The circulation of blood Flashcards
What are the core components of the cardiovascular system?
- Heart
- Blood Vessels
- Brain
- Kidneys
- Adrenal Glands
What is the function of the cardiovascular system?
- to maintain an adaptable supply of blood to tissues in order to supply nutrients and signalling molecules and to remove waste products
- to establish pressure differentials across tissues for capillary exchange
What is the physics of blood flow called?
Haemodynamics
What is the flow of blood from point A to point B determined by?
- Resistance, R
- Pressure difference, P
What is the equation to work out flow?
Flow = difference in pressure/ difference in resistance
What is resistance determined by?
- Length of vessel (easier to flow through smaller vessel)
- Radius of vessel
- Fluid viscosity
What is the flow of blood proportional to?
The radius of the vessel to the power of 4 (r^4)
What is the rate of blood flow through the vessels proportional to?
The diameter of the vessel
What do small changes in arteriole diameter do?
Drastically alter tissue blood flow
What has the greatest impact on how we control the flow of blood through the body?
The diameter of the blood vessel
How is a pressure gradient generated?
Through contraction of the heart muscle
What is systole?
Contraction of the chambers of the heart
What is diastole?
Relaxation of the chambers of the heart
What units is cardiac pressure in?
mm of mercury (mmHg)
Are cardiac pressures higher during systole or diastole?
Systole
Why is systole in the left ventricle greater?
Because it needs to pump blood around the body
How do the elastic vessels ensure that a pressure wave is continued as blood enters the circulation?
Bulges at high pressure because of the presence of blood and then undergoes a recoil in order to move the blood through the circulation and keep it at high pressure
When do the large and medium elastic arteries need to act as ‘pressure reservoirs’? (maintain the pressure gradient)?
During the diastolic phase
List the vessels in order of pressure gradient from highest to lowest
- left ventricle
- aorta
- large arteries
- small arteries
- arterioles
- capillaries
- veins (very low)
What is a high blood pressure?
Over 140 systolic pressure and over 90 diastolic pressure
What is pre-high blood pressure?
120-140 systolic pressure and 80-90 diastolic pressure
What is ideal blood pressure?
90 – 120 systolic pressure and 60 – 80 diastolic pressure
What is low blood pressure?
70-90 systolic pressure and 40-60 diastolic pressure
What is low blood pressure called?
hypotension
What is high blood pressure called?
Hypertension
What happens to people’s blood pressure as they age?
Their blood pressure increases as their blood vessels become less elastic (doesn’t mean they are hypertensive)
In a graph showing blood pressure where with you see the systolic pressure and the diastolic pressure?
the systolic pressure will be the higher value, the diastolic pressure will be the lower value
When will the pressure gradient be interrupted in a blood pressure graph and what is this called?
When the valves open and close. This is called the dicrotic notch
What is the pulse pressure?
the difference in values between the systolic and diastolic pressure
What is the mean arterial pressure?
MAP is the average arterial pressure throughout one cardiac cycle. MAP value is considered to be a more accurate reflection of tissue perfusion in an individual that systolic pressure or diastolic pressure alone
How do you work out the mean arterial pressure?
Diastolic pressure + 1/3 pulse pressure
What does the cardiac cycle determine?
the force placed upon blood as it is ejected from the heart
What are the three considerations in the cardiac cycle?
- Electrical events (drive mechanical events)
- Mechanical Events
- Electro-mechanical contraction coupling
What is the timing of mechanical relaxation and contraction crucial for?
in order to maintain the right amount of blood in each chamber
What is the electrical process of the cardiac cycle?
- SA node initiates electrical response
- Distribution of electrical signal to conduction system of the heart
- Electrical signal triggers cardiac contraction
- Followed by cardiac relaxation
- Followed by another cardiac cycle
- Contractions and relaxations of blood need to be perfectly timed for the ventricle of the blood to eject the maximum amount of blood possible into the circulatory system and then relax back
What is the series of electrical events in the cardiac cycle?
- Initiated by pacemaker – the sinoatrial node
- Signal dissipated to atria which contracts - signal travels at 1 m/s to the atrioventricular node
- Signal received by atrioventricular node - delays the cycle by 0.1s to allow atrial contraction so that all the blood enters the ventricles (signal travels at 0.05 m/s)
- Passes signal to bundles of His and into the Purkije fibre - rapid signal to enable the ventricular cells to contract in unison – 5 m/s
- Out to the ventricular myocardium - about 1 m/s)
- Ventricles contract
In addition to stimulation contraction what else does the conduction pathway do?
Control the speed of conduction through different parts of the heart
What is the duration of the cardiac cycle?
800 ms
How long are the period of systole and diastole?
Ventricular systole: 270 ms
Ventricular systole: 530 ms
Atrial systole: 100 ms
Atrial Diastole: 700 ms
What is the order of mechanical events?
- Atrial Systole begins: atrial contraction forces a small amount of additional blood into relaxed ventricles
- Atrial systole ends’ atrial diastole begins
- Ventricular systole – first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves
- Ventricular systole – second phase: As ventricular pressure rises and exceeds pressure in the arteries the semilunar valves open and blood is ejected. This is associated with isometric ventricular contraction (significant increase in pressure in chambers without change in volume) associated with significant contraction of the ventricular chambers.
- Ventricular diastole – Early: As ventricles relax, pressure in ventricles drop’ blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria
- Ventricular diastole – late: all chambers are relaxed. Ventricles fill passively
What does the ECG detect?
Electrical responses across the heart
What is the ECG profile an amalgamation of?
Many action potentials across the heart
How is an ECG carried out?
Surface electrodes are placed at strategic points across the chest
What are the discrete stages of the cardiac cycle and ECG shows?
Atrial contraction/ relaxation
Ventricular contraction/ relaxation
Conduction velocities of the electrical signals
What is the P-wave in an ECG?
atrial depolarization and contraction
What is the QRS complex in an ECG?
spread of the electrical signal causing ventricular myocyte depolarization and contraction (the atrial relaxation event happens here but is masked by the larger ventricle event)
What is the T wave in an ECG?
ventricle repolarization and relaxation (it is an upward deflection too)
What is the QT interval in an ECG?
; time from the initiation of ventricular contraction to the end of ventricular relaxation
What is a single cardiac cycle?
he period between the start of one heartbeat and the beginning of the next
What is always a fluid’s net movement and how does this relate to blood?
From an area of high pressure to an area of low pressure. Blood only flows from one chamber to another if the pressure in the first exceeds the second
At the start of atrial contraction how much are the ventricles already filled and why?
They are filled to 70% of their volume due to the passive blood flow at the end of the previous cardiac cycle
Why during atrial ejection can blood from the veins not enter the atria and why is there no backflow of blood into the veins?
Because atrial pressure exceeds venous pressure and there is no backflow of blood into the veins despite the lack of valves because the blood takes the path of least resistance?
What is the end-diastolic volume?
At the end of the atrial systole when each ventricle contains the maximum amount of blood it will hold in that cardiac cycle
What does it mean to say that isovolumetric ventricular contraction occurs?
tension and pressure rise inside the ventricles but blood does not flow out (the semilunar valves are not open)
When does isotonic ventricular contraction occur?
Once the pressure in the ventricles exceeds that in the arterial trunks
How does the dicrotic notch come about?
Blood in the aorta and pulmonary trunk now starts to flow back toward the ventricles and this movement closes the semilunar valves. As the backflow begins, pressure decreases in the aorta. When the semilunar valves close, pressure rises again as the elastic arterial walls recoil. This produces a valley in the aortic pressure tracing called a dicrotic notch
What happens when ventricular pressure falls below atrial pressure?
the atrial pressure forces the AV valves open. Blood now flows from the atria into the ventricles
How does passive filling occur?
Both the atria and ventricles are in diastole but the ventricular pressure continues to fall as the ventricular chambers expand. Throughout this period pressures in the ventricles are so far below those in the major veins that blood pours through the relaxed atria and on through the open AV valves into the ventricles. This passive flow of blood is the main method of ventricular filling.
What is flow directly proportional and inversely proportional to?
- Directly proportional to pressure
- inversely proportional to resistance
Where is the largest pressure gradient found?
between the base of the aorta and the proximal ends of peripheral capillary beds
How does the cardiovascular system alter the largest pressure gradient and change the rate of capillary blood flow?
by adjusting cardiac output and peripheral resistance
What does blood pressure refer to?
Arterial pressure
What is hydrostatic pressure?
the force exerted by a fluid pressing against a wall
What is capillary hydrostatic pressure (CHP)?
the pressure of blood within capillary walls
What is Venous pressure?
the pressure of the blood within the venous system
What must the circulatory pressure overcome in order for resistance to occur?
total peripheral resistance (the resistance of the entire cardiovascular system)
What is vascular resistance?
the force that opposes blood flow in blood vessels. It’s most important factor is friction between blood an the vessel walls. The friction depends on vessel length and internal vessel diameter
Is friction increased by increasing or decreasing the length of a blood vessel?
Increasing
Do differences in diameter or length have more significant effects on resistance?
Diameter
How can you control vessel diameter?
Through vasoconstriction or vasodilation
