6. The Heart

Question 1

What are the walls of the heart made of? What property does this material have? What is the name for this property?

Answer 1

cardiac muscle

• it can contract on its own without being stimulated by a nerve
• myogenic contraction

Question 2

What supplies the capillaries in the heart? What does the blood bring that the heart needs?

Answer 2

• the coronary arteries, which branch off the aorta, close to the semilunar valve
• nutrients and oxygen for aerobic cell respiration, which provides energy for cardiac muscle contraction

Question 3

What is the role of valves in the heart?

Answer 3

prevents backflow

Question 4

What is the difference between the atria and ventricles?

Answer 4

• atria = collecting chambers

- ventricles = pumping chambers

Question 5

Draw and label the structure of the heart. (p74)

Answer 5

rah this is effort

Question 6

What is the first step in the cycle of the beating heart?

Answer 6

• walls of atria contract = pushing blood from the atria into ventricles through the atrio-ventricular valves, which are open.
• semilunar valves are closed, so the ventricles fill with blood

Question 7

What is the second step in the cycle of the beating heart?

Answer 7

• walls of ventricles contract powerfully and the blood pressure rises rapidly inside the,m.
• this first causes the atrio-ventricular valves to close, preventing back-flow to the atria and then causes the semilunar valves to open, allowing blood to be pumped out into the arteries.
• at the same time the atria start to refill by collecting blood from the veins

Question 8

What is the third step in the cycle of the beating heart?

Answer 8

• ventricles stop contracting so pressure falls inside them
• semilunar valves close, preventing back-flow from the arteries to the ventricles. When the ventricular pressure drops below the atrial pressure, the atrio-ventricular valves open.
• blood entering the atrium from the veins then flows on to start filling the ventricles

the next cardiac cycle begins when the walls of the atria contract again

Question 9

Draw the graph of pressure changes in the left atrium, the left ventricle, and the aorta during the cardiac cycle. Also indicate which of the three phrases the heart is in. (p74)

Answer 9

-

Question 10

Which part of the heart is the pacemaker? What/where is it?

Answer 10

• sinoatrial (SA) node

- one region of specialized cardiac muscle cells in the wall of the right atrium

Question 11

How does the SA node act as a pacemaker in the heart?

Answer 11

• by initiating each contraction
• sends out an electrical signal that stimulates contraction as it is propagated first through the walls of the atria and then through the walls of the ventricles

Question 12

How can messages be carried by the SA node? Give an example of each.

Answer 12

by nerves and hormones:

• impulses brought from the medulla of the brain by two nerves can cause the SA node to change the heart rate. One nerve speeds up the rate and the other slows it down.
• the hormone epinephrine increases the heart rate to help prepare the body for vigorous physical activity

Question 13

What is coronary heart disease caused by? What else can happen as a secondary effect of this?

Answer 13

• fatty plaque building up in the inner lining of coronary arteries, which become occluded (narrowed)
• minerals often become deposited in the plaque making it hard and rough

Question 14

What happens when a person has increasingly occluded arteries?

Answer 14

blood flow to cardiac muscles is restricted, causing chest pain.

Question 15

Which 5 factors have been shown to be associated with coronary artery disease? Are these causes?

Answer 15

• high blood cholesterol levels
• smoking
• high blood pressure (hypertension)
• high blood sugar levels, usually due to diabetes
• genetic factors (thus a family history of the disease)

these are likely causes