embryology of the heart Flashcards
why bother with embryology
- 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
another name for embryology
developmental biology
what is descriptive embryology
very descriptive
repeated observation of post mortem species to determine stages of development
what is mechanistic embryology
mechanistic
experimentation ( accidental or deliberate) to determine role of genes / proteins / environmental factors in cardiac development
what is gastrulation
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)
- ectoderm
- mesoderm ( middle layer )
- endoderm
when does gastrulation occur
during the 3rd week
what is the ectoderm
the outer layer of a gastrula
what comes from the ectoderm
it gives rise to structures that are outside of the body
- Central nervous system
- Peripheral nervous system
- Sensory epithelium of nose, ear and eye
- Epidermis of skin, hair and nails
- Pituitary, mammary
& sweat glands - Enamel of teeth
- neural crest ( which contributes to cardiac outflow, coronary arteries)
what comes from the mesoderm
all types of muscle
most system
kidneys
blood
bone
where is the mesoderm
the middle (inner) layer of a gastrula
what are the 3 parts of the mesoderm
- paraxial plate mesoderm
- intermediate plate mesoderm
- lateral plate mesoderm
where does most of the cardiovascular system come from
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
what do heart and blood vessels sometimes try to turn into
bone
what colour is first heart field
Red
what colour is second heart field
yellow
what does the first heart field turn into
future left ventricle
what does the 2nd heart field turn into
outflow tract
future right ventricle
atria
what are some cardiac transcription factors
Nkx 2.5
GATA
Hand
Tbx
MEF2
pitx2
Fog-1
what has caused increasing complexity of development
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
what are the 3 stages of cardiac formation
- Formation of the primitive heart tube
- Cardiac looping
- Cardiac septation
what does the paraxial plate mesoderm do
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)
what does the intermediate plate mesoderm:
generates the urogenital
system
- the kidneys, gonads,
and their respective duct
systems
what does the lateral plate mesoderm do
is found at the periphery of the
embryo. Splits into two layers;
- Somatic (parietal) layer mesoderm forms:
- Future body wall - Splanchnic (visceral) layer mesoderm forms:
- Circulatory system
- Connective tissue for glands
- Muscle, connective tissue and peritoneal components, of the wall of the gut
what does the endoderm give rise to
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
what causes improper left-right positioning
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.
what is the first stage of the development of the heart
formation of primitive heart tube
what is the second stage of the development of the heart
cardiac looping
what is the 3rd stage of the development of the heart
cardiac septation
what happens at the 3rd week of development (before day 19)
the heart is formed from cells that form a horseshoe shaped region called the cardiogenic region
what happens at day 19 (still third week)
two endocardial tubes form.
These tubes will fuse to form a single, primitive heart tube
what happens at day 21 (still third week)
as the embryo undergoes lateral folding, the two endocardial
tubes have fused to form a single heart tube
END OF STAGE 1
what are the 5 regions of the primitive heart tube from top to bottom
- truncus arteriosus
- bulbus cordis
- primitive ventricle
- primitive atrium
- sinus venosus
what does the proximal 1/3rd of the bulbus cordis give rise to
the muscular right ventricle
what is the lower part of the bulbus cordis called
conus cordis
what does the lower part of the bulbus cordis give rise to
smooth outflow portion
of the right and left ventricles
what is the upper part of the bulbus cordis called
truncus cordis
what does the upper part of the bulbus cordis give rise to
the proximal aorta & pulmonary trunk
what does the primitive/ primordial ventricle give rise to
the left ventricle
what does the primitive/ primordial atrium give rise to
- the anterior part of the right atrium
and - the entire left atrium
and - the left and right auricles
what does the sinus venosus (right and left horns) give rise to
forms part of the right atrium, vena cava and coronary sinus
what does the aortic sac give rise to
forms the aorta and pulmonary artery
what happens on day 22
heart begins to beat
what happens on day 23
heart tube begins to fold
what is cardiac looping
by approximately day 22-23
the heart tube elongates and alters its configuration again, forming a cardiac loop
during the folding of the heart tube how does the bulbus cordis move
inferiorly, anteriorly and to the embryo’s
right
during the folding of the heart tube how does the primitive ventricle move
to the embryo’s left side
during the folding of the heart tube how do the primitive atrium and the sinus venosus move
superiorly and posteriorly - resulting in the sinus venosus being posterior to the primitive atrium
what is the interatrial septum
a thin wall of tissue that separates the right and left atria of the heart
why is pressure greater in the right side of the heart than the left side in the developing fetus
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
what happens at the end of the 4th week
a crescent-shaped tissue
called the septum primum starts to grow towards the endocardial cushions
what is cardiac septation
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
when does aortic arch develop
week 4 - 7
how does blood flow in early heart development
- 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
what happens at the end of the 4th week (aorta pulmonary trunk development)
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
what happens at the end of the 5th week (aorta pulmonary trunk development)
- 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
what happens by week 8 (aorta pulmonary trunk development)
- 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
what do aortic archs develop from
aortic sac
describe aortic arches
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
describe 1st aortic arch
regresses early, but a remnant forms a portion of the maxillary artery.
describe 2nd aortic arch
regresses early, but a remnant forms portions of the hyoid and stapedial arteries.
describe 3rd aortic arch
contributes to the formation of the common carotid arteries bilaterally and the proximal internal carotid arteries bilaterally.
describe 4th aortic arch
The right arch contributes to the R proximal subclavian artery.
The left arch gives rise to the medial portion of the aortic arch.
describe 5th aortic arch
never forms or incompletely forms and regresses.
describe 6th aortic arch
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.
describe fetal circulation
- 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
describe post natal circulation (afterbirth)
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
