Structure and Function
The function of the circulatory system is to act as the transportation system for the body. The circulatory system carries nutrients, gases, hormones, electrolytes, water and wastes throughout the body. The system includes a pump called the heart. The heart pumps blood throughout the body through tubes called arteries, veins and capillaries.
The heart is located on the left side of the chest. The heart is about the size and shape of a closed fist. The heart is hollow inside and divided into four chambers. The two top chambers are called the atria. The atria receive blood into the heart. The two lower chambers, called ventricles, pump blood out of the heart. The walls of the heart are made of a special kind of muscle called the myocardium. The heart is covered with a sac called the pericardium.
The heart works by contracting the myocardium. The atria contract together, then the ventricles contract. These contractions force blood to continuously flow through the heart. Valves keep the blood flowing in one direction. Contractions force blood from one chamber to the next and into the body. Each time the heart beats, the valves between the heart chambers are forced open. When the valves close, they make a “lub dub” sound. This sound is the heartbeat heard through a stethoscope. One complete “lub dub” sound equals one heartbeat.
When blood leaves the right side of the heart, it goes to the lungs. In the lungs, the blood leaves behind the waste product carbon dioxide, and picks up oxygen. The blood then returns to the heart on the left side. The left side of the heart pumps the blood into the body through the aorta. The aorta is the artery located just outside the left ventricle and is the largest artery in the body.
Contraction of the heart is called systole. When the heart rests between contractions it is called diastole. Blood pressure is the force exerted by the blood on the walls of the vessels. Blood pressure is higher during systole and lower during diastole. Systole is the top (higher) number of a blood pressure reading. Diastole is the smaller (lower) number of a blood pressure reading.
The heartbeat is controlled by nerve centers in the brain. Electrical activity across the heart muscle coordinates muscle contraction. This electrical activity is what is recorded when an electrocardiogram (EKG) is performed. The pulse is the rhythmic expansion and contraction of the artery walls and corresponds with the heartbeat. A pulse can be felt with the fingertips when placed over an artery close to the skin surface and often over a bone.
Blood vessels include arteries, veins and capillaries. Arteries carry blood away from the heart. Arteries are thick-walled to withstand the force of the heart contracting and are usually located deep within the body to protect the vessels from injury.
Veins carry blood toward the heart. They are usually thin-walled as pressure is significantly lower when blood is transported back to the heart. Veins have valves to keep blood moving in one direction back to the heart.
Capillaries are a network of blood vessels that connect arteries to veins. Capillaries have very thin walls to allow nutrients and wastes to pass easily between tissues and the blood.
blood Blood is made up of fluid called plasma and three different types of blood cells. First, red blood cells (RBCs) carry oxygen; second, white blood cells
(WBCs) fight infection; and third, platelets are necessary for the blood to clot and seal leaks. Plasma is the liquid portion of the blood. Plasma carries substances circulating in the body such as nutrients, wastes, hormones, proteins, antibiotics and glucose. Blood also plays a critical role in the prevention of bleeding from injuries. Blood clotting is the process of sealing leaks and preventing blood loss when vessels are damaged. Blood clotting establishes a framework to allow tissue repair to occur.
The lymphatic system also carries fluid throughout the body. Lymph vessels are very similar to veins and capillaries. Because the lymph system has no pump, it depends on gravity and muscle activity to move lymph fluid throughout the body. Lymph nodes are clustered in several areas in the body and work to filter bacteria, viruses and cancer cells from the body. The lymph system is one of the body’s defenses against infection and illness. It plays a large role in providing immunity to the body. Immunity is the ability to resist infection and diseases by activating specific defenses.
Lifestyle, environment and age all contribute to changes in the circulatory system. Factors that contribute to heart and vascular disease include heredity, gender, race, age, cholesterol level, blood pressure, diabetes, smoking, body weight, diet, lack of exercise and stress.
With age, the heart becomes less elastic and electrical activity becomes less accurate. The myocardium thickens as the chambers of the heart enlarge. The heart pumps blood less effectively and less blood is pumped with each heartbeat. Damaged heart muscle is replaced with scar tissue, which makes the heart weaker. Blood vessels may also become less elastic and more rigid. Blood vessel walls become thicker, and the inner lining of the vessels may be coated with calcium and fatty deposits, making the opening much smaller. Blood vessels may become very fragile and break easily. There is an increased incidence of blood clots that can block vessels and blood flow to the limbs, heart, brain, lungs and other organs. Pooling of blood occurs in the legs because the veins’ valves are less efficient. The immune system becomes less efficient at combating diseases. Vaccines are strongly recommended because of a decreased ability to fight infections such as flu or pneumonia. There is a higher incidence of cancer due to the lymph system not eliminating cancer cells effectively.
Myocardial infarction (mi) is also called a heart attack. It occurs when areas of the heart are deprived of blood and oxygen, resulting in tissue death and destruction. Ischemia is the result leading to necrosis. Necrosis is tissue death. Clot formation is the most common cause of MI. The prognosis depends on the location and the amount of tissue destruction of the heart. Access to prompt medical care and treatment of preexisting conditions is vital.
Symptoms of MI
- Chest pain not relieved by nitrates
- Sudden pain: substernal, severe and unrelenting
- Extreme pressure to the chest, shoulders, arms, abdomen, neck or jaw
- Severe indigestion
- Feeling of impending doom
- Feeling of suffocation
- Arrhythmia: an abnormal heartbeat pattern.
Drugs that Affect the Circulatory System
- Vaccines are substances containing weakened or dead disease-causing organisms; they are given to allow an individual to develop immunity to that disease.
- Oxygen is used as a supplement to room air. It increases the amount of oxygen available to the lungs, blood and cells.
- Diuretics promote fluid loss by increasing urine excretion. Diuretics work on different chemicals and parts of the kidney, and are divided into several categories according to their actions. Side effects may include low potassium, muscle weakness, dehydration, postural hypotension headaches and/or muscle cramps.
- Antibiotics prevent or treat infections. Side effects may include allergic reaction, nausea, vomiting, diarrhea and/or constipation.
- Antihypertensive agents treat hypertension. These medications do not cure hypertension but control it. There are multiple sub-classifications of antihypertensives. Side effects may include hypotension, slow heart rate, drowsiness, nausea and/ or vomiting.
- Antiarrhythmics correct irregular heartbeat patterns. Side effects may include slow heart rate, hypotension, dry mouth, urinary retention, heart irregularities and/or fatigue.
- Vasodilators reduce blood pressure by causing blood vessels to relax. Side effects may include headache, rapid heart rate and/or fluid retention.
- Calcium channel blockers help slow the movement of calcium across cells and slow electrical conduction in cells. These medications help dilate the arteries of the heart, control heart irregularities and treat hypertension. Side effects may include weakness, dizziness, fainting and/or falls.
- Beta-adrenergic blockers block certain receptors in the heart, reduce the heart rate and reduce the force of the heart muscle contraction. Side effects may include slow heart rate, fatigue, insomnia and/or sexual dysfunction.
- ACE (angiotension converting enzymes) inhibitors prevent the changing of a chemical in the liver and lungs that raises the blood pressure. Side effects may include cough and high potassium levels in the blood. Pregnant women should not take ACE inhibitors.
- Antianginal drugs relax the blood vessels of the heart to increase blood flow to the heart muscle and are used primarily to relieve the pain accompanying angina.
- Nitrates work directly on the blood vessel muscles, causing them to relax. Nitrates work on both the arteries and the veins, and can be administered by many routes. Side effects may include headache and/ or low blood pressure.
- Analgesics relieve pain. Morphine is the drug of choice for pain related to a myocardial infarction. Side effects may include drowsiness, nausea and/or gastric upset.
- Cardiac glycosides/cardiotonics make the heart beat stronger and slower. Toxicity is a significant concern, particularly in the elderly. An apical pulse should be checked before each dose is given. If the heart rate is too low, the dose may be held. If a dose of any medication is held, the person providing direction and monitoring must be notified.
- Anticoagulants prevent the formation of blood clots. Some diseases of the blood vessels promote the formation of blood clots. Blood clots within blood vessels are the main cause of heart attack and stroke. Anticoagulants act by interfering with the normal blood-clotting mechanism. Aspirin has a side effect of reducing blood-clotting ability and is sometimes given in small doses as an anticoagulant. A commonly used anticoagulant is warfarin (Coumadin). Side effects may include diarrhea, nausea, vomiting, poor appetite, bruising, sores in the mouth, cramps, blood in the urine and/or skin rash. A blood test called an international normalized ratio (INR) may be performed regularly to be sure the resident’s blood-clotting mechanism does not become too depressed, resulting in excessive bleeding. INR is maintained between 2.0 and 3.0 by adjusting the dose of anticoagulant.
- Hematinics are known as iron preparations. Iron is an essential mineral needed for the production of blood components. Iron is used to treat types of anemia. Residents who become anemic may take an iron preparation daily. Most hematinics begin with the name “ferrous,” which is the scientific name for iron. The major side effects of these drugs are the production of dark-colored stool and constipation.
- Vitamins are chemicals needed by body cells to carry out their normal functions. There are several vitamins that affect circulation. Vitamin K is necessary for the proper functioning of the blood clotting mechanism; it works antagonistic to anticoagulants. Nicotinic acid (Niacin) has been used as a peripheral vasodilator and for some forms of high blood cholesterol levels. Vitamin B-12 is used to treat some types of anemia. Folic acid is necessary for the normal formation and function of red blood cells. Vitamins may be given by themselves or as a multi-vitamin that contains most of the normal daily requirements.