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BioMed > Somatotropic Axis > Flashcards

Somatotropic Axis Flashcards

1
Q

Outline the pathway of the somatotropic axis

A

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

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2
Q

Overview of Somatotropic Axis

A

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

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3
Q

Background on GH

A

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

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4
Q

GH secretion patterns

A

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

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5
Q

What keeps growing throughout your whole life ?

A

Cartilage

ie/ nose and ears

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6
Q

GH : transport in blood

A

GH may be transported as free hormone but much of GH is bound to binding protein (GHBP)

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7
Q

Which regulators of GH INCREASE secretion ?

hint : 6

A
  • Sleep
  • Exercise
  • Hypoglycemia
  • High dietary protein
  • Steroids
  • Ghrelin
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8
Q

Which regulators of GH DECREASE secretion ?

A
  • Hyperglycemia
  • Glucocorticoids
  • Endocrine disruptors
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9
Q

How are IGF-1 transported in blood

A

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)

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10
Q

The physiological roles of GH and IGF-1

A

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

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11
Q

what does GH do to liver glucose release ?

A

Increases release

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12
Q

What does IGF-1 do to liver glucose release ?

A

Decrease

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13
Q

What does GH do to plasma glucose concentration ?

A

Increase

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14
Q

What does IGF-1 do to plasma glucose concentration ?

A

Decrease

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15
Q

What does GH do to the sensitivity of tissue to insulin ?

A

Decrease

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16
Q

What does IGF-1 do to sensitivity of tissue to insulin ?

A

Increase

17
Q

What does GH do to lipolysis in adipocytes ?

A

Increase

18
Q

What does IGF-1 do to lipolysis in adipocytes ?

A

Decrease

19
Q

What does GH do to muscle amino acid uptake & protein synthesis

A

Increase

20
Q

What does IGF-1 do to muscle amino acid uptake & protein synthesis

A

Increase ? **unproven

21
Q

What are the metabolic effects of GH

A

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

22
Q

How do children grow ?

A

Children have 2 periods of rapid growth: postnatal & puberty

Children grow unproportionate

23
Q

Will children grow normally without GH ?

A

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)

24
Q

How is bone formed ?

A

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

25
Q

How does bone grow ?

A

Bone DIAMETER increases; when growth occurs around the bone. Matrix deposits on the outer surface of bone

Bone LENGTH increases; when growth occurs at EPIPHYSEAL PLATES

26
Q

How does linear bone growth from epiphyseal plates work ?

A

The epiphyseal plates are near the end of the bone contains CHONDROCYTES; columns of collagen-producing cells

As the collagen layer thickens, the old cartilage calcifies

CHONDROCYTES then degenerate

Osteoblasts invade and lay bone matrix on top of the cartilage base

27
Q

Overall affect of GH on bone growth

A

GH directly stimulates chondrocytes

GH stimulates production of IGF-1 in liver

IGF-1 helps stimulate chondrocyte & osteoblast activity, to promote bone

28
Q

GH-related disorders: underproduction or decreased sensitivity in growing animals

A

Result is :

pituitary dwarfism;

  • small size, juvenile proportions
  • normal shape at maturity but stunted

pygmies (laron-type dwarfism);

  • decreased responsiveness to GH (receptor deficieny)
29
Q

GH-related disorders:

Overproduction of GH in growing animals

A

Pituitary Gigantism

30
Q

GH-related disorders:

underproduction or decreased sensitivity in adults

A

Alopecia

Thin skin, hair loss

Cushing’s syndrome

increase in cortisol inhibits GH synthesis

31
Q

GH-related disorders:

over production in adults

A

Acromegaly

> thickening of bones/joints and skin

> enlargement of internal organs (tongue, liver, spleen)

32
Q

Progression of GH deficiencies in children vs adults

A

Severe GH (or GHR) deficiency in childhood - dwarfism

Oversecretion of GH in children- gigantism

Oversecretion in adults - acromegaly

BioMed (10 decks)

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