Circulation 2

Circulation 2

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Circulation 2...

Circulation 2:

CAPILLARIES

Capillaries are the smallest blood vessels. They are only seen by a compound microscope. capillaries are the tiniest of arteriole divisions.

Capillary walls are extremely thin and allow for selective permeability of various cells and substances.

Tiny openings in capillary walls allow for WBC's to leave the blood stream and enter the tissue spaces to help destroy invading bacteria.

The internal diameter of a capillary is so small that RBC's often pass through single file. Capillaries are ultimately responsible for transporting blood to all tissues.

VEINS

Veins carry deoxygenated blood away from the capillaries and to the heart. The smallest vein or venule is barely larger than a capillary but it contains a muscle layer that is not present is capillaries.

Veins, as we know are similar to arteries but they do not have the same elasticity or muscular structure. Also veins are much thinner as they do not have to withstand the same type of pressure that arteries must.

Because of this thin walled characteristic, we have had the term “veins collapsing” used when we talk about phlebotomy. Veins have valves along the length of them. These valves go in only one direction to prevent backflow or reflux back toward the capillaries. There are many valves in the lower extremities where blood must oppose the force of gravity.

VENUS RETURN

Since blood almost has to go uphill from the legs to the heart, the valves that we just learned about take on a very important function. ( prevention of backflow)

In addition to these valves our skeletal muscles assist in the return of blood flow back to the heart.

Think of how sleepy you get when you drive for long periods of time like on a car ride. The reason for this is because blood isn't getting back to the heart for oxygen. If you get out and walk around you will notice that this improves because when you get out and start to move around this improves the circulation and thus your oxygenation.

BLOOD PRESSURE

Why is blood pressure an important measurement? When we were talking about the hill of the blood pressure we talk about the blood pressure gradient. The blood pressure gradient is the difference between the aortic pressure and the pressure in the vena cavae. The blood pressure gradient is vital in keeping the blood flowing. When the gradient is present this keeps the blood circulating and when the gradient is not present there is no blood circulating in the body. When there is no gradient or push to the circulatory system life itself ceases to function. This is why when we see a rapid fall in the blood pressure quickly measures must be taken to reverse this trend.

Hemorrhage demonstrates the relationship between blood volume and blood pressure. With a loss of blood there is a decreased amount of pressure in the veins and arteries therefore there is a drop in blood pressure.

The average systolic blood pressure in an adult is 120mm/Hg. The average diastolic is 80mm/Hg. or 120/80 Normal blood pressure is different in every individual

Kortokoff sounds are named after a Russian M.D. and represent the sounds heard when using a stethescope and a syphgmomanometer with the brachial artery being compressed with the cuff and then released in order to hear the two distinct sounds of the systolic and diastolic measurements.

Five mechanisms that help to keep the venous blood flowing through the circulatory system include:

a strongly beating heart, an adequate arterial blood pressure, valves in the veins, the “milking action of the skeletal muscles as they contract, and the changing pressures in the chest cavity caused by breathing.

PULSE

A pulse is the alternating expansion and contraction of an artery as blood flows through it. To feel a pulse, you must place your fingertips over an artery that lies near the surface of the body and over a bone or another firm base. The pulse is a valuable clinical sign. It can be obtained with little to no discomfort and can offer information regarding the rate, intensity and rhythm of the heart.

Here are some locations where you may locate a pulse that can be palpated or felt.

brachial artery- located above the crook of the elbow and along the inner border of the biceps muscle

common carotid artery- found in the neck along the front margin of the sternocleidomastoid muscle near the lower edge of the thyroid cartilage

dorsalis pedis- on the anterior surface of the foot below the ankle joint

facial artery- at the lower edge of the mandible on a line with the corners of the mouth

radial artery- at the wrist on the anterior surface of the radius

temporal artery- slightly above the outer edge of the eye

axillary artery- in the axilla over the axillary artery

femoral artery- in the groin area

popliteal artery- behind and just proximal to the knee

You should be aware of and locate many of the pulse sites listed above.

DISORDERS OF BLOOD VESSELS

Aneurysm- is a sac caused by an enlargement of a blood vessel which is also thinning out in the area where the enlargement is located. Almost like having a bubble in the tire. An aneurysm pulsates with each systolic beat causing a murmur. The symptoms are pain and pressure or their may be no symptoms at all. The most common site for an aneurysm is the aorta.

Arteriosclerosis- is the disease which occurs when the arterial walls thicken due to a loss of elasticity as aging occurs.

Atherosclerosis is the disease which occurs when a deposit of fatty substances form along the walls of the arteries.

Both of these diseases cause a narrowing of the blood vessel opening which may reflect a problem with impaired circulation in the lower extremities or a memory loss or in an advanced case impaired circulation to the coronary vessels.

Gangrene- is death of a body tissue due to an insufficient blood supply caused by disease or injury

Phlebitis- is an inflammation of the lining of a vein. accompanied by a clotting of the blood in the vein. Swelling, pain and redness along the vein are most common symptoms.

Embolism- is atraveling blood clot to the lungs

Varicose veins- are the swollen veins that are a result of slowing of blood flow back to the heart. Blood backs up into the veins if the muscles do not massage them. The weight of the stagnant blood distends the valves and causes distension and loss of elasticity of the vessels. There is a hereditary weakness to the walls of the vessel structure. Age and pregnancy are other factors that may contribute to this disorder.

Hemorrhoids- are varicose veins in the walls of the lower rectum and the tissues surrounding the anus.

Cerebral hemorrhage- bleeding from blood vessels within the brain. It can be caused by disease and /or injury or from arteriosclerosis.

Hypertension- is high blood pressure in which the systolic reading is over 140mm/Hg and the diastolic is over 90. This disease may be asymptomatic or it can be referred to as a silent killer. Causes may be familial, stress, or atherosclerosis.