Cardiology health and medicine presentation

1. CARDIOVASCULAR SYSTEM

2. PRIMARY HEART FIELDS
• Commences by the middle of the third week.
• Progenitor heart cells lie on the epiblast , adjacent to the cranial
end of the primitive steak and migrate though this to the
splachnic layer of the lateral plate mesoderm forming a hosrse
shoe shaped cluster of cells
• Called the Primary Heart Field
• These PHC are specified to become the atria, left ventricle and
most of the right ventricle.

4. THE SECONDARY HEART FIELD
• Appear later on (day 20-21)
• Is a cluster of cells located in the splanchnic mesoderm ventral to the
posterior pharynx.
• Forms part of the right ventricle and outflow tract (conuc cordis and
truncus arteriosus)
• Cells from the PHF are induced are form cardiac myoblasts and blood
islands that will later form blood cells and vessels (vasculogenesis)
• The islands unite and form a horseshoe-shaped endothelial-lined tube
surrounded by myoblast known cardiogenic region and the
intraembryonic cavity over it then develops into pericardial cavity.
• Other blood islands appear bilaterally and parallel to the midline of the
embryonic shield and form dorsal aortae

5. FORMATION AND POSITIONING OF HEART
TUBE
• Initially the cardiogenic area is anterior to the oropharyngeal membrane
but with the rapid growth of the brain and forming of the neural tube,
the oropharyngeal membrane is pulled forward and the heart and
pericardiac cavity moves caudally to the cervical then thoracic region.
(165. fig. 13.4)
• Also the caudal region of the tube merges except at the caudal most
ends and the central part expands and forms the outflow tract and
ventricles forms a tube consisting of inner endothelial lining and outer
myocardial layer.
• receives venous drainage on caudal pole and begins to pump blood out of
the first aortic arch into the dorsal aorta at its cranial pole. Pg. 165 fig.
13.5

7. • Fig 13.5 the dorsal mesocardium holds the tube attached to the
pericardial cavity, later disappears and forms the transverse
pericardial sinus and so the heart is now suspended by blood
vessels in the pericardiac cavity.
• The mesothelial cells give rise to the 3 layers of the heart:
• 1. endocardium: internal endothelial lining of the heart
• 2. myocardium forms the muscular wall
• 3. epicardium covers outside of the heart and forms the coronary
arteries (endothelial lining and smooth muscle)

8. CARDIAC LOOP
• The tube elongates as cells from the SHF are added to the cranial
pole
• Neural crest cells migrate from the hindbrain and pass near the
SHF in the pharyngeal arches to septate the outflow tract.
• Pg 167 fig. 13.8 the cephalic portion of the tube bends ventrally,
caudally, and to the right; the caudal portion (atrial) shifts
dorsocranially and to the left.
• Completed by 28th day.

9. • Pg. 168 fig 13.10The atrial portion initially paired structure outside the
pericardial cavity forms a common atrium and is incorporated into the
pericardial cavity.
• The atrioventricular junction remains narrow and forms the atrioventricular
canal which connects the common atrium and early ventricle.
• The bulbos cordis narrow except for proximal one third that will form the
trabeculated part of right ventricle.
• The mid portion, conus cordis, forms the outflow tract of both ventricles
• The distal portion, truncus arteriosus, form the roots and proximal portion of
the aorta and pulmonary artery.
• The bulboventricular sulcus remains narrow called the primary interventricular
foramen.

10. • By the end of thegins loop formation the smooth walled heart tube
begins to form primitive trabeculae.
• The primitive ventricle is now the primitive left ventricle
• The proximal third of the bulbus cordis ((pg 168 fig. 13.10) is now
the primitive right ventricle.
• The conotroncal portion of the tube initially on the right now
moves to a more medial position resulting in the formation of 2
transverse dilatations of the atrium bulging on each side of the
bulbus cordis.

11. SINUS VENOSUS
• Mid 4TH week the sinus venosus receives venous blood from the right and
left horns which in turn receive blood from 3 veins
• 1. vitelline or omphalomesenteric vein
• 2. umbilical vein
• 3. common cardinal vein
• The sinus venosus have a wide communication with the atrium but
because of the left to right shunts of blood the entrance of the sinus
shifts to the right.
• Causing the left horn’s vessels to obliterate and all that remains is the
oblique vein of the left atrium and coronary sinus.

13. • The right horn is now incorporated into the right atrium forming the
smooth walled part of the atrium and is now the only communication
between the original sinus venosus and the atrium.
• Its entrance the sinoatrial orifice has a valvular fold on each side (right
and left venous valves) pg 171 fig 13.14
• Septum spurium: formed by the dorsocranial fusion of the valves
• The left valve and the septum spurium fuse with the developing atrial
septum.
• The superior portion of right valve disappears completely
• The inferior portion forms: 1. valve of the inferior vena cava
• 2. valve of the coronary sinus

16. FORMATION OF THE CARDIAC SEPTA
• Formed between 27th to 37th day
• Are formed in 2 separate forms: 1. two actively growing masses of tissue
that approach each other until they fuse dividing the lumen into 2 canals
or active growth of a single tissue mass that continues to expand until it
reaches the opposite side of the lumen.
• These masses are known as endocardial cushions and develop the
atrioventricular and conotroncal regions.
• And give rise to the formation of the atrial and venricular septa (
membranous portion), the atrioventricular canals and valves, aortic and
pulmonary channels.

18. • 2. when a narrow strip of tissue in the wall of the atrium or
ventricle fail to grow while areas on each side of it expand
rapidly, a narrow ridge forms between the two expanding
portions.
• This septum never completely divides the original lumen but
leaves a narrow communication canal between the two expanded
sections and closed by tissue of neighbouring proliferating tissue.
• This tissue partially divides the atria and ventricles.
• Pg 172 fig 13.15

19. SEPTUM FORMATION IN ATRIA
30 days

20. • 4TH week theres a crest on the roof of the common atrium known
as the septum primum, this extends towards the endocardial
cushion in the atrioventricular canal.
• The opening between these structures is the ostium primum
• The ostium primum is then closed by the growth of the
endocardial cushions along the dege of the septum primum.
• But before this, cell death causes perforation on the upper part of
the septum primum. Coalescence of these form the osstium
secundum.
• Fxn: allows free blood flow from right to left primitive atrium,

21. SEPTUM SECUNDUM

22. • The lumen of the right atrium expands secondary to the introduction of
the sinus horn and form a crescent-shaped fold called the septum
secundum.
• The left venous valve and the septum spurium fuse with the right side of
the septum secundum, the free concave edge of the septum secundum
overlaps the ostium secundum.
• The opening left is called the oval foramen.
• When the upper part of the septum primum disappears the remaining
part becomes the valve of the oval foramen.
• Probe patency: the fusion of the septum primum and septum secundum
is incomplete and leaves a narrow oblique cleft between the two atria.

25. 37 Days 7 Weeks

26. SEPTUM FORMATION IN THE
ATRIOVENTRICULAR CANAL
• Initially the atrioventricular canal gives access only to the
primitive left ventricle but towards the 5th week the anterior and
posterior and the lateral cushions appear on the right and left side
of the canal.
• The anterior and posterior lumen project more and more into the
lumen until they fuse together resulting in complete division of
the canal into right and left atrioventricular orifices.

28. Further differentiation of Atria
• The primitive left atrium also expands with the incorporation of a single embryonic
pulmonary vein that develop as an outgrowth of the posterior left atrial wall, just
to the left of the septum primum.
• Fig 13.17a
• This vein gains connection with veins of the developing lung buds.
• The pulmonary vein and its branches are incorporated into the left atrium forming
the large smooth walled part of the adult atrium.
• Ultimately four veins enter the atrium wall fig 13.17b.
• In the adult heart, the original left embryonic atrium becomes the trabeculated
atrial appendage and the smooth walled part is formed from the pulmonary veins.
• The original embryonic right atrium becomes the trabeculated right atrial
appendage containing the pectinate muscles and the smooth walled sinus venarum
originates from the right horn of the sinus venosus.

29. Septum formation in atrioventricular canal
• End of 4th week, two mesenchymal cushions appear, the atrioventricular
endocardial cushions, appear at the anterior and posterior borders of the
atrioventricular canals. Fig 13.18.
• Initially the the AV canal gives access only to primitive left ventricle and is
separated from bulbos cordis by bulbo ventricular flange fig 13.10.
• By ending of 5th week the posterior end of the flange terminates almost midway
along the base of the superior endocardial cushion and is much less prominent
than before. Fig 13.19.
• Another two lateral AV cushions appear on the right and left borders of the
canal. Fig 13.18 and 13.19
• The anterior and posterior cushions project further into the lumen and fuse
causing the complete division of the canal into right and left AV orifices.

30. FORMATION OF ATRIOVENTRICULAR VALVES
7th Week

31. • Each atrioventicular orifice is surrounded by local proliferations of
mesenchymal tissue.
• When the bloodstream hollows out and thins tissue on the surface
of the proliferations, it forms the valves.
• They are attached to the ventricular wall by means of papillary
muscles and the chordae tendinae.
• Mitral valve: two valve leaflet, bicuspid form in the left
atrioventricular canal
• Tricuspid valve: three valve leaflet, form in the right canal.

33. SEPTUM FORMATION IN TRUNCUS ARTERIOSUS
AND CONUS CORDIS
35 Days

35. • The right superior truncus swelling grows distally and to the left
• The left inferior truncus swelling grows distally and to the left
• These grow toward the aortic sac and twist around each other, foreshadowing
the spiral course of the future septum. Fig 13.24
• After complete fusion they form the aorticopulmonary septum dividing the
truncus into aortic and pulmonary channel.
• 2 truncus swellings appear:
• The right dorsal and left ventral swellings of the conus cordis, these grow
toward each other distally to unite with the truncus septum.
• The conus is then divided by the septum into anterolateral portion (outflow
tract of the right ventricle) and the posteromedial portion (outflow of left
ventricle). Fig 13.25 and 13.26

36. SEPTUM FORMATION IN VENTRICLES
• The two primitive ventricles begin to expand and as the medial walls of
the expanding ventricles become apposed, they gradually merge forming
the muscular portion of the interventricular septum.
• The interventricular foramen located above the muscular portion of the
septum shrinks on completion of the conus septum.
• With further development outgrowth of tissue from the inferior
endocardial cushion along the top of the muscular septum closes the
foramen and this fuses with the abutting part of the conus septum.
• Complete closure of the interventricular foramen forms the membranous
part of the interventricular septum. Fig 13.16f

37. 35 Days

38. SEMILUNAR VALVES
• Right before the septum of the troncus is almost complete, small
tubercles appear on the main truncus swellings.
• One of each pair is assigned to the pulmonary and aortic channels
and a third tubercle appears in both channels opposite the fused
truncus swellings
• They gradually hollow out at their upper surface and form the
semilunar valves.
• (neural cells contribute to the formation of these valves)

39. FORMATION OF THE CONDUCTING SYSTEM
• Initially the pacemaker for the heart lies on the caudal part of the
left cardiac tube.
• As the sinus enters the right atrium, pacemaker tissue lies near
the opening of the superior vena cava forming the sinuatrial node.
• The atrioventricular and bundle of His are derived from :
• 1. cells in the left wall of the sinus venosus
• 2. cells from the atrioventricular canal
• Once the sinus venosus is incorporated into the right atrium, these
cells lie in their final position, base of the interatrial septum.

40. VASCULAR DEVELOPMENT
• Two mechanisms:
• 1. vasculogenesis: vessels arise by coalescence of angioblasts
• Eg. Dorsal aorta, cardinal veins
• 2. angiogenesis: vessels sprout from existing vessels.
• Forms the rest of the vascular system
• Patterned by guidance cues involving the vacular endothelial
growth factor VEGF and other growth factors.

41. ATERIAL SYSTEM
• The aortic arches arise from the aortic sac (the most distal part of
the truncus arteriosus)
• They terminate in the left and right dorsal aortae.
• The dorsal aortae fuses in its caudal end to form one a single
vessel.
• The pharyngeal arches and their vessel appear in a cephalocaudal
manner and so the aortic sac gives rise to a total of 5 pairs of
arteries.
• The fifth pair either never forms or is incomplete and regreses.
Therefore the arches are numbered I, II, III, IV, VI

43. Each Pharyngeal Arch Contains an Aortic
Arch
4 Weeks

45. • The truncus arteriosus if divided by the aorticopulmonary septum which divides
the outflow channel of the heart into ventral aorta and pulmonary trunk.fig
13.36b
• The aortic sac then form left (proximal segment of the aortic arch) and right
(brachiocephalic artery) horns. Fig 13.37 b c
• Day 27 first aortic arch disappears except for small portion that forms the
maxillary artery
• Second aortic artery disappears and the remaining portion forms the hyoid and
stapedial arteries.
• The third arch is large
• The fourth and sixth are in formation.
• 6th arch forms primitive pulmonary artery

46. • Day 29
• 1st and 2nd have disappeared, 3rd, 4th and 6th are large and the conotruncal
region has divided so that the the 6th arches are continuous with the pulmonary
trunk.
• 3rd aortic arch: common carotid artery, first part of the internal carotid artery
and the remaining part of the internal carotid is formed by the cranial portion
of the dorsal aorta, the external carotid artery is a sprout of the 3rd arch.
• 4th aortic arch: persists on both sides,
• Left side- forms part of the aortic arch between the left common carotid and
left subclavian arteries
• Right side- forms the most proximal segment of the right subclavian artery and
the distal part formed by a portion of the right dorsal aorta and the seventh
intersegmental artery. Fig 13.37b

47. • 5th either never forms or forms incompletely
• 6th aortic arch: (pulmonary arch) gives a branch that grows toward
the lung bud.
• Right side: proximal part forms the proximal segment of the right
pulmonary artery and the distal portion loses its connection with
the dorsal aorta and disappears.
• Left side: distal part persists during intrauterine life as the ductus
arteriosus and later becomes the ligamentum arteriosus. Fig 13.37
b and c.

48. Other changes
• 1. the carotid duct is obliterated ( dorsal aorta between the 3rd and 4th
arches)
• 2. right dorsal aorta disappears between the origin of the seventh
intersegmental artery and the junction with the left dorsal aorta.
• 3. the carotid and brachiocphalic arteries elongate considerably as a
result of the final anatomical position of the heart in the chest.
• 4. the recurrent laryngeal nerves courses become different on the left
and right side, due to the caudal shift of the heart and disappearance of
various portions of the aortic arches. These are branches of the vagus
nerve and initially supply the 6th arch, when the heart descends they
hook on to the sixth aortic arch and ascend again to the larynx giving it
its recurrent pattern. Fig 13.37 b c

49. • Right side: when the distal part of the 5th and 6th aortic arch
disappear, the nerve moves up and hooks around the right
subclavian artery.
• Left side: does not move up since the distal part of the 6th aortic
arch persists as the ductus arteriosus which later forms the
ligamentum arteriosum.

50. VITELLINE AND UMBILICAL ARTERIES
• Vitelline initially are a number of paired arteries that supply the
yolk sac gradually fuse and form arteries in the dorsal mesentery
of the gut (fore, mid and hindgut).
• In the adult they become the Celiac and superior mesenteric
arteries
• The inferior mesenteric arteries are derived from the umbilical
arteries.

51. UMBILICAL ARTERIES
• After birth the proximal portion form the internal iliac artery,
superior vesical arteries.
• Distal portion obliterates and forms the medial umbilical
ligaments.

52. CORONARY ARTERIES
• Derived from: 1. angioblasts formed from sprouts off the sinus
venosus that are distributed over the heart’s surface by cell
migration.
• 2. epicardium itself
• Epicardial cells go thru epithelial-mesenchymal transition induced
by the underlying myocardium forming the endothelial and smooth
muscle cells of the coronary arteries.
• The coronary arteries connect to the aorta because of the
ingrowth of arterial endothelial cells from the arteries into the
aorta.

53. VENOUS SYSTEM
• 5th week
• 1. vitelline/omphalomesenteric veins: carries blood from the yolk
sac to the sinus venosus
• Umbilical veins: originating in the chorionic villi, carries
oxygenated blood to the embryo.
• Cardinal veins: drains the embryo properly

55. VITELLINE VEINS
• Before entering the sinus venosus they form a plexus around the duodenum (this
anastomotic network forms the portal vein) and pass through the septum
transversum and the liver buds growing into the septum interrupt the course of
the veins forming an extensive vascular network hepatic sinusoids.
• Secondary to the obliteration of the left sinus venosus, blood from the left is
rechanneled to the right side of the liver causing enlargement of the right
vitelline vein (right hepatocardiac channel) and this forms the hepatocardiac
portion of the vena cava.
• The proximal part of the the left vitelline vein disappears.
• The anastomotic network around the duodenum forms a single vessel, the portal
vein.
• The superior mesenteric vein is derived from the right vitelline vein.

56. 4 Weeks 5 Weeks

57. 8 Weeks 12 weeks

58. UMBILICAL VEINS
• Initially each umbilical vein passes to the sides of the liver and
some connect to the liver.
• Eventually the left is the only that remains and carries blood from
the placenta to the liver.
• With the increase of placental circulation this makes a direct
connection to the right hepatocardiac channel (ductus venosus)
• After birth the left umbilical vein and the ductus venosus
obliterate and form the ligamentum teres hepatis and ligamentum
venosum. Fig 13.45

59. 8 Weeks 12 weeks

60. CARDINAL VEINS
• The system consists of the anterior (drains the cephalic part of the
embryo) and posterior (drains the rest of the embryo) cardinal veins that
join before entering the sinus horn and form the common cardinal vein.
• 5th to 7th week various veins are formed:
• 1. subcardinal veins: kidneys
• 2. sacrocardinal veins: lower extremities
• 3.supracardinal veins: body wall by the intercostal veins
• Fig 13.46
• Vena cava system: by the anastomosis of right and left side so that the
blood from the left is channeled to the right side.

61. • Left brachiocephalic vein: anastomosis of both anterior cardinal
veins
• Left superior intercostal vein: terminal portion of the left
posterior cardinal vein entering the left brachiocephalic vein is
retained as a small vessel.
• Superior vena cava: right common cardinal vein and proximal
portion of right anterior cardinal vein
• Internal jugular vein: anterior cardinal vein
• External jugular vein: plexus of venous vessels in the face and
drain the face and side of the head to the subclavian vein.

62. • Left renal vein: anastomosis of the subcardinal veins
• Left gonadal vein: distal portion of the left subcardinal vein
• Renal segment of the inferior vena cava: right subcardinal vein
• Left common iliac: anastomosis of sacrocardinal veins
• Sacrocardinal segment of the inferior vena cava: right sacrocardinal vein
• Renal and hepatic segment connects
• Inferior vena cava: hepatic, renal and sacrocardinal segments
• Fig 13.46

63. • Azygos veins: right supracardinal vein and portion of the posterior
cardinal vein. Drains the 4th to 11th intercostal veins
• Hemiazygos veins: left supracardinal vein. Drains 4th to 7th
intercostal veins.
• Hemiazigos veins empty into the azygos veins.

65. ASSIGNMENT
• Summarize and compare blood circulation before and after birth.