Growth Hormone |Somatotrophin| Human Physiology|Hormone

Growth Hormone or Somatotrophin

In this article, we will learn about the Growth hormone, its site of secretion, its mechanism of action, its effects on different cells of our bodies, and much more. Growth hormone is also known as Somatotrophic hormone.

Keywords:  Growth hormone| Somatotropin| lipolysis |proteoglycan | chondrocytesl chondroblast|Somatomedins | Insulin-like Growth Factor -I (IGF-1)|collagen fibre-I 

 

Table of contents

1.	Introduction
2.	Functions
3.	Mechanism of Action
4.	Stimulant of GH secretion
5.	Decrease of GH secretion.

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Introduction

Acidophilic somatotroph cells present in the anterior Pituitary gland secrete growth hormone. Somatotrophs are acidophilic, which means they love acidic dyes and become red when exposed. Somatotrophs constitute about 50% of the anterior pituitary gland's cells.

Daily secretion: 

Daily secretion is 0.2 to one milligram. Growth hormone is secreted episodically and circulates in the blood bound to a plasma protein.

The average concentration is 2 to 4 nanograms/milliliter of blood. It is higher in children and lower in old age.

Chemical structure: 

It is a straight-chain peptide hormone with 191 amino acids without branching. Prolactin and Human chorionic somatomammotrophin (HCS) share marked structural similarities to growth hormone.

The function of growth hormone

Action on liver:

1. Synthesis of Insulin-like Growth Factor -I (IGF-1)

2. Gluconeogenesis

Action on adipose tissue

1. Lipolysis

Action on muscles

1. Increases amino acid uptake.

Mechanism of action:

Growth hormone binds to its specific receptor protein on the hepatocyte. When the receptor protein combines with the Growth hormone, it stimulates phosphokinase. It causes the phosphorylation of JAK, which is present on the receptor protein's inner (cytoplasmic) side.

After phosphorylation, JAK forms diamer and phosphorylates the tyrosine amino acid present in the cytoplasm.

This causes the phosphorylation of the SH domain of STAT(Signal Transducer Activation of Translation). Two molecules of the phosphorylated STAT molecule form a diameter and enter the nucleus, where they combine with the Specific CIS Regulatory Segment of the DNA. After this combination causes transcription, the same sequence of DNA forms mRNA(Translation).

Now, m RNA migrates in the cytoplasm, forming a protein called insulin-like Growth Factor -I (IGF-1) in the hepatocytes.

[JAK (JANUS Kinse.)that triggers JAK-STAT(Signal Transducer Activation of Translation) Pathways. Janus is a Roman God with two faces.]

Insulin-like Growth Factor I (IGF-1) enters the circulation and affects the muscles, bones, and cartilage.

Mechanism of action of Insulin-like Growth Factor -I (IGF-1) on muscles:

Insulin-like Growth Factor -I (IGF-1) binds with specific receptors on sarcolemma and enters into the muscles. It increases amino acid entry into the muscles and initiates protein synthesis -actin and myosin etc, leading to muscle hypertrophy.

On bones

Insulin-like Growth Factor -I (IGF-1)attaches with specific receptors, enters into the bone, and causes

1. Increase in collagen fibre-I synthesis.

2. Increases osteoblastic activity

3. Increases osteoclastic activity.

A balance between the osteoblastic and osteoclastic activities leads to endochondrial ossification.

Action on epiphysial plate

Insulin-like Growth Factor -I (IGF-1) attaches with specific receptors and acts on the epiphyseal plate to

1. Increase the number and size of chondrocytes.

2. Increase proliferation of interstitial tissues of bones.

3. Increase proteoglycan formation

4. Increase differentiation and proliferation of chondroblast.

So, before puberty, bone increases in length and thickness after puberty.

'Somatomedins' mediate effects of growth hormone on skeletal growth. Somatomedins are a family of polypeptides synthesized mainly in the liver.

Action on adipose tissue

Mechanism of lipolysis action:

Growth hormone binds to its specific receptor on the adipocyte. This causes lipolysis, which releases glycerol and fatty acids into the circulation.

In the liver ( mainly), to some degree in the kidneys, free fatty acids and glycerol are used in gluconeogenesis.

Effects on protein metabolism

Protein anabolic increases protein synthesis.

Effects on carbohydrate metabolism

Reduces muscles and adipocytes glucose uptake.

Hepatic glucose output increases

Increases gluconeogenesis

Effects on fat metabolism

Catabolic effect -causes lipolysis.

It is ketogenic, also.

Effects on mineral metabolism

Increases calcium ion absorption from the gastrointestinal tract.

Decreases sodium, potassium, calcium, and phosphate excretion from the kidneys.

Factors increasing growth hormone secretion

Factors stimulating the Arcuate nucleus to release GHRH will increase growth hormone secretion. Factors stimulating the Arcuate nucleus are

1. Hypoglycemia, fasting

2. Low free fatty acid concentration in plasma.

3. High amino acid concentration

4. Exercise

5. Stress

6. Other hormones, e.g., estrogen, androgen, and glucagon.

Factors decreasing growth hormone secretion

Factors stimulating the Arcuate nucleus to release GHIH will decrease growth hormone secretion. Factors stimulating the Arcuate nucleus to release GHIH are

1. Old age

2. Increase free fatty acid concentration.

3. Late pregnancy.

Physiology # Endocrine #Growth hormone #| Somatotropin # lipolysis #proteoglycan # chondrocytes # chondroblast #Somatomedins # Insulin-like Growth Factor -I (IGF-1)| collagen fiber -I                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Please submit your comments about this article. The team will work hard to evaluate the statement and make appropriate corrections. Your comments will help improve the content.

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Internal links: 

https://blog.totalphysiology.com/2022/01/pituitary-gland secretion hormones.html

https://blog.totalphysiology.com/2024/09/pituitary-gland master-gland.html

External links:

Pituitary gland - Wikipedia. https://en.wikipedia.org/wiki/Pituitary_gland

 Pituitary gland – Health Blog. http://kress.tomsk.ru/pituitary-gland/

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