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Organ system development
Development of the cardiovascular system
Development of the ear
Development of the eye
Development of the face and palate
Pharyngeal arches, pouches, and clefts
Development of the digestive system and body cavities
Development of the gastrointestinal system
Development of the teeth
Development of the tongue
Development of the integumentary system
Development of the axial skeleton
Development of the limbs
Development of the muscular system
Development of the nervous system
Development of the renal system
Development of the reproductive system
Development of the respiratory system
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The cardiovascular system starts developing at the beginning of week 3 of intrauterine life.
At that point, the embryo is a flat little pancake made up of two layers: the epiblast on the dorsal, or back, side, and the hypoblast on the ventral, or front, side.
A line called the primitive streak appears on the epiblast back of this two-layered creature.
Cells migrate along the primitive streak during gastrulation, resulting in a three-layered embryo pancake, with each layer containing germ cells that form organs and tissues of the body.
The ventral, or bottom, germ layer is called endoderm, the dorsal, or top, germ layer is called ectoderm, and the layer in between these two is called mesoderm.
The heart derives from a part of the mesoderm called the visceral mesoderm.
Let’s look at this three-week-old creature from above. Mesoderm cells go through the primitive streak and make their way up to the embryo’s head, forming an area that’s called the primary heart field, a horseshoe-shaped area that has two limbs, with one on either side of the future brain.
This region lies on a blanket of endoderm cells that secrete vascular endothelial growth factor, which is called VEGF for short.
VEGF signals the cells in the limbs of the horseshoe to self-organize into two heart tubes.
A primitive pericardial cavity also appears lateral to each endocardial tube.
At its inferior end, each endocardial tube connects to a vitelline vein, which comes from an extraembryonic tissue called the yolk sac and through which blood enters the endocardial tube.
Blood exits each endocardial tube at its superior end through a dorsal aorta, which then continues down the embryo’s back.
The cardiovascular system develops at the beginning of week three during prenatal life. The development of the primitive heart starts with a horseshoe-shaped structure called the primary heart field, which has a pair of tubes that fold so that the heart structures will be in the proper position. Next, septa appear, which help to partition the heart into two atria and two ventricles.
The electrical conduction system of the primitive heart initially lies in the sinus venosus. As the sinus venous becomes absorbed by the right atria, the pacemaker cells appear in the sinoatrial node in the right atrium wall. The development of blood vessels involves the endothelium, which undergoes a process called angiogenesis, which is the formation of new blood vessels from pre-existing ones. This process is driven by growth factors such as VEGF (vascular endothelial growth factor).
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