Physiology of growth and development Flashcards
Puberty
Sexual maturity - secondary sexual characteristics appear and reproductive organs become functional
Adenarche
Release of androgens from adrenals - precedes puberty by 2 years
Changes that occur in male puberty
- Growth spurt
- Increase in lean muscle mass
- Changes in body composition
- Increase in penile length and first ejaculation
- Pubic hair
- Testicular enlargement
Normal age of male puberty
9-14
Changes in female puberty
- Growth spurt
- Breast development
- Changes in body composition
- Pubic hair
- Period
- Increase in fat
Normal age of female puberty
8-13 (breasts) or 15 (period)
How is growth controlled in children?
Growth hormone
How does GH work?
Increases fatty acid levels in blood - accelerates triglyceride breakdown and decreases glucose uptake from muscles
Stimulates production of insulin-like growth factors
Hypertrophy and hyperplasia
IGF-1
- Synthesised by GH
- Released from the liver into the blood stream by GH stimulation
- Dependent on adequate nutrition and age
IGF-2
- Not influenced by GH
- Important during foetal development
How do bones thicken?
Osteoblasts within the periosteum which deposit new bone on the external surface of the bone. Whilst this happens, osteoclasts dissolve bone on the inside of the bone so the marrow cavity enlarges in proportion to the lengthening
How do bones lengthen?
Multiplication of chondrocytes in the epiphyseal plates - older cartilage cells in the diaphysis are enlarging which widens the gap between the epiphyseal plate and diaphysis and fills it with cartilage. The matrix around the oldest hypertrophied cartilage calcifies, killing the cells. Ossification lengthens te bone
GH secretion regulation
- GHRH (stimulatory and dominant) and GHIH (inhibitory)
- GHRH and somatostatin act on anterior pituitary somatotropes by binding with GPCR (GHRH increases cAMP and somatostatin decreases cAMP)
- GH stimulates IGF-1 secretion by the liver but IGF-1 is primary inhibitor of GH secretion from anterior pituitary
- IGF-1 inhibits somatotropes in pituitary and decreases GH by inhibiting GHRH cells and stimulating somatostatin secreting cells in hypothalamus
GH excess
- Tumour of GH producing cells in anterior pituitary
- Gigantism: overproduction of GH in childhood before epiphyseal plates close = rapid growth in height without distorting body proportions
- Acromegaly: hypersecretion occurs after adolescence when epiphyseal plates have already closed and prevented further growth in height = bone thickening
How does thyroid hormone help you grow?
Allows GH to act
