Cell Adaptations Flashcards
What does the size of a cell population in adults depend on?
Rate of proliferation
Rate of differentiation
Rate of cell death
What are the possible outcomes of signalling?
Divide (enter the cell cycle)
Die (apoptosis)
Differentiate
Survive (resist apoptosis)
What is autocrine signalling?
When the cell responds to the signal that itself produces
What is paracrine signalling?
A cell produces a signalling molecule which acts on adjacent cells.
What is endocrine signalling?
When a hormone is produced by an endocrine organ and this is converted in the blood stream to target cells.
What modes of cell to cell signalling are there?
Hormones
Direct cell-cell or cell-stroma contact
Local mediators
What do growth factors affect?
Proliferation Cell locomotion Contractility Differentiation Angiogenesis
Mechanism of action for growth factors?
Bind to receptors and stimulate the transcription of genes that regulate the entry of the cell into the cell cycle and the cell’s passage through it.
Epidermal growth factor
- produced by?
- cells it acts on?
- receptor?
- what it does
Produced by macrophages, keratinocytes, inflammatory cells
Acts on epithelial cells, hepatocytes, fibroblasts
Binds to epidermal growth factor receptor
Mitogenic for the above cells
What does vascular endothelial growth factor do? Which situations?
Induces blood vessel development (vasculogenesis) and blood vessel growth (angiogenesis)
Works in tumours, wound healing and chronic inflammation
What is platelet-derived growth factor produced by?
Stored in alpha granules in platelets. Released on platelet activation. Also produced by macrophages, endothelial cells, smooth muscle cells and tumour cells.
What does platelet-derived growth factor do?
Causes migration and proliferation of fibroblasts, smooth muscle cells and monocytes.
Phases of the cell cycle?
G1 - S - G2 - M
What is interphase?
Contains the stages G1, S and G2
What happens in G1?
Cell growth
What happens in S?
DNA is replicated
What happens in G2?
Cell prepares to divide
When are the different check-points?
R - towards the end of G1
G1/S
G2/M
What happens at the G1/S checkpoint?
Checks DNA damage before DNA replication
What happens at the G2/M checkpoint?
Checks DNA damage after DNA replication
What happens if there is something wrong at the checkpoint?
p53 protein delays the cell cycle and triggers DNA repair mechanisms or apoptosis if DNA cannot be repaired.
What regulates progression through the cell cycle?
Cyclin proteins
Cyclin-dependent kinases (enzymes)
What does labile mean? Example?
Stem cells divide persistently to replenish losses
Surface epithelial such as epidermis, gut epithelium and bone marrow cells
What stage of the cell cycle are stable cells in?
G0
What does stable mean?
Cells which are in G0 but can enter G1 by activation of a large number of genes such as proto-oncogenes
Examples of stable cells?
Hepatocytes Bone osteoclasts Fibroblasts Vascular endothelial cells Smooth muscle cells
Examples of permanent cell populations?
Cardiac and skeletal muscle
Brain neurones
What are permanent cell populations?
Stem cells cannot mount an effective, proliferative response to significant cell loss. The mature cells have left the cell cycle and cannot replicate.
What replaces neurones if they are destroyed?
Glial cells
What is asymmetric replication?
When stem cells divide, they produce two daughter cells
- one a stem cell
- one differentiates into a mature, non-dividing cell
What is cell adaptation?
The state between a normal, unstressed cell and an injured, overstressed cell
What is regeneration?
The replacement of cell losses by identical cells in order to maintain the size of a tissue or organ
Under what conditions can regeneration and resolution not occur?
If the harmful agent persists
If there is extensive tissue damage
If the tissue damaged is permanent tissue
Give two examples of when regeneration is seen
In the liver after a hepatectomy
In the epidermis by keratinocytes after a burn
What is hyperplasia?
Increase in tissue or organ size due to an increase in cell numbers
In which types of populations can hyperplasia occur in?
Labile and stable cell populations
Two types of physiological hyperplasia?
Hormonal - increase in function capacity
Compensatory - increase in tissue mass after tissue damage
Examples of physiological hyperplasia?
Increased production of erythrocytes in bone marrow due to low oxygen content of blood
Proliferation of endometrium under influence of oestrogen
Examples of pathological hyperplasia?
Epidermal thickening in eczema and psoriasis
Enlargement of the thyroid gland in response to iodine deficiency
What is hypertrophy?
Increase in organ/tissue size due to an increase in cell size, not cell number!
What makes the cells bigger in hypertrophy?
More structural components
What is hypertrophy done in response to?
Increased functional demand
Hormones
Examples of physiological hypertrophy?
Skeletal muscle - body builders
Smooth muscle in a pregnant uterus
Examples of pathological hypertrophy?
Ventricular cardiac muscle hypertrophy
What is atrophy?
Shrinkage of a tissue/organ due to an decrease in cell size/number.
What is atrophy due to?
A decrease in supply of growth factor/nutrients
Example of physiological atrophy?
Ovarian atrophy in post-menopausal women
Decrease in size of uterus after parturition
Causes of pathological atrophy?
Denervation Disuse Inadequate blood supply Inadequate nutrition Loss of endocrine stimulation Persistent injury Ageing Pressure
What is metaplasia?
The reversible change of one differentiated cell type to another
Examples of metaplasia?
Bronchial pseudostratified columnar epithelium to stratified squamous in the lung from cigarette smoke
Change of oesophageal stratified squamous to gastric-type epithelium with persistent acid reflux
What is aplasia?
The complete failure of a tissue/organ to develop
It is an embryonic developmental disorder
What is hypoplasia?
The under development or incomplete development of a tissue/organ
What is dysplasia?
The abnormal maturation of cells within tissues
How do CDKs drive the cell cycle?
Phosphorylate proteins that are critical for the progression of the cell into the next stage of the cycle
