Blood- formed elements

Types of formed elements

Erythrocytes= Red blood cells (RBCs)

Leukocytes= White blood cells (WBCs)

Platelets = Cell fragments

Erythrocytes (red blood cells, or RBCs)

Main function is to carry oxygen

Anatomy of circulating erythrocytes

Biconcave disks

Essentially bags of hemoglobin

Anucleate (no nucleus)

Contain very few organelles

5 million RBCs per cubic millimeter of blood is the normal count

Hemoglobin

Iron-containing protein

Binds strongly, but reversibly, to oxygen

Each hemoglobin molecule has four oxygen binding sites

Each erythrocyte has 250 million hemoglobin molecules

Normal blood contains 12-18 g of hemoglobin per 100 mL of blood

Homeostatic imbalance of RBCs- Anemia

A decrease in the oxygen-carrying ability of the blood

Homeostatic imbalance of RBCs- Sickle-cell anemia (SCA)

Sickle cell anemia (SCA) results from abnormally shaped hemoglobin

Homeostatic imbalance of RBCs- polycythemia

Excessive or abnormal increase in the number of RBCs. May be caused by bone marrow cancer (polycythemia vera)

May be a response to life at higher altitudes (secondary polycythemia).

Increase in RBCs slows blood flow and increases blood viscosity which impairs circulation.

Leukocytes (white blood cells, or WBCs)

Crucial in body's defense against disease

Complete cells, with nucleus and organelles

Able to move into and out of blood vessels (diapedesis)

Move by amoeboid motion

Respond to chemicals released by damaged tissues (known as positive chemotaxis)

4,800 to 10,800 WBCs per cubic millimeter of blood

Abnormal numbers of leukocytes- Leukocytosis

WBC count above 11,000 cells/mm3

Generally indicates an infection

Abnormal numbers of leukocytes- Leukopenia

Abnormally low leukocyte level

Commonly caused by certain drugs, such as corticosteroids and anticancer agents

Abnormal numbers of leukocytes- Leukemia

Bone marrow becomes cancerous; turns out excess WBCs

Types of leukocytes- Granulocytes

Granules in their cytoplasm can be stained

Possess lobed nuclei

Include neutrophils, eosinophils, and basophils

Types of leukocytes- Agranulocytes

Lack visible cytoplasmic granules

Nuclei are spherical, oval, or kidney-shaped

Include lymphocytes and monocytes

List of the WBCs, from most to least abundant

Neutrophils- Never

Lymphocytes- Let

Monocytes- Monkeys

Eosinophils- Eat

Basophils- Bananas

Types of granulocytes- Neutrophils

Cytoplasm stains pale pink and contains fine granules

Deep purple nucleus contains three to seven lobes

Function as phagocytes at active sites of infection

Numbers increase during infection

3,000-7,000 neutrophils in a cubic millimeter of blood (40-70 percent of WBCs)

Types of granulocytes- Eosinophils

Red, coarse cytoplasmic granules

Figure-8 or bilobed nucleus stains blue-red

Function to kill parasitic worms and play a role in allergy attacks

100-400 eosinophils in a cubic millimeter of blood

(1-4 percent of WBCs)

Types of granulocytes- Basophils

Sparse but large blue-purple granules

U- or S-shaped nucleus stains dark blue

Release histamine (vasodilator) at sites of inflammation

Contain heparin (anticoagulant)

20-50 basophils in a cubic millimeter of blood

(0-1 percent of WBCs)

Types of agranulocytes- Lymphocytes

Cytoplasm is pale blue

Dark purple-blue nucleus

Functions as part of the immune response

B lymphocytes produce antibodies

T lymphocytes are involved in graft rejection, fighting tumors and viruses

1,500-3,000 lymphocytes in a cubic millimeter of blood (20-45 percent of WBCs)

Types of agranulocytes- Monocytes

Largest of the white blood cells

Gray-blue cytoplasm

Dark blue-purple nucleus is often kidney-shaped

Function as macrophages

Important in fighting chronic infection

100-700 monocytes per cubic millimeter of blood

(4-8 percent of WBCs)

Formed elements- platelets

Derived from ruptured multinucleate cells (megakaryocytes)

Needed for the clotting process

Platelet count ranges from 150,000 to 400,000 per cubic millimeter of blood

300,000 is considered a normal number of platelets per cubic millimeter of blood