1. Lecture 11 General med_2nd semester
Development of the heart and blood vessels
Blood islands and constitution of the primitive blood circulation in the embryo
Development of the heart and large arteries, especially aortic arches
Fetal blood circulation
Congenital malformations of the heart and major blood vessels

2. CVS is the first system to function in embryos
blood begins to circulate by the end of the 3rd week
earliest blood vessels develop from cell aggregations called blood islands
(insulae sanguineae)
Cells of blood islands differentiate into 2 cell lines:
- central cells - hematogoniae or hemoblasts - they give rise to primitive
red blood corpuscles (erythrocytes)
- outer or peripheral cells - angioblasts - they become flattened and give rise to endothelial cells
angioblasts then join up to form primitive blood vessels

3. blood islands appear as red spots and gradually
develop in 3 locations /sites/:
1) in the extraembryonic mesoderm of the yolk sac -
at about day 17 after fertilization - the vitelline
vasa
2) in the extraembryonic mesoderm of the
connecting stalk - at about day 18 after
fertilization – the umbilical vasa
3) in the mesenchyme of the embryo -
between day
here they give rise to embryonic blood vessels
- ventral and dorsal aortae that are interconnected
by branchial or aortic arches of the branchial apparatus
(future neck region)
in total, are 6 pairs of aortic arches
in the 21 st day, the vessels of all 3 regions join up
and connect with the primitive heart, so
that the primitive blood circulation is constituted
also, the primitive heart begins to beat in this time

4. Primitive blood circulation
at each contraction of the primitive heart, the blood is pumped through ventral aortae in the aortic arches
aortic arches run within branchial arches and open into the dorsal aortae (paired cranially), from which the precursors of the internal carotid artery run forwards to supply the head on the left as well as on the right side
from the mid-cervical region, the dorsal aortae fuse in one common trunk - unpaired dorsal aorta

5. The dorsal aorta sends off branches of 3 types:
- intersegmental arteries - run between developing somites
- vitelline arteries - (several pairs) - run to the yolk sac
- umbilical arteries - one pair
that run to the villous chorion (chorion frondosum) and conduct deoxygenated blood from the embryo to the placenta
to the heart the blood returns through superior cardinal veins (left and right) from the cranial portion of the embryonic body and through inferior cardinal veins from the caudal part of the embryo
near the heart, both veins they join at each side and form common cardinal vein
from the chorion frondosum, blood returns at first via paired umbilical veins, from which the left vein persists and brings oxygenated blood to the embryo)
from the yolk sac, blood returns to the embryo through vitelline veins (several pairs)

6. Development of the heart
the first indications of the heart development are seen in embryos aged days
the anlage of the heart forms in the cephalic end of the embryonic disc and is paired
the splanchnic mesoderm (= mesoderm adjacent to the endoderm) becomes thicker and forms on the right and left side so called cardiogenic area
cells of the area migrate between mesoderm and endoderm and arrange as to longitudinal cellular strands called cardiogenic cords
cords become canalized to form two thin-walled endothelial tubes - called endocardial heart tubes

7. as the lateral folds develop, the endocardial heart tubes gradually approach each other and fuse from the cephalocaudal direction to form a single unpaired heart tube
fusion of endocardial heart tubes in one single is followed by a fusion of paired pericardial cavities so that finally
single (common) pericardial cavity arises

8. if fusion of both tubes is completed, the
heart tube lies within the pericardial
cavity and is attached to its dorsal
side by a fold of mesodermal tissue -
the dorsal mesocardium
the dorsal mesocardium is transitory
structure and soon degenerates
after disappearing of the mesocardium,
the heart tube is freely housed in the
pericardial cavity, being firmly fixed only
at two sites:
at arterial (cranial) and
venous (caudal) ends
a single heart tube stage is
achieved during the day
when the heart begins regularly to
beat

9. Formation of the heart wall
as the heart tubes fuse, the mesenchyme around them proliferates and forms a thick layer of cells - myoepicardial mantle
from the endothelium of the heart tube the myoepicardial mantle is separated by cardiac jelly - a gelatinous connective tissue
cells of the myoepicardial mantle differentiate into:
- mesothelial cells - outermost layer called epicardium (visceral pericardium)
- myoblasts - cardiomyocytes of myocardium
cells of cardiac jelly give rise to subendocardial layer of endocardium
the mentioned processes result in three-layered composition of the heart wall known from microscopic anatomy:
the inner endocardium, the middle myocardium, and the outer epicardium

10. in caudocranial axis there are as follows: sinus venosus - venous end,
development of the heart tube then continues by its uneven growth in the width and in the
length
as a result of uneven growth of the heart tube in the width, it distinguishes in several portions:
in caudocranial axis there are as follows:
sinus venosus - venous end,
receiving blood from the umbilical,
vitelline and common cardiac
veins on each side
primitive atrium - separated
from the sinus by a terminal sulcus,
primitive ventricle - separated
from the atrium by the atrioventricular
sulcus,
both portions are connected each other
with an atrioventricular foramen
bulbus cordis - is continuous with ventricle through the primary interventricular foramen; this portion will give rise to part the definitive right ventricle
truncus arteriosus - arterial end of the tube, which divides into paired ventral aortae
(in human embryos the situation is rather complicated - the truncus enlarges direct into aortic sac, blood from
the aortic sac enters the aortic arches)

11. Heart looping - formation of heart loop
heart tube then grows rapidly in length and forms a S-shaped loop in craniodaudal axis
heart looping is accompanied by changes in topography of individual portions of the heart tube:
the cephalic portion of the tube bends in ventral and caudal directions and to the
right
the caudal atrial portion shifts in dorsocranial direction and to the left
after heart looping, portions of the heart become to lie their definitive places

13. Septation of the heart (formation of cardiac septa)
the septation process = division of the heart into two halves down midline
the process begins in the 5th week and ends in a week later
3 septae take part in division of the heart in the right and left chamber
there are as follows:
interatrial septum
interventricular septum
aorticopulmonary septum
Development of the interatrial septum
the definitive interatrial septum shows a complicated development
septum originates from two septae that fuse each other after birth of the fetus:
the septum primum and
the septum secundum

14. the septum primum is based upon the roof of the common atrium
it continues to grow towards the atrioventricular foramen
the septum never divides the atrium in two parts because it does not reach to
atrioventricular foramen
a gap - called ostium primum - remains between border of the septum and
the atrioventricular foramen
when the ostium primum will close over, near the roof another opening called the
ostium secundum begins to form in the septum primum

15. the septum secundum (the second septum ) then begins to grow down on the right hand side of the septum primum
from the beginning, the septum has semilunar shape and its border delineates oval foramen - the foramen ovale
as the ostium secundum and oval foramen lie in different levels, the blood may pass from the right atrium into the left atrium in the fetal period
through the oval foramen into the gap between both septae and through the ostium secundum

16. after birth, the blood pressure on the left side of the heart rapidly rises as a result
of opening of pulmonary circulation and closing of the ductus arteriosus
the increased pressure forces cause fusion the septum primum with the septum
secundum and the fetal communication between the left and right atrium is closed

17. Development of the interventricular septum
the septum develops in the common ventricle
it begins to grow up the primitive heart apex to the atrioventricular
foramen

18. Development of the aorticopulmonary septum
this septum divides bulbus cordis into 2 main arterial trunks: aorta and pulmonary artery
it has spiral path that results in final topographical relations of both vessels that are known from the anatomy

19. Development of the valves

20. Aortic arches
aortic arches are short vessels connecting ventral and dorsal aortae on each side
they run within branchial (pharyngeal) arches
are based gradually the 4th and 5th week, in six pairs in total
the first, second and fifth pairs are developmental inperspective and they soon disappear

21. the 1st aortic arch – disappears (a small portion persists and forms a piece of the maxillary artery)
the 2nd aortic arch – disappears (small portions of this arch contributes to the hyoid and stapedial arteries)
the 3rd aortic arch - has the same development on the right and left side
it gives rise to the initial portion of
the internal carotid artery,
the remainder of its trunk is
formed by the cranial portion of
the dorsal aorta + primitive internal
carotid
the external carotid is deriving from
the cranial portion of the ventral aorta
the common carotid corresponds to a
portion of the ventral aorta between
exits of the third and fourth arches

22. the 4th aortic arch - has ultimate fate different on the right and left side
on the left - it forms a part of the arch of the aorta between left
common carotid and left subclavian artery
on the right - it forms the proximal segment of the right subclavian artery
the 5th aortic arch - is transient and soon obliterates

23. the 6th aortic arch - pulmonary arch - gives off a branch on each side that grows toward the developing lung bud
on the right side, the proximal part transforms into the right branch of the pulmonary artery and the distal part disappears
on the left side, the distal part persists as the ductus arteriosus during intrauterine life
the proximal part gives rise to the left branch of the pulmonary artery

24. The great arteries in the adult

25. Fetal blood circulation
from the placenta well-oxygenated blood is conducted to the fetus via umbilical vein (about 80% saturated with oxygen)
about 1/3 of the blood passes through the liver (hepatic sinusoids), whereas the remainder bypasses the liver going through the ductus venosus direct into the inferior vena cava
the inferior vena cava enters the right atrium of the heart
the blood from the inferior vena cava is largely directed through the foramen ovale into the left atrium (mixing with blood of pulmonary veins), from which passes into the left ventricle and leaves it via the ascending aorta
blood continues through descending aorta and is conducted via branches of it to the individual organs
a small volume of oxygenated blood from inferior vena cava remains in the right atrium and mixes with deoxygenated blood from the superior vena cava
the blood from the right atrium passes into the right ventricle and leaves it via pulmonary trunk
because the lungs are collapsed and have the high pulmonary vascular resistance, most of blood in the pulmonary trunk passes through the ductus arteriosus into the aorta (through lungs 5 % blood only goes)

27. in order of reoxygenation, the blood returns to the placenta via pair of umbilical arteries
3 shunts are in the fetal blood
circulation:
- ductus venosus - obliterates
in the ligamentum venosum,
- foramen ovale - normally
closes functionally at birth,
- ductus arteriosus - obliterates
in the ligamentum arteriosum

28. Congenital malformations of the heart and great blood vessels
are relatively frequent
they occur in children from at birth
their etiology is not clear and consists in rather complicated development of the heart and blood vessels
most of malformations are of multifactorial origin
Anatomical and functional classification of malformations
1) malformations with the left-right shunt (short circuit)
oxygenated blood flows from the left to the right part of the heart, respectively from the aorta to the pulmonary trunk
clinically: absence of cyanosis
- atrial septal defect (s)
- ventricular septal defect
- persistent ductus arteriosus

29. 2) malformations with the right-left shunt (short circuit) –
complicated malformations characterized by passage of venous blood from the right
to the left side
clinically: permanent hypoxia, cyanosis of the central type, polyglobulia and asthma
- tetralogy of Fallot or morbus coerulleus (= a complex of 4 anomalies: stenosis of the pulmonary artery,
ventricular septal defect, dextroposition of
the aorta, hypertrophy of the right ventricle)
- transposition of the great vessels
- tricuspid atresia

30. - aortic valvular stenosis or atresia - coarctation of the aorta
3) malformations without shunts (short circuits) - the pulmonary and systemic circulations are separated
blood volumes on the right and the left sides are equal
the group includes:
- aortic valvular stenosis or atresia
- coarctation of the aorta
- double aortic arch
- right aortic arch
- valvular stenosis of the pulmonary artery
4) abnormalities in heart position:
- dextrocardia - the heart lies on the right side
- ectopia cordis - the heart is located on the surface of the chest
Sequency of CM of the heart and great vessels:
- persistent ductus arteriosus
- ventricular septal defect
- tetralogy of Fallot
- atrial septal defect (s)
- stenosis of pulmonary trunk

31. DEVELOPMENT OF THE SPLEEN
a spleen is entirely mesodermal in origin; developmentally it has close relations to the stomach
an anlage of the spleen occurs during weeks 4-5 within the dorsal mesentery, just dorsal to the greater curvature of the stomach (at this time the stomach still lies in midline of the body). The spleen develops between the mesothelial layer covering the dorsal mesentery. Initially it forms as isolated spleen islands, which then coalesce (in some ungulates, the spleen remains as islands).
adult position of the spleen: As the stomach rotates the spleen is carried to the left with the dorsal mesentery. The mesentery fuses to the dorsal wall of the coelom where the left urogenital ridge is developing. A short stretch of mesentery joining the spleen to the ridge is known as the lienorenal ligament. The artery to the spleen is a branch of the coeliac artery and runs in the mesentery in a tortuous way.
an accessory spleen tissue arises (sometimes even in the pancreas) in as many as 10 % of the population; this anomalous situation in humans therefore corresponds to that found normally in some animals.
the spleen makes lymphocytes and produces, stores and destroys red blood cells both in the fetus and after birth