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
How does insulin help you grow?
Protein synthesis
What is responsible for pubic hair growth ?
Adrenals
Turner’s syndrome
hypergonadotropic hypogonadism → ovarian failure
Klinefelter’s syndrome
hypergonadotropic hypogonadism → gonadal failure in males (XXY) - start puberty normal and then testicles are destroyed
Kallmann’s sundrome
Hypogonadotropic hypogonadism
Anosmia
Reduce sexual development
What is hypogonadotropic hypogonadism
The hypothalamus/pituitary has failed
Low FSH and LH, low sex hormones
What is hypergonadotropic hypogonadism?
High FSH and LH, low sex hormone
Sex organs have failed
McCune-Albright syndrome
Gonadotropin-independent precocious puberty
Triad of cafe-au-lait spots, precocious puberty and fibrous dysplasia
Hypothalamic hamartoma
- Gonadotropin-dependent precocious puberty
- Precocious puberty and gelastic epilepsy
- Spontaneous GnRH from hypothalamus
- GnRH release caused by hypothyroidism, head trauma, CNS infection or tumour
Actions of GH
- Direct: increased lipolysis and protein synthesis, decreased glucose uptake
- Indirect: via IGF - stimulates cell growth and proliferation (chondrocytes and myoblasts)
What is gigantism?
GH excess in puberty before epiphyses fuse
