Blood Disorders

before you start

As you have learned, blood is a complex, fluid connective tissue that is essential to proper functioning of the human body. There are numerous disorders associated with blood. In this lesson, you will learn about some of the more commonly recognized disorders associated with components of the blood and bloodstream.

1. Erythrocyte Disorders

The size, shape, and number of erythrocytes (red blood cells, RBCs) and the number of hemoglobin molecules can have a major impact on a person’s health. When the blood is unable to transport enough oxygen to the body because RBC numbers are low or hemoglobin is deficient, the general condition is called anemia.

The effects of the various anemias are widespread because reduced numbers of RBCs or hemoglobin will result in lower levels of oxygen being delivered to body tissues. Because oxygen is required for tissue functioning, anemia produces fatigue, lethargy, and an increased risk of infection. An oxygen deficit in the brain impairs the ability to think clearly and may prompt headaches and irritability. Furthermore, lack of oxygen leaves the patient short of breath, even as the heart and lungs work harder in response to the deficit.

There are more than 400 types of anemia, and more than 3.5 million Americans suffer from this condition. Blood loss anemias (hemorrhagic anemias) are fairly straightforward. In addition to bleeding from wounds or other lesions, these forms of anemia may be due to ulcers, hemorrhoids, inflammation of the stomach (gastritis), and some cancers of the gastrointestinal tract. The excessive use of aspirin or other nonsteroidal anti-inflammatory drugs such as ibuprofen can trigger ulceration and gastritis. Excessive menstruation and loss of blood during childbirth are also potential causes.

Anemias caused by faulty RBC production or removal include sickle cell anemia, iron deficiency anemia, vitamin deficiency anemia, and diseases of the bone marrow and stem cells.

• A characteristic change in the shape of RBCs is seen in sickle cell disease (also referred to as sickle cell anemia). A genetic disorder, it is caused by the production of an abnormal type of hemoglobin that delivers less oxygen to tissues and causes RBCs to assume a sickle (or crescent) shape, especially at low oxygen concentrations. These abnormally shaped cells can then become lodged in narrow capillaries because they are unable to fold in on themselves to squeeze through, blocking blood flow to tissues and causing a variety of serious problems from painful joints to delayed growth and even blindness and cerebrovascular accidents (strokes). Sickle cell anemia is a genetic condition particularly found in individuals of African descent due to its benefit as protective against malaria, a mosquito-borne infectious disease prominent in tropical and subtropical regions.

• Iron deficiency anemia is the most common type of anemia and results when the amount of available iron is insufficient to allow production of sufficient heme. This condition is especially common in teens and children (increased iron need), vegans and vegetarians (decreased iron intake), and menstrual females (increased iron loss).
• Vitamin deficiency anemias generally involve insufficient vitamin B₁₂ and folate.
  • Megaloblastic anemia involves a deficiency of vitamin B₁₂ and/or folate and often involves diets deficient in these essential nutrients. Lack of meat or a viable alternate source, and overcooking or eating insufficient amounts of vegetables may lead to a lack of folate.
  • Pernicious anemia is caused by poor absorption of vitamin B₁₂ and is often seen in patients with Crohn’s disease (a severe intestinal disorder often treated by surgery), surgical removal of the intestines or stomach (common in some weight loss surgeries), intestinal parasites, and AIDS.
  • Pregnancies, some medications, excessive alcohol consumption, and some diseases such as celiac disease are also associated with vitamin deficiencies. It is essential to provide sufficient folic acid during the early stages of pregnancy to reduce the risk of neurological defects, including spina bifida, a failure of the neural tube to close.
• Assorted disease processes can also interfere with the balance of RBC production and removal.
  • Hemolytic anemia is a general condition for when RBC removal is faster than production. This can be caused by a number of conditions either slowing down production, increasing removal, or both.
  • Aplastic anemia is the condition in which there are deficient numbers of RBC stem cells. Aplastic anemia is often inherited, or it may be triggered by radiation, medication, chemotherapy, or infection.
  • Thalassemia is an inherited condition typically occurring in individuals from the Middle East, the Mediterranean, Africa, and Southeast Asia, in which maturation of the RBCs does not proceed normally. The most severe form is called Cooley’s anemia.
  • Lead exposure from industrial sources or even dust from paint chips of iron-containing paints or pottery that has not been properly glazed may also lead to destruction of the red marrow.
• Various disease processes also can lead to anemias. These include chronic kidney diseases often associated with a decreased production of erythropoietin (EPO), hypothyroidism, some forms of cancer, lupus, and rheumatoid arthritis.

A mild form of polycythemia is chronic but normal in people living at high altitudes. Some elite athletes train at high elevations specifically to induce this phenomenon. The primary concern with polycythemia is not with oxygen delivery to the tissues, but rather the increased viscosity of the blood, increasing blood pressure and making it more difficult for the heart to circulate the blood.

terms to know

Anemia

Deficiency of oxygen transport due to a deficiency of erythrocytes or hemoglobin.

Sickle Cell Disease

An inherited form of anemia in which hemoglobin is malformed, leading to the erythrocyte having a sickle shape.

Iron Deficiency Anemia

A form of anemia caused by a lack of iron.

Hemolytic Anemia

A form of anemia caused by a greater rate of erythrocyte destruction compared to production.

Polycythemia

A blood disorder characteristic of increased numbers of erythrocytes.

2. Platelet and Clotting Disorders

Thrombocytosis is a condition in which there are too many platelets. This may trigger formation of unwanted blood clots (thrombosis), a potentially fatal disorder. If there is an insufficient number of platelets, called thrombocytopenia, blood may not clot properly, and excessive bleeding may result.

Either an insufficient or an excessive production of platelets can lead to severe disease or death. As discussed earlier, an insufficient number of platelets, called thrombocytopenia, typically results in the inability of blood to form clots. This can lead to excessive bleeding, even from minor wounds.

Another reason for failure of the blood to clot is the inadequate production of functional amounts of one or more clotting factors. This is the case in the genetic disorder hemophilia, which is actually a group of related disorders, the most common of which is hemophilia A, accounting for approximately 80% of cases.

key concept

Hemophilia A results in the inability to synthesize sufficient quantities of factor VIII. Hemophilia B is the second most common form, accounting for approximately 20% of cases, and is a deficiency of factor IX. Patients with hemophilia bleed from even minor internal and external wounds, and leak blood into joint spaces after exercise and into urine and stool.

Both of these defects are linked to the X chromosome and are typically passed from a healthy (carrier) female to their male offspring since males only have one X chromosome (XY). Females would need to inherit a defective gene from each parent to manifest the disease since they have two X chromosomes (XX).

Hemophilia C is a rare condition that is triggered by an autosomal (not sex) chromosome that renders factor XI nonfunctional. It is not a true recessive condition because even individuals with a single copy of the mutant gene show a tendency to bleed.

Regular infusions of clotting factors isolated from healthy donors can help prevent bleeding in hemophiliac patients. At some point, genetic therapy, in which a patient's defective gene is replaced by a functioning gene, will become a viable option.

In contrast to the disorders characterized by coagulation failure is thrombocytosis, also mentioned earlier, a condition characterized by excessive numbers of platelets that increases the risk for excessive clot formation, known as thrombosis. A thrombus (plural, thrombi) is an aggregation of platelets, erythrocytes, and even WBCs typically trapped within a mass of fibrin strands.

While the formation of a clot is normal following blood vessel damage, thrombi can form within an intact or only slightly damaged blood vessel. In a large vessel, a thrombus will adhere to the vessel wall and decrease the flow of blood and is referred to as a mural thrombus. In a small vessel, it may completely block the flow of blood and is termed an occlusive thrombus.

Thrombi are most commonly caused by vessel damage to the endothelial lining, which activates the clotting mechanism. These may include venous stasis, when blood in the veins, particularly in the legs, remains stationary for long periods.

did you know

This is one of the dangers of long airplane flights in crowded conditions and may lead to deep vein thrombosis.

Thrombophilia, also called hypercoagulation, is a condition in which there is a tendency to form a thrombus. This may be familial (genetic) or acquired. Acquired forms include the autoimmune disease lupus, immune reactions to heparin, polycythemia vera, thrombocytosis, sickle cell disease, pregnancy, and even obesity. A thrombus can seriously impede blood flow to or from a region and will cause a local increase in blood pressure. If flow is to be maintained, the heart will need to generate greater pressure to overcome the resistance.

When a portion of a thrombus breaks free from the vessel wall and enters the circulation, it is referred to as an embolus. An embolus that is carried through the bloodstream can be large enough to block a vessel critical to a major organ. When it becomes trapped, an embolus is called an embolism. In the heart, brain, or lungs, an embolism may accordingly cause a heart attack, a stroke, or a pulmonary embolism. These are medical emergencies.

Among the many known biochemical activities of aspirin is its role as an anticoagulant. Aspirin (acetylsalicylic acid) is very effective at inhibiting the aggregation of platelets.

EXAMPLE

Aspirin is routinely administered during a heart attack or stroke to reduce the adverse effects. Physicians sometimes recommend that patients at risk for cardiovascular disease take a low dose of aspirin on a daily basis as a preventive measure. However, aspirin can also lead to serious side effects, including increasing the risk of ulcers. A patient should consult a physician before beginning any aspirin regimen.

A class of drugs collectively known as thrombolytic agents can help speed up the degradation of an abnormal clot. If a thrombolytic agent is administered to a patient within 3 hours following a thrombotic stroke, the patient’s prognosis significantly improves.

However, some strokes are not caused by thrombi, but by hemorrhage. Thus, the cause must be determined before treatment begins. Tissue plasminogen activator is an enzyme that catalyzes the conversion of plasminogen to plasmin, the primary enzyme that breaks down clots. It is released naturally by endothelial cells but is also used in clinical medicine. New research is progressing using compounds isolated from the venom of some species of snakes, particularly vipers and cobras, which may eventually have therapeutic value as thrombolytic agents.

terms to know

Thrombocytosis

A condition in which too many platelets are produced.

Thrombocytopenia

A condition in which too few platelets are produced.

Hemophilia

A genetic disorder characterized by the inadequate synthesis of clotting factors.

Thrombosis

A condition with an elevated risk of excessive blood clot formation.

Thrombus

An aggregation of formed elements in a fibrin net within an intact blood vessel.

Embolus

A freely circulating thrombus in the blood.

Embolism

When an embolus becomes trapped in a blood vessel.

3. Leukocyte Disorders

Leukopenia is a condition in which too few leukocytes are produced. If this condition is pronounced, the individual may be unable to ward off disease. Excessive leukocyte proliferation is known as leukocytosis. Although leukocyte counts are high, the cells themselves are often nonfunctional, leaving the individual at increased risk for disease.

As you learned in a previous lesson, leukemia is a cancer involving an abundance of leukocytes. It may involve only one specific type of leukocyte from either the myeloid line (myeloid leukemia) or the lymphoid line (lymphocytic leukemia). In chronic leukemia, mature leukocytes accumulate and fail to die. In acute leukemia, there is an overproduction of young, immature leukocytes. In both conditions, the cells do not function properly.

Lymphoma is a form of cancer in which masses of malignant (referring to the presence of cancerous cells) T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues. As in leukemia, the malignant leukocytes do not function properly, and the patient is vulnerable to infection. Some forms of lymphoma tend to progress slowly and respond well to treatment. Others tend to progress quickly and require aggressive treatment, without which they are rapidly fatal.

terms to know

Leukopenia

A condition in which too few leukocytes are produced.

Leukocytosis

A condition in which too many leukocytes are produced.

Leukemia

A cancer involving an over-proliferation of leukocytes.

Lymphoma

A cancer in which malignant T and B lymphocytes collect in peripheral lymphatic tissues (lymph nodes, spleen, liver).

4. Bloodstream Disorders

Toxemia is the spreading of toxins in the bloodstream and is also sometimes known as blood poisoning. In this disorder, metabolic wastes are not properly removed. Different organs and structures in your body usually take care of metabolic waste and dispose of it properly, but when this does not happen, that metabolic waste will build up in your blood.

This can lead to:

• Anemia
• Improper clotting
• Possibly death

EXAMPLE

A staph infection is a type of bacterial infection caused by the bacteria Staphylococcus aureus. MRSA (methicillin-resistant Staphylococcus aureus) is a type of staph infection that is resistant to many antibiotics and is prevalent in hospitals and other healthcare settings.

terms to know

Toxemia

A general term to describe blood poisoning.

Septicemia

When organisms, such as bacteria, get into the circulating blood and cause a system-wide infection.

SOURCE: THIS TUTORIAL HAS BEEN ADAPTED FROM OPENSTAX “ANATOMY AND PHYSIOLOGY 2E”. ACCESS FOR FREE AT OPENSTAX.ORG/BOOKS/ANATOMY-AND-PHYSIOLOGY-2E/PAGES/1-INTRODUCTION. LICENSE: CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL.