Q4 LONG ANSWER 10M ★ High-yield

Classify leucocytes and give their normal values. Describe the functions of neutrophils and discuss the types of immunity.

Physiology · 1st Professional — Pre-Clinical

Normal Values

Cell	Percentage	Absolute count/µL
Total WBC	—	4000–11,000
Neutrophils	50–70%	2500–7500
Lymphocytes	20–40%	1500–4000
Monocytes	2–8%	200–800
Eosinophils	1–4%	40–400
Basophils	0–1%	10–100

Classification

Granulocytes (polymorphonuclear)	Agranulocytes (mononuclear)
Neutrophil	Lymphocyte
Eosinophil	Monocyte
Basophil	—

Neutrophils

Lifespan — 6–8 hours in blood, 4–5 days in tissue
First cell to reach the site of acute inflammation
Functions — phagocytosis, the body's first line of cellular defence

Margination → Diapedesis (squeeze between endothelial cells) → Chemotaxis → Opsonisation (IgG, C3b) → Phagocytosis → Killing — respiratory burst (H2O2, superoxide) + lysosomal enzymes

Arneth count — classifies by nuclear lobes

– Shift to left — more immature (fewer lobes) → acute infection

– Shift to right — more hypersegmented → megaloblastic anaemia

Other Leucocytes

Cell	Chief functions	Increased in
Eosinophil	Detoxifies histamine; kills parasites (major basic protein)	Allergy, asthma, parasitic infestation (mnemonic NAAACP)
Basophil	Releases heparin and histamine; IgE-mediated hypersensitivity	Chronic myeloid leukaemia
Monocyte	Becomes tissue macrophage; phagocytosis; antigen presentation	Chronic infection, tuberculosis, kala-azar
Lymphocyte	Immunity — see below	Viral infection, tuberculosis, whooping cough

Leucopoiesis

Pluripotent stem cell → Myeloid or lymphoid stem cell → Myeloblast / lymphoblast → Promyelocyte → myelocyte → metamyelocyte → Band form → Mature granulocyte

Regulated by colony stimulating factors — G-CSF, M-CSF, GM-CSF, and interleukins
Granulocytes take 7–10 days to develop
Marrow holds a reserve pool about 20× the circulating number

Immunity

	Innate (natural)	Acquired (adaptive)
Present	From birth	Develops after exposure
Specificity	Non-specific	Highly specific
Memory	Absent	Present
Components	Skin, mucosa, gastric acid, lysozyme, complement, neutrophils, NK cells, inflammation	B and T lymphocytes

Acquired immunity — two arms

	Humoral	Cell-mediated
Cell	B lymphocyte → plasma cell	T lymphocyte
Matures in	Bone marrow (bursa equivalent)	Thymus
Mediator	Antibodies	Cytokines, direct cytotoxicity
Against	Extracellular bacteria, toxins, viruses in blood	Intracellular organisms (TB, virus), fungi, tumour cells, grafts
Subtypes	IgG, IgA, IgM, IgE, IgD	CD4 helper, CD8 cytotoxic, regulatory, memory

IgG — most abundant; only one that crosses the placenta
IgM — largest; first antibody in a primary response
IgA — secretory; in milk, saliva, tears, gut
IgE — allergy and parasites

Applied Aspects

Leukaemia — malignant proliferation of WBC; acute (blast cells) vs chronic
Agranulocytosis — neutrophils < 500/µL → severe infection; caused by chloramphenicol, carbimazole, cytotoxics
AIDS — HIV destroys CD4 T cells → failure of cell-mediated immunity → opportunistic infection
Leucocyte adhesion deficiency → failure of margination
Chronic granulomatous disease → defective respiratory burst → phagocytosis without killing

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