Flashcards in 5. The Heart Deck (40):
What is the heart?
The heart is a muscular organ that lies in the thoracic cavity behind the sternum.
The heart is two separate pumps lying side by side - which side deals with oxygenated blood and which side deals with deoxygenated blood?
The left deals with oxygenated blood and the right with deoxygenated
Each pump of the heart has two chambers:
Describe the atrium
thin-walled and elastic and streches as it collects blood. It only has to pump blood a short distance to the ventricle and therefore only has a thin muscular wall.
Describe the ventricle
It has a much thicker muscular wall as it must pump blood some distance, either to the lungs or to the rest of the body.
Why do we have a double circulatory system e.g two pumps
Because of the large drop in pressure in the capillaries in the lungs which would cause the blood to be distributed very slowly to the rest of the body.
How far does the right ventricle have to pump blood and what consequence does this have?
It pumps blood to the lungs-a distance of only a few centimetres and therefore it have a thinner muscular wall than the left ventricle.
How thick is the wall of the left ventricle?
It has a thick muscular wall as it must pump blood to the extremities of the body - a distance of 1.5m
Each of the sides of the heart contract...
At the same time as each other.
Name the valves on the left side of the heart.
The left avioventricular (bicuspid) valves - they form two cup shaped flaps on the left side of the heart
Name the valves on the right side of the heart.
The right avioventricular (tricuspid) valves - three cup-shaped flaps on the right side of the heart.
Where do the ventricles pump blood?
Away from the heart and into the arteries
Which vessel does the atria receive blood from?
Vessels connecting the heart to the lungs are called...
Where is the aorta connected and which type of blood does it carry?
The aorta is connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.
Where is the vena cava connected and which type of blood does it carry?
The vena cava carries deoxygenated blood to the heart from the body and it is connected to the right atrium.
Where is the pulmonary artery connected and which type of blood does it carry?
The pulmonary artery is connected to the right ventricle and carries deoxygenated blood to the lungs, where oxygen is replenished and it's carbon dioxide removed.
Why is the pulmonary artery unusual?
Unusually for an artery it carries deoxygenated blood
Where is the pulmonary vein connected and which type of blood does it carry?
It is connected to the left atrium and it brings oxygenated blood back from the lungs
Why is the pulmonary vein unusual?
It carries oxygenated blood and not deoxygenated blood
Which blood vessels supply the heart muscle with oxygenated blood?
The coronary arteries which branch off the aorta shortly after it leaves the heart
What does blockage (e.g by a blot clot)of the coronary arteries result in and why?
Myocardial infarction or a heart attack because an area of the heart muscle is deprived of oxygen and so dies.
What are the two phases of the cardiac cycle?
Contraction (systole) and relaxation (diastole)
What happens in the relaxation of the heart?
This is diastole.
- as the atria fill the pressure in them rises, pushing open the atrioventricular valves and allowing the blood to pass into the ventricles.
- the muscular walls of the atria and ventricles are relaxed
- the relaxation of the ventricle walls reduces the pressure in them
- this causes the pressure to be lower than that in the aorta so the semi lunar valves close - this is the 'dub' sound.
What happens in the contraction of the atria?
This is atrial systole.
- the muscles of the atrial walls contract, forcing the remaining blood which they contain (20 per cent) into the ventricles
- ventricles remain relaxed
What happens in the contraction of the ventricles?
This is ventricular systole.
- short delay to let ventricles fill with blood - then they contract.
- this increases the blood pressure inside of them forcing shut the atrioventricular valves, preventing back flow of blood into atria
- this is the lub sound
- after this the pressure rises further, forcing open the semi-lunar valves and pushing blood into the pulmonary artery and aorta.
Why are valves used?
To prevent any unwanted back flow of blood (the blood, as with all liquids and gases, will always move from a region of higher pressure to a region of lower pressure)
When are valves in the cardiovascular system designed to open?
Whenever the difference of blood pressure either side of them favours the required direction. When blood would flow in the opposite direction they close.
What do the atrioventricular valves prevent?
The back flow of blood into the atria when ventricular pressure exceeds atrial pressure after ventricular systole.
What do the semi-lunar valves prevent?
The backflow of blood into the ventricles when the recoil action of the elastic walls of these vessels creates a greater pressure in the vessels than in the ventricles.
What do pocket valves prevent?
Ensures that when the veins are squeezed, blood flows back to the heart rather than away from it.
Which valves have string like tendons?
The atrioventricular walls have have string like tendons attached to pillars of muscle in the ventricular wall to prevent the atrioventricular valves becoming inverted under the pressure during ventricular systole.
What type of muscle is cardiac muscle and what does this mean?
Myogenic - it's contraction is initiated from within the muscle itself rather than by nervous impulses.
What is the sinoatrial node (SAN) and where is it located?
It is a group of cells in the wall of the right atrium - it is where the initial stimulus for contraction originates.
What is the sinoatrial node also known as?
What is the official name for the pacemaker?
The sinoatrial node (SAN)
What are the sequence of events that controls the cardiac cycle?
- a wave of electrical activity spread out from the SAN across both atria causing them to contract
- a layer of non-conductive tissue (the atrioventricular septum) prevents the wave crossing to the ventricles
- the wave is allowed to pass through a second group of cells (atrioventricular node, AVN) which lies between the atria
- the AVN conveys a wave of electrical activity between the ventricles along a series of muscle fibres called the bundle of His
- the bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles where the bundle branches into smaller fibres.
- the wave of electrical activity is released from these fibres causing the ventricles to contract quickly.
Cardiac output = ...................................
Cardiac output = heart rate (rate at which heart pumps blood) x the stroke volume (volume of blood pumped out at cycle)
Cardiac output is measure in dm^3min^-1
Why do mammals have a closed circulatory system?
The blood is confined to vessels and this allows the pressure within them to be maintained and regulated.