Dr.Tariq
07-25-2010, 08:04 PM
بسم الله الرحمن الرحيم
حقيقة الدكتور ابراهيم بيعتذر من كل الأعضاء ما رح يقدر ينزل الموضوع هو، فاتفقنا أنه أنا نزله بداله
الكلمات الملونة باللون الأزرق اضغط عليها و سترى التوضيح المناسب
I. Introduction
The development of the cardiovascular system is an early embryological event. From fertilization, it takes eight weeks for the human heart to develop into its definitive fetal structure. During this period the system develops so it can:i
1i) supply nutrients and oxygen to the fetus
2i) immediately function after birth.i
II. Early Development of the Circulatory System
A. Blood Islands
During the third week of gestation angioblastic blood islands (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img008.gif) of mesoderm (angiogenic clusters) iمappear in the yolk sac, chorion and body stalk. The innermost cells of these blood islands are hematopoietic cells that give rise to the blood cell lines. The outermost cells give rise to the endothelial cell layer of blood vessels. A series of blood islands eventually coalesce to form blood vessels.i
B. Heart Tube
By the middle of the third week of gestation angioblastic blood islands from the splanchnic mesoderm appear and form a plexus of vessels lying deep to the horseshoe-shaped prospective pericardial cavity (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img009.gif). These small vessels develop into paired endocardial heart tubes (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img019.gif).i
The bilateral endocardial heart tubes continue to develop and connect with a pair of vessels, the dorsal aortae, located on either side of the midline.i
http://www.mda-sy.com/up//uploads/images/mda-sy-5570ff0c0e.jpg (http://www.mda-sy.com/)
III. Formation of the Primitive Four Chambered Heart.i
As the endocardial heart tubes fuse, several bulges and sulci appear. From the cephalic end, the bulges are the bulbus cordis (truncus arteriosus and the conus arteriosus) (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img023.gif), the primitive ventricle, the primitive atrium (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img024.gif) and the sinus venosus. The veins connect to the heart tube via the sinus venosus, while the paired dorsal aortae arise from aortic arches that in turn arise from the aortic sac. The aortic sac is at the most cephalic end of the bulbus cordis. The sulci present are the bulboventricular sulcus, between the bulbus cordis and the ventricle, and the atrioventricular sulcus, between the atrium and the ventricle.i
Septation of the Heart
During the second month, the heart begins to septate into two atria, two ventricles, the ascending aorta and the pulmonary trunk. i
A. Atrial Septation.i
http://www.mda-sy.com/up//uploads/images/mda-sy-3cc4c58a03.gif (http://www.mda-sy.com/)
Endocardial cushions (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img033.gif) develop in the dorsal (inferior) and ventral (superior) walls of the heart. These grow toward each other as the cardiac jelly mesenchyme proliferates deep to the endocardium. These cushions fuse and divide the common AV canal into the left and right AV canals. i
B. Ventricular Septation
The muscular interventricular (I.V.) septum grows as a ridge of tissue from the caudal heart wall toward the fused endocardial cushions. The remaining opening is the interventricular foramen (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img006.gif). The IV foramen is closed by the conal ridges, outgrowth of the inferior endocardial cushion, the right tubercle, and connective tissue from the muscular interventricular septum. This portion of the I.V. septum is called the membranous part of the interventricular septum (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img011.gif).i
Cardiac Valve Fromation
Semilunar valves develop in the aorta and pulmonary artery as localized swellings of endocardial tissue. The atrioventricular valves develop as subendocardial and endocardial tissues and project into the AV canal. These bulges are excavated from the ventricular side and invaded by muscle. Eventually, all the muscle, except that remaining as papillary muscle disappear and three cusps of the right AV (tricuspid) valve, and two cusps of the left AV (mitral) valve remain as fibrous structures.i
IV. Development of the Major Arteries
http://www.mda-sy.com/up//uploads/images/mda-sy-bffae3a4ad.gif (http://www.mda-sy.com/)
The six pairs of aortic arches (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img041.gif), develop in a cephalocaudal direction and interconnect the ventral aortic roots and the dorsal aorta. They are never all present in the developing human heart. Of the six pairs of aortic arches, most of the first, second and fifth arches disappear. i
V. Development of the Veins
The veins develop from the three major vascular circuits. As with the arteries they develop in a cephalocaudal direction and as a consequence the precursors to the veins are never all present at the same time. In addition, as new structures develop the course of veins changes.i
حقيقة الدكتور ابراهيم بيعتذر من كل الأعضاء ما رح يقدر ينزل الموضوع هو، فاتفقنا أنه أنا نزله بداله
الكلمات الملونة باللون الأزرق اضغط عليها و سترى التوضيح المناسب
I. Introduction
The development of the cardiovascular system is an early embryological event. From fertilization, it takes eight weeks for the human heart to develop into its definitive fetal structure. During this period the system develops so it can:i
1i) supply nutrients and oxygen to the fetus
2i) immediately function after birth.i
II. Early Development of the Circulatory System
A. Blood Islands
During the third week of gestation angioblastic blood islands (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img008.gif) of mesoderm (angiogenic clusters) iمappear in the yolk sac, chorion and body stalk. The innermost cells of these blood islands are hematopoietic cells that give rise to the blood cell lines. The outermost cells give rise to the endothelial cell layer of blood vessels. A series of blood islands eventually coalesce to form blood vessels.i
B. Heart Tube
By the middle of the third week of gestation angioblastic blood islands from the splanchnic mesoderm appear and form a plexus of vessels lying deep to the horseshoe-shaped prospective pericardial cavity (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img009.gif). These small vessels develop into paired endocardial heart tubes (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img019.gif).i
The bilateral endocardial heart tubes continue to develop and connect with a pair of vessels, the dorsal aortae, located on either side of the midline.i
http://www.mda-sy.com/up//uploads/images/mda-sy-5570ff0c0e.jpg (http://www.mda-sy.com/)
III. Formation of the Primitive Four Chambered Heart.i
As the endocardial heart tubes fuse, several bulges and sulci appear. From the cephalic end, the bulges are the bulbus cordis (truncus arteriosus and the conus arteriosus) (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img023.gif), the primitive ventricle, the primitive atrium (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img024.gif) and the sinus venosus. The veins connect to the heart tube via the sinus venosus, while the paired dorsal aortae arise from aortic arches that in turn arise from the aortic sac. The aortic sac is at the most cephalic end of the bulbus cordis. The sulci present are the bulboventricular sulcus, between the bulbus cordis and the ventricle, and the atrioventricular sulcus, between the atrium and the ventricle.i
Septation of the Heart
During the second month, the heart begins to septate into two atria, two ventricles, the ascending aorta and the pulmonary trunk. i
A. Atrial Septation.i
http://www.mda-sy.com/up//uploads/images/mda-sy-3cc4c58a03.gif (http://www.mda-sy.com/)
Endocardial cushions (http://isc.temple.edu/marino/embryology/Heart98/heart97a/img033.gif) develop in the dorsal (inferior) and ventral (superior) walls of the heart. These grow toward each other as the cardiac jelly mesenchyme proliferates deep to the endocardium. These cushions fuse and divide the common AV canal into the left and right AV canals. i
B. Ventricular Septation
The muscular interventricular (I.V.) septum grows as a ridge of tissue from the caudal heart wall toward the fused endocardial cushions. The remaining opening is the interventricular foramen (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img006.gif). The IV foramen is closed by the conal ridges, outgrowth of the inferior endocardial cushion, the right tubercle, and connective tissue from the muscular interventricular septum. This portion of the I.V. septum is called the membranous part of the interventricular septum (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img011.gif).i
Cardiac Valve Fromation
Semilunar valves develop in the aorta and pulmonary artery as localized swellings of endocardial tissue. The atrioventricular valves develop as subendocardial and endocardial tissues and project into the AV canal. These bulges are excavated from the ventricular side and invaded by muscle. Eventually, all the muscle, except that remaining as papillary muscle disappear and three cusps of the right AV (tricuspid) valve, and two cusps of the left AV (mitral) valve remain as fibrous structures.i
IV. Development of the Major Arteries
http://www.mda-sy.com/up//uploads/images/mda-sy-bffae3a4ad.gif (http://www.mda-sy.com/)
The six pairs of aortic arches (http://isc.temple.edu/marino/embryology/Heart98/heart97b/img041.gif), develop in a cephalocaudal direction and interconnect the ventral aortic roots and the dorsal aorta. They are never all present in the developing human heart. Of the six pairs of aortic arches, most of the first, second and fifth arches disappear. i
V. Development of the Veins
The veins develop from the three major vascular circuits. As with the arteries they develop in a cephalocaudal direction and as a consequence the precursors to the veins are never all present at the same time. In addition, as new structures develop the course of veins changes.i