Structure of heart 2 L8

Question 1

What is the direction of the oxygenated and deoxygenated blood?

Answer 1

Question 2

What is the mass of the heart that lies to the right of the midline of the body?

Answer 2

About two thirds to the left

Question 3

What is the direction of the apex?

Answer 3

Points inferiorly (down), anteriorly, and to the left

Question 4

Where is the right border formed?

Answer 4

Formed mainly by the right atrium

Question 5

Where is the inferior border formed?

Answer 5

Mainly by the right ventricle

Question 6

Where is the left border formed?

Answer 6

Mainly by the left ventricle

Question 7

Where is the superior border formed?

Answer 7

Blood vessels, base

Question 8

Pericardium

Answer 8

Serous membrane around the heart

Question 9

Pleura

Answer 9

Serous membrane around the lung

Question 10

Peritoneum

Answer 10

Serous membrane around the gut

Question 11

Name the pericadiums in order

Answer 11

Visceral pericardium -> pericardial space -> parietal pericardium -> fibrous pericardium

Question 12

What cells are found within the inner and outer wall of the pericardium?

Answer 12

Squamous mesothelial cells

Question 13

Answer 13

Question 14

Fibrous skeleton

Answer 14

The fibrous skeleton forms the foundation to which the heart valves are anchored. It consists of four fibrous rings (anuli fibrosi) that surround the bases of the heart valves: the mitral, tricuspid, aortic, and pulmonary valves. These rings provide structural support and maintain the proper shape and alignment of the valves.

The fibrous skeleton acts as an electrical insulator between the atria and ventricles. It prevents the direct spread of electrical impulses from the atria to the ventricles, ensuring that the heart’s electrical conduction system properly controls the timing of contractions. This insulation allows the atria to contract first, followed by the ventricles, which is crucial for efficient blood pumping.

Most support in high pressure areas - arteries

Question 15

SA node

Answer 15

The SA node is located in the right atrium, near the junction where the superior vena cava enters the heart.

The SA node is often referred to as the heart’s natural pacemaker because it generates electrical impulses that initiate each heartbeat. These impulses cause the atria to contract, pushing blood into the ventricles. The SA node typically fires at a regular rate, setting the pace for the entire heart, usually between 60 to 100 beats per minute in a resting adult.
Once the SA node generates an impulse, it spreads rapidly through the atria, causing them to contract. The electrical signal then travels to the AV node.

Question 16

AV nodes

Answer 16

The AV node is located in the lower part of the right atrium, near the atrioventricular septum, which separates the atria from the ventricles.

The AV node acts as a critical gateway between the atria and the ventricles. It receives the electrical impulses from the SA node and briefly delays them before transmitting them to the ventricles. This delay is crucial because it allows the ventricles enough time to fill with blood from the atria before they contract.

After the brief delay, the AV node sends the electrical impulses down the bundle of His, which branches into the right and left bundle branches, and then into the Purkinje fibers. This network ensures that the ventricles contract in a coordinated manner, pumping blood out of the heart.

Question 17

Speed of SA node to atrial muscle pathway

Answer 17

Slow 0.5m/sec

Question 18

Result of SA node -> atrial muscle

Answer 18

Even atrial contraction
(Remember stops at fibrous skeleton as it acts as an electrical insulator)

Question 19

Speed of Antrioventricular node

Answer 19

Very slow - 0.05 m/sec

Question 20

Result of Antrioventricular node

Answer 20

100 msec delay

Question 21

Speed of AV bundle to purkinje fibres

Answer 21

Fast - 5m/sec

Question 22

Result of AV bundle to purkinje fibres

Answer 22

Complete venti contraction - systole

Question 23

Stages of the cardiac cycle

Answer 23

Ventricular filling -> Atrial contraction -> Isovolumetric ventricular contraction (systole) -> Ventricular ejection -> Isovolumetric ventricular relaxation

Question 24

Ventricular filling

Answer 24

The phase commences as pressure in the ventricle drops below that in the atrium. The mitral valve opens quietly and blood enters the ventricle. The ventricle will fill to about 80% of its capacity during this phase.

Question 25

Atrial contraction (density of dots indicate pressure, while crosses indicate contraction of the cardiac muscle)

Answer 25

The left atrium contract to complete the filling of the ventricle. The rise in atrial pressure in small, for two reasons. Firstly, the atrial muscle layer is thin, and secondly there are no valves where the pulmonary veins enter the atrium, (and therefore nothing to prevent backflow into the veins)

Question 26

Isovolumetric ventricular contraction (systole) (density of dots indicate pressure, while crosses indicate contraction of the cardiac muscle)

Answer 26

The ventricle begins to contract. Blood within it lifts backwards towards the atrium and the mitral valve closes - first heart sound. Ventricular pressure is still below that in the aorta so the aortic valve remains closed. (atrial P < vent P (going up) < arterial P). For this brief period of rising pressure the ventricle is isolated from the rest of the circulation, with both its inlet and outlet valves closed.

Question 27

Ventricular ejection (density of dots indicate pressure, while crosses indicate contraction of the cardiac muscle)

Answer 27

Systole (contraction) continues, but now ventricular pressure exceeds aortic pressure and the aortic valve cusps open quietly. Blood leaves the ventricle. Because blood is ejected into the aorta faster than it can run-off into the distributing arteries, the pressure in the ventricle and aorta continues to rise steeply; but later in this phase the rate of ejection falls below the rate of run-off, and aortic and ventricular pressures level-off and then begin to decrease.

Question 28

Isovolumetric ventricular relaxation

Answer 28

The ventricle relaxes, as it does so ventricular pressure drops suddenly, flow reverses in the aorta and the aortic valve closes (second heart sound) as blood tries to re-enter the ventricle. The mitral valve is now closed because ventricular pressure, although failing, still exceeds atrial pressure （atrial P < vent P < arterial P). For a brief period the ventricle is again isolated from the rest of the circulation. When this phase is completed the heart re-enters the stage of ventricular filling.