Pulmonary, Bronchial, and Systemic Circulation and the Blood

Pulmonary, Bronchial, and Systemic Circulation

  • Pulmonary circulation:
    • Begins in the right ventricle.
    • Transports deoxygenated blood from the right ventricle via the pulmonary artery to smaller branching arteries known as the pulmonary arterioles.
    • These arteries branch into capillaries that cover the alveoli, where respiration occurs.
  • Bronchial circulation:
    • Supplies blood to the lung tissue itself.
    • Arteries originate from the aorta and carry oxygenated blood.
    • Blood travels along the tracheobronchial tree to the level of the terminal bronchioles.
  • Systemic circulation:
    • Carries oxygenated blood throughout the body.
    • Collects deoxygenated blood.
    • Returns blood to the right atria of the heart.
  • Arteries vs. Veins:
    • Systemic circulation:
      • Arteries carry oxygenated blood away from the heart.
      • Veins carry deoxygenated blood to the heart.
    • Pulmonary circulation:
      • Arteries carry deoxygenated blood from the heart to the lungs.
      • Veins carry oxygenated blood from the lungs to the heart.

Normal Cardiopulmonary Values

  • Measurement:
    • Pressure and flow of blood provide insight into various disease processes.
    • Echocardiogram.
    • Right heart catheterization.

Echocardiography

  • Noninvasive imaging procedure using ultrasound waves (4 to 7 MHz).
  • Also referred to as ultrasounds or ultrasonography.
  • Can be used as a stand-alone procedure or in combination with other techniques.
  • Types:
    • Intracardiac echocardiography (ICE):
      • Uses catheters to insert a probe inside the heart.
      • Enables a view of the heart structures from within the heart.
    • Intravascular ultrasound (IVUS):
      • Uses a catheter to insert the probe inside the cardiac blood vessels.
      • Assesses the internal diameter of the blood vessels and their patency.
    • Contrast echocardiography:
      • Also called contrast-enhanced ultrasound.
      • Uses a contrast medium (imaging agent) along with traditional echocardiography.
      • Tracks the movement of the contrast medium through the heart and vasculature.
  • Basic "modes”:
    • Two-dimensional (2D) imaging:
      • Provides a view of structures in real-time.
      • Used for detecting abnormal anatomy or the motion of the heart structures.
    • M-mode echocardiography:
      • Provides a one-dimensional image.
      • Used for fine measurements and assessment of the functioning of the heart valves.
      • Often combined with other imaging modalities, such as Doppler imaging.
    • Doppler echocardiography:
      • Subtypes: continuous-wave (CW), pulsed-wave (PW), and color-flow mapping (CFM).
      • Compares the frequency change between transmitted and reflected sound waves to estimate the velocity of blood flow through the heart and pulmonary system.
    • Four-dimensional (4D) echocardiography:
      • Detailed anatomic assessment of cardiac pathology, particularly valvular defects.
      • Provides a real-time moving image of the heart.

Right Heart Catheterization

  • Invasive procedure performed in a catheterization laboratory (cath lab).
  • A pulmonary artery (PA) catheter is inserted into a vein (groin or neck) and threaded through the right atrium and right ventricle into the pulmonary artery.
  • Measurements:
    • Pressures.
    • Blood flow.
  • Cardiac output:
    • The amount of blood the heart pumps through the circulatory system in 1 minute.
    • Normal range: 4 to 8 L/min.
    • Formula: CO = SV \times HR where SV is stroke volume, and HR is heart rate.
  • Cardiac index:
    • Measure of a person’s cardiac output in relation to their size.
    • Normal range: 2.8 to 4.2 liters per minute per square meter of body surface area.
  • Right atrial pressure:
    • Normal range: 0 to 7 mm Hg.
  • Pulmonary artery systolic pressure:
    • Normal range: 17 to 32 mm Hg.
  • Pulmonary artery mean pressure:
    • Normal range: 9 to 19 mm Hg.
  • Pulmonary diastolic pressure:
    • Normal range: 4 to 13 mm Hg.
  • Pulmonary capillary wedge pressure:
    • Normal range: 4 to 12 mm Hg.

Abnormalities of the Pulmonary Circulation

  • Venous Thromboembolism (VTE):
    • Blood clot in the venous system.
    • Often begins as deep vein thrombosis (DVT) in the legs.
    • Pulmonary Embolism (PE):
      • A portion of the clot breaks off and travels to the lungs.
      • Can stop blood flow, preventing oxygen pickup.
      • Can cause localized death of the tissue (necrosis).
      • It can obstruct the blood supply to an area of the lungs, causing localized death of the tissue. the obstruction of blood flow is called an infarction, the death of the tissue is called necrosis.

Pulmonary Hypertension (PH)

  • Progressive diseases characterized by:
    • Pulmonary vascular resistance.
    • Remodeling and occlusion of the pulmonary arterioles.
    • Right heart ventricular dysfunction.
    • Right heart failure.
  • Five groups based on etiologies:
    • Pre- or postcapillary determination influences appropriate therapeutic management.
  • Group 1: Pulmonary Arterial Hypertension (PAH):
    • Precapillary.
    • Associated with narrowing of small blood vessels in the lungs.
    • Subgroups:
      • Idiopathic PAH: Unknown origin.
      • Heritable PAH: Genetic causes.
      • Drug- and toxin-induced PAH: Exposure to medications/toxins (e.g., amphetamines, methamphetamines, cocaine, fenfluramine-phentermine).
      • PAH associated with systemic diseases: Connective tissue diseases (e.g., scleroderma, lupus, rheumatoid arthritis), HIV, portal hypertension, congenital heart disease.
      • PAH and long-term responders to calcium channel blockers: Vasodilators used successfully in some PAH patients for at least 1 year.
      • Pulmonary veno-occlusive disease (PVOD) and pulmonary capillary hemangiomatosis (PCH):
        • PVOD: Constriction/occlusion of pulmonary veins and venules.
        • PCH: Alveolar capillary proliferation (rare).
        • Etiology unknown.
      • Persistent pulmonary hypertension of the newborn (PPHN):
        • Occurs when fetal circulation fails to transition to normal circulation at and after birth.
  • Group 2: Pulmonary Hypertension Related to Left Heart Disease:
    • Pre- and postcapillary.
    • Caused by changes in the pulmonary vasculature over time due to conditions affecting the left side of the heart.
    • Subgroups:
      • PH due to left-sided heart failure with preserved ejection fraction (HFpEF): Left ventricle becomes stiff and cannot adequately fill, resulting in pressure back into the lungs.
      • PH due to heart failure with reduced ejection fraction (HFrEF): Left ventricle unable to function correctly and does not pump enough blood to the body.
      • Valvular heart disease: Narrowing or leaky left heart valves.
      • Congenital/acquired cardiovascular conditions leading to postcapillary PH: Obstruction of blood flow into or out of the left heart.
  • Group 3: Pulmonary Hypertension due to Lung Disease and/or Chronic Hypoxia:
    • Precapillary.
    • Develops because of lung diseases such as:
      • Obstructive lung diseases.
      • Restrictive lung disease.
      • Diseases with a mixed restrictive/obstructive pattern.
      • Chronic hypoxia without lung disease.
      • Developmental lung disorders.
  • Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH):
    • Precapillary.
    • Caused by blood clots that obstruct the flow of blood through the pulmonary arteries.
    • Requires a pulmonary angiogram for diagnosis (unlike other forms diagnosed via right heart catheterization).
  • Group 5: PH of Unclear or Multifactorial Mechanisms:
    • Both precapillary and postcapillary.
    • Etiologies associated with a disease state, but mechanisms not clearly understood.
    • Secondary to hematologic disorders, systemic disorders, metabolic disorders, or congenital conditions.

Diagnosis of PH

  • Right heart catheterization:
    • Used to measure pressures in the heart and pulmonary artery.
    • Mean pulmonary artery pressure (MAP) \ge 25 mm Hg at rest is considered diagnostic for PH.
  • Elevations in MAP may be caused by:
    • Variations in cardiac output (CO).
    • Left-to-right cardiac shunts.
    • Pulmonary vascular disease (PVD) associated with structural changes of small pulmonary arterioles.
  • Pulmonary capillary wedge pressure (PCWP) and pulmonary vascular resistance (PVR) measurements:
    • Determine if PH is a result of pre- or postcapillary changes.
    • Used to further define the pathophysiology and guide treatment.
  • Precapillary PH:
    • Suggestive of PVD.
    • Most often found in groups 1, 3, 4, and some group 5 patients.
  • Postcapillary PH:
    • Affects group 2 and some group 5 patients.
  • Hemodynamic definitions:
    • Defined using measurements from right heart catheterization to differentiate pre- and post-capillary PH.

Blood

  • Fluid that circulates through arteries and veins.
  • Carries oxygen from the lungs to the tissue.
  • Collects carbon dioxide and transports it to the lungs for removal.
  • Volume:
    • Approximately 7% of an individual’s total body weight.
    • Average healthy adult (150-180 pounds): approximately 1.2 to 1.5 gallons (4.5 to 5.6 L).
    • Average woman: approximately 1 to 1.3 gallons (3.8 to 4.9 L).
    • Average man: approximately 1.3 to 1.5 gallons (4.9 to 5.7 L).

Bone Marrow

  • Semisolid tissue that fills the cavities of the bones.
  • Types:
    • Red bone marrow:
      • Hematopoietic tissue.
      • Contains hematopoietic stem cells (HSCs) that give rise to blood cells (erythrocytes, platelets, leukocytes).
      • Blood cell development is known as hematopoiesis.
      • Found primarily in flat bones (hip, breast, skull, ribs, vertebrae, shoulder blades) and cancellous material at the ends of long bones (femur, humerus).
    • Yellow bone marrow:
      • Fatty tissue.
      • Contains mesenchymal stem cells (marrow stromal cells).
      • Produces fat, cartilage, and bone cells.

Blood Components

  • Red blood cells (erythrocytes).
  • White blood cells (leukocytes).
  • Platelets (thrombocytes).
  • Plasma:
    • Liquid component.
    • Approximately 55% of the blood volume.
    • Straw-colored.
    • Contains water, salts, enzymes, antibodies, and other proteins, in addition to the blood cells.

Erythrocytes

  • Biconcave disks without a nucleus.
  • Shape allows them to easily change and squeeze into small capillaries.
  • Increases surface area for oxygen uptake and gas release.
  • Primary function: transport oxygen and carbon dioxide.
  • Originate in the hematopoietic stem cells in the red bone marrow.
  • Development controlled by the renal hormone erythropoietin.
  • Average lifespan: approximately 120 days.

Hemoglobin

  • Protein within the erythrocyte (Hgb or Hb).
  • Enables erythrocytes to carry oxygen from the lungs to the rest of the body and then return carbon dioxide to the lungs.
  • Made up of four protein molecules (globulin chains), each containing an iron atom bound to a heme group.
  • Healthy adults: two alpha-globulin chains and two beta-globulin chains.
  • Fetuses: fetal hemoglobin (HbF) molecules are composed of two alpha chains and two gamma chains. the gamma chains are gradually replaced by beta chains, forming the adult hemoglobin structure of two alpha and two beta chains.
  • Gives blood its red color.
  • Normal hemoglobin levels:
    • Males: 14 to 18 g/dL.
    • Females: 12 to 16 g/dL.

Measuring Erythrocytes

  • Mean corpuscular volume (MCV):
    • Average size of erythrocytes.
    • Smaller than usual may indicate iron deficiency anemia.
    • Larger than normal may indicate vitamin B12 deficiency, folic acid deficiency, liver disease, or hypothyroidism.
  • Mean corpuscular hemoglobin (MCH):
    • Amount of hemoglobin per erythrocyte.
  • Mean corpuscular hemoglobin concentration (MCHC):
    • Average concentration of hemoglobin in a given volume of red blood cells.
  • Red cell distribution width (RDW):
    • Variation in the volume and size of the erythrocytes.
    • Variation in the size of erythrocytes may suggest disorders such as anemia.
  • Hematocrit (HCT), also known as the packed-cell volume (PCV):
    • Measures the number of red blood cells compared to total blood volume.
    • Normal hematocrit values:
      • Males: 40–54%.
      • Females: 36–48%.
  • Hemoglobin and hematocrit values are based on whole blood volume and are dependent on plasma levels.
    • Lower than normal plasma levels will appear higher than if the plasma levels were normal.
    • Higher than normal plasma levels will appear lower or diluted.
  • Independent radionuclide evaluation of the red cells and plasma: used to evaluate both plasma levels and the accuracy of the hemoglobin and the hematocrit measurements.

Blood Types

  • Determined by the presence or absence of antigens on the erythrocytes and antibodies in the plasma.
  • Four common blood types/groups:
    • Group A: A antigens on erythrocytes, B antibodies in the plasma.
    • Group B: B antigens on the erythrocytes, A antibodies in the plasma.
    • Group AB: Both A and B antigens on the erythrocytes, no A or B antibodies in the plasma.
    • Group O: No A or B antigens on the erythrocytes, both A and B antibodies in the plasma.
  • Rh factor:
    • Protein on the blood, if the Rh protein is present, the blood is Rh positive (+). if the protein is absent, the blood is said to be Rh negative (−).
    • Most common blood types:
      • A+, A−, B+, B−, AB+, AB−, O+, and O−.
  • Erythroblastosis fetalis:
    • Condition that occurs when a developing fetus has an incompatibility with the mother’s blood type. The incompatibility may be related to different blood types, wherein the fetus may have one type (AB or O) and the mother has another (AB or O), or it may be related to having differing Rh factors.
  • Rh isoimmunization:
    • Develops when fetal blood cells containing a D antigen (Rh+), which the mother lacks (Rh−), crosses the placenta into the maternal circulation.
    • The Rh+ fetal blood stimulates the production of maternal antibodies that then cross back into the fetal circulation and destroy the fetal red blood cells.
    • Infants born with this condition may present with a range of symptoms, from mild jaundice and anemia, to more serious cardiac and liver complications.

Leukocytes

  • Approximately 1% of blood volume.
  • Principally involved in the immune response.
  • Larger than erythrocytes and have a nucleus and organelles.
  • Leave the bloodstream to fight infections in the body’s tissues (leukocyte extravasation).
  • Undergo several steps to leave the circulatory system and attack an infection:
    • Margination, in which it the leukocytes move closer to and collect at the blood vessel wall.
    • Rolling, where the leukocytes move or “roll” along the vessel wall.
    • Adhesion to the endothelium of the vessel wall.
    • Passage through the vessel wall.
    • Migration to the damaged or infected tissue.
  • Take on an amoeba-like movement toward the infected area.
  • Grouped based on the presence of granules in their cytoplasm and their staining properties:
    • Granulocytes (neutrophils, eosinophils, and basophils).
    • Monocytes.
    • Lymphocytes (natural killer cells, T cells and B cells).
  • Granulocytes:
    • Originate from the hematopoietic stem cells of the red bone marrow.
    • Short life span of hours to days.
    • Multilobed nucleus.
    • Also called polymorphonuclear leukocytes.
  • Neutrophils:
    • Most common granulocytes.
    • Appear lilac in color and have a nucleus that has two to five lobes when treated with a chemically neutral stain .
    • 10 to 12 μm in diameter.
    • First responders of the immune system.
    • Capable of phagocytosis.
    • Approximately 65% of the overall leukocyte count.
    • High levels (neutrophilia) suggest an acute infection, stress, eclampsia, gout, myelocytic leukemia, rheumatoid arthritis, rheumatic fever, thyroiditis, or trauma.
    • Low levels (neutropenia) may be related to aplastic anemia, chemotherapy, radiation therapy or exposure to radiation, influenza, viral infection, or severe bacterial infection.
  • Eosinophils:
    • Appear red to orange in color when an acidic stain called eosin is used during laboratory examination.
    • Characteristically have a nucleus with two to three lobes.
    • 10 to 12 μm in diameter.
    • Utilize phagocytosis to remove infectious agents from the body.
    • Granules include antihistamine molecules that play a role in the inflammatory process.
    • Approximately 2–5% of the overall leukocyte count.
    • High level (eosinophilia) may indicate Addison disease, allergies, cancer, chronic myelogenous leukemia, collagen vascular disease, hypereosinophilic syndromes, or a parasitic infection.
    • Low level (eosinopenia) may be related to drug toxicity, alcohol abuse, and/or stress.
  • Basophils:
    • 8 to 10 μm in diameter and appear dark blue to purple during laboratory examination
    • Have a two-lobed nucleus that is visible when an alkaline (basic) stain is used.
    • Play a role in the inflammatory process by releasing histamines and in the blood-clotting process by releasing heparin.
    • Approximately 1% or less of the overall leukocyte count.
    • High levels (basophilia) is associated with postoperative splenectomy, allergies, chronic myelogenous leukemia, collagen vascular disease, myeloproliferative diseases, and infections such as chickenpox.
    • Low levels (basopenia) may be associated with acute infections, cancer, and trauma.
  • Monocytes:
    • Originate from myeloid progenitor cells in the red bone marrow.
    • Largest white blood cell (12 to 20 μm in size) and have an indented or horseshoe-shaped nucleus.
    • Will appear as larger cells with a bean-shaped nucleus when using a modified Wright-Giemsa stain.
    • Leave the circulatory system to ingest pathogens and dead cells are known as macrophages.
    • Macrophages may release antimicrobial and chemotactic chemicals that attract other leukocytes to the area to assist in fighting the infection.
    • Approximately 4–8% of the overall leukocyte count.
    • High levels of monocytes in the blood are associated with chronic inflammatory diseases, leukemia, parasitic infection, tuberculosis, or viral infections.
  • Lymphocytes:
    • Originate from lymphoid progenitor cells in the red bone marrow and are therefore referred to as being of the lymphoid lineage.
    • Travel from the bone marrow to the lymph nodes, spleen, and thymus to mature.
    • Range in size from 6 to 17 μm.
    • Three main types:
      • Natural killer (NK) cells: Provides generalized, nonspecific immunity and can kill some tumor cells or cells infected with a virus.
      • T cells: After leaving the bone marrow, they mature in the thymus. The two primary types of T cells are helper T cells and cytotoxic T cells. Both play a role in fighting infections.
      • B cells: Secrete antibodies when an infection or foreign antigen is detected in the body. There are several different types of B cells, and they have varying life spans and functions in the immune response.

Platelets

  • Also known as thrombocytes.
  • Sticky cell fragments that originate in the red bone marrow.
  • Range from 2 to 4 μm in diameter and have a biconvex discoid shape.
  • Play an active role in minimizing bleeding by clumping together to form a platelet plug or blood clot.
  • Normal platelet count: 150,000 to 450,000 platelets per microliter of blood.
  • Low level of platelets is known as thrombocytopenia and may occur due to an inherited or acquired condition or as a side effect of taking certain medications.
  • Mean platelet volume (MPV) is a measure of the average size of the platelets in the blood and are usually assessed as part of a CBC.
  • Older platelets tend to be smaller in size than newer platelets.
  • Smaller result may indicate that something is interrupting platelet production and development.

Assessment of Clotting

  • Prothrombin time (PT):
    • Assesses the blood’s ability to clot.
    • Normal PT values are 10 to 12 seconds.
  • International normalized ratio (INR):
    • Calculated in the laboratory based on the PT value.
    • A normal INR value for a healthy individual is 1.1 or below.
  • Partial thromboplastin time (PTT):
    • Test to assess clotting time and/or to evaluate the presence of a clotting disorder.
    • Used to monitor the effectiveness of anticoagulant therapy with heparin.
    • Normal PTT value is 25 to 35 seconds.
    • Individuals on heparin therapy may have clotting times up to two and half times longer.
  • The PT and PTT assess clotting time and do not directly measure platelet levels.

Complete Blood Count (CBC)

  • Blood test that is often done as part of a medical history and assessment.
  • Identifies the number of erythrocytes, leukocytes, and platelet cells in a blood sample.
  • Often accompanied by a differential analysis, which identifies the total number of each of the different types of leukocytes in a blood sample.
  • The results of a differential analysis are usually reported as a percentage of the total as well as an actual or absolute value.

Conditions of the Blood

  • Anemia:
    • Lower-than-normal amount of red blood cells, hemoglobin, or both in the blood.
    • Limits the body’s ability to transport oxygen to the tissues.
    • May feel tired or weak and may also experience shortness of breath, dizziness, headaches, or an irregular heartbeat.
    • Iron deficiency anemia: Related to low levels of iron and may be caused by poor iron intake or a loss of blood.
    • Iron-refractory iron deficiency anemia (IRIDA) is a rare, genetic form of iron deficiency anemia.
    • Megaloblastic anemia: Characterized by very large erythrocytes and an overall decrease in the number of erythrocytes. This form of anemia is also known as vitamin deficiency anemia and includes both pernicious and folate deficiency anemia.
      • Pernicious anemia occurs because of vitamin B12 deficiency.
      • Folate deficiency anemia occurs as a result of low levels of folic acid in the blood.
    • Aplastic anemia: Occurs when the bone marrow does not produce enough blood cells overall, including erythrocytes, leukocytes, and platelets. The origins of this condition are idiopathic (i.e., unknown), though infection by hepatitis, Epstein-Barr virus (EBV), cytomegalovirus (CMV), or human immunodeficiency virus (HIV) may be linked to the development of aplastic anemias. Exposure to certain medications and toxins such as benzene or exposure to radiation may also be related to the development of the condition.
    • Fanconi anemia (FA): A genetic condition, is also characterized by the bone marrow’s inability to produce enough erythrocytes, leukocytes, and platelets. Several genetic mutations have been identified in individuals with this condition.
    • Sideroblastic anemia: Occurs when there is a low number of erythrocytes because the bone marrow fails to produce an adequate number of healthy cells and the erythrocytes are unable to produce functional hemoglobin. Iron accumulates inside the cell, and the nucleus develops a ringed appearance due to the buildup of the iron. Sideroblastic anemia may be either congenital or acquired.
    • Hemolytic anemia: Occurs when there is a low number of erythrocytes. However, in this case, the low number of erythrocytes is caused by the destruction of the cells, rather than underproduction by the bone marrow. Thalassemia is a genetic form of hemolytic anemia. There are several genetic variants and subtypes.
    • Autoimmune hemolytic anemia (AIHA): A rare acquired disorder that occurs when the individual’s immune system attacks and destroys the erythrocytes. The causes of this disease are not well known. However, it has been associated with several conditions, including EBV, lymphoma, systemic lupus erythematosus, immunodeficiency disorders, and rheumatoid arthritis.
    • Infectious anemias: Acquired hemolytic anemias that occur because of an infection such as malaria.
    • Sickle cell disease (SCD): A group of inherited red blood cell disorders that affects individuals of African descent and Hispanics of Caribbean ancestry.
      • Erythrocytes become stiff, sticky, and take on a curved or sickle shape like the letter C.
      • Altered shape and stickiness cause the erythrocytes to clump, slow the natural passage of the blood through the vessels, and potentially block the blood vessels. This may result in pain, organ dysfunction, and hypoxia.
      • Occurs when an individual inherits a sickle cell gene from both of his or her parents. The most severe form of the disease is sickle cell anemia and is classified as hemolytic anemia.
      • Sickle cell trait occurs when an individual inherits a sickle cell gene from one of his or her parents. This single gene does not usually cause SCD, and sickle cell trait is not considered a disease. However, an individual with sickle cell trait can pass this gene to their children.
    • Polycythemia: Occurs when there are a high number of erythrocytes in the bloodstream.
      • It may be caused by an abnormal increase in erythrocyte production in the bone marrow or secondary to chronic hypoxia related to diseases such as chronic obstructive pulmonary disease (COPD) or pulmonary hypertension or from a tumor that secretes erythropoietin.
  • Blood disorders that affect the leukocytes most often impact the neutrophils and lymphocytes.
    • Neutropenia: A lower-than-normal level of neutrophils and may be related to aplastic anemia, chemotherapy, radiation therapy or exposure to radiation, influenza, viral infection, or severe bacterial infection.
    • Kostmann disease: A genetic disorder characterized by severe neutropenia and frequent bacterial infections early in life. Cyclic neutropenia, which is characterized by recurrent episodes of decreased neutrophils in the blood, is another rare genetic disorder.
    • Leukocyte adhesions deficiency (LAD) syndromes: A group of genetic disorders that alter the capabilities of leukocytes to respond to a wound or infection.
    • Leukemia: Cancer of the blood that develops in the bone marrow and produces abnormal leukocytes.
      • Acute lymphocytic leukemia (ALL)
      • Chronic lymphocytic leukemia (CLL)
      • Acute myeloid leukemia (AML)
      • Chronic myeloid leukemia (CML)
    • Lymphoma: A type of blood cancer that originates in the lymphatic system.
      • Non-Hodgkin lymphoma, which may originate in either the B cells or T cells, and Hodgkin lymphoma, which is characterized by the presence of an abnormal B cell called a Reed-Sternberg cell.
  • Blood disorders may also affect the platelets.
    • Thrombocytopenia: A condition characterized by a low number of platelets in the blood.
    • Immune thrombocytopenia (ITP): Also called immune thrombocytopenic purpura or idiopathic thrombocytopenic purpura, occurs when the immune system attacks and destroys the platelets. The origins of this condition are unknown.
    • Heparin-induced thrombocytopenia: A reaction by the body to the use of the blood thinner heparin that results in lower than normal platelet levels.
  • Bleeding disorders
    • Hemophilia A, also called factor VIII (FVIII) deficiency, is a genetic condition in which the blood is unable to clot due to a missing or defective factor VIII, a clotting protein.
    • Hemophilia B, also called factor IX (FIX) deficiency or Christmas disease, is a genetic condition associated with a missing or defective factor IX clotting protein.
    • Von Willebrand disease (VWD) is a genetic disorder related to a missing or defective von Willebrand factor (VWF) clotting protein.