Somatotropic Axis Flashcards
(32 cards)
Outline the pathway of the somatotropic axis
Hypothalamis hormone is GHRH
Anterior Pituitary hormone is GH
>inhibited by GHIH
Endocrine target is the liver which secretes IGFs
Non-Endocrine target is many tissues
Overview of Somatotropic Axis
GHRH
Hypothalamus & Paraventricular Nucleus secrete GHRH (Somatostatin)
Anterior Pituitary secretes GH (Somatotropin) which acts on the liver
Liver creates IGF-1,2 (Somatomedians) which acts on cartilage
Background on GH
Protein
Half-life: 6-20 min
Most abundant anterior pituitary hormone (10x more)
Plays an important role in growth
191AA polypeptide, synthesized, stored and secreted by somatotropic cells in the lateral wings of the anterior pituitary gland
GH secretion patterns
GH secretion occurs as several large pulses or peaks each day, 10-30 minutes in duration
The largest GH peak occurs about 1 hour after onset of sleep (Circadian Pattern)
Lifetime : basal levels highest early in life; the amplitude and frequency of peaks are greatest during the pubertal growth spurt and then decline throughout adult life
What keeps growing throughout your whole life ?
Cartilage
ie/ nose and ears
GH : transport in blood
GH may be transported as free hormone but much of GH is bound to binding protein (GHBP)
Which regulators of GH INCREASE secretion ?
hint : 6
- Sleep
- Exercise
- Hypoglycemia
- High dietary protein
- Steroids
- Ghrelin
Which regulators of GH DECREASE secretion ?
- Hyperglycemia
- Glucocorticoids
- Endocrine disruptors
How are IGF-1 transported in blood
IGF-1 is almost entirely bound to transport proteins (IGF-BP’s)
Some IGF-1 transport/binding proteins have an endocrine function (ie/ there are receptors for these proteins)
The physiological roles of GH and IGF-1
GH stimulates the synthesis and release of IGF-1 in many tissues, not just the liver
> therefore, it is very difficult to differentiate between the direct actions of GH and those of IGF-1
HOWEVER, GH and IGF-1 appear to exert opposite actions in some tissues which suggests that they do have independent roles
what does GH do to liver glucose release ?
Increases release
What does IGF-1 do to liver glucose release ?
Decrease
What does GH do to plasma glucose concentration ?
Increase
What does IGF-1 do to plasma glucose concentration ?
Decrease
What does GH do to the sensitivity of tissue to insulin ?
Decrease
What does IGF-1 do to sensitivity of tissue to insulin ?
Increase
What does GH do to lipolysis in adipocytes ?
Increase
What does IGF-1 do to lipolysis in adipocytes ?
Decrease
What does GH do to muscle amino acid uptake & protein synthesis
Increase
What does IGF-1 do to muscle amino acid uptake & protein synthesis
Increase ? **unproven
What are the metabolic effects of GH
Acts on liver, adipose tissue and most tissue
Liver creates IGF-1 which works stimulates cartilage and bone growth and stimulates protein synthesis growth in muscle and other organs
In adipose tissue it encourages lipolysis release of fatty acids and it decreases glucose utilization in most tissues
How do children grow ?
Children have 2 periods of rapid growth: postnatal & puberty
Children grow unproportionate
Will children grow normally without GH ?
GH (somatotropin) is made in the anterior pituitary
It is released throughout life, though its biggest role is in children, and peaks during teenage years.
GH stimulates growth of:
1) bone & cartilage growth
2) soft tissue growth
- hypertrophy (increased cell size)
- hyperplasia (increased cell number)
How is bone formed ?
Bone contains calcified ECM formed when calcium phosphate crystals precipitate and attach to a lattice support.
The most common form of calcium phosphate is HYDROXYAPATITE
Bone forming cells are called OSTEOBLASTS
