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Cardiovascular System > Week 3 - Development of the CVS, Heart Chambers and Congenital Heart Defects > Flashcards

Week 3 - Development of the CVS, Heart Chambers and Congenital Heart Defects Flashcards

1
Q

Which part of the adult heart do the primitive ventricles form?

A

Left ventricles

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2
Q

Which part of the adult heart does the trunks arteriosus form?

A
  • Aortic roots
  • Proximal aorta
  • Pulmonary trunk
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3
Q

Which part of the adult heart does the bulbus arteriosus form?

A

Gives rise to the ventricles (along with the primitive ventricle)

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4
Q

Which part of the adult heart does the sinus venosus form?

A

It is incorporated into the wall of the right atrium to form a smooth part called the sinus venosum

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5
Q

Which part of the adult heart does the primitive atrium form?

A

Auricles of definitive atria

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6
Q

What is the first step of septation?

A
  • Endocardial cushions develop in the atrioventricular region, on the dorsal and ventral sides of the atrioventricular canal
  • These grow towards each other to divide the heart into right and left channels
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7
Q

How does atrial septation occur?

A

Involves the formation of 2 septa with 3 holes

  • Septum primum grows down towards the fused endocardial cushions
  • The ostium primum is the hole present before the septum primum fuses with the endocardial cushions (underneath the septum primum)
  • Before the ostium primum closes, a 2nd hole, the ostium secundum appears in the septum primum (this occurs by programmed cell death)
  • Finally, a second crescent-shaped septum, the septum secundum grows
  • The hole in the septum secundum is the foramen ovale
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8
Q

What is the foramen ovale?

A

The right to left shunt, used in-utero to bypass the lungs

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9
Q

What is the fossa ovalis?

A

The adult remnant of the foramen ovale

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10
Q

What is the ventricular septum made of?

A

2 components:

  • Muscular (forms most of the septum)
  • Membranous (formed by connective tissue from endocardial cushions)
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11
Q

How does ventricular septation occur?

A
  • The muscular portion grows upwards towards the fused endocardial cushions
  • It leaves a hole at the top (the primary interventricular foramen)
  • This primary interventricular foramen can be filled by the membranous portion of the interventricular septum
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12
Q

How does septation of the outflow tract occur?

A
  • Endocardial cushions appear in the trunks arteriosus
  • As they grow towards each other, they twist around each other
  • This forms a spiral septum
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13
Q

Describe foetal circulation

A
  • Lungs are non-functional
  • Circulation by-passes lungs and liver
  • Receives oxygenated blood from mother via placenta and umbilical vein
  • Returns to the placenta via a pair of umbilical arteries
  • The change in circulation when born must happen immediately
  • Blood flow = placenta -> (via ductus venosus) inferior vena cava -> right atrium (some blood passes to the right ventricle then the pulmonary trunk) -> (via foramen ovale) left atrium -> left ventricle -> aorta (also receives blood from the pulmonary trunk via the ductus arteriosus) -> body -> placenta
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14
Q

What happens to foetal circulation when respiration begins?

A 
Pressure increases in the left atrium, above that of the right atrium
- The ductus arteriosus contracts
- The foramen ovale closes
Placental support is removed
- Ductus venosus closes
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15
Q

What is the fate of the foetal shunts?

A
  • Foramen ovale –> fossa ovalis
  • Ductus arteriosus –> ligamentum arteriosum
  • Ductus venosus –> ligamentum venosum
  • Umbilical veins –> ligementum teres
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16
Q

Describe the internal structure of the right atrium

A
  • Smooth, thin-walled posterior part (sinus venarum) on which the venue cavae and coronary sinus open, bringing poorly oxygenated blood into the heart
  • Rough, muscular anterior wall composed of pectinate muscles
  • Right AV orifice through which the right atrium discharges the poorly oxygenated blood it has received into the right ventricle
  • The smooth and rough parts of the atrial wall are separated externally by a shallow vertical groove (the sulcus terminalis)
  • They are separated internally by a vertical ridge, the crust terminalis
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17
Q

Describe the internal structure of the left atrium

A
  • A larger smooth-walled part and a smaller muscular auricle containing pectinate muscles
  • 4 pulmonary veins entering the smooth posterior wall
  • A slightly thicker wall than that of the right atrium
  • An interatrial septum that slopes posteriorly and to the right
  • A left AV orifice through which the left atrium discharges the oxygenated blood it receives from the pulmonary veins into the left ventricle
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18
Q

Why is the left ventricle wall thicker than the wall of the right ventricle?

A
  • Arterial pressure is much higher in the systemic than in th pulmonary circulation
  • So the left ventricle performs more work than the right ventricle
  • Hence the walls are 2-3 times thicker to withstand the high pressure
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19
Q

Where is the tricuspid valve found?

A

In the right ventricle, guarding the right atrioventricular orifice

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20
Q

When does the tricuspid valve open/close?

A

The right atrium contracts when the right ventricle is empty

  • The cusps of the valve are pushed aside, opening it
  • Blood is forced through the tricuspid valve
  • The valve closes when the right ventricle contracts
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21
Q

What is the role of papillary muscles?

A

They attach to the cusps of the atrioventricular valves, preventing their separation and inversion

  • This blocks regurgitation of blood
  • Provide support
  • Allows the valves to resist pressure developed during contractions
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22
Q

Where is the mitral valve found?

A

In the left ventricle

- Attached to the papillary muscles

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23
Q

When does the mitral valve open/close?

A

At the same time as the tricuspid valve

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24
Q

What are the semilunar valves?

A

Pulmonary and aortic valves

  • They have 3 cusps
  • Not supported by muscles
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25
Q

When do the semilunar valves open/close?

A
  • Open when the ventricular pressure > arterial pressure
  • After relaxation of the ventricle, the elastic recoil of the wall of the pulmonary trunk or aorta forces the blood back towards the heart
  • This regurgitation of blood causes the cusps to snap shut
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26
Q

Describe the circulation of blood in the left-side of the heart

A
  • Oxygen-rich blood from the lungs enters the left atrium from the pulmonary vein
  • Blood flows from the left atrium to the left ventricle via the mitral valve
  • When the ventricle is full, the mitral valve shuts
  • The ventricle contracts and the aortic valve opens
  • Blood flows into the aorta from the left ventricle and goes to the body
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27
Q

Describe the circulation of blood in the right-side of the heart

A
  • Oxygen-poor blood enters the right atrium via the inferior and superior vena cava
  • Blood flows from the right atrium to the right ventricle through the tricuspid valve as the atrium contracts
  • Tricuspid valve shuts when the ventricle is full
  • The ventricle contracts and blood enters the pulmonary artery (then the lungs) via the pulmonary valve
28
Q

What can congenital heart defects be caused by?

A
  • Genetics (e.g. Down’s, Turner’s, Marfan’s)
  • Environment (e.g. teratogenicity from drugs, alcohol)
  • Maternal infections (e.g. rubella)
29
Q

How common are congenital heart defects?

A

Common

  • Incidence = 6-8 per 1000 births
  • Most common = ventricular septal defects, then atrial septal defects
30
Q

How can you classify congenital heart defects?

A

They are cyanotic (i.e. cause cyanosis; low O2 saturation) or acyanotic

31
Q

What are ventricular septal defects?

A

An abnormal opening in the inter ventricular septum

32
Q

Are ventricular septal defects cyanotic or acyanotic?

A

Acyanotic

33
Q

Where can ventricular septal defects occur?

A

Most commonly in the membranous portion of the septum

- Can occur at any point

34
Q

How is blood flow affected in a ventricular septal defect?

A
  • Since left ventricular pressure is much higher than the right, blood will flow from left to right through the abnormal opening
  • The amount of flow depends on the size of the lesion
  • Causes pulmonary venous congestion, and eventually pulmonary hypertension
35
Q

How do ventricular septal defects present?

A

In infancy, with left heart failure

- Unless very small

36
Q

How do atrial septal defects present?

A

Usually asymptomatic until adulthood

- Eventually, there is right heart failure and late onset arrhythmia

37
Q

Are atrial septal defects cyanotic or acyanotic?

A

Acyanotic

38
Q

What are atrial septal defects?

A

An opening in the septum/wall between the 2 atria which persists following birth

  • The foramen ovale exists prenatally to permit prompt right to left shunting of oxygenated placental venous return to the left side of the circulation
  • It normally closes after birth
  • Failure to close, or an abnormal communication, allows blood to continue to flow between the 2 atria postnatally
39
Q

How is blood flow affected in an atrial septal defect?

A

Because left atrial pressure is normally higher than the right, flow will mainly be from left to right
- There is no mixing of deoxygenated blood with the oxygenated blood being pumped around the systemic circulation

40
Q

Where can atrial septal defects occur?

A

Can occur almost anywhere along the atrial septum

  • Most common site = foramen ovale (an ostium secundum ASD)
  • An ostium septum ASD occurs in the inferior portion of the septum and is less common
41
Q

What are the effects of a left to right shunt?

A
  • Requires a hole
  • Blood from the left heart is returned to the lungs instead of going to the body
  • Increased lung blood flow by itself is not damaging, but increased pulmonary artery/venous pressure is
  • The extent of problems depends on the degree of shunting
  • Can lead to vascular remodelling of the pulmonary circulation and an increase in pulmonary resistance
  • If the resistance of the pulmonary circulation increases beyond that of the systemic circulation, the shunt will reverse direction
42
Q

What are some cyanotic congenital heart defects?

A
  • Tetralogy of Fallot
  • Transposition of the Great Arteries
  • Total anomalous pulmonary venous drainage
  • Univentricular heart
43
Q

What are some acyanotic congenital heart defects?

A
  • Left to right shunts (ASD, VSD, patent ductus arteriosus)

- Obstructive lesions: aortic stenosis, pulmonary stenosis, coarctation of the aorta, mitral stenosis

44
Q

What is tetralogy of Fallot?

A

A group of 4 lesions occurring together as the result of a single development defect
- It places the outflow portion of the interventricular septum too far in the anterior and cephalad directions

45
Q

What are the 4 anomalies seen in tetralogy of Fallot?

A
  • Ventricular septal defect
  • Overriding aorta
  • A variable degree of pulmonary stenosis
  • Right ventricular hypertrophy
46
Q

What is the effect of pulmonary stenosis?

A

It causes persistence of the foetal right ventricular hypertrophy, because:
- The right ventricle most operate at a higher pressure to pump blood through the pulmonary artery

47
Q

What is the effect of tetralogy of Fallot?

A

The increased pressure on the right side of the heart along with the VSD and overriding aorta allows:

  • Left to right shunting
  • Mixing of deoxygenated blood with the oxygenated blood going to the systemic circulation, resulting in cyanosis
48
Q

What determines the severity of tetralogy of Fallot?

A

The severity of the pulmonary stenosis

49
Q

How does tetralogy of Fallot present?

A

With cyanosis or spells of cyanosis in infancy

- Mild cases can present in adulthood

50
Q

What are the different types of pulmonary stenosis?

A
  • Valvar: the valve leaflets are thickened and/or narrowed
  • Supravalvar: the portion of the pulmonary artery just above the pulmonary valve is narrowed
  • Subvalvar: the muscle under the valve area is thickened, narrowing the outflow tract from the right ventricle
  • Branch peripheral: the right or/and left pulmonary artery is narrowed
51
Q

What is tricuspid atresia?

A

Lack of development of the tricuspid valve

- Leaves no inlet to the right ventricle

52
Q

How can tricuspid atresia be survivable?

A

There must be a complete right to left shunt of all the blood returning to the right atrium
- ASD or patent foramen ovale
And to allow blood flow to the lungs:
- A VSD or patent ductus arteriosus

53
Q

What is transposition of the great vessels?

A

2 unconnected parallel circulations instead of 2 circulations in series
- The right ventricle is connected to the aorta and the left ventricle to the pulmonary trunk (wrong way round!)

54
Q

What are the effects of transposition of the great vessels?

A

Not compatible with life after birth:

  • Unless a shunt exists to allow the 2 circulations to communicate
  • A shunt must be maintained or created immediately following birth to sustain life
  • E.g. the ductus arteriosus can be maintained patent, and/or an ASD formed
55
Q

What is patent ductus arteriosus?

A

The ductus arteriosus is a vessel that exists in the foetus to shunt blood from the pulmonary artery to the aorta before the lungs are functioning

  • This vessel should close shortly after birth as the pressure in the pulmonary artery drops following perfusion of the lungs
  • If it fails to close after birth, it causes a PDA
  • An cyanotic defect
56
Q

How does patent ductus arteriosus affect blood flow?

A

Blood flow through the PDA, from the aorta to the pulmonary artery (high to low pressure)

57
Q

What is coarctation of the aorta?

A

A narrowing of the aortic lumen in the region of the ligament arteriosum (former ductus arteriosus)
- Acyanotic defect

58
Q

What is the effect of coarctation of the aorta?

A

Increased afterload on the left ventricle

  • Can lead to left ventricular hypertrophy
  • Because the vessels to the head and upper limbs usually emerge proximal to the coarctation, the blood supply to these regions is not compromised
  • Blood flow to the rest of the body is reduced
59
Q

What determines the severity of coarctation of the aorta?

A

The severity of the narrowing

60
Q

How does coarctation of the aorta present?

A
  • If severe: an infant may present with symptoms of heart failure shortly after birth
  • If mild: defect may be detected in adult life
61
Q

What is patent foramen ovale?

A

The foramen ovale remains open after birth

  • Not a true ASD
  • May be present in 20% of the population
62
Q

What is the effect of patent foramen ovale?

A

Generally clinically silent:
- The higher left atrial pressure causes functional closure of the flap valve
But it may be the route by which a venous embolism reaches the systemic circulation if pressure on the right side of the heart increases even transiently

63
Q

What is hypoplastic left heart?

A

Failure of the left ventricle and ascending aorta to develop properly
- A PFO and ASD are also present

64
Q

What is the effect of hypoplastic left heart?

A

It is lethal without surgical correction

65
Q

How is blood flow affected in hypoplastic left heart?

A

Blood supply to the systemic circulation is via a PDA

Cardiovascular System (11 decks)

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