Cell Adaptations

Question 0

Describe labile, stable and permanent cells

Answer 0

Labile - stem cells divide persistently to replenish losses e.g. epithelia
Stable - normally quiescent or proliferate very slowly, but proliferate persistently when required (injury) e.g. hepatocytes, osteoblasts, fibroblasts
Permanent - stem cells present but cannot mount an effective proliferative response to significant cell loss e.g. neurones, cardiac myocytes

Question 1

Describe the different phases of the cell cycle and their control

Answer 1

G1 - cell growth 
S - DNA synthesis
G2 - cell prepares to divide
M - cell division (mitosis, cytokinesis)
G0 - terminal differentiation
Controlled by 'checkpoints':
R (restrictive) point - at end of G, passage determined by retinoblastoma protein (pRb)
Cyclins and CDKs
Inhibition/stimulation, growth factors, vascular and metabolic factors, balance of cell proliferation and cell death

Question 2

List the different types of cellular adaptations

Answer 2

Regeneration
Hyperplasia
Hypertrophy
Atrophy
Metaplasia 
Aplasia
Hypoplasia 
Dysplasia

Question 3

Define the term ‘regeneration’ and explain the cell types involved and the physiological and pathological causes

Answer 3

Regeneration - replacement of cell loses by identical cells to maintain tissue or organ size e.g. superficial burn, liver regeneration, melanocytes, periphery neurones
(Reconstitution - replacement of a lost part of the body)

Question 4

Define the term ‘hyperplasia’ and explain the cells/organs concerned, the physiological causes and the effects

Answer 4

Hyperplasia - increase in tissue or organ size due to increased cell numbers.
Can only occur in labile or stabile cell populations, remains under physiological control, is reversible.
Physiological - proliferating endometrium under influence of oestrogen, bone marrow produces erythrocytes in response to hypoxia
Pathological - eczema, thyroid goitre

Question 5

Define the term ‘hypertrophy’ and explain. The cell types involved and the physiological and pathological causes

Answer 5

Hypertrophy - increase in tissue or organ size due to increased cell size
Occurs especially in permanent cells, caused by increased functional demand or hormonal stimulation.
Physiological - skeletal muscle (body building), pregnant uterus
Pathological - right ventricular hypertrophy, urinary bladder

Question 6

Define the term ‘atrophy’ and explain the physiological and pathological causes and effects

Answer 6

Atrophy - shrinkage of a tissue or organ due to an acquired decrease in size and/or number of cells
May be due to ageing or disease.
Physiological - ovarian atrophy,
Pathological - muscle after disuse, denervation, peripheral vascular disease, inadequate nutrition, cerebral (Alzheimer’s)

Question 7

Define the term ‘metaplasia’ and explain the cells concerned and the causes and effects

Answer 7

Metaplasia - reversible change of one differentiated cell type to another.
Most clearly adaptive in epithelial tissue, sometimes a prelude to dysplasia and cancer, no metaplasia across germ layers
Bronchial pseudostratified ciliated –> stratified squamous (smokers)
Stratified squamous –> gastric glandular (Barrett’s oesophagus - acid reflux)

Question 8

Explain the terms ‘hypoplasia’, ‘aplasia’ and ‘dysplasia’, ‘atresia’ and ‘involution’

Answer 8

Hypoplasia - underdevelopment or incomplete development of a tissue or organ at the embryonic stage, inadequate number of cells e.g. kidneys, breast, testes (Klinefelter), chambers of the heart.
In a spectrum with aplasia, congenital condition.
Aplasia - complete failure of a specific tissue or organ to develop e.g. kidney, bone marrow in aplastic anaemia
Embryonic developmental disorder.
Dysplasia - abnormality of development or an epithelial anomaly of growth and differentiation, change in phenotype
Aplasia - imperforation of an opening e.g. anus, vagina
Involution - normal programmed shrinkage e.g. uterus after childbirth