Session 3 Flashcards

1
Q

In which week of embryonic development does folding occur?

A

4th week

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2
Q

The cardiogenic field is an area of what type of embryonic tissue?

A

Mesoderm

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3
Q

What happens in the cardiogenic field to begin the development of the heart?

A

The beginnings of differentiation start and blood islands appear

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4
Q

What are blood islands?

A

Areas of differentiating cells in the cardiogenic field that have the capacity to make blood cells/vessels/heart muscle

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5
Q

How is the primitive heart tube formed?

A

2 endocardial tubes with blood islands exist in the embryo before it folds.
As the embryo folds, the tubes meet at the midline and fuse to from a single primitive heart tube

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6
Q

What are some possible causes of congenital heart defects?

A

Genetic

Exposure to chemicals/drugs/infectious agents

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7
Q

Describe the basic structure of the primitive heart tube

A

Effectively a modified blood vessel with an inlet and outlet

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8
Q

Describe the different parts of the primitive heart tube from inlet to outlet

A
Sinus venosus 
Atrium 
Ventricle 
Bulbus cordis 
Truncus arteriosus 
Aortic roots
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9
Q

What does the sinus venosus consist of?

A

4 inlet tubes

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10
Q

How does blood flow in the primitive heart tube?

A

Straight from inlet to outlet with nothing to regulate the flow - simple contractile tube

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11
Q

When does cardiac looping take place? What is cardiac looping? What is its function?

A

When the primitive heart tube elongates and runs out of room

The twisting and folding up of the primitive heart tube

Places the inflow and outflow of the heart in the correct orientation

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12
Q

What part of the primitive heart tube does the right atrium develop form?

A

Most of the primitive atrium and a small part of the sinus venosus

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13
Q

What part of the primitive heart tube does the left atrium develop from?

A

A small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins

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14
Q

Which atrium has smooth walls? Why?

A

Left atrium

Absorbs parts of the proximal pulmonary veins

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15
Q

Do the lungs work in a foetus?

A

No - no gas exchange can take place

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16
Q

Where does oxygenation and removal of carbon dioxide from the blood take place in a foetus?

A

At the placenta

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17
Q

What structures are required to maintain fetal life with regards to the blood circulation in a foetus?

A

Shunts

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18
Q

Name three shunts found in a foetus

A

Foramen ovale
Ductus arteriosus
Ductus venosus

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19
Q

Blood enters the foetus through which vessel?

A

The umbilical vein

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20
Q

What is the first shunt encountered by the blood entering the umbilical vein?

A

Ductus venosus

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21
Q

Describe what happens to the blood at the ductus venosus. What is the purpose of this?

A

It is shunted around the liver to the inferior vena cava

The liver is highly metabolically active in fetal life so could easily consume all of the oxygenated blood

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22
Q

What is the function of the foramen ovale?

A

Shunts blood from the right atrium across to the left atrium to be pumped around the body

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23
Q

Does any blood enter the right ventricle?

A

A small amount to allow for its development

24
Q

What is the function of the ductus arteriosus?

A

Shunts blood from the pulmonary trunk to the aorta

25
Q

When do the foetal shunts close?

A

At birth

26
Q

What causes the foramen ovale to close at birth?

A

First breath taken, increasing LA pressure, closing the foramen ovale

27
Q

What causes the ductus arteriosus to close at birth?

A

Muscular contraction

28
Q

What causes the ductus venosus to close at birth?

A

Removal of placental support

29
Q

Describe the layout of the early arterial system

A

Bilateral symmetrical system of arched vessels - aortic arches

30
Q

Which aortic arch forms the the proximal part of the right subclavian artery ?

A

The right side of the 4th arch

31
Q

Which aortic arch forms the arch of the aorta?

A

The left side of the 4th arch

32
Q

Which aortic arch forms the right pulmonary artery?

A

Right side of the 6th arch

33
Q

Which aortic arch forms the left pulmonary artery and ductus arteriosus?

A

The left side of the 6th arch

34
Q

Where in the foetus does the heart begin to develop? What happens to this?

A

Embryonic neck

Descends into the chest as it develops

35
Q

The left recurrent laryngeal nerve innervates the…

A

Larynx

36
Q

What happens to the left recurrent laryngeal nerve as the developing heart descends from the embryonic neck to the chest?

A

It becomes hooked around the 6th aortic arch - around the shunt between the pulmonary trunk and aorta (ductus arteriosus)

37
Q

What happens in patent ductus arteriosus? Where is it most common? What effect will this have on blood in the heart?

A

The ductus arteriosus doesn’t close immediately at birth

Premature infants

Will shunt from left to right

38
Q

Describe the structure of the foramen ovale and how blood is shunted through it

A

Consists of two wedges of tissue - septum secundum and septum primum with misaligned holes

The high pressure of blood in the right atrium compared to the left atrium shunts blood from right to left through both holes

39
Q

What happens to close the foramen ovale at birth?

A

At birth, the pressure in the left atrium rises greater than the pressure in the right atrium

Septum primum is pushed against septum secundum, stopping the flow of blood as the holes are misaligned

40
Q

What can result from either septum primum or septum secundum defects?

A

Atrial septal defects

41
Q

What happens in hypoplastic left heart syndrome?

A

Left ventricle is not normally developed due to inadequate blood supply during development

42
Q

What is the name given to the process that develops and separates the ventricles?

A

Ventricular septation

43
Q

Ventricular septum has both ________ and _________ components

Which portions forms most of the septum?

A

Muscular
Membranous

The muscular portion

44
Q

Describe the process of ventricular septation

A

Muscular portion grows upwards towards the fused endocardial cushions leaving a small gap called the primary interventricular foramen
Membranous portion formed from connective tissue derived from endocardial cushions fills the gap

45
Q

What is the most common cause of a ventricular septal defect?

A

No closure of the primary interventricular foramen by the membranous portion of the septum

46
Q

How is the common outflow tract of the developing heart split into the distinct aorta and pulmonary trunk?

A

Endocardial cushions in the truncus arteriosus grow and twist around each other to form a spiral septum

47
Q

What is transposition of the great arteries?

A

Congenital heart defect, where the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle

48
Q

What symptom is commonly seen in transposition of the great arteries?

A

Cyanosis

49
Q

What is cyanosis?

A

Bluish discolouration of the skin, nail beds and mucous membranes due to deoxygenated Hb in arteries

50
Q

What is tetralogy of fallot?

A

Ventricular septal defect where you get an overriding aorta which straddles both ventricles

51
Q

What can result from tetralogy of fallot? What causes tetralogy of fallot?

A

RV hypertrophy as RV outflow tract is blocked

Defect in normal formation of spiral septum in the truncus arteriosus

52
Q

What specific type of embryonic cells play an important role in septation? What are they derived from? What are they particularly sensitive to?

A

Neural crest cells

Neuroectoderm

Alcohol

53
Q

What is the typical % saturation of Hb with oxygen in the…

I) arterial system
II) venous system

A

~100%

~67%

54
Q

Give an example of a maternal infection that can cause congenital heart disease

A

Rubella

Toxoplasmosis

55
Q

What sorts of congenital heart defects are commonly seen in Down’s syndrome?

A

Atrio-ventricular septal defects

56
Q

What is tricuspid atresia?

A

Congenital heart defect where there is no RV inlet so there is a right to left shunt of entire venous return and blood is pumped to the lungs via ventricular septal defect

57
Q

What is pulmonary atresia?

A

Where there is no RV outlet, there is right to left shunt of the entire venous return and blood flows to the lungs via patent ductus arteriosus