Development of the Cardiovascular System 3 Flashcards

1
Q

Explain the division of the primitive atrium

A
  • To be divided into the right and left atrium
  • The septum primum and septum secundum being involved
  • the SP grows down from the roof of the atrium, with the foramen primum (FP) between it and the endocardial cushions
  • The FP disappears leaving the SP to fuse with the endocardial cushions = foramen secondum
  • The SS then grows down beside the FS
  • SS leaves an oval opening = foramen ovale allowing +O2 blood flow between the two atria R →L
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2
Q

What are the 3 important bypasses?

A
  • Ductus venosus
  • Foramen ovale
  • Ductus arteriosus
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3
Q

What is the difference between before and after birth in the heart

A

Before birth
- The right atrium has higher pressure than the left
- The septum secundum has the foramen ovale to regulate blood flow
After birth
- The left atrium has higher pressure than the right
- Instant physiological closure of the foramen ovale = oval fossa
- septum primum acts as a valve

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4
Q

how is the primitive ventricle divided

A
  • The primitive ventricle needs to be divided to left and right
  • The muscular part of the interventricular (IV) septum grows upward as a muscular ridge
  • Growth stops short of the endocardial cushions = IV foramen (communication btw the ventricles)
  • at the end of week 7, the membranous part of the IV septum grows down to complete the growth
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5
Q

Explain the closure of the IV foramen

A

This closure results in the fusion of tissues from
- The right and left bulbar ridge
- The endocardial cushion
- After its closes, the pulmonary trunk communicates with the right ventricle and the aorta communicates with the left ventricle

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6
Q

What changes happen to the sinus venosus

A
  • There are initially left and right horns opening into the atrium
  • Shift of blood flow from L → R with R horn increasing and L decreases
  • An orifice (opening) moves to the R horn to open into the right atrium (RA) which then gets incorporated into the wall of the RA with SVC and IVC
  • The L horn becomes the coronary sinus
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7
Q

How is the left atrium (LA) formed

A
  • The primordial pulmonary vein is incorporated into the LA making most of the wall smooth
  • The expanding atrium gets the pulmonary vein and its branches are incorporated into its wall
  • 2 branches on both left and right main veins then split into 4 individual pulmonary veins bringing -O2 blood from the lungs
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8
Q

Explain the partitioning of the BC and TA

A
  • Muscular, bulbar and truncated ridges (derived from the neural crest mesenchyme) fuse at the aorticopulmonary septum
  • The neural crest cells move thru the pharynx and it’s arches to form the ridges
  • The partitioning is a 180º spiral dividing the BC and TA into 2 channels: pulmonary trunk (RV) and aorta (LV)
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9
Q

what does the spiral partitioning of the TA and BC channels prevent

A
  • The LV sends +O2 blood to the aorta and the RV sends -O2 blood to the lungs
  • without the spiralled septum, +O2 blood will go to the lungs and -O2 blood goes to the aorta
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10
Q

what is the fate of the bulbus cordis

A
  • It ends up being incorporated into the walls of the ventricles
  • RV: it is the conus arteriosus giving origin to the pulmonary trunk
  • LV: forms the walls of the aortic vestibule which is inferior to the aortic valve
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11
Q

What are some structural anomalies of the CV system

A
  • Atrial Septum Defects (ASD): excessive reabsorption of the septum primum, defective development of the septum secundum. Can result in patent foramen ovale/primum
  • Ventricular septal defects (VSD): involves the membranous part of the septum. Results in patent interventricular foramen
  • Transposition of the Great Arteries (TGA): happens when aorticopulmonary septum doesn’t spiral
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12
Q

Explain the fetal circulation

A
  • +O2 blood returns to the fetus from the umbilical vein
  • Half goes through the liver and half goes through the ductus venosus to the IVC
  • IVC → RA either goes through the foramen ovale to the LA or to the RV
  • RV → pulmonary trunk to either the aorta via the ductus arteriosus or the lungs
  • ~O2 blood leaves lungs to the LV to the aorta the intersegmental arteries has umbilical arteries carrying blood to the placenta
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13
Q

what is the difference between the pre and postnatal circulation

A
  • The lungs are nonfunctional
  • The placenta serves in gas exchange
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14
Q

Explain postnatal circulation

A
  • At the time of birth, placental circulation is replaces with pulmonary circulation
  • ductus venosus and arteriosus and foramen ovale close
  • Decrease in pressure in the IVC and right side of the heart bc the placental blood flow is lost and inflation of the lungs decrease the pulmonary vascular resistance
  • Increase in pressure of the left side of the heart be of increase in pulmonary flow
  • blood pressure LA > RA so septum primum is pressed against secundum and the foramen ovale closes
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15
Q

What are the adult derivatives of fetal structures

A
  • Umbilical vein = ligamentun teres
  • Ductus venosus = ligamentum venosum
  • Umbilical arteries = medial umbilical arteries and vesicular arteries
  • Foramen ovale = fossa ovalis
  • ductus arteriosus = ligamentum arteriosum
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16
Q

What occurs with the patent bypasses

A
  • Patent ductus arteriosus (PDA): blood flows from PT to aorta
  • Patent foramen ovale: blood flows from LA to RA and cardiac output is decreased