Digestive System

Anatomy of Gastric Glands

I am savouring very fresh fish chowder. The digestive system enzymes in my mouth break down the potatoes first, the fish meat, will have to wait to meet its enzyme in the most acidic part of the human anatomy, yeap - stomach.

Before the chowder was served, I was famished. If you had x-ray eyes, you would see gastric folds wrinkling inside my empty stomach. I don't want to starve myself too long as my stomach churns out as much as three liters of acid brew so potent it can dissolve nails - everyday.

Digestive System Anatomy of a hungry Stomach - don't start thinking your stomach is as colourful as this one, the colours are only for the sake of easy labelling :-)

1.Esophagus 2.Longitudinal layer 3.Circular layer 4.Oblique layer 5.Gastric folds 6.Pyloric orifice 7.Duodenum

Hey, don't you entertain any ideas of swallowing nails, silly goose! After all the potent hydrochloric acid is encased in flesh, easily punctured by the nails. How come the gastric acid does not make holes in my stomach? The answer lies in a very, very thin 1.5mm layer of stomach lining which secretes viscous and alkaline mucous to protect my stomach against ulceration caused by the acid.

Indented on the stomach lining are depressions called gastric pits. At the base of gastric pits are the gastric glands ( drums rolling...) the manufacturer of the enzyme to digest my fish meat! There are five types of secretory cells here but my fish meat is only interested in the chief cells.

Digestive System Anatomy of the stomach lining and below

1. Gastric pits 2. Gastric glands 3. Oblique layer 4. Circular layer 5. Longitudinal layer

The chief cells secrete an inactive enzyme pepsinogen. How does pepsinogen get out of its pit to meet my fish meat? Well there are three smooth muscle layers beneath the gastric pits: an inner oblique, a middle circular and an outer longitudinal layer. These muscles help expel pepsinogen out of its pit as the stomach contracts.

Digestive System Anatomy of enlarged gastric glands, chief cells are situated at the base in orange colour

By the time the chowder comes in, my stomach is no longer wrinkly, it has expanded to make room for a huge bowl of yummy meal. The stomach contracts and pepsinogen is pushed out to come into contact with hydrochloric acid in the gastric juice which converts it into the active enzyme pepsin.

When pepsin breaks down my fish meat, this marks the beginning of protein digestion and is essentially the only enzymatic digestion in the stomach. I said "essentially" because pepsin also digests collagen in the deliciously succulent freshest fish skin. Chief cells which secrete the pepsin appear to also secrete an insignificant amount of fat-digesting enzyme lipase. Children's little stomachs secrete another enzyme rennin that acts on milk protein. But now I am too old to produce rennin to digest the milk in my chowder...

Pepsin only accounts for twenty per cent of total protein digestion. Enzymes in the small intestine will complete the digestion of the fish meat which by now, has consistency of "fish paste soup".

Epilogue

Next leg of journey into the duodenum is extremely gradual and slowww. Each peristaltic contraction pours only a few millimeters of my chowder into the duodenum. The carbohydrate-rich potatoes move through the duodenum quickly, so the remaining food in the stomach doesn't have to wait too long. On the other hand, deep-fried fish and chips tend to stay longer in the duodenum.

That explains why I am hungry again pretty soon and need a second helping of chowder. Fried fish and chips may be more filling but I am more likely to have constipation the next day because it takes longer time for the duodenum to open its "door" to fish and chips in the stomach.

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