d4 heart Flashcards
1
Q
how does the structure of cardiac muscle cells allow propagation of stimuli through heart wall?
A
- 1 of 3 main types of muscles present in the human body, besides skeletal and smooth muscles
- compared to skeletal muscles, cardiac muscles are shorter and have smaller diameter, but like skeletal muscles there is striation present
- not fused together but are connected to each other via intercalated discs
- cardiac muscle cells capable of generating own impulse, hence do not need to be stimulated by nerve impulses from central nervous system to work (unlike skeletal muscles)
- heavily branched, helps in signal propagation throughout heart muscles
- due to constant non-stop contractions in heart, cardiac muscle cells contain more mitochondria than skeletal muscle cells
2
Q
how do the signals from the sinoatrial node that cause contraction pass from atria to ventricles?
A
- signals from sinoatrial node that cause contraction cannot pass directly from atria to ventricles
- signals that propagate throughout heart, leading to heart contractions, start from sinoatrial node
- sinoatrial node is pacemaker of heart, responsible for heart rate in humans
- electrical impulses that leads to cardiac muscle contraction can propagate along cardiac muscle fibres
- cardiac muscle cells not fused, hence gap junctions present between cardiac muscles within intercalated discs
- technically each cardiac muscle is capable of independent contractions
- layer of connective tissue belonging to cardiac skeleton that separates atria and ventricles
- prevents spreading of impulse from atrial myocardial cells to ventricles
- only place where impulse can pass over to ventricles is at atrioventricular node
- after short pause, nerve impulses generated from AV node and propagates to rest of ventricular muscle cells
3
Q
why is there a delay between the arrival and passing on of a stimulus at the atrioventricular node?
A
- it is believed part of the reasons for delay is narrow diameter of cells in AV node which slows down impulse transmission
- reduced capacity in cells in AV node to conduct impulse between cells, leading to a delay
- delay approximately 100ms counting time taken for impulse to pass through entire AV node
4
Q
what is the purpose of the delay between the arrival and passing on of a stimulus at the atrioventricular node?
A
- delay allows for full contraction of atrial muscular walls to ensure maximum efficiency of pumping blood from atria to ventricles
- if delay is too short, ventricular contraction may start early, forcing AV valves to close and preventing any more blood from entering ventricles from atria
5
Q
how is coordinated contraction of the entire ventricle wall ensured? (describe how bundle of His and Purkinje fibres assist)
A
- conducting fibres ensure coordinated contraction of entire ventricle wall
- impulse conduction in heart carried out by heart muscle cells instead of nerve cells
- heart muscle cells are capable of generating action potentials like a nerve cell
- main form of impulse conduction is via all cardiac muscle cells, but there are specialised cardiac muscle cells that shows adaptation for specific paths of conduction in heart
- examples of such fibres include Bundle of His and Purkinje Fibres
- bundle of His connects sinoatrial node to Purkinje fibres at base of heart, and runs along interventricular septum
- bundle of His allows for better coordinated and synchronised ventricular contraction
- bundle of His branches into two fibres in septum
- Purkinje fibres made up of heart muscle cells larger in size, and also help in coordination and synchronization of ventricular contractions
6
Q
how to map the cardiac cycle other than mechanical perspective?
A
- normal cardiac cycle consists of systole (heart contraction) and diastole (heart relaxation)
- besides viewing the heart from mechanical perspective (changes in blood pressure, or checking on chamber size via ultrasound), it is possible to map a cardiac cycle in terms of electrical conductivity
- electrocardiograph can detect electrical impulses of the heart via electrodes and present data in form of an electrocardiogram
7
Q
what are the normal heart sounds caused by?
A
- normal heart sounds caused by atrioventricular valves and semilunar valves closing causing changes in blood flow
- atrioventricular valves refer to bicuspid (left) and tricuspid (right) valves that prevent backflow of blood from ventricles to atria
- semilunar valves in aorta and pulmonary artery prevents backflow of blood from arteries into ventricles
- valves ensure unidirectional flow of blood
- heart beat made up of sets of two sounds, often
described as “lub – dub” - 1st sound (lub) caused by closure of AV valves
- 2nd sound (dub) caused by closure of semilunar valves
8
Q
what is the equation of cardiac output?
A
cardiac output = heart rate (bpm) x stroke volume (ml/beat)
- heart rate: measured in beats per minute ; measure of number of cardiac cycles per minute
- stroke volume: capacity of heart ; volume of blood pumped out from heart per cycle
9
Q
how to interpret systolic and diastolic blood pressure measurements?
A
- blood pressure made up of 2 components, systolic pressure and diastolic pressure
- systolic pressure: shows pressure generated in blood vessels due to contraction of heart
- diastolic pressure shows pressure in between heart contractions
- in the arteries, this (diastolic) pressure maintained by semi-lunar valves of aorta and other factors (elasticity and smooth muscle contraction) in arterial walls
- average normal blood pressure for adults is around 120/80 mmHg (equated to pressure of a column of mercury)
- high systolic and diastolic pressures: indicative of hypertension
- low systolic and diastolic pressures (hypotension): indicative of problems like internal bleeding, shock, hormonal imbalances, etc
10
Q
what are the causes and consequences of hypertension?
A
- hypertension: condition characterized by abnormally high blood pressure
- often associated with sedentary lifestyle, or could be caused by underlying problems like kidney problems, substance abuse, gland or hormonal problems
- high pressures generated will cause heart to enlarge and weaken over time, leading to further health problems
11
Q
what are the causes and consequences of thrombosis?
A
- formation of clot within blood vessels
- thrombosis occurs in arteries when vessels are damaged from deposition of cholesterol (atherosclerosis)
- atheromas (fat deposits) develop in arteries and significantly reduce diameter of vessel (leading to hypertension)
- high blood pressure damages arterial wall, forming lesions known as atherosclerotic plaques
- if a plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
- if thrombus becomes dislodged it becomes an embolus and can cause blockage at another site
- thrombosis in coronary arteries leads to heart attacks, while thrombosis in brain causes strokes
12
Q
what results are shown by the analysis of epidemiological data relating to the incidence of coronary heart disease?
A
through studies of data collected as part of epidemiology (studies of occurrences and distribution of disease), many factors that affect incidence of coronary heart disease (CHD) is discovered:
- age (older people more likely to have CHD)
- sedentary lifestyle and being overweight
- other correlated diseases like diabetes can increase risks of CHD
- smoking and other substance abuse can affect CHD rates
- genetic basis of having CHD
- males more likely to suffer from CHD
13
Q
how can artificial pacemakers be used to regulate heart rate?
A
- artificial pacemaker: small device placed next to heart via surgery
- consists of larger body which may contain a computer to collate data and send impulses
- electrodes that can either take data (heart rate, and even temperature and respiratory rate) or send impulses to trigger action potential and contraction of heart muscles
14
Q
how can life-threatening cardiac conditions be treated?
A
- defibrillation can be used to treat life-threatening cardiac conditions
- fibrillation refers to state where heart is not beating in a coordinated manner, and beats rapidly and irregularly
- often happens as part of cardiac arrest
- defibrillator is a device that sends a high voltage that
produces an electric shock to heart - aim of defibrillator is to shock the heart, causing a massive depolarisation to heart muscles, and gives a chance for SA node in heart to reset and reestablish a normal heart rhythm
- defibrillator cannot shock a non beating heart (in asystole) to start beating again
