Vasoconstriction, the tightening/narrowing of blood vessel diameter, is the "how" blood flow is limited when it's cold. The "why" deals mainly with your body attempting to keep its core warm. So anything around your heart mainly. Therefore, all extremities get less blood.
Air sacs; blood vessels that surround the air sacs
The capillaries allow diffusion of nutrients, waste, and oxygen through their walls, which are one cell thick. This diffusion allows transportation of nutrients and waste materials throughout the body.
Not in a healthy person, unless there is a cut in the blood vessel. Someone with high cholesterol or other health problems might have a clot occur otherwise, but those will typically be in capillaries, as they are more narrow.
This is really a biology question.The general gist of it is that every cell in your body needs nutrients and oxygen, and give off waste products and carbon dioxide. Imagine making a flat sheet of cells (pack them in real tight for efficiency). The area of that sheet would be an estimate for the number of square miles of capillaries needed to feed them all.Another way of estimating is think of slicing your body into sheets that are as thick as one cell, see how many sheets that would be, and multiplying by the area of that cross-section. This would be a rough estimate (very very rough) but it might be fun.
== == Arterioles are very tiny arteries. In some areas of the body there are places where arteries and veins come together in tiny formations to swap oxygenated blood (in the arteries) for unoxygenated blood (in the veins). (As the veins get smaller they become capillaries, then caprioles.) The arteries are responsible for delivering blood with oxygen from the lungs to the rest of the body. Veins carry the "used blood" with no oxygen back to the heart where it passes into the lungs and picks up more oxygen and gets rid of the carbon dioxide that builds up as our bodies use the oxygen. The arterioles and caprioles come together to swap this blood. Well the above might be true but...... Arterioles are small arteries that deliver blood to the Capillaries. While Venules are small veins that are connected to the Capillaries.
Depending on the depth of your question, I would say 1) The Heart 2) Arteries 3) Veins a little more in depth might say 1) Heart 2) Arteries & Veins 3) Capilleries but I'd probably go with the first three (especially if you don't know what capilleries are).
There is normally no blood in semen. However, if a guy ejaculates especially strongly, some tiny capillaries might burst, injecting a small amount of blood into the semen. Especially in older men, if there is cancer in the prostate, there can be quite a bit of blood in the semen.
no red blood does not keep blood from leaking but white might or might not
It depends a lot on the location of the wound, its size and depth, and if it includes any arteries, veins, or capillaries. Elevation of the wound is also a factor. If an artery is severed completely. You might die very suddenly as you would lose a lot of blood in a very short time. If it is just a paper cut or a bloody nose or lip. The blood will clot most likely before you run out of blood supply.
By laws
You might need a blood transfusion.
As blood passes through capillaries, oxygen and nutrients can diffuse out of these tiny blood vessels and into our surrounding body cells. Waste products might include lactic acid and carbon dioxide. Some of these waste materials diffuse back into the bloodstream, but most of it is taken up into the lymphatic system. The simple analogy is that the lymph system is our body's binmen.