Cardiovascular System - Lymphatic Development
Introduction
An important part of the cardiovascular system is the lymphatic vasculature, which functions to return interstitial fluid (lymph) to the bloodstream.
This system was first identified by Aselli G. 1627 in a paper "De Lacteibus sive Lacteis Venis", Quarto Vasorum Mesarai corum Genere novo invento. Milan: Mediolani
Lymphatic Vessels
- Lymph capillaries
- Lymph collecting vessels
- Lymph ducts
Lymphatic Vessel Contraction
Lymphatic vessels undergo spontaneous rhythmic contractions which aid lymph flow. This is most easily demonstrated in models based upon mesentry lymphatics of the gastrointestinal tract. Contractile activity is regulated by physical factors (transmural pressure) and neurological (alpha-adrenergic, histamine, bradykinin) acting on lymphatic smooth muscle. Contractility and receptor expression may also be different in different parts of the lymphatic system.
Alpha-adrenergic - alpha 1- and not alpha 2-adrenoceptors.
Histamine - lymphatic smooth muscle via stimulation of H(1) (and in some vessels H(2)) receptors.
Bradykinin - chronotropic but not inotropic effects on lymphatic pump activity via stimulation of B1 receptors.
Molecular Development
Angiopoietins (Ang1–Ang4)
Notch probably mediates choice of fate between arterial and venous.
Prox1 Prospero-related Homeobox 1 - expressed in a subpopulation of blood endothelial cells that then generate, by both budding and sprouting, cells of the lymphatic vascular system. (OMIM - PROSPERO-RELATED HOMEOBOX 1; PROX1)
Tie (Tie1 and Tie2) tyrosine kinase receptors.
Vascular endothelial growth factor (VEGF) family of proteins and angiopoietin/Tie, Notch, and ephrin/Eph pathways play major roles in eary vessel development.
Abnormalities
Lymphangioma - dysplasia of childhood form lymphatic capillaries or collectors, which form fluid-filled cysts.
lymphatic spaces lined by endothelium smooth muscle fascicles in the septa between the lymphatic spaces lymphoid aggregates in the delicate collagenous stroma
