Growth Flashcards
What is hyperplasia?
Increase in cell numbers
What is hypertrophy?
Increase in cell size
Name factors that affect growth
Genes, heredity
Environment: nutrition, disease, growth factors, hormones
Which hormones influence growth?
Thyroid hormones, growth hormones, sex hormones
Others: cortisol, insulin, vitamin D, parathyroid hormone
What do thyroid hormones do?
- Essential for normal growth and development
- Essential for protein synthesis in brain of foetus and infant
- Required for normal development of neurons
- Necessary for childhood growth
- Indirect effects on growth
- Facilitates actions of GH and sympathetic NS
What is hypothyroidism?
Condition where the thyroid gland is unable to produce sufficient thyroid hormones
Describe the effects of foetal/neonate hypothyroidism
- Sparse hair
- Large tongue
- Permanent mental impairments
Describe the effects of childhood hypothyroidism
- Impedes both brain development and skeletal growth
- Delayed tooth eruption
- Growth defects can be rectified by thyroxine supplements
- Some improvements in mental functions
What does growth hormone (GH) do?
- GH has metabolic and growth-promoting actions
- Main growth-promoting effects in postnatal period, infancy and adolescence
- Metabolic effects include: increase blood glucose levels, decreased glucose uptake by cells, increased lipolysis, facilitates uptake of amino acids for protein synthesis
Why is growth hormone described as ‘anti-insulin’?
GH increases blood glucose levels and decreases glucose uptake by cells (opposite effect of insulin)
Describe the growth promoting effects of growth hormone (GH)
- Growth-promoting effects are mainly indirect
- Some effects are exerted by IGF-1 produced in the liver
- Cartilage, bone, soft tissues, viscera
- IGF-1 -> cartilage proliferation in long bones
What are the ‘growth centres’ of long bones called?
Epiphyses
What are the two types of dwarfism?
- Hypothyroid: thyroid hormones deficiency
- Hypopituitary: growth hormone deficiency
Where is growth hormone produced?
Anterior pituitary gland
Testosterone and oestrogen are examples of what?
Sex hormones
What are testosterone and oestrogen responsible for?
- Pubertal growth spurt
- Stimulate bone growth but accelerate closure of epiphyseal growth plates
- Testosterone has anabolic effects on protein synthesis, increasing muscle bulk
- Effects of oestrogen and testosterone mediated by GH and IGF-1
Which sex hormone is described as ‘the anabolic steroid’?
Testosterone
How does insulin influence growth?
- Has no direct growth promoting actions
- Contributes to growth by: promoting foetal growth, stimulating secretion of IGF-1 (promotes post-natal growth), facilitates protein synthesis (by making glucose available for energy production)
What effect does cortisol have on growth?
- In high levels, cortisol inhibits growth
- Stimulates protein catabolism
- Suppresses bone growth and promotes bone resorption (-> osteoporosis)
- Raised levels of cortisol in stress account for growth-retarding effects of childhood illness
What effects do vitamin D and parathyroid hormone have on growth?
- Contribute to growth by ensuring adequate amounts of calcium and phosphate are available for bone formation
- Vitamin D is responsible for Ca2+ absorption from the gut
- PTH raises plasma Ca2+ levels
What effect does excess growth hormone have in childhood?
Accelerates normal growth -> gigantism
What effect does excess growth hormone have in adulthood?
- Longitudinal growth is not possible, and so appositional growth occurs in extremities
- Hands, feet and jaw increase in bulk -> acromegaly
Describe ‘acromegaly’
- Visual field changes
- Enlargement of hands
- Prognathism (mandible protruding)
- Greater spacing between teeth in mandible
What are acromegaly and gigantism usually associated with?
Increased levels of growth hormone
What is achondroplasia?
- Defective cartilage growth
- Affects long bones and cartilage growth centres e.g. spheno-occipital synchondrosis in cranial base
Describe ‘ageing’ and changes on population ageing
- Involves the gradual deterioration of all parts of the body
- Complicated by disease; many ‘age changes’ are really disease changes
- The population average age has increased
- More patients will be ‘senior citizens’
What does an individual’s life-span depend on?
- Genetics
- Environment (good nutrition, lifestyle, absence of disease)
Describe the biology of ageing
- Decline in the ability of cells to divide over time
- As cells divide, there is an accumulation of damage: errors in DNA sequence, abnormal proteins, damage to organelles (e.g. mitochondria)
- Free radicals: shortening of telomeres
What is apoptosis and when might it occur?
- Programmed cell death
- Cells programmed to ‘self-destruct’
- Apoptosis occurs in: development (e.g. tooth germ, nervous system), to replace ‘worn out’ cells, to destroy tumour cells
