mean arterial blood pressure (MAP)
MAP = DP + (SP-DP)
SP - systolic pressure
DP - diastolic pressure
pressure that determines the flow
what is the systolic pressure determined by?
Stroke volume
Aortic/arterial distensibility
ejection velocity
DP of previous beat
What leads to an increase in SP?
EDV increase leading to SV increase (more venous return)
Increased contractility leading to increased SV (exercise, circulating catecholamines)
What determines MAP?
Arteriolar resistance
aortic/arterial distensibility
Heart Rate
What is the effect of ageing on the elastin in elastic fibres?
Cannot stretch the aorta as much and therefore there is an increase in systolic pressure but also since the aorta is not stretched, the pressure falls further during diastole.
Increased pulse pressure
What is the effect of exercise on systolic pressure and total peripheral resistance?
Increased SV
Decreased TPR
Increased systolic pressure and decreased diastolic pressure (therefore increased pulse pressure)
How does breathing maintain constant gases in the alveolar space?
Breathing is an intermittent pump but results in constant gases in the alveolar space since a relatively small volume is added to a larger constant volume.
As long as the CO2 out is matched to the CO2 in, then there will be a constant blood gas
What is the function of the capillaries?
the circulations exchange vessels which are involved in diffusion and filtration
What are the composition of capillaries?
Endothelium (mostly)
Elastin
Smooth muscle
Collagen
how do we set up conditions for good diffusion in the capillaries?
Flow = velocity x cross sectional area
Blood velocity in capillaries is very slow - good conditions for exchange by diffusion and filtration.
This is due to having a large number of capillaries in parallel and therefore an increased cross sectional area which leads to a decreased flow velocity.
how is filtration brought about?
Forces favouring filtration,
Forces favouring reabsorption
Hydrostatic pressure and oncotic pressure
How do you calculate net filtration?
Kf x [(Pc + πi) – (Pi + πp)]
Net filtration = Kf x (forces favour filtration) – (forces favouring reabsorption)
Kf reflection coefficient (leakiness of capillary)0]0
What are the forces favouring filtration in capillaries?
Capillary hydrostatic pressure
interstitial oncotic pressure
What are the forces favouring reabsorption in the capillaries?
Interstitial hydrostatic pressure
Plasma oncotic pressure
What are starlings forces on peripheral capillaries?
Blood enters capillary with a hydrostatic pressure of 35mmHg
Blood leaves capillary with a hydrostatic pressure of 15mmHg
Plasma oncotic pressure of 25mmHg stays constant.
What happens at the arterial end of the capillaries in terms of filtration?
at the arteriolar end of the capillary: Net filtration 𝜶 Pc - p
35 – 25 mmHg = 10mmHg favouring filtration of fluid out of capillary
What happens at the venous end of the capillaries in terms of filtration?
at the venous end of the capillary: Net filtration 𝜶 Pc - p
15 – 25 mmHg = – 10mmHg favouring reabsorption of fluid into capillary
What is the effect of pre-capillary vasoconstriction on net filtration?
downstream capillary hydrostatic pressure decreases as blood moves through the capillaries. Overall net reabsorption of fluid due to filtration < reabsorption at a the venular end of the capillary.
What is the effect of pre-capillary vasodilation on net filtration?
Overall net filtration of fluid due to increased filtration and decreased reabsorption as there is an increase in Pressure within the capillaries.
What happens to the excess net fluid taken up
Taken up by the lymphatic vessels which then take the fluid back to the heart via the subclavian veins in the chest.
