Lecture 11General med_2nd semester

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 19 - 20
• 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

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 18 -19 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 23 -24 day
• when the heart begins regularly to

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

• 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

12
(No Transcript)
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)

26
(No Transcript)
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 6 - 8 children from 1 000 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

• 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)

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

32
(No Transcript)