Embryology parts 5-8 Flashcards
The formation of the heart tube occurs through fusion of what
Endocardial tubes
State the structures in heart tube
Truncus arteriosis
Bulbus cordis
Primative ventricles
Primative atrium
Just look at the folding of the heart, the diagram is excellent
…… figure 5.5.1
Give a brief overview of the development of the heart tube
The cardiogenic cells develop in a U (or horseshoe) pattern outside the embryo proper.
These form a pair of heart tubes (endocardial tubes), which fuse to form a single heart tube by ~21 days post-fertilisation.
This tube is already able to pump blood unidirectionally.
T/f, vessels attached to the correct heart region following the looping and septation of chambers
F… during looping and septation
the vascular connections are maintained, so that the major veins are connected to the atria, and major arteries to the ventricles.
3 key steps in heart development
- Looping.
- Septation
- Valves develop
What is the reason for the difference between heart in utero and after delivery
The provision of oxygen to the embryo and fetus from the placenta is linked to the main structural difference between the heart in utero, and after delivery.
Blood returning to the right atrium in utero can be described as
Well oxygenated
Differences between heart in utero and in life
- Little blood flow to the lungs is needed, there is a gap between the atria, the foramen ovale.
Blood returning goes striaht into left atrium, then left ventricle then aorta to the rest of body - Main artery from right ventricle (i.e. pulmonary artery) connected to aorta via ductus arteriosis. Any blood that got into pulmonayr circulation goes through this into the aorta
What changes should occur to the heart following birth
ductus arteriosus and foramen ovale should close, converting the circulation to the ‘figure of 8’ system and allowing oxygenation within the lungs
What usually corrects cardiac abnormalities
As most abnormalities are structural, surgical procedures have been developed to correct some abnormalities
Why does surgery have to occur shortly after delivery in babies with cardiac defects
As these complications may become clinically significant at the time of birth (as the blood flow needs to be changed to include the lungs), surgery may need to be done shortly after delivery.
2 important conditions in the tetraology of fallot
- Pulmonary artery stenosis (decreasing blood flow to the lungs)
- Septal defect between ventricles (allow deoxygenated blood into the left ventricle)
other 2 are
thickened right ventricle wall
and
aorta overriding septal defect
Outline a case of transposition of blood vessels
- Aorta attached to right ventricle
- Pulmonary arteries attached to left
Blood comes from body deoxygenated into right side of heart, then back through aorta to body
Blood goes from left side of the heart to the pulmonayr arteries to lungs, then back through pulmonary veins to the left atrium again, so oxygenated blood just passing between heart and lungs and not getting to rest of body
Why is transposed blood vessels not a problem before birth . What happens after birth
the foreman ovale and ductus arteriosus allow mixing of the blood flows sufficiently to sustain fetal growth and development. The closure of these connections after delivery separates the blood flows, so the infant becomes cyanotic (‘blue baby syndrome’).
What is treatment for transposed blood vessels leading to cyanosis
Administering prostaglandins to keep the ductus arteriosus open (PGE2)
perhaps opening of a link between the atria
Definitive treatment would usually involve the switching of the two arteries, to restore the normal blood flows
T/f spina bifida is very rare
The incidence of spina bifida is 1-2 per 1000 pregnancies, with variation between study populations. This makes it one of the most common developmental defects.
T/f surgery is a cure for spina bifida
F…. skin can be placed to protect the neural tissue instead of exposed spinal cord,
however
it will not address any functional problems
defects in the spinal cord often lead to damage to the nerves supplying associated tissues
Most effective treatment for spina bifida
folic acid; if the maternal diet is low in folate, then the risks of spina bifida increase
The timing of spinal development is early, so folate needs to be given before conception, preferably about 3 months beforehand.
T/f low maternal folate accounts for all spina bifida
F t has been calculate that about 70% of cases of spina bifida are due to low maternal folate, so this does not explain all of this developmental abnormality.
T/f spina bifida occurs on the lower back
F…
spina bifida refers to two spines (the unclose neural tube)…
not necessarily a single defect, not necessarily on lower back
When does formation of neural tube occur
Formation of the neural tube, the precursor of the central nervous system occurs early in pregnancy, about 3 weeks after fertilisation (Figure 5.6.2). Fusion should occur through the neural tube, but in spina bifida this process is not completed.
What is anencephaly
compromised development of the head and skull
General aetiology is thought to be similar to spina bifida, though the result of a lack of closure of the anterior neuropore.
T/f anencephaly linked to low folate
Some studies have suggested that folic acid can also decrease the incidence of anencephaly, although the smaller numbers make it difficult to determine the scale of the benefit.
Why must the folate be taken 3 motnhs before conception to reduce spina bifida incidence
Because the maturation of the oocyte is happening at this stage
3 types of spina bifida with increasing severity
Occulta
Meningocele
Myelomeningocele
The bottom 2 likely to involve nerves and have functional implications below the level of the lesion
What does the malformation of bone tell us in spina bifida
That it is the nerves in spinal cold controlling development of the vertebral body
There is nerve defect and results in bone defect
Where does neural tube closure usually start
Starts in the middle of the neural tube and spreads from there up to head and down to tail
Differentiate the structural defect in anencephaly and spina bifida
An= anterior neiuropore
spina= posterior neuropore
Taking folic acid when you realise you are pregnant will help
F….
it’s too late
it’s porbbaly already 2 weeks PF…
you need folate from maturation of the egg 3 months before
Anencaphy happens in which babies most commonly
Girls
Where can eyes and other primary features of the dace be found during development
primary structures of the face form on the sides of the head – for example the eye. This pattern persists until at least 5 weeks post-fertilisation
When are precursors of nose, cheeks, lips, mouth and chin formed
Also around 5 weeks PF (like eyes)
When do the face structures move from the side of head to central
structures then move over a period of about 5 weeks until the reach the expected positions, with the nose centrally placed, and the eyes facing forwards on the face
Why is facial development not completely understoof with regard to eyes
requires the movement of pre-existing structures (e.g. eyes) through the tissues of the developing face, a process that is not fully understood.
How is the nose formed
There are medial and lateral nasal prominences on each side of the head which merge in the midline
Nasal pit in between these becoes nostril
How do tissues move to the correct place in the face
It seems that repeated formation of clefts in the face, and then filling in of the clefts, leads to sequential loss of tissue from the centre of the face, and the movement of tissues to the correct places.
Outline a structual process leading to clef lip
There is a groove create where the medial and lateral nasal prominences have not yet fused
Groove filling occurs on one side (normal)
On the other side, there is a persistance labial groove. The medial nasal prominences fuse fine, but there is a seaparate lateral part of the lib
=complete unilateral cleft lip
T/F development of the facial tissues on the separate sides of the head is distinct to humans
The development of the facial tissues on the separate sides of the head is common in vertebrate development; most fish and birds retain this arrangement, with the eyes remaining on the side of the head into adult life.
What clefting may occur and why
need to form the face from two separated halves
May give rise to cleft lip, cleft palate or both
Outline the symmetrical or asymmetrical nature of cleft lip and palate
Clefting in both lip and palate may also be found. Note that cleft lip is often asymmetric, as only one of the two clefts does not function correctly, whereas cleft palate is usually symmetric as the halves of the palate do not meet and fuse correctly.
Why is surgery to correct facial congenital defects often successful
The turnover of cells in infants is normally very rapid, and healing often occurs with little or no scarring, so surgical outcomes can be very impressive.
When does it occur that the eyes don’t remain on the side of the head
Binocular vision
When does surfactant production begin
early in the third trimester of pregnancy (Figure 5.8.1) and gradually increases
Why is lung surfactnat important to be produced
Adequate production of surfactant is necessary for normal lung function at birth.
What is respiratory distress syndrome
Preterm infants often suffer from lung complications due to low levels of surfactant (Respiratory Distress Syndrome, RDS).
What can you do if the baby is likely to be born very early, crreating problems due to reduced surfactatn
- Delaying the birth of a preterm infant may give more time for surfactant to be produced
- injection of glucocorticoid to the mother, which also increases surfactant production in the infant’s lungs
When is a glucocorticoid injection to the mother useful to increase foetal surfactant?
Optimal timings are not fully established, although 24-48 hours between administration and delivery of the infant or infants is often the aim.
What can be given to preterm babies with low surfactant
Artificial surfactant has also been developed, and this can be administered to preterm infants while their lungs develop sufficiently to produce enough surfactant to allow normal function.
State the 5 stages of lung development
- Embryonic (3-8 weeks PF)
- Pseudoglandulat (5-17)
- Canalicular (16-26)
- Saccular (24-38)
- Alveolar (36-38)
When are alveolar produced in utero
Only last two weeks PF (i.e. from 36 weeks PF which is actually 4 weeks before term)
From when is surfactnat produced
25-27 weeks
What distinguishes conducting and respiratory zones
In the conducting zone, all branches of the bronchial tree, the walls of which contain cartilage tissue and seromucous glands, are bronchi. As soon as cartilage and glands are no longer present, bronchioli are involved.
What proporton of babies will have RDS, who are born at:
24 weeks
26-28 weeks
30-31 weeks
100%, 50%, 25%
What is surfactant made of
lipids, proteins and glycoproteins
Which organs complete development at a very late stage
Brain completes late, as do lungs and digestive system
