Cellular adaptations Flashcards
Briefly describe cell communication and signalling
Final outcomes of signalling are limited to: divide, differentiate, survive (resist apoptosis) or die (undergo apoptosis).
Autocrine - cells respond to the signalling molecules that they themselves produce.
Intracrine - type of autocrine signal which binds to an intracellular receptor
Paracrine - signalling molecule which acts on adjacent cells. Usually a different type of cell.
Endocrine - hormones synthesised by an endocrine organ.
Outline the role of growth factors
They only act over short distances so can be considered as local hormones. They stimulate cell proliferation or inhibition, but may also influence cell locomotion, contractility, differentiation, viability activation or angiogenesis. They bind to specific receptors and stimulate transcription of genes that regulate the entry of the cell into the cell cycle and the cell’s passage through it.
Outline the cell cycle
Cell cycle: G1-S (DNA synthesis)-G2-M (mitosis)+/- G0, in which the cell arrests. Here it may also go into terminal differentiation.
Checkpoints:
R phase at end of G1: restriction point, most critical checkpoint. Cells which pass this phase go on to divide. May activate p53 protein which suspends cell cycle ad initiates DNA repair or apoptosis,
Outline the cell cycle
Cell cycle: G1-S (DNA synthesis)-G2-M (mitosis)+/- G0, in which the cell arrests. Here it may also go into terminal differentiation.
Checkpoints:
R phase at end of G1: restriction point, most critical checkpoint. Cells which pass this phase go on to divide. May activate p53 protein which suspends cell cycle and initiates DNA repair or apoptosis.
G1/S: checks DNA before replication
G2/M: checks DNA after replication
Defective cell cycle checkpoints are a major cause of genetic instability in cancer cells.
Outline the cell cycle and the checkpoints
Cell cycle: G1-S (DNA synthesis)-G2-M (mitosis)+/- G0, in which the cell arrests. Here it may also go into terminal differentiation.
Checkpoints:
R phase at end of G1: restriction point, most critical checkpoint. Cells which pass this phase go on to divide. May activate p53 protein which suspends cell cycle and initiates DNA repair or apoptosis.
G1/S: checks DNA before replication
G2/M: checks DNA after replication
Defective cell cycle checkpoints are a major cause of genetic instability in cancer cells.
How is the cell cycle controlled?
progression through the cycle is tightly regulated by proteins called cyclin-dependent-kinases (CDK). They become active by binding to cyclins and phosphorylating proteins that are critical for cell cycle progression.
What are labile, permanent and stable cells? give examples of each
Labile cells: continue to multiply throughout life e.g. epithelium or bone marrow
Stable cells: can multiply in a regenerative burst but are usually quiescent e.g. liver and kidney.
Permanent: cells which cannot proliferate, e.g. myocytes
Define and explain which tissues can go through regeneration
Labile and permanent cells can go through regeneration. This is because they are already in the cell cycle, or can be induced into the cell cycle to undergo mitosis and synthesis the necessary cell machinery such as ribosomes.
Define and explain which tissues can go through regeneration
regeneration is the replacement of old or damaged cells with new cells to maintain the cell population. It can be a physiological process such as the replacement of RBC after 120 days, or it can be pathological, often persistent and heals with a scar.
Usually regains full morphology and function although this can take months or years to reach.
May infer benefit, e.g. influenza virus cannot attack new pneumocytes as they haven’t yet regenerated the right receptors for the virus to use.
Define and explain which tissues can go through regeneration
regeneration is the replacement of old or damaged cells with new cells to maintain the cell population. It can be a physiological process such as the replacement of RBC after 120 days, or it can be pathological, often persistent and heals with a scar.
Usually regains full morphology and function although this can take months or years to reach.
May infer benefit, e.g. influenza virus cannot attack new pneumocytes as they haven’t yet regenerated the right receptors for the virus to use.
Cells can regenerate many times dependent on telomere length. This is referred to as the Hayfick number
Define and explain which tissues can go through regeneration
regeneration is the replacement of old or damaged cells with new cells to maintain the cell population. It can be a physiological process such as the replacement of RBC after 120 days, or it can be pathological, often persistent and heals with a scar.
Usually regains full morphology and function although this can take months or years to reach.
May infer benefit, e.g. influenza virus cannot attack new pneumocytes as they haven’t yet regenerated the right receptors for the virus to use.
Cells can regenerate many times dependent on telomere length. This is referred to as the Hayflick number
What is hyperplasia and give some physiological and pathological examples
Increase in cell or tissue size due to increase in cell numbers. It is a response to increased functional demand or external stimulation but can ONLY occur in labile and stable cell populations. It differs to regeneration as the net tissue size increases.
Physiological hyperplasia occurs through hormonal stimulation or as a result of tissue damage, whereas pathological occurs as a result to excessive stimulation such as thickened epidermis in chronic eczema or enlarged thyroid as a result of iodine deficiency.
Define reconstitution
Reconstitution is the replacement of a lost part of the body. It requires the coordinated regeneration of several types of cells. This is a limited process and few things can be reconstituted i.e. small blood vessels and tips of fingers if
What is hypertrophy? give some physiological and pathological examples
An increase in tissue or organ size due to an increase in cell size without an increase in cell number. Cells become bigger because they contain more structural components and it usually occurs in permanent cell populations as they have no or little replicative ability.
stimulation can either be hormonal or external. Physiological examples include body builders muscle bulk whereas a pathological example may include ventricular/ cardiac hypertrophy.
note: once you develop adipocytes, they can never be removed!
What is compensatory hyperplasia?
Compensatory hyperplasia occurs when there is an increased demand placed on one organ, e.g. having a kidney removed puts all of the workload on only one kidney, hence it undergoes hypertrophy and hyperplasia.
