Digestive Secretions

Home Up Digestive Enzymes Control of Secretion

    Since the purpose of the digestive system is to break down food into absorbable bits, and then absorb as many nutrients as possible, it may seem odd to you that a major digestive system job is to secrete material.  However, everything secreted by the digestive system facilitates food break down and nutrient absorption, or at least, prevents digestion of the digestive system tissues themselves.  Here are some major categories of digestive secretions:

bulletdigestive enzymes:  these are responsible for much of the break down of food.  Keep in mind that food is made of the same four macromolecules that our cells and tissues are made of:  proteins, carbohydrates, fats, and nucleic acids.  If we want to break food down we will need to break these molecules apart into their building blocks.  Reactions that break macromolecules down are called catabolic reactions.  Do you remember what the building blocks, or monomers, are for proteins, carbohydrates and nucleic acids?  (we will do fats separately, since they aren't really made of building blocks)  In order, the monomers for these three macromolecules are amino acids, monosaccharides (simple sugars), and nucleotides.
bulletregulatory secretions:  our digestive systems are not always in high gear... when we haven't eaten in a while, it makes sense that we aren't actively secreting digestive enzymes.  How do our bodies know when to kick into action?  You will see that many regions of the digestive system secrete regulatory chemicals that function to activate the secretion of enzymes.
bulletprotective secretions:  the digestive system has to protect itself while attacking food.  One of its major protective secretions is mucus.
bulletaids for digestion, absorption or immunity:  some chemicals are secreted just to assist the digestion or absorption that is occurring.   For example, the stomach secretes "intrinsic factor" which allows for vitamin B12 absorption.  Also, the stomach secretes HCl, which causes the pH of the stomach to drop, killing bacteria and activating a digestive enzyme.
bulletbacterial secretions:  We actually have some beneficial bacteria that live within our intestines.  These bacteria help us with the breakdown of some of the tougher foods we eat-- literally!  If you think about something that you eat that seems like a good challenge for your digestive system, celery may come to mind.  Plant cells are surrounded by tough cell walls made mainly of cellulose... and our digestive system finds it rather difficult to digest cellulose unaided.
     Have you ever taken antibiotics for an infection and had a side-effect of trouble digesting your food?  "Stomach" pains?  That is because the antibiotics kill off the beneficial bacteria along with the infectious ones.   And without the bacteria to assist us in the digestion of cellulose, we have trouble with it.  That causes the digestive discomfort from the antibiotics.
     People often refer to the beneficial bacteria that continually live in our small intestines as "intestinal flora."  If you have to take antibiotics and don't want to kill off your intestinal flora in order to prevent pains, you can easily add more to your body.  Acidophilus tablets, acidophilus-supplemented milk, and yogurt all contain the beneficial bacteria for you to ingest.  By ingesting more acidophilus, you are re-supplying your body with the good bacteria while, at the same time, the antibiotics are killing them off.

    Most of Chapter 17 deals with which chemicals are released from which organs at what time.  I have separated these secretions functionally, so that there is an entire page devoted to digestive enzymes and another one devoted to regulatory secretions.  The last three are not covered much more in my pages, except for the acid secretion in the stomach.

2011 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.