WEEK 2: GROWTH HORMONE Flashcards
Why is growth hormone referred to as a tropic hormone?
It exerts its growth promoting effect indirectly by stimulating IGF 1( insulin like growth factor I release from the liver which is a tropic hormone too
* Production of IGF 1 is mostly dependant on adequate nutrition.That is even if the growth hormone is produced as long as there is no food then the GH would not be able to active IGF I. It is also influenced by age related factors.( A dramatic increase in in circulating IGF I levels accompanies the moderate increase in GH at puberty.
NoTe:IGF II is not influenced by GH.It is primarily important during fetal development.
What is a tropic hormone?
A hormone that regulates the production and secretion of another hormone
State the functions of the growth hormone
- regulates body growth
Helps children get taller
*maintains healthy muscles and bones,impacts fat distribution in adults - Also impacts metabolism ( increase glucose levels in hypoglycemia for energy production#stimulates protein synthesis #spares glucose for the brain )
What influences continuous net protein synthesis to occur in growing children?
Growth Hormone
What are the main characteristics of growth?
- increase in size
- Lengthening of bones
*Increase in number of cells ( cell division)
NOTE: Growth requires net synthesis of proteins
What hormone is responsible for fetal growth?
Placental growth hormone
* It’s stimulates IGF I which stimulates foetal growth when nutrients are available.It production is sensitive to undernutrition.
*IGF II stimulates placenta growth and nutrients transfer
NOTE: Growth Hormone has a diurnal rythm:low and mostly constant during the day,has great outburst when in deep sleep
It release is mainly to keep the levels of Glucose, fatty acids and amino acids in right proportions
It saves more glucose for the brain and mostly uses fatty acids for energy usage by muscles
What is the function of bone marrow?
Site for blood cell production
What are the functions of the precipitation of calcium phosphate crystals within the osteoid?
- gives the bone it’s ability to hold its shape when squeezed or compressed
Differentiate between osteoclasts and osteoblasts
Osteoblasts: bone formation,reduce blood calcium
Osteoclasts: bone resorption , increase blood calcium
How is growth in length of bone achieved?
Page 709 Sherwood
Name other hormones responsible for growth apart from Growth Hormone
- Insulin: Hyperinsulinism and the fact that the IGF1 receptors is similar to the insulin receptor so it can act on then and stimulate growth
*Androgens: but they only work when the GH is present
State the constituents of osteoid
*collagen fibers in a semisolid gel
Has a rubbery consistency
List some factors influencing growth
*Genetic Determination of an individual’s maximum growth capacity
*Adequate diet ( enough protein+ ample amino acids to accomplish protein synthesis necessary for growth
*Freedom from stress and chronic diseases
* Normal levels of growth influencing hormones
What the other name for Insulin like growth factors (IGF’s)?
Somatomedins
State the difference between a bone and a cartilage
Cartilage is not calcified
Study the anatomy of a long bone (Sherwood page 708)
How is growth in thickness of the bone achieved?
- Adding new layer of bone on top of the outer surface of existing bone.
Osteoblasts:their activity within the periosteum ( connective tissue that covers the outer bone) deposit new bone on the external surface
*Osteoclasts: dissolve bony tissue on the inner surface next to the marrow cavity allowing enlargement of the marrow cavity to keep with the increased circumference of bone shaft.
How do GHRH and GHIH regulate Growth hormone?
Somatostatin acts on the anterior pituitary gland somatotropes by binding on the with G protein coupled receptors linked to the cAMP second messenger pathway decreasing cAMP
GHRH: acts on the same way as Somatostatin but increases cAMP
State the factors that influence GH secretion
- low blood glucose,fatty acid and high amino acids,exercise,stress
- Also ghrelin hormone: appetite stimulator,released from the stomach
Describe the negative feedback pathway of regulating Growth Hormone ( hypothalamus -liver axis)
*In the liver, GH stimulates IGF -1 release which inhibits somatotropes in the anterior pituitary gland directly to secrete GH
*It further inhibits GHRH secreting cells and stimulates Somatostatin secreting cells in the hypothalamus,thus somatotropes stimulation by hypothalamus is decreased.
*GH itself inhibits hypothalamic GHRH secretion and stimulates GHIH when in excess
State the functions of osteoid
- makes the bone resistant to breakage when tension is applied
What is the relationship between GH and IGF 1?
*GH stimulates IGF I synthesis which mediates it’s growth promoting factors.
Most IGF I comes from the liver.They work via tyrosine kinase pathway.They bind to receptor- enzymes that activate designated effector proteins within the target cell by phosphorylating the tyrosines.
