cell turnover Flashcards
Growth
the process of increase in size resulting from the synthesis of specific tissue components
Type of growth in tissue are
Multiplicative: Increase in the number of cells by mitosis. Present in all tissues during
embryogenesis
Auxetic: Increase size of individual cells (eg. Skeletal muscle)
Accretionary: An increase in intercellular tissue components (eg. Bone and cartilage)
Combined
Differentiation
process whereby a cell develops an overt specialized function or morphology
that distinguished it from its parent cell. In this process, genes are expressed selectively, and gene
products act to produce a cell with a specialised function
Morphogenesis
the highly complex process of development of structural shape and form of
organs, limbs, facial features etc. from primitive cells masses during embryogenesis. This involves
growth and differentiation with movement of cell groups relative to others, and focal apoptosis to
remove unwanted features.
Cell proliferation is fundamental to
Development
Maintenance of steady-state tissue homeostasis
Replacement of dead or damaged cells
Cell proliferation can be stimulated by pathologica
After cell death or tissue injury
Cell proliferation can be stimulated by physiological
Endometrial tissue during the menstrual cycle
o Thyroid tissue during pregnancy
G1
Presynthetic growth phase
o Restriction point
G1/S checkpoint
monitors the integrity of DNA before irreversibly committing cellular
resources to DNA replication
S
DNA synthesis
G2
Premitotic growth
G2/M checkpoint
The G2/M checkpoint ensures accurate genetic replication before the
cell divides
M
Mitosis
The cell cycle is regulated by activators and inhibitors
Cyclins
Cyclin-dependent kinases (CDKs)
Cyclin-dependent kinase inhibitors (CDKIs)
Stem cells
undifferentiated cells that can differentiate into multiple types of other cells. Stem
cells are characterized by two important properties:
Self-renewal: allows maintenance of stem cell pool
Asymmetric division: one daughter cell enters the differentiation pathway and gives rise to
mature cells, whilst the other cell remains undifferentiated and retains its self-renewal
capacity.
Embryonic stem cells
Most undifferentiated
o Present in the inner mass of the blastocyst
o Virtually limitless self-renewal capacity
o Can give rise to any cell in the body = totipotent
Tissue (adult) stem cells
Found within differentiated tissues
o Protected within stem cell niches
o Can only produce cells that are constituents of that particular tissue
Labile
Proliferate continuously in postnatal life
o The cells have a short life span with a rapid turnover time
o Cells are frequently lost and replaced by stem cell division
o This high cell turnover renders the tissue susceptible to the toxic effects of radiation
and drugs
o Haemopoietic cells of the bone marrow, skin, GIT, exocrine gland ducts, urinary
tract, vagina, cervix and endometrium
Stable
Divide very infrequently under normal conditions
o Stem cells may be stimulated to divide rapidly when cells are lost
o Liver, endocrine glands, bone, renal tubules
Permanent
Active stem cells in these tissues do NOT persist long into postnatal life
o Cells cannot be replaced when they lost
o Neurons, cardiac muscle, photoreceptors.
