Cardiovascular Physiology Flashcards
What are the general functions of the cardiovascular system
- Circulate gas
- Provide cells with nutrients
- Remove waste products of metabolism
- stop bleeding/ clot
- regulate body temp
- transport hormones
What is diastole
Relaxation of heart muscle, blood enters atrium
What is systole
Heart muscle contracts, pressure in chamber increases as volume decreases to move blood
What is the name of the valve between the right atrium and ventricle
Tricuspid valve
What is the name of the valve between the right ventricle and pulmonary artery
Pulmonic valve
What is the name of the valve between the left atrium and ventricle
The mitral or bicuspid valve
What is the name of the valve between the left ventricle and the aorta
Aortic valve
What is the difference between the superior and inferior vena cava
Superior transports deoxygenated blood from upper body, infer transports deoxygenated blood from lower body to right atrium
What happens to vessel diameter as you move through the arterial system
Decreases
What happens to blood pressure as you move from the aorta to the vena cava
Decreases as blood moves down a pressure gradient
What happens to cross sectional area as you move through the arterial system
Increases as there is a greater sum of arterioles and capillaries
What happens to blood flow velocity as you move through the arterial system
Decreases as higher cross sectional area so more area for blood to flow
Why are arterioles resistance vessels
Contain circular layers of smooth muscle for vasoconstriction and vasodilation to regulate and redistribute blood flow
Why is the elastic tissue in the aorta important
Enables recoil as blood pressure decreases so constant flow is maintained as blood leaves the heart
How do you calculate blood pressure
Cardiac output x total peripheral resistance
What contributes to total peripheral resistance
Arterioles as diameter decreases
What is the normotensive systolic blood pressure
120 mmHg
What is normotensive diastolic blood pressure
80 mmHg
What does blood pressure measure
The force exerted on the walls of the vessel by the blood
What are the determinants of total peripheral resistance
Vessel diameter, vessel length and blood viscosity
What is the role of pre-capillary sphincters
Encircle capillaries at their origin and contact or relax to regulate blood flow to meet metabolic requirements
Why is a high cross sectional area and slow blood flow velocity beneficial in capillaries
Large surface area and plenty of time for exchange
What happens to blood flow velocity in the venous system and why
Increases as smaller cross sectional area than capillaries
Why is there a lower blood pressure in the venous system
Enables veins to be squeezed by contracting muscles towards the heart
What are cardiomyocytes
Cardiac muscle cells
What is depolarisation
Positively charged ions flow into the cell, causing it to become less polarised
What is repolarisation
Positively charged ions flow out of the cell, causing it to be polarised again. (greater negative charge inside)
At rest why can’t Na+ and Ca++ enter the cardiomyocyte
Membrane is impermeable to them
What alters the permeability of the membrane enabling Na+ and Ca++ to enter
Action potential reaches cell
What initiates muscle contraction in cardiomyocytes
Influx of Ca++ initiates a cascade of events to cause the interaction of actin and myosin in the myofibril and generate a force (shorten the sarcomere)
What initiates electrical impulses/ action potentials in cardiomyocytes
The Sinoatrial node (SAN)
Describe the SAN and it ‘s role in initiation of heart muscle contraction
The SAN is specialised muscle tissue in the right atrium which spontaneously depolarises and repolarises, which spreads through the RA to the AVN
Describe the Atrioventricular node and it’s role in muscle contraction
The AVN is specialised muscle tissue by the interatrial septum of the heart which receives signals from the SAN and holds onto them for a brief delay before transmitting them to the ventricles for contraction
What is an Electrocardiogram
Electrodes placed on the skin which detect voltage from electrical events of the cardiac cycle to record the electrical activity of the heart in various phases
What are the 3 main waves of the ECG
P wave, QRS complex and T wave
What does the P wag represent
Atrial depolarisation
What does the QRS complex represent
Ventricular depolarisation and simultaneous atrial repolarisation
What does the T wave represent
Ventricular repolarisation
What are the three intervals in an ECG
PR, QT and TP
What does the PR interval represent and where is it on an ECG
Start of P wave till start of QRS complex, represents transmission from the atria to the ventricles
What does the QT interval represent and where is it on an ECG
Start of QRS to end of T wave, represents the duration between ventricular depolarisation and repolarisation
What does the TP interval represent and where is it on an ECG
End of T wave to start of P wave, represents duration between ventricular repolarisation and atrial depolarisation
What is the end diastolic volume
The volume of blood remaining in the left ventricle
What is end systolic volume
Volume of blood left in the ventricle following stystole
What is an isovolumetric contraction
Where all valves are closed so there is no change in volume in the left ventricle, while pressure rapidly increases until it exceeds aortic pressure
What is stroke volume
The volume of blood ejected from the heart per beat
How do you calculate stroke volume
End diastolic volume- end systolic volume
What is an ejection fraction
The fraction of blood within the left ventricle ejected during systole
How does you calculate the ejection fraction
Stroke volume/ end diastolic volume
How do you calculate cardiac output
HR X SV
What are the mechanisms that regulate heart rate (and therefore cardiac output)
Sympathetic NS, parasympathetic NS and circulating epinephrine
How does the parasympathetic NS affect HR
Parasympathetic cardioinhibitory nerves innervate the SA and AV node via the vagus nerve, releasing acetylcholine to reduce depolarisation of the SA node, reducing HR and the conduction velocity (speed of spread)
How does the sympathetic nervous system influence HR
Sympathetic cardioacceleror nerves innervate the SA and AV nodes, releasing norepinephrine to accelerate SA node depolarisation so the heart beats faster and conduction velocity increases
What gland is epinephrine secreted from
The adrenal gland
What mechanisms regulate stroke volume (and therefore cardiac output)
Sympathetic nerves and circulating epinephrine, preload and afterload
How does the sympathetic NS influence stroke volume
Sympathetic nerves innervate cardiomyocytes and release norepinephrine to increase the contractile force of cardiomyocytes
What is preload
The increased filling pressure in the ventricles during diastole which causes greater tension and an increased stroke volume
What is the Frank-Starling mechanism
Stroke volume will increase as left ventricular volume increases (preload)
What is Afterload
The resistance the left ventricle must overcome to circulate blood through the aorta
How does afterload influence stroke volume
The greater the afterload, the higher the pressure that must be exceeded for blood to be ejected
How does epinephrine influence SV
Released from adrenal gland and stimulates increased contractile force of cardiomyocytes
What are neuro-hormones
Responses elicited by the autonomic NS which bind to the target cell or organ to cause and increase (sympathetic) or decrease (parasympathetic) in activity
What is the neuro-hormone of the SNS
Norepinephrine (catecholamines)
What is the primary neuro-hormone of the PNS
Acetylcholine
What are the distribution vessels
Aorta, large arteries, small arteries and arterioles
What are the resistance vessels
Arterioles
What are the exchange vessels
Capillaries
What are the capacitance vessels
Venules and veins
What is aortic systolic pressure
Max pressure in aorta after ejection
What is aortic diastolic pressure
Minimum pressure in aorta before ejection
How do you calculate mean arterial pressure
Cardiac output x total peripheral resistance
What variables can be altered to regulate blood pressure
Cardiac output and total peripheral resistance
Why must blood flow be regulated via alterations in total peripheral resistance
As if all arteries dilated the heart would not be able to pump enough blood to meet metabolic demand
What is Poiseuille’s Law
Flow (Q)= pressure gradient x radius of arteriole ^4/ 8x blood viscosity x vessel length
OR
Flow= pressure gradient/ resistance
How do you calculate resistance
Viscosity x vessel length/ radius of vessel^4
How does the sympathetic NS influence resistance vessel
Increased input = vasoconstriction
Decreased input = vasodilation
Is the sympathetic or parasympathetic NS more involved in the regulation of vasoconstriction and dilation in resistance vessels
Sympathetic
How do baroreceptors regulate blood pressure within restricted limits
When BP decreases there is a reduction in frequency of signals sent from baroreceptors to the cardiovascular control centre in the medulla, the control centre sends signals to the heart and blood vessels to increase cardiac output and vasoconstrict
What are the local metabolic influences on arteriole radius and blood flow
Decreased oxygen pressure in blood, decreased pH, increased K+, increased CO2, increased blood lactate, increased temp
How does nitric oxide increase blood flow
NO is synthesised with increased arterial stress (increased blood flow) and released by endothelial cells too reduce constriction and increase dilation
How does the aorta dampen pulsatile pressure
The aorta has a high content of elastic tissue making it compliant to high blood pressure when heart contracts
How much of total peripheral resistance is provided by resistance vessels
60-70%
What are the four fundamental mechanisms responsible for cardiovascular changes during exercise
Mechanical, metabolic, autonomic and hormonal
What are the receptors within muscles and how do they initiate the increase in sympathetic activity during exercise
Mechanoreceptors are sensitive to mechanical tension and metaboreceptors are sensitive to metabolic disturbances, during exercise they transmit signals to the cardiovascular control centre evoking alterations in sympathetic and/or parasympathetic response
