Biology

Intracellular Digestion vs. Extracellular Digestion

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What is the Difference Between Intracellular Digestion and Extracellular Digestion? 

In this article, we explore the definitions and difference between Intracellular and Extracellular Digestion.

Intracellular Digestion = Digestion that occurs inside our cells (literally in the cytoplasm)

Extracellular Digestion = Digestion that occurs outside our cells

intracellular digestion versus extracellular digestion

Lo and behold! Welcome our holy grail – glucose! While glucose’s essence as the holy grail may be debatable, glucose undeniably serves as an essential energy source for our bodies. In order to utilize glucose as our energy, we must first digest food that contains glucose. There are two main types of digestion: intracellular and extracellular.

Our Human Digestive System: Wonderful, isn’t it? 🙂

Definitions of Intracellular Digestion and Extracellular Digestion

Let’s first dissect the ‘anatomy’ of our word “intracellular.” The prefix intra means “on the inside” or “within,” and the suffix cellular literally refers to our cells. Intracellular digestion thus means digestion that occurs inside our cells. As for the word “extracellular,” with the prefix extra meaning “on the outside,” we can thus infer that extracellular digestion means digestion that occurs outside our cells.

Intracellular Digestion = Digestion that occurs inside our cells (literally in the cytoplasm)

Extracellular Digestion = Digestion that occurs outside our cells

1280px-stomach_with_prominent_parietal_cells_-_intermed_mag
Pretty Pink: A view of our stomach’s parietal cells

Alimentary Canal versus Lumen of the Digestive System

To elaborate more, extracellular digestion in our human digestive system occurs in the alimentary canal. The alimentary canal runs from the starting point of digestion, our mouths, to the end of the digestive system, our anuses. Releasing enzymes, such as pepsinogen and pepsin, to the outside of our cells also means extracellular digestion.
For digestion to be considered intracellular, the nutrients – glucose, fatty acids, proteins, etc – must be inside our cells, not the lumen or opening of our digestive system.

L0037817 Anatomy of the small intestine in ancient Chinese medicine

And, just for kicks, single-celled organisms such as paramecium and amoeba undergo intracellular digestion to get their nutrients. This relates back to the intracellular digestion in us humans because in order for intracellular digestion to occur, it must be performed physically inside the individual cell.

Do humans do intracellular digestion or extracellular digestion? We do both!

Bonus Practice Question: Can you guess if the photograph below is demonstrating extracellular or intracellular digestion?

Hint: This is fungi releasing its enzymes to digest a decaying leaf.*

White hyphae of fungi digesting a browning leaf: Yum for nutrients!

Sources:

  1. Intracellular and Extracellular Digestion. http://study.com/academy/lesson/intracellular-extracellular-digestion.html
  2. The Digestive System by Alexander Stone Macnow, MD. MCAT Kaplan Biology Review.

*Answer: Extracellular! This fungi (the white hyphae) produces extracellular enzymes to digest the leaf, which is outside of its body and outside of its cells.

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