Lecture 11Lecture 11 ESS_2nd semesterESS_2nd semester

Development of the heart and Development of the heart and blood vessels blood vessels

Blood islBlood islandsands and constitution of the primitive and constitution of the primitive blood blood circulation in the embryocirculation in the embryo

Development of the heart and large arteries,Development of the heart and large arteries, especially aortic archesespecially aortic arches

Fetal blood circulationFetal blood circulation

Congenital malformations of the heart andCongenital malformations of the heart and major major blood vesselsblood vessels

CVS is the first system to function in the embryoblood begins to circulate by the end of the 3rd weekearliest blood vessels develop from blood islands (insulae

sanguineae)- Mesenchymal origin?

blood islands consists of 2 cell lines:- central cells - hematogoniae or hemoblasts - they give rise to

primitivered blood corpuscles (erythrocytes)

- peripheral cells - angioblasts - they become flattened and give rise to endothelial cells

angioblasts then join up and form primitive blood vessels

blood islands appear as red spots and gradually develop at 3 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 19 - 20 here they give rise to the embryonic blood vessels - ventral and dorsal aortae that are interconnectedby branchial or aortic arches in the future cephalic and neck regionin total, 6 pairs of aortic arches occur

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 constitutes

the primitive heart begins to beat in this time period

Primitive blood circulation

At each contraction of the primitive heart, the blood is pumped through ventral aortae in the aortic archesaortic 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

In the mid-cervical region, the dorsal aortae fuse in one common trunk - unpaired dorsal aorta

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 pairthat run to the villous chorion (chorion frondosum) and conduct deoxygenated blood from the embryo to the placentato 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 embryonear the heart, both veins they join at each side and form common cardinal vein

from the villous chorion, 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)

Ventral aorta

1 Development of the heartthe first indications of the heart development are seen in embryos aged 18 -19 daysthe anlage of the heart forms in the cephalic end of the embryonic disc and is paired. The splanchnic ,intraembryonic, mesoderm (= mesoderm adjacent to the endoderm ) becomes thicker and forms on the right and left side so called cardiogenic area. The mesenchymal cells migrate around the prechordal plate. Cells of the area migrate between mesoderm and endoderm and arrange as to longitudinal cellular strands called cardiogenic cordscords become canalized to form two thin-walled endothelial tubes - called endocardial heart tubes

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 into one single is followed by a fusion of paired pericardial cavities so that finallysingle (common) pericardial cavity arises

DAY: 20 & 21

If the fusion is completed, theheart tube lies within the pericardial cavity and is attached to its dorsalside by a fold of mesodermal tissue -the dorsal mesocardium

The dorsal mesocardium is transitory

structure that soon degenerates

After disappearing of the mesocardium,

the heart tube is freely housed in thepericardial cavity, being firmly fixed

onlyat two sites:at arterial (cranial) and venous (caudal) ends

the single heart tube stage is achieved during the 23 -24 day when the heart begins regularly to beat

2 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(PURKiNjE FIBERS)

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

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 cardialveins on each side

primitive atrium - separated

from the sinus by a terminal sulcus,

primitive ventricle - separated from the atrium by the atrioventricularsulcus,both portions are connected each otherwith 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)

3 Heart looping - formation of heart loop

heart tube then grows rapidly in length and forms a S-shaped, lateral view, 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

rightthe caudal atrial portion shifts in dorsocranial direction and to the left

after heart looping is finished, the portions of heart become to lie their definitive places

4 Septation of the heart (formation of cardiac septa)

the septation process = division of the heart into two halves down midlinethe 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 chamberthere are as follows:

interatrial septuminterventricular 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

the septum primum is based upon the roof of the common atriumit continues to grow towards the atrioventricular foramenthe septum never divides the atrium in two parts because it does not reach toatrioventricular foramena gap - called ostium primum - remains between border of the septum and the atrioventricular foramenwhen the ostium primum will close over, near the roof another opening called

the ostium secundum begins to form in the septum primum

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

after birth, the blood pressure on the left side of the heart rapidly rises as a resultof 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

Development of the interventricular septum

the septum develops in the common ventricleit begins to grow up the primitive heart apex to the AV-foramen

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

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Aortic archesAortic arches are short vessels connecting ventral and dorsal aortae on each sidethey run within branchial (pharyngeal) archesare based gradually the 4th and 5th week, in 6 pairs in totalthe first, second and fifth pairs are developmental inperspective and they soon disappear

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 sideit gives rise to the initial portion ofthe 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

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 arteryon the right - it forms the proximal segment of the right

subclavian arterythe 5th aortic arch - is transient and soon obliterates

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

The great arteries in the adult

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 cavathe 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 aortablood 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 cavathe 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)

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

Congenital malformations of the heart and great blood vessels

are relatively frequentthey occur in 6 - 8 children from 1 000 at birththeir etiology is not clear and consists in rather complicated development of the heart and blood vesselsmost of malformations are of multifactorial origin

Anatomical and functional classification of malformations1) 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

2) malformations with the right-left shunt (short circuit) – complicated malformations characterized by passage of venous blood from

the rightto the left sideclinically: 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

3) malformations without shunts (short circuits) - the pulmonary and systemic circulations are separatedblood 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