# Blood Histology

> Red cells, differential white cell counts with identifying features, platelets and normal values, with clinical correlations for MBBS Anatomy histology.

- Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/blood-histology
- Exam / course: MBBS · Subject: Anatomy
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Blood Histology", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/blood-histology

## Direct answer

Blood is a liquid connective tissue of plasma (about 55 per cent) and formed elements (about 45 per cent) — red cells, white cells and platelets. Red cells are anucleate biconcave discs packed with haemoglobin; the leucocytes defend the body as neutrophils, eosinophils, basophils, lymphocytes and monocytes; and platelets, cytoplasmic fragments of megakaryocytes, plug vascular breaches and start coagulation. On a Leishman-stained smear each type is recognised by size, nuclear shape and granule colour.

## What you must remember

- **Red cells:** 7 to 8 micrometres across, 4.5 to 5.5 million per microlitre, lifespan about 120 days; haemoglobin 13 to 18 grams per decilitre in men and 12 to 16 in women; reticulocytes 0.5 to 1.5 per cent reflect marrow activity; rouleaux formation is normal.
- **Packed cell volume:** about 45 per cent in men and 40 per cent in women; anaemia is subclassified on the smear as microcytic, macrocytic or normocytic.
- **Total leucocyte count:** 4000 to 11,000 per microlitre; neutrophilia in acute bacterial infection, lymphocytosis in viral infection, eosinophilia in allergy and parasitosis, monocytosis in chronic infection such as tuberculosis.
- **Neutrophil** (40 to 75 per cent): 12 to 15 micrometres, nucleus of two to five lobes, granules with myeloperoxidase; hypersegmentation suggests vitamin B12 or folate deficiency, and a left shift releases band cells.
- **Eosinophil** (1 to 6 per cent): bilobed nucleus with large refractile red-orange granules containing major basic protein; raised in asthma and helminth infestation.
- **Basophil** (0 to 1 per cent): dark metachromatic heparin and histamine granules hiding the nucleus; raised in chronic myeloid leukaemia.
- **Lymphocyte** (20 to 40 per cent): small round cell 8 to 10 micrometres with a dense nucleus; B cells make antibodies, T cells mediate cell-mediated immunity, natural killer cells act without sensitisation.
- **Monocyte** (2 to 10 per cent): the largest leucocyte, 12 to 20 micrometres, with a kidney-shaped nucleus and grey-blue cytoplasm — the circulating macrophage.
- **Platelets:** 150,000 to 400,000 per microlitre, megakaryocyte fragments with dense and alpha granules; deficiency causes petechiae and a prolonged bleeding time.

## Common confusion

Neutrophil and monocyte are mixed up on smears: the neutrophil has a lobed, deeply stained nucleus with specific granules; the monocyte is larger, with grey-blue ground-glass cytoplasm and an indented nucleus. Basophils of blood and mast cells of tissue share granules but are distinct lineages; platelets are anucleate fragments whose count, not morphology, matters clinically.

## Exam-focused takeaway

Histology practicals require identification of all formed elements on a stained smear with a differential count. Theory questions ask for the identifying features, counts and functions of each leucocyte, the red cell lifespan, and correlations such as hypersegmented neutrophils in megaloblastic anaemia and eosinophilia in parasitosis. In the viva, define packed cell volume and explain rouleaux.

## Frequently asked questions

### How is a neutrophil identified on a blood smear?

By its 12 to 15 micrometre size, a nucleus of two to five lobes, and fine lilac granules; it is the commonest leucocyte.

### What distinguishes a monocyte from other leucocytes?

It is the largest, 12 to 20 micrometres, with a kidney or horseshoe-shaped nucleus and opaque grey-blue cytoplasm; it becomes a macrophage in tissues.

### Why do eosinophils increase in parasitic infestation?

Their granule proteins, chiefly major basic protein, damage the surface of parasites too large to phagocytose; they also moderate allergic inflammation.

### What is the normal platelet count and what happens when it falls?

150,000 to 400,000 per microlitre; when it falls, bleeding time lengthens and petechiae appear, with serious spontaneous bleeding under about 20,000 per microlitre.

### Which cells are the agranulocytes?

Lymphocytes and monocytes — lymphocytes mount immune responses as B, T and natural killer cells, while monocytes become tissue macrophages.