Cardiovascular System
Veins

Introduction

Located throughout the body, blood veins are flexible hollow tubes that circulate blood back towards the heart.

The blood conveyed by veins is laded with carbon dioxide and other waste from cellular metabolism, and it is channeled to the kidneys and lungs for replenishment before ultimately returning to the heart for another circulation.
The smallest veins run into progressively bigger veins with the largest veins leading directly to the organs, in a similar manner to how tributaries, brooks and streams find their way into a river.

The veins that deliver blood to the heart via the lungs are called Pulmonary veins, whilst veins, which lead to the heart via the other organs, are Systemic Veins.

Composition

Veins are structured similarly to arteries in that they have a tough outer layer of tissue, a muscular middle layer, and a smooth inner layer of epithelial cells, however, they are not as robust as arteries because the blood they convey is at a much lower pressure than that of corresponding arteries. The vein layers are therefore much thinner than that of arteries.

The middle muscular layer imparts elasticity properties to the veins, which allows them to expand and constrict in unison with heart impulses. With each surge of blood, veins expand thus making the passage of blood in them easier and blood pressure lower.

It is important that the waste laden blood does not flow backward but keeps moving in the direction of the heart. This is accomplished by many pairs of gate-like valves located inside the veins which both allow blood to move in one direction only, and helps the blood-flow defy gravity when it needs to travel upwards, e.g. from the feet and the legs.

Articles | Newsletter

  Copyright © 1998-2007 by Bilal Rose. All rights reserved