Cardiovascular System Development
Development of the heart and vascular system begins very early in mesoderm both within (embryonic) and outside (extra embryonic) the embryo. Vascular development therefore occurs in many places, the most obvious though is the early forming heart, which grows rapidly creating an externally obvious cardiac "bulge" on the early embryo.
The heart forms initially in the embryonic disc as a simple paired tube inside the forming pericardial cavity, which when the disc folds, gets carried into the correct anatomical position in the chest cavity.
Throughout the mesoderm, small regions differentiate into "blood islands" which contribute both blood vessels (walls) and fetal red blood cells.
These "islands" connect together to form the first vessels whcih connect with the heart tube.
Some Recent Findings
- "uring early gastrulation, vertebrate embryos begin to produce endothelial cells (ECs) from the mesoderm. ECs first form primitive vascular plexus de novo and later differentiate into arterial, venous, capillary, and lymphatic ECs. In the heart, the five distinct EC types (endocardial, coronary arterial, venous, capillary, and lymphatic) have distinct phenotypes. For example, coronary ECs establish a typical vessel network throughout the myocardium, whereas endocardial ECs form a large epithelial sheet with no angiogenic sprouting into the myocardium. Neither coronary arteries, veins, and capillaries, nor lymphatic vessels fuse with the endocardium or open to the heart chamber. The developmental stage during which the specific phenotype of each cardiac EC type is determined remains unclear. The mechanisms involved in EC commitment and diversity can however be more precisely defined by tracking the migratory patterns and lineage decisions of the precursors of cardiac ECs."