Growth physiology Flashcards
What is growth
Increase in cell numbers
-Hyperplasia
Increase in cell size
-Hypertrophy
What cells cannot grow
Neurons
What affects growth
Genes, heredity
Environment
-Nutrition
-Disease
-Growth factors, such as hormones
What hormones typically influence growth
Thyroid hormones
Growth hormone
Sex hormones
Others
-Insulin
-Cortisol
-Vitamin D, parathyroid hormone
Why do we have thyroid hormones
Essential for normal development and growth
Essential for protein synthesis in brain of fetus and infant
Required for normal development of neurons
Necessary for childhood growth
Facilitates actions of Growth hormone and Sympathetic NS
What are the affects of hypothyroidism
Fetal / neonate hypothyroidism
Sparse hair
large tongue
Permanent mental impairments
What is hypothyroidism
Deficiency of thyroid hormones in childhood impedes both brain development and skeletal growth
How can growth effects be rectified
By thyroxine supplements
What affects does hypothyroidism have on the teeth
Delayed tooth eruption
What are the metabollic actions of growth hormone
Increased blood glucose levels (“anti-insulin”)
Decreased glucose uptake by cells
Increased lipolysis, making fatty acids available for energy production
Facilitates uptake of amino acids for protein synthesis (especially liver, muscle)
What effect does IGF-1 have on bones
Cartilage proliferation in long bones, until epiphysis (growth centres) close
What is the anabolic steroid
Testosterone
What mediates the effects of sex hormones
Secretion of GH and IGF-1
How does insulin contribute to growth
Promoting foetal growth
Promoting post-natal growth by stimulating secretion of IGF-1
Facilitating protein synthesis (by making glucose available for energy production)
When are cortisol levels raised
Stress and illness
Why may individuals who were ill fora prolonged period of time as children have stunted growth/reduced growth
Increased cortisol levels during period of illness
How do the PTH and Vit D increase growth
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 does excess growth hormone cause
CHILDHOOD
-gigantism
ADULTHOOD
-acromegaly (hands, feet etc)
What is achondroplasia
Defective cartilage growth
What is ageing
Involves a gradual deterioration of all parts of the body
What impacts lifespan
Genetics
Environment
-Good nutrition
-Lifestyle
-Absence of disease
No evolutionary advantage in old age; reproductive ‘fitness’ takes priority
What causes ageing
There is a decline in the ability of cells to divide over time
As they divide, there is accumulation of damage:
-Errors in DNA sequence
-Abnormal proteins
-Damage to organelles (e.g. mitochondria)
Free radicals; shortening of telomeres
When does apoptosis occur
In development; e.g. tooth germ, nervous system
To replace ‘worn out’ cells
To destroy tumour cells
What is apoptosis
Programmed cell death
Cells programmed to ‘self-destruct’
