Veins

All veins carry blood towards the heart. The ones that are attached to the heart are the superior and inferior vena cavae.

Portal vein bypass, also called portacaval shunting.In portacaval shunting, blood from the portal vein is diverted into the inferior vena cava (one of the main veins leading back to the heart). This is the most common type of bypass.

Veins carry blood to the heart while arteries carry blood away.i

No. Pulmonary veins take blood from the lungs to the right atrium.(veINs take blood IN to the heart.) Pulmonary arteries take blood from the heart(left ventricle) to the lungs.

But pulmonary veins are the only veins in the body to carry oygenated blood, and pulmonary arteries are the only arteries to carry deoxygenated blood.

"No but depending on the size of the human being it may be long enough to cross New York or a reall tall person mabey California"

I don't know where this person gets there information but this is wrong. If you take out all your circulatory system and put it end to end it would cirlce the earth more than once. It is between 50k and 100k miles long.

cause their prevent bac flow

Veins help regulate your body temperature. When the body temperature is too warm, the veins will pop out. Veins will also be more prominent in those who have less body fat, and in the elderly because their skin is thin.

Arteries carry oxygenated blood to the heart while blood exchange is done in the capillaries

There are three different types of blood vessels: arteries (which carry blood away from the heart) veins (which carry blood toward the heart) and capillaries (which carry blood from arteries to veins). So veins are a type of vessel, but not the only type.

The inferior vena cava is a large vein. The two common iliac veins join to make the inferior vena cava, which receives blood from the lower body and empties it into the right atrium of the heart.

It is the azygos vein that is located on right side of abdominal and thoracic aorta and in front of right vegus nerve that drains into superior vena cava on its posterior aspect just before vena cava drains into right atrium.
azygos vein

It is possible to see capillaries through your skin if your skin is thin and pale.

Inflammation in superficial or surface veins, such as those used to insert IV lines in the arm or to draw blood, can produce pain, redness, warmth, and discomfort. Blood clots that form in superficial veins rarely break loose and travel in the blood to cause blockage (in places such as the lungs) and complications.

It's the only vein that carries oxygenated blood. It brings this oxygenated blood back to the heart (into the left atrium) where it can then be pumped around the body.

Think of it this way. Anything Phrenic has to do with the diaphram. We have the superior and inferior parts of a diaphram. Herein lies the answer - the superior portion is drained by the Superior Phrenic vein and the inferior portion (follows the same logic) drained by the Inferior Phrenic vein. Both of these dump blood into the IVC. On another matter, remember the heart (cardia) rests on the diaphragm and the diaphram is a muscle? We also have the Pericardiacophrenic vein and Musculophrenic veins both of which dump their blood into the Internal Thoracic vein to take it up to the Brachiocephalic vein. I am sure you will agree with me that we always need another exit strategy, just in case. Anatomy is a challenge and that is how I try to learn it - by anatomical relations. Black Moses JCU Med

That you are a human.

another fetal structure ?

Arteries do not have valves because the heart provides the pressure needed to send blood through the system. Veins have valves because venous pressure is often not great enough (as the blood must overcome gravity and other forces) to return the blood to the heart.

collecting vessels

The Inferior Mesenteric Vein (iMV) drains into the splenic vein. The splenic vein ultimately "meets up" with the Superior Mesenteric Vein (SMV) to form the Hepatic Portal Vein (HPV)

the jagular vein is in the carotid triangle in the neck next to the vagus nerve and carotid artery.

You have not provided enough information for an answer, and a guess would be dangerous. Since pain is usually a symptom of another problem, and pain in your head can be serious, especially when connected with other symptoms, I urge you to have a talk with a physician about it. This is not an issue that should be addressed by amateurs.

It all depends on the amount of air. Medical personnel take pains to avoid introducing any air into an IV line at any time. Most of the time, a tiny amount of air presents no problem - but that's most of the time.

The two major factors at play are emboli and clotting. Emboli (plural of embolus) are "plugs" or blockages that are actually air bubbles, which jam a blood vessel and prevent blood from passing through it unimpeded. Lack of blood through a vessel means lack of oxygen, and the tissue itself can die. If the tissue is skin tissue over a small area (as would happen with emboli blocking capillaries at the skin), you'll eventually slough off the involved dead tissue and no harm done. On the other side of the equation, blocking blood flow in the brain can be lethal or highly damaging.

The other problem is clotting. When your blood is exposed to air, it starts to clot. On the surface of your skin, this is a good thing - it stops bleeding and forms a sort of bandage. However, inside your circulatory system this too can be problematic, and even lethal.

While there's no way of telling for certain what the effects of a given injection will be, the more air injected, the greater the danger. Tiny bubbles in an IV line or hypodermic are to be avoided, but rarely will have an effect on the patient. Large injections (the prior writer mentioned 50 cc) are potentially lethal.