Embryology

Question 1

How is the primitively heart tube moved into the thoracic region?

Answer 1

By cephalocaudal folding

Question 2

From the cranial to caudal end of the primitively heart tube, name its regions

Answer 2

Aortic roots; truncus arteriosus; bulbus cordis; ventricle; atrium; sinus venosus

Question 3

What direction is blood pumped through the primitively heart tube?

Answer 3

Caudal to cranial

Question 4

Describe how the primitively heart tube loops

Answer 4

• Cephalic, cranial portion bends centrally, caudally and to the right
• Caudal portion bends dorsally, cranially and to the left

Question 5

What does looping of the primitively heart tube achieve?

Answer 5

• Places the inflow and outflow cranially with the inflow behind the outflow
• Causes atrium to communicate with the ventricle via the atrioventricular canal
• Transverse pericardial sinus is formed

Question 6

What is the transverse pericardial sinus?

Answer 6

The space behind the inflow and in front of the outflow of the heart through which an object can be inserted

Question 7

How does the sinus venosus develop

Answer 7

• Initially left and right sinus horns are equal in size
• As venous return shifts to the right the left sinus horn recedes
• Enlarging right atrium absorbs the right sinus horn

Question 8

Describe the development of the right atrium

Answer 8

• Develops from most of the primitively atrium

- Absorbs the right horn of the sinus venosus

Question 9

Describe the development of the left atrium

Answer 9

• Develops from a small portion of the primitively atrium

- Absorbs the proximal parts of the pulmonary veins

Question 10

What is the left auricle?

Answer 10

The remainder of the primordial atrium in a fully developed heart, it is situated in the bottom of the left atrium

Question 11

What is the oblique pericardial sinus?

Answer 11

The oblique sinus found around the back of the heart

Question 12

How is the oblique pericardial sinus formed?

Answer 12

Formed when the left atrium expands and absorbs the pulmonary veins

Question 13

What does the 4th aortic arch develop into?

Answer 13

• Right arch develops into the proximal part of the right subclavian artery
• Left arch develops into the arch of the aorta

Question 14

What does the 6th aortic arch develop into?

Answer 14

• Right arch develops into the right pulmonary artery

- Left arch develops into the left pulmonary artery and Ductus Arteriosus

Question 15

How do the great vessels develop?

Answer 15

• Early arterial system begins as a bilaterally symmetrical system of arched vessels
• Vessels undergo remodelling to create major vessels
• 6 aortic arches develop into vessels but aortic arch 5 has no derivatives

Question 16

How does separation occur in the heart?

Answer 16

• Constriction between the primitively atrium and ventricle (atrioventricular canal) creates the first division
• Endocardial cushion develops on the dorsal and ventral sides of the atrioventricular canal
• Endocardial cushions grow towards each other to divide the heart into right and left channels

Question 17

After division of the common atrium which holes are present?

Answer 17

• Ostium primum is the hole present before the septum primum fuses with the endocardial cushions
• Ostium secundum appears in the septum primum via apoptosis before the ostium primum closes
• Foramen ovale appears in the septum secundum

Question 18

How does atrial septation occur?

Answer 18

• Septum primum grown down towards the fused endocardial cushions
• Septum secundum grown in a crescent shape

Question 19

What is the purpose of the holes present after atrial septation?

Answer 19

Allows right to left shunting of blood

Question 20

What is the fossa ovalis?

Answer 20

The adult reminant of the shunt used to bypass the lungs in utero

Question 21

Describe ventricular septation

Answer 21

• Muscular portion of the septum grows up towards the fused endocardial cushions and forms the majority of the septum
• Membranous portion is derived from the spiral septum that grows to separate the truncus arteriosus
• Membranous septum fills the gap above the muscular septum and closes the primary interventricular foramen

Question 22

Describe foetal circulation

Answer 22

• Lungs are non-functional so little blood flows through them
• Foetus receives oxygenated blood via the placenta and umbilical vein
• Deoxygenated blood bypasses the lungs and returns to the placenta via the umbilical arteries

Question 23

What is the ductus venosus?

Answer 23

Vessel which transports oxygenated blood from the placenta to the inferior vena cavae in a foetus

Question 24

What is the ductus arteriosus?

Answer 24

Vessel which allows blood to pass from the pulmonary trunk to the aorta in a foetus

Question 25

WHat is the remnant of the foramen ovale in an adult?

Answer 25

Fossa ovalis

Question 26

What is the remnant of the ductus arteriosus in an adult?

Answer 26

Ligamentum arteriosum

Question 27

What is the remnant of the ductus venosus in an adult?

Answer 27

Ligamentum venosum

Question 28

What is the remnant of the umbilical vein in an adult?

Answer 28

Ligamentum teres

Question 29

How is the primitively heart tube formed?

Answer 29

• Pair of endocardial tubes develop from the cardiogenic field
• Lateral folding puts the endocardial tubes together to create the heart tube