MoD Cell adaptations Flashcards
What are the 5 types of cell adaptation?
- Regeneration
- Hyperplasia
- Hypertrophy
- Atrophy
- Metaplasia
Define regeneration
Which tissues can undergo regeneration and which can’t?
Replacement of cell losses by identical cells to maintain tissue or organ size
Epidermis and liver have good capacity, whereas tendons and melanocytes have poor capacity
Define Hyperplasia
Which tissues can undergo hyperplasia and which can’t?
Increased in tissue or organ size due to increased cell numbers
Only labile and stable cell populations can undergo hyperplasia (reversible)
What are some physiological and pathological examples of hyperplasia?
Physiological:
Endometrium proliferates under the influence of oestrogen
Bone marrow produces rbc in response to hypoxia (e.g. at high altitudes)
Pathological:
Skin in psoriasis
Thyroid goitre in iodine deficiency
Define hypertrophy
Which tissues can undergo hypertrophy?
Increase in tissue or organ size due to increased cell size
Hypertrophy happens in many tissues but especially PERMANENT cell populations (they can’t undergo hyperplasia so hypertrophy is the only way to increase in size)
Caused by functional demand or hormone stimulation
What are some physiological and pathological examples of hypertrophy?
Physiological
Skeletal muscle in bodybuilding
Pregnant uterus (+hyperplasia)
Pathological
Right ventricular hypertrophy in pulmonary embolism
Urinary bladder hypertrophy due to enlarged prostate
What is compensatory hypertrophy?
Occurs when there is an increased work load e.g. when one kidney is absent or dysfunctional the other kidney enlarges to compensate
Define atrophy
What are some physiological and pathological examples of atrophy?
Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells
Physiological
Ovarian atrophy post menopausal
Pathological
Muscle atrophy of disuse
Wasted hand muscles after median nerve injury
Cerebral atrophy (alzheimers)
Define metaplasia
Why does it occur?
Reversible change of one differentiated cell type to another
Metaplasia is an adaptive response in epithelial tissues- substitutes sensitive cells to ones able to withstand more adverse environments.
No metaplasia across germ layers, and only occurs in cells that can replicate.
Give some examples of metaplasia?
Barrett’s oesophagus: persistent acid reflux causes stratified squamous epithelium to turn to gastric glandular epithelium (risk for carcinoma)
Cigarette smoke: bronchial pseudostratified ciliated epithelium turns to stratified squamous epithelium
Define hypoplasia and give examples
Underdevelopment or incomplete development of a tissue/organ at the embryonic stage
e.g. kidneys, heart chambers
Define aplasia and give examples
Complete failure of a specific organ or tissue to develop (embryonic disorder)
e.g. thymic aplasia which results in infections and auto-immune problems
Define involution and give examples
Normal programmed shrinkage of an organ
e.g. the uterus after child birth
Define atresia and give examples
A condition where an opening or passage is abnormally narrowed or absent
e.g. anal opening not present
Define dysplasia and give examples
Abnormal growth and development of cells
e.g. abnormal cells present in cervix
Define reconstitution and give examples
Replacement of a lost part of the body
There is no real reconstitution in adults, the closest is that small capillaries can reconstitute in the uterine lining
What are the four types of cell signalling?
Intracrine: nothing released, everything stays in cytoplasm
Autocrine: exerts effect on itself
Paracrine: exerts effect on nearby cell
Endocrine: travels in bloodstream to distant target
What is the role of growth factors?
They are local mediators involved in cell proliferation
Act on cell surface receptors
Coded by photo-oncogenes
they stimulate transcription of genes that regulate entry of the cell into and though the cell cycle
What is the role of epidermal growth factor
Mitogenic for epithelia cells, fibroblasts and hepatocytes
What is the role of vascular endothelial growth factor?
Development of new blood vessels
What is the role of platelet derived growth factor?
Development of new blood vessels, mitogenic for fibroblasts, smooth muscle cells and glial cells.
What is the role of granulocyte colony-stimulating factor?
Stimulates bone marrow, can be given as a medication to patients to increase neutrophil count
Which phase of the cell cycle is visible under the light microscope?
The M phase (mitosis and cytokinesis)
What are the phases of the cell cycle?
G1 –> S –> G2 –> M
G1 gap 1 - pre synthetic, cell grows
S - DNA synthesis
G2 gap 2 - permitted, cell prepares to divide
Where are the two important check points in the cell cycle?
The RESTRICTION (R) POINT checkpoint just before S phase is the most critical checkpoint, point of no return
Checkpoint activation delays cell cycle - triggers DNA repair or apoptosis via p53 gene
(is the cell big enough, is DNA damaged?)
The G2 checkpoint just before M phase
(Is the cell big enough, is all DNA replicated?)
Describe the control of the cell cycle
Cyclins (proteins) and CDK’s (enzymes)
Cyclin binds to the substrate (RB protein)
Cyclin activates CDK enzyme
CDK enzyme phosphorylates the RB protein which drives the cell to the next phase of the cycle
The cyclin-CDK complexes are tightly regulated by CDK inhibitors.
