Metaplasia and dysplasia
How chronic injury makes a lining change its cell type (metaplasia), what the new lining gains and loses, and how disordered, atypical growth (dysplasia) marks the road from a changed lining towards carcinoma.
By the end, you can
- Define metaplasia and explain why it arises from reprogrammed stem cells, not from mature cells changing type.
- Describe squamous metaplasia of the bronchus and columnar metaplasia of the oesophagus, and what each gains and loses.
- Describe the cellular and architectural features of dysplasia and how it is graded.
- Distinguish dysplasia, carcinoma in situ and invasive carcinoma by the basement membrane.
- Explain why metaplasia and low-grade dysplasia can regress while high-grade dysplasia more often progresses.
- Recognise the classic appearances, grading systems and screening tests of metaplasia and dysplasia, and explain how removing the stimulus, vaccination, and ablation or excision act on the sequence to carcinoma.
What it is
Metaplasia is the replacement of one mature (differentiated) cell type by another mature type, usually one better able to withstand a chronic stress; it is an adaptation and is often reversible. Dysplasia is disordered growth in which cells become atypical in size, shape and nucleus and lose their orderly maturation. In an epithelium it is a precancerous, neoplastic change confined above the basement membrane, also called intraepithelial neoplasia.
4 types to tell apart
- Squamous metaplasia
- Columnar or ciliated epithelium replaced by stratified squamous epithelium: the bronchi of smokers, the cervical transformation zone, ducts irritated by stones, and lack of vitamin A.
- Columnar (glandular) metaplasia
- Squamous epithelium replaced by columnar epithelium, as in Barrett’s oesophagus, or the stomach lining becoming intestinal in type in chronic gastritis.
- Connective tissue metaplasia
- Bone or cartilage forms in soft tissue, as in muscle after a deep injury (myositis ossificans).
- Dysplasia and carcinoma in situ
- Graded low or high (or mild, moderate and severe) by how atypical the cells are and how much of the epithelium they occupy; full-thickness change with an intact basement membrane is carcinoma in situ.
US spelling: oesophagus → esophagus.
Normal function
Linings renew from their stem cells
Epithelia are renewed throughout life from stem cells near their base. The airways are lined by : on the replace the , whose sweep mucus from the up towards the throat.
Which cell type the stem cells make is set by signals around them: growth factors, cytokines, the matrix and retinoic acid (from vitamin A) switch on the transcription factors that define a lineage. Each lining suits its job: thin and ciliated in the airways, many-layered and tough in the oesophagus and the skin.
In a stratified lining, cells divide only in the basal layer; as they rise they mature and flatten, and their nuclei stay small and regular. This orderly maturation is what dysplasia disturbs.
Underlying change · Step 1 of 5
Metaplasia: a tougher lining
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Columnar and connective tissue metaplasia
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 5
Dysplasia: disordered, atypical growth
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
Grading: from low grade to carcinoma in situ
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
Regression, persistence or invasion
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .