Heart development Flashcards
بسم الله الرحمن الرحيم وبه نستعين
The time: It develops in the ؟. it is the first system to function in the embryo.
Middle of 3rd week of intrauterine life
The cause: as the rapidly growing embryo ?
Can no longer maitain nurition and oxygenation by simple diffusion
Source:
The C.V.S. is totally ??????????????
in origin.
mesodermal
Mesodermal angiogenic cells form masses called ?
Blood islands. The islands acquire
lumens forming endothelial channels which spread and become interconnected together.
The surrounding mesoderm forms the muscular and connective tissue coats of the blood vessels
Two sets of blood vessels appear in the embryo:
Extra-embryonic vessels (appear earlier): derived from the extra embryonic mesoderm and include:
a. Vitelline vessels: develop around the yolk sac.
b. Umbilical vessels: run in the connecting stalk and extend to the chorion.
Intra-embryonic vessels (appear two days later): derived from the intra-embryonic splanchnic mesoderm as:
the two dorsal aortae.
Two sets of blood vessels appear in the embryo:
Extra-embryonic vessels (appear earlier): derived from the extra embryonic mesoderm and include:
a. Vitelline vessels: develop around the yolk sac.
b. Umbilical vessels: run in the connecting stalk and extend to the chorion.
Primitive blood cells develop from
The Endothelial lining of the vitelline and umbilical vessels.
Later, they are formed in the liver, spleen, bone marrow and lymph nodes.
❑ After birth, the bone marrow + lymph nodes are the sites of
haemopoiesis.
Development of The Heart
3 Mesodermal sources:
1-Pericardial Sac
2-Endocardial Heart Tube
3-MyoEpicardial Mantle
Pericardial sac?
It is the transverse part of the U-shaped intraembryonic coelom.
✓ It is situated between the oral membrane (caudally) and the septum transversum (cranially).
(The cardiogenic plate).
The angiogenic cells in the area between the pericardial sac cranially and the oral membrane ventrally aggregate and form a horseshoe shape area called cardiogenic plate
The angiogenic cells in the cardiogenic plate form clusters, then these clusters acquire lumens and fuse together forming right and left endocardial heart tubes.
Later (after lateral folding), the middle portions of the two tubes fuse together forming a single heart tube
Myoepicardial Mantle ?
It is a Layer of Splanchnic mesoderm situated between the pericardial sac and endocardial heart tube
As the endocardial heart tube invaginates into the pericardial sac, the myoepicardial mantle
forms ?
a Coat which surrounds the heart tube. But separated from it by a layer of cardiac jelly
(connective tissue)
- Pericardial sac
- Endocardial heart tube
- Myoepicardial mantle
1-pericardium
2-endocardium
3-myocardium and epicardium
As a result of folding, the heart tube and the pericardial sac rotate ……° with the head fold
180
Results of rotation in Relations ?
Crainal to septum transversum
Caudal to bucopharyngeal membrane
Ventral to foregut
Dorsal to Pericardial Sac
Four changes of Heart tube?
Invade pericardial sacs
Develop into chambers
Elongates and bends
Migarates caudally
The endocardial heart tube invades the pericardial sac from its dorsal aspect dividing it into a
Visceral layer (epicardium) and
a Parietal layer.
A double-layered fold called dorsal mesocardium is attached to the dorsum of the tube. Later,
the dorsal mesocardium becomes absorbed forming the transverse sinus of pericardium.
Heart developing chambers?
Truncus Arteriosus Bulbs cordis Ventricle Atrium Sinus venosus
Causes of bending:
- Elongation of the heart tube, while its 2 ends are fixed.
- Disproportionate growth between the heart tube and pericardial sac.
- Disproportionate growth between the different parts of the heart tube.
Bending of tube
- The bulbus cordis and ventricle elongate more rapidly than the rest of the tube, forming a U-shaped bulboventricular loop
- The cardiac loop becomes S-shaped as the atrium and sinus venosus are dragged inside the pericardial sac, with approximation of the arterial and venous ends of the loop.
Bending of tube
- The Bulbus cordis and ventricle elongate more rapidly than the rest of the tube, forming a U-shaped Bulboventricular loop.
- The cardiac loop becomes S-shaped as the atrium and sinus venosus are dragged inside the pericardial sac, with approximation of the arterial and venous ends of the loop.
- The bulbus cordis shifts to the right side of the ventricle. The junction between both is marked on the outside by the bulbo-ventricular sulcus
4-The atrium expands transversely, bulging on either side of the bulbus
cordis.
The heart and pericardium
migrate caudally from the
level of 3rd- 4th somites to
the level of 17th- 20thsomites.
Sinus venosus if formed of
Body + 2 Horns
Sinus venosus opens into?
It opens into the center of the dorsal wall of the primitive atrium.
It is formed of a body and two horns (right & left).
E
Each horn of Sinus venosus recevies blood from?
1- Vitlline vein
2- Umbilical vein
3- Common cardinal Vein
The opening between the Sinus venosus and the atrium has the shape of a vertical slit.
Its edges are called the right and left venous valves (Sino-atrial valves). Both valves fuse together cranially forming ??
The septum spurium.
At first, communication between the sinus and the atrium is wide. Then, the entrance of the
sinus shifts to the right.
It is incorporated into the right atrium to form the smooth-walled part of the right atrium
(sinus venarum)
Fates of Right Horns of sinus venosus?
Right common cardinal > Lower SVC
Right vitline vein > IVC opening
Right Umbilical vein > disappear