Sunday, July 17, 2016

GI Hormones: Gastrin

Hi everyone, so this is my first post in the series of GI hormones!

There are 2 families of GI hormones -
1. Gastrin family (Gastrin , CCK)
2. Secretin family (Secretin, glucagon, VIP, GIP)
Others - Motilin, Peptide YY, Substance P, Ghrelin, Guanylin

In this post, I'll be talking about one of the members of the gastrin family, gastrin itself! :D


⛔⛔GASTRIN⛔

I. Produced by: 
■ G cells - enteroendocrine cells located in antral gastric mucosa.

II. Physiology of secretion:     
■ Acts via CCK-B receptor
■ Progastrin is cleaved to form 3 different residues :G 14, 17,34.
■ Sulfated and carboxylated forms also exist.
■ Amidated form is more stable.
■ G17 is principal form w.r.t. GI actions.
■ G34 has longer t1/2 than others.
■ Inactivated in SI, kidneys

III. Functions: 
■ Stimulates Gastric acid and Pepsin secretion
■ Trophic action - stimulates growth of mucosa of Gut.

IV. Regulation:

A. Factors that increase secretion of gastrin: 

■ Luminal:
- Amino Acids (Aromatic) in stomach 
- Distension
Because the job of this hormone is to bring about protein breakdown via pepsin and increase pH of the stomach, Hence it is released in response to protein and other contents entering the stomach. Tells the stomach it's time to do its job!

■ Neural:
- Vagal discharge as it secretes GRP at the postganglionic fibres.
Both sympathetic and parasympathetic fibres in gut are stimulatory (dual ANS stimulation).. What can we do about it?

■ Bloodborne:
- Epinephrine
- Ca2+
Calcium is a universal stimulant of motility and exocytosis from glands; epinephrine = dual ans stimultion.
Factors that decrease secretion of gastrin:

■ Luminal:
- Acid
- Somatostatin
Acid tells the G cell to shut up. There's enough acidity. No need for stomach to yap.
Somatostatin keeps all other hormones in check!

■ Bloodborne:
- Secretin family (Secretin, VIP, GIP, glucagon) (archnemesis)

Applied aspects of Gastrin:
■ Normal S. Gastrin levels = upto 100pg/ml
■ Hypergastrinemia:
- Pathological Increase (eg. Gastrin secreting tumor)
- Compensatory Increase (eg. Pernicious Anemia i.e. Type A Gastritis; due to destruction of    acid secreting cells compensation with increased  gastrin.)
■ Hypogastrinemia:
- Antral loss eg. Antrectomy, Achlorhydria.
- H pylori associated ulcers/gastritis may show hypogastrinemia, but association is not very clearly established. 

My next post will be on Zollinger Ellison Syndrome.  Excited? :D I know I am 😎
Hope you guys like it. 

~ A. P. Burkholderia

3 comments:

  1. Can I know the reference book please!I have my exams and I don't know which book to follow!

    ReplyDelete
    Replies
    1. Hi! So I've used Ganong and Harrison''s for this particular post.:) are you asking me about book's I refer to in general? Then those are too many :p but for Physio Ganong, Guyton and Harrison (yes I love reading physiology from harrison) are pretty good.

      Delete

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