Human Heart Flashcards
Describe the structure of of the human heart
The heart is formed from cardiac muscle (heart is a muscular organ)
Has two completely separate sides
The heart consists of four chambers
The top two chambers are called the atria
They have relatively thin muscular walls
The bottom two chambers are called the ventricles
The ventricles have a much thicker muscular wall than the atria
How are the atria separated from the ventricles
What are these valves attached to
The atria are separated from the ventricles by the atrioventricular valves (AV valves)
The left AV valve is also called the bicuspid valve
The right AV valve is also called the tricuspid valves
These valves are attached to tendons which ensure that the valves open in the right direction
What is the right and left side of the heart separated from each other by
What is the role of this.
The right and left sides of the heart are completely separated from each other by a wall called the septum
The septum prevents any blood from passing directly between the two sides of the heart
Describe the blood vessels of the heart
Describe the pattern of blood flow through the human heart
Deoxygenated blood enters the right atrium through the vena cava
The vena cava has two branches.
The superior vena cava brings in blood from the head and upper parts of the body
The inferior vena cava brings in blood from the lower parts of the body
The deoxygenated blood is now pumped from the right atrium to the right ventricle
The right ventricle now pumps the deoxygenated blood out of the heart to the lungs through the pulmonary artery (has two branches - one going to left lung, one going to right lung)
In the lungs, the blood becomes oxygenated
Oxygenated blood now returns from the lungs back to the heart in the pulmonary vein (also has two branches - one coming from left lung to heart and another coming from right lung to the heart)
The pulmonary vein brings blood to the left atrium
The blood then passes to the left ventricle which pumps the blood out of a large blood vessel called the aorta
The aorta transfers the oxygenated blood to all the parts of the body including the head (branches to body - other branch going to head)
Right and left sides of the heart contract at the same time
Explain why the left ventricle has a thicker muscular wall than the right ventricle
The left ventricle has a thicker muscular wall than the right ventricle
This is because the left ventricle pumps blood around the whole body whereas the right ventricle only pumps blood to the lungs
What does the pulmonary artery and aorta contain
In the pulmonary artery and the aorta - these blood vessels contain valves
Which blood vessel branches directly from the aorta and what is its function
The coronary artery is a blood vessel which directly branches from the aorta
This supplies the heart muscle with oxygen and nutrients
Describe how the action of the heart is initiated
How the heart beat is initiated
During the heart beat, the muscular walls of the heart contract
The heart beat is initiated from within the heart itself
The heart does not need an external signal in order to beat
Because the heart triggers its own beat, it is said that the heart muscle is myogenic
In the wall of the right atrium there is a group of specialised cells called the sino-atrial node (SAN). This is also called the pacemaker
The cells in the SAN depolarise (they become electrically excited). This triggers a wave of electrical excitation to spread across the atria.
This causes the atria to contract
This contraction of the atria is called the atrial systole
This wave of electrical excitation crossing the atria cannot pass directly down the ventricles
This is because the ventricles are separated from the atria by a layer of non-conducting tissue
This layer of tissue will not pass the electrical excitation through it
However, between the atria there is another group of specialised cells called the atrio-ventricular node (AVN)
The AVN is connected to conducting fibres called Purkyne fibres
Initially the Purkyne fibres are bundled together. This is called the Bundle of His
However, this then branches, with Purkyne fibres running down to the apex/base of the heart and then up the walls of the ventricles
The AVN detects the electrical excitation passing over the atria
After a short delay, the AVN transmits the electrical excitation down the Purkyne fibres
This electrical excitation causes the ventricles to contract
Describe how the action of the heart is coordinated
How the heart beat is coordinated
The heart beat is initiated from within the heart itself
The heart does not need an external signal in order to beat
Because the heart triggers its own beat, it is said that the heart muscle is myogenic
In the wall of the right atrium there is a group of specialised cells called the sino-atrial node (SAN). This is also called the pacemaker
The cells in the SAN depolarise (they become electrically excited). This triggers a wave of electrical excitation to spread across the atria.
This causes the atria to contract
/// This contraction of the atria is called the atrial systole
This wave of electrical excitation crossing the atria cannot pass directly down the ventricles
This is because the ventricles are separated from the atria by a layer of non-conducting tissue
This layer of tissue will not pass the electrical excitation through it
However, between the atria there is another group of specialised cells called the atrio-ventricular node (AVN)
The AVN is connected to conducting fibres called Purkyne fibres
Initially the Purkyne fibres are bundled together. This is called the Bundle of His
However, this then branches, with Purkyne fibres running down to the apex/base of the heart and then up the walls of the ventricles
The AVN detects the electrical excitation passing over the atria
After a short delay, the AVN transmits the electrical excitation down the Purkyne fibres
This electrical excitation causes the ventricles to contract
Explain why the ventricles contract from the apex upwards
The ventricles contract from the apex upwards
This ensures that the maximum volume of blood is pumped out of the ventricles
Explain why there is a slight delay before the AVN triggers electrical excitation down the Purkyne fibres
There is a slight delay before the AVN triggers electrical excitation down the Purkyne fibres
This slight delay ensures that the venticles after the atria have contacted
Describe the events taking place in the heart during the cardiac cycle
events taking place in the heart during the heart beat/when blood moves through the heart
systole - contracting
atrial systole - contraction of the atria
diastole - relaxing
diagram of heart just as previous cardiac cycle is ending
Both the atria and ventricles are in diastole (relaxed)
Blood flows into the atria through the vena cava and pulmonary vein
This causes the pressure in the atria to rise
At a certain point, the pressure in the atria is greater than the pressure in the ventricles
This causes the atrioventricular valves to open allowing blood to flow down from the atria into the ventricles
Now the atria contract (atrial systole takes place)
This pushes the remaining blood from the atria down to the ventricles
After a short period of time, the ventricles contract. They enter ventricular systole
The pressure in the ventricle now rises rapidly
Because the ventricular pressure is now greater than the atrial pressure, the atrioventricular valves close
This prevents any blood from moving back into the atria from the ventricles
The semilunar valves in the pulmonary artery and aorta also open and blood is pumped from the ventricles out of the heart
When the ventricles contracted, the atria relaxed
Finally the ventricles relax - they enter ventricular diastole
At some point, the pressure in the ventricles falls below the pressure in the pulmonary artery and aorta. This causes the semilunar valves to shut
This prevents blood from flowing back into the ventricles
At this point, the heart is ready to enter the next cardiac cycle
Interpret graphs showing the pressure and volume changes taking place in the heart during the cardiac cycle
The top graph shows the pressure changes taking place
The bottom graph shows the volume of the ventricle
one line shows the pressure in the left atrium
another shows the pressure in the left ventricle
one shows the pressure in the aorta which takes blood out of the left ventricle
At the start, the left atrium is undergoing systole
This causes the pressure in the left atrium to increase
The atrioventricular valve is open, so blood flows down into the left ventricle
This causes the pressure of the left ventricle to increase
Now the left ventricle contracts - enters systole
Pressure in the left ventricle massively increases
Because the pressure in the left ventricle is now greater than in the left atrium, av valve shuts#
When the pressure in the left ventricle is greater than in the aorta, the semilunar valve in the aorta opens
Blood now flows out of the left ventricle through the aorta. The pressure in the left ventricle now falls as blood is leaving
At a certain point, the pressure in the left ventricle is less than in the aorta
Now the semilunar valve in the aorta closes, preventing blood being draw back into the left ventricle
While the ventricle was contracting, the atrium was relaxing
This means that the atrium is now refilling with blood
The left ventricle now starts to relax, causing the pressure in the ventricle to fall
Eventually the pressure in the left ventricle, falls below the pressure in the left atrium causing the av valve to open and blood to begin to flowi nto the left ventricle from the left atrium
As the atria and ventricles refill, the heart is now ready to enter the next cardiac cycle
One line shows blood volume in the left ventricle
Blood volume increases as it is pumped into the left ventricle when the left atrium contracts
when the left ventricle contracts. blood volume falls as blood passes out through the aorta
finally blood volume increases again as the left ventricle relaxes and blood flows down from the left atrium
what is meant by cardiac output
The cardiac output is the volume of blood pumped into the circulatory system in one minute
what is meant by heart rate
Heart rate is the number of heart beats in one minute
heart rate can rise significantly during exercise
what is meant by stroke volume
The volume of blood pumped out of a ventricle during each contraction is the stroke volume
normally consider the left ventricle since it pumps blood around the body
typical stroke volume around 70cm3
calculate cardiac output
cardiac output (cm3/min) = heart rate (beats/min) x stroke volume (cm3)
to convert the cardiac output from cm3 /min to dm3/min divide by 1000
calculate cardiac output using an ECG
We need to measure the time taken for one heart beat
to do that, measure the time from the start of one P wave to the start of the next P wave = 0.8s
60/0.8 = 75bpm
