A neutrophil is a type of white blood cell. It is the most common type of white blood cell in the body. Neutrophils engulf and destroy microbes through a process called phagocytosis.

Leukocytosis is an abnormally high level of white blood cells.

Leukodystrophies are disorders affecting the white matter of the brain.

Leukopenia is a low white blood cell count.

Leukoplakia is white patches in the mouth.

The intrinsic pathway is also known as the contact activation pathway, because it is triggered by contact with certain surfaces, such as collagen.

Tissue factor pathway is another name for the extrinsic pathway. It is called the tissue factor pathway because it is activated by tissue factor, a protein released from damaged tissues.

Angiotensin I is a biologically inactive precursor to angiotensin II. The angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II. Angiotensin II exerts various effects on the body, including stimulating the release of vasopressin (antidiuretic hormone).

The major groups of proteins in plasma are albumin, fibrinogen, and globulin. Albumin is the most abundant plasma protein. It helps maintain osmotic pressure, transports substances, and regulates blood volume. Fibrinogen is a clotting factor. It converts into fibrin, forming a clot to stop bleeding. Globulins are a diverse group of proteins. There are three types of globulins: alpha, beta, and gamma. Alpha globulins transport lipids, fatty acids, and certain vitamins. Beta globulins transport iron and other substances. Gamma globulins, also known as antibodies, are used in immune responses.

Hemostasis can be divided into four stages:

1. Vascular phase: Constriction of the blood vessel
2. Platelet phase: Formation of a temporary “platelet plug"
3. Coagulation phase: Activation of the coagulation cascade
4. Clot formation: Formation of the “fibrin plug” or the final clot

The coagulation phase is where most of the clotting factor activity happens. The intrinsic and extrinsic pathways converge here, involving a complex cascade of clotting factor activations that ultimately lead to clot formation.

Damage to blood vessels releases tissue factor (also known as factor III). It binds with factor VII and calcium to form a complex that activates the extrinsic pathway of the coagulation cascade.

Hemostasis has three major steps:

1. vasoconstriction
2. temporary blockage of a break by a platelet plug
3. blood coagulation

During hemostasis, fibrin monomers polymerize (link together) to form long chains. These chains create a mesh that traps platelets and red blood cells, forming a blood clot that seals the wound.

Factor IIa (also known as thrombin) cleaves fibrinogen into the fibrin monomers that form a fibrin clot.

Oncotic pressure is the osmotic pressure exerted by large molecules in the blood, mainly albumin.

Formed elements are cells and cell fragments suspended in the plasma. The three classes of formed elements are red blood cells, white blood cells, and platelets.

The formed elements are the cells in the blood. The three classes of formed elements are red blood cells, white blood cells, and platelets.

Amylase is an enzyme that breaks down starch into disaccharides and trisaccharides. Other enzymes then convert these into glucose.

Osteocytes are found in bone tissue.

Neutrophils and lymphocytes together make up around 92% of all white blood cells in adults.

Neutrophils are the most common type of white blood cell in normal blood. They are easy to recognize on a blood smear because they usually have a segmented, multi-lobed nucleus, often with 3–5 lobes. Their cytoplasmic granules are usually pale and hard to see, so they may be described as inconspicuous.

Leukocytes, also known as white blood cells, protect the body from infection.

Plasma is the liquid part of blood. It contains plasma proteins (albumin, globulin, and fibrinogen), clotting factors, electrolytes, antibodies, antigens, and hormones. Serum is the liquid portion that is left over when blood clots. It is similar to plasma but lacks fibrinogen and some clotting factors, which are used during clotting.

Fibrinogen is found in plasma. Serum lacks fibrinogen because it is used up in the clotting process.

Plasma and serum do not contain platelets.

Plasma and serum do not contain red blood cells.

The scientific name for red blood cells is erythrocytes. The word comes from erythro, meaning 'red', and cyte, meaning 'cell'.

Red blood cells have two tasks: carrying oxygen and carrying carbon dioxide. They carry oxygen from the lungs to the body's tissues to ensure the tissues have enough oxygen. At the same time, they carry carbon dioxide to the lungs for removal from the body.

Red blood cells are mostly made of hemoglobin (about 95% of their solid material is hemoglobin). They have no nucleus or organelles, which gives them extra space to carry hemoglobin.

Lymphocytes are a type of immune cell. The two main types of lymphocytes are B cells and T cells. B cells make antibodies while T cells help kill tumor cells and control immune responses.

Cytotoxic cells and helper cells are different functions of T cells.

Phagocytes are a type of white blood cell that ingest and destroy pathogens. They include monocytes, macrophages, neutrophils, and dendritic cells. White blood cells that are not phagocytes include lymphocytes (B cells, T cells, and natural killer cells), basophils, and eosinophils.

Neutrophils are part of the innate immune system, which is the body's first line of defense against pathogens. Neutrophils capture and destroy invading microorganisms, through methods such as phagocytosis.

Erythrocytes are red blood cells, not white blood cells.

Macrophages are a type of white blood cell that engulf and digest pathogens. Kupffer cells are macrophages found in the liver. Other macrophages include alveolar macrophages (found in the lungs), microglia (found in the central nervous system), and histiocytes (found in connective tissue).

Basophils are the rarest type of white blood cell, making up only 1% of the white blood cells in the blood.

Platelets are blood cells that help in clotting by forming a plug in the holes of damaged blood vessels.

Lipase is an enzyme that breaks down fats into fatty acids and glycerol during digestion.

Prothrombinase converts prothrombin to thrombin, not vitamin K.

The enzyme plasmin breaks down fibrin and dissolves clots, not vitamin K.

Vitamin K is essential for the liver's production of prothrombin as well as several other proteins involved in blood clotting.

Vitamin K is fat-soluble, not water-soluble.

White blood cells are the preferred source of DNA samples. Red blood cells and plasma proteins do not contain DNA and therefore cannot be used for DNA testing. Sweat can contain DNA because it can contain shed cells, but white blood cells is the best answer.

Red blood cells lacking the Duffy antigen are relatively resistant to infection by Plasmodium vivax, the parasite that causes Plasmodium vivax malaria. The Duffy antigen is absent from the red blood cells of 90% of sub-Saharan Africans, conferring malaria resistance in this population.

People with type B blood cannot receive any blood that has A antigens (i.e. type A or AB blood), because their immune system makes anti-A antibodies. If they receive blood with A antigens, it can cause a dangerous hemolytic reaction. Furthermore, Rh-negative patients are usually given Rh-negative red blood cells to avoid exposure to the D antigen and possible anti-D formation. So, a person with B− blood should receive B− or O− blood, which do not have A or D antigens.

Blood group classification is based on the presence or absence of antigens on the surface of red blood cells. Blood group A has A antigens on the red blood cells, blood group B has B antigens on the red blood cells, blood group AB has both A and B antigens on the red blood cells, and blood group O has neither the A nor the B antigens on the red blood cells.

"Rhesus positive" means a person has the D antigen on the surface of their red blood cells. This antigen is part of the Rhesus (Rh) blood group system, which is significant for blood transfusions and pregnancy.

Blood group B individuals have B antigens on their red blood cells and anti-A antibodies in their bloodstream.

People with type AB blood can only donate red blood cells to other people with type AB blood. AB red blood cells have both A and B antigens, and recipients with type A, B, or O blood have anti-A and/or anti-B antibodies that attack these cells and cause a hemolytic transfusion reaction.

People with AB+ blood are often called universal red blood cell recipients. Their plasma does not contain anti-A or anti-B antibodies, so they can receive red blood cells from any ABO group. Because they are RhD positive, they can also receive RhD-positive or RhD-negative red blood cells without forming anti-D.

The ABO blood group system is based on two antigens on red blood cells: the A antigen and the B antigen. The presence or absence of these antigens determines a person's ABO blood type.

People with type A blood have A antigens on their red blood cells.

In the ABO blood group system, people make antibodies against the antigens they do not have on their red blood cells. For example, a person with A antigens but no B antigens produces anti-B antibodies.