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Define Agenesis

No primordium i.e. there is no development of a structure
Is a congenital problem


Define Aplasia

A structures rudiment is present i.e. starts developing, then stops
Is a congenital problem


Define Hypoplasia

Lack of development to full size
Is a congenital problem


Are atrophy, hypertrophy and hyperplasia quantitative or qualitative adaptive responses?

Quantitative - there is a change in size or number of cells


Define atrophy

A structure was a normal size, but is now reduced in either size or number or cells


Define hypertrophy

Was normal, is now reversibly increased in size because of an increase in SIZE of component cells


Define hyperplasia

Was normal, is now reversibly increased in size because of an increase in NUMBER of cells


Which stage of the cell cycle is altered in hypertrophy?

Cells remain in the RNA/protein synthesis stage, inhibiting DNA synthesis and causing cell enlargement without division


Which stage of the cell cycle is altered in hyperplasia?

More cells pass through mitosis because of a block in the pathway to G0


What are some consequences of starvation?

Generalised atrophy, with replicating cells the most affected aka liver, spleen and skeletal muscles.


What are some causes of localised atrophy?

Ischaemia, pressure, disuse, denervation, reduced blood supply


Give an example of localised atrophy?

If a salivary gland duct stone forms (usually because of stasis), back pressure builds up in the duct and moves back into the mucous producing cells. This causes irreversible damage, and atrophies these cells


Give an example of physiological hyperplasia

Lymph nodes will enlarge and become painful in response to infection because they develop germinal centres, which cause cellular dividing


How can thyroid hyperplasia be both physiological and pathological?

Physiological - higher concentrations of thyroxin can increase the number of follicular epithelial cells. This is usually in response to puberty or pregnancy
Pathological - Grave's disease causes an excess of hormones produces by the thyroid, necessitating hyperplasia


What happens in cardiac cells that undergo hypertrophy to meet demand?

There's an increase in synthesis of RNA, mitochondria, myofilament proteins etc. However, this can only occur up to a certain point, which is limited by blood supply, oxidative capacity of mitochondria etc. There is degenerative change after this point


Can compensatory hypertrophy occur?

Yes, usually in response to atrophy i.e. one kidney may atrophy and in response the other will undergo hypertrophy


Define metaplasia and describe the pathway by which it may occur

Metaplasia is a reversible condition in which there is a change of one type of differentiated cell to another type of differentiated cell
This usually arises via a proliferation of stem cells with transformation along a different pathway


Give an example of metaplasia in the oesophagus

This is called Barrett's oesophagus and occurs in response to acid reflux. The epithelium changes from squamous to glandular to that the skin can cope with the acid. This does cause a higher susceptibility to adenocarcinoma


What is the significance of metaplasia?

Metaplasia and neoplasia may result from the same causative agent. Metaplastic tissues provide a fertile ground for neoplasia to develop, and neoplasia can become malignant.
Metaplasia also occurs in malignancy


What are the four mechanisms of atrophy?

1. Decrease in anabolism
2. Increase in catabolism
3. Reduction in cell replication
4. Increased apoptosis


What induces metaplasia?

Changes i signals generated by a mixture of cytokines, growth factors and extracellular matrix changes

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