Development of the Heart Flashcards
What are some achievements of early embryonic development
The first two weeks created tissues of the future embryo and future placenta…
The third week created the three germ layers
– ectoderm, mesoderm and endoderm
– the primordia of all tissues
The fourth week created a recognisable body form and the mesoderm began to organise
Describe the positioning of the cardiogenic area prior to folding
What does lateral and cephalocaudal folding of the heart achieve?
Lateral folding
– Creates a heart tube
Cephalocaudal folding
– Brings the tube into the thoracic region
Pair of heart tubes pushed together form primitive heart tube (lateral folding).
and then pushed into pericardial cavity (cephalocaudal)
How is primitive heart tube held in pericardial cavity?
Describe the structure of the primitive heart tube
Describe the initial looping of the primitive heart tube
Continued elongation results in bending – begins ~d23, complete ~d28
• Cephalic portion
– ventrally, caudally & to the right
• Caudal portion
– dorsally, cranially & to the left
What does looping achieve, with respect to inflow and outflow?
What are the general outcomes of looping?
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Label the heart as it would look on day 28
How does the atrium communicate with the ventricle, following looping?
via atrioventricular canal
Describe the development of the sinus venosus
Give a general overview of the development of the atria
Describe the development of the left atirum
How is the oblique sinus formed?
Oblique pericardial sinus formed as left atrium expands absorbing the pulmonary veins
Describe fetal circulation
Lungs are non-functional
Receives oxygenated blood from mother via placenta and umbilical vein
By-passes the lungs
Returns to the placenta via umbilical arteries BUT the change in circulation must happen immediately
Describe shunts in the foetal circulation
How are the aortic arches formed?
4th arch
R = proximal part of R subclavian A
L = arch of aorta
6th arch = “pulmonary arch”
R = R pulmonary artery
L = L pulmonary artery & Ductus Arteriosus
What are the recurrent laryngeal nerves?
Each aortic arch has a corresponding nerve.
The nerve corresponding to the 6th is the recurrent laryngeal nerve (br vagus, CN X)
– right descends to T1-T2, & left descends to T4-T5
Two factors influence the course of the nerve on left & right sides
– caudal shift of the developing heart & expansion of the developing neck region
– the need for a fetal shunt between PT & aorta
What happens as the heart “descends”, with regards to the aortic arches?
The aortic arches are remodelled to create the mature disposition.
As the heart “descends” the nerve hooks around the 6th aortic arch and “turns back on itself”, the left recurrent laryngeal nerve becomes hooked around the shunt between the PT & aorta
What are endocardial cushions?
Endocardial cushions – developing in the atrioventricular region
Divide the developing heart into right & left channels
Describe the process of atrial septation
Septum primum grows down towards the fused endocardial cushions.
The ostium primum is the hole present before the septum primum fuses with the endocardial cushions.
Before ostium primum closes, a second hole, the ostium secundum appears in the septum primum (via apoptosis)
Finally a second crescent shaped septum, the septum secundum grows; the hole in the septum secundum is the foramen ovale.
Describe remnants of atrial embryonic development
Both left & right atria have components derived from the primitive atrium (i.e. auricles)
The right atrium absorbs the sinus venosus
The left atrium sprouts the pulmonary vein then
grows to absorb it and its first 4 branches
The fossa ovalis is the adult remnant of the shunt used in utero to by-pass the lungs
What are the components of the ventricular septum?
Ventricular septum has 2 components:
– Muscular
– Membranous
• Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions
How is the primary interventicular foramen formed?
Muscular portion grows upwards towards the endocardial cushions leaving a small gap, the 1° interventricular foramen
How is the primary interventricular foramen formed?
Membranous portion of the interventricular septum formed by connective tissue derived from endocardial cushions to “fill the gap”
Describe septation of the outflow tract
Endocardial cushions also appear in the TA. As they grow towards each other they twist around each other they form a spiral septum
Describe the differences in foetal circulation and circulation post-birth?
How is the foramen ovale closed at birth?
What happens to the fetal shunts?
What are the differences between the foetal heart and the developed heart?
