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Leukocytes (White Blood Cells)

Medical Physiology, Guyton/Hall, 12th ed, Chapter 33

Mary C. Karlet

2015

Leukocytes

• Mobile units that work to prevent disease and infection

– Destroy invading agents by phagocytosis

– Form antibodies and sensitized lymphocytes, which also destroy the invader

– Upon release, wbc’s are transported in the blood to the area where they are needed

– Normal wbc count = 4,000 to 10,000 cells/mm3

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Leukocytes – Six Types

1. Neutrophils

2. Eosinophils

3. Basophils

4. Monocytes → tissue macrophages

5. Lymphocytes (“T” and “B”)

6. Plasma cells

Granulocytes“polys”

Genesis of WBC’s

1. pluripotent stem

cell

3. megakaryocyte

7. neutrophil

10. eosinophil

12. basophil

13-16. stages of

monocyte

formation

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Leukocytes

• Granuloctes and monocytes ingest invading organisms (bacteria, viruses, etc.) by phagocytosis

• Lymphocytes and plasma cells function as part of acquired immunity

• Formed and stored in bone marrow: – Granulocytes and monocytes

• “Formed” in lymph tissue (thymus, tonsils, lymph nodes, spleen)– Lymphoctes and plasma cells

Leukocyte Values in Peripheral Blood

Neutrophils 1800-7200 cells/mm3 55%

Lymphocytes 1500-4000 cells/mm3 36%

Eosinophils 0-700 cells/mm3 2%

Basophils 0-150 cells/mm3 1%

Monocytes 200-900 cells/mm3 6%

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Important Definitions

• Chemotaxis ≡ chemical

released from inflamed tissue

or foreign invader cause

neutrophils and macrophages

to move toward source of

chemicals

• Ameboid motion ≡ neutrophils

and macrophages move

through tissue by ameboid

motion by the extension of

pseudopods

http://video.search.yahoo.com/video/play?p=chemo

taxis&ei=UTF-8&fr=yfp-t-

501&tnr=21&vid=0001387379

Important Definitions

• Diapedesis ≡ wbc’s

(neutrophils and

macrophages) squeeze

through very small capillary

pores towards the

chemotactic source

• Opsonization ≡ wbc’s

recognize foreign material

that has been tagged by an

Ab and the C3b product of

the complement cascade

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Important Definitions

• Phagocytosis ≡ the most

important function of

neutrophils and

macrophages is to

recognize, engulf, and

destroy pathogens or

diseased tissue

Neutrophils

• Neutrophils are among the first to arrive at

the site of infection, followed by

macrophages, and then the lymphocytes

• Major role of neutrophils (and macrophages)

is to attack and destroy invading bacteria,

virus, and other toxic agents

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Monocytes & Macrophages

• Monocytes have limited ability to fight infectious

agents except when they enter tissues →

macrophages (become filled with lysosomes and

swell to diameter 5X normal)

• Macrophages are extremely capable of

combating infectious agent through phagocytosis

• Macrophages provide a continuing defense in the

tissue against infection

– Cells can last for years in tissues

Monocyte Macrophage

System

(Reticuloendothelial

System)

• A generalized system present

in all tissues that exhibits

phagocytic properties from

tissue macrophages

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Tissue

Macrophages1. Skin and subcutaneous

tissue

– Histiocytes

2. Lymph nodes

– Trap and destroy invading

organisms

3. Alveoli

– Alveolar macrophages

4. Liver

– Kupffer cells

5. Spleen

– Especially effective at

removing unwanted

organisms and debri from

blood (especially old or

abnormal rbc’s)

Alveolar Macrophage

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Eosinophils

• Weak phagocytes

• Prominent role in protection against parasitic

infection

– Schistosomiasis

– Trichinosis (Trichinella – “pork worm”)

• Elevated in patients with history of allergic

reactions and asthma (atopic individuals)

Basophils

• Participate in allergic reactions

• After their release from the bone marrow,

migrate to respiratory tract, gastrointestinal tract,

and superficial layers of skin

• Behave like mast cells in these locations

– Release histamine, serotonin, bradykinin, heparin,

slow reacting substance of anaphylaxis (SRSA), platelet

activating factor

– ⇒ vasodilation, watery eyes, itching, urticaria, edema

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InflammationDescribes tissue changes

associated with injury

1. Increased blood supply to

the region

2. Increased capillary

permeability → edema

3. Emigration of cells out of

blood vessels into tissues

– Migration of granulocytes

and monocytes and

activation of tissue

macrophages

4. After several days, cavitation

of necrotic tissue, dead

wbc’s = pus

Leukopenia (wbc < 4,000)

• Drugs that depress the bone marrow function– Thiouricil

– Many chemotherapeutic agents

– Phenothiazines

– Radiation

– In general, anesthetic agents depress the immune system, but probably of no clinical significance

• wbc < 2,000 – minor infections

• wbc < 1,000 – serious infections (pneumonia, wound infections)

• wbc < 500 – life-threatening infections

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Leukocytosis (wbc > 10,000)

• White blood cell differential

– “shift to the left” – more immature (band or blast) cells; occurs with acute infection

– “shift to the right” – abnormally large number of mature cells; occurs with chronic infection (e.g. chronic hepatitis)

• Leukocytosis may be caused by infection, steroid ingestion, leukemia, mononucleosis, and nonbacterial tissue injury

Leukemias

• Cancerous mutations of bone marrow (myelogenous) or lymphoid cells (lymphogenous) -produce uncontrolled production of wbc’s and growth of leukemic cells in abnormal parts of the body.

• White blood cells are bizarre and nonfunctional – Patient susceptible to infection

• Rapid metastatic growth of leukemic cells: – other cells starve– tissue destruction– bone pain and fractures– Anemia, thrombocytopenia (displacement of nl bone

marrow with nonfunctional cells)