Cardiology Flashcards
What are the 5 layers of the heart?
Outside the heart
Fibrous pericardium
Serous pericardium- parietal
Pericardial fluid
(on the heart)
Serous pericardium- visceral (epicardium)
Myocardium
Endocardium
How long is systole and diastole?
Systole- 0.3 seconds
Diastole- 0.5 seconds
During ejection, what proportion of blood is released from the ventricles?
2/3 of ventricular volume is ejected
Diastasis
The stage of diastole where the initial passive filling of the ventricles have slowed (before the atria contracts to complete active filling)
Stages of the cardiac cycle
Filling phase (passive filling followed by contraction of the atria for active filing after diastasis), isovolumetric contraction, outflow phase, isovolumetric relaxation
How many percent of ventricular refill is passive?
80% passive, 20% due to atrial contraction
What is the P wave on an ECG and how long does it take?
Atrial depolarisation/atrial systole
0.08-0.1s
What is the PR interval on an ECG and how long does it take?
Time between atrial depolarisation and ventricular depolarisation (Time taken for atria to depolarise and electrical activation to get to the AVN)
0.12-0.2
Prolonged PR interval- possibility of first degree heart block
What is the QRS complex on an ECG and how long does it take?
Ventricular depolarisation (hidden atrial repolarisation)
0.06-0.1s (less than 0.12s)
Prolonged QRS could be due to bundle branch block (M shape right bundle block, W/V left bundle block)
What is the ST segment?
Interval between ventricular depolarisation and repolarisation
ST elevation- indication of Myocardial infarction
Intrinsic autoregulation
Intrinsic autoregulation: A local mechanism of blood flow control that is driven by the metabolic needs of tissues and organs.
Some examples include
Active hyperemia- local vasodilation when there is increased metabolic activity to increase blood flow to organs that have increased metabolic demands.
Release of nitric oxide by endothelial cells cause vasodilation
Myogenic autoregulation
Myogenic autoregulation (contraction): A local mechanism of blood flow control that relies on the ability of blood vessels to constrict or dilate in response to changes in intravascular pressure.
When blood pressure is increased, stretching the vascular smooth muscle, the muscle automatically constricts until the diameter is normalised or slightly reduced. (vice versa, when the smooth muscle isn’t getting stretched as much due to low blood pressure, the muscle relaxes and dilates in response.- increases blood flow) – in order to maintain constant blood flow
This is to maintain blood flow
What is active and reactive hyperemia?
Active- a metabolic response due to an increase in physical activity for example- exercise for example
Reactive- during occlusion of tissue, less or no blood flows, after occlusion is removed, there is increased blood flow to the tissue
What are peripheral chemoreceptors?
What is their strongest stimulus?
They are receptors located in the Aortic bodies (aortic arch) and carotid bodies (carotid sinus)
They respond to changes in partial pressure of CO2, O2 and pH although the STRONGEST STIMULUS is a reduction in oxygen (when partial pressure of oxygen is less than 60%).
How do peripheral chemoreceptors work when there is decreased O2, decreased pH and increased CO2?
Glossopharyngeal and vagus nerve brings signals from the peripheral chemoreceptors in the carotid and aortic bodies to the Dorsal respiratory group, stimulating the VRG –> which increases inspiratory signals, increasing the frequency of action potentials travelling along the phrenic and intercostal nerves (C3-5, T1-11) –> increasing the frequency of contractions of the external intercostals and diaphragm, thus increasing respiration rate and ventilation, more CO2 expelled and more O2 inspired.
What are baroreceptors?
They are receptors found in the carotid sinus and aortic arch that function as arterial blood pressure sensors.
How do baroreceptors act when blood pressure is low?
Decreased bp –> less stretch of the walls of the carotid sinus and aortic arch –> baroreceptors fire less frequently –> decreased signals to the cardiovascular centre (pressor region) in the brain stem by CN9 and CN10 –> sympathetic nervous system is stimulated and parasympathetic nervous system is inhibited –> arterioles constrict which increases total peripheral resistance, increasing bp.
Also,
- Cardioacceleratory centre triggers release of noradrenaline, increasing heart rate, cardiac ouput and bp
- Cardiac decelerator centre is deactivated, reducing parasympathetic effect on the heart, increasing heart rate, cardiac ouput and bp
constriction of veins, higher EDV, increased preload, increased sarcomere stretch, increased contractility, increased CO, increased BP
How do baroreceptors act when bp is high?
Increased bp –> increased baroreceptors firing due to more stretch in walls of aortic arch and carotid sinus –> more signals to the cardiovascular centre (depressor region) by CN9 and 10 –> sympathetic nervous system inhibited, parasympathetic stimulated -> arterioles dilate (vasomotor centre) –> tpr decreases –> bp decreases
There is also increased dilation of veins which decreases venous return and TPR thus reducing bp
Where are cardipulmonary baroreceptors located?
Atria, ventricles and pulmonary arteries. They respond to blood volume and act to regulate blood pressure.
What are central chemoreceptors?
They are receptors located in the medulla which sense (small) changes in partial pressure of carbon dioxide or pH of the cerebral spinal fluid.
How do central chemoreceptors respond to high CO2 levels, and low pH?
High CO2 levels lead to low pH level in the CSF (due to CO2+H2O-> H2CO3 -> H+ + HCO3-
High CO2 leads to Low pH (high protons) which stimulates the central chemoreceptors which in turn stimulate the DRG and pneumotaxic centre –> inspiratory signals are sent to the ventral grey horn –> increasing impulses along the intercostal and phrenic nerves –> more frequent contractions of muscles, increased ventilation –> decreased CO2, increase pH levels.
What is Cardiac output and what is its equation?
The volume of blood each ventricle pumps as a function of time (litres per minute)
Cardiac output = HR x SV
Blood pressure equation
BP = CO x TPR
What is pulse pressure and what is its equation?
The force the heart generates each time it contracts
PP = Systolic - diastolic pressure
Mean arterial pressure equation
MAP = Diastolic pressure + ⅓ PP
What is stroke volume and what is its equation?
The volume of blood ejected from each ventricle during systole
SV = EDV-ESV
Starling’s law of the heart
Increased end diastolic volume causing increased myocyte stretch leads to an increased contraction of the heart during systole
What is preload?
The volume of blood present in the left ventricle before contraction occurs. (amount of myocyte stretch)
What is afterload?
The pressure that the left ventricle must overcome to eject blood during systole
How does a dilation of arteries affect afterload?
It decreases it. Dilation of arteries results in decreased pressure in the aorta and pulmonary trunk, so less pressure is needed to eject blood from the ventricles.
What is poiseuille’s law?
Q (flow) = pi x Pressure x r^4 / 8 x length x viscosity
Flow equation
Pressure/resistance
What are some local responses that lead to vasodilation and vasoconstriction?
Vasodilators- hypoxia, decreased pH/increased CO2/increased H+, NO and prostacyclin (secreted by healthy endothelium)
Vasocontrictors- endothelin 1(injured endothelium)
What are some hormones responsible for vasodilation and vasoconstriction?
Vasodilation- Ach at M2 receptors, Atrial natriuretic peptide
Vasocontrictors- angiotensin 2, ADH, noradrenaline
Difference between central and peripheral chemoreceptors
Central - responds to changes in PaCO2, located in the medulla, slower
Peripheral- responds to changes in O2 mainly (pH and CO2 at a smaller proportion), located in aortic and carotid bodies, faster
Why is a hypoxic drive bad?
In people with COPD where their levels of CO2 are chronically high, their drive becomes hypoxic and they mainly rely on their peripheral chemoreceptors for breathing. Meaning that they only breath in response to low oxygen levels.
It is bad to give someone with a hypoxic drive large amounts of oxygen as peripheral chemoreceptors would decrease respiration, possibly leading to respiratory arrest.
What is total peripheral resistance?
It is the total peripheral systemic resistance that are mainly due to arterioles.
What is contractility?
The force of contraction of the heart
What is compliance?
How easily the heart chamber expands when filled with blood
What are the neurotransmitters and receptors responsible for parasympathetic and sympathetic stimulation of the heart?
Acetylcholine at M2 receptors
Noradrenaline at B1 adrenergic receptors
Differences between elastic and muscular arteries
Muscular arteries contain more smooth muscle cells in the tunica media
Elastic arteries contain more elastic tissue in the tunica media
Muscular arteries are found further away from the heart (radial, ulnar arteries)
Elastic arteries are those nearest to the heart (aorta and pulmonary arteries)
Elastic arteries have larger lumens than muscular arteries
(Elastic arteries need to withstand greater pressures of blood)