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CV I > Cardiorespiratory development > Flashcards

Cardiorespiratory development Flashcards

1
Q

Describe the earliest events of cardiac development

A

A. Cardiogenic mesoderm migrates to cranial-most extent of embryo.
B. As a result of embryonic folding, the heart migrates caudally though neck and into thorax.

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2
Q

Describe heart tube formation

A

A. Initially forms as paired endothelial-lined tubes.

B. As the embryo folds laterally the paired tubes fuse, forming one continuous heart tube.

C.Receives venous blood at caudal end and pumps arterial blood to body at cranial end

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3
Q

Describe the formation of the cardiac loop

A

A. Heart elongates and develops 4 dilations: bulbus cordis, ventricle, atrium, sinus venosus.

B. The ventricles grow faster than other regions, causing the heart to loop.

 a. The cranial portion bends ventrally, caudally,       and to the right.
 b. The caudal portion bends dorsally, cranially, and to the left.
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4
Q

What does the sinus venosus form

A
  1. Composed of left and right venous horns (receiving blood from major veins).
  2. Left sinus horn forms coronary sinus.
  3. Right sinus horn is incorporated into right atrium (sinus venarum).
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5
Q

How does the primitive atrium form the auricles of the right and left atria?

A
  1. Final steps in development of right atrium
    a. Sinus venosus is incorporated into right atrium and forms sinus venarum.
    b. Original embryonic atrium forms atrial auricle.
  2. Final steps in development of left atrium
    a. Proximal portion of pulmonary vein is incorporated into left atrium and forms smooth walled portion of chamber.
    b. Original embryonic atrium forms atrial auricle.
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6
Q

What will the primitive ventricle form

A

Primitive ventricle will form trabeculated portion of left ventricle

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7
Q

What does the bulbus cordis form

A
  1. Caudal portion forms trabeculated region of right ventricle.
  2. Conus cordis (midportion) will form outflow region of both ventricles (right ventricle – conus arteriosus; left ventricle – aortic vestibule)
  3. Truncus arteriosus (cranial portion) will form pulmonary trunk and aorta.
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8
Q

Explain the circulation through the primitive heart

A

A. Coordinated contractions of the heart begin in week 4.

B. Blood enters through sinus venosus → primitive atrium → primitive ventricle → bulbus cordis → aortic sac → to embryo.

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9
Q

What are the steps in the partitioning of the atrium

A

Step 1 – septum primum forms; this is a thin, membranous septum.
Step 2 – ostium primum forms; this is a short-lived opening along the inferior portion of the septum primum.
Step 3 – ostium primum closes as endocardial cushions fuse to septum primum.
Step 4 – ostium secundum forms from small area of apoptosis in upper portion of septum primum.
Step 5 – septum secundum forms; this is a thick, muscular septum which forms to the right of the septum primum. This will form the bulk of the interatrial septum.
Step 6 – foramen ovale forms within the septum secundum.
Septum primum becomes the valve of the foramen ovale

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10
Q

What is patent foramen ovale

A

Results when the valve of the foramen ovale does not completely fuse to the septum secundum. Usually asymptomatic. However, any increase in pulmonary pressure (coughing, sneezing, pulmonary hypertension) can cause the foramen ovale to re-open.

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11
Q

Explain the steps leading to communication of primitive atria w/left and right ventricles

A

a. Initially, only primitive left ventricle is in contact with atria.
b. Right ventricle is separated from atria by the bulboventricular flange.
c. Bulboventricular flange regresses during 5th week; at the same time the atrioventricular canal enlarges and shifts to the right.
d. These two events provide communication of atria with left and right ventricles.

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12
Q

Explain the partitioning of left and right atrioventricular canals

A

a. Endocardial cushions (superior, inferior, left, right) are derived from neural crest.
b. Superior and inferior endocardial cushions project into the atrioventricular canal and fuse, separating the AV canal into right and left orifices

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13
Q

What forms the atrioventricular valves

A

Atrioventricular valves form from neural crest of endocardial cushions

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14
Q

Explain the partitioning of the ventricles

A
  1. Muscular portion of septum derived from muscle of ventricle walls.
  2. Membranous septum derived from endocardial cushions.
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15
Q

Explain the partitioning of conus cordis and truncus arteriosus

A
  1. Conotruncal ridges (2) derived from neural crest.
  2. Conotruncal ridges undergo 180° of spiraling.
  3. Conotruncal ridges fuse to form aorticopulmonary septum (spiral septum).
    a. Conus cordis forms conus arteriosus (right ventricle) and aortic vestibule (left ventricle).
    b. Truncus arteriosus forms pulmonary trunk and ascending aorta.
  4. Semilunar valves form from neural crest of conotruncal ridges.
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16
Q

What are some ventricular septal defects

A
  1. Membranous septal defect (most common)
  2. Muscular septal defect
  3. Severity depends on size of defect; often results in left-to-right blood shunt.
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17
Q

What is Ostium secundum defect

A

a. Large opening between left and right atria
b. Cause: excessive degeneration of septum primum
c. Cause: insufficient proliferation of septum secundum

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18
Q

What causes an Ostium primum defect

A

Ostium primum defect due to endocardial cushion defect

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19
Q

What is a common atrium

A

a. Complete absence of atrial septum

b. Almost always associated with other major heart defects

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20
Q

What is an Endocardial cushion defect

A
  1. Cause: underdeveloped endocardial cushions.
  2. Results in :
    a. Persistent atrioventricular canal
    b. Ostium primum defect (ASD)
    c. Membranous interventricular septum defect
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21
Q

What is Pulmonary/Aortic valve stenosis

A
  1. Pulmonary trunk or aorta very narrow or completely occluded due to malformation of semilunar valve.
  2. Often present with both patent foramen ovale and ductus arteriosus.
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22
Q

What is the Tetralogy of Fallot

A
  1. Cause: unequal division of truncus arteriosus by conotruncal ridges
  2. 4 components
    a. Overriding aorta
    b. Pulmonary stenosis
    c. Ventricle septal defect
    d. Right ventricular hypertrophy
23
Q

What is Transposition of Great Vessels

A
  1. Cause: conotruncal ridges fail to spiral.
  2. Aorta arises from right ventricle.
  3. Pulmonary trunk arises from left ventricle
  4. Usually occurs with patent ductus arteriosus, patent foramen ovale
24
Q

What is Persistent Truncus Arteriosus

A
  1. Cause: conotruncal ridges fail to form.
  2. Undivided truncus receives blood from right and left ventricles
  3. Usually occurs with patent ductus arteriosus, patent foramen ovale
25
Q

What is DiGeorge Syndrome

A
  1. Cause: deletion on long arm of Chromosome 22.
  2. Abnormal neural crest development.
  3. Cardiac abnormalities (usually defects of conotruncal ridge formation)
  4. Craniofacial defects
  5. Thymic hypoplasia
  6. Parathyroid dysfunction
26
Q

What is Dextrocardia

A

Heart loops in opposite direction; lies in right thorax (a mirror image).

27
Q

What is Ectopic Cordis

A
  1. Results from failure of ventral body wall to close

2. Heart lies on surface of chest

28
Q

Explain vasculogenesis

A
  1. Under the influence of VEGF, mesodermal cells differentiate into blood islands.
  2. Blood islands give rise to hemagioblasts.
  3. The major embryonic arterial and venous systems and arise via vasculogenesis.
29
Q

What are the primary vascular systems of the embryo/fetus

A 
A. Intraembryonic system
    1. Aortic arch arteries
    2. Cardinal system of veins
B. Yolk sac (vitelline) system
    1. Vitelline artery
    2. Vitelline veins
C. Placental system
    1. Umbilical arteries (2)
    2. Umbilical vein (1)
30
Q

How does the aortic arch form

A
  1. Originate from aortic sac (receives blood from truncus arteriosus)
  2. Drain to dorsal aortae (paired cranially, fused caudally)
31
Q

What are the derivatives of the aortic arch

A

a. Aortic sac will form proximal portion of aortic arch and brachiocephalic artery.
b. Third aortic arch – common carotid artery
c. Fourth aortic arch – right artery forms right subclavian artery; left artery forms a portion of aortic arch
d. Sixth aortic arch – right artery forms the pulmonary artery; left artery forms the pulmonary artery and ductus arteriosus
e. Seventh intersegmental artery – right artery forms distal part of right subclavian; left artery forms left subclavian a.

32
Q

What is the ductus arteriousus

A

Arterial blood shunt allowing blood in pulmonary trunk to bypass lungs and re-enter aorta. After birth, it closes to form ligamentum arteriosum.

33
Q

Explain the location of the Recurrent laryngeal nerves as they relate to the aortic arch

A

Recurrent laryngeal nerves originally loop around the distal portion of the sixth aortic arch. On the right, the distal portion of sixth aortic arch regresses, fifth aortic arch also regresses, thus right recurrent laryngeal nerve loops around 4th aortic arch (subclavian artery). On the left, the distal portion of the sixth aortic arch becomes the ductus arteriosus (thus, left recurrent laryngeal nerve loops around arch of aorta near ligamentum arteriosum).

34
Q

What does the Vitelline arteries supply

A
  1. Supply yolk sac.

2. Derivatives: celiac, superior mesenteric, inferior mesenteric arteries.

35
Q

What does the Umbilical arteries supply

A
  1. Paired branches of common iliac arteries; supply placenta.
  2. Derivatives: proximal portion remains patent (umbilical artery), distal portion form the medial umbilical ligament.
36
Q

What is Patent ductus arteriosus

A
  1. Ductus arteriosus normally closes after birth to form ligamentum arteriosum.
  2. Left-right blood supply.
  3. Pulmonary hypertension.
37
Q

What is Coarcation of the aorta

A
  1. Preductal – presents at birth because collateral cirulation does not develop prentally.
  2. Postductal – usually presents in later part of first decade, early adolescence. Does not typically present at birth because collateral circulation is established between internal thoracic and intercostal aa. Prenatally.
38
Q

What is Retroesophageal of right subclavian artery

A
  1. Subclavian artery normally forms from the right 4th aortic arch.
  2. In rare cases, the right 4th aortic arch degenerates; leaving the 7th intersegmental artery and a small portion of the dorsal aorta to form right subclavian artery.
  3. Differential growth shifts right subclavian to lie distal to origin of left subclavian a.
  4. Does not usually cause esophageal or tracheal constriction.
  5. If there is esophageal compression this is called dysphagia lusoria (difficulty swallowing due to compression by a vessel).
39
Q

What is Double aortic arch

A
  1. Right dorsal aorta between original of seventh intersegmental a. and fusion with left dorsal aorta persists.
  2. The vascular ring surrounding trachea and esophagus usually causes constriction.
40
Q

What is Absent inferior vena cava

A
  1. Right subcardinal vein fails to make connection with hepatic portion of vena cava.
  2. Caudal portion of body drains to azygos system of veins.
41
Q

What is Left superior vena cava

A
  1. Left common cardinal vein persists and forms a left superior vena cava.
  2. Right common cardinal vein degenerates.
  3. Left superior vena cava drains into right atrium via coronary sinus.
42
Q

What is Double superior vena cava

A
  1. Left and right common cardinal veins persists.
  2. Right superior vena cava drains into right atrium directly.
  3. Left superior vena cava drains into right atrium via coronary sinus.
43
Q

Explain early Lung bud development

A

A. Gives rise to larynx, trachea, bronchi, bronchioles, alveoli.
B. Develops during week 4 as a ventral diverticulum from the foregut.

44
Q

Explain the separation of the Lung bud from the foregut

A

Lung bud is initially in full communication with the foregut.

  1. Later separated from esophagus by 2 tracheoesophageal ridges.
  2. Tracheoesophageal ridges fuse to form tracheoesophageal septum.
  3. Fully separates trachea and esophagus.
  4. Pharynx and lung bud remain in contact via the primordial laryngeal inlet.
45
Q

What is a trecheoesophageal fistula

A

Results from abnormal division of the cranial part of foregut into respiratory and esophageal portions. This condition is most likely caused by a spontaneous deviation of the tracheoesophageal septum. Often associated with esophageal atresia (blind-ending esophagus), polyhydramnios, pneumonitis (lung inflammation).

46
Q

Explain the development of the Larynx

A
  1. Derived from lung bud.
  2. Cartilages and muscle from pharyngeal arches 4 an 6
  3. Rapid growth of laryngeal epithelium during week 6 results in occlusion of laryngeal lumen. Lumen is recanalized later in development, by week 10. Laryngeal atresia is a rare, life-threatening anomaly resulting from a failure of larynx to recanalize.
47
Q

Describe the development of the Bronchi and Lungs

A
  1. 5th week - lung bud divides into left and right primary bronchial buds.
  2. 6th week - secondary bronchial buds
  3. 7th week - tertiary bronchial buds (8-10).
  4. Branching into alveoli continues postnatally.
48
Q

How are congenital lung cysts formed

A

Formed by a dilation of terminal bronchi. These are often fluid-filled and in some cases can become malignant. If several cysts are present, the lungs will have a honeycomb appearance.

49
Q

What is the Pseudoglandular stage of Lung maturation

A

(5-16 weeks)

  1. Terminal bronchioles are formed, no respiratory bronchioles.
  2. Respiration not possible; fetuses born during this time are not viable.
  3. Fetal breathing movements typically start during 12th week of development.
    a. Strengthen thoracic muscles.
    b. Vital for lung development as amniotic fluid is breathed in.
    c. CLINICAL CORRELATION: Oligohydramnios (low level of amniotic fluid) often results in severe lung hypoplasia.
50
Q

What is the Canalicular stage of Lung maturation

A

(16-26 weeks)

  1. Lung tissue becomes highly vascular.
  2. By 24 weeks, respiratory bronchioles and alveolar ducts have formed.
  3. Type II alveolar cells begin forming surfactant at 20 weeks, but surfactant levels do not reach adequate amounts until about 26-28 weeks.
  4. Surfactant reduces surface tension in alveoli, facilitating expansion during inhalation.
  5. Fetuses born during this time may be viable (~50% or less chance) with intensive care, but often are not viable due to underdevelopment of alveoli at this stage (as well as underdevelopment of other systems).
51
Q

What is the Terminal sac stage of Lung maturation

A

(26 weeks to 32 weeks)

  1. Primitive alveoli form.
  2. Epithelium of alveoli becomes very thin and establishes close contact with capillaries.
  3. Fetuses born during this period may survive (80-95% chance); but still require intensive care.
  4. Sufficient surfactant production and adequate pulmonary vasculature are the most critical factors in determining survival and growth of premature infants.
52
Q

What is the Alveolar stage of Lung maturation

A

(32 weeks to 8 years postnatally)

  1. Fetus born during this period are almost as likely as full-term babies to survive.
  2. Alveoli continue to be formed during first 8 years of life (up to 300 million alveoli).
  3. On chest x-rays, the lungs of newborns will appear much more dense than adults.
53
Q

What is the cause of respiratory distress syndrome in premature infants

A

Premature infants often suffer a condition called respiratory distress syndrome (hyaline membrane disease) evidenced by respiratory distress (labored breathing) caused by the lack of surfactant production. Surfactant secretion can be induced by administering glucocorticoids to the mother prenatally. Postnatally, exogenous surfactants can be delivered to the preterm infant.

54
Q

Postnatal Cardiovascular derivatives

A

Foramen ovale = fossa ovalis
Ductus arteriosus = ligamentum arteriosum
Umbilical vein = ligamentum teres hepatis
Ductus venosus = ligamentum venosum
Umbilical arteries = medial umbilical ligaments

CV I (3 decks)

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