Lecture 5+6

Question 1

What does the heart develop from?

Answer 1

cardiogenic mesoderm

Question 2

3rd week of development

Answer 2

formation of the heart tubes (angioblastic cords/endothelial strands)

heart tubes will fuse to form the tubular heart

Question 3

Epicardium, myocardium, and endocardium development

Answer 3

Epi: from mesothelial cells arising from the external surface of the sinus venosus

myo: from myoblasts from the first heart field
endo: from the primitive heart tube

Question 4

Transverse pericardial sinus

Answer 4

communicates between both sides of the pericardial cavity

formed from the degeneration of the central part of the dorsal mesocardium

in adult: posterior to aorta and pulmonary trunk, anterior to SVC

Question 5

Subdivisions of the tubular heart?

Answer 5

1. truncus arteriosus
2. bulbous cordis
3. primitive ventricle
4. primitive atrium
5. sinus venosus (receives paired veins)

Question 6

Cardiac looping

Answer 6

days 23-28

Bulbus cordis and ventricle grow faster than other regions causing it to bend on itself

Question 7

Dextrocardia and situs inverus

Answer 7

dextrocardia:
The L-loop positions the apex to the right instead of the left (D-loop, normal)

situs inverus:
major organs are reversed

Question 8

Fate of the primitive atrium

Answer 8

becomes the right and left auricle

internal surface has a rough, trabeculated appearance

Question 9

Fate of the left and right horns of the sinus venosus

Answer 9

left horn - mostly obliterates
remnants: the coronary sinus and the oblique vein of the LA

right horn - seen as the sinus venarum
smooth-walled part of RA

Question 10

fate of the primitive ventricle

Answer 10

Trabeculated part of the wall of the right and left ventricles

Question 11

Fate of the bulbous cordis

Answer 11

Majorly contribute to form outflow tracts of the right and left ventricles

• Right – conus arteriosus (infundibulum)
• Left – Aortic vestibule

Question 12

Fate of the truncus arteriosus

Answer 12

left = ascending aorta

right = pulmonary trunk

Question 13

End of the 4th week

Answer 13

partitioning of the AV canal:

AV endocardial cushions develop from the cardiac jelly and neural crest cells

the endocardial cushions grow towards each other and fuse (forms AV valves)

Question 14

Formation of the right atrium and left atrium

Answer 14

Right atrium:
The right horn of the sinus venosus and the primitive atrium enlarge. The primitive atrium absorbs the right horn, thus forming the RA. Later becomes the sinus venarum.

Left atrium:
Primordial pulmonary veins forms the left atrium. These veins are incorporated into the walls of the LA.

Forms the oblique pericardial sinus which is an area of pericardium between the pulmonary veins

Question 15

arterial partitioning (end of 4th week)

Answer 15

The septum primum grows from the roof of the atrium towards the endocardial cushions

foramen primum - space between inferior edge of septum primum and endocardial cushions.
The growth of the septum primum closes the foramen primum

foramen secundum: appear in septum primum
septum secundum grows downward, eventually overlapping foramen secundum

The opening between the free edges septum secundum and septum primum is called foramen ovale

Question 16

Ostium secundum defect (atrial defect)

Answer 16

In the area of the fossa ovale

disrupted or absent septa
defects of both septa primum and secundum

usually leads to an patent/open foramen ovale

Question 17

Endocardial cushion defect with a foramen primum defect (atrial defect)

Answer 17

septum primum - not fused with endocardial cushions

patent foramen primum defect

Question 18

Sinus venosus defect (atrial defect)

Answer 18

located in the sinus venarum

Defect:
• incomplete resorption of the right horn of sinus venosus into the right atrium
•abnormal development of the septum secundum
• or a combination of these factors

Question 19

Common atrium (ASD)

Answer 19

Prevalent in patients with ostium primum, ostium secundum and sinus venosus defects

Complete absence of interatrial septum

Question 20

Partitioning of the common ventricle

Answer 20

Muscular interventricular septum develops first from myocytes from the primitive ventricle.

IV foramen allows for the communication between the right and left ventricles

Question 21

Week 5

Answer 21

The bulbar ridges and truncal ridges will fuse to form the aorticopulmonary septum

this septum divides the truncus arteriosus and bulbous cordis into the pulmonary trunk and ascending aorta

Question 22

The two types of VSD’s

Answer 22

Muscular:
No muscular septum results in a common ventricle
occurs anywhere throughout the septum (in isolation or “swiss cheese”)

membraneous: Most common
No membranous septum - incomplete closure of the IV foramen

Question 23

What cardiac structures are derived from neural crest cells

Answer 23

1. endocardial cushions
2. bulbar ridges
3. truncal ridges
4. spiral septum
5. membranous interventricular septum
6. semilunar valves
7. AV valves
8. pharyngeal arches

Question 24

What does increasing the resting muscle fiber length do?

Answer 24

increases the force of contraction (length-tension relationship)

this is done by increasing the preload such as blood volume

Question 25

How can one increase the amount of force from a given length with no change in preload

Answer 25

Norepinephrine (NE) (beta-1 activation)
increases contractility (+ inotropic effect)
greater tension
increase Vmax

Question 26

How do calcium blockers impact contractility

Answer 26

decreased contractility (- inotropic effect)
less tension
decrease Vmax