The heart (cardiac cycle + structure + conduction)

Question 1

Cardiac Cycle of the heart

Answer 1

1. The atria and ventricles begin in diastole (relaxed)
2. Blood flows into the atria via the pulmonary artery or the vena cava
3. This causes the pressure in the atria to increase, and at a certain point the pressure in the atria is higher than the pressure in the ventricles
4. This causes the atrioventricular valves to open and blood flows from the atria to the ventricles
   5.Atrial systole then occurs and the remaining blood is squeezed from the atria down into the ventricles
5. Ventricular systole then occurs, causing the pressure in the ventricles to increase rapidly
6. When the pressure in the ventricles is higher than the pressure in the atria, then the atrioventricular valves close, preventing backflow of blood and causing atrial diastole
7. When the pressure in the ventricles is higher than the pressure in the aorta/pulmonary artery, this also causes the semilunar valves to open, and blood flows from the ventricles out of the heart via the pulmonary vein or the aorta
8. Ventricular diastole then occurs, and when the pressure in the aorta and pulmonary vein is higher than the pressure in the ventricles, the semilunar valves close, preventing backflow of blood into the ventricles
9. The heart is then ready for it’s next cardiac cycle

Question 2

General Structure of the heart

Answer 2

-The heart is split into four chambers, the left and right atria and the left and right ventricles
-The atria are separated from the ventricles by the atrioventricular valves
-The left AV valve is known as the bicuspid valve
-The right AV valve is known as the tricuspid valve
-The left and right sides of the heart are completely separated by the septum

Question 3

Comparison between atria and ventricles

Answer 3

-Ventricles have a thicker muscular wall than atria
-This is because ventricles pump blood out of the heart towards the body, meaning it requires a greater force of contraction
-The left ventricle has a thicker muscular wall than the right ventricle, as it pumps blood to the whole body, not just the lungs

Question 4

Pathway of blood (from deoxygenated to oxygenated)

Answer 4

-Deoxygenated blood enters the right atrium via the vena cava
-The vena cava is split into two branches:
-The superior vena cava carries 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 blood is then pumped from the right atrium to the right ventricle
-The right ventricle then pumps the blood out of the heart to the lungs via the pulmonary artery
-The blood is then oxygenated at the lungs
-The blood then returns to the heart from the lungs via the pulmonary vein
-The pulmonary vein delivers the oxygenated blood to the left atrium
-The blood is then pumped from the left atrium to the left ventricle
-The left ventricle then pumps the oxygenated blood out of the heart to the rest of the body via the aorta

Question 5

Coronary artery

Answer 5

-The coronary artery is a blood vessel that branches directly from the aorta that supplies the heart with oxygen and nutrients

Question 6

Cardiac conduction

Answer 6

SAN
-The sino-atrial node (SAN), located in the right atrium, generates an electrical impulse
-This electrical impulse causes atrial systole
AVN
-The Atrioventricular node (AVN), located in between the atria and the ventricles, delays the impulse by about 0.1 seconds to allow full atrial contraction and full ventricular filling
-This slight delay also ensures that the ventricles contract after the atria have contracted (atrial systole)
BUNDLE OF HIS
-Bundle of his, located in the septum of the heart, splits the impulse from the AVN into two
-The left and right bundle branches then conduct the impulse to the Purkinje fibers
-PURKINJE FIBERS
-The Purkinje fibers, located on the walls of both ventricles, cause atrial systole (squeezes the blood out of the heart)
-This ensures that the maximum volume of blood is pumped out of the ventricles

Question 7

pressure changes in the heart

Answer 7

-When atrial pressure> ventricular pressure AV valves open
-When ventricular pressure> atrial pressure AV valves close
-When ventricular pressure> aortic pressure the semi lunar valve opens
-When aortic pressure> ventricular pressure the semilunar valve is closed

Question 8

Ventricular volume

Answer 8

When volume of ventricles is high (ventricular systole) AV valves close and semi lunar valves open
-When they are low (ventricular diastole) semi lunar valves are closed and AV valves are open

Question 9

Examining the heart practical

Answer 9

-Obtain a fresh mammalian heart e.g a sheep’s heart
1. Examine the external anatomy of the heart:
-Identify major blood vessels e.g aorta, pulmonary vein, pulmonary artery, and vena cava
2. Make careful incisions to expose the ventricles and atria as well as the heart valves (atrioventricular and semi-lunar valves)
3. Compare wall thickness
-The left ventricle wall is thicker than the right as it pumps blood to the rest of the body at high-pressure
-The right ventricle wall is thinner to prevent damage to the lungs as it only delivers blood to the lungs (pulmonary circulation)