Question

Identify the gland that secretes growth hormone, identify 3 targets of growth hormone, identify 3 specific effects of growth hormone, and explain why these effects occur considering the ultimate effect of growth hormone.

Answer 1

GROWTH HORMONE (GH)

• pituitary glands are 2 types anterior pituitary (API),posterir pituitary
• Somatotropes of anterior pituitary secretes growth hormone
• Targets :
• 1) stimulating body growth is to stimulate the liver and other tissues to secrete IGF-I
• IGF-I stimulates proliferation of chondrocytes (cartilage cells) ,resulting in bone growth.
• (2) Direct action of GH is seen in : (a) for its anti insulin activity (b) lipolysis (c) protein synthesis
• (3) IGF-II is perhaps important for foetal growth
• EFFECTS
• On metabolism :
• Blood sugar level is increased : GH opposes the effect of insulin
• Plasma free fatty acid level is increases because GH increases lipolysis.It is speculated that the higher levels of blood glucose and Free fatty acid (FFA) provide fuel to the tissues.
• GH diminishes the plasma amino acid level,because amino acids are utilized to produce protein.Thus GH causes protein accretion particularly in muscles.
• Blood urea level falls ,because less catabolism of amino acid
• GH causes +ve nitrogen balance and fall of blood urea level .Blood glucose level is increased
• On muscles
• Glucose uptake is reduced (anti - insulin effect) while amino acid uptake and protein synthesis increase
• Fat (adipose) tissue
• Lipolysis increases but glucose uptake reduced
• the body muscles increase but percentage of fat decreases.
• i.e, the lean body mass increases
• Viscera
• the different visceral mass (eg; masses of kidney,heart,pancreas etc,) increase
• Bones,cartilage
• In the young,in whom epiphyses are yrt to be closed (in the long bones),bone lengthens,the person becomes taller
• Growth of cartilage increases
• collagen deposition increases.
• Control of growth hormone
• major roles are played by 1)hypothalamus
• 2) peripheral feedback control (!) GHRH (growth hormone releasing hormone) : it stimulates GH secretion
• (!!) somatostatin : it inhibits GH production
• Applied physiology
• Pituitary gigantism and acromegaly
• In gigantism - excess of GH secretion in young age
• Acromegaly - over secretion of GH starts after closure of epiphysis.