Flashcards in MoD 8 Cellular Adaptations Deck (22):
What is the most critical checkpoint in the cell cycle?
Restriction (R) point towards end of G1
What different methods of cell signalling are there?
Autocrine- cell reponds to signalling molecules its made itself
Paracrine- cell produces signalling molecule that acts on ajacent cells which are often a different type
Endocrine- response to hormones
What happens is G1?
What happens in S?
What happens in G2?
cell prepares to divide
What happens at R?
Cell is checked for damage, passage governed by phosphorylation of Retinoblastoma protein pRB
p53 acts here to delay cell cycle, trigger reparative mechanisms or apoptosis if DNA cant be repaired
How does pRB regulate R?
cyclin dependent kinases bind to cyclins, activating them and these phosphorylate rPB which allows cycle to continue
What are labile cells?
e.g epithelial or haematopoeitic
normal state active cell division
usually rapid proliferation
What are stable cells?
e.g hepatocytes, osteoblasts, fibroblasts
resting state- G0
Variable regeneration speed
What are permanent cells?
e.g neurones, cardiac mycocytes
unable to divide G0
unable to regenerate
What do stem cells do in labile cell populations?
Divide persistently to replenish losses
What do stem cells so in stable cell populations?
Normally quiescent(dormant) or proliferate very slowly
proliferate persistently when required
What do stem cells do in permanent cell populations?
Present but can't mount an effective proliferative response to significant cell loss (none present in cardiac muscle
What is regeneration?
Replacement of cell losses by identical cells to maintain tissue or organ size
What is hyperplasia?
Increase in tissue or organ size due to increased cell numbers
Can only occur in labile and stable populations
Physiological- proliferative endometrium
bone marrow at altitude
Pathological- thyroid goitre
What is hypertrophy?
Increase in tissue or organ size due to increased cell size
Permanent cells cant divide so increase in size
In cells that can divide may occur alongside hyperplasia
Physiological- skeletal muscle
pregnant uterus (hyperplasia and hypertrophy)
Pathological- ventricular cardiac muscle hypertrophy
Bladder smooth muscle hypertrophy
What is atrophy?
Shrinkage of tissue or organ due to decrease in size and/or number of cells
Organ/tissue atrophy typically due to a combo of atrophy and apoptosis
Physiological- ovarian atrophy postmenopause
Pathological- Muscle atrophy (denervation)
Cerebral atrophy (alzheimer's)
What is metaplasia?
Reversible change of one differentiated cell type to another
change in epithelium to be more suited to new environment
e.g smoker pseudostratified ciliated->squamous (robust)
sometimes prelude to dysplasia and cancer
What is aplasia?
complete failure of a specific tissue or organ to develop
What is hypoplasia?
Incomplete development of a tissue or organ
What is dsyplasia?
Abnormal maturation of cells within a tissue