Monday, May 22, 2017
Breast Cancer: Causes, Symptoms and Treatments
- Chest wall.
- Pectoralis muscles.
- Lobules (glands that make milk).
- Nipple surface.
- Areola.
- Lactiferous duct tube that carries milk to the nipple.
- Fatty tissue.
- Skin.
Breast cancer is a kind of cancer that develops from breast cells.
Breast cancer usually starts off in the inner lining of milk ducts or the lobules that supply them with milk. A malignant tumor can spread to other parts of the body. A breast cancer that started off in the lobules is known as lobular carcinoma, while one that developed from the ducts is called ductal carcinoma.
The vast majority of breast cancer cases occur in females. This article focuses on breast cancer in women. We also have an article about male breast cancer.
Breast cancer is the most common invasive cancer in females worldwide. It accounts for 16% of all female cancers and 22.9% of invasive cancers in women. 18.2% of all cancer deaths worldwide, including both males and females, are from breast cancer.
Breast cancer rates are much higher in developed nations compared to developing ones. There are several reasons for this, with possibly life-expectancy being one of the key factors - breast cancer is more common in elderly women; women in the richest countries live much longer than those in the poorest nations. The different lifestyles and eating habits of females in rich and poor countries are also contributory factors, experts believe.
According to the National Cancer Institute, 232,340 female breast cancers and 2,240 male breast cancers are reported in the USA each year, as well as about 39,620 deaths caused by the disease.
Contents of this article:
- Breast anatomy and breast cancer symptoms
- Causes and diagnosis
- Treatments and prevention
- Latest research
Symptoms of breast cancer
The first symptoms of breast cancer are usually an area of thickened tissue in the woman's breast, or a lump. The majority of lumps are not cancerous; however, women should get them checked by a health care professional.A symptom is only felt by the patient, and is described to the doctor or nurse, such as a headache or pain. A sign is something the patient and others can detect, for example, a rash or swelling.
Women who detect any of the following signs or symptoms should tell their doctor (NHS, UK):
- A lump in a breast
- A pain in the armpits or breast that does not seem to be related to the woman's menstrual period
- Pitting or redness of the skin of the breast; like the skin of an orange
- A rash around (or on) one of the nipples
- A swelling (lump) in one of the armpits
- An area of thickened tissue in a breast
- One of the nipples has a discharge; sometimes it may contain blood
- The nipple changes in appearance; it may become sunken or inverted
- The size or the shape of the breast changes
- The nipple-skin or breast-skin may have started to peel, scale or flake.
Causes of breast cancer
Experts are not definitively sure what causes breast cancer. It is hard to say why one person develops the disease while another does not. We know that some risk factors can impact on a woman's likelihood of developing breast cancer. These are:
1) Getting older
The older a woman gets, the higher is her risk of developing breast cancer; age is a risk factor. Over 80% of all female breast cancers occur among women aged 50+ years (after the menopause).
2) Genetics
Women who have a close relative who has/had breast or ovarian cancer are more likely to develop breast cancer. If two close family members develop the disease, it does not necessarily mean they shared the genes that make them more vulnerable, because breast cancer is a relatively common cancer.
The majority of breast cancers are not hereditary.
Women who carry the BRCA1 and BRCA2 genes have a considerably higher risk of developing breast and/or ovarian cancer. These genes can be inherited. TP53, another gene, is also linked to greater breast cancer risk.
3) A history of breast cancer
Women who have had breast cancer, even non-invasive cancer, are more likely to develop the disease again, compared to women who have no history of the disease.
4) Having had certain types of breast lumps
Women who have had some types of benign (non-cancerous) breast lumps are more likely to develop cancer later on. Examples include atypical ductal hyperplasia or lobular carcinoma in situ.
5) Dense breast tissue
Women with more dense breast tissue have a greater chance of developing breast cancer.
6) Estrogen exposure
Women who started having periods earlier or entered menopause later than usual have a higher risk of developing breast cancer. This is because their bodies have been exposed to estrogen for longer. Estrogen exposure begins when periods start, and drops dramatically during the menopause.
7) Obesity
Post-menopausal obese and overweight women may have a higher risk of developing breast cancer. Experts say that there are higher levels of estrogen in obese menopausal women, which may be the cause of the higher risk.
8) Height
Taller-than-average women have a slightly greater likelihood of developing breast cancer than shorter-than-average women. Experts are not sure why.
9) Alcohol consumption
The more alcohol a woman regularly drinks, the higher her risk of developing breast cancer is. The Mayo Clinic says that if a woman wants to drink, she should not exceed one alcoholic beverage per day.
10) Radiation exposure
Undergoing X-rays and CT scans may raise a woman's risk of developing breast cancer slightly. Scientists at the Memorial Sloan-Kettering Cancer Center found that women who had been treated with radiation to the chest for a childhood cancer have a higher risk of developing breast cancer.
11) HRT (hormone replacement therapy)
Both forms, combined and estrogen-only HRT therapies may increase a woman's risk of developing breast cancer slightly. Combined HRT causes a higher risk.
12) Certain jobs
French researchers found that women who worked at night prior to a first pregnancy had a higher risk of eventually developing breast cancer.
Canadian researchers found that certain jobs, especially those that bring the human body into contact with possible carcinogens and endocrine disruptors are linked to a higher risk of developing breast cancer. Examples include bar/gambling, automotive plastics manufacturing, metal-working, food canning and agriculture. They reported their findings in the November 2012 issue of Environmental Health.
Cosmetic implants may undermine breast cancer survival
Women who have cosmetic breast implants and develop breast cancer may have a higher risk of dying prematurely form the disease compared to other females, researchers from Canada reported in the BMJ (British Medical Journal) (May 2013 issue).
The team looked at twelve peer-reviewed articles on observational studies which had been carried out in Europe, the USA and Canada.
Experts had long-wondered whether cosmetic breast implants might make it harder to spot malignancy at an early stage, because they produce shadows on mammograms.
In this latest study, the authors found that a woman with a cosmetic breast implant has a 25% higher risk of being diagnosed with breast cancer when the disease has already advanced, compared to those with no implants.
Diagnosing breast cancer
Women are usually diagnosed with breast cancer after a routine breast cancer screening, or after detecting certain signs and symptoms and seeing their doctor about them.
If a woman detects any of the breast cancer signs and symptoms described above, she should speak to her doctor immediately. The doctor, often a primary care physician (general practitioner, GP) initially, will carry out a physical exam, and then refer the patient to a specialist if he/she thinks further assessment is needed.
Below are examples of diagnostic tests and procedures for breast cancer:
1) Breast exam
The physician will check both the patient's breasts, looking out for lumps and other possible abnormalities, such as inverted nipples, nipple discharge, or change in breast shape. The patient will be asked to sit/stand with her arms in different positions, such as above her head and by her sides.
2) X-ray (mammogram)
Commonly used for breast cancer screening. If anything unusual is found, the doctor may order a diagnostic mammogram.
3)Breast ultrasound
This type of scan may help doctors decide whether a lump or abnormality is a solid mass or a fluid-filled cyst.
4) Biopsy
A sample of tissue from an apparent abnormality, such as a lump, is surgically removed and sent to the lab for analysis. It the cells are found to be cancerous, the lab will also determine what type of breast cancer it is, and the grade of cancer (aggressiveness). Scientists from the Technical University of Munich found that for an accurate diagnosis, multiple tumor sites need to be taken.
Treatments for breast cancer
A multidisciplinary team will be involved in a breast cancer patient's treatment. The team may consists of an oncologist, radiologist, specialist cancer surgeon, specialist nurse, pathologist, radiologist, radiographer, and reconstructive surgeon. Sometimes the team may also include an occupational therapist, psychologist, dietitian, and physical therapist.
The team will take into account several factors when deciding on the best treatment for the patient, including:
The team will take into account several factors when deciding on the best treatment for the patient, including:
- The type of breast cancer
- The stage and grade of the breast cancer - how large the tumor is, whether or not it has spread, and if so how far
- Whether or not the cancer cells are sensitive to hormones
- The patient's overall health
- The age of the patient (has she been through the menopause?)
- The patient's own preferences.
The main breast cancer treatment options may include:
- Radiation therapy (radiotherapy)
- Surgery
- Biological therapy (targeted drug therapy)
- Hormone therapy
- Chemotherapy.
Surgery
- Lumpectomy - surgically removing the tumor and a small margin of healthy tissue around it. In breast cancer, this is often called breast-sparing surgery. This type of surgery may be recommended if the tumor is small and the surgeon believes it will be easy to separate from the tissue around it.
- Mastectomy - surgically removing the breast. Simple mastectomy involves removing the lobules, ducts, fatty tissue, nipple, areola, and some skin. Radical mastectomy means also removing muscle of the chest wall and the lymph nodes in the armpit.
- Sentinel node biopsy - one lymph node is surgically removed. If the breast cancer has reached a lymph node it can spread further through the lymphatic system into other parts of the body.
- Axillary lymph node dissection - if the sentinel node was found to have cancer cells, the surgeon may recommend removing several nymph nodes in the armpit.
- Breast reconstruction surgery - a series of surgical procedures aimed at recreating a breast so that it looks as much as possible like the other breast. This procedure may be carried out at the same time as a mastectomy. The surgeon may use a breast implant, or tissue from another part of the patient's body.
Radiation therapy (radiotherapy)
Controlled doses of radiation are targeted at the tumor to destroy the cancer cells. Usually, radiotherapy is used after surgery, as well as chemotherapy to kill off any cancer cells that may still be around. Typically, radiation therapy occurs about one month after surgery or chemotherapy. Each session lasts a few minutes; the patient may require three to five sessions per week for three to six weeks.
The type of breast cancer the woman has will decide what type of radiation therapy she may have to undergo. In some cases, radiotherapy is not needed.
Radiation therapy types include:
- Breast radiation therapy - after a lumpectomy, radiation is administered to the remaining breast tissue
- Chest wall radiation therapy - this is applied after a mastectomy
- Breast boost - a high-dose of radiation therapy is applied to where the tumor was surgically removed. The appearance of the breast may be altered, especially if the patient's breasts are large.
- Lymph nodes radiation therapy - the radiation is aimed at the axilla (armpit) and surrounding area to destroy cancer cells that have reached the lymph nodes
- Breast brachytherapy - scientists at UC San Diego Moores Cancer Center revealed that patients with early-stage breast cancer in the milk ducts which has not spread, seem to benefit from undergoing breast brachytherapy with a strut-based applicator. This 5-day treatment is given to patients after they have undergone lumpectomy surgery. The researchers found that women who received strut-based breast brachytherapy had lower recurrence rates, as well as fewer and less severe side effects.
Side effects of radiation therapy may include fatigue, lymphedema, darkening of the breast skin, and irritation of the breast skin.
Chemotherapy
Medications are used to kill the cancer cells - these are called cytotoxic drugs. The oncologist may recommend chemotherapy if there is a high risk of cancer recurrence, or the cancer spreading elsewhere in the body. This is called adjuvant chemotherapy.
Monday, May 8, 2017
Anatomy Of Ankle
The ankle is a large joint made up of three bones:
- The shin bone (tibia)
- The thinner bone running next to the shin bone (fibula)
- A foot bone that sits above the heel bone (talus)
The bony bumps (or protrusions) seen and felt on the ankle have their own names:
- The medial malleolus, felt on the inside of your ankle is part of the tibia's base
- The posterior malleolus, felt on the back of your ankle is also part of the tibia's base
- The lateral malleolus, felt on the outside of your ankle is the low end of the fibula
The ankle joint allows up-and-down movement of the foot. The subtalar joint sits below the ankle joint, and allows side-to-side motion of the foot. Numerous ligaments (made of tough, moveable tissue) surround the true ankle and subtalar joints, binding the bones of the leg to each other and to those of the foot.
Ankle Conditions
- Sprained ankle: Damage to one of the ligaments in the ankle, usually from an accidental twist or turn of the foot. Rehabilitation can prevent pain and swelling from becoming a long-term problem.
- High ankle sprain: The ligament joining the two bones of the lower leg (tibia and fibula), called the syndesmotic ligament, is injured. A high ankle sprain causes pain and swelling similar to a true ankle sprain, but can take longer to heal.
- Ankle fracture: A break in any of the three bones in the ankle. Most commonly, the bones of the lower leg (tibia or fibula) is fractured.
- Ankle arthritis: While it’s not common, osteoarthritis, the most common form of arthritis, can affect the ankle.
- Rheumatoid arthritis: An autoimmune form of arthritis in which the body attacks joint tissue, causing inflammation, pain, and swelling. Any joint may be affected by rheumatoid arthritis, including the ankle.
- Gout: A form of arthritis in which crystals periodically deposit in joints, causing severe pain and swelling. The ankle may sometimes be affected by gout.
- Psoriatic arthritis: This form of arthritis, which causes swelling and pain, is associated with the skin condition psoriasis. Many joints, including the ankle, may be affected by psoriasis.
- Septic arthritis: Caused by bacterial infections that may occur in the ankle, this form of arthritis develops quickly, causing severe pain, swelling, fever, and difficulty moving the ankle.
Ankle Tests
- Physical examination: A health-care provider's examination of the ankle may identify whether an ankle fracture, sprain, or another condition is present.
- Ankle X-ray: An X-ray film of the ankle is most commonly used to determine a fracture, arthritis, or other problems.
- Stress X-ray: A doctor puts pressure on an injured ankle and takes an X-ray film. Also called a stress film or a stress test, this may uncover ankle problems unseen on regular X-rays.
- Magnetic resonance imaging (MRI scan): An MRI scanner uses a high-powered magnet and a computer to create high-resolution images of the ankle.
Ankle Treatments
- RICE therapy: RICE stands for Rest, Ice, Compression (as with an athletic bandage), and Elevation. RICE therapy is good initial treatment for most ankle injuries.
- Pain medicines: Over-the-counter or prescription pain relievers such as acetaminophen (Tylenol), ibuprofen (Motrin), and naproxen (Aleve) can ease most ankle pain.
- Cortisone injections: Injecting cortisone into the ankle can help with some forms of ankle arthritis. Cortisone suppresses inflammation in the ankle joint, reducing swelling and pain.
- Ankle immobilization: Immobilizing the ankle (usually with a cast) is necessary for most ankle fractures. Some health-care providers believe immobilization may help ankle sprains as well.
- Ankle surgery: Surgery may be required for many serious ankle conditions. In general, ankle surgery is performed in order to make the ankle more stable. Various techniques are used to keep the ankle bones in place.
- Syndesmotic screw: A surgeon places a screw connecting the bones of the lower leg. This keeps the bones together, giving a high ankle sprain time to heal. Once healed, the screw is removed.
- Ankle arthroscopic surgery: Ankle surgery using tools inserted through small incisions in the ankle. One of the tools, an endoscope, allows a surgeon to view the inside of the ankle joint on a video screen.
- Ankle fusion surgery: Surgery to fuse the bones of the ankle together, limiting movement in the ankle. Ankle fusion surgery can relieve the pain of severe ankle arthritis
- Ankle replacement surgery: Although some surgeons perform ankle replacement surgery, the results are generally poor, compared to knee replacement surgery. Watch the video.
Anatomy Of the Achilles Tendon
The Achilles tendon is a tough band of fibrous tissue that connects the calf muscles to the heel bone (calcaneus). The Achilles tendon is also called the calcaneal tendon.
The gastrocnemius and soleus muscles (calf muscles) unite into one band of tissue, which becomes the Achilles tendon at the low end of the calf. The Achilles tendon then inserts into the calcaneus. Small sacs of fluid called bursae cushion the Achilles tendon at the heel.
The Achilles tendon is the largest and strongest tendon in the body. When the calf muscles flex, the Achilles tendon pulls on the heel. This movement allows us to stand on our toes when walking, running, or jumping. Despite its strength, the Achilles tendon is also vulnerable to injury, due to its limited blood supply and the high tensions placed on it.
Achilles Tendon Conditions
- Achilles tendon tear: Tears of the Achilles tendon can be tiny (microtears), or large, causing pain, swelling, and impaired movement. They may occur suddenly during activity, or gradually over time.
- Achilles tendon rupture: A complete rupture of the Achilles tendon may make a "pop" sound, followed by pain and swelling of the lower leg. Treating an Achilles tendon rupture requires surgery or long-term immobilization of the ankle.
- Achilles tendinitis (tendonitis): Frequent activity (running or walking) can gradually inflame the end of the Achilles tendon, causing pain and stiffness at the back of the heel. Rest, ice, and stretching may speed healing, which can take weeks.
- Achilles peritendonitis: Similar to Achilles tendonitis, but inflammation and pain occur in the tissue surrounding the tendon, often two or more inches above the heel.
- Achilles tendinosis: Gradual thickening of the Achilles tendon without apparent inflammation, due to aging or overuse. Despite the thickening, the tendon is weakened and prone to further injury or rupture.
- Achilles tendinopathy: A general term for tendinitis or tendinosis affecting the Achilles tendon.
- Achilles or heel (calcaneal) bursitis: Low-riding shoes can irritate the bursa, a sac of fluid cushioning the Achilles tendon at the heel. Pain in the back of the heel, worse with shoes on, is the common symptom.
Achilles Tendon Tests
- Physical examination: To look for Achilles tendon problems, an examiner checks for pain, swelling, warmth, thickening, or discoloration around the heel and leg. A knot on the back of the leg may be present with Achilles tendon rupture. Most cases of tendinopathy without a rupture can be diagnosed by physical exam and often do not need further testing.
- Thompson test: Lying prone (on one’s stomach) or while kneeling on a chair, an examiner squeezes the calf. The end of the foot should move down in response; if it does not, an Achilles tendon rupture may be present.
- Knee flexion (Matles) test: A person lies face down and bends the knee slowly to a right angle. During this movement, the toe end of the foot should point away from the leg slightly; if it doesn't, an Achilles tendon rupture may be present.
- Magnetic resonance imaging (MRI scan): An MRI scanner uses a high-powered magnet and a computer to create highly detailed images of the ankle and leg. An MRI scan is the best test to diagnose an Achilles tendon rupture or other problems but it may not always detect tendinopathy.
- Achilles tendon ultrasound: A probe on the skin reflects high-frequency sound waves off the ankle, producing images of the Achilles tendon. Ultrasound can often diagnose an Achilles tendon rupture.
- Computed tomography (CT scan): A CT scanner takes multiple X-rays, and a computer constructs detailed images of the ankle and leg. An MRI scan is superior to a CT scan in diagnosing Achilles tendon problems.
- X-ray film: A plain X-ray film may identify problems with the bones or ankle joint, but it cannot diagnose Achilles tendon problems.
Achilles Tendon Treatments
- RICE therapy: Most Achilles tendon injuries can be treated with RICE: Rest, Ice, Compression with a sports bandage, and Elevation.
- Pain relievers: Over-the-counter medicines like acetaminophen (Tylenol), ibuprofen (Motrin), and naproxen (Aleve) can lessen the pain of most Achilles tendon problems. For more severe pain, prescription pain relievers may be necessary.
- Heat: Alternating ice and heat therapy may improve the pain of bursitis near the Achilles tendon.
- Footwear: Wearing shoes with good support that are right for your feet may help avoid continual injury to the Achilles tendon. Custom-made orthotics, heel lifts, and certain splints and braces are sometimes helpful.
- Physical Therapy: Although modifying or decreasing activity is important, particular stretches and exercises may be helpful to rehabilitate tendon problems, especially when they are persistent.
- Immobilization: Many moderate to severe Achilles tendon conditions require immobilization of the ankle joint. This may require wearing a special boot or a leg cast for several weeks.
- Achilles tendon surgery: Surgery can often reattach a ruptured Achilles tendon. Following surgery, immobilization of the ankle is necessary for several weeks.
Anatomy Of Shoulder
The shoulder is one of the largest and most complex joints in the body. The shoulder joint is formed where the humerus (upper arm bone) fits into the scapula (shoulder blade), like a ball and socket. Other important bones in the shoulder include:
- The acromion is a bony projection off the scapula.
- The clavicle (collarbone) meets the acromion in the acromioclavicular joint.
- The coracoid process is a hook-like bony projection from the scapula.
The shoulder has several other important structures:
- The rotator cuff is a collection of muscles and tendons that surround the shoulder, giving it support and allowing a wide range of motion.
- The bursa is a small sac of fluid that cushions and protects the tendons of the rotator cuff.
- A cuff of cartilage called the labrum forms a cup for the ball-like head of the humerus to fit into.
The humerus fits relatively loosely into the shoulder joint. This gives the shoulder a wide range of motion, but also makes it vulnerable to injury.
Shoulder Conditions
- Frozen shoulder: Inflammation develops in the shoulder that causes pain and stiffness. As a frozen shoulder progresses, movement in the shoulder can be severely limited.
- Osteoarthritis: The common "wear-and-tear" arthritis that occurs with aging. The shoulder is less often affected by osteoarthritis than the knee.
- Rheumatoid arthritis: A form of arthritis in which the immune system attacks the joints, causing inflammation and pain. Rheumatoid arthritis can affect any joint, including the shoulder.
- Gout: A form of arthritis in which crystals form in the joints, causing inflammation and pain. The shoulder is an uncommon location for gout.
- Rotator cuff tear: A tear in one of the muscles or tendons surrounding the top of the humerus. A rotator cuff tear may be a sudden injury, or result from steady overuse.
- Shoulder impingement: The acromion (edge of the scapula) presses on the rotator cuff as the arm is lifted. If inflammation or an injury in the rotator cuff is present, this impingement causes pain.
- Shoulder dislocation: The humerus or one of the other bones in the shoulder slips out of position. Raising the arm causes pain and a "popping" sensation if the shoulder is dislocated.
- Shoulder tendonitis: Inflammation of one of the tendons in the shoulder's rotator cuff.
- Shoulder bursitis: Inflammation of the bursa, the small sac of fluid that rests over the rotator cuff tendons. Pain with overhead activities or pressure on the upper, outer arm are symptoms.
- Labral tear: An accident or overuse can cause a tear in the labrum, the cuff of cartilage that overlies the head of the humerus. Most labral tears heal without requiring surgery.
Shoulder Tests
- Magnetic resonance imaging (MRI scan): An MRI scanner uses a high-powered magnet and a computer to create high-resolution images of the shoulder and surrounding structures.
- Computed tomography (CT scan): A CT scanner takes multiple X-rays, and a computer creates detailed images of the shoulder.
- Shoulder X-ray: A plain X-ray film of the shoulder may show dislocation, osteoarthritis or a fracture of the humerus. X-ray films cannot diagnose muscle or tendon injuries.
Shoulder Treatments
- Shoulder surgery: Surgery is generally performed to help make the shoulder joint more stable. Shoulder surgery may be arthroscopic (several small incisions) or open (large incision).
- Arthroscopic surgery: A surgeon makes small incisions in the shoulder and performs surgery through an endoscope (a flexible tube with a camera and tools on its end). Arthroscopic surgery requires less recovery time than open surgery.
- Physical therapy: An exercise program can strengthen shoulder muscles and improve flexibility in the shoulder. Physical therapy is an effective, nonsurgical treatment for many shoulder conditions.
- Pain relievers: Over-the-counter relievers like acetaminophen (Tylenol), ibuprofen (Motrin) and naproxen (Aleve) can relieve most shoulder pain. More severe shoulder pain may require prescription medications.
- RICE therapy: RICE stands for Rest, Ice, Compression (not usually necessary), and Elevation. RICE can improve pain and swelling of many shoulder injuries.
- Corticosteroid (cortisone) injection: A doctor injects cortisone into the shoulder, reducing the inflammation and pain caused by bursitis or arthritis. The effects of a cortisone injection can last several weeks.
How Does Blood Flow Through the Heart?
The right and left sides of the heart work together. The pattern described below is repeated over and over, causing blood to flow continuously to the heart, lungs, and body.
Right side
- Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium.
- As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.
- When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.
- As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.
Left side
- The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium.
- As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
- When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
- As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.
How Does Blood Flow Through Your Lungs?
Once blood travels through the pulmonic valve, it enters your lungs. This is called the pulmonary circulation. From your pulmonic valve, blood travels to the pulmonary artery to tiny capillary vessels in the lungs.
Here, oxygen travels from the tiny air sacs in the lungs, through the walls of the capillaries, into the blood. At the same time, carbon dioxide, a waste product of metabolism, passes from the blood into the air sacs. Carbon dioxide leaves the body when you exhale. Once the blood is purified and oxygenated, it travels back to the left atrium through the pulmonary veins.
What Are the Coronary Arteries?
Like all organs, your heart is made of tissue that requires a supply of oxygen and nutrients. Although its chambers are full of blood, the heart receives no nourishment from this blood. The heart receives its own supply of blood from a network of arteries, called the coronary arteries.
Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet:
- Right coronary artery supplies the right atrium and right ventricle with blood. It usually branches into the posterior descending artery, which supplies the bottom portion of the left ventricle and back of the septum with blood.
- Left main coronary artery branches into the circumflex artery and the left anterior descending artery. The circumflex artery supplies blood to the left atrium, side, and back of the left ventricle, and the left anterior descending artery supplies the front and bottom of the left ventricle and the front of the septum with blood.
These arteries and their branches supply all parts of the heart muscle with blood.
When the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), a network of tiny blood vessels in the heart that aren't usually open called collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to the heart muscle, protecting the heart tissue from injury.
How Does the Heart Beat?
The atria and ventricles work together, alternately contracting and relaxing to make the heart beat and pump blood. The electrical system of your heart is the power source that makes this possible.
Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart.
- The impulse starts in a small bundle of specialized cells called the SA node (sinoatrial node), located in the right atrium. This node is known as the heart's natural pacemaker. The electrical activity spreads through the walls of the atria and causes them to contract.
- A cluster of cells in the center of the heart between the atria and ventricles, the AV node (atrioventricular node) is like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do.
- The His-Purkinje network is a pathway of fibers that sends the impulse to the muscular walls of the ventricles, causing them to contract.
At rest, a normal heart beats around 50 to 99 times a minute. Exercise, emotions, fever, and some medications can cause your heart to beat faster, sometimes to well over 100 beats per minute.
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