cellular adaptations Flashcards
Hypertrophy
• Increase in the size of cells that results in an increase in the size of the
affected organ
• Physiologic - increased functional demand or stimulation by hormones and growth factors
• Pathologic - increased functional demand or stimulation secondary to pathological process
Example of Hypertrophy
• Size increase
• Size of myocardial fibers does not mean increase in number of cells
• Marked thickening of the left ventricle - systemic hypertension
Hyperplasia
• Increase in the number of cells in an organ or tissue in response to a
stimulus.
• Physiologic
• Action of hormones or growth factors when there is a need to increase
functional capacity of hormone sensitive organs, or when there is
need for compensatory increase after damage or resection.
• Pathologic
• Most forms of pathologic hyperplasia are caused by excessive or
inappropriate actions of hormones or growth factors acting on target
cells
Examples of physiological hyperplasia
• Hyperplasia of bone marrow cells
- Red blood cells: growth factor erythropoietin
• Lymphoid hyperplasia
- Inflammation or antigenic stimulation
• Regenerative hyperplasia
- Regeneration of tissues (liver or skin)
• Hyperplasia of breast tissue
- Puberty, pregnancy and lactation: several hormones
Examples of pathologic hyperplasia
• Thyroid Hyperplasia
- Increased thyroid stimulating hormone: anterior pituitary
• Endometrial hyperplasia
- Occurs in post menopausal women with increased oestrogen
- Predisposes to malignant tumours of the endometrium
• Prostatic hyperplasia
- Hyperplasia of the stromal & epithelial components of the prostate.
- Prostatic glands increase in size & have a nodular surface.
- Caused by an imbalance between androgens and oestrogens
Atrophy
• Reduction in the size of an organ or tissue due to a decrease in cell size and
number
- Physiologic
- Embryonic structures – Notochord, thyro-glossal duct,
- Uterus post-partum
- Pathologic
- Disuse atrophy
- Denervation atrophy
- Diminished blood supply
- Inadequate nutrition
- Loss of endocrine stimulation
- Pressure.
Physiologic atrophy
- Is common during normal development.
- Embryonic structures: notochord & thyroglossal duct
- Size of the uterus after parturition
- Thymus undergoes physiologic atrophy at puberty
- As one ages the organs & tissues decrease in size: senile atrophy
Pathological atrophy
- Localised/generalised
- Occurs in the following conditions
Decreased workload (atrophy of disuse).
• Reduced functional activity
- Results in a diminished demand for nutrition causing cell atrophy.
- E.g. an immobilised arm post fracture.
- Usually reversible when activity is restored
• Loss of innervation (denervation atrophy)
- Destruction to nerves:paralysis and wasting atrophy
- Poliomyelitis
• Diminished Blood Supply
- Reduction of the oxygen and nutrient supply to cells.
- A fall in cell activity occurs; cell shrinkage.
- Narrowing of coronary arteries; myocardial atrophy
• Pressure atrophy
- Interruption of the blood supply & interference with function
- A neoplasm pressing on surrounding structures
Infections;
- Thymus atrophy before puberty due to infections
• Loss of endocrine stimulation
- Reduced metabolic activity in dependent tissues
- Pituitary deficiency: atrophy of the thyroid and adrenals
cerebral atrophy
• Gyri are narrowed and the intervening sulci are widened
Metaplasia
• Reversible change in which one differentiated cell type is replaced by
another differentiated cell type.
• Epithelial
• Columnar to squamous epithelium – lung
• Squamous to columnar epithelium – Oesophagus
• Connective tissue metaplasia
Squamous metaplasia
- Most common type of metaplasia.
- Important sites: bronchus, endocervix and the urinary bladder
Bronchus
• Lined by pseudostratified columnar ciliated epithelium.
• Squamous metaplasia occurs when there is chronic irritation by
cigarette smoke or chronic inflammation caused by bronchitis.
• There is loss of the protective mechanism against infection
Endocervix
• Squamous metaplasia: transformation zone.
• Commonly caused by infection with Human papilloma virus (HPV)
• Can lead to cervical cancer
Bladder
• The transitional epithelium of the bladder undergoes squamous metaplasia
• Chronic irritation by schistosomiasis, chronic cystitis and bladder calculi
Intestinal metaplasia
Intestinal metaplasia
• In the stomach intestinal metaplasia occurs as a result of chronic
gastritis or chronic peptic ulceration
Connective tissue metaplasia
• Is the formation of cartilage, bone, or adipose tissue (mesenchymal
tissues) in tissues that normally do not contain these elements
• For example, bone formation in muscle; myositis ossificans,
occasionally occurs after intramuscular hemorrhage.
• Less clearly seen as an adaptive response, and may be a result of cell
or tissue injury
Dysplasia
- Disorderly growth pattern
* Covered in neoplasia
