Session 7 ILOs - Cellular Adaptation Flashcards
Understand and describe the principles of the cell cycle
When a cell receives an instruction to divide, the cell enters the cell cycle (G1->S->G2->M).
After cell cycle completion, the cell either re-starts the process from G1 or exits (G0) until further growth signals occur.
M phase (mitosis and cytokinesis) Interphase (other phases!)
Cell proliferation is controlled by:
- Proto-oncogenes and tumour supressor genes
- Chemical mediators/signals from the local environment
- Signalling molecules binding to a receptor leading to modulation of gene expression
Main check points:
1. Restriction point - p53 (most critical = guardian of the genome)
- end of G1
- either triggers DNA repair mechanisms or apoptosis via p53
PLUS Cyclins and cyclin-dependent kinases - phosphorylate other proteins (downstream events)
- e.g. phosphorylation of the retinoblastoma gene by cyclin D/CDK4 (normally bound to a complex that prevents proliferation), so free to proliferated once phosphorylated
Increase cell growth:
- Cyclins and cyclin-dependent kinases
- Proto-oncogenes
- Growth factors
Inhibit cell growth:
- Cyclin-dependent kinase inhibitors
- Tumour supressor genes (e.g. P53 and retinoblastoma gene)
Explain and define: Hyperplasia
Give an example related to the human body (physiological and pathological)
Hyperplasia = increased cell numbers leading to increase in tissue or organ size
- In response to increased functional demand and/or external stimulation
- Only occurs in labile or stable cell populations and it remains under physiological control and is reversible
- Risk of neoplasia with hyperplasia!
Physiological:
- Increased bone marrow production of erythrocytes in response to hypoxia and the resulting increased erythropoietin
- Proliferation of the endometrium under the influence of oestrogen
Pathological:
- Epidermal thickening in chronic eczema or psoriasis
- Enlargement of the thyroid gland in response to iodine deficiency
Explain and define: Hypertrophy
Give an example related to the human body (physiological and pathological)
Hypertrophy = increase in cell size leading to an increase tissue or organ size (without an increase in cell numbers)
- Can occur in many tissues but it is seen especially in permanent cell populations
Physiological:
- Skeletal muscle hypertrophy of a bodybuilder
- Smooth muscle hypertrophy of a pregnant uterus (which also involves hyperplasia)
Pathological:
- Ventricular cardiac muscle hypertrophy in response to hypertension or valvular disease
- Bladder smooth muscle hypertrophy with bladder obstruction due to an enlarged prostate gland
Explain and define: Atrophy
Give an example related to the human body (physiological and pathological)
Atrophy = Decrease in size AND/OR number of cells, leading to shrinkage of a tissue or organ
- Cellular atrophy is a decrease in cell size
- Organ/tissue atrophy is typically due to a combination of cellular atrophy and apoptosis
- Can be caused by a reduced supply of growth factors and/or nutrients
- More often linked with disease (best treated by removal of the cause)
Physiological:
- Ovarian atrophy in post- menopausal women
- Decrease in size of the uterus after parturition
Pathological:
- Inadequate nutrition
- Aging (senile atrophy)
Explain and define: Metaplasia
Give an example related to the human body (physiological and pathological)
Metaplasia = reversible replacement of one adult differentiated cell type by another of a different type
- There is no proven metaplasia across germ layers (e.g., bone to nerve) or from a connective tissue (mesenchyme) to epithelium
- Only occurs in cell populations that can replicate, it is not known to occur in adult striated muscle cells or in neurones
Physiological:
- With bone marrow destroyed by disease, splenic tissue undergoes metaplasia to bone marrow (myeloid metaplasia)
- Columnar epithelium lining ducts such as those of salivary glands, pancreas, bile ducts or the renal pelvis can change to stratified squamous epithelium secondary to chronic irritation by stones
Pathological:
- Transformation of bronchial pseudostratified ciliated columnar epithelium to stratified squamous epithelium due to the effect of cigarette smoke
Explain and define: Aplasia
Give an example related to the human body
Aplasia = complete failure of a specific tissue or organ to develop (embryological)
e.g. Thymic aplasia (infection and autoimmune problems) or kidney aplasia
Explain and define: Hypoplasia
Give an example related to the human body
Hypoplasia = the congenital underdevelopment or incomplete development of a tissue or organ (embryological)
e.g. Renal hypoplasia or breast hypoplasia
Explain and define: Involution
Give an example related to the human body
Involution = Normal programmed shrinkage of an organ (overlaps with atrophy)
e.g. uterus after childbirth and thymus in early life
Explain and define: Atresia
Give an example related to the human body
Atresia = ‘no orifice’, the congenital imperforation of an opening
e.g. atresia of the anus or vagina
Explain and define: Reconstitution
Give an example related to the human body
Reconstitution = regeneration in that it is the replacement of a lost part of the body rather than a small group of cells
ONLY REALLY HAPPENS IN OTHER MAMMALS
Explain and define: Dysplasia
Give an example related to the human body
Dysplasia = the abnormal maturation of cells within a tissue
- Potentially reversible but is often a pre-cancerous condition
e.g. in cancer conditions
