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MICROCIRCULATION

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Tasly MICROCIRCULATION

Post by pmmutiti on Sat May 31, 2008 4:47 pm

Microcirculation deals with the flow of blood from arterioles to cappillaries or sinusoids to venules.

Blood flows freely between an arteriole and a venule through a vessel channel called a thoroughfare channel. Capillaries extend from this channel and structures called precapillary sphincters control the flow of blood between the arteriole and capillaries

What are capillaries?

Capillaries are extremely small vessels located within the tissues of the body that transport blood from the arteries to the veins. Capillary walls are thin and are composed of endothelium (a single layer of overlapping flat cells). Oxygen, carbon dioxide, nutrients and wastes are exchanged through the thin walls of the capillaries.

The flow of blood is controlled by structures called precapillary sphincters. These structures are located between arterioles and capillaries and contain muscle fibers that allow them to contract. When the sphincters are open, blood flows freely to the capillary beds of body tissue. When the sphincters are closed, blood is not allowed to flow through the capillary beds.

Capillary Size

Capillaries are so small that red blood cells can only travel through them in single file.


* 5-10 microns in diameter.


Sinusoids

What are sinusoids?

The liver, spleen and bone marrow contain vessel structures called sinusoids instead of capillaries. Similar to capillaries sinusoids are composed of endothelium. The individual endothelial cells however do not overlap as in capillaries and are spread out. Oxygen, carbon dioxide, nutrients, proteins and wastes are exchanged through the thin walls of the sinusoids.

Sinusoid Size

* 30-40 microns in diameter.

The precapillary sphincters contain muscle fibers that allow them to contract. When the sphincters are open, blood flows freely to the capillary beds where gases and waste can be exchanged with body tissue. When the sphincters are closed, blood is not allowed to flow through the capillary beds and must flow directly from the arteriole to the venule through the thoroughfare channel.

It is important to note that blood is supplied to all parts of the body at all times but all capillary beds do not contain blood at all times. Blood is diverted to the parts of the body that need it most at a particular time. For instance when you eat a meal blood is diverted from other parts of your body to the digestive tract.

Vessel Sizes:

Vessel Diameter in Microns
Arterioles 20-50
Capillaries 5-10
Sinusoids 30-40
Venules 30-40


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Peter Mwaura Mutiti : Teaching old blood cells new tricks:
When you hear someone mention circulation you probably think of the heart and major arteries—and for good reason. Circulatory disorders such as hypertension (high blood pressure) and atherosclerosis (hardening of the arteries) are major risk factors for heart disease, heart attacks, and stroke.

But there’s more to it than that. With all the attention on the heart and arteries, it’s easy to overlook serious health problems affecting the smallest components of the circulatory system—microscopic blood vessels called microcapillaries, where the critical exchange of oxygen and nutrients actually takes place. If blood isn’t flowing through this web properly, it can trigger all sorts of health problems, many of which may not seem related to circulation at all.

A number of factors contribute to poor circulation as we age. Arteries and veins become stiff and congested as cholesterol and calcium plaques accumulate and restrict blood flow. Spasms in the smooth muscles surrounding the circulatory arteries and veins can also choke off circulation. These same processes also occur in our microcapillaries, reducing microcirculation and impairing the critical exchange of nutrients and gases in tissues and major organs.

This problem only gets worse as we get older because of changes in the composition and structure of blood cells. As you reach middle age, the blood starts to thicken and congeal as platelets and blood proteins make cells sticky. Plus, the spleen—the organ that removes old, damaged blood cells from circulation—begins to slow down with age, which means new, healthy blood cells are replaced at a sharply reduced rate. And to make matters even worse, as blood cells age, they become stiff and no longer appear round and evenly shaped. This makes it harder for them to pass smoothly through the capillaries. In fact, the angular, jagged shape of the old cells can damage the fragile microcapillaries even further.

Eventually, these age-related changes take their toll on the microcapillaries, reducing circulation to the tissues and blocking the flow of nutrients and oxygen. Removal of carbon dioxide and other metabolic waste products is also hindered. This leads to a slow buildup of metabolic garbage that can gradually bury the cells in their own waste products. In time, the cells, poisoned by their own metabolic byproducts, begin to waste away and ultimately cease to function altogether.

The combined effect of poor circulation and old blood contributes to a host of symptoms, including deep fatigue, fuzzy thinking, frequent infections, and lowered sex drive—all conditions usually considered just “normal parts of aging.”

If circulation doesn’t improve, it can lead to more serious conditions, such as high blood pressure, heart attack, stroke, diabetes, and arthritis. But giving your body a fresh supply of healthy blood may target all of these problems and more.
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