Effects of Growth Hormone and IGF

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Questions and Answers

What is a potential consequence of growth hormone deficiency pre-puberty?

Accelerated pubertal development

Increased metabolism

Delayed skeletal maturation (correct)

Excessive growth of facial features

Which imaging study is primarily used to assess bone age in children suspected of growth hormone deficiency?

CT scan of the skull

MRI of the brain

X-ray of the hand (correct)

Ultrasound of the abdomen

What is Laron syndrome primarily caused by?

Genetic mutations of the growth hormone receptor gene (correct)

Pituitary adenomas

A deficiency in thyroid hormones

Excess secretion of growth hormone

Which symptom is NOT associated with lack of growth hormone post-puberty?

Excessive growth of extremities Signup and view all the answers

Which of the following is a characteristic manifestation of acromegaly?

Thickened skin Signup and view all the answers

Which hormone stimulation test is commonly used in the diagnosis of growth hormone deficiency?

Arginine Signup and view all the answers

What is one of the psychological effects associated with growth hormone deficiency post-puberty?

Anxiety Signup and view all the answers

What typically precedes the condition of acromegaly in adults?

A benign tumor of the pituitary gland Signup and view all the answers

Which of the following conditions is characterized by GH insensitivity?

Laron syndrome Signup and view all the answers

What is a common clinical assessment performed for suspected growth hormone deficiency?

Recording height and weight on a growth chart Signup and view all the answers

What is the primary role of IGFBP-3 in the circulation of IGF?

Promotes IGF mediated somatic growth Signup and view all the answers

Which of the following is a stimulus for the secretion of IGF-1?

Growth Hormone (GH) Signup and view all the answers

GH deficiency before puberty typically results in which of the following growth velocities?

Less than 6 cm/year before age 4 years Signup and view all the answers

What effect does growth hormone primarily have on glucose metabolism?

Increases plasma glucose Signup and view all the answers

Which of the following proteins is associated with growth inhibition when present in high amounts?

IGFBP-1 Signup and view all the answers

Which statement is true regarding the IGF family?

IGF-1 has 70 amino acids and shows 50% homology with insulin Signup and view all the answers

What is a common characteristic of individuals with GH deficiency pre-puberty?

Normal proportionality between upper and lower body segments Signup and view all the answers

The effect of increased IGFBP levels on IGF activity is typically to:

Inhibit IGF availability to tissues Signup and view all the answers

What does high IGFBP-3 correlate with in terms of growth effects?

Stimulation of somatic growth Signup and view all the answers

What is a key function of IGFBPs in relation to IGF?

They provide high specificity in binding to IGF Signup and view all the answers

Study Notes

Effects of Growth Hormone (GH)

GH has direct effects on various tissues and organs
Increases amino acid (AA) uptake
Increases protein synthesis
Decreases protein breakdown
Influences glucose entry into cells
Directly alters lipid metabolism
Decreases glucose uptake
Increases lipolysis (fat breakdown)
Leads to increased free fatty acids (FFA)
Results in insulin resistance
Causes hyperglycemia (high blood glucose)
Increases insulin secretion
Stimulates IGF-1 production
Stimulates gluconeogenesis
Stimulates glycogenolysis
Impacts protein synthesis
Affects AA uptake

IGF and Insulin Receptors

IGF-1, Insulin, and IGF-1 receptors share structural similarities
Hybrid receptors exist between insulin and the IGF-1 receptor
Metabolic effects and mitogenic effects are both influenced by these receptors

IGF Family: Receptors and Binding Proteins

IGF binding proteins (IGFBPs) are crucial for IGF function
IGFBPs bind circulating IGFs with high affinity
They act as carriers for IGFs in the bloodstream
Prolong the half-life of IGFs
Regulate IGF access to its receptors
Function through receptor interaction, regardless of the presence of IGFs

Insulin-like Growth Factor Binding Proteins (IGFBPs)

IGFBPs bind circulating IGFs with high affinity
Act as carriers for IGFs
Prolong IGF half-life
Regulate IGF access to receptors
Function independent of IGFs

IGFBPs—Modify IGF Activity

IGFBP-3 is the most prevalent form of IGFBP
Main carrier of IGF in circulation
Promotes somatic growth related to IGF
Associated with growth stimulation
IGFBP-1 is typically present in small amounts
Associated with growth inhibition

Binding Proteins Regulate Free IGF Availability

Binding proteins influence IGF availability to receptors
Decidual IGFBP-1 and placental IGFs have critical roles during implantation
High levels of placental IGF with low levels of decidual IGFBP-1 lead to abnormal invasion
Controlled invasion leads to a normal placenta
Low levels of placental IGF with high levels of decidual IGFBP-1 lead to shallow implantation, abortion, and placental dysfunction
High levels of both are linked to tubal pregnancies and abnormal placental structures (increta/percreta)

Insulin-like Growth Factors - Somatomedins

IGF-1 and IGF-2 are somatomedins
IGF-1 (somatomedin-C):
- 70 amino acids
- 50% homology with insulin
- Stimuli for secretion: GH, nutritional status
IGF-2:
- 67 amino acids
- 70% homology with insulin
Stimuli for secretion: Nutritional status, GH

Bone Cell-Specific Effects of IGFs

IGFs promote bone cell proliferation and maturation
Regulate the stem cells pool and lineage commitment
Affect mesenchymal and hematopoietic stem cells
Influence osteoclast activity and fusion-induced multinucleation
Impact osteocyte network integrity
Promote differentiation and mineralization of osteoblasts
Affect growth plate zones

Other Effects of Growth Hormone

Adipose tissue: Increased lipogenesis
Extra skeletal tissue: Cell growth proliferation and protein synthesis
Blood glucose: Overall increase in plasma glucose, insulin resistance, decreased glucose uptake, and pituitary diabetes

GH Hormone Deficiency: Pre-Puberty

Most common pituitary hormone deficiency in children
Isolated or accompanied by deficiency in other pituitary hormones
Panhypopituitarism: Rare condition – reduced production of all pituitary hormones
GH deficiency leads to slow growth and short stature

Growth Hormone Deficiency: Pre-puberty Manifestations

Growth failure: Height below 3rd percentile
Slow growth velocity: <6 cm/year before age 4, <5 cm/year from age 4 to 8, <4 cm/year before puberty
Short stature
Normal proportionality
Skeletal maturation delayed by more than 2 years
May have delayed tooth development
Delayed or absent pubertal development
Relative obesity

GH Pre-Puberty Deficiency: Clinical Assessment

Height and weight data are recorded on a growth chart
Imaging studies: X-rays (bone age), MRI (pituitary gland and hypothalamus)
Hormone and binding protein measurements
GH stimulation tests (arginine)

Growth Deficiencies Unrelated to GH Deficiency

Laron syndrome: GH insensitivity or primary IGF-1 deficiency
Rare genetic disease (autosomal recessive manner)
Genetic mutations in the growth hormone receptor gene
Defect in GH and IGF-1 signaling pathway
Genetic IGF deficiency
Nutritional neglect

Undersecretion Post Puberty

Lack of GH leads to altered metabolism, increased adiposity, excessive tiredness, increased cardiovascular disease (CVD), anxiety, depression, and reduced quality of life

Over-Secretion of GH

Age-dependent Gigantism (prepuberty)
Post-puberty Acromegaly

Acromegaly (Over-Secretion)

Rare condition, develops between ages 30-50
Mostly due to benign pituitary tumors (>99% of cases)
Symptoms include thickened skin, coarse facial features, enlarged hands, feet, lips, nose, and tongue; jaw protrusion; thickened ribs, barrel chest, organ enlargement; cardiovascular (CVS) disease; upper airway obstructions, sleep apnea; carbohydrate intolerance, pituitary diabetes, and general tiredness

Fetal Growth

Fetal growth is controlled by various factors, including growth hormones.

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Description

This quiz explores the complex effects of Growth Hormone (GH) on various tissues and its relationship with Insulin-like Growth Factor (IGF). Learn about GH's impact on metabolism, protein synthesis, and its interactions with Insulin receptors. Test your knowledge on the roles of IGF and its binding proteins in metabolic functions.