Disorders of Growth & Differentiation Flashcards
State the different ways in which cells can grow
- Multiplicative growth
- Auxetic growth
- Accretionary growth
- Combined pattern of growth
Multiplicative growth
Cells can grow by making more copies of the identical cell.
Auxetic growth
Cells can grow by becoming larger in size.
Accretionary growth
Cells can grow by excreting more extracellular matrix.
Combined pattern of growth
Cells can grow by a combination of growth methods.
Differentiation
Start with cells of one type and end with cells of a different type.
Hyper- meaning
Above normal
Hypo- meaning
Below normal
Hyperplasia
Increased number of cells
Hypertrophy
Same number of cells, but they have increased in size.
Combined hypertrophy and hyperplasia
Increased number of cells and increase in cell size.
What can increased growth also be perceived as ?
Decreased apoptosis
Physiological hypertrophy - example
Athletes muscle
Pathological hypertrophy - example
Right ventricular hypertrophy
- cardiac muscle increased in size due to problems in sending blood flow to the lungs
- So, the heart has to work harder, increases its muscle, although this puts the heart under significant strain
Physiological hyperplasia - example
Adaptation to altitude
- Increased number of RBCs in higher altitudes
- Helpful for athletes
Mammary Cycle
- Increase in cells that are able to produce milk during the lactation stage
Pathological hyperplasia - example
Psoriasis
- Cells in the epidermis are stimulated to grow
- Abnormal stratum corneum
- Increased proliferation in epidermis
- Generation of more keratinocytes that don’t differentiate normally
Hyperplasia in tissue repair
- Angiogenesis
- Wound healing
- Liver regeneration
- Heart
State the stages leading to cirrhotic liver
Normal liver
Inflamed liver
Fibrotic liver
Cirrhotic liver
What term is used to describe decreased/regressed growth ?
Atrophy
Atrophy
Reduction in cell size or number or both
May require apoptosis
Physiological atrophy - example (thymus)
Thymus gland
- function is to generate T cells and cell mediated immunity
- As we age, the bone marrow takes over this function and so we don’t need such a large thymus
- So, it decreases in size as we age (now mainly made up of fat)
Physiological atrophy - ageing
Ageing
- Shrinkage as we age
Pathological Atrophy examples
Muscle - fractures
Nerves - paraplegics
Blood supply - circulatory problems
Pressure - bedsores
Diet - anorexia
State some problems that underlie systemic growth disorders
Problems with:
Hormones and growth factors
Genetics
Nutrition
Environmental disease
Secondary effects of disease
State some diseases associated with proportionate alterations of skeletal growth
Turner’s syndrome
Down syndrome
Beckwith-Wiedemann syndrome
Pituitary Gigantism
Turners Syndrome
Chromosome 45
XO
Female
- lack one sex chromosome
- only have one copy of the SHOX gene
SHOX
Gene found on the tip of the X and Y chromosome.
Normal individuals have 2 copies of the SHOX gene, one on each sex chromosome.
Mutations within SHOX gene
SHOX gene is mutated in short stature syndrome.
- the SHOX mutation is the only mutation that seems to relate to short stature
Where is the SHOX gene found ?
The pseudo-autosomal region of the X and Y chromosomes.
This region escapes X chromosome inactivation.
What is the SHOX gene associated with ?
Growth
The SHOX gene is a transcription factor, which binds to a specific sequence in DNA.
Where is the SHOX gene expressed ?
SHOX is expressed in chondrocytes of the human growth plate.
Mainly seen in the hypertrophic zone.
Hypertrophic zone
Cells are getting larger, but not increasing in number.
SHOX protein is seen as black dots in the histological slides of the hypertrophic zone.
Down syndrome
Trisomy 21
Small stature
Hypotonia
Heart defects
Learning difficulties
Beckwith-Wiedemann syndrome cause
Inheriting 2 copies of a chromosome from one parent (paternal) and none from the other.
Results of Beckwith-Weidemann Syndrome
Increased expression of IGF-II
Decreased expression of H19
Overgrowth especially in early childhood
Pituitary Gigantism
Increased IGF-1
Increased growth hormone
Often from pituitary tumours
What do pituitary tumours cause:
- In children
- In adults
- Gigantism
- Acromegaly: Increased sized hands, feet, jaw, forehead
Disproportionate alterations of skeletal growth - uneven distributions of growth
Achondroplasia
- head and trunk normal size
- limbs are shorter than average
They show mutations in FGFR3
Achondroplasia
Disease inherited in an autosomal dominant manner.
50% chance
Describe FGFRs
Normal FGFR (fibroblast growth factor receptor)
FGF binds; FGFR forms a dimer
Normal receptors pair, become activated and transmit signal.
State the mutation in people with achondroplasia
Achondroplasia mutation 98% of cases in transmembrane domain G380R.
The FGFR remains dimerised - so no way to switch off signal.
It is constitutively active.
FGFR3 function
FGFR3 represses growth
- sends a negative signal to repress growth
- long bones are affected
- specifically proliferative zone of growth or epiphyseal plate affected (hypertrophic zone)
What does the mutation of FGFR3 have the most effect on ?
Most effect in chondrocytes
State some factors that influence differentiation
Location
Growth factors
Hormones
Adjacent cells
Autocrine factors
What is metaplasia ?
Change of differentiated cell type
Response altered cellular environment (e.g. stress)
Often epithelial or mesenchymal cels
Example of metaplasia
Lungs of smokers.
Epithelium of trachea and bronchi in smokers.
Columnar epithelium –> Squamous epithelium
What is dysplasia ?
Expansion of immature cells
- Increased cell proliferation
- Atypical morphology
- Decreased differentiation
- Often pre-malignant
What is neoplasia ?
Abnormal uncoordinated, excessive cell proliferation.
Persists after initiating stimulus is withdrawn.
Example of dysplasia
Cervix
- smear for cervical screening
- expansion of immature cells
- cells continue to proliferate, but remain in their least differentiated form
Disorders of differentiation and morphogenesis
Anomalies of organogenesis
Congenital abnormalities
Abnormalities of organogenesis
Agenesis
Atresia
Hypoplasia
Ectopia/heterotopia
Mal-differentiation
What is agenesis ?
Failure to develop an organ or structure
- Renal agenesis (only developed 1 kidney)
What is atresia ?
Relating to tube formation/closure:
Failure to develop a lumen
Failure to close
Failure to close
Spina bifida
Cleft palate
What is hypoplasia ?
Failure of an organ to develop to a normal size.
May only apply to a segment of an organ
Failure to develop a lumen
Oesophageal atresia
Duodenal atresia
Imperforate anus
What is ectopia / heteropia ?
Small areas of mature tissue from one organ present in another
- Endometriosis
What is maldifferentiation ?
Failure of normal differentiation.
Persistence of primitive embryological features.
- e.g. Multicystic renal dysplasia
Wilms tumour
Developmental malignancy
(defects in growth and differentiation)
- childhood kidney cancer
- can weigh up to 2kg
- tumours can contain cartilage, bone and smooth muscle
