Fig 1.
Experimental setup, involving three-day old chick embryo, showing the vitelline vascular network.
The egg was situated in an onstage incubator. The shell’s blunt end and the associated membrane were removed. The embryo lies on the top-middle of the egg yolk; vitelline arteries and veins grow out of the embryo, and connect to the marginal vein, whose approximate location is marked with the dashed red circle. The marginal vein forms the external boundary of the network. Anterior and posterior vitelline veins connect the marginal vein with the embryo. Because of the veins’ non-branching nature and relatively uniform diameter, the midpoints of either the anterior or posterior vitelline vein, marked with yellow circles, were selected as regions of interest (ROI) for quantitative blood flow measurements. Pilot experiments showed that the blood flow velocities were similar in the two veins; hence, vein selection was based primarily on accessibility.
Fig 2.
Experimental configuration for applying IR to the chick embryo.
Fig 3.
Postmortem blood flow empties arteries.
(A) Vitelline artery and vein in live chick embryo. Artery and vein overlap, the artery lying partially beneath the vein. Blue arrows indicate the direction of venous flow, red arrows, arterial flow. (B) Vitelline artery and vein in a postmortem chick embryo, 20 minutes after the heart had stopped. Blood tends to exit arteries, leaving them pale.
Fig 4.
Exclusion Zone (EZ) in vitelline arteries 150 seconds after cardiac arrest.
Note the erythrocyte-free region between the vessel wall and the boundary of the blood stream. The image is a snapshot from S5 Movie.
Fig 5.
Effect of IR exposure on venous postmortem blood flow (n = 6).
Flow velocity increased appreciably after IR was turned on, diminishing when the IR source was removed. Error bars show standard deviations.
Fig 6.
Effect of IR on live chick-embryo venous blood flow.
Venous blood flow velocity increased appreciably when IR was turned on, and then decreased after removal (n = 5). Error bars show standard deviations.
Fig 7.
Effect of IR deficiency on live chick embryo circulation.
(A) Vitelline vascular network with embryo just removed from onstage incubator. (B) Same as left but exposed to room temperature for ~50 minutes. Compared to Fig 7A, the arteries and veins (black dotted rectangle) appear thinner and less defined, indicating that those vessels contained less blood. Capillaries (black dashed oval), on the other hand, appear darker, indicating more blood.
Fig 8.
Potential driving mechanism of surface-induced flow.
(A) In a tube with non-uniform diameter but uniform surface activity, an axial concentration gradient can form [20]. (B) An axial concentration gradient can also form in a tube with uniform diameter but nonuniform surface activity.
Fig 9.
Surface-induced flow in a capillary bed.
(A) Compared to venules (blue), the arterioles (red) are narrower; thus, the water-surface interaction drives capillary flow from arteries to veins. (B) As fluid (mainly water) leaves the capillaries through the capillary wall at the arteriolar end, a surface-induced flow is generated pointing from the arteries to the capillaries. Meanwhile, as fluid enters the capillaries at the venular end, a surface-induced flow is generated, pointing from the capillaries to the venules.