Part 3 of Chapter 6: The heart and the cardiac cycle🫀

Question 1

Where is the human heart located in the human body?

Answer 1

• The heart sits between the lungs in the centre of the chest, and it is slightly tilted to the left of the breastbone.

Question 2

How many chambers does the human heart have?

Answer 2

• The heart has 4 chambers, the upper 2 chambers of the heart are known as the ATRIA, and it has thinner muscular walls than the ventricles as they only have to pump blood into the ventricles.
• The lower 2 chambers of the heart are known as VENTRICLES, and they have thick muscular walls that force blood out of the heart to the other parts of the body.
• The wall of the left ventricle is thicker than the wall of the right ventricle as it must pump blood to the rest of the body which requires high pressure.
• The right ventricle of the heart has thinner walls than the left ventricle as it only pumps blood to the lungs.

Question 3

What is the median septum?

Answer 3

• The median septum is a muscular wall that runs down the middle of the heart and separates the right and left sides of the heart.
• This prevents deoxygenated blood in the right side of the heart from mixing with oxygenated blood in the left side.
• Mixing deoxygenated with oxygenated blood will reduce the amount of oxygen carried to the tissue cells.
• Patients with a hole in the median septum are said to have a hole in the heart and they may suffer from shortness of breath, fatigue and in serious cases, heart FAILURE.

Question 4

What is an advantage of the valves in the heart?

Answer 4

• The valve in the heart prevents the backflow of blood by ensuring blood flows only in one direction.

Question 5

What are the 3 valves that are present in the heart?

Answer 5

• triscupid valve
• biscupid valve
• semi-lunar valve
  and they are all in the aorta and pulmonary vein

Question 6

What are the parts of the heart that aids in the returning of deoxygenated blood to various parts of the body?

Answer 6

• Deoxygenated blood from the various parts of the body is returned to the right atrium by the upper and lower vena cavae.

Question 7

What happens when the muscles of the right atrium contract?

Answer 7

• As the muscles of the right atrium contract, blood flows into the right ventricle.
• the triscupid valve between the right atrium and right ventricle will open when the blood pressure in the right ventricle becomes lower than the pressure in the right atrium.
• The valve has 3 flaps which are attached to the walls of the right ventricle by the chordae tendineae.
• The flaps point downwards to allow for the easy flow of blood from the atrium to the ventricle.

Question 8

What is the chordae tendineae?

Answer 8

• The chordae tendineae helps in the attachment of the 3 flaps of the tricuspid valves to the walls of the right ventricle.

Question 9

what happens when the muscles on the right ventricle contract?

Answer 9

• When the muscles of the right ventricle contract, the blood pressure forces the flaps of the valve to close.
• The closure of the valve prevents the backflow of blood into the atrium.
• The chordae tendineae prevents the flaps from being reverted into the atrium when the muscles of the right ventricle contract.

Question 10

what happens when the blood leaves the right ventricle via the pulmonary arteries?

Answer 10

• When blood leaves the right ventricle via the pulmonary arteries, it reaches the lungs and the semi-lunar valves in the pulmonary artery, preventing blood backflow from the pulmonary artery into the right ventricle.

Question 11

Why is the blood in the pulmonary artery at a lower pressure than the blood in the aorta?

Answer 11

• The blood in the pulmonary arteries is at a lower pressure than the blood in the aorta because the low pressure reduces the rate of blood flow in the pulmonary arteries.
• This gives more time for gaseous exchange in the lungs.

Question 12

what is the pulmonary vein?

Answer 12

• The pulmonary vein allows oxygenated blood from the lungs to be brought back to the left atrium.
• When the muscles of the left atrium contract, the blood pressure in the left atrium becomes higher than the pressure in the left ventricle.
• The high pressure will then force open the bicuspid valve that separates the left atrium from the left ventricle. Thus, this allows the blood to enter the left ventricle.
• The biscupid (2 valves) valve is similar to the triscupid (3 valves) valve in terms of structure and function except that it has 2 flaps instead of 3.

Question 13

What happens when the muscles of the left ventricle contract?

Answer 13

• When the muscles of the left ventricle contract, blood leaves through the aorta.
• From the aorta, blood is distributed to all parts of the body except the lungs.
• The aorta possesses semi-lunar valves which is known as the aortic valve and the aorta then prevents the backflow of blood into the left ventricle.
• Blood then enters the aorta at very high pressure.

Question 14

What are the aorta valves?

Answer 14

• The aorta valves are the semi-lunar valves that the aorta possesses.

Question 15

what is the role and function of the coronary arteries?

Answer 15

2 small coronary arteries branch out of the aorta, and they bring/take in oxygen and nutrients to the heart or cardiac muscles.

Question 16

How do we define a ventricular systole and a ventricular diastole?

Answer 16

• The cardiac cycle takes place in one heartbeat and a heartbeat is defined by one ventricular systole and one ventricular diastole.
• Ventricular systole is described by the contraction of muscles in both ventricles.
• Ventricular diastole is described by the relaxation of muscles in both ventricles.

Question 17

What is the process of the cardiac cycle, including the muscle movements?

Answer 17

1. The atrial muscles contract. (top part of heart)
2. Ventricular muscles contract. (bottom part of the heart)
3. Ventricular and atrial muscles are relaxed. (whole heart is relaxed)

Question 18

What happens when the muscles in both atria contract-

Answer 18

When the muscles in both the atria contract (atrial systole), the slight increases in atrial pressure force blood into the relaxed ventricles.

Question 19

what happens when the muscles in the ventricles contract?

Answer 19

• After a short pause, the muscles in the ventricles contract (ventricular systole) and the:
• The muscular contracts cause the ventricular pressure to RISE, and the triscupid and biscupid valves to close.
• This then prevents the backflow of blood into the atria, thus it produces a loud ‘lub’ sound.
• Once the ventricular pressure exceeds the pressure in the aorta, the semi-lunar valves in the aorta are forced open. (through pressure and force)
• Blood then flows out of the right ventricle to the pulmonary arteries and from the left ventricle to the aorta.
• As the muscles of the ventricles contract, the muscles of the atria relax.
• The right atrium will then receive blood from the vena cavae while the left atrium receives blood from the pulmonary veins.

Question 20

What happens when the muscles of the ventricles (ventricular muscles) relax (ventricular diastole)?

Answer 20

• When the muscles of the ventricles relax (ventricular diastole), the pressure in the ventricles decreases.
• The decrease in pressure causes the semi-lunar valves to close, and this produces a ‘dub’ sound.
• The biscupid and triscupid valves then open, and blood flows from the atria into the ventricles as the pressure in the ventricle becomes lower than the atria.
• The pressure in the ventricles gradually increases as blood continues to enter the ventricles from the atria.

Question 21

What is the last step before the whole cardiac cycle repeats?

Answer 21

• The muscles of the atria contract again and the whole cycle then repeats.

Question 22

SUMMARY of cardiac cycle:

Answer 22

1. Muscle contractions
   - Atrial systole; The atrial muscles contract and the ventricular muscles relax.
   - Ventricular systole; The ventricular muscles contract and the atrial muscles relax.
   - Diastole; The atrial muscles relax, and ventricular muscles relax.
2. Blood flow
   - Atrial systole; From the atria to ventricles.
   - Ventricular systole; From the ventricles to the aorta and pulmonary arteries.
   - Diastole; Into the atria and ventricles.
3. Valves
   - Atrial systole; The biscupid and triscupid valves open and semi-lunar valves close.
   - Ventricular systole; The biscupid and triscupid valves close and semi-lunar valves open.
   - Diastole; the biscupid and triscupid valves open and semi-lunar valves close.

Question 23

When is a pulse produced?

Answer 23

• A pulse is produced after every ventricular contraction.

Question 24

How do we get the number of heartbeats per minute?

Answer 24

• We can get the number of heart beats per minute by counting the number of pulse beats per minute.

Question 25

How does the rate of the heartbeat vary among an individual?

Answer 25

• The rate of the heartbeat varies with the age and size of an individual.

Question 26

What is the average heartbeat of an adult?

Answer 26

• The average normal heartbeat of an adult is 72 heartbeats per minute.