5 - endocrine control of growth

what are the 3 factors affecting growth

genetics

nutrition

hormones

what hormones affect growth

growth hormone

IGF-1

insulin

thyroid hormones

sex steroids - puberty

cortisol

what are the 2 periods of rapid growth

infancy

puberty

what is growth in the foetal period mainly controlled by

nutritional intake

thyroid hormones

insulin

at what age does growth hormone become significant

10 months

what is puberty growth mainly due to

androgens, oestrogens producing spikes in GH secretion increasing IGF-1 leading to increased growth

before plate fusion in normal puberty, what do GH and IGF-1 cause

promote bone elongation and increased height, weight and body mass

hormones that control growth

GH

IGF-1

sex steroids

glucocorticoids

insulin

when do sex steroids influence growth

during puberty

when does GH influence growth

no effect on foetal period - 10 months starts to become relevant

what hormones are important for intra-uterine growth

thyroid hormone, insulin and IGF-2

why are thyroid homrones essential for normal growth

particularly important for development of normal nervous system in utero and early childhood

what is congential hypothyroidism

a condition where babies are born normal size but cannot produce own thyroid hormones

- stunted growth and development if untreated

what does maternal iodine deficiency result in

stunted intra-uterine growth

what type of hormone is growth hormone

peptide hormone

what is GH released from

anterior pituitary gland somatotroph cells

what is GH release controlled by

growth hormone inhibiting hormone (somatostatin)

growth hormone releasing hormone

in adult life, what is the function of GH

maintenance and repair of tissues

- GH promotes increase in cell size (hypertrophy) and cell division (hyperplasia)

What type of receptors does growth hormone act on?

Tyrosine kinase receptors

What is the result of growth hormone acting on tyrosine kinase receptors?

Influence intracellular targets by phosphorylation

How does growth hormone influence the growth of long bones?

Indirect action via IGF-1

What is the direct action of growth hormone in terms of metabolism regulation?

Regulation of metabolism

what is the indirect effect of GH

growth of long bones

how does GH have indirect effects om growth

achieved through action of intermediate IGF-I aka somatostatin C

what is IGF-1

insulin-like growth factor 1 with insulin like qualities

function of IGF-1

insulin life effects

- stimulates glucose uptake in muscle and bone

where is IGF-1 produced and released from

liver

when is IGF-1 secreted

in response to GH

what type of hormone are IGF-1 and GH

peptide hormones

how are peptide hormones transported in the blood

bound to carrier proteins

- to provide a reservoir

what is the IGF-1 negative feedback loop on GH

GHRH released by hypothalamus and somatostatin inhibited in response to circadian rhythm or fasting

anterior pituitary responds by releasing GH

GH acts on liver to release IGF-1 resulting in cartilage growth, bone and tissue growth and increased BG

why do epiphyseal growth plates close during adolescence

in repsonse to sex steroid hormones

how does GH directly regulate metabolism

- increased gluconeogenesis by liver

- reduces ability of insulin to stimulate glucose uptake

- makes adipocytes more sensitive to lipolyitic stimuli

- increased amino acid uptake and protein synthesis

when is the majority of GH released

first 2 hours of sleep - deep delta wave sleep

what stimuli increase GHRH secretion

decrease in energy supply to cells

increased amino acids

physical stress and illness

delta sleep

oestrogen and testosterone

what stimuli increase GHIH or somatostatin

glucose

free fatty acids

ageing

cortisol

what is gigantism

excess GH hormone in children before epiphyseal growth plates close

- 7ft tall

what is acromegaly

excess GH due to pituitary tumour usually AFTER epiphyseal growth plates close

- growth in other places like face, hands and feet

treatment of acromegaly

surgical removal of tumour

what is hyposecretion of GH usually caused by?

deficiency of GHRH

GH deficiency

genetic mutation or under-expression of genes on GH receptor - decreased IGF-1

precocious puberty (Excess GnRH)

hypothyroid dwarfism