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hi everyone welcome to this short
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tutorial from pathology Made Simple at
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IOP pathology in the last few tutorials
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I have uh completed the topic
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inflammation in great detail I think you
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you might have seen that videos if you
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have not seen please go back and have a
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look at those videos in the next few
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parts I will be discussing about the
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concepts and the various things you need
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to know about the tissue repair so this
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is part one of tissue repair where uh we
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will be uh knowing about the definition
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of repair and healing we will know what
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is regeneration and what is car
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formation we will move on to understand
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the different types of tissue and then
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understand the mechanism of tissue
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regeneration in great detail taking
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liver as an example okay now whenever
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there is an injury to a given tissue
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what can happen Okay one yes the
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inflammation will be there which helps
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in watering of the inflammatory agents
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the Infectious agents but then it also
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has to restore the tissue isn't it back
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to its normal functioning so restoration
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of tissue architecture and function
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after an injury is called as repair it
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is also called as healing so repair and
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healing are almost synonymous words but
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in general repair is a term used when we
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talk about restoration of paranal and
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connective tissue whereas healing is
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generally the word used when we talk
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about restoration of surface epithelium
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but then still repair and healing can be
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interchangeably
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used now repair occurs via two processes
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one regeneration which means there is
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restoration of normal cells and two
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scarring which means there is connective
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tissue
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deposition now restoration of normal
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cells in the case of regeneration occurs
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only in tissues which have cells with
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capacity to
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proliferate whereas scarring occurs in
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the tissues where cells don't have the
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capacity to proliferate that's one
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scenario in the second scenario even in
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the tissue where the cells have capacity
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to proliferate if that tissue is very
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severely damaged the part of the tissue
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will be uh replaced by the normal cells
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but the remaining part of the tissue
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will be replaced by connected tissue and
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that is scar formation the scarring can
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occur in two scenarios one in those
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tissues where cells don't have capacity
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to proliferate and two if any of the
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tissue which has which is severely
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damaged okay now let us understand
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regeneration and scarring in Greater
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detail some Basics about these two
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entities so the repair process is
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dependent on few important things one
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the proliferative capacity of the cells
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as we already know and two the
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interaction between these cells and the
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extracellular Matrix okay so the
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proliferation of cells is again further
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dependent on I mean they are basically
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driven by the growth factors whereas the
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interaction between the cells and
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extracellular Matrix all these things
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depends on Integrity of extracellular
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Matrix as well okay and secondly it also
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depends that is repair process is also
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dependent on the development of mature
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cells by the progenitor cells or the
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stem cells now once we know that the
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cells do proliferate in the process of
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repair now we need to understand what
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are those cells what are those cell
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types which proliferate during the
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repair process so three important cell
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typs we need to understand one the cells
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they mean the remnants of the injure
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tissue okay which tries to attempt to
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restore to the normal tissue and to the
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vascular endothelial cells the vascular
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endothelial cells proliferation is very
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important because that is one which
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creates the blood vessels and the
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formation of blood vessels is is very
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important for nutrition of the cells
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during the repair process the third one
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is the fibroblast which essentially
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forms scar it synthesizes collagen and
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then it forms scars and then it fills
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those defects in those tissues where the
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cells cannot regenerate now the ability
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of tissues to repair themselves is
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determined partly by the proliferative
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capacity of the cells and two presence
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of stem cells so remember only these two
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things the proliferative capacity of of
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the cells is very important and the
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presence of stem cells is important for
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uh for us to understand the concepts of
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tissue repair So based on these
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parameters based on the proliferative
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capacity of the cells the tissues in the
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body are subdivided into three types one
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leile tissue which are nothing but the
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continuously dividing tissue and two
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stable tissue and three permanent tissue
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the lebile tissues are the ones which
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contain cells which are continuously
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being lost replaced examples being
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hematopoetic cells of bone marrow
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surface epithelia it could beamus
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epithelium of your skin it could be cual
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epithelium of your glands it could be
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colar epithelium in the glands
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transitional epithelium of the eurogen
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system any epithelium M surface
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epithelium these are the areas where the
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cells are continuously being lost and
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replaced stable tissue is a tissue where
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there are cells which are quent okay
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they are the cells which are in g0 phase
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of cell cycle in the earlier videos I
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have talked about the concepts of cell
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cycle I think you can go back and look
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at that particular video to understand
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the various parts of cell cycle for now
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know that the stable tissue have cells
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which are in Quant phase they have a
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many very minimal proliferative activity
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okay they can proliferate only in
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response to injury or loss of these
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cells okay they divide in response to
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injury or loss examples being parenchima
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of Sol tissue like the liver the kidney
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the spleen they could be endothelial
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cells they could be fibroblast and
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smooth muszle cells the permanent tissue
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are the ones where the cells are
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terminally differentiated and they are
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non proliferate you in the postnatal
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life okay examples being neurons the
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cardiac muszle the skeletal muszle so
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consider injury to the neuronal tissue
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that is brain the cardiac muscle and
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skeletal muscle they do not regenerate
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okay the injured tissue is replaced by
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deposition of connective tissue and that
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is what we call it as
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scar so basically we have three types of
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tissue one is leile tissue where the
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cells are continuously being lost and
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replaced and two you have stable tissue
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which is in the Quant stage and then
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they assume proliferative capacity they
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move from g0 to G1 phase in response to
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injury and loss loss and then the third
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one is the terminally differentiated
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cells where they become nonproliferative
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in the postnatal life so these are the
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three types of tissue we need to
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understand for us to know better about
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the tissue regeneration and repair now
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we know that the cells proliferate right
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what are those cells which proliferate
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they are the remnants of the Ino tissue
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the endotherial cells the FI blast right
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all these cells proliferate by signals
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and what are these signals these signals
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are provided by the growth factor
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factors okay the signals are provided by
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the growth factors and the extracellular
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Matrix the growth factors are produced
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by the cells near the SES of damage the
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growth factors acts as signals for cells
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to proliferate and these growth factors
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are produced by the cells near the sight
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of damage and the most important the
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most predominant cells which synthesizes
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or produces growth factors are the
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macras and the rest being the epithelial
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are the stromal cells
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The extracellular Matrix now what is the
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role the growth factors which are
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produced by these cells they are bound
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to The extracellular Matrix proteins
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okay they provide signals for the cells
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to
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proliferate what do they do finally they
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activate signaling Pathways that
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stimulate DNA replication and that's how
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the cells multiply and the cells divide
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now let us understand in detail about
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the tissue regeneration taking liver as
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an example example because liver is an
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organ which has a remarkable capacity to
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regenerate so liver regeneration occurs
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via two Pathways I mean two ways where
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the liver can be regener liver can be
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restor to normal f for example if you
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knockout part of a liver in the case of
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partial hepatectomy the remaining part
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of the liver know starts proliferating
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okay so one uh one way the liver can
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regenerate is by proliferation of
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remaining heyes and and two is
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repopulation from progenitor cells okay
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so these are stem cells proliferation of
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remaining heyes repopulation from prenit
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cells so proliferation of remaining
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heyes occurs in three different phases
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one is a priming phase two is a growth
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factor phase and the three is a
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termination phase let us understand a
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bit in detail about these phases so what
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happens in the priming phase is that you
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have a hepy here once you have he and
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then you have the C vils which are the
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macrophases these macras secrete inin
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six and then makes these cells you know
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responsive for these growth factors okay
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how do they become responsive by
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expressing The receptors on their
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surface okay The receptors for the
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growth factors one of the example being
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epidermal growth factor another growth
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factor being Hite growth factors so this
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particular phase the cells are being
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primed for them to be receptive for the
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growth factors is referred to as a
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priming phase now what happens next once
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these growth factors goes and sits on
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the receptors okay that is when the
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cells get signals and then they move
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from g0 to G1 phase so once the cell
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enters the cell cycle in the form of
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entering into the G1 phase of cell cycle
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the cells proliferate so the hepto sites
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proliferate the rest of the epoy start
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proliferating and this is referred to as
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a growth factor phase where the cells
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grows the cells proliferate by the help
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of these growth factors on the primed
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heyes okay after achieving a
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requisite organ size or a tissue size
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the cell stops proliferating and then
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these return back to the quent stage
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this is called as termination phase and
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and the factors responsible for the
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cells to get back to termination phase
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is by these set of by these transforming
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growth factor beta family TG of beta
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family set of proteins now we understood
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proliferation of remaining Hees liver
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regeneration occurs by proliferation of
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remaining heyes by priming phase growth
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factor phase and termination phase right
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and the second one if this does not
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happen the second way the liver can
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regenerate is by repopulating from the
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progenitor cells okay so how when does
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this happen this happens usually after
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chronic liver injury or after chronic
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inflammation okay what happens in that
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condition the proliferative capacity of
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the hepto sites is impaired okay so the
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epidos sites the native eposides epidos
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sites cannot proliferate because it is
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severely injured okay that is when the
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prenat cells comes to
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play so that is when the progenitor
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cells helps to repopulate
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now what are these pren Cs and where are
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they located so these are the heyes okay
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so that's a bile canaliculus that's a
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bile ductule and that's an intralobular
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bile duct and this is I me these are
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heyes this particular area in between
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the bile canaliculus and the duct is
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called Canal of hering where you find
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these different types of cells these are
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stem cells this is called a stem cell
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nishe okay so these are the cells these
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are the progenitor cells which helps in
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repopulating the liver repopulating the
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hepto sites when these Ides are unable
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to proliferate because of chronic injury
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okay so that is when repopulation of
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progenitor cells occurs when the
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proliferative capacity of the hepto sdes
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are impaired okay how do they how do how
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do that occur how does progen cells
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assimilated but this particular know
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mechanism is actually not known this is
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an area of active investigation as of
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now so as of now remember regeneration
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takes place by proliferation of the
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Native cells in the case of liver it is
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proliferation of remaining iddes if this
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does not happen if this is impaired
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because of inflammation or chronic
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inflammation or whatever reasons the
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proliferation can also occur by
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repopulation by progenitor cells okay
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which are basically stems this is the
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same in almost all the organs we have
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just understood by taking liver as an
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example example right so this completes
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today's topic we understood what is
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repair we understood the basic concepts
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of regeneration and what is car
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formation we talked about the various
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types of tissue and then in detail about
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tissue regeneration okay in the next
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part I'll talk about the connective tis
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deposition or the scar formation thank
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you for watching if you have likeed this
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