NORMAL CELL GROWTH
Cell growth first what tumour mean the tumour literally means swelling is either physiological or pathological ,physiological swelling eg. pregnant uterus pathological swelling eg. neoplastic or non neoplastic eg abscess inflammatory and bony callus what neoplasia means is an abnormal mass of the tissue , the growth of which is uncoordinated exceeds that of the normal tissue and persists in the same manner after cessation of the stimuli that evoked the change
Normal cell growth
Cells fall into several different categories according to their propensity to divide and
their degree of differentiations into three types of cells as
labile cells: which are constantly renewed cells (eg stratified squamous epithelium of the skin
Stable cells: usually quiescent cells but can be stimulated to divide eg hepatocytes
Permanent cells: do not undergo mitosis in post-natal life (eg neurones, skeletal muscle tissue , glomeruli . Cells divide as they progress through the cell cycle
There are many regulatory points inherent in the cycle, and disruption of these genes
results in uncontrolled replication explanation of the cell cycle first DNA structures deoyxibonucleic acid (DNA) is a strand-like molecule consisting of four building blocks adenine(A) thymine (T) cytosine (C), and guanine (G). These are paired (A with T and C with G and their affiliation for each other zips the two strands of DNA into the double helix DNA is stored in the cellular nucleus as a folded form called chromatin. This is wrapped around proteins called histones to form complexes called nucleosomes (that look like a bead .on a string). Active genes unwrap from the histones opening out the DNA for access tarnscriptional proteins
When the cell divides, the nucleosomes become very tightly folded condensing into chromosomes. the nucleus of most human cells contains two sets of chromosomes,one set given by each parent.: Each set has 23 single chromosomes, 22 autosomes, and a sex chromosome (X orY),there are therefore 46 chromosomes in each cell
what are the phases of the cell cycle
Cell cycle is divided into phases
G1 Pre-synthetic S
DNA synthesis (chromosome replication G2
Pre-mitotic M
Mitotic (cell division) G0 Quiescent resting phase
Mitosis is divided into several phases
• interphase: this comprises phases G1, S, and G2 of the cell cycle when the cell is in preparation for division. The chromosomes have replicated and there are two copies of each in the cell (ie 92 chromosomes
• Prophase: the chromatin begins to condense and is seen as chromosomes. centrioles move to opposing ends of the cell and fibres stretch between them forrning mitotic spindle
• Prometaphase: the nuclear membrane dissolves and the chromosomes start to move towards the centre of the cell under the control of microtubules• Metaphase: the spindle fibres align with the chromosomes along the metaphase plate this allows accurate separation of the paired replicated chromosomes to the two cells
• Anaphase: the paired chromosomes separate and are dragged to the opposite side of the cell by the microtubules• Telophase: the chromatids arrive at the opposite poles of the cell and disperse after new nuclear membranes are formed
Cytokinesis: an actin fibre forms around the centre of the cell and contracts, pinching it into two daughter cells, each with 23 pairs of chromosomes control of the cell cycle there are regulatory points between the different phases of the cell cycle most adult cells are In Go (ie outside the cell cycle) and quiescent. The length of the G1 phase is variable. The length of the S, G2, and M phases are fairly constant because these
processes have a limit as to how quickly they can be performed.entry Go cells into the cycle and transition from G1 to S phase are the two crucial regulatory points
of the cell cycle
They are controlled by
.intracellular enzymes: cyclin-dependant kinases (CDKs) cause cells to move from G1 to S and also from G2 to M. They are:Up-regulated by platelet-derived growth factor (PDGF), epidermal growth factor EGF), and insulin-like growth factor (lGF-l) in the serum Down-regulated by transforming growth factor beta TGF-beta
-protein p53: this protein blocks the cell cycle in G, phase if DNA is damaged. This allows for DNA repair or, if the damage is severe, cellular apoptosis. High levels of p53 are seen in damaged cells and loss of p53 activity by gene mutation or deletion is associated with tumour development cellular
differentiations a complex and incompletely understood process occurring during development of the fetus and occurs continuously in certain systems of the body (eg hacmatopoicsis
DEFINITION RELATED TO DIFFERENTIATION
Differentiation means: cell specialisation that occurs at the end of the developmental pathway. Selective genes are activated to produce the differentiated phenotype
Stem cell: a cell from an embryo, fetus, or adult that can reproduce itself for long periods of time and can give rise to specialised cells and tissues
Totipotent: a cell capable of expressing any of the genes of the genome (can give nise to any part of the later embryo or adult). In humans, the fertilised egg is totipotent until the 8-cell stage
Pluripotent: a cell with the potential to generate cell types and tissues from all three primary germ layers of the body
Plasticity: the ability of a stem cell of one tissue type to generate cells from another tissue type
Progenitor or precursor cell: occurs when a stem cell divides into two partially differentiated cells, neither of which can replicate itself but may continue along the path of
differentiation i will complete next time
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