The Heart

Question 1

What are the heart strings of the heart called?

Answer 1

The Chordae Tendinae

Question 2

What are the three major cell type layers of the heart?

Answer 2

Endocardium, Myocardium and Pericardium.

Question 3

What are the three main functions of the pericardium?

Answer 3

1) It fixes the heart and limits it’s movement.
2) It protects the heart against infection.
3) It lubricates the heart.

Question 4

Why does left ventricle have the thickest myocardium (walls)?

Answer 4

The left ventricle is thicker because it needs to pump blood to most of the body (the right ventricle needs to only fill the lungs).

Question 5

What is the major gap junction of the ventricles and atria?

Answer 5

Ventricles = Connexin 43

Atria = Connexin 40

Question 6

What is the ability of the heart to generate signals that trigger contraction on a periodic basis?

Answer 6

It is termed “autorhythmicity”.

Question 7

What are the two types autorhythmic cells and what are their functions?

Answer 7

Pacemaker cells function to initiate action potentials in the SA and AV nodes.

Conduction fibres (i.e Purkinje fibres) function to transmit action potential through the heart.

Question 8

What is a “funny current”?

Answer 8

A funny current is a slow inward Na+ current that gradually depolarises the membrane.

Question 9

What is the affect of adrenaline on the heart?

Answer 9

It acts on the SA node to increase heart rate.

It acts on the ventricles to increase contractility.

Question 10

What effect does the vagus (parasympathetic) nerve have on the heart?

Answer 10

It acts the decrease heart rate.

Question 11

What effect does sympathetic nerves have on the the heart rate?

Answer 11

It increase heart rate and increase contractility.

Question 12

What is a “Funny Current”?

Answer 12

It is a slow inward Na+ current that gradually depolarises the membrane.

Question 13

Which gene encodes the funny channel expressed in the SA node?

Answer 13

The HCN4 gene.

Question 14

How is the funny current activated?

Answer 14

It is activated by cAMP e.g. β-adrenoceptor stimulation.

Question 15

What two beta-blockers are able to increase the heart rate and reduce the heart rate?

Answer 15

Isopernaline stimulates heart rate and Atenolol reduces heart rate.

Question 16

How do you work out the cardiac output?

Answer 16

Cardiac output = stroke volume x heart rate

Question 17

What affect does increased sympathetic activity have on Ventricular Contractility?

Answer 17

Increase sympathetic activity will result in an increase in epinephrine (adrenaline) release, causing an increase in both the strength and rate of contractility.

Question 18

How does the release of epinephrine (adrenaline) result in an increase in Ventricular Contractility?

Answer 18

Epinephrine causes the release of protein kinase A (PKA). Protein kinase increases the probability of the L-type Ca2+ channels and Ryanodine receptors, opening. It also increases the rate of Ca2+ dissociation from troponin, and increases Ca2+ re-uptake to the sarcoplasmic reticulum.

Question 19

The Frank Sterling Effect is an intrinsic control mechanism of the heart. What is the Frank-Starling Law of the Heart?

Answer 19

The Law represents the relationship between the stroke volume and end-diastolic volume. It states that the stroke volume will increase in response to an increase in the volume of blood in the ventricles before contraction (end-diastolic volume), when all factors remain constant.

Question 20

Why does an increased end-diastolic volume result in an increased stroke volume?

Answer 20

An increased end-diastolic volume of blood will stretch the muscle fibres to their optimum length. Muscle fibres at their optimum length will have a greater force of contraction, thus resulting in an increased stroke volume.

Question 21

What are the factors that influence the End-Diastolic volume?

Answer 21

The filling time, atrial pressure,

Question 22

How do you calculate the total blood flow along a vessel?

Answer 22

Blood flow = pressure difference x resistance.

Question 23

What is the Baroreceptor Reflex?

Answer 23

It is the body’s homeostatic mechanism that helps to maintain blood pressure. it provides a negative feedback loops in which an elevated blood pressure reflexively causes the heart rate to decrease.

Question 24

What determines the response of baroreceptors to blood pressure changes?

Answer 24

The frequency of action potentials.