Session 3 - Heart Development (2)

Question 1

What does the following embryonic structure form in adult heart? Ductus Arteriosus

Answer 1

Ligamentum arteriosum

Question 2

What does the following embryonic structure form in adult heart? Foramen ovale

Answer 2

Fossa ovalis

Question 3

Why is the LA smooth?

Answer 3

Due to its absorption of the pulmonary veins

Question 4

Why is the RA trabeculated?

Answer 4

Due to its formation from the primordial atrium - also absorbs sinus venosus

Question 5

What does the following embryonic structure form in adult heart? Primitive atrium

Answer 5

Left and right auricles

Question 6

Describe the initial process of septation

Answer 6

* Neural crest cells form the endocardial cushions which develop in the atrioventricular region * These grow towards one another and divide the developing heart into right and left channels

Question 7

What needs to happen after the heart has been developed into right and left channels?

Answer 7

Atria, ventricles and outflow tract must be divided.

Question 8

What happens in the outflow tract during septation?

Answer 8

In outflow tract: endocardial cushions also appear in the truncus arteriosus, as they grow towards each other they twist around each other to form a spiral septum

Question 9

Give four steps of inter-atrial septation

Answer 9

1. Septum primum grows down towards the fused endocardial cushions 2. The ostium primum is the first hole present before the septum primum fuses with the endocardial cushions 3. Before the ostium primum closes, a second hole, the ostium secundum appears in the septum primum via apoptosis 4. Finally a second crescent shaped septum, the septum secundum grows,; the hole in the septum secundum is the foramen ovale

Question 10

What are the two components of the ventricular septum?

Answer 10

* Muscular * Membranous

Question 11

Describe fromation of the interventricular septum

Answer 11

1. Muscular portion grows towards the endocardial cushions leaving a small gap – the 1° interventricular foramen 2. Membranous portion of the interventricular septum formed by connective tissue derived from endocardial cushions to “fill the gap”

Question 12

How are the lungs bypassed in foetal circulation?

Answer 12

Via foramen ovale, a right to left shuntq

Question 13

In utero, how does left atrial pressure compare to right?

Answer 13

In utero: pressure LA < pressure RA

Question 14

What occurs at first breath?

Answer 14

At birth: first breath causes pressure LA > pressure RA Þ septum primum pushed against septum secundum. Foreman ovale shuts.

Question 15

What does the foramen ovale become after birth?

Answer 15

Fossa ovalis

Question 16

What does the ductus arteriosus become after birth and why?

Answer 16

* Ductus arteriosus > ligamentum arteriosum o At birth, high oxygen in the lungs and reduced pulmonary vascular pressure trigger closure

Question 17

What happens to ductus venosus after birth?

Answer 17

Ligamentum venosum

Question 18

What happens to the umbilical vein after birth

Answer 18

Ligamentum teres

Question 19

What is A?

Answer 19

The foramen ovale

Question 20

What is the location and purpose of the foramen ovale?

Answer 20

The foramen ovale is formed from two holes in the septum primum and septum secundum in the atrial septum. Its purpose is to provide allow blood to move from the right atrium to the left, down a pressure gradient.

Question 21

What is B?

Answer 21

The ductus arteriosus

Question 22

What is the ductus arteriosus and what is its purpose?

Answer 22

The ductu arteriosus is a blood vessel connecting the pulmonry artery to the aortic arch. Allows most of the blood from the right ventricle to bypass the lungs in the foetus

Question 23

What is C?

Answer 23

The ductus venosus

Question 24

Where is C found, and what is its purpose?

Answer 24

The ductus venosus shunts half of the blood flow from umbilical veins to inferior vena cava, thus avoiding the liver.