Pathology of Growth Disorders
1. Define disorders of growth and differentiation: atrophy, hyperplasia, hypertrophy,
hamartoma, metaplasia, dysplasia, neoplasia
Atrophy:
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Diminished cell size due to loss of cell substance. If a sufficient number of
cells are involved, the tissue or organ may also decrease in size.
Common causes:
Reduced use of cells.
Lack of hormonal or nervous stimulation.
Decrease in nutrition.
Reduced blood flow to tissue.
Natural ageing.
Hyperplasia: Increase in the number of cells resulting in enlargement of tissue mass or
organ size. The affected part becomes larger but retains its normal form.
Can be grouped by 2 main causes, physiological and pathological:
- Physiological Hyperplasia:
Hormonal: Breast and uterine enlargement due to increased oestrogen production
during pregnancy.
Compensatory
 Refilling of organ: Liver regeneration after partial hepatectomy.
 Primary signals: Degradation of matrix, NA and insulin. Convert inactive
growth factors to active growth factors to make the cells replicate.
 Proliferation: Transcription factors, cell cycle proteins, growth factors,
cytokines. These increase the mitotic rate and cellular growth.
- Pathological Hyperplasia:
Response is inappropriate and usually caused by:
 Excess hormonal stimulation: Endometrial hyperplasia
 Excess growth factors: Viral infection causing skin warts
Hypertrophy: Increase in cell size, due to increased synthesis of more structural components,
resulting in an increase in the size of the tissue or organ. Occurs in situations
where organ or tissue cannot adapt to an increased demand by formation of
more cells. Can be physiological or pathological:
- Physiological hypertrophy:
Hormonal: Hormonal stimulation of the uterus in pregnancy leads to increased
synthesis of smooth muscle protein.
Mechanical: Cardiac and skeletal muscle are unable to divide to form more cells. The
cells grow to improve cardiac output. (becomes pathological)
Increased activity: Increase in size of kidney after other has been removed.
- Pathological (inappropriate) hypertrophy:
Cardiac Hypertrophy: When the growth of the cells leads to inefficient pumping on
the part of the heart, causing further growth etc. etc.
Hamartoma:
A focal overgrowth of cells and tissues native to the organ in which it occurs.
The overgrowth consists of a disordered arrangement of cells, with one cell
type usually predominating
Metaplasia:
The conversion from one type of mature cell to another type of mature cell due
to an adaptive response. Often occurs with chronic irritation and inflammation.
This results in tissue more resistant to the external stress as the replacement
cells are capable of survival under circumstances in which the original cell
type would not survive.Cellular changes usually result in loss of original
function
Examples:
 Oesophageal stratified squamous epithelium are replaced by the columnar cells
of the stomach. This occurs when a person suffers from chronic reflux of acid
from stomach into oesophagus.
 The pseudo-stratified ciliated columnar of the lung being replaced with
stratified squamous in a smoker.
Dysplasia:
Abnormal cell changes or deranged cell growth in which the cells are
structurally changed in size, shape and appearance from the original cell type.
Organelles also become abnormal. Causes include chronic irritation and
infection. eg. The atypical cervical cells that precede cervical cancer
Neoplasia:
An abnormal mass of tissue, the growth of which exceeds and is uncoordinated
with that of normal tissue and persists in the same excessive manner after
cessation of the stimuli, which caused the change.
Neoplasia means “new growth” and the new growth is the neoplasm.
Characteristics of Neoplasms:
They are a new growth.
Growth is autonomous (carried out by itself).
The lesion is clonal.
The underlying disorder is caused by alterations at the genetic level.
2. Describe the nature, causes and complications of benign prostatic hypertrophy (BPH)
Nature:
Hyperplasia of mucosal cells - peri-urethral region. Most common benign neoplasm in
men.
Causes:
Stromal cells (of the prostate) synthesize dihydrotestosterone (DHT), a metabolite of
testosterone, which is the ultimate mediator of the normal proliferation of the epithelia
and stroma of the prostate.
This is done by the enzyme 5-reductase, converting testosterone into DHT which
binds to nuclear receptors and signals the transcription of growth and mitotic factors.
With age, the relative levels of oestrogen increase which causes an increase in the
expression of androgen receptors for DHT. This causes excessive growth of cells.
Complications:
Compression of urethra.
Distension and hypertrophy of the bladder due to the blockage of the urethra
Cystitis: Inflammation of the bladder.
Hydronephrosis: Distension of the pelvis and calices of the kidney with urine as a
result of obstruction.
Nephritis: Inflammation of the kidney.
Renal failure.