Lecture 25 Flashcards
What is morphogenesis?
The formation of shape and organisation of organs involving co-ordinated growth, differentiation and destruction
What occurs to growth and differentiation in adult life?
Cells undergo a constant cycle of death replacement and growth impacted by both physiological and pathological stimuli, these can be positive or negative impacts
What is multiplicative growth?
Increases in cell number via mitotic division
What is auxetic growth?
Increased size of individual cells
What is accretionary growth?
Increase in extracellular tissue in-between cells
What type of growth occurs in the embryo?
A combination of growth patterns therefore it is termed ‘combined pattern’
What determines growth rate? and how does this change with age?
Balance between cell proliferation and cell death
In fetal development growth is rapid with apoptosis playing a key role in morphogenesis
Adult cell replication is slower and usually due to the need to regenerate or replace damaged cells
What is an oligopotent stem cell? And what are some examples?
A stem cell able to differentiate into a small number of cell types
examples include skin keratinocytes, bone marrow hematopoietic system and the gastrointestinal epithelium
What are liable cells?
Cells that divide and proliferate continuously and are very sensitive to toxic injury
What are stable cells?
Cells that divide infrequently under normal conditions as they have been arrested in the G0 phase of the cell cycle
What are examples of stable cells?
Fibroblasts of connective tissue
Endothelial cells of blood vessels
Parenchymal cells of most organs
Melanocytes of epithelium
What are the adaptive responses of cells with regards to cell growth and differentiation?
Atrophy, Hypertrophy, Hyperplasia, Metaplasia
What is atrophy?
Decrease from normal size by either change in cell size or cell number which is associated with a diminished functional ability
What are the different types of atrophy?
Physiological atrophy which occurs during aging (reduction of endometrium post-menopause)
Nutritional Atrophy, loss of blood supply or starvation may result in loss of fat and muscle tissue
Disuse atrophy decreased amount of tissue due to loss of use eg muscles during limbe fracture
What is the difference between atrophy and hypoplasia?
Hypoplaisa is failur of a tissue to initially develop to a normal size
While Atrophy is a reduction from an initial size
What is the difference between hyperplasia and hypertrophy?
Hyperplasia is increase in cell number while hypertrophy is an increase in cell size
Hyperplasia is usually seen in conjunction in hypertrophy, though hypertrophy maybe seen on its own as it is the only option for permanent tissues
Hypertrophy is a more risky option as increasing DNA content without mitosis may cause polyploidy
What is an example of hypertrophy seen in disease?
Cadiac hypertrophy where the ventricle wall thickens
What are the two methods via which hyperplasia can be produced?
Increase in cell replication or a decrease in the level of cell apoptosis
Where does normal hyperplasia occur?
The erythropoietic system where red blood cell number increases with altitude
How can hyperplasia contribute to disease processes?
Proliferation of myofibroblasts in scar tissues and regeneration of parenchymal tissue
Or in endometrial hyperplasia where there is an abnormal increase in the amount of endometrial glandular cells
What is metaplasia?
When a cell changes its differentiation, this typically occurs in response to either genetically inherited features or interactions of the environment with the genes of the cell
This is a reversible process
Why might metaplasia be an advantage?
It allows the cell to adapt to changes in the environment by changing which genes it expresses to deal with the scenario
What are the two common types of metaplasia?
Squamous where the cell changes from a complex structure to a more simplistic structure
Glandular where a complex cell structure changes to a another complex cell structure
What are examples of altered cell expression as a consequence of addition of chromosomes?
Down's Syndrome where there is mental delay abnormalities of the face, ears, pelvis Klinefelters syndrome (extra X chromosome) associated with testicular hypoplasia, absence of spermatogenesis, gynaecomastia and mental delay
What single gene defects cause altered cell expression?
Many inherited genes, occasionally novel mutations but uncommon
Deficiency of phenylalanine hydroxylase causes mental delay as phenylalanine will accumulate (mutation in PAH)
Mutation in CFTR leads to cystic fibrosis
What is the payoff of the metaplasia induced by barretts oesphagus?
While the columnar epithelium is better at coping with the constant acid reflux of the stomach it has lost the protective keratin layer
What is trans-differentiation?
Change from one cell type to another, this a reversible process which is adaptive, protective and a normal physiological function
What is dysplasia?
abnormal alteration is size, shape and organization of the cellular components of a tissue
What are the results of dysplasia?
Premalignant condition which is reversible if the stimulus is removed from early/mild conditions
if the dysplasia is severe however then there will be progression to a neoplasm
What are the features of dysplasia?
increased growth, atypical cells and altered differentiation this allows for a window of screening before dysplasia becomes neoplastic
What is a neoplasia?
Abnormal tissue mass with excessive growth and disordered differentiation which is unco-ordinated with normal tissue
What are the characteristics of neoplasms?
Loss of specialized functions, acquisition of new properties like uncontrolled growth
Lack of feedback mechanisms
Only stop growing due to a lack of nutrients
What do neoplasms arise from?
A single cell which has undergone neoplastic transformation
