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Flashcards in this deck (6)
  • Lymphocytes are the smallest of the leucocytes and the second commonest (30%); produced in lymphoid tissue of lymph nodes, spleen, thymus, GIT; ultimately derived from lymphocytic stem cells in the bone marrow; these migrate to the lymphoid tissue before and after birth.

    lymphocytes hematology
  • Two major types of lymphocytes: - T-lymphocytes responsible for cellular immunity - B-lymphocytes responsible for humoral immunity - antibodies

    lymphocytes immunology
  • Monocytes are the largest of the leucocytes and moderately common (5%); they have the ability to phagocytose invading organisms and leave the circulation, enlarge and transform in the tissues into macrophages; widely distributed in lymph nodes, lung, alveoli, liver, spleen.

    monocytes macrophages
  • Neutrophils are the commonest leucocyte (62%) with a characteristic lobed nucleus; they have purplish granules in cytoplasm which appear to be lysosomes; where tissue is damaged they leave the capillaries and commence the phagocytosis of damaged cells and invading pathogens; the pus in wounds is largely composed of dead neutrophils.

    neutrophils phagocytosis
  • Eosinophils' acidiphilic granules are considered to be lysosomes; they are only weakly phagocytic but increase in parasitic infections.

    eosinophils parasites
  • Basophils are the rarest of the leucocytes (0.4%) and contain basophilic granules; they contain quantities of heparin and histamine; their function is unclear but they may have relationship with tissue mast cells involved in allergic reactions.

    basophils allergy
Study Notes

Leukocytes — concise notes

Overview

  • White blood cells (leukocytes) are immune cells produced in bone marrow and lymphoid organs.
  • Two broad groups: agranulocytes (lymphocytes, monocytes) and granulocytes (neutrophils, eosinophils, basophils).

Lymphocytes

  • Smallest leukocyte and the second most common (\(30\%\)).
  • Produced and maintained in lymphoid tissues (lymph nodes, spleen, thymus, GIT); derived from bone marrow stem cells.
  • Two main types: T-lymphocytes (cell-mediated immunity) and B-lymphocytes (humoral immunity — produce antibodies).

Monocytes

  • Largest leukocyte, about \(5\%\) of circulating WBCs.
  • Phagocytic; exit the bloodstream and differentiate into macrophages in tissues.
  • Widely located in lymph nodes, lung alveoli, liver, spleen and other tissues.

Neutrophils

  • Most common leukocyte (~\(62\%\)) with a multilobed nucleus.
  • Cytoplasmic granules act like lysosomes containing degradative enzymes.
  • Rapidly migrate into damaged tissue to phagocytose microbes and debris; pus is largely dead neutrophils.

Eosinophils

  • Contain acidophilic granules (lysosome-like).
  • Only weakly phagocytic but increase markedly in parasitic infections and certain allergic responses.

Basophils

  • Rarest leukocyte (~\(0.4\%\)) with basophilic granules.
  • Contain heparin and histamine; function linked to allergic reactions and similar to tissue mast cells.

Quick comparison table

Cell type Relative frequency Key features Primary role
Lymphocytes ~\(30\%\) Small; T and B cells Adaptive immunity (cellular and humoral)
Monocytes ~\(5\%\) Largest; become macrophages Phagocytosis, antigen presentation
Neutrophils ~\(62\%\) Multilobed nucleus; lysosomes Acute bacterial defense, phagocytosis
Eosinophils (low) Acidophilic granules Parasite defense, modulate allergy
Basophils ~\(0.4\%\) Basophilic granules; heparin/histamine Allergy and inflammation

Clinical relevance (brief)

  • Neutrophilia: suggests bacterial infection or acute inflammation.
  • Eosinophilia: suggests parasitic infection or allergic disease.
  • Monocytosis: often seen in chronic infections or long-standing inflammation.
  • Lymphocytosis: commonly associated with viral infections or immune activation.

Memory aids

  • Mnemonic for WBC order by frequency: Never Let Monkeys Eat Bananas (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils).

Key takeaways

  • Five principal leukocyte types differ in appearance, abundance, and immune role.
  • Lymphocytes provide adaptive immunity (T cells cellular; B cells produce antibodies).
  • Neutrophils are the primary rapid phagocytes in acute infection.
  • Monocytes become macrophages in tissues and handle cleanup and antigen presentation.
  • Eosinophils and basophils are specialized for parasitic defense and allergic/inflammatory responses.