GASTRIC JUICE

Gastric juice is the mixture of secretions from all the glands present in the stomach

The total amount of gastric juice secreted per day is about 2 – 3 litres

Gastric juice is highly acidic in nature with a pH of 0.9-1.5.

The gastric juice contains 99.45 % water and 0.55% solid.

I. Constituents of Gastric Juice

Hydrochloric acid (HCl):

Gastric juice contains hydrochloric acid (HCL).

HCL is present in gastric juice in high amount about 40-60 meq/litre.

Oxyntic cells secrete HCL

HCL gives antiseptic property to the gastric juice

HCl converts pepsinogen into pepsin

HCl stimulates the secretion of different hormones from the small intestine.

Intrinsic Factor :

It is secreted by oxyntic cells of gastric mucous membrane

Intrinsic factor is a glycoprotein

It combines with Vit-B12 (extrinsic factor) and helps in its absorption

Gastric mucin:

Mucin is a glycoprotein

Provides defense against the damage which may be caused by the acid

Gastric mucin is of two types -Visible mucin and soluble mucin

Visible mucin is secreted by surface mucous cells of the gastric mucous membrane

Forms a slippery layer on gastric mucous membrane.

Prevents injury from solid food and moving fluids within the stomach

The soluble mucin secreted by the neck cells

Helps to buffer HCL to some extent

Pradeep Kumar.G Faculty of Medicine, Omar Al Mukhtar University 1

Enzymes of Gastric Juice

Pepsinogen & Pepsin:

Is an inactive precursor for enzyme pepsin

It is secreted by chief cells of gastric glands

Pepsinogen is activated to pepsin at a pH of 2.0 to 3 by HCL

Pepsin is a proteolytic enzyme which breaks down protein molecule into pep-tones and peptides.

Rennin:

This enzyme coagulates milk, thus prevents rapid passage of milk from the stomach.

Gelatinase:

It liquifies gelatin, a protein contained in connective tissues.

Gastric lipase:

This is a weak fat splitting enzyme from stomach.

It acts at the optimal pH of 4 - 4.5.

Gastric lipase gets inactivated at pH 2.5.

Lysozyme: is a bactericidal enzyme.

Urease: The enzyme urease hydrolyze urea to produce ammonia.

Carbonic anhydrase : is present in small amounts.

II. Gastric acidity:

Free acidity: The acidity due to free HCl (not combined with other substances) present in gastric juice

Total acidity: The acidity due to free HCl, HCl bound to mucin, organic acids, acid proteins and other acidic substances in gastric juice.

Normal Range:

Free acidity: 18 – 25 mEq/L

Total acidity: 28 – 48 mEq/L

Pradeep Kumar.G Faculty of Medicine, Omar Al Mukhtar University 2

III. Clinical significance:

Hyperchlorhydria: increase of free acidity of gastric juice more than normal is termed as hyperchlorhydria.

In individuals with duodenal ulcers

Hypochlorhydria: Decrease of free acidity of gastric juice less than normal is termed as hypochlorhydria.

Achlorhydria: if the free gastric HCl concentration in zero then it is termed as Achlorhydria.

Achlorhydria is divided in to true achlorhydria and False Achlorhydria.

In true achlorhydria the secretion of HCl is completely absent

In false achlorhydria free HCl in gastric juice is neutralized by alkaline substances

In false achlorhydria secretion of free HCL can be seen after injecting subject with histamine

The slowing of the body's basal metabolic rate associated with hypothyroidism

Achlorhydria is seen in case of

Autoimmune disorders

The use of antacids

Helicobacter pylori infection

Pernicious anemia, stomach cancer. Etc.

Achylia gastrica: Both HCl and pepsin are not secreted

Pradeep Kumar.G Faculty of Medicine, Omar Al Mukhtar University 3

Estimation of free and total acidity of gastric juice

Principle: Free and total acidity of gastric juice is measured by titrating against know concentration of NaOH using different indicators

Reagents:

NaOH (0.1 N solution)

Phenolphthalein indicator

Topfer’s reagent (dimethylaminobenzine 0.5 % w/v in 95% ethanol)

Procedure:

Total acidity:

Take 10 ml of gastric juice in a 100 ml conical flask

Add 2 – 3 drops phenolphthalein indicator

Titrate contents against 0.1 NaOH taken in a burette

Stop the titration when you observe pale pink color (end point)

Record the NaOH titer value

Free acidity:

Take 10 ml of gastric juice in a 100 ml conical flask

Add 2 – 3 drops of topfer’s reagent

Titrate contents against 0.1 NaOH taken in a burette

Stop the titration when the colour changes from red to orange-yellow color

Record the NaOH titer value

Pradeep Kumar.G Faculty of Medicine, Omar Al Mukhtar University 4

Calculation:

Note: 1 mEq of NaOH (40 mg) = 1 mEq of HCl (36.5 mg)

Total acidity = titer value (ml) X 100 = __________ mEq/L

Free acidity = titer value ( ml) X 100 = ___________ m Eq/L

Result:

Comment:

Pradeep Kumar.G Faculty of Medicine, Omar Al Mukhtar University 5