Structure and closure mechanism of the human umbilical artery

The structure of the fully-patent umbilical artery and rearrangement of its structural elements with postnatal closure were examined in 10 centimeter long umbilical cord segments which were double-clamped at different time intervals after delivery. The fully-patent umbilical artery consists of two main layers: an outer layer of circularly arranged smooth muscle cells and an inner layer which shows rather irregularly and loosely arranged cells embedded in abundant metachromatic ground substance. No predominantly longitudinal arrangements of cells and fibers reported by earlier investigators could be identified in the inner layer. Closure of the umbilical arteries is initiated by numerous loc…

26. ATHEROSCLEROTIC CHANGES OF THE ILIAC ARTERIES IN CHILDREN WITH A SINGLE UMBILICAL ARTERY — THE EARLIEST FORM OF ATHEROSCLEROSIS IN HUMANS

�ber die Struktur und den Verschlussmechanismus Des ductus venosus

Das Gefasrohr des Ductus venosus schliest nur geringe Mengen der glatten Muskulatur ein. Ein muskularer Sphinkter ist an seinem Abgang nicht vorhanden. Auch andere vorgebildete Strukturen, z. B. die im Schrifttum gelegentlich erwahnten „Lippenbildungen“, die den Ductusabgang postnatal sofort verschliesen sollen, liegen nicht vor. Die postnatale funktionelle Ausschaltung des Ductus venosus ist Folge des Druckabfalles im portalen Sinus (Recessus umbilicalis) und beruht im Wesentlichen auf der Retraktion und Engstellung seines Abganges, dessen lichte Weite vom Gefasinnendruck in hohem Mase abhangig ist. Die Retraktion des Ductusabganges wird wahrscheinlich durch die muskularen Elemente geforde…

Transition radiation in the x-ray region from a low emittance 855 MeV electron beam

A quasi-monochromatic hard x-ray beam with a photon energy of 33 keV has been produced from transition radiation (TR) at the Mainz Microtron MAMI. The radiator was a stack of 30 polyimide foils of 25 μm thickness and 75 μm separation and the monochromator a highly-oriented pyrolytic graphite crystal. The intrinsic bandwidth was measured with a critical absorption technique to be 100 eV. On the basis of these experiments a photon flux of 4⋅109/mm2s over an illuminated area of 5.7×125 mm2 can be expected from an optimized beryllium radiator at a beam current of 100 μA. At the K-absorption edge of titanium at 5 keV narrow band transition radiation has been observed from a stack of four foils o…