Development of Arteries and Veins Flashcards
Blood vessel formation
- Extraembryonic vasculogenesis
- Intraembryonic vasculogenesis
Extraembryonic vasculogenesis
- vessels forming within the membranes
- Mammals: blood vessels established in yolk sac (even without yolk) and in the allantois
Intraembryonic vasculogenesis
vessels forming within the embryo
Processes required for blood vessel development
- vascuologenesis
- Angiogenesis
Vasculogenesis
- The initial formation of blood vessels
- A network of blood vessels is formed de novo from the lateral plate mesoderm
Angiogenesis
The sprouting of blood vessels from existing ones and remodeling of vascular beds
Hemangioblasts and vasculogenesis
- Hemangioblasts are cells more posterior to the cardiogenic or heart fields. Within the splanchnic mesoderm
- The hemangioblasts condense into aggregates called blood islands
- They are the precursors for both blood cells and blood vessels in the yolk sac and allantois
Angioblasts
Precursors for blood vessels within embryo
Steps of extra-embryonic vasculogenesis (yolk sac)
- Cell formation
- The inner cells of the blood islands (hemangioblasts) become Hematopoietic stem cells for blood cell formation
- The outer cells become angioblasts (progenitor cells for blood vessels) - Angioblasts will proliferate and differentiate into endothelial cells to line the new blood vessels and these endothelial cells will form tubes and connect to form a capillary plexus or network
- Lumen formation from creation and fusion of vacuoles created by endocytosis
- Results in vitelline and umbilical veins
Importance of vasculogenesis in yolk sac
Important to produce vessels that will bring nutrients to embryo, aid gas exchange, and bring blood cells to heart for distribution
- Vitelline and umbilical veins
Steps of intra-embryonic vasculogenesis
- Vascular networks arise from individual angioblast progenitor cells originating in most mesodermal tissues of body
- Developing organs produce paracrine factors that induce blood vessel formation in their own mesenchyme. This allows the developing vessel or capillary network to have specific properties for that organ or group of organs
Arterial vs. venous system
Arteries and veins do differ from one another despite originating from same endothelial precursor (angioblasts). Arterial or venous identity of endothelial cells is established very early on before angiogenesis sets in and before onset of circulation
- 2 types of endothelial cells are present within the primary vascular plexus. Allows for distinction, anastomosis (joining together) or arteries and veins, and fusion of capillaries to make larger vessels
Arterial programming
- Notch stimulation
- Ephrin B2
Venous programming
- Less notch stimulation
- Ephrin B4
Arterial system
- Folding places heart with pericardial cavity and bends developing aortae
- Anterior extensions become 2 ventral aortae
- Posterior extensions join with developing venous system
- Dorsal part become dorsal aortae - Aortic arches form