Cell Histology

Also written as Cytology, Histopathology basics.

Cell histology describes the microscopic structure of cells and their organelles, linking form to function. Understanding normal histology guides interpretation of tissue pathology in low‑resource settings.

Overview

Cells are the basic units of life. Histology uses light microscopy and simple stains (e.g., H&E) to visualise nuclei, cytoplasm, membranes and extracellular matrix.

• Nucleus contains DNA, appears dark with H&E
• Cytoplasm stains pink, shows organelles with special stains
• Cell borders may be visible with PAS or trichrome

Location and structure

Different tissues have characteristic cell shapes: squamous (flat), cuboidal (cube‑shaped), columnar (tall) and transitional. Organelles vary with function – e.g., abundant rough ER in secretory cells.

• Epithelial cells line surfaces; polarity (apical vs basal) matters for transport
• Muscle cells contain many mitochondria and sarcoplasmic reticulum
• Neurons have long axons and Nissl substance

Relations

Cells interact with basement membrane, neighbouring cells via tight junctions, desmosomes and gap junctions, influencing barrier function and signal transmission.

• Tight junctions prevent paracellular leak
• Desmosomes provide mechanical strength
• Gap junctions allow electrical coupling

Blood supply

Capillary networks supply oxygen and nutrients; in low‑resource hospitals, tissue hypoxia is common in severe anaemia or sickle‑cell crises.

• Ischemia leads to loss of nuclear staining (coagulative necrosis)
• Reperfusion may cause hemorrhagic transformation

Nerve supply

Sensory and autonomic fibres innervate many tissues; loss of innervation alters cell morphology (e.g., atrophic smooth muscle).

• Denervation atrophy shows reduced cell size and cytoplasmic eosinophilia

Function

Cell structure determines function: secretory granules in endocrine cells, cilia in respiratory epithelium, contractile filaments in muscle.

• Goblet cells produce mucus seen as pale vacuoles
• Podocytes have foot processes forming filtration slits

Clinical relevance and injuries

Histologic patterns help diagnose infections, malignancy and inflammatory diseases common in East Africa.

• H&E stain: What basic tissue architecture looks like? – Shows cell size, nuclear features and overall pattern; if unavailable, use rapid Giemsa smear for cytology
• Ziehl‑Neelsen stain: Does acid‑fast bacilli exist? – Positive indicates Mycobacterium tuberculosis; if not available, rely on clinical TB score and chest X‑ray
• PAS stain: Is there fungal or glycogen‑rich material? – Highlights fungi (yeast buds) and basement membrane; if unavailable, use mucicarmine or consider clinical context

• Granulomas with caseation suggest TB
• Schistosome eggs cause eosinophilic granulomas in liver
• HIV‑related Kaposi sarcoma shows spindle cells and vascular channels

Exam pearls

Focus on pattern recognition, not memorising every cell type. Correlate microscopic findings with bedside clues (e.g., chronic cough → granulomas).

• Look for nuclear pleomorphism and mitoses to suspect malignancy
• Identify eosinophilic infiltrates for parasitic infection
• Recognise loss of polarity in dysplasia

Questions an examiner may ask

• A patient with chronic cough and weight loss has a lung biopsy showing caseating granulomas — what is the next diagnostic step? — Order sputum GeneXpert; if unavailable, start empirical anti‑TB therapy based on clinical score.
• You see sheets of atypical lymphoid cells in a lymph node; how do you distinguish reactive hyperplasia from lymphoma? — Look for loss of nodal architecture, monoclonality on immunohistochemistry; if stains unavailable, correlate with systemic B‑symptoms.
• A biopsy from a liver lesion shows eosinophilic granulomas with central necrosis; which tropical infection is most likely? — Schistosomiasis; treat with praziquantel and assess for portal hypertension.
• In a patient with sickle‑cell disease, bone marrow shows hypercellular marrow with erythroid hyperplasia — what does this indicate? — Compensatory response to chronic haemolysis; monitor for aplastic crisis.
• A skin punch biopsy shows spindle cells forming slit‑like vascular spaces; what condition should you consider and why is it relevant in HIV patients? — Kaposi sarcoma; it signals advanced immunosuppression and may need chemotherapy.
• During a rapid autopsy, you cannot obtain special stains; how would you still identify TB in lung tissue? — Look for caseating necrosis, Langhans giant cells, and clinical history; start anti‑TB if suspicion high.
• A patient on long‑term antiretroviral therapy presents with oral ulceration; biopsy shows viral cytopathic changes with Cowdry bodies — what virus is likely and what is the management implication? — HSV; start acyclovir and review immune status.
• You notice loss of brush border in renal tubular cells on a biopsy; what functional defect does this explain and how does it guide treatment? — Impaired reabsorption leading to Fanconi‑type syndrome; manage with electrolyte replacement and avoid nephrotoxic drugs.

When to seek help

• Rapidly progressive organ failure with histologic evidence of necrosis (e.g., fulminant hepatitis)
• Severe sepsis with unidentified pathogen on tissue stain
• Unexplained massive hemorrhage from tissue biopsy

Quick questions

Why is H&E the first stain used?

It provides a quick overview of cell and tissue architecture, differentiating nuclei (dark) from cytoplasm (pink).

Can I diagnose malaria from tissue histology?

Malaria parasites are best seen in blood smears; tissue sections may show pigment but are not reliable for diagnosis.

What does a ‘ground‑glass’ appearance indicate?

Uniform pale cytoplasm often reflects viral infection or early fibrosis; context determines significance.