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IMMS lectures > embryology of the heart > Flashcards

embryology of the heart Flashcards

1
Q

why bother with embryology

A
  • gives insight into genetic evolution
  • gives insight into post natal anatomy
  • helps understand congenital heart disease
  • increasing hope that adult diseases could be treated by invoking embryonic processes
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2
Q

another name for embryology

A

developmental biology

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3
Q

what is descriptive embryology

A

very descriptive
repeated observation of post mortem species to determine stages of development

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4
Q

what is mechanistic embryology

A

mechanistic
experimentation ( accidental or deliberate) to determine role of genes / proteins / environmental factors in cardiac development

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5
Q

what is gastrulation

A

the mass movement and invagination of the blastula to form three layers. -

it is the process by which a blastula (single layer of cells) forms a gastrula which has 3 layers (trilaminar structure)

  1. ectoderm
  2. mesoderm ( middle layer )
  3. endoderm
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6
Q

when does gastrulation occur

A

during the 3rd week

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7
Q

what is the ectoderm

A

the outer layer of a gastrula

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8
Q

what comes from the ectoderm

A

it gives rise to structures that are outside of the body

  1. Central nervous system
  2. Peripheral nervous system
  3. Sensory epithelium of nose, ear and eye
  4. Epidermis of skin, hair and nails
  5. Pituitary, mammary
    & sweat glands
  6. Enamel of teeth
  7. neural crest ( which contributes to cardiac outflow, coronary arteries)
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9
Q

what comes from the mesoderm

A

all types of muscle
most system
kidneys
blood
bone

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10
Q

where is the mesoderm

A

the middle (inner) layer of a gastrula

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11
Q

what are the 3 parts of the mesoderm

A
  1. paraxial plate mesoderm
  2. intermediate plate mesoderm
  3. lateral plate mesoderm
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12
Q

where does most of the cardiovascular system come from

A

derived from cells in the mesoderm ( blood, heart, smooth muscle, endothelium)

Even though there is some contribution from cardiac neural crest cells from the ectoderm

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13
Q

what do heart and blood vessels sometimes try to turn into

A

bone

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14
Q

what colour is first heart field

A

Red

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15
Q

what colour is second heart field

A

yellow

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16
Q

what does the first heart field turn into

A

future left ventricle

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17
Q

what does the 2nd heart field turn into

A

outflow tract
future right ventricle
atria

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18
Q

what are some cardiac transcription factors

A

Nkx 2.5
GATA
Hand
Tbx
MEF2
pitx2
Fog-1

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19
Q

what has caused increasing complexity of development

A

as organisms evolve, gene duplication occurs sporadically ( from single gene to entire genome)
each copy of each gene can then evolve separately into different ( but related ) gene

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20
Q

what are the 3 stages of cardiac formation

A
  1. Formation of the primitive heart tube
  2. Cardiac looping
  3. Cardiac septation
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21
Q

what does the paraxial plate mesoderm do

A

gives rise to somites
somites give rise to supporting tissues of the body:
a. Myotome (muscle tissue)
b. Sclerotome (cartilage and bone)
c. Dermatome (dermis of the
skin)

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22
Q

what does the intermediate plate mesoderm:

A

generates the urogenital
system
- the kidneys, gonads,
and their respective duct
systems

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23
Q

what does the lateral plate mesoderm do

A

is found at the periphery of the
embryo. Splits into two layers;

  1. Somatic (parietal) layer mesoderm forms:
    - Future body wall
  2. Splanchnic (visceral) layer mesoderm forms:
    - Circulatory system
    - Connective tissue for glands
    - Muscle, connective tissue and peritoneal components, of the wall of the gut
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24
Q

what does the endoderm give rise to

A

gives rise to the:
a. Epithelial lining of the gastrointestinal tract, respiratory tract and urinary
bladder
b. Parenchyma of the thyroid gland, parathyroid glands, liver and pancreas
c. Epithelial lining of the tympanic cavity and auditory tube

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25
Q

what causes improper left-right positioning

A

all vertebrate hearts have a leftward ventricle

many mutations are associated with improper left-right positioning eg kartagener’s syndrome

during development, the node secretes nodal, which circulates to the left due to ciliary movement.

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26
Q

what is the first stage of the development of the heart

A

formation of primitive heart tube

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27
Q

what is the second stage of the development of the heart

A

cardiac looping

28
Q

what is the 3rd stage of the development of the heart

A

cardiac septation

29
Q

what happens at the 3rd week of development (before day 19)

A

the heart is formed from cells that form a horseshoe shaped region called the cardiogenic region

30
Q

what happens at day 19 (still third week)

A

two endocardial tubes form.
These tubes will fuse to form a single, primitive heart tube

31
Q

what happens at day 21 (still third week)

A

as the embryo undergoes lateral folding, the two endocardial
tubes have fused to form a single heart tube
END OF STAGE 1

32
Q

what are the 5 regions of the primitive heart tube from top to bottom

A
  1. truncus arteriosus
  2. bulbus cordis
  3. primitive ventricle
  4. primitive atrium
  5. sinus venosus
33
Q

what does the proximal 1/3rd of the bulbus cordis give rise to

A

the muscular right ventricle

34
Q

what is the lower part of the bulbus cordis called

A

conus cordis

35
Q

what does the lower part of the bulbus cordis give rise to

A

smooth outflow portion
of the right and left ventricles

36
Q

what is the upper part of the bulbus cordis called

A

truncus cordis

37
Q

what does the upper part of the bulbus cordis give rise to

A

the proximal aorta & pulmonary trunk

38
Q

what does the primitive/ primordial ventricle give rise to

A

the left ventricle

39
Q

what does the primitive/ primordial atrium give rise to

A
  • the anterior part of the right atrium
    and
  • the entire left atrium
    and
  • the left and right auricles
40
Q

what does the sinus venosus (right and left horns) give rise to

A

forms part of the right atrium, vena cava and coronary sinus

41
Q

what does the aortic sac give rise to

A

forms the aorta and pulmonary artery

42
Q

what happens on day 22

A

heart begins to beat

43
Q

what happens on day 23

A

heart tube begins to fold

44
Q

what is cardiac looping

A

by approximately day 22-23
the heart tube elongates and alters its configuration again, forming a cardiac loop

45
Q

during the folding of the heart tube how does the bulbus cordis move

A

inferiorly, anteriorly and to the embryo’s
right

46
Q

during the folding of the heart tube how does the primitive ventricle move

A

to the embryo’s left side

47
Q

during the folding of the heart tube how do the primitive atrium and the sinus venosus move

A

superiorly and posteriorly - resulting in the sinus venosus being posterior to the primitive atrium

48
Q

what is the interatrial septum

A

a thin wall of tissue that separates the right and left atria of the heart

49
Q

why is pressure greater in the right side of the heart than the left side in the developing fetus

A

the lungs (and thus the pulmonary circulation) are not fully functional

  • this creates increased vascular resistance in the pulmonary arterial circulation
  • and increased pressure in the right side of the heart (which
    supplies the pulmonary arterial circulation)

As a result, as blood enters the right atrium, much of this
blood is shunted to the left atrium - down its pressure gradient

50
Q

what happens at the end of the 4th week

A

a crescent-shaped tissue
called the septum primum starts to grow towards the endocardial cushions

51
Q

what is cardiac septation

A

the superior and inferior endocardial cushions grow and meet at the AV canal
- superior grows from bottom up,
inferior grows from top down

superior continues up to divide LA/RA (interatrial septum) - embryological deficit here = foramen ovale (allows blood R –> L)
closed off at birth to fossa ovalo

inferior continues down to form IV septum separating LV/RV
- has an upper membranes part, lower muscular part

52
Q

when does aortic arch develop

A

week 4 - 7

53
Q

how does blood flow in early heart development

A
  • blood will flow from the atria, through the left and right atrioventricular canals and into the common ventricle
  • blood then leaves the heart via the truncus arteriosus
  • which will eventually be partitioned into an aorta and a pulmonary trunk
54
Q

what happens at the end of the 4th week (aorta pulmonary trunk development)

A

a muscular ventricular septum grows superiorly from the floor of the ventricle. This septum divides this
area in to left and right ventricles.

  • An opening still remains between the muscular ventricular septum and the fused endocardial cushion.
    This opening is called the interventricular foramen
55
Q

what happens at the end of the 5th week (aorta pulmonary trunk development)

A
  • two ridges of tissue appear
    on the sides of the truncus arteriosus. These masses of tissue are called the conotruncal ridges (truncoconal
    swellings)
  • These ridges grow towards each other and make a spiral shaped septum, called the aorticopulmonary septum
    which divided the truncus arteriosus into the aorta and pulmonary trunk
  • As the conotruncal rises grow and fun to form the aorticopulmonary septum, they also grow inferiorly into
    the ventricles themselves
  • The aorticopulmonary septum will fuse with the already fused endocardial cushions and the muscular
    ventricular septum
56
Q

what happens by week 8 (aorta pulmonary trunk development)

A
  • Once the aorticopulmonary septum, endocardial cushions and muscular ventricular septum fuse (by
    week 8), they from the membranous ventricular septum - this septum closes off the opening known as the interventricular foramen
  • Now, blood enters the right ventricle through the right atrioventricular opening and leaves via the
    newly developed pulmonary trunk
  • Blood enters the left ventricle through the left atrioventricular opening and leaves via the newly developed aorta
57
Q

what do aortic archs develop from

A

aortic sac

58
Q

describe aortic arches

A

have a pair of branches (right and left) traveling within each pharyngeal arch and ending in the dorsal aorta. Initially, the arches arise in symmetrical pairs, but after remodeling, the arches become asymmetric, and several of the arches regress. All six pairs are not present simultaneously; they develop and regress at different stages

59
Q

describe 1st aortic arch

A

regresses early, but a remnant forms a portion of the maxillary artery.

60
Q

describe 2nd aortic arch

A

regresses early, but a remnant forms portions of the hyoid and stapedial arteries.

61
Q

describe 3rd aortic arch

A

contributes to the formation of the common carotid arteries bilaterally and the proximal internal carotid arteries bilaterally.

62
Q

describe 4th aortic arch

A

The right arch contributes to the R proximal subclavian artery.
The left arch gives rise to the medial portion of the aortic arch.

63
Q

describe 5th aortic arch

A

never forms or incompletely forms and regresses.

64
Q

describe 6th aortic arch

A

The right and left arches separate into ventral and dorsal segments.

The ventral segments are responsible for the formation of the pulmonary arteries bilaterally.

The left ventral arch also contributes to the formation of the pulmonary trunk.

The right dorsal arch regresses.

The left dorsal arch forms the ductus arteriosus, which later closes and is termed the ligamentum arteriosum.

65
Q

describe fetal circulation

A
  • Oxygenated blood from the placenta enters the foetus though the umbilical vein
  • Most of the newly oxygenated blood bypasses the liver via the ductus venosus and
    combines with DEOXYGENATED BLOOD in the inferior vena cava
  • Blood then join deoxygenated blood from the superior vena cava and empires into
    the right atrium
  • Since pressure in the right atrium is larger than the presses in the left atrium, most
    blood will be shunted through the foramen ovale
  • Some blood does travel from the right atrium to the left atrium via the pulmonary
    trunk but most blood moves directly to the aorta via the DUCTOS ARTERIOSUS
  • Deoxygenated blood returns to the placenta via the UMBILICAL ARTERIES
    originating from the internal iliacs near the bladder
66
Q

describe post natal circulation (afterbirth)

A

With the first breath, increased alveolar O2 pressure causes vasodilation in the
pulmonary vessels
- Obstetrical climbing induces spontaneous constriction and change of the
UMBILICAL VEIN to the LIGAMENTUM TERES
- The UMBILICAL ARTERIES also change to
the MEDIAL UMBILICAL LIGAMENTS
- Within 10-15 hours after birth, the DUCTUS
ARTERIOSUS constricts to become the
LIGAMENTUM ARTERIOUSUM
- Increased left atrial pressure and
decreased right atrial pressure causes the FORAMEN OVALE to close and
become the FOSSA OVALIS
- The DUCTUS VENOSUS also constricts and will become the LIGAMENTUM
VENOSUM

IMMS lectures (22 decks)

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