Physiology of WBC

Question 1

Where does WBC reside?

Answer 1

1) BV
2) Skin
3) Lymph
4) Eye membrane
5) Mouth
6) Respiratory system
7) Intestinal tract
8) Urinary tract

• RBC and platelets are only found in the BV’s

Question 1

What is a WBC?

Answer 1

• They are mobile units of the body’s protective system
• There are 4,800-11,000 WBCs in an adult human <1% of blood volume
• They are complete cells with cytoplasmic organelles
• They are not confined to the circulatory system but use it as a mean of transport

Question 2

What are the types of WBC?

Answer 2

1) Agranular:
-Lymphocytes (B-cells “plasma cells”, T-cells “CD4+, CD8+ TRegs”, NK cells)
- Monocytes (converts to macrophages)

2) Granular:
- Basophils (involved in inflammation and allergy)
- Neutrophils (can perform phagocytosis)
- Eosinophils (can directly attack pathogens, and perform phagocytocis)

Question 3

Describe the development and maturation of WBC’s

Answer 3

1) Lymphocytes maturations occurs in the lyphatic organs (lymphoid tissues, spleen, thymus, lymph nodes)

2) Myelocytes maturation occurs in the bone marrow

Question 4

What are the storage sites of WBC?

Answer 4

1) 300% of WBC is stored in the bone marrow

2) In the circulation 50% of WBC are active while the other 50% are just patroling waiting for a command

3) WBC are the only blood cells that are found in the peripheral tissues

Question 5

What is the life span of different WBCs?

Answer 5

1) Granulocytes: their life span in the circulation is 4-8hrs, while 4-5 days in peripheral tissues

2) Monocytes: 10-20hrs in the circulation while months-years in the peripheral tissues

3) Lymphocytes: weeks to months and they can travel between the lymphatics and circulation providing us with immunity

Question 6

What are the different functions of WBCs?

Answer 6

1) Neutrophils: Phagocytosis of bacteria, fungi, & damaged cells

2) Eosinophils: They release cytotoxic chemicals killing parasites involved in allergy (for large pathogens)

3) Basophils: They release chemicals, and they are involved in allergy and inflammation

4) Lymphocytes: They release antibodies & cytotoxic chemicals (the immune responders “generate memory”)

5) Monocytes/macrophages: Phagocytosis, they eat pathogens, debris, and bacteria

Question 7

Describe the mechanism of phagocytosis by neutrophils and macrophages

Answer 7

1) Neutrophils & macrophages circulate the body

2) Once a pathogen enters the body and resides in the skin, it releases chemotactic substances (like bacterial and viral toxins, & inflammatory cytokines are released by the surrounding WBCs) that attract neutrophils and macrophages

3) Neutrophils and macrophages can then enter the asking through the endothelial pores via diapedesis and phagocytize the pathogen (by their lysozyme and enzymes >60)

Question 8

What are the pathogens that are attacked by neutrophils and macrophages?

Answer 8

1) Bacteria
2) Viruses
3) Fungi
4) Cancer cells
5) Cellular debris

Question 9

What are the safe measures taken by neutrophils and macrophages to not phagocytize normal body cells?

Answer 9

1) Is the cell surface smooth?

2) Does the cell have a protective protein coating?

3) Is the cell tagged (opsonized) with antibodies for phagocytosis?

Question 10

Where are macrophages located in the body (route of pathogen entries)?

Answer 10

1) Kupffer cells: reside in the liver in case you eat a pathogen

2) Alveolar macrophages: specialized macrophages in the lungs in case you inhale a pathogen

3) Histiocytes: specialized macrophages in the skin and connective tissues in case the skin barrier is breached

4) Macrophages in the lymph nodes: In case histiocytes could not kill the pathogen and they managed to enter into the connective tissues

5) Macrophages in the spleen and bone marrow: in case the histiocytes could not kill the pathogen and they managed to enter into the bloodstream

Question 11

What is the reticuloendothelial system?

Answer 11

It is the monocyte-macrophage system (specialized endothelial cells) that phagocytize pathogens, dead cells, cellular debris, and even proteins like Hb

Question 12

What is the mechanism of action of eosinophils?

Answer 12

• They are produced in large amounts in people with parasitic infections
• They kill those parasites by sticking to them, releasing hydrolytic enzymes, reactive forms of oxygen, and polypeptides
• They destroy pathogens that cannot be engulfed due to their large size

Question 13

What is the mechanism of action of basophils?

Answer 13

• They play an important role in allergy
• Activated by the attachment of IgE which will cause them to release histamine, bradykinin, serotonin, heparin, & lysosomal enzyme
• They cause inflammation which will enable them to deal with pathogens

Question 14

What is the difference between mast cells and basophils?

Answer 14

Mast cells are larger and have a longer lifespan

Question 15

What is the mechanism of action of lymphocytes?

Answer 15

• They make the immune system

1) Innate immunity
- Active since birth
- Non-specific
- Inherited in the genetic makeup

2) Acquired immunity
- Very specific
- Acquired through exposure to different pathogens

1- Cell-mediated
- Slow T-cell responders (CD4 Helper T-cells, Suppressor T-cells, CD8+ cytotoxic T-cells, & Regulatory T-cells)

2- Antibody-mediated
- Fast but less efficient B-cell responders (they make antibodies)

Question 16

What are the disorders of leucocytic count?

Answer 16

1) Leukopenia
- Decreased in the total number of WBC <4,000, due to bone marrow suppression

2) Leukocytosis
- Increased in the total count of WBC >11,000, this is triggered by physiological (pregnancy, physical exercise & stress) or pathological (tissue damage, infections, and & worm infestations) disorders or even bone marrow cancers

Question 17

What is leukemia?

Answer 17

It is an uncontrolled production of abnormal WBC that is mainly caused by a cancerous mutation, there are two forms of leukemia, lymphocytic and myelogenous

• WBC can reach 70,000-100,000 cells per mm^3