cardiovascular system - cardiac function and dysfunction Flashcards
all events of the cardiac cycle associate with what
1 heartbeat (800msec)
what happens normally in the cardiac cycle
2 atria contract while 2 ventricles relax, then while 2 ventricles contract, the 2 atria relax
define systole
contract
define diastole
relax
name the 3 phases of cardia cycle
P
QRS
T
summarise the relaxation period occurs after T-wave
ventricular & atrial diastole/relaxation
- Ventricular pressure drops below atrial & AV valves open, so ventricular filling occurs
summarise what happens after the P wave
atrial systole/contraction and ventricular diastole
- Ventricles fill with remaining blood (~25%)
summarise what happens after QRS wave
ventricular systole and atria diastole
- Pressure pushes AV valves closed
- Pushes semilunar valves open and ejection occurs
- Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves
name the divisions of the cardiac cycle
- atrial systole
- early ventricular systole
- late ventricular systole
- early ventricular diastole
- late ventricular diastole
explain the atrial systole division of cardiac cycle
atria contract, AV valves open, semilunar valves closed
explain the early ventricular systole division of cardiac cycle
atrial relax, ventricles contact, AV valves forced closed, semilunar valves forced open
explain the late ventricular systole division of cardiac cycle
atria relax, ventricles contract, AV valves remain closed, semilunar valves forced open
explain the early ventricular diastole division of cardiac cycle
atria and ventricles relax, AV valves and semilunar valves closed, atria begin passively filling with blood
explain the late ventricular diastole division of cardiac cycle
atria and ventricles relax, atria passively fill with blood as AV valves open, semilunar valves closed
how do heart sounds occur
From blood turbulence caused by closing of heart valves
which heart sounds are heard through a stethoscope
During each cardiac cycle only the 2 loudest of 4 heart sounds
explain the 4 heart sounds
S1 = ‘lub’ louder, longer, closure of AV valves soon after ventricular systole
S2 = ‘dub’ quieter, shorter, closure of semilunar valves at beginning of ventricular diastole
S3 = rapid ventricular filling
S4 = atrial contraction
what is a heart murmur
Abnormal sound (rushing/gurgling) before, between, after or masking normal sounds
what does a heart murmur indicate and explain this
Indicates valve disorder e.g.,
- mitral/aortic stenosis (narrowing)
- mitral valve prolapse (MVP) – protrude into L atrium during ventricular contraction
= not always serious
= occurs in 10-15% of population - 65% of which are females
what is cardiac output
CO = Volume of blood ejected from L (or R) ventricle into aorta (or pulmonary trunk) each minute
how is cardiac output calculated
CO (ml/min) = stroke volume (SV)(ml/beat) x heart rate (beats/min)
SV- volume ejected by ventricle with each contraction
Entire blood volume flows through what and when
the pulmonary & systemic circulation each minute
what happens to cardiac output when we exercise
it increases by about double during mild exercise and by almost 4 times as much during intense exercise
rest - 5.25L/min
mild exercise - 10L/min
intense exercise- 19L/min
what is cardiac reserve
ratio between max CO & rest CO
- Average = 4 - 5x
- Top endurance athlete = 7-8x
- Severe heart disease = None (thus daily living tasks limiting)
what is the regulation of stroke volume
volume ejected by ventricle
name the 3 important factors related to regulation of stroke volume
preload
contractility
afterload
explain preload in terms of stroke volume regulation
degree of stretch Frank-Starling Law of the Heart:
- Increase diastolic volume increases strength of contraction which increased stroke volume
explain contractility in terms of stroke volume regulation
forcefulness of contraction of individual ventricular muscle fibres
explain afterload in terms of stroke volume regulation
pressure to exceed to eject ventricular blood i.e., to open semilunar valve;
- Increased by elevated BP (hypertension) & narrowing of arteries by atherosclerosis.
explain the homeostasis and control in the regulation of heart rate
During exercise
- CO rises to supply working tissues with more O2 & nutrients
Stroke Volume may fall
- if ventricular myocardium damaged or blood volume reduced by bleeding
Homeostatic mechanisms
- act to maintain adequate CO by increasing heart rate & contractility.
name the most important factors that regulate heart rate
automimic nervous system
Hormones, released by adrenal medulla
- * epinephrine & norepinephrine
Autonomic Regulation of Heart Rate originates where
in cardiovascular centre in medulla oblongata
name and explain the 2 ways the nervous system controls the heart
Input to CV centre
- From higher brain centres (e.g., hypothalamus)
- From sensory receptors:
Proprioceptors
Chemoreceptors
Baroreceptors
Output to heart
- Increased depolarisation in SA node: increases heart rate
- Increased contractility of A & V: increases stroke volume
- Decreased depolarisation in SA node: decreases heart rate
explain chemical regulation of the heart
Hormones – released with exercise, stress & excitement
- epinephrine & norepinephrine, these increase both heart rate & contractility
- thyroid hormones (do same as above)
Ions
- increase in K+ or Na+ decreases heart contraction & rate
- high conc of Na+ blocks Ca2+ influx during cardiac AP, so contraction decreased
- high conc K+ blocks generation of AP
- increase Ca2+ speeds heart rate & strengthens heart
name 4 other factors that regulate heart rate
age
gender
physical fitness
body temp
explain how age and gender regulate heart rate
Age
As you grow older, pulse rate is about same as before. But upon exercise, it may take longer for pulse to increase & longer to slow down afterward. Highest heart rate with exercise is also lower than when younger.
Gender
(female resting > male resting)
i.e., female resting heart rate is faster than the male resting heart rate (on average)
explain how physical fitness regulates heart rate
Over time, with chronic cardio training, resting heart rate drops because each beat delivers a bigger burst of blood, so fewer beats needed. This takes work off your heart and is why cardio exercise is recommended for heart health.
explain how body temp regulates heart rate
(>temp > rate)
i.e., the higher the body temperature the faster the heart rate
explain Long Q-T Syndrome
Conduction disorder
Rare, genetic problem
Repolarisation abnormality
Prone to very rapid heartbeats
- Poor supply to brain, lack of O2 May cause fainting, fits, seizures
name the 2 forms of treatment for long Q-T syndrome
beta blockers
defibrillator
explain how beta blockers are a treatment for long Q-T syndrome
Block b adrenoceptors
Decrease electrical impulse that passes through AV node
Prevents sudden increase in heart rate
explain how defibrillators are a treatment for long Q-T syndrome
Depolarises entire myocardium simultaneously
With luck, after repolarisation, the SA node will be the 1st to reach threshold.
what is arrhythmia
Irregular heart rhythm due to defect in conduction system of heart
name the causes of arrhythmia
drugs (caffeine, nicotine, alcohol etc.,)
anxiety
Hyperthyroidism
K+ deficiency
certain heart diseases.
name and explain some examples of arrhythmia
Heart block
- serious; conduction system slowed or blocked, commonly at AV node
Atrial flutter
- abnormal rapid atrial contraction (300x/min)
Atrial fibrillation
- asynchronous contraction of atrial fibres (400-600x/min), thus chamber fails to pump blood as effectively (reduces by 20-30% in strong heart, so person still lives)
Ventricular fibrillation
- quick death as blood not ejected from ventricles
Representative Heart Conditions Detectable through what
ECGs
tachycardia = very regular and high spikes
extrasystole (beat) - large and wide dip and then increase within the normal heart beat
ventricular fibrillation - flatter line so few peaks
complete heart block - large gaps between heart beats
myocardial infraction - wide R wave
Asystole - almost flat line
heart disease is caused by the build up of what
Atherosclerotic Plaque
lumen of blood vessel becomes smaller due to the presence (build up) of the plaque.
