Session 7 - Cellular Adaptations

Question 1

Which phase(s) of the cell cycle are distinctive under a light microscope?

Answer 1

Mitosis only. The rest of the cell cycle is called interphase and you cannot see much at all under a light microscope.

Question 2

Where do you find the restriction point?

Answer 2

Towards the end of the G1 phase.

Question 3

What happens in the following stages of the cell cycle:

• G1
• S
• G2
• M

Answer 3

• G1 - The cell grows. It makes the proteins that it needs and also makes more ribosomes.
• S phase - DNA synthesis
• G2 - Makes the organelles it requires ready for cellular division. Last chance to make more proteins
• M phase - mitosis (prophase, metaphase, anaphase, telophase, cytokinesis)

Question 4

What is so relevant about the restriction point?

Answer 4

The majority of cells that pass the restriction point are highly likely to complete the cell cycle.

Question 5

What happens when check point activation occurs?

Answer 5

p53 protein is activated - this protein suspends the cell cycle and triggers DNA repair mechanisms or if the DNA cannot be repaired apoptosis is initiated.

Question 6

What are the two other main checkpoints in the cell cycle other than the restriction point?

Answer 6

1. The G1/S transition - checks for DNA damage before DNA replication
2. G2/M transition - checks for DNA damage after DNA replication.

Question 7

What are a major cause of genetic instability of cancer cells?

Answer 7

Defective cell cycle checkpoints. This means that defective cells will progress through the cell cycle.

Question 8

What proteins regulate the cell cycle, particularly at the G1/S transition?

Answer 8

Cyclin-dependent kinases. They become active by binding to and complexing with cyclins.

Question 9

What is the role of activated cyclin dependent kinases? How are they regulated?

Answer 9

They phosphorylate proteins therefore driving the cell cycle. They are regulated by CDK inhibitors.

Question 10

What is cellular adaptation?

Answer 10

This is the state between a normal unstressed cell and an overstressed injured cell. It is usually reversible.

Question 11

What are the four different types of cellular adaptation?

Answer 11

1. increase in number above normal (hyperplasia)
2. Increase in size (hypertrophy)
3. Become smaller in size (atrophy)
4. Replacement by a different type of cell (metaplasia)

Question 12

Why does hypertrophy occur?

Answer 12

Due to an increased functional demand or increased external stimulation.

Question 13

Provide some examples of physiological hyperplasia

Answer 13

1. Proliferation of the endometrium under the influence of oestrogen
2. Increased erythrocyte production in response to hypoxia and the resulting increased EPO.

Question 14

Provide some examples of pathological hyperplasia

Answer 14

1. Epidermal thickening in chronic eczema or psoriasis
2. Enlargement of the thyroid gland in response to iodine deficiency

Question 15

In what cell type is permanent hypertrophy often seen?

Answer 15

Permanent cells as they have little or no replicative potential.

Question 16

Provide examples of physiological hypertrophy.

Answer 16

1. Hypertrophy of skeletal muscle in a body builder
2. Smooth muscle hypertrophy in a pregnant uterus (smooth muscle can also undergo hyperplasia)

Question 17

Provide some examples of pathological hypertrophy?

Answer 17

1. Ventricular hypertrophy in cardiac muscle
2. Bladder smooth muscle hypertrophy due to enlarged prostate gland

Question 18

What is atrophy?

Answer 18

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

Question 19

What is the difference between cellular atrophy and organ atrophy?

Answer 19

Cellular atrophy is a decrease in cell size and organ/tissue atrophy is typically due to a combination of cellular atrophy and apoptosis.

Question 20

In atrophic organs what cells tend to undergo apoptosis first. Parenchymal or stromal?

Answer 20

Parenchymal tend to undergo apoptosis first and therefore this is why atrophic organs tend to be abundant in connective tissue.

Question 21

Provide some examples of physiological atrophy.

Answer 21

1. ovarian atrophy in post menopausal women
2. Decrease in size of the uterus after parturition (giving birth)

Question 22

What are some pathological reasons for the occurence of atrophy?

Answer 22

1. reduced functional demand/workload - eg. leg in a cast
2. loss of innervation
3. Inadequate blood supply - eg. thinning skin on the legs due to peripheral vascular disease
4. Inadequate nutrition
5. Persistent injury - eg. polymyositis
6. aging - eg. usually occurs in permanent tissues such as the brain and heart.
7. Toxic agents and drugs - eg. on the bone marrow and testes
8. immunological - eg. atrophic gastric mucosa in pernicious anaemia.

Question 23

What is metaplasia?

Answer 23

This is the reversible replacement of one adult differentiated cell type by another of a different type.

Question 24

Where does metaplasia occur in humans?

Answer 24

Varieties of epithelia and connective tissue.

Question 25

Why does columnar epithelia often undergo metaplasia to form squamous epithelium?

Answer 25

Columnar epithelium is quite fragile and squamous epithelium is much more resilient.

Note: results in loss of mucus production.

Question 26

Provide an example of when metaplasia proves to be useful.

Answer 26

If the bone marrow is destroyed by disease then splenic tissue undergoes metaplasia to form bone marrow (myeloid metaplasia)

Question 27

Describe the metaplasia that occurs due to the effect of cigarette smoke? Why is this detrimental?

Answer 27

Transformation of bronchial pseudostratified cilitated columnar epithelium to stratified squamous epithelium. The squamous cells cannot produce mucus and do not have cilia to move the mucus along.

Question 28

Provide an example of when non secreting epithelium are replaced by secretory epithelium?

Answer 28

Barretts oesophagus - stratified squamous epithelium changes to gastric/intestinal type epithelium (squamous epithelium is converted to columnar epithelium). This is due to acid reflux.

Question 29

What is reconstitution?

Answer 29

This is the regeneration of a lost part of the body rather than a small group of cells.

Question 30

What is aplasia?

Answer 30

The complete failure of a specific tissue or organ to develop eg. aplasia of a kidney. It is also used to describe an organ whose cells have ceased to proliferate eg. aplasia of the bone marrow in aplastic anaemia.

Question 31

What is involution?

Answer 31

A term which overlaps with atrophy. It is the normal programmed shrinkage of an organ. Eg. uterus after child birth or the thymus early on in life.

Question 32

What is hypoplasia?

Answer 32

The congenital underdevelopment or incomplete development of a tissue or organ. eg. renal hypoplasia, breast hypoplasia, testicular hypoplasia in Klinefelter’s syndrome.

Question 33

What is atresia?

Answer 33

This is where you have no orifice, it is the congenital imperforation of an opening. eg. atresia of the anus or vagina.

Question 34

What is dysplasia?

Answer 34

The abnormal maturation of cells within a tissue. It is potentially reversible but known as a pre-cancerous condition that results in a decline in organisation of the tissues and can progress onto neoplasia.

Question 35

If a patient had an endometrial biopsy that was found to show endometrial hyperplasia and then upon observation you can see the patient is overweight, why is this relevant?

Answer 35

This is because obesity is a large risk factor for endometrial cancer. This is because adipocytes secrete oestrogen, usually progesterone would oppose its effects however in post-menopausal ages you dont have progesterone to do this.

Question 36

What is the pharmacological mechanism of tamoxifen?

Answer 36

It is an oestrogen receptor modulator and therefore in breast cancer it can inhibit cancer growth through the inhibition of the oestrogen receptor.

However in the endometrium it has the opposite effect and this can give rise to endometrial cancer.