Cardiovascular 2

Question 1

Why does the heart not beat as soon as the sino atrial node generates and submits an action potential? (In a healthy person )

Answer 1

The SAN transmits to the AVN where there is a delay of around -120-200ms. (If longer than this, then there is a problem in the conduction)

Question 2

How many action potentials constitute one heart beat and how long does the action potential last for ?

Answer 2

1 heart beat = 1 action potential 
Each contraction (hence one action potential) is 280ms. Quite long.

Question 3

Describe the spread of excitation in systole

Answer 3

• SAN fires an AP which spreads over the atria causing atria systole.
• AP reaches the AVN where it’s delayed by 120ms
• then spreads down the septum between the ventricles
• then spreads through ventricular myocardium from endo to epicardium
• ventricle contracts from the apex upwards forcing blood out

Question 4

What is stroke volume ?

Answer 4

It is the amount of blood ejected per contraction of the ventricles.
It’s the difference between end diastolic volume and end systolic volume.

Question 5

Describe the pressure changes needed for each of the valves of the heart to open.

Answer 5

Aortic - LV pressure»_space; aorta
Mitral - LA pressure»_space; LV
Pulmonary - RV»_space; PA
Tricuspid - RA»_space; RV

Question 6

What is isovolumetric contraction ?

Answer 6

The part of the cardiac cell where the ventricles are contracting however the volume of the blood in the ventricles isn’t decreasing
- the outflow valves haven’t opened as the pressure generated isn’t high enough

Question 7

What is isovolumetric relaxation?

Answer 7

The part of the cardiac cycle where the ventricle pressure is atrial pressure. The ventricles are relaxing but they are not being filled by blood.

Question 8

What brings the endocardial tubes into the thoracic region?

Answer 8

Cephalocaudal folding of the embryo.

Question 9

What is the cardiogenic field and where does it lie?

Answer 9

This is the future heart and what the future blood vessels and blood cells develop from. It’s created during gastrulation and lies in the cranial end before folding occurs.

Question 10

In the primitive heart, where does blood enter and leave ?

Answer 10

Inflow through sinus venosus (caudal) and outflow through aortic roots (cranial)

Question 11

What are the different sections of the primitive heart?

Answer 11

From cranial to caudal;
Aortic roots (most cranial) 
Truncus arteriosus
Bulbus cordis
Ventricle
Atrium
Sinus venosus (most caudal)

Question 12

In the primitive heart tube, the inflow and outflow tracts are caudally and cranially respectively located. How is it that in the neonate the inflow is behind the outflow and both are cranially located?

Answer 12

Around day 23, folding occurs of the primitive heart tube.
The Cephalic portion bends ventrally, caudally and to the right
- IE forwards, downwards and to the right.

The caudal portion bends dorsally, cranially and to the left.
- IE backwards, upwards and to the left.

Question 13

After looping, how does the atrium communicate with the ventricle ?

Answer 13

Via the atrioventricular canal. This represents the first division of the atrium and ventricle.

Question 14

Describe in brief the development of the atria.

Answer 14

• Sinus venosus receives blood from all the placenta yolk sac and the embryo body.
• the R and L horns are both equal size but as blood going into the sinus venosus switches to the right horn, then the left horn slowly recedes. The right horn becomes absorbed by the enlarging right atria.

RA

• formed from most of the primitive atrium.
• absorbs the right horn of the sinus venosus.

LA

• formed from a small portion of the primitive atrium
• absorbs proximal portion of the pulmonary veins.

Question 15

How many aortic arches arise early in the arterial system and which paired branches recede completely ?

Answer 15

6 pairs of arched vessels

5th paired arched vessels recede completely.

Question 16

Which arched vessels go on to form the aorta and the proximal part of the right subclavian artery?

Answer 16

The 4th arch.

Question 17

What arched vessel goes on to form the right and left pulmonary retry as well as part of the ductus arteriosus

Answer 17

6th aortic arch.

Question 18

Why can thoracic pathology sometimes appear as a change in voice?

Answer 18

The laryngeal nerves:
Right laryngeal -descends to T1-T2 and then back up to innervate larynx

Left laryngeal - descends to T4-T5 and then ascends back up to the larynx. Hooks around the ductus arteriosus.

They are in the thoracic cavity and therefore sometimes they can become damaged or compressed by thoracic pathology hence a change in voice

Question 19

Where is the ductus arteriosus ?

Answer 19

Between the pulmonary artery and the aorta, distal to the branch to the head.

Question 20

Describe the properties of cardiac muscle

Answer 20

• striated
• intercalated disks
• centrally positioned nuclei (1 or 2 per cell)
• T Tubules in line with Z bands (not A I bands like skeletal)
• gap junctions for electrical coupling