NDEGWA DRMAKANYAANDREW. "
Intussusceptive angiogenesis and its role in vascular morphogenesis, patterning, and remodeling.". In:
International Course Of Organized Self-Help Housing Planning & Development. HRDU, University of Nairobi; 2009.
AbstractNew blood vessels arise initially as blood islands in the process known as vasculogenesis or as new capillary segments produced through angiogenesis. Angiogenesis itself encompasses two broad processes, namely sprouting (SA) and intussusceptive (IA) angiogenesis. Primordial capillary plexuses expand through both SA and IA, but subsequent growth and remodeling are achieved through IA. The latter process proceeds through transluminal tissue pillar formation and subsequent vascular splitting, and the direction taken by the pillars delineates IA into overt phases, namely: intussusceptive microvascular growth, intussusceptive arborization, and intussusceptive branching remodeling. Intussusceptive microvascular growth circumscribes the process of initiation of pillar formation and their subsequent expansion with the result that the capillary surface area is greatly enhanced. In contrast, intussusceptive arborization entails formation of serried pillars that remodel the disorganized vascular meshwork into the typical tree-like arrangement. Optimization of local vascular branching geometry occurs through intussusceptive branching remodeling so that the vasculature is remodeled to meet the local demand. In addition, IA is important in creation of the local organ-specific angioarchitecture. While hemodynamic forces have proven direct effects on IA, with increase in blood flow resulting in initiation of pillars, the preponderant mechanisms are unclear. Molecular control of IA has so far not been unequivocally elucidated but interplay among several factors is probably involved. Future investigations are strongly encouraged to focus on interactions among angiogenic growth factors, angiopoetins, and related receptors.
NDEGWA DRMAKANYAANDREW. "
Parabronchial angioarchitecture in developing and adult chickens.". In:
J Appl Physiol. 2009 Jun;106(6):1959-69. Epub 2009. HRDU, University of Nairobi; 2009.
AbstractThe avian lung has a highly sophisticated morphology with a complex vascular system. Extant data regarding avian pulmonary angioarchitecture are few and contradictory. We used corrosion casting techniques, light microscopy, as well as scanning and transmission electron microscopy to study the development, topography, and distribution of the parabronchial vasculature in the chicken lung. The arterial system was divisible into three hierarchical generations, all formed external to the parabronchial capillary meshwork. These included the interparabronchial arteries (A1) that ran parallel to the long axes of parabronchi and gave rise to orthogonal parabronchial arteries (A2) that formed arterioles (A3). The arterioles formed capillaries that participated in the formation of the parabronchial mantle. The venous system comprised six hierarchical generations originating from the luminal aspect of the parabronchi, where capillaries converged to form occasional tiny infundibular venules (V6) around infundibulae, or septal venules (V5) between conterminous atria. The confluence of the latter venules formed atrial veins (V4), which gave rise to intraparabronchial veins (V3) that traversed the capillary meshwork to join the interparabronchial veins (V1) directly or via parabronchial veins (V2). The primitive networks inaugurated through sprouting, migration, and fusion of vessels and the basic vascular pattern was already established by the 20th embryonic day, with the arterial system preceding the venous system. Segregation and remodeling of the fine vascular entities occurred through intussusceptive angiogenesis, a process that probably progressed well into the posthatch period. Apposition of endothelial cells to the attenuating epithelial cells of the air capillaries resulted in establishment of the thin blood-gas barrier. Fusion of blood capillaries proceeded through apposition of the anastomosing sprouts, with subsequent thinning of the abutting boundaries and ultimate communication of the lumens. Orthogonal reorientation of the blood capillaries at the air capillary level resulted in a cross-current system at the gas exchange interface.