a venous valve is an infolding of the tunica ?
22. The venous valve is the tunica membrane of the vessel. The valve has cusps, its function is 23. Fill in the graph with examples of locations in the body where each type of capillary is located. It is a flexible artery or a muscular artery 25. Describe the role that arteries play in regulating blood flow
PURPOSE: The purpose of this study was to investigate the changes in blood flow and venous wall movements that occur in the peri-valvular region during venous outflow, to see how these physiological events affect the movements of the valve cusps, and to learn how the valves move. Valve cusps affect venous outflow.
MATERIALS AND METHODS: Twenty healthy volunteers (10 males, 10 females, ages 18–52 years) were the subjects of this study. Each volunteer was examined in a standing and semi-recumbent position at rest and during active foot movements. Ultrasound examinations were performed in B-flow mode supplemented by B-mode and pulsed Doppler scanning.
RESULTS: Four phases of the valve cycle are described. During the opening phase (0.27 +/- 0.05 sec), the cusps move from the closed position towards the sinus wall. After a certain point is reached, the valves stop opening and enter the equilibrium phase. During this phase (0.65 +/- 0.08 s), the leading edges remain suspended in the flowing current and undergo self-excited oscillations with amplitudes from 0.01 to 0.16 cm. During the closing phase (0.41 +/- 0.07 sec), the leaflets synchronously move towards the center of the vein. The duration of the subsequent closed phase is 0.45 +/- 0.05 seconds when the porches remain closed. During the equilibrium phase, flow separation occurs at the leading edge of the septum with reconnection to the sinus wall. At this point, the flow splits into two streams at each valve end. Part of the flow is directed into the sinusoidal cusp behind the valve cusp, forming a vortex along the top of the valve before reappearing in the main stream into the vein. When the valve is maximally open, the cusps create a narrowing of the lumen about 35% smaller than the distal vein of the valve. In this narrow area, the flow accelerates, forming a nearby directed jet.
Conclusions: Valve covers are subject to the four phases that make up the valve cycle. Local hemodynamic events, such as flow separation and reconnection, and eddy flow in the sinuses play important roles in valve operation. In addition to preventing backflow, the valve acts as a modulator of venous outflow. The eddy current behind the valve flanges participates in the operation of the valve, preventing stagnation within the valve pocket. The central jet may facilitate the outflow.