# General Histology of Blood

> Blood histology for BDS Oral Histology: RBC and WBC morphology, differential counts, platelets, plasma versus serum and dental bleeding relevance.

- Canonical URL: https://prepelephant.com/topics/bds/oral-histology/general-histology-blood-dental
- Exam / course: BDS · Subject: Oral Histology
- 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: "General Histology of Blood", PrepElephant, https://prepelephant.com/topics/bds/oral-histology/general-histology-blood-dental

## Direct answer

Seven to eight micrometres across, biconcave and anucleate, the erythrocyte is the reference cell of the entire body — the yardstick by which histologists size everything else on a smear. Blood is plasma (about 55 per cent, water plus albumin, globulins and fibrinogen) and formed elements (about 45 per cent, the haematocrit): red cells at roughly 4.5 to 5.5 million per cubic millimetre with a 120-day lifespan, leukocytes at 4,000 to 11,000 per cubic millimetre, and platelets at 150,000 to 400,000 per cubic millimetre. The leukocyte differential runs neutrophils (55-70 per cent, the dominant granulocyte with three to five nuclear lobes), lymphocytes (25-33 per cent), monocytes (3-8 per cent, the largest leukocyte at 15-18 micrometres with a kidney-shaped nucleus), eosinophils (1-6 per cent, bilobed) and basophils (under 1 per cent, heparin- and histamine-packed). Serum is simply plasma minus fibrinogen and clotting factors. For dental practice this is the pre-operative page: bleeding history, platelet counts and anaemia assessment all begin here.

## What you must remember

- **Erythrocyte payload:** 7-8 micrometres diameter, biconcave disc for gas exchange surface, anucleate, about 4.5-5.5 million per cubic millimetre, lifespan 120 days, removed by splenic macrophages; reticulocytes are the marrow-release index.
- **Differential count with personalities:** neutrophil 55-70 per cent (lobed nucleus, azurophilic and specific granules, first responder, pus); lymphocyte 25-33 per cent (small round cell, dense nucleus; B and T families); monocyte 3-8 per cent (largest, 15-18 micrometres, kidney/horseshoe nucleus, steel-blue cytoplasm, becomes tissue macrophage); eosinophil 1-6 per cent (bilobed, red-orange granules of major basic protein, allergies and parasites); basophil under 1 per cent (large purple metachromatic granules, heparin and histamine).
- **Platelet facts:** 2-4 micrometre cell fragments from megakaryocytes, 150,000-400,000 per cubic millimetre, open canalicular system plus alpha granules and dense granules (ADP, serotonin) — primary haemostasis in one line.
- **Plasma versus serum:** serum is plasma after fibrinogen is consumed in clotting — the distinction behind every "clotted sample" laboratory rejection.
- **Dental bleeding thresholds commonly taught:** platelet counts below about 100,000 per cubic millimetre (and certainly below 50,000) prolong surgical bleeding; abnormal counts, leukaemia and anticoagulant therapy require investigation before extractions.
- **Oral mucosa as a blood-health window:** pallor of lips and mucosa suggests anaemia; gingival hypertrophy with bleeding suggests leukaemic infiltration; spontaneous gingival bleeding suggests thrombocytopenia or coagulation defect — the classic triad of haematology presentations in the mouth.
- **Granulocyte-oral link:** qualitative neutrophil defects (such as leucocyte adhesion deficiency) present with rapidly destructive periodontitis in children — histology explaining aggressive periodontitis syndromes.

## Reading a peripheral smear systematically

Train the eye with a grid. Scan at low power for the evenness of the film, then move to the monolayer where red cells just touch. Use the erythrocyte as your ruler: any cell the size of one red cell is a small lymphocyte; one and a half times is a neutrophil; twice is a monocyte. Read the nucleus next — segmented lobes joined by filaments make a neutrophil, two smooth lobes make an eosinophil, an S-shaped or bilobed dark mass buried under purple granules makes a basophil, a kidney bean makes a monocyte, and a single dense round nucleus with a sliver of cytoplasm makes a lymphocyte. Then read the granule colour: lilac-pink neutrophil, brick-red eosinophil, deep purple basophil. Platelets appear as tiny anucleate blue specks between cells, and their honest scarcity on a smear is the first hint of thrombocytopenia when a patient reports gum bleeding. This drill matters in dental training because the oral physician, not the haematologist, is usually the first to see the signs: a pale, sallow patient with smooth sore tongue and angular cheilitis points toward iron-deficiency or megaloblastic anaemia, and punch-out gingival bleeding with petechiae points toward a platelet problem that must be investigated before any extraction.

## Dental relevance examiners probe

Two questions recur. First, "why ask about bleeding history before extraction" — the credited answer walks the haemostasis ladder: platelet number and function (primary plug), coagulation factors (fibrin clot, measured as prothrombin time and activated partial thromboplastin time), and vessel integrity; each rung has a dental flag, from prolonged oozing in thrombocytopenia to inherited haemophilia unmasked by a simple extraction. Second, "which blood diseases show in the mouth first" — anaemia (pallor, glossitis, angular cheilitis), leukaemia (hypertrophic, boggy, bleeding gingiva with infiltration), thrombocytopenia (spontaneous gingival bleeding, petechiae), and the neutrophil-defect syndromes of childhood aggressive periodontitis. A neat closing flourish for vivas: the basophil and the connective-tissue mast cell carry the same granule cargo but differ in lineage and location, which links this page back to general connective tissue histology in a single comparative sentence.

## Frequently asked questions

### Which is the largest and which the most numerous leukocyte?

The monocyte is largest (15-18 micrometres with a kidney-shaped nucleus), while the neutrophil is the most numerous (55-70 per cent of the differential in health).

### What distinguishes eosinophils and basophils on a smear?

Eosinophils have bilobed nuclei and brick-red granules containing major basic protein (allergy, parasitic response); basophils have obscured bilobed nuclei and large purple granules of heparin and histamine.

### What is the difference between plasma and serum?

Plasma is the liquid portion of unclotted blood containing fibrinogen; serum is what remains after clotting has consumed fibrinogen and other clotting factors.

### Why are platelets essential before dental extraction?

They initiate primary haemostasis by adhesion, aggregation (ADP from dense granules) and providing phospholipid surfaces for coagulation; counts below roughly 100,000 per cubic millimetre risk prolonged post-operative bleeding.

### How does anaemia present in the oral cavity?

As mucosal and lip pallor, atrophic glossitis with a smooth sore tongue, and angular cheilitis — findings that often prompt the haemogram in dental practice.