MoD Cell adaptations

Question 1

What are the 5 types of cell adaptation?

Answer 1

1. Regeneration
2. Hyperplasia
3. Hypertrophy
4. Atrophy
5. Metaplasia

Question 2

Define regeneration

Which tissues can undergo regeneration and which can’t?

Answer 2

Replacement of cell losses by identical cells to maintain tissue or organ size

Epidermis and liver have good capacity, whereas tendons and melanocytes have poor capacity

Question 3

Define Hyperplasia

Which tissues can undergo hyperplasia and which can’t?

Answer 3

Increased in tissue or organ size due to increased cell numbers
Only labile and stable cell populations can undergo hyperplasia (reversible)

Question 4

What are some physiological and pathological examples of hyperplasia?

Answer 4

Physiological:
Endometrium proliferates under the influence of oestrogen
Bone marrow produces rbc in response to hypoxia (e.g. at high altitudes)

Pathological:
Skin in psoriasis
Thyroid goitre in iodine deficiency

Question 5

Define hypertrophy

Which tissues can undergo hypertrophy?

Answer 5

Increase in tissue or organ size due to increased cell size
Hypertrophy happens in many tissues but especially PERMANENT cell populations (they can’t undergo hyperplasia so hypertrophy is the only way to increase in size)
Caused by functional demand or hormone stimulation

Question 6

What are some physiological and pathological examples of hypertrophy?

Answer 6

Physiological
Skeletal muscle in bodybuilding
Pregnant uterus (+hyperplasia)

Pathological
Right ventricular hypertrophy in pulmonary embolism
Urinary bladder hypertrophy due to enlarged prostate

Question 7

What is compensatory hypertrophy?

Answer 7

Occurs when there is an increased work load e.g. when one kidney is absent or dysfunctional the other kidney enlarges to compensate

Question 8

Define atrophy

What are some physiological and pathological examples of atrophy?

Answer 8

Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells

Physiological
Ovarian atrophy post menopausal

Pathological
Muscle atrophy of disuse
Wasted hand muscles after median nerve injury
Cerebral atrophy (alzheimers)

Question 9

Define metaplasia

Why does it occur?

Answer 9

Reversible change of one differentiated cell type to another

Metaplasia is an adaptive response in epithelial tissues- substitutes sensitive cells to ones able to withstand more adverse environments.
No metaplasia across germ layers, and only occurs in cells that can replicate.

Question 10

Give some examples of metaplasia?

Answer 10

Barrett’s oesophagus: persistent acid reflux causes stratified squamous epithelium to turn to gastric glandular epithelium (risk for carcinoma)

Cigarette smoke: bronchial pseudostratified ciliated epithelium turns to stratified squamous epithelium

Question 11

Define hypoplasia and give examples

Answer 11

Underdevelopment or incomplete development of a tissue/organ at the embryonic stage
e.g. kidneys, heart chambers

Question 12

Define aplasia and give examples

Answer 12

Complete failure of a specific organ or tissue to develop (embryonic disorder)
e.g. thymic aplasia which results in infections and auto-immune problems

Question 13

Define involution and give examples

Answer 13

Normal programmed shrinkage of an organ

e.g. the uterus after child birth

Question 14

Define atresia and give examples

Answer 14

A condition where an opening or passage is abnormally narrowed or absent
e.g. anal opening not present

Question 15

Define dysplasia and give examples

Answer 15

Abnormal growth and development of cells

e.g. abnormal cells present in cervix

Question 16

Define reconstitution and give examples

Answer 16

Replacement of a lost part of the body

There is no real reconstitution in adults, the closest is that small capillaries can reconstitute in the uterine lining

Question 17

What are the four types of cell signalling?

Answer 17

Intracrine: nothing released, everything stays in cytoplasm
Autocrine: exerts effect on itself
Paracrine: exerts effect on nearby cell
Endocrine: travels in bloodstream to distant target

Question 18

What is the role of growth factors?

Answer 18

They are local mediators involved in cell proliferation
Act on cell surface receptors
Coded by photo-oncogenes
they stimulate transcription of genes that regulate entry of the cell into and though the cell cycle

Question 19

What is the role of epidermal growth factor

Answer 19

Mitogenic for epithelia cells, fibroblasts and hepatocytes

Question 20

What is the role of vascular endothelial growth factor?

Answer 20

Development of new blood vessels

Question 21

What is the role of platelet derived growth factor?

Answer 21

Development of new blood vessels, mitogenic for fibroblasts, smooth muscle cells and glial cells.

Question 22

What is the role of granulocyte colony-stimulating factor?

Answer 22

Stimulates bone marrow, can be given as a medication to patients to increase neutrophil count

Question 23

Which phase of the cell cycle is visible under the light microscope?

Answer 23

The M phase (mitosis and cytokinesis)

Question 24

What are the phases of the cell cycle?

Answer 24

G1 –> S –> G2 –> M
G1 gap 1 - pre synthetic, cell grows
S - DNA synthesis
G2 gap 2 - permitted, cell prepares to divide

Question 25

Where are the two important check points in the cell cycle?

Answer 25

The RESTRICTION (R) POINT checkpoint just before S phase is the most critical checkpoint, point of no return

Checkpoint activation delays cell cycle - triggers DNA repair or apoptosis via p53 gene
(is the cell big enough, is DNA damaged?)

The G2 checkpoint just before M phase
(Is the cell big enough, is all DNA replicated?)

Question 26

Describe the control of the cell cycle

Answer 26

Cyclins (proteins) and CDK’s (enzymes)
Cyclin binds to the substrate (RB protein)
Cyclin activates CDK enzyme
CDK enzyme phosphorylates the RB protein which drives the cell to the next phase of the cycle

The cyclin-CDK complexes are tightly regulated by CDK inhibitors.