2. Role of hGH,throid hormones and sex steroids in the control of growth

Trophic Hormones

Hormones that promote growth and development

Before puberty

hGh, IGFs, thyroid hormones and glucorticoids

During adolescence

Sex steroids and GH/IGF-1- PUBERTAL GROWTH SPURT

What ends rapid growth phase during puberty 

Ossification of bone growth plates, due mainly to actions of sex steroids

Ossification is the process of converting cartilage or other soft tissue into bone

hGH function

increase in: growth; metabolism; protein and bone synthesis

hGH Malfunction

• Growth Hormone Deficiency

• Gigantism/ acromegaly

Functions of IGFBPs

• reservoir of IGFs

• Limits availability of IGFs to receptors on target tissues ie increasing their half-lifes

• transport in plasma

• Inhibit/ potentiate IGF-1- influence how IGFs are represented to receptors

When is a high level of IGF-1 produced

• postnatal period 

• pubertal stage

Somatopause

age-related decline in GH and IGF-1

IGF-2 

foetal growth factor- embryonic delevopment

What does IGF-1 bind to?

Tyrosine kinase receptors 

• IGF1R- PI3K-Akt pathway

• Insulin-R

What is Acromegaly

GH Excess in Adults

• foot enlargement

• degenerative joint disease in mid-foot/ankle

• tarsal tunnel syndrome

GH deficiency

• Osteoporosis

• Impaired wound healing

• unexplained stress fractures

c-cells

located on the thyroid gland

secrete calcitonin- decrease Ca++ levels in the blood, antagonist for PTH

Follicular cells

Secrete 2 iodine-containing compounds

• T3

• T4

increase meta

and growth

Calcitrol

Active form of Vit D

Activated by PTH

Increase plasma Ca

What do T3/T4 bind to?

Thyroxine-binding globulins (TBCs)

For thyroid hormone feedback loop what inhibits TSH and TRH?

TRbeta

Congenitial iodine deficiency syndrome (CIDS)

may occur at birth- impaired physical and mental development

• hypothyroidism

• insufficient dietary iodine during pregnancy

What influences girls height velocity

• hGh

• oestradiol

• androstenedione

What influences a boys height velocity

• hGH

• Testosterone

• Oestradiol

In terms of growth-promoting and anabolic effects, what is testosterone dependent on?

hGH, it will not enhance IGF-1 growth response otherwise