3.2.6 Practical: Mammilian Heart Dissection

Question 1

The Cardiac Cycle

Answer 1

The contraction of the heart is called systole, while the relaxation of the heart is called diastole
Arterial systole is the period when the atria are contracting and ventricular systole is when the ventricles are contracting
During ventricular systole, blood if forced out of the pulmonary artery (to the lungs) and the aorta (to the rest of the body)
One systole and diastole makes a heartbeat and lasts around 0.8 seconds in humans
This is the cardiac cycle

Question 2

Pressure Changes

Answer 2

During systole and diastole, heart valves open and close as a result of pressure changes
Valves are an important mechanism to stop blood flowing backwards
During diastole, the heart is relaxing
- the atrioventricular valves open and the semilunar valves are close
During systole, the heart contracts and pushes blood out of the heart
- during this time, the atrioventricular valves are closed and semilunar valves are open

Question 3

The Cardiac Cycle Process

Answer 3

A cardiac cycle is the sequence of events that make up a single heartbeat
It includes periods of heart muscles contraction and relaxation
One cardiac cycle is followed by another in a continuous process
- there is no gaps between cycles where blood stops flowing
The contraction of muscles in the wall of the heart reduces the volume of the heart chambers and increase the pressure of the blood within that chamber
When the pressure within a chamber/vessel exceeds that in the next chamber/vessel, the valves are forced open and the blood moves through them
When the muscles in the wall of the heart relax and recoil, which increases the volume of the chamber/vessel and decreases the pressure so that the valves close

Question 4

Analysing the Cardiac Cycle

Answer 4

pair with the corresponding paper flash card
There are several key points to keep in mind when analysis the cardiac cycle
The curves on the graph represent the pressure of the left atria, aorta and the left ventricle
The point at which the curves cross each other are important because they indicate when valves open and close
POINT A - both left atrium and left ventricle are relaxed
- pressure sits at roughly 0 kPa
BETWEEN POINTS A AND B - atrial systole
- left atria contracts and empties blood into the left ventricle
POINT B - beginning of the ventricular systole
- left ventricular pressure increases
- AV valve shuts
- pressure in the left atria drops as the left atrium expands
POINT C - pressure in the left ventricle exceeds that in the aorta
- aortic valve opens
- blood enters the aorta
POINT D - diastole
- left ventricle has been emptied of blood
- muscles in the walls of the left ventricle relax and pressure falls below that in the aorta
- aortic valve closes
- AV valve opens
POINT E - expansion of the left ventricle
- there is a short period of time during which the left ventricle expands
- this increases the internal volume of the left ventricle which decreases the pressure