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Sem 2 - The Cardiovascular System > Embryology > Flashcards

Embryology Flashcards

1
Q

What one of the three germ layers creates the heart?

A

Mesoderm

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2
Q

When does folding ensure the cardiogenic field is in the right place?

A

4th week

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3
Q

What are blood islands?

A

A primitive tissue - Beginning of blood vessels and blood tissue

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4
Q

What effect does literal folding have?

A

It creates a heart tube

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5
Q

What effect does cephalocaudal folding have?

A

Brings the heart tube into the thoracic region

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6
Q

When does the heart begin to beat?

A

22 days after fertilisation - first system to function

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7
Q

What must occur to the primitive heart tube for it to become an adult heart?

A

The primitive heart tube must divide to create four chambres.

The inflow and outflow vessles must be remodelled. This will create a configuration of vessles retuning blood from the systemic circulation and the great vessels and taking blood away from the heart.

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8
Q

What are the names of the different zones of the primitive hart tube?

A
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9
Q

What happens in cardiac looping?

A
  • Tube elongates
  • Runs out of room
  • Twists and folds up
  • Places the inflow and outflow in correct orientation with each other.
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10
Q

What is the percardial sinus?

A

A gap between pulmonary trunk and aorta

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11
Q

How does the sinus venosis (venous inlet) develop?

A

At the start, the left and right sinus horns are the same size.

Venous retun then shifts to the right hand side which causes the left sinus to recede.

The right sinus horm is absorbed by enlarging the right atruim.

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12
Q

What does the right atria develop from?

A

Most of the primitive atrium

Sinus venosis

Receives venous drainage from the body (venae cava) and the heart (coronary sinus)

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13
Q

What does the left atrium develop from?

A

A SMALL portion of the primitive atrium

Absorbs the porximal parts of the pulmonary veins.

Recieves oxygenated blood from the lungs

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14
Q

How does the oblique sinus form?

A

Oblique pericardial sinus forms as the left atrium expands absorbing the pulmonary veins.

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15
Q

How is foetal circulation different to mature circulation?

A

Foetus:

  • Lungs not work
  • Oxygenation and removal of CO2 occurs at the placenta.
  • So shuts are required to maintain foetal life.
  • Shunts MUST be reversible at birth.
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16
Q

Where is there the highest pO2 in foetus?

A

Umbilicus

17
Q

How does blood circulate in the foetus?

A
18
Q

What are the names of foetal shunts?

A
  • Foramen ovale - takes blood from right atrium to left atrium
  • Ductus Venosus - takes blood from pulmonary trunk to aorta (bipass lungs)
  • Ductus Arteriosus - Takes blod from placenta to IVC.
19
Q

How does foetal circulation become adult circulation?

A
  • Respiration starts
  • Left Atrium pressure increases and foramen ovale closes
  • Ductus Arteriosus contracts.
  • Placental support removed
  • Ductus Venosus closes. (No flow through umbilical vein)
20
Q

What are aortic arches?

A

Early arterial system begins as a bilaterally symmetrical system of arched vessels.

These arched vessles undergo entensive remodelling to create the major arteries leaving the heart.

21
Q

What aortic arches are important? Why?

A

4th:

Right = proximal part of Right subclavian artery

Left = arch of aorta

6th:

Right = right pulmonary artery

Left = Left pulmonary artery and ductus arteriosus

22
Q

How are aortic arches remodelled?

A

As the heart “descends” the nerve hooks around the 6th aortic arch and it “turns back on itself”

The left recurrent (goes back on itslef) laryngeal nerve becomes hooked around the shunt between the pulmonary trunk and the aorta.

23
Q

PDA?

A

Patent Ductus Arteriosus

DA should normally contract with first breach but it doesn’t.

So, persistence communication between the descending aorta and the pulmonary artery.

Failure of physiological closure. Blood will shunt from aorta to right (high to low pressure).

24
Q

What three things get separated in septation?

A

Interatrial septum (atria get separated)

Interventricular septum (ventricles get separated)

Septation of ventricular outflow tract (pulmonary trunk and aorta)

25
Q

How does the inter-atrial septum form?

A

There is already a narrowing but, endocardial cushions form in the atrioventricular region.

It divides the developing heart into left and right channels

26
Q

How does atrial sepation occur?

A

Division of the common atrium formation of two septa with three “holes”

Septum primum grows form towards the fused endocardial cushions.

Th optimum primula is the hole present before the septum proimum fuses with the endocardial cushions.

Before optimum primum closes, a second hole, the optimum secundum, appears in the septum premium.

Finally, a second crescent shaped septum, the septum secundum grows. The hole in the septum secundum is the foramen ovale.

This process is only complex as they need to maintain the flow from right to left.

27
Q

How does arrangement of atrium septum allow flow?

A

Pressure in RA higher than LA. This means blood moves through foramen ovale and then ostium secundum into LA from RA.

28
Q

Give a summary of atrial septation.

A

Both left and right atria components derived from the primitive atrium (i.e. auricles)

The right atrium absorbs the sinus venosus

The left atrium sprouts the pulmonary vein then grows to absorb it and its first 4 branches.

Interatrial septum forms to divide the chamber into left ad right chambers.

The fossa ovalis is the adult remnant of the shunt used in utero to by-pass the lungs.

29
Q

How does the atrial septum close?

A

Septum premium is pushed against septum secundum because the pressure in the LA become larger than that in the RA.

30
Q

What could result in an atrial septal defect?

A

Ostium secundum defect -

  • If septum premium is resorbed or too short.
  • If septum secundum is too smal.
31
Q

What is hypoplastic left heart syndrome?

A

Exact cause is unknown…

Defect in development of mitral and aortic valves

-resulting in atresia and limited flow.

Ostium secundum is too small therefore right to left flowis inadequate in Utero.

“Use it or loose it” -means the left heart is underdeveloped.

32
Q

What occurs in ventricular septation?

A

Starting with a single ventricular chamber

Ventricular septum forms which has 2 components:

  • Muscular
  • Membranous

Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions. It forms a small gap, the 1st interventricular foramen.

The membranous portion of the interventricular septum is formed by connective tissue derived from endocardial cushions to “fill the gap.”

33
Q

What is the most common ventricular septal defect?

A

Most commonly, the membranous portion fails to obliterate the small hole between the two ventricles.

34
Q

How do the outflows then get separated?

A

Endocardial cushions appear in the truncus arteriosus (Grow in the lumen).

As they grow towards each other, they twist around each other and form a spiral septum.

35
Q

What can congenital birth defects be?

A

Structural abnormalities (not form properly)

Complete absence of a structure.

36
Q

What could the causes of congenital birth defects be?

A
  • Genetic
  • Exposure to chemical / drugs / infectious agents
  • Unexplained.
37
Q

When do congenital heart defects occur?

A

Congenital heart defects occur when there is…

  • A structural defect of the chambers
  • A structural defect of the vasculature

These is an obstruction

Communication between pulmonary and systemic circulation.

Additional complexity due to the differing circulatory needs of the foetus as compared to the newborn (mature).

38
Q

Describe the transposition of the great arteries

A

Aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle.

-Cyanosis will occur

Likely to relate to the development of the aortic and pulmonary valves which need to be carefully positions to ensure normal “pluming”

39
Q

What is tetralogy of Fallot?

A

Large ventricular septal defect

Overring aorta

Right ventricular outflow tract obstruction

Right ventricular hypertrophy

Conotruncal septum formation defective (neural crest cells are important)

Sem 2 - The Cardiovascular System (20 decks)

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