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CIRCULATORY SYSTEM. The cardiovascular, or circulatory, system in humans is composed of the heart and the blood
vessels--arteries, veins, and capillaries. Its purpose is to provide nutrients and oxygen to the tissues and to remove wastes from them. It is also where the body fights infections.
The human heart is a pear-shaped muscular organ about the size of a fist. A wall of muscle, the septum, divides the right side from the left. Each of these two sides is further divided into an atrium, or upper chamber, and a ventricle, or lower chamber. The human heart beats 60 to 80 times a minute while a person is at rest. The heart rests only about 0.4 second between beats.
Circulation of blood consists of two main circuits. Pulmonary circulation carries blood from the heart to the lungs where waste gases, mostly carbon dioxide, are removed from the blood, and oxygen is taken on by hemoglobin in the erythrocytes, or red blood cells. The blood then returns to the heart and is pumped to other parts of the body in the systemic circulation, which comprises the blood supply to the entire body except the lungs. Within the systemic circulation is the portal circulation, which supplies blood to the liver. Capillaries and veins carrying nutrient-rich blood from the digestive organs merge to form the portal vein, leading to the liver. Blood from the liver reenters the systemic circulation via the inferior vena cava.
Bright red, oxygen-rich blood from the pulmonary circulation flows from the left atrium into the left ventricle. With each beat of the heart, blood is forced through the large artery of the heart, called the aorta, and throughout the body by a network of arteries. The large arteries of this network are the carotid arteries in the neck and head, the axillary arteries in the arms, the abdominal arteries in the abdomen, and the external iliac arteries in the legs.
Numerous smaller arteries branch off these major ones, and each branching yields smaller and smaller arteries until the blood passes from the smallest arteries into the arterioles. These tiny structures connect to venules, forming a structure called a capillary. It is here that most of the blood-tissue exchange occurs, with the blood giving up its oxygen, nutrients, and fluid to the tissues, and the tissues giving up carbon dioxide and fluid wastes to the blood.
Several organs interact with the circulatory system in very specific ways. Nutrients and fluids are absorbed from the digestive organs. The spleen then filters the blood, removing old blood cells and microorganisms. Phagocytes, a type of white blood cell, engulf these materials and destroy them. The liver also filters the blood and detoxifies wastes such as ammonia into less toxic urea. The liver adds fibrinogen and prothrombin to the blood, which are necessary for clotting. The kidneys extract water, minerals, urea, and other waste products from the blood. These materials are later excreted in the urine.
The blood that travels into the veins from the capillaries is now oxygen-poor and dark red. The veins, like the arteries, branch into larger and larger structures and eventually return to the heart. Here the blood enters the right atrium and then the right ventricle, where it is again pumped to the lungs, and the process repeats.
The arteries are the thickest of all blood vessels and have muscular walls that contract to keep the blood moving away from the heart. The veins are not as muscular, but they contain valves to prevent the blood from flowing backward.
Blood Pressure and Pulse
Arteries near the surface of the skin can be used to measure one aspect of the functioning of the circulatory system--blood pressure. Blood pressure is measured by wrapping the cuff of an instrument called a sphygmomanometer around the arm just above the elbow. With a stethoscope over the brachial artery at the inside of the elbow, the rushing sounds of blood through the artery can be heard. The blood pressure, written as a fraction and measured in millimeters of mercury, is usually 100 to 120 over 60 to 80 in a resting, healthy person. The higher number represents the minimum pressure needed to stop completely the flow of blood. This is called the systolic blood pressure. The lower number represents the maximum pressure at which the beats heard through the stethoscope change from loud to soft--that is, when full blood flow is restored. This is called the diastolic blood pressure.
Blood pressure is governed by five elements--the strength of the heartbeat, the volume of blood, the viscosity of the blood, the resistance of the arterioles, and the elasticity of the arterial walls. An abnormality of any of these can cause the blood pressure to be too high or too low.
Another measurement of the circulation is made by taking the pulse.With the fingers (not the thumb) over the radial artery inside the wrist, the number of heartbeats is counted for one minute. Normally the heart will beat 68 to 80 times a minute, though exercise and stress will cause both the pulse and the blood pressure to rise temporarily. Other pulse points of the body are the temple, side of the neck, back of the knee, top of the foot over the ankle, and groin.
Disorders of Circulation
Because the circulatory system is necessary for life, diseases that affect any part of it can have serious or fatal consequences. Hypertension, or high blood pressure, can be caused by an increase in the volume of blood pumped by the heart or by an increased resistance to blood flow in the arterioles. Several diseases, including kidney disease, may cause hypertension, or the cause may be unknown. Called the "silent killer," hypertension is often symptomless but can lead to heart disease and stroke.
Arteriosclerosis is a group of diseases of the arteries. One of the most common types of arteriosclerosis is atherosclerosis, a condition in which fatty deposits of cholesterol form in the arteries. These deposits can break away and travel to the heart or brain, causing heart attacks or strokes. Diets that are high in certain fats called saturated fats encourage the production of these deposits.
Brief Overview of Circulatory System.
1. Types of blood vessels
Once blood leaves the heart, it is transported around the body in three main types of blood vessels:
| a. Arteries | |
| b. Veins | |
| c. Capillaries |
Veins transport used blood from all over the body back to the heart and lungs for re-oxygenation. Veins are often visible through your skin as blue lines. They are blue because they carry blood that is full of waste products, and are low in oxygen. The "motorways" of the venal system are the Vena Cavae. The Superior Vena Cava carries blood to the heart from the upper body, while the Inferior Vena Cava carries blood from the lower body.
Another unique feature of veins is that they have valves. Like the valves in the heart, they are there to prevent a backflow of blood. The blood must flow in one direction only, against gravity in most cases, back to the heart.
Capillaries are minute blood vessels that join onto the arterioles. They are one cell thick and are exchange points where the nutrients (oxygen and glycogen) cross into the tissue cells (muscles) from the arterioles. Waste products from the tissues cross back into the bloodstream in the capillaries then into the venules (small veins).
|
Arteries |
Veins |
| Take blood away from the heart |
Take blood to the heart |
| Walls are thick and elastic | Walls are thin |
| Transports oxygenated blood |
Transports de-oxygenated blood |
| Has small lumen (tubular cavities inside) |
Has large lumen |
| Has a pulse and blood travels in spurts |
Has no pulse and blood travels smoothly |
| Has no valves |
Has valves |
 Artery |
|
|
| Vein |
3. Circulation
The complete circuit of a blood cell around the body is:
Veins have no pulse-unlike arteries, there is no pump to push the blood through the venal system. Veins fight gravity to get the blood from the feet to the heart by using small and large muscular contractions that massage the veins, and push the blood along. Any small movement of the leg muscles push the blood on up.
Have you ever noticed when you stand in line at a grocery
store for a long time you begin to wiggle you toes to
get the blood moving along.
| Atrium | Either of the two (left and right) upper chambers of the heart. Also called auricles |
| Pulmonary | Used to describe blood vessels that carry blood between the heart and the lungs |
| Aorta | The largest artery which directs blood to every organ but the lungs |
| Lumen | The inner open space of a tubular organ, in this case the blood vessels |
| Vena Cava | Either of two large veins which carry blood into the right side of the heart |
| Cardiovascular | Of or involving the heart and blood vessels |
Assignment:
1. Describe what happens to a person having a heart attack?
2. What is your pulse and blood pressure? Take your pulse and if you have means of taking you blood pressure, do so.
3. What is the difference between arterial flow and vein flow?
4. If you accidentally cut yourself, how can you tell if a vein or artery has been affected?
5. Where is your femoral artery? Can you feel your femoral artery?
6. Which one(or two) of the following is not part of the circulatory system?
Aorta7. Research a specific heart disease and report back to me.
8. What is an EKG?
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