S7: cellular adaptations

Question 1

Name the phases of the cell cycle and what happens in each

Answer 1

G1 = where the cells grow 
S = DNA synthesis 
G2 = cell prepares for division 
M = mitosis & cytokinesis 
After cell cycle completion, the cell either re-starts the process from G1 or exits (G0) until further growth signals occur

Question 2

Describe the different checkpoints in the cell cycle

Answer 2

Restriction point (end of G1) = if checkpoint activation occurs, protein p53 triggers DNA repair mechanisms, or if the DNA cannot be repaired, apoptosis 
G1/S transition = checks for DNA damage before DNA replication
G2/M transition = checks for DNA damage before DNA replication

Question 3

Explain how the cell cycle is controlled

Answer 3

Tightly regulated by cyclins and associated enzymes CDKs
Activated CDKs drive the cell cycle by phosphorylating proteins that are critical for progression in the cycle
Activity of cyclin-CDK complexes tightly regulated by CDK inhibitors

Question 4

Define hyperplasia and give examples

Answer 4

Increase in tissue or organ size due to increased cell numbers (labile/stable tissues)
Increased functional demand/external stimulation
Physiological: proliferative endometrium under influence of oestrogen, bone marrow produces RBCs in response to hypoxia
Pathological: eczema, thyroid goitre in iodine deficiency

Question 5

Define hypertrophy and give examples

Answer 5

Increase in tissue or organ size due to increased cell size (especially permanent tissues)
Increased functional demand or hormonal stimulation
Physiological: skeletal muscle, pregnant uterus
Pathological: right ventricular hypertrophy (cardiac hypertrophy normal in athletes)

Question 6

Define atrophy and give examples

Answer 6

Shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells
Physiological: ovarian atrophy in post-menopausal women
Pathological: atrophy of disuse, denervation atrophy, senile atrophy

Question 7

Define metaplasia and give examples

Answer 7

Reversible change of one differentiated cell type to another (labile/stable cell types)
Can lead to dysplasia and cancer
Bronchial pseudostratified ciliated epithelium -> stratified squamous epithelium due to effect of cigarette smoke; stratified squamous epithelium -> gastric glandular epithelium with persistent acid reflux (Barrett’s oesophagus)

Question 8

Define aplasia and give examples

Answer 8

Complete failure of a specific tissue or organ to develop
Thymic aplasia (infections & auto-immune problems), aplasia of a kidney

Question 9

Define hypoplasia and give examples

Answer 9

Underdevelopment or incomplete development of tissue or organ at embryonic stage, inadequate number of cells
Renal, breast, chambers of heart (hypoplastic left heart syndrome)

Question 10

Define involution and give examples

Answer 10

Normal programmed shrinkage of an organ

Uterus after childbirth, thymus in early life

Question 11

Define atresia and give examples

Answer 11

Congenital imperforation of an opening

Pulmonary valve, anus, vagina, small bowel

Question 12

Define reconstitution and give examples

Answer 12

Replacement of a lost part of the body

Angiogenesis

Question 13

Define dysplasia

Answer 13

Abnormal maturation of cells within a tissue

Often pre-cancerous condition