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CVS1 > Embryology > Flashcards

Embryology Flashcards

1
Q

What effect does folding of the embryo have on the early development of the heart

A

• Lateral folding
• Creates a heart tube
• Cephalocaudal folding
• Brings the tube into the thoracic region
Primitive heart tube - beginning of functioning cvs

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2
Q

Describe the formation of the primitive heart tube

A

Once embryos folds in the plane, the tubes fuse to form heart tube
Endocardial tubes fuse to form a single tube
Embryo cannot survive unless it has own circulatory system. Which is hwy it develops early on

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3
Q

What must happen to the primitive heart tube?

A

• The primitive heart tube must be divided
• to create the 4 chambers
• The inflow vessels and the outflow vessels must be remodelled
• creating the familiar configuration of vessels returning blood from the systemic circulation and the great vessels taking blood away from the heart
Tube- blood squeezed alone - suffiecint for early embryo
But needs to be divided into 4 chambers

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4
Q

What are the regions of the primitive heart tub e

A 
Blood enters the sinus venosus 
Atrium
Ventricle
Bulbus cordis
Truncus arteriosus
Aortic roots (blood leaves)

Blood is squeezed up and ou

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5
Q

Which regions of the primitive heart tube are located in the pericardial sac

A

Ventricle, bulbus cordis, truncus arteriosus

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6
Q

What is looping?

A
  • Tube elongates - expansion of zones within it
  • Runs out of room
  • Twists and folds up - ventricle moves forwards and downwards, atria pushed backwards and upwards
  • regular and predictable
  • Places the inflow and outflow in the correct orientation with respect to each other
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7
Q

How does the sinus venosus develop?

A

Sinus venosis is venous inlet - blood coming up into tube
Initially 2 horns - initially same size - receiving veins from placenta, yolk sac & embroyinic body
Over time venous return shifts to RHS, L horn recedes, right horn absorbed by enlarging oprimitive atrium
One of the contributors to wall of left atrium is wall of vessels

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8
Q

How do the atria develop?

A
  • RA develops from
  • most of the primitive atrium
  • sinus venosus
  • receives venous drainage from the body
  • LA develops from
  • a small portion of the primitive atrium
  • absorbs proximal parts of primordial pulmonary veins to leave 4 entrances
  • receives oxygenated blood from the lungs (venae cava) and the heart (coronary sinus)
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9
Q

How does the oblique pericardial sinus form?

A

See slide for positioning

• Oblique pericardial sinus formed as left atrium expands absorbing the pulmonary veins
LA expands and stretches out pericardial sac around pulmonary veins

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10
Q

Why does the fetal heart need shunts?

A

Lungs don’t work - sending blood to pulmonary circulation could damage lungs
• Oxygenation and removal of CO2 occur at the placenta - circulation takes blood from uteroplacenta circulation to heart
• So shunts are required to maintain fetal life
• AND – these shunts must be reversible at birth
Oxygenated blood comes from umbilicus
Highest pO2 in umbilical vein - comes in at right side of heart

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11
Q

Decsribe fetal circulation

A

Oxygenated blood coming in at interface between maternal circulation and fetal circulation - from placenta to umbilicus
Drains into IVC (draining into aorta would be a short circuit)
Highest pO2 blood in RA - not where we want it to be
Need it in left - need to bypass right ventricle and lungs to get oxygenated blood into left side (hole between RA and LA)
Small amount of blood enters the RV from RA - its muscle so needs blood to develop normally
RV empties into pulmonary trunk - needs to bypass lungs to get to aorta
High pO2 blood in the LA goes to LV then round to body - back to mother in uteroplacenta circulation to lose the CO2

See slide for diagram

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12
Q

What are the fetal circulatory shunts?

A

Ductus venosis - short vessel between placenta and IVC
Foramen ovale - hole in heart between atria
Ductus arteriosus - vessel that connected pulmonary trunk to aorta - ensures that we protect lungs - functional only in fetal life

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13
Q

How are the shunts closed at birth?

A

Need to close the shunts at birth
When baby takes first breath - pulmonary circulation starts
LA pressure increases - rise over RA pressure - closes FO
DA contracts - wall has special tissue sensitive to rises in pO2
Initial breath - increase in pO2 - causes vessel to contract and obliterate the connection between pulmonary trunk and aorta
When placental support removed, the DV closes because no longer a big volume of blood coming through umbilical vein

Closing of shunts - resolve circulation

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14
Q

Which major arteries are formed early on?

A
  • arteries that supply head & upper limb
  • route blood to lungs for oxygenation
  • ascending, arch and descending thoracic aorta
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15
Q

Hold egos the early arterial system begin?

A
  • Early arterial system begins as a bilaterally symmetrical system of arched vessels
  • Undergo extensive remodelling to create the major arteries leaving the heart

See slide for diagram

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16
Q

What are 2 important arches and what are their derivatives?

A
  • 4th arch
  • R = proximal part of R subclavian A
  • L = arch of aorta
  • 6th arch = “pulmonary arch” - gives vessels to supply pulmonary circulation
  • R = R pulmonary artery
  • L = L pulmonary artery & Ductus Arteriosus
17
Q

How are the aortic arches remodelled?

A
  • The aortic arches are remodelled to create the mature disposition
  • As the heart “descends” the nerve hooks around the 6th aortic arch and “turns back on itself”
  • The left recurrent laryngeal nerve becomes hooked around the shunt between the PT & aorta

Remodelling of 4th and 6th arteries - variant remodelling on either side
Purple vessel = ductus arteriosis
Yellow - nerves - recurrrent laryngeal nereve - descends down into thorax and turns back on itself - this never gets tangles in system of reorganisation of aortic vessel - SEE SLIDE

18
Q

What is patent ductus arteriosus?

A

Patent ductus arteriosis
DA should normally contract with first breath - in this condition it doesnt
Persistent route of communication between aorta and pulmonary artery
Initial spasm of artery - originally prostaglandin based - becomes anatomical
Blood shunt from higher to lower pressure- left to right

19
Q

What happens after looping of the heart tube?

A

• Atrioventricular canal links atrium & ventricle
• Don’t yet have the “two pumps
in series” configuration

20
Q

What is septation?

A

Interatrial septum - Divide primitive atrium into left and right chambers
Left atrium gets bulk of chamber size from incorporation of pulmonary vermin

Interventricular septum - Divide primitive ventricle into left and right

Create 4 chambers to achieve selective outflow

21
Q

What is the first step in septation?

A

Endocardial cushions - develop in AV region - narrowing of heart tube at this point - new tissues calls endocardial cushions forming - divides developing heart into left and right channels
Narrowing of junction between primitive atrium and primitive ventricle = atrioventricular canal
Division of cells - bumps on dorsal and ventral walls - endocardial cushions - dependent on a particular subgroup of cells migrating in - neural crest cells
Bumps for and meet in the middle - above it primitive atrium, below it primitive ventricle

22
Q

Describe atrial septation

A
  • Septum primim grows down from room of primitive atrium onto fused cushions
  • As first septum is forming, as it grows will maintain an opening for blood to travel freely between
  • Ostium primum is the hole present before the septum primum fuses with the endocardial cushions
  • Before ostium primum closes, a second hole, the ostium secundum appears in the septum primum
  • Finally a second crescent shaped septum, the septum secundum grows; the hole in the septum secundum is the foramen ovale

During embryonic/fetal life, when RA pressure higher than left, umbilical vein to IVC - relative pressure difference will push 2 leaves apart -
Holes staggered so blood flows
Exploiting the real active pressures in the 2 chambers

23
Q

Give a summary of the development of the atria

A
  • Both left & right atria have 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 and right chambers
  • The fossa ovalis is the adult remnant of the shunt used in utero to by- pass the lungs
24
Q

What are ostium secundum defects?

A
  • Ostium secundum defect
  • septum primum
  • resorbed
  • too short
  • septum secundum too small
25
Q

What is hypoplastic left heart syndrome?

A 
• Exact cause not known 
• Some embryological speculation......
• defect in development of mitral and aortic valves
   - Resulting in atresia 
   - Limited flow
• ostium secundum too small
• therefore right to left flow inadequate in utero
• use it or loose it rule applies
• left heart is underdeveloped
26
Q

What are the 2 components of the ventricular septum?

A
  • Starting with a single ventricular chamber
  • Ventricular septum forms, which has 2 components - muscular and membranous
  • Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions
27
Q

How does the interventricular septum form?

A

Muscular portion grows upwards towards the endocardial cushions leaving a small gap, the 1° interventricular foramen
Membranous portion of the interventricular septum formed by
connective tissue derived from endocardial cushions to “fill the gap”

28
Q

What is ventricular septal defect?

A

• (most commonly) Membranous portion of interventricular septum involved

Failure of formation of membrane in intraventricylar septum leads to ventricular septal defect - membrane didnt completely obliterate gap

29
Q

How is the outflow tract separated?

A
  • Endocardial cushions also appear in the truncus arteriosus - they are staggered and grown into lumen of tube
  • As they grow towards each other they twist around each other
  • Form a spiral septum so blood from the right side is channeled to pulmonary trunk and blood from left side channeled into aorta
30
Q

What are congenital birth defects?

A 
Congenital birth defects
• Can be
• structural abnormalities
• complete absence of a structure 
• Result from interference with / interruption of normal developmental processes
  • Causes can be
  • genetic
  • exposure to chemicals / drugs / infectious agents
  • unexplained
31
Q

What are congenital heart defects?

A

• The developing heart is subject to the same vulnerabilities as all other systems

• Occur when there is
• a structural defect - Failure of structure or valve to develop normally
- of the chambers
- of the vasculature
• There is an obstruction
• There is communication between pulmonary and systemic circulations
•because…….
• Additional complexity due to the differing circulatory needs of the fetus as compared to the newborn (mature)

32
Q

What is transposition of the great arteries?

A

• Aorta arises from right ventricle
• Pulmonary trunk arises from left ventricle
• What will happen?
• Cyanosis
• Likely to relate to the development of the
• Depending on what other if any defects are present
aortic and pulmonary values which need to be carefully positioned to ensure normal “plumbing”

33
Q

What is tetralogy of Fallot?

A

4 features
• Large ventricular septal defect
• Overriding aorta - over both ventricles
• Right ventricular outflow tract obstruction
• Right ventricular hypertrophy

Underlying problem
• Conotruncal septum formation defective
• Importance of neural crest cells

CVS1 (20 decks)

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