Embryology Of The Heart

Question 1

Describe the heart tube formation and compartments. What does each form?

Answer 1

The heart tube begins as 2 tubes which fuse and then fold. Sinus venosus, atrium, ventricle, bulbous cordis and truncus arteriosum.
Smooth wall of R atrium, SAN and coronary sinus
Rough walls of both atria
Both ventricles
Outflow tract
Aorta and pulmonary trunk

Question 2

Describe the process of atrial separation

Answer 2

Septum prinum, foramen prinum, foramen secundum (via controlled apoptosis), septum secundum, foramen ovalis

Question 3

Describe the process of ventricular septation

Answer 3

A muscular growth from the ventricular floor. Met by membranous growth from the bulbar ridges and from the endocardial cushion. Multiple contributing parts means there is greater risk of defects - particularly in the membranous part of the septum.

Question 4

Describe the embryonic aortic arches and their relation to the pharyngeal arches. Explain how great vessel asymmetry arises.

Answer 4

Growth from the aortic sac, initially paired vessels but some degenerate. The embryonic aortic arches sit within their corresponding pharyangeal arch (1-6, no 5). Only 3, 4 and 6 persist. The R side of the 6th embryonic aortic arch degenerates. The L side forms the ductus arteriosum.

Question 5

Describe the function of the ductus arteriosum and the defects that result if it does not close after birth

Answer 5

Functions to shunt blood from the right ventricle to systemic circulation, allowing blood to bypass the non-functioning lungs. If it fails to shut the oxygenated blood of the aorta will travel into the pulmonary trunk (due to the pressure within the aorta being greater than that in the pulmonary trunk).
Prostaglandins may be used to keep it open in heart defects.
Theory that the remnant may be the cause of aortic coarctation (narrowing).

Question 6

Describe the pericardial layers

Answer 6

Fibrous pericardium
Parietal serous pericardium
Visceral serous pericardium

Question 7

Describe the surfaces of the heart

Answer 7

Base (LA)
Left and right pulmonary
Anterior (costal)
Inferior (diaphragmatic)

Question 8

Describe the function of the foramen ovale

Answer 8

The foramen ovale forms a valve between the right and left atria. The valve allows blood to shunt from the high pressure right atria to the left, allowing foetal blood to bypass the non-functioning lungs of the foetus.

Question 9

Describe the function of the ligamentum arteriosum

Answer 9

A connective vessel seen between the pulmonary trunk and the aorta. Acts to allow foetal blood to by pass the non-functioning lungs.

Question 10

Describe the function of the sinus venosum

Answer 10

A vessel arising from the umbilical cord which allows blood to bypass the liver within the foetus. This allows blood to reach foetal circulation sooner.

Question 11

Changes in circulation at birth

Answer 11

At birth the first breath of the baby causes resistance within the lungs to decrease as the capillaries of the alveoli dilate. This also causes the pressure in the left ventricle and atria to decrease.
The pressure within the left side of the heart increases, These changes cause the foramen ovale to close.

Question 12

State the days at which atrial and ventricular septation are complete

Answer 12

Atrial: Day 34
Ventricular: Day 38