HESI^® A2 Reading Comprehension Practice Test

There are a number of health problems related to bleeding in the esophagus and stomach. Stomach acid can cause inflammation and bleeding at the lower end of the esophagus. This condition, usually associated with the symptom of heartburn, is called esophagitis, or inflammation of the esophagus. Sometimes a muscle between the esophagus and stomach fails to close properly and allows the return of food and stomach juices into the esophagus, which can lead to esophagitis. In another unrelated condition, enlarged veins (varices) at the lower end of the esophagus rupture and bleed massively. Cirrhosis of the liver is the most common cause of esophageal varices. Esophageal bleeding can be caused by a tear in the lining of the esophagus (Mallory-Weiss syndrome). Mallory-Weiss syndrome usually results from vomiting, but may also be caused by increased pressure in the abdomen from coughing, hiatal hernia, or childbirth. Esophageal cancer can cause bleeding.

The stomach is a frequent site of bleeding. Infections with Helicobacter pylori (H. pylori), alcohol, aspirin, aspirin-containing medicines, and various other medicines (such as nonsteroidal anti-inflammatory drugs [NSAIDs]—particularly those used for arthritis) can cause stomach ulcers or inflammation (gastritis). The stomach is often the site of ulcer disease. Acute or chronic ulcers may enlarge and erode a blood vessel, causing bleeding. Also, patients suffering from burns, shock, head injuries, cancer, or those who have undergone extensive surgery may develop stress ulcers. Bleeding can also occur from benign tumors or cancer of the stomach, although these disorders usually do not cause massive bleeding.

Usher syndrome is the most common condition that affects both hearing and vision. The major signs of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. Retinitis pigmentosa causes night blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. The retina, which is crucial for vision, is a light-sensitive tissue at the back of the eye. As RP progresses, the field of vision narrows, until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems.

The immune system is a network of cells, tissues, and organs that defends the body against attacks by foreign invaders. These invaders are primarily microbes—tiny organisms such as bacteria, parasites, and fungi—that can cause infections. Viruses also cause infections, but are too primitive to be classified as living organisms. The human body provides an ideal environment for many microbes. It is the immune system’s job to keep the microbes out or destroy them.

The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can secrete fluids and cells to wipe out nearly all of them. The secret to its success is an elaborate and dynamic communications network. Millions of cells, organized into sets and subsets, gather and transfer information in response to an infection. Once immune cells receive the alarm, they produce powerful chemicals that help to regulate their own growth and behavior, enlist other immune cells, and direct the new recruits to trouble spots.

Although scientists have learned much about the immune system, they continue to puzzle over how the body destroys invading microbes, infected cells, and tumors without harming healthy tissues. New technologies for identifying individual immune cells are now allowing scientists to determine quickly which targets are triggering an immune response. Improvements in microscopy are permitting the first-ever observations of living B cells, T cells, and other cells as they interact within lymph nodes and other body tissues.

In addition, scientists are rapidly unraveling the genetic blueprints that direct the human immune response, as well as those that dictate the biology of bacteria, viruses, and parasites. The combination of new technology with expanded genetic information will no doubt reveal even more about how the body protects itself from disease.