Cardiovascular system in action Flashcards
What does the cardiac cycle refer to?
the series of steps undergone by the heart during one heartbeat
During the cardiac cycle what do the different chambers of the heart go through?
periods of systole (contraction) and periods of diastole (relaxation)
What is the average heart beat lasts for?
around 0.8 seconds (although this can vary significantly)
How do stages of the cardiac cycle occur?
in the same order simultaneously in both sides of the heart.
Describe diastole?
Blood flows into the atria via vena cavae and pulmonary veins. The heart muscle is in a relaxed states with the valves of the heart closed until the pressure of the blood in the atria is greater than that in the ventricles and the AV valves are pushed open allowing the blood to enter the ventricles.
Describe atrial systole?
The left and right atria contract simultaneously to force the remaining blood from the atria into the ventricles. The ventricles, which are still in diastole, fill up with blood and the pressure increases (greater than the atria), causing the AV valves to snap shut/close to prevent the backflow of blood from the ventricles to the atria.
Describe ventricular systole?
The ventricles then contract and the pressure exerted forces open the semi-lunar valves, allowing blood to be pushed into the aorta and pulmonary artery. When the ventricles empties, the semi-lunar valves close and the heart can return to a diastolic state.
How long does atrial and ventricular diastole last?
0.4 seconds
How long does atrial systole and ventricular diastole last?
0.1 seconds
How long does atrial diastole and ventricular systole last?
0.3 seconds
What must the order of these steps remain?
constant although the rate at which they happen may fluctuate
What are the sounds of the heart beat caused by?
the closing of valves
What causes the initial lubb sound?
the closing of the AV valves
What causes the secondary dupp sound?
the closing of the semi-lunar valves
How can we remember the sequence of valve movements?
Closed AV valves
Open semi-lunar valves
Closed semi-lunar valves
Open AV valves
What is the cardiac cycle predominantly under the control of?
the nervous system
What is the sino-atrial node?
it is positioned over the right atrium and is the pacemaker of the heart. It functions by initiating electrical impulses that spread across the atria to make the cardiac muscle contract. The function of the SA node is independent of the rest of the nervous system (auto-rhythmic) and continues to send impulses even in the absence of nerves from the nervous system
What does the initial wave of excitation that spreads across the atria stimulate?
atrial systole
After atrial systole what does the initial wave of excitation also do?
passed to the atrio-ventricular node
What does the AV node do?
passes the signal down conducting fibres which branch left and right to stimulate ventricular systole from the base of the heart upwards
What must each step in the excitation of the heart be?
perfectly in sync to ensure correct functions of the heart
Why are impulses from the AV node sent after those from the SA node?
to allow blood to flow into the ventricles before they start to contract.
What is an electrocardiogram?
a graphical display which represents the electrical activity of the heart as the cardiac cycle progresses
What does the P wave show in a normal ECG?
the excitation spreading across the atria from the SA node
What does the QRS complex show in a normal ECG?
the excitation of the ventricles
What does the T wave show in a normal ECG?
the electrical recovery of the ventricles after contraction
What can ECG’s show?
abnormal activity of the heart and can indicate current or past irregularities
What is ventricular tachycardia?
the rapid, uncontrolled beating of the ventricles out of sequence with the atria
What is ventricular fibrillation?
the uncontrolled and sporadic beating of the ventricles in no particular order. This can also happen in the atria.
What can a defibrillator be used to do?
'’reset’’ the electrical activity of the heart
What is atrial flutter?
the rapid contraction of the atria, meaning they contract more timed than the ventricles
What can be fitted to correct abnormal heart rhythms?
an artificial pacemakers
What does the autonomic nervous system control?
the heart rate along with numerous other body functions, meaning its control is entirely involuntary.
What does the medulla do?
sends nerve impulses to the SA node to control the speed of its action
What are the two antagonistic branches of the autonomic nervous system?
the sympathetic and parasympathetic, determine whether this is to increase or decrease the heart rate.
What does the sympathetic branch do?
An increase in the number of nerve impulses from the sympathetic (accelerator) nerve will increase the heart rate through the neurotransmitter noradrenaline
What does the parasympathetic branch do?
An increase in the number of nerve impulses from the parasympathetic nervous system will decrease the heart rate through the release of neurotransmitter, acetylcholine.
Apart of nervous control, what is heart rate also controlled by?
hormones
During periods of physical stress or potential physical stress, what does the sympathetic nervous system do?
stimulate the release of adrenaline which in turn increases the heart rate.
What is blood pressure?
the pressure that is exerted against the walls of the blood vessels as blood flows through them.
What is the pressure of the blood generated by?
the contraction of the ventricles forcing blood round the body
The pressure of the blood generated by the contraction of the ventricles forcing blood round the body. As a result what are the 2 readings blood pressure is shown as?
systolic measurement and a diastolic measurement which is represented as a ‘‘faction’’ and is measured in mmHg by a device called a sphygmomanometer
What is generally accepted normal value for blood pressure?
120/70 mmHg
What happens as blood flows from the heart to the rest of the body?
it gradually loses pressure
Where is the highest pressure found?
aorta
Where is the biggest decrease in blood pressure?
as blood flows through the arterioles
When is there an increase in friction?
as blood travels through progressively narrower blood vessels (known as peripheral resistance). This friction occurs between the blood and the vessel walls and as a result, the pressure decreases.
What is hypertension?
prolonged elevated blood pressure
If hypertension is left untreated what can it be a major risk factor for?
cardiovascular disease
heart attacks
strokes
How can blood pressure be raised?
diets high in salt
stressful lifestyle
strong genetic component (leading to patterns of hypertension through families)
What is hypertension generally?
asymptomatic
