255. Physiology of growth Flashcards
What regulates growth (7)
Growth hormone vs GHIH release
Thyroid hormone
Insulin
Sex steroids
Availability of nutrients
Stress (bad)
Genetics
What are the actions of growth hormone?
Growth and development (indirect action)
Regulation of metabolism (direct action)
What hormones must be present to allow GH to be affective?
Thyroid hormones and insulin- permissive
Insulin-like growth factor 1- mediates action of GH
What affects do GH/IGF-1 have on bone growth?
GH stimulates chondrocyte precursor cells in epiphyseal plates to differentiate into chondrocytes
Cells secrete IGF-1 and become responsive to it
IGF-1 acts as an autocrine or paracrine agent to stimulate chondrocytes to produce cartilage, the foundation of bone growth
What is the action of growth hormone?
Mobilises glucose stores to increase blood glucose
Inhibits actions of insulin
Promotes lipolysis
Promotes amino acid uptake
How is growth hormone secreted?
Spontaneous fluctuations, typically seen in the first 2 hours of sleep. majority is released qt nigh with little seen in waking hours.
IGF-1 stays constant perhaps buffering the effects of GH release
What stimulus increase GH release?
Energy supply to cells Increased AA in plasma Stress (e.g. infection) Delta sleep Oestrogen and testosterone
What stimulus decrease GH release?
Glucose
Free fatty acid
REM sleep
Cortisol
Different hormones control growth at various parts of life. What hormones control when?
Thyroid hormones- 0-4 years dominant, reduce from 4-20
Growth hormone- 2-18
Androgens and estrogens-10-20, peaking at around 16
When are the two periods of rapid growth in children?
Infancy: Amazing growth spurts, 2.5cm in a few days
Puberty: due to androgens and oestrogens produce growth spurts.
What causes dwarfism
Deficiency of GH
End organ is unresponsive
Failure to produce IGF-1
Precocious puberty
Hypothyroidism
