Circulatory System Info:
Circulatory System Info:
Blood Vessels
After blood leaves the heart, it is pumped through a network of blood vessels to different parts of the body. As it is seen in the picture left, there are three types of blood vessels that form this network. These are
[pic]arteries
[pic]capillaries
[pic]veins
With the exception of capillaries and tiny veins, blood vessels have walls made up of three (3) layers of tissue. The inner layer is epithelial tissue. The middle layer is smooth muscle tissue and elastic fibers. The outer layer is connective tissue.
|Arteries |
|Arteries carry blood from the heart to all the tissues of the body. |
| |
|**Except for the pulmonary arteries, all arteries carry oxygen-rich blood. |
The artery that carries oxygen-rich blood from the left ventricle to all parts of the body is the aorta. The aorta, with a diameter of 2.5 centimeters, is the largest artery in the body. As the aorta travels away from the heart, it branches into smaller and smaller arteries so that all parts of the body are supplied with blood. The smallest arteries are called arterioles.
The walls of arteries are thicker than those of veins. The smooth muscle cells and elastic fibers that make up these walls make arteries tough and flexible. These characteristics enable arteries to withstand the high pressure of blood as it is pumped from the heart.
|Capillaries |
|Arterioles branch into networks of very small blood vessels called capillaries. The real work of the circulatory system is done |
|in these thin-walled capillaries. They |
|[pic]provide oxygen and nutrients for the cells and then they |
|[pic]collect carbon dioxide and waste products from the cells. |
The walls of the capillaries consist of only one (1) layer of cells . They are extremely narrow blood vessels, so narrow that blood cells moving through them must pass in single file. That makes it easy for oxygen and nutrients to diffuse from the blood into the tissues. The forces of diffusion drive carbon dioxide and waste products from the tissues into the capillaries.
|Veins |
|The flow of blood moves from capillaries into veins. The smallest veins are called venules. Veins |
| |
|[pic]collect oxygen-poor blood from every part of the body |
|[pic]carry oxygen-poor blood back to the heart. |
The walls of veins are thinner and less elastic than those of arteries. Although the walls are less elastic, they are more flexible and are able to stretch out readily. This is important, because it reduces the resistance the flow of blood on its way back to the heart.
Large veins contain valves that keep blood from flowing backward. These valves play an important role, because blood must frequently flow against the force of gravity.
Blood flowing through veins gets quite a push from the contractions of skeletal muscles, especially those in the arms and the legs. When these muscles contract, they squeeze against veins and help force blood toward the heart. When these muscles are not used for long periods of time, this extra push is lost and blood accumulates in different parts of the body.
Pathways of Circulation
Blood moves through the body in a continuous pathways. In this pathways, there are two major circulation stated below.
[pic]Pulmonary cirulation: it carries blood between the heart and the lungs. This circulation begins at the right ventricle and ends at the left atrium.
[pic]Systemic Circulation: it starts at the left ventricle and ends at the right atrium, carries oxygen-rich to the rest of the body.
Pulmonary Circulation
As you see in the picture, pulmonary circulation starts at the right ventricle, and ends at the left atrium of the heart. Oxygen-poor blood is pumped out of the right ventricle of the heart into the lungs through the pulmonary arteries. These are the only arteries in the body that carry oxygen-poor blood.
After blood gets oxgen from the lungs, it returns to the heart through the pulmonary veins, which are the only veins in the body that carry oxygen-rich blood.
The lungs are the only organs directly connected to both chambers of the heart.
Systemic Circulation
Systemic circulation starts at the left ventricle, and ends at the right atrium of the heart.
Oxygen-rich blood leaving the heart passes through the aorta and into a number of arteries that supply blood to every part of the body. Systemic circulation supplies each major organ with blood, including the heart.
A pair of coronary arteries leading from the aorta carry blood through the tissues of the heart. These arteries branch into arterioles and then into capillaries, forming a network throughout the heart. After capillaries, oxgen-poor blood passes into veins and returns to the right atrium.
In general, blood travels through only one set of capillaries before it returns to the heart. However, there is a special circulation known as the hepatic portal system that is an exception to this rule.
Blood
Blood is referred to as the river of life. It is a fluid medium that transport material throughout the body in the circulatory system. Blood is made of plasma and blood cells . (See chart bottom of page 88 in text).
Functions of the blood
[pic]transports nutrients and dissolved gases (oxygen and carbon dioxide), enzymes, hormones, and waste products
[pic]regulates body temperature, pH, and electrolytes (ions in solution that conduct electric current)
[pic]protects the body from invaders (wh
[pic]restricts the loss of fluid.
The human body contains 4 to 6 liters of blood, only 8 % of the total mass of the body. Approximately 55% of blood is made of fluid portion called plasma. The remaning 45% consists of blood cells.
The Aorta and the Arterial System
The aorta leaves the heart and heads toward, what else, the head. We have to keep our brains well nourished so we can make good grades in school. The arteries that take the blood to the head are located on something called the *aortic arch.* After the blood passes through the aortic arch it is then distributed to the rest of the body. The *descending aorta* goes behind the heart and down the center of the body.
Sometimes, if you are lying flat on your back, you can look down toward your feet and actually see your abdomen pulsate with each heart beat. This pulsation is really the aorta throbbing with each heart beat. Do not be alarmed, this is normal.
From the aorta, blood is sent off to many other arteries and arterioles (very small arteries) where it gives oxygen and nutrition to *every* cell in the body. At the end of the arterioles are, guess what, capillaries. The blood gives up its cargo as it passes through the capillaries and enters the venous system.
The Venous System
The venous system carries the blood back to the heart. The blood flows from the capillaries, to venules (very small veins), to veins. The two largest veins in the body are the *superior* and *inferior* vena cavas. The superior vena cava carries the blood from the upper part of the body to the heart. The inferior vena cava carries the blood from the lower body to the heart. In medical terms, *superior* means above and *inferior* means under. Many people believe that the blood in the veins is *blue*; it is not. Venous blood is really dark red or maroon in color. Veins do have a bluish appearance and this may be why people think venous blood is blue. Both the superior and inferior vena cava end in the right atrium. The superior vena cava enters from the top and the inferior vena cava enters from the bottom.
This completes our little journey through the circulatory system. I hope the blood has continued to flow to your brain as you read this and you managed to stay awake. If you dozed off, it's o.k., I doze off myself from time to time when I read really boring stuff. There are lots of things that I did not talk about, such as how the cooling system works, but I thought that you might like to look some of this stuff up by yourself. As usual, I know you will have questions for me. I can't wait to hear from you.
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