cell turnover

Question 1

Growth

Answer 1

the process of increase in size resulting from the synthesis of specific tissue components

Question 2

Type of growth in tissue are

Answer 2

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

Question 3

Differentiation

Answer 3

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

Question 4

Morphogenesis

Answer 4

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.

Question 5

Cell proliferation is fundamental to

Answer 5

Development
 Maintenance of steady-state tissue homeostasis
 Replacement of dead or damaged cells

Question 6

Cell proliferation can be stimulated by pathologica

Answer 6

After cell death or tissue injury

Question 7

Cell proliferation can be stimulated by physiological

Answer 7

Endometrial tissue during the menstrual cycle

o Thyroid tissue during pregnancy

Question 8

G1

Answer 8

Presynthetic growth phase

o Restriction point

Question 9

G1/S checkpoint

Answer 9

monitors the integrity of DNA before irreversibly committing cellular
resources to DNA replication

Question 10

S

Answer 10

DNA synthesis

Question 11

G2

Answer 11

Premitotic growth

Question 12

G2/M checkpoint

Answer 12

The G2/M checkpoint ensures accurate genetic replication before the
cell divides

Question 13

M

Answer 13

Mitosis

Question 14

The cell cycle is regulated by activators and inhibitors

Answer 14

Cyclins
 Cyclin-dependent kinases (CDKs)
 Cyclin-dependent kinase inhibitors (CDKIs)

Question 15

Stem cells

Answer 15

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.

Question 16

Embryonic stem cells

Answer 16

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

Question 17

Tissue (adult) stem cells

Answer 17

Found within differentiated tissues
o Protected within stem cell niches
o Can only produce cells that are constituents of that particular tissue

Question 18

Labile

Answer 18

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

Question 19

Stable

Answer 19

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

Question 20

Permanent

Answer 20

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.