Embryology

Question 0

Where does the primitive heart receive blood from?

Answer 0

At its caudal pole (inflow) and the blood flows out (outflow) from the cranial pole

Question 1

When is the cardiogenic field created?

Answer 1

During gastrulation and initially it lies at the cranial end of the embryo.

Question 2

Describe the segments of the primitive heart

Answer 2

Aortic roots A
Truncus arteriosus Tad
Bulbus cordis Bit
Primitive ventricle Vicious
Primitive atrium and sinus venosus Allan

Question 3

How is the heart tube created?

How is the tube brought into the thoracic region?

Answer 3

Lateral folding

Cephalocaudal folding

Question 4

What is the point of looping?

Answer 4

It puts the primordium of the right ventricle closest to the outflow tract, primordium of the left ventricle closest to inflow tract and atrium dorsal to the bulbus cordis. (i.e. inflow is dorsal to outflow)

Baso - places inflow & outflow cranially with the inflow dorsal to outflow

Question 5

What does the primitive atrium form?

Answer 5

Small component of each atrium (muscular/rough parts)

Question 6

What does the bulbus cordis form?

Answer 6

Gives rise to the smooth part of the right ventricle

Question 7

What does the primitive ventricle form?

Answer 7

Muscular/rough part of the left ventricle

Question 8

What does the truncus arteriosus form?

Answer 8

Gives rise to roots and proximal portions of the pulmonary trunk and aorta

Question 9

Describe the development of the sinus venosus

Answer 9

Right and left sinus horns initially equal in size. Venous return shifts to RHS, L sinus horn recedes. Right sinus horn is absorbed by enlarging RA.

Question 10

What gives rise to the left atrium?

Answer 10

As well as the primitive atrium, the left atrium is partly formed by absorbed primordial pulmonary vein tissue

Question 11

What is the oblique sinus?

Answer 11

The oblique pericardial sinus is formed as the left atrium expands, absorbing the pulmonary veins.

Question 12

How does the foetus receive oxygenated blood?

Answer 12

From mother via placenta and umbilical vein. Blood by-passes the foetal lungs (they aren’t functional at this point) and returns to the placenta via umbilical arteries but foetal heart needs to work to develop muscular tone

Question 13

What is the purpose of the aortic arches?

Answer 13

They are the basis of the vessels. Begins as a bilaterally symmetrical system of arched vessels. Undergoes extensive remodelling to create the major arteries leaving the heart.

Question 14

What is the sixth arch of the aortic arches and what does it create?

Answer 14

Pulmonary arch.
R - R pulmonary artery
L - L pulmonary artery and Ductus Arteriosus

Question 15

Which nerve supplies the sixth aortic arch?

Answer 15

Recurrent laryngeal nerve

Question 16

Describe the recurrent laryngeal nerves position and explain how it got like that

Answer 16

As the aortic arches are remodelled to create the mature formation, the heart ‘descends’ and the nerve hooks around the 6th aortic arch. It therefore turns back on itself when returning. Left recurrent laryngeal nerve becomes hooked around the shunt between the pulmonary trunk and the aorta.

Question 17

Define septation

Answer 17

Process in which the primitive heart tube divides into chambers and the outflow tract is subdivided into pulmonary trunk and the aorta

Question 18

How is the atrioventricular canal formed?

Answer 18

Junction between the atrium and the ventricles becomes constricted, creating a narrow channel

Question 19

How is the heart divided?

Answer 19

Endocardial cushions form in the region of the atrioventricular canal and provide a platform toward which the septa grow inferiorly or superiorly, dividing the heart into left and right hand sides.

Question 20

What is the foramen ovale?

Answer 20

A right to left shunt which is needed in utero but must be instantly sealed after birth (fossa ovalis)

Question 21

Describe the division of the common atrium

Answer 21

Septum primum grows towards the fused endocardial cushions. Ostium primum is the hole present before the septum primum does so. A second hole, ostium secondum, appears in the septum primum before the atrium primum closes. A second, crescent shaped septum (septum secundum) grows.

Question 22

What are the auricles?

Answer 22

An area derived from the primitive atrium, present on both the left and right atria.

Question 23

Describe ventricular septation

Answer 23

Two components –> muscular and membranous. Muscular - forms most of the septum and grows up towards the fused endocardial cushions, leaving a small gap (primary interventricular foramen). Membranous - connective tissue derived from endocardial cushions to ‘fill the gap’.

Question 24

What does the foramen ovale become in an adult?

Answer 24

Fossa ovalis

Question 25

What does the ductus arteriosus become in an adult?

Answer 25

Ligamentum arteriosum

Question 26

What does the ductus venosus become in an adult?

Answer 26

Ligamentum venosum

Question 27

What does the umbilical vein become in an adult?

Answer 27

Ligamentum teres (hepatis)

Question 28

What is the function of the umbilical vein?

Answer 28

Provides oxygenated blood to the foetus

Question 29

What are the layers of heart muscle?

Answer 29

Endocardium (endothelial and subendothelial lining)
Myocardium
Epicardium (serous layer of visceral pericardium)
Pericardial cavity
Parietal layer of serous pericardium
Fibrous pericardium

Question 30

Which germ layer does the heart originate from?

Answer 30

The mesoderm

Question 31

What can cause heart murmurs during systole?

Answer 31

Aortic stenosis, mitral regurgitation

MRSAS - mitral regurgitation, systole, aortic stenosis

Question 32

What causes murmurs in diastole?

Answer 32

Aortic regurgitation and mitral stenosis

DARMS - diastole, aortic regurgitation and mitral stenosis

Question 33

Describe the right atrium’s composition

Answer 33

Sinus vinera - smooth –> SVC/IVC (from sinus venosus)
Fossa ovalis (remnant of foramen ovale) - round depression in septum between atria
Muscular portion of RA - auricle

Question 34

What does the sinus venosus form?

Answer 34

Smooth part of right atrium

Question 35

Describe the route of the recurrent laryngeal nerve

Answer 35

The route is slightly different on both sides of the body. On the right side, the nerve loops under the right subclavian artery before its ascent to the larynx whereas the left recurrent laryngeal nerve loops beneath the aorta.

Question 36

How are the primitive ventricles separated?

Answer 36

The primitive ventricle becomes divided by a septum (the septum inferius or ventricular septum) which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow.

Question 37

What are the three shunts present in the embryo?

Answer 37

Foramen ovale
Ductus arteriosus
Ductus venosus

Question 38

What is the role of the ductus arteriosus?

Answer 38

It connects the pulmonary artery to the proximal descending aorta, by passing the lungs.

Question 39

What is the role of the ductus venosus?

Answer 39

Shunts most of the left umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver.

Question 40

What is the role of the foramen ovale?

Answer 40

It allows blood to enter the left atrium from the right atrium.