Cellular Adaptations Flashcards
What are the four outcomes of cellular signalling?
Survive - i.e. resists apoptosis
Divide - i.e. enters cell cycle
Differentiate - i.e. takes on specialised form and function
Die - i.e. undergoes apoptosis
What factors affect cell population size?
Rate of cell proliferation
Rate of cell differentiation
Rate of apoptosis
How does cellular signalling work?
Signalling occurs through binding of a signalling molecule to a receptor either on the cell surface or within the cell
This binding causes a change to gene expression
Through what methods can cell signalling occur?
Hormones
Local mediators
Direct cell-cell contact
What are the three types of cellular signalling?
Autocrine - cell produces a signal that it itself responds to
Paracrine - cell produces a signal that acts on a neighbouring cell
Endocrine - cell produces a hormone that travel through circulation to target cell
What are growth hormones?
Local mediators involved in cell proliferation
The stimulate the transcription of genes that regulate entry of cells into the cell cycle
Act on specific cell surface receptors
Coded for by proto-oncogenes
What do growth hormones affect?
Cell proliferation and inhibiton Locomotion Contractility Differentiation Viability Activation Angiogenesis
Name some growth hormones/factors
Epidermal growth factor
Vascular derived growth factor
Platelet derived growth factor
Granulocyte-colony stimulating factor
What are the stages of the cell cycle?
G1-S-G2-M
From G1 can go to G0 and then to terminal differentiation
How can you increase proliferation?
Shortening the cell cycle
Conversion of quiescent cells to proliferating cells
What are the two checkpoints in the cell cycle?
At the end of G1
At the end of G2
Checkpoints are activated by the p53 protein
What is the restriction point?
The checkpoint after G1
It very critical and the most commonly altered in cancerous cells
How is the cell cycle controlled?
By cyclins and cyclin-dependent kinases
They form a complex which phosphorylate proteins that are needed for progression to the next stage of the cell cycle
Define Labile cell populations and give examples
Divide persistently
e.g. Surface epithelia and bone marrow
Define Stable cell populations and give examples
Normally quiescent but proliferate persistently when required
e.g. liver hepatocytes and bone osteoclasts
Define permanent cell populations and give examples
Can’t proliferate
e.g. brain neurones and cardiac and skeletal muscle
Describe asymmetric replication
When a stem cell replicates one daughter cell remains a stem cell while the other differentiates into a mature, non-dividing cell
Define regeneration
Replacement of cell loses by identical cells to maintain tissue or organ size
Different tissues have different regeneration capacities
Give examples of when regeneration occurs
In the liver after a partial hepatectomy
Replacement of the epidermis of the skin after a burn
How do neurones regenerate?
They don’t, instead they undergo plasticity in which the brain develops alternative pathways
What is the Hayflick number?
It is the average number of times a cell can regenerate, in humans this number is 61.3
What is reconstitution?
The replacement of a lost part of the body through regeneration of several cell types
Define hyperplasia
Increase in tissue or organ size due to increase cell numbers
Only occurs in liable or stable cell populations
Give some physiological examples of hyperplasia
Proliferation of endometrium under influence of oestrogen
Bone marrow produces erythrocytes in hypoxia
Give some pathological examples of hyperplasia
Epidermal thickening in chronic eczema or psoriasis
Thyroid goitre in iodine deficiency
Define Hypertrophy
Increase in tissue or organ size due to increased cell size
Mostly occurs in permanent cell populations
Give some physiological examples of hypertrophy
Skeletal muscle hypertrophy of body builders
Smooth muscle hypertrophy of a pregnant uterus
Give some pathological examples of hypertrophy
Ventricular smooth muscle hypertrophy in response to systemic hypertension or valvular disease
Bladder smooth muscle hypertrophy with bladder constriction due to an enlarged prostrate
What is compensatory hypertrophy?
e.g. when you remove one kidney the other enlarges by hypertrophy and hyperplasia to compensate
Define atrophy
The shrinkage of a tissue or an organ due to an acquired decrease in size and/or number of cells
The cell can survive but it has fewer cellular components and reduced function
Give some physiological examples of atrophy
Ovarian atrophy in post menopausal women
Decrease in the size of the uterus after parturition
Give some pathological examples of atrophy
Atrophy of disuse - reduced functional demand/workload
Denervation atrophy - loss of innervation
Inadequate blood supply
Inadequate nutrition
Aging
Loss of endocrine stimuli
Define metaplasia
Reversible change of one differentiated cell to another
Most commonly happens in epithelial tissue
Give examples of when metaplasia happens
Cigarrete smoke - pseudostratified epithelium of the bronchi become stratified squamous epithelium
Persistent acid reflux - stratifies squamous epithelium of gut becomes gastric-type epithelium
Chronic irritation by stones - columnar epithelium lining ducts becomes stratified squamous epithelium
Define hypoplasia
Underdevelopment or incomplete development of a tissue or organ at the embryonic stage
Define aplasia
Complete failure of a specific tissue or organ to develop
Define dysplasia
Abnormal maturation of cells within a tissue
Define atresia
Absence or abnormal narrowing of an opening or passage in the body
Define involution
Normal programmed shrinkage of an organ
