Development of the heart & blood vessels

Question 1

List the stages of heart development

Answer 1

1) Formation of the 4 chambered heart tube
2) Cardiac looping
3) Division of the atrioventricular canal into left and right channels
4) Formation of the atrial septa
5) Formation of the conotruncal cushions and division of the outflow tract

Question 2

List the potential defects at each stage

Answer 2

1) Situs inversus
2) Dextocardia
3) Ventricular septal defect
4) Atrial septal defect - foramen ovale
5) Tetralogy of fallot

Question 3

Stages of human embryo development

Answer 3

1) Fertilised egg has 2 pronuclei - 1st sign of fertilisation
2) Developing embryo contains 6-8 cells 3 days after fertilisation
3) 5 days after fertilisation is is called a blastocyst and has approximately 100 cells

Question 4

Morula

Answer 4

Solid ball of cells formed as the zygote undergoes cleavage

Question 5

Early blastocyst

Answer 5

Hollow ball of cells with a fluid filled cavity

Question 6

Late blastocyst

Answer 6

Pre-embryo, with the embryonic disk, 2 layers of cells that become the embryo proper

Question 7

Gastrula

Answer 7

Embryo with 3 primary germ layers: ECTODERM, MESODERM, and ENDODERM

Question 8

Ectoderm

Answer 8

Skin (epidermis) brain spinal cord (CNS) sensory organs

Question 9

Mesoderm

Answer 9

Heart, skeletal muscle, kidneys, urogenital, connective tissue

Question 10

Endoderm

Answer 10

Lining of gastrointestinal tract and lungs, pancrease, liver

Question 11

18 days

Answer 11

Gastrulation

Question 12

Formation of the heart tube

Answer 12

18 days - heart develops from the primitive streak via the blood islands in the splanchinic mesoderm
20 days - the blood islands slowly form together into 2 tubes called CARDIOGENIC CORDS
22 days - further development gives rise to tube with asymmetric openings forming a arterial and venous end. Beginning of asymmetry in bulge to the left

Question 13

Situs inversus

Answer 13

congenital condition in which the major visceral organs are reversed or mirrored from their normal positions.

Question 14

Cardiac looping

Answer 14

22 days - the cells at each end of the heart proliferate making the tube longer. The entire structure is in a confined space so begins to fold up on itself
23 days/24 days - the primitive atrium loop up above and behind the primitive ventricle. The looping process brings the primitive areas of the heart into proper spatial relationship for development
35 days - The beating foetal heart can be seen on ultrasound. But the 4 interior chambers are not yet divided

Question 15

Dextrocardia

Answer 15

Rare heart condition in which your heart points toward the right side of your chest instead of the left side.

Question 16

Division of the atrioventricular canal

Answer 16

30 days - the left side of the atrium grows pulmonary veins sending growing veins to the developing lungs

SEPTUM PRIMUM - grows along the midsagital plane separating the atria except for a temporary space called the FORAMEN PRIMUM

A ventricular septum will eventually grow upwards to forming a division between the 2 ventricles. It will attach to the division between atria and ventricle

Question 17

Ventricular septal defect

Answer 17

During ventricular contraction some of the blood from the left ventricle leaks into the right ventricle, passes through the lung re-enters the left ventricle via the pulmonary veins and left atrium

Question 18

2 main effects of ventricular septal defect

Answer 18

1) Systemic circulation doesn’t receive all the blood being pumped by the left ventricle
2) Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension

Question 19

What is a cause of ventricular septal defect

Answer 19

Failure of the endocardial cushions to provide an anchor point for the developing ventricular septum

Question 20

Formation of the atrial septa

Answer 20

40 days - Initially, the temporary hole in the septum primum called the FORAMEN PRIMUM permits the right to left shunt of foetal blood, because there is no pulmonary circulation
This closes before a 2nd hole called the FORAMEN SECUNDUM opens

Anterior and posterior endocardial cushions have fused leaving left and right atrio-ventricular canals

43 days - septum secundum grows but leaves the FORAMEN OVALE, a space permitting the right to left shunt of blood

Septum primum - foramen secundum is partially obscured by the septum secundum, but foramen ovale remains providing an alternative left to right shunt the foramen primum is closed

ventricular septum grows to fuse with the now fused endocardial cushions

Question 21

SEPTUM SECONDUM

Answer 21

A 2nd more muscular and robust septum grows down from the roof of the atria just lateral to the septum primum. It obscures the place where the foramen primum was

Question 22

Separation of the ventricles results from the union of the:

Answer 22

Conotruncal septum
Endocardial cushions
Ventricular septum

Question 23

CONOTRUNCAL SEPTUM

Answer 23

Grows as a spiral down the CONUS ARTERIOSUS
Meets the endocardial cushions and the ventricular septum
All 3 of them makes the final full separation of the left and right sides

If misaligned - get differently sized aorta and pulmonary artery. Or it won’t meet with the endocardial cushion correctly giving rise to a septal defect - ultimate complication - TETROLOGY OF FALLOT

Question 24

PULMONARY STENOSIS

Answer 24

Spiral valve grown off centre so large aorta and small pulmonary artery, restricts blood to lungs

Question 25

OVERRIDING AORTA

Answer 25

Aortic opening is positioned over a ventricular septal defect allowing blood from both sides of the heart to enter the aorta, some deoxygenated blood pumped around the body

Question 26

VENTRICULAR SEPTAL DEFECT

Answer 26

During systole blood from the left ventricle leaks into the right ventricle, passes through the lungs and re-enters the left ventricle via the pulmonary veins and left atrium
Increases pressure in pulmonary circulation and also causes volume overload in left ventricle

Question 27

RIGHT VENTRICULAR HYPERTROPHY

Answer 27

Right ventricular wall increases in size to deal with obstruction in pulmonary artery

Question 28

DUCTUS ARTERIOSUS

Answer 28

Blood vessel connecting the main pulmonary artery to the proximal descending aorta. It allows most of the blood from the right ventricle to bypass the foetal fluid filled non functioning lungs
Upon closure at birth, it becomes ligementum arteriosum

Question 29

FORAMEN OVALE

Answer 29

Allows blood to enter the left atrium from the right atrium. Along with the ductus arteriosis it allows blood to bypass the pulmonary circulation
In most individuals, the foramen ovale closes at birth. It later forms the FOSSA OVALIS