7. Cellular adaptations

Question 1

Why do cells adapt?

Answer 1

• To respond to challenges that aren’t severe enough to cause injury, by adaptations that aren’t truly pathogenic, although they may open the door to disease.
• Adaptation is the state between a normal unstressed cell and an overstressed injured cell.

Question 2

What are the 5 important types of cell adaptation?

Answer 2

1. regeneration: multiply to replace losses
2. hyperplasia
3. hypertrophy
4. atrophy
5. metaplasia

Question 3

Are cellular adaptations reversible?

Answer 3

Usually yes, though atrophy is less so

Question 4

What is hyperplasia and why does it occur?

Answer 4

Increase in tissue/organ size due to increased cell numbers.

Response to:

i) increased functional demand, via external/hormonal stimulation
ii) tissue damage -increase in tissue mass (compensatory)

Question 5

In which types of tissue does hyperplasia occur?

Answer 5

labile or stable tissues

Question 6

What is the difference between hyperplasia and neoplasia?

Answer 6

Hyperplasia

• under physiological control
• reversible

Neoplasia

• not under physiological control
• irreversible

Question 7

Why is neoplasia a risk in hyperplastic tissue?

Answer 7

• repeated cell divisions expose the cell to mutation risk (commonly occur in DNA replication)
• pathological hyperplasia usually occurs secondary to excessive hormonal stimulation or growth factor production

Question 8

Give 2 examples of physiological hyperplasia.

Answer 8

1. increased bone marrow production of erythrocytes in resp. to low oxygen/hypoxia
2. proliferation of endometrium under influence of oestrogen

Question 9

Give 2 examples of pathological hyperplasia.

Answer 9

1. epidermal thickening in chronic eczema/psoriasis

2. thyroid goitre in iodine deficiency

Question 10

What is hypertrophy?

Answer 10

Increase in tissue/organ size due to increase in cell size (without increase in cell no.)

Question 11

In which tissue types does hypertrophy occur?

Answer 11

Labile, stable but esp. permanent tissues (as these cell pops. have no replicative potential so any increase in organ size must occur via hypertrophy)

Question 12

What causes cellular hypertrophy?

Answer 12

Same stimuli as hyperplasia - increased functional demand or hormonal stimulation - so in labile and stable tissues, hypertrophy usually occurs with hyperplasia.

Question 13

How do cells mediate hypertrophy?

Answer 13

Synthesise more cytoplasm (i.e. protein) - contain more structural components so cellular workload is shared by a greater mass of cellular components.

Question 14

Give 2 examples of physiological hypertrophy.

Answer 14

1. skeletal muscle hypertrophy of body builder
2. smooth muscle hypertrophy (+hyperplasia) of pregnant uterus - body of uterus enlarges approx. 70x under influence of oestrogen

Question 15

Give 3 examples of pathological hypertrophy.

Answer 15

1. ventricular cardiac muscle hypertrophy in resp. to systemic hypertension or valvular disease
2. smooth muscle hypertrophy proximal to an intestinal stenosis due to extra work of pushing intestinal contents through narrowing
3. bladder smooth muscle hypertrophy with bladder obstruction due to an enlarged prostate gland (which has undergone both hypertrophy and hyperplasia)

Question 16

Why don’t athletes get cardiac muscle hypertrophy?

Answer 16

Some hypertrophy but limited as can always rest and recuperate after effort, whereas in pathology, always relatively hypoxic.

Question 17

What is compensatory hypertrophy?

Answer 17

Enlargement of 1 organ of a pair, if the other is damaged/removed (e.g. kidney)

Question 18

What are cellular and tissue/organ atrophy?

Answer 18

Cellular = decrease in cell size to a size where survival is still possible

Tissue/organ = shrinkage of a tissue/organ due to a decrease in size and/or number ( via apoptosis) of cells

Question 19

What causes atrophy?

Answer 19

reduced supply of growth factors and/or nutrients

Question 20

What happens in cellular atrophy?

Answer 20

Reduction in amount of inessential structural components (digested via phagosomes - residual bodies), leading to reduced function.
But cell shrinkage is limited as most cellular organelles are essential for survival.

Question 21

Why do atrophic organs often contain large amounts of connective tissue?

Answer 21

In organs undergoing atrophy by cell deletion, parenchymal cells will apoptose before stromal cells.

Question 22

Give 2 examples of physiological atrophy.

Answer 22

1. ovarian atrophy in post-menopausal women

2. decrease in uterus size after childbirth

Question 23

Give examples of pathological atrophy causes.

Answer 23

1. reduced functional demand/workload (atrophy of disuse), e.g. muscle atrophy after immobilisation (reversible with activity)
2. loss of innervation (denervation atrophy), e.g. wasted hand muscles after median nerve damage
3. chronic inadequate blood supply, e.g. thinning of skin on legs with peripheral vascular disease
4. inadequate nutrition, e.g. muscle wasting with malnutrition
5. loss of endocrine stimulation, e.g. breast, reproductive organs
6. aging (senile atrophy), usually in permanent tissues (brain and heart)
7. pressure, e.g. tissues around an enlarging benign tumour (probably secondary to ischaemia)

Question 24

What is atrophy of extracellular matrix?

Answer 24

loss of bone substance (rather than calcium) in osteoporosis, often as a consequence of inactivity (as stimulus for bone formation is movement and pressure)

Question 25

What is metaplasia? How does this occur?

Answer 25

Reversible change of 1 differentiated cell type to another: 1- cells of original phenotype are eliminated 2- stem cells within the tissue are reprogrammed and differentiate into a different type of progeny

Question 26

Why does metaplasia occur?

Answer 26

may represent adapative substitution of cells sensitive to stress by cells better able to withstand the adverse environment

Question 27

What is the difference between metaplasia, dysplasia and cancer?

Answer 27

Metaplasic cells - fully differentiated - process is reversible - sometimes a prelude to dysplasia and cancer Dysplasia = abnormal maturation of cells within a tissue. - disorganised and abnormal differentiation - potentially reversible but is often pre-cancerous. Cancer - disorganised and abnormal differentiation - irreversible

Question 28

What cell types can metaplasia give rise to?

Answer 28

- Only occurs in cell populations that can replicate (not known to occur in adult striated muscle or neurons) - labile or stable. - Occurs only within varieties of epithelia and within varieties of connective tissue (mesenchyme), but not across germ layers (e.g. bone to nerve or mesenchyme to epithelium).

Question 29

In what tissue type is metaplasia seen most commonly?

Answer 29

Epithelial tissues on surface linings - exposed to insults. Columnar epithelium (fragile) commonly undergoes metaplasia to squamous epithelium (more resilient).

Question 30

Give 2 examples of adaptive/useful metaplasia.

Answer 30

1. If BM is destroyed, splenic tissue undergoes metaplasia to BM (myeloid metaplasia), e.g. megakaryocytes for platelet production. 2. columnar epithelium lining ducts, e.g. in salivary glands, pancreas, bile ducts or renal pelvis, can change to stratified squamous epithelium (more resistant to mechanical abrasion) secondary to chronic irritation by stones.

Question 31

Give 2 examples of metaplasia that are detrimental.

Answer 31

1. Transformation of bronchial pseudostratified ciliated columnar epithelium to stratified squamous epithelium due to effect of cigarette smoke. Squamous epithelium doesn't produce cleansing mucus and lacks cilia to move mucus along. 2. Stratified squamous epithelium to gastric glandular epithelium due to persistent acid reflux (Barrett's oesophagus).

Question 32

What is traumatic myositis ossificans?

Answer 32

- Metaplastic bone can develop in skeletal muscle following trauma - fibroblasts to osteoblasts. - Often seen in young people after a premature return to activity before proper healing has occurred. - Often disappears by metaplasia in opposite direction.

Question 33

Does metaplasia predispose to cancer?

Answer 33

Several types of epithelial metaplasia predispose to dysplasia and malignant epithelial cancers, e.g. - Barrett's epithelium and oesophageal adenocarcinoma (with chronic infection by Helicobacter pylori) - Intestinal metaplasia of stomach and gastric adenocarcinoma

Question 34

What is aplasia?

Answer 34

- Embryonic developmental disorder involving complete failure of a specific tissue or organ to develop. - E.g. thymic aplasia (infections and autoimmune probs), aplasia of a kidney. - (Also used to describe an organ whose cells have ceased to proliferate, e.g. aplasia of BM in aplastic anaemia).

Question 35

What is hypoplasia?

Answer 35

- congenital underdevelopment or incomplete development (inadequate no. of cells) of tissue/organ at embryonic stage - in a spectrum with aplasia - e.g. testicular in Klinefelter's syndrome, heart chambers, renal. breast

Question 36

What is involution?

Answer 36

normal programmed shrinkage of an organ, e.g. uterus after childbirth, thymus in early life, temporary foetal organs such as pro- and mesonephros - overlaps with atrophy

Question 37

What is atresia?

Answer 37

congenital imperforation of an opening ('No orifice'), e.g. of anus or vagina

Question 38

What is reconstitution? Can it occur in humans?

Answer 38

- Replacement of a lost body part (e.g. antlers). - Cannot occur in humans (e.g. pale, hairless scars) except: - angiogenesis (some argue) - some cases of tip of finger regrowth after clean cut if <4.5 yo