Cardiovascular system: Lecture 8 - Development of the Cardiovascular System 2

Question 1

What is dextrocardia?

Answer 1

Dextrocardia is a rare heart condition in which your heart points toward the right side of your chest instead of the left side

Question 2

What causes dextrocardia?

Answer 2

Abnormal cardiac looping or may be induced during gastrulation (week 3) when laterality (left and right sides) is determined

Question 3

Should the apex of the heart be pointing to the right or left?

Answer 3

Left

Question 4

What is a ductus arteriosus?

Answer 4

The ductus arteriosus is a blood vessel in the developing foetus connecting the trunk of the pulmonary artery to the proximal descending aorta

It allows blood to bypass the lungs as the mother oxygenates blood for the foetus via the placenta

Question 5

Why does the ductus arteriosus close soon after birth?

Answer 5

Due to increasing oxygen tension and a decrease in circulating prostaglandins (cells contract)

Question 6

What is a patent ductus arteriosus and why is this dangerous?

Answer 6

Ductus arteriosus fails to close

• allows shunting of blood from aorta to pulmonary artery
• oxygenated blood travels back to the lungs then returns to the heart and has to be pumped out again (increases hearts workload)
• can lead to pulmonary hypertension (increase in BP in the pulmonary system), ventricular hypertrophy and heart failure

Question 7

How do we treat patent ductus arteriosus?

Answer 7

Treated with prostaglandin inhibitors - could begin closing of ductus arteriosus

Question 8

What are 2 causes of atrial septal defects?

Answer 8

1. Failure of the septum primum and secundum to fuse after birth e.g if the septum sucundum just dosen’t develop enough so we have excessive apoptosis
2. Malformations in the development septum primum or secundum such that they do not overlap and therefore leave a gap

So can have septal defects whether its through our foramen and secundum

Question 9

What is a probe patent foramen ovale?

Answer 9

• occurs in 1 in 4
• usually asymptomatic
• usually, higher pressure in LA pushes septum primum against septum secundum and mecanically shuts valve
• if there is high pressure in RA e.g pulmonary hypertension, this can push flimsy septum primum open and sllow blood to shunt from right to left
• could be a risk factor for stroke/migraine
• only opens if probed

Question 10

What are ostium (opening) secundum (second opening of atrial septum) defects caused by?

Answer 10

Can be caused by excessive apoptosis in septum primum or by inadequate development of septum secundum such as foramen ovale and foraemn secundum overlap

Question 11

What occurs in ostium secundum defects?

Answer 11

• Due to the difference in pressure, blood flows from the left to the right - can cause enlargement of right atrium and ventricle
• small defects may be asymptomatic, however larger defects may require surgical repair

Question 12

What is a common atrium?

Answer 12

• rare cardiac defect with complete absence of atrial septum
• failure of development of the septum primum and septum secundum

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Question 13

Why is the premature closure of the foramen ovale during prenatal life a cardiac defect that usually results in death shortly after birth?

Answer 13

-increased amount of blood on right side (and therefore less in the left) results in hypertrophy (enlargement) of the right side of the heart and undevelopment of the left side of the heart

Question 14

What are the most common congenital heart defects?

Answer 14

Ventricular septal defects - often associated with other congenital malformations e.g down’s syndrome

Question 15

Which two different parts of the ventricle can ventricular septal defects affect?

Answer 15

• the muscular part of the interventricular septum (often resolves as child grows)
• membranous part of the interventricular septum

Question 16

Why are ventricular septal defects dangerous?

Answer 16

• allows left to right shunting of blood
• can result in pulmonary hypertension and hypertrophy of right ventricle

Question 17

how is the conotruncal septum formed?

Answer 17

the conotruncal swellings that form the conotruncal septum rely in the migration of neural crest cells from the neural tube

Question 18

What can abnormal neural crest cell development or migration cause?

Answer 18

a number of defects in septation of the truncus arteriosus into pulmonary trunk and aorta

Question 19

Name 3 septation defects of the truncus arteriosus

Answer 19

1. persistent truncus arteriosus - one alpha tract
2. transportation of the great vessels - abnormal connections of the chambers of the heart
3. tetralogy of fallot

Question 20

What is a persistant truncus arteriosus?

Answer 20

• conotruncal septum completely absent therefore cannot fuse with interventricular septum - ventricular septal defect
• undivided truncus is in communication with both ventricles, recieves oxygenated and deoxygenated blood

Question 21

What are the symptoms of persistant truncus arteriosus?

Answer 21

• cyanosis (blue colour) at birth
• lethargy
• breathlessness
• delayed growth

all due to mixing of blood - tissues arent being perfused well enough with oxygenated blood

Question 22

What is transposition of great vessels?

Answer 22

• conotruncal septum does not form in spiral but instead runs straight down
• aorta arises from right ventricle and pulmonary artery from left ventricle (deoxygenated blood goes to body, oxygeanted blood goes back to lungs)
• incompatible with life unless an accompanying shunt such as a VSD, patent foramen ovale or patent ductus arteriosus exists
• similar symptoms persist to persistent truncus arteriosus including cynaosis but can borrected surgically

Question 23

What is the tetralogy of fallot?

Answer 23

4 abnormalities caused by the same primary deect

Question 24

What is the underlying cause of tetralogy of fallot?

Answer 24

Unequal division of the truncus arteriosus caused by anterior displacement of the aorticopulmonary septum

Question 25

What are the 4 classic defects in the tetralogy of fallot?

Answer 25

1. Pulmonary stenosis (slightly smaller pulmonary trunk)
2. Ventricular septal defect - membronous part of ventricular septum dosen’t form
3. Overriding aorta (rightward displacement of the aorta)
4. right ventricular hypertrophy caused by higher pressure on the right side

Question 26

What is coarctation of the aorta?

Answer 26

• narrowing of the aorta that occurs near the ductus arteriosus
• cause is unknown but may be due to abnormal migration of cells from the ductus arteriosus

Question 27

What are the two classifications of coarctation of the aorta?

Answer 27

Preductal (A) and postductal (B) in relation to ductus arteriosus

see last image

Question 28

Explain features of pre ductal coarctation of the aorta?

Answer 28

During development, the ductus arteriosus compensates for the narrowing

• After birth, the ductus arteriosus usually remains patent
• Obliteration of the ductus arteriosus causes rapid decline of infant with hypoperfusion of the lower body
• Can be treated by administering prostaglandins to keep ductus arteriosus open
• Differential cyanosis – upper body and head well perfused, lower body cyanotic

Question 29

What is postductal coarctation of the aorta?

Answer 29

More common than preductal

• During development, a collateral circulation is established to bypass the narrowing
• Blood passes through the subclavian arteries to the internal thoracic arteries to intercostal arteries to the descending aorta
• Internal thoracic and intercostal arteries enlarge to carry greater blood flow