Growth and ageing Flashcards
Define hyperplasia
increase in cell numbers
Define hypertrophy
increase in cell size
Which cells can grow/regenerate?
labile and stable cells (e.g. liver, skin, blood cells)
Which cells cannot grow/regenerate?
permanent cells e.g. neurons, podocytes
What factors affect growth?
genetic (hereditary e.g. ethnicity) and environmental factors
Examples of environmental factors that affect growth
nutrition, disease, growth factors e.g. hormones
How many growth spurts are there?
2
What is the first growth spurt associated with?
brain development
What is the second growth spurt associated with?
growth of reproductive organs (sex hormones)
Why is the recommended intervention age for orthodontics 12 years old?
Because brain growth is related to facial development and it plateaus at ~10 years old
When does brain development plateau?
approximately 10 years of age
What type of orthodontic appliances are used if intervention is required before 10 years of age?
removable / non-fixed appliances
How are sex hormones related to total body height?
sex hormones cause the closure of epiphyseal plates which stops the growth of long bones
What are the main hormones that influence growth?
thyroid hormones, growth hormone, sex hormones
Aside from thyroid hormones, growth hormones and sex hormones, which other hormones influence growth?
insulin (glucose), cortisol, vitamin D and parathyroid hormone (Ca)
Functions of thyroid hormones
normal development and growth including neuronal, protein synthesis in the brain of foetus and infant, facilitates actions of growth hormone and sympathetic NS
What is the name of the deficiency of thyroid hormones?
hypothyroidism
What is the name of hypothyroidism in infants?
foetal / neonate hypothyroidism
What are the symptoms of foetal / neonate hypothyroidism?
sparse hair, enlarged tongue, delayed tooth eruption, permanent mental impairments
What types of growth does hypothyroidism impede on?
brain development and skeletal growth
How can growth defects due to hypothyroidism be rectified?
thyroxine supplements
Can thyroxine supplements lead to complete recovery from hypothyroidism?
recovery of mental functions may not be complete (effects of missed development already in place) - depends on onset and duration of hypothyroid state
What two areas of development does growth hormone affect?
metabolic and growth-promoting
Does growth hormone have mainly direct or indirect effects on metabolism and growth-promotion?
indirect actions
What are the metabolic actions of growth hormone?
increase blood glucose levels, decrease glucose uptake by cells, increase lipolysis, facilitates uptake of amino acids
Why can growth hormone be referred to as anti-insulin?
because GH increases blood glucose concentration by reducing glucose uptake into cells
What is the advantage of growth hormone increasing lipolysis?
to make more fatty acids available for energy production
What is the advantage of growth hormone facilitating amino acid uptake?
increases protein synthesis
Which cells does growth hormone particularly increase amino acid uptake for?
liver and muscle cells
When do the main growth-promoting effects of growth hormone occur?
post-natal period, infancy and adolescence
Which type of growth hormone exerts effects on cartilage, bone, soft tissues and viscera?
IGF-1 (insulin-like growth factor)
Where is IGF-1 produced?
liver
How does IGF-1 affect long bones?
IGF-1 stimulates cartilage proliferation in long bones until epiphyses close
Name 2 types of dwarfism
hypothyroid and hypopituitary dwarfism
What is the appearance of a hypothyroid 8 year old?
infant proportions (height of 2yo) but chubbier and wider face shape
What is the appearance of a hypopituitary 8 year old?
normal proportions but height of 2 year old and lean
Name the sex hormones
oestrogen and testosterone
Which hormones are responsible for the pubertal growth spurt?
sex hormones
How are the effects of sex hormones mediated?
by increased secretion of GH and IGF-1
What is the effect of sex hormones on bone development?
Sex hormones stimulate bone growth but accelerate closure of epiphyseal growth plates (fast growth but limited to shorter time)
Which hormone is the anabolic steroid?
testosterone
What is the effect of testosterone?
testosterone has an anabolic effect on protein synthesis, increasing muscle bulk
Which hormone does insulin promote the secretion of?
insulin-like growth factor IGF-1
How does insulin contribute to growth?
promotes foetal and post-natal growth, facilitates protein synthesis
How does insulin promote post-natal growth?
insulin stimulates the secretion of IGF-1 (results in cartilage proliferation in long bones)
How does insulin facilitate protein synthesis?
insulin stimulates glucose uptake into cells for energy production
What is the effect of higher than normal cortisol levels?
growth inhibition
How does cortisol inhibit growth?
stimulates protein catabolism, suppresses bone growth, promotes bone resorption
What bone condition is related to stress?
osteoporosis (cortisol stimulates bone resorption)
Why does childhood illness cause growth-retarding effects?
illness and stress cause raised cortisol levels which inhibits growth
How do vitamin D and parathyroid hormone contribute to growth?
ensure adequate amounts of calcium and phosphate are available for bone formation
What aspect of development are calcium and phosphate essential for?
bone growth
Effect of vitamin D (1,25 (OH)2 cholecalciferol / calcitriol)
increase plasma Ca and PO4
Effect of PTH
increase plasma Ca
What is the effect of excess growth hormone in childhood?
normal growth is accelerated leading to gigantism
What is the name of the condition that occurs when a child has excess growth hormone?
gigantism
What happens when adults have excess growth hormone?
appositional growth occurs in extremities
What is appositional growth?
new bone tissue is added to the surface of existing bone
Why does longitudinal growth not occur if there is excess growth hormone in adults?
epiphyseal plates are sealed
What is the name of the condition that occurs when there is excess growth hormone in adults?
acromegaly
What happens during acromegaly?
hands, feet and jaw increase in bulk
How may acromegaly impact oral health?
wider mandible leads to diastema - interproximal caries reduced, masticatory mucosa keratinised
Where is growth hormone produced?
anterior pituitary gland (adenohypophysis)
What can cause gigantism in children or acromegaly in adults?
tumour of the pituitary gland (causing excess GH secretion)
Where is the pituitary gland located?
in a saddle-shaped depression of the sphenoid bone called the sella turcica
How can a tumour of the pituitary gland be identified in a radiograph of the head?
increased area of radiolucency shows an enlarged sella turcica
What is the name of the disorder that causes defective cartilage growth?
achondroplasia
What does achondroplasia affect?
long bones and cartilage growth centres e.g. spheno-occipital synchondrosis in cranial base. Leads to dwarfism
What factors does an individuals lifespan depend on?
genetic and environmental factors
Which environmental factors affect lifespan?
nutrition, lifestyle, absence of disease
What is cellular ageing?
a decline in the ability of cells to divide over time due to accumulation of damage and shortening of telomeres
Where does damage accumulate in cells as they divide?
errors in DNA sequence, abnormal proteins, damage to organelles
What is apoptosis?
programmed cell death
When does apoptosis occur?
during development, to replace worn out cells, to destroy tumour cells
