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57 terms

Cardiovascular system- heart part 2

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Cardiac cycle
time between 1 heartbeat and the next
systole
phase of contraction
atrial systole
atria contract together (follows P wave)
ventricle systole
ventricles contract together (follows QRS complex)
diastole
phase of relaxation
atrial diastole
atria relax (follows QRS)
ventricular diastole
ventricles relax (follows T wave)
1 cardiac cycle
atria systole, ventricular systole, ventricular diastole
atria systole in the cardiac cycle
atria contract, pressure increases in atria, blood flows through open AV valves into relaxed ventricles, end-diastolic volume of filled ventricle
ventricular systole in the cardiac cycle
ventricles contract, (simultaneous atrial diastole- atria relax) pressure increases in ventricles, AV valves close, isovolumetric contraction, semilunar valves open, ventricular ejection
isovolumetric contraction
pressure in ventricle increases but volume stays the same until pressure is greater than pressure in aorta or pulmonary trunk
ventricular ejection
ventricles continue to contract, blood pumped into aorta/pulmonary trunk
isovolumetric relaxation
pressure in ventricle decreases but volume stays the same until pressure is less than atrial pressure
blood pressure
pressure in systemic circulation (pulmonary pressure is lower)
systolic pressure
due to maximum left ventricular contraction
diastolic pressure
during ventricular relaxation, pressure maintained by smooth muscle in arteries
Heart sounds
due to turbulence as blood flow patterns are altered, there are 4 sounds
1st sound
closing of AV valves
2nd sound
closing of semilunar valves
3rd sound
opening of AV valves
4th sound
contraction of atria
murmurs
abnormal sounds (valve disorders, septal defects)
Circulation in the fetal heart
2 shunts: by-pass lungs (no oxygen in fetal lungs )
2 shunts
foramen ovale, ductucs arteriosus
foramen ovale
hole between right and left atria, shunts blood from right atrium to left atrium.
fossa ovalis
foramen ovale closes following birth
ductus arteriosus
artery between pulmonary trunk and aorta, shunts blood from pulmonary trunk to aorta.
ligamentum arteriosum
ductus arteriosus closes following birth
Cardiodynamics
stroke volume, heart rate, cardiac output, regulation of heart rate, autonomic nervous system regulation, chemical regulation, other factors
stroke volume (SV)
ml of blood ejected by each ventricle/cardiac cycle
SV
=end diastolic volume(EDV) - end systolic volume(ESV)
heart rate (HR)
heart beats/minute
cardiac output (CO)
volume of blood ejected by each ventricle/minute (equal for right and left ventricles)
CO
=stroke volume x heart rate (eg. 70ml/beat x 75 beats/min = 5.25 liter/min)
CO changes to meet body needs
cardiac reserve
cardiac reserve
difference between maximum cardiac output and resting cardiac output, normally 4-5 times resting CO
Increasing cardiac output
increases stroke volume
3 factors affect SV
preload, contractility, afterload
1. preload
stretch (fullness) of ventricle before contraction >EDV = >preload = stronger contraction, pericardial sac prevents overstretching heart muscle, preload is affected by filling time and venous return
2. contractility
strength of contraction, positive inotropic agents and negative inotropic agents
positive inotropic agents
increase contractility (most increase Ca entering cardiac muscle cells) sympathetic NS, epinephrine, digitalis, Ca ions
negative inotropic agents
decrease contractility, parasympathetic NS, calcium-channel blockers, beta-blockers (block sympathetic response)
3. afterload
pressure in aorta/pulmonary trunk, resists ejection of blood from ventricles, high blood pressure and atherosclerosis decrease SV
increase heart rate
up to maximum heart rate (too high HR decreases filling time = decreases preload
regulation of heart rate
heart rate depends on tissue demands and stroke volume
tissue demands
basal metabolic rate and activity level
stroke volume
as SV decreases HR must increase
autonomic nervous system regulation
cardiovascular center
cardiovascular center
medulla oblongata, inputs, output
inputs
emotions (fear, excitement, anxiety) sensory-proprioceptors: physical activity, chemoreceptors: oxygen, carbon dioxide levels, baroreceptors: blood pressure
output- sympathetic (norepinephrine)
cardiac accelerator nerves- bets receptors in SA and AV, nodes- increases depolarization rates
output- parasympathetic (acetylcholine)
vagus nerves- SA and AV nodes, decreases depolarization rates, predominate at rest
chemical regulation
hormones, adrenal medulla (sympathetic) - epinephrine, norepinephrine, increases heart heart rate, thyroid hormone- increases heart heart rate
other factors affecting heart rate
body temperature: hyperthermia (faster HR), hypothermia (slower HR), fitness (decreases HR), electrolyte levels (Na and K decreases HR, Ca increases HR)
arrhythmia
abnormal heart rhythm
tachycardia
high resting heart rate
bradycardia
low resting heart rate