Human Internal Environment and Circulatory System Functions
1. The Internal Environment
The internal environment is a set of fluids surrounding the cells of an organism. From it, cells extract the nutrients and oxygen they need and dump the waste and carbon dioxide produced in metabolism.
In people, the internal environment consists mainly of interstitial fluid and the circulating fluids: blood and lymph.
- Interstitial Fluid: It is a liquid, with defensive and nutritious duties, which lies between the cells. It originates from the blood that has been filtered through the thin walls of capillaries.
- Blood: It is a means of transport of substances, passing through the body in line with the blood vessels.
- Lymph: It is a liquid that is formed from interstitial fluid, circulating through the lymph vessels or ducts that, after traveling much of the body, flow into blood vessels.
The proper functioning of cells depends on the internal environment remaining constant; that is, its properties (composition, temperature, etc.) must not change. The maintenance of these properties is called homeostasis, and this task is performed by different devices and systems of the body.
The circulatory system transports blood throughout the body and lymph. Thanks to this transport, the internal environment is continually renewed.
Circulatory System Components in Humans
In humans, the circulatory or transport system comprises two systems:
- The blood circulation system, which circulates blood.
- The lymphatic circulatory system, which circulates lymph.
2. The Blood Circulatory System
The circulatory system distributes nutrients and oxygen throughout the body, while collecting waste products of cellular metabolism and leading them to the bodies responsible for their elimination.
The circulatory system of people, like that of other vertebrates, consists of blood vessels, blood, and the booster body: the heart.
Vasculature
These are the conduits through which blood circulates to all parts of the body. They can be of three types:
Arteries
Carry blood from the heart to various body organs. Their walls are very thick, strong, and elastic to withstand the high pressure with which blood flows, driven by the heart.
Veins
Carry blood from various organs back to the heart. Their walls are thinner and less elastic than arteries, as blood circulates through them at a lower pressure. Inside, they have valves that facilitate the upward flow of blood and prevent its decline.
Capillaries
They are microscopic vessels forming a network connecting the terminations of the arteries with the start of the veins. Through their thin epithelial wall, exchange of food, oxygen, carbon dioxide, and waste products occurs with the cells of all body parts.