Bovine biology series

Part - 29 Tongue

The tongue

Of course, I have a story about the tongue. And the story begins, appropriately, when I was a youngster watching a skilled man butcher a down cow. As he removed the head, he opened the mouth very wide, reached far into it and drew the tongue out. At its roots, he cleverly sliced it from some connective tissue, and into a pan it was placed. I remember thinking to myself that this organ was a rather large one, for just the tip of it was shown when a cow chewed or drunk water.

Later on, we would eat this tongue like one would a roast, or in some cases, ground into a sandwich spread like tuna fish. There seemed to me, anyway, something strange about eating a cow's tongue. But then again, at least it did not go to waste.

We visit the tongue once more.

The word tongue is derived from the Latin word "lingua," for the originators of this word recognized they needed to call this part of the mouth something resembling sound, or linguistics. The Latin folks were clever in naming parts of the body that described, in part anyway, a function.

Why do animals need a tongue? And for what purpose does the tongue serve?

Animals, cows, and you and me, require a tongue so that several functions of the mouth can be enhanced. The tongue helps control the passage of air into the air passageway leading to the lungs, the windpipe, or the bronchial tubes (there are two of these, and they split or bifurcate very near the trachea portion of the throat. Each of them led to either the left or right lung in the chest).

In all animals, the opening of the mouth is the entryway for air to enter the lungs when the diaphragm is contracted downward, or away from the mouth. This is an involuntary action of the musculature and nerves controlling breathing. Air enters the mouth, the pharynx is open, and the epiglottis is upward so that air does not enter the stomach by way of the esophagus. In this way, we can breath without thinking about it, and all the right muscles are controlling the passageway properly; air goes to the lungs.

The tongue does play a minor role, in that as it is elongated into the mouth, it does not physically obstruct this passageway. We have heard of someone who has "swallowed their tongue." This condition can lead to suffocation, for the physical obstruction of this organ blocks air entering the trachea and thus the lungs are starved for air intake and gaseous discharge.

Swallowing, however, is a much different. The action of eating, chewing, swallowing, and in the rumen, eructation (belching, or the discharge of gas from the rumen or stomach) and regurgitation (the backwards flow of food, as the cow does when some contents of the rumen is sent back to the mouth for further physical degradation, as is chewing her cud), are all digestive processes with some or all voluntary action.

As such, the animal must think about them, albeit after awhile the physical act of these actions becomes second nature.

However, the tongue is heavily involved in swallowing. The tongue is almost entirely a skeletal muscle. The physical action of swallowing requires a large muscle to shove food out of the buccal cavity, through the pharynx, past the Epiglottis, into the open esophageal sphincter and finally towards the rumen or stomach via the esophagus.

During swallowing, the larynx, or voice box, is closed. Which is why we cannot talk during the act of swallowing. For when the pharynx is closed, no air is entering the trachea and bronchial tubes, and since no air is entering, none can be discharged. Thus no sound is made.

Interestingly, isn't it, that when we watch a cow eat, she is almost always calm and contented, in a safe place. Why? Well, common sense would tell us that if she were threatened or felt a sense of fear, the mind would send a signal to her that she better not eat until this threat has passed. For if she needs to either fight or run away, she will need extra air coming in to fuel muscles that can prepare her for a fight or move her rapidly away.

So I think eating is largely a voluntary act. We should ensure that when we feed cows, she is in a safe place, one that is comfortable for her, free of peripheral sounds or strange movement. Some of these ideas we take for granted. But thank goodness the entry of air is favored over the entry of food or ration. Otherwise I suspect the specie would not have survived very long.

Note here please, that even though the action of swallowing is a voluntary one, once the food bolus has past the upper esophageal sphincter at the entryway of the esophagus, the action of the muscles lining the esophagus are involuntary. That is, food is passed into the rumen or stomach on its own once it reaches the esophagus.

Another function of the tongue is a physical one. That is, food that is brought into the mouth by means of the jawbone and teeth is chewed. The purpose of this action is really threefold: one, the addition of saliva, a buffer that in the cow has a pH of 8.4 (for review, a cow produces 20 to 30 gallons of saliva daily, although some workers report even higher amounts). Saliva is a buffer because it contains sodium, potassium, and calcium and magnesium cations that help neutralize the anionic compounds that result from the production of fermentation products, such as volatile fatty acids, in the rumen.

This brings a further comment: why do we add magnesium oxide sodium bicarbonate to the ration? Well, these are buffers that supplant what is already in the saliva secretions, and therefore working together, they help maintain the pH of the rumen at 6.4, slightly acidic, so that the proper mix of VFA's and bacterial populations are ensured. [[That is why, of course, cations help increase pH in soils too, for the contents of lime and lime products are largely calcium and magnesium.]]

Two, the addition of saliva provides moisture for feed in the mouth. Saliva is 1.0 - 1.4 percent dry matter, which means it is just about all water. Water aids in the physical breakdown of feed, and surely helps the cow with getting this feed swallowed. You might say, saliva acts as a lubricant in aiding the passage of food into the rumen or stomach. [I am thinking now of those very popular Got Milk commercials, where the consumption of some dry food cannot be easily swallowed without a drink of milk!]

Three, saliva contains some enzymes, namely salivary lipase, which aids in the catabolism or breakdown chemically of large molecules of fats in feed. Ruminant saliva does not contain high amounts of amylase, an enzyme found in monogastric animals that aid in carbohydrate breakdown.

Additionally, the tongue helps in regurgitation, as when the cow is sending a feed bolus back to the mouth for further physical breakdown. The cow slides her tongue against the upper palate, with the feed contains in the middle. The rough texture of the skin on top the tongue can withstand many chewings. This is a time when more saliva is released too.

In fact we know that one of the main reasons we feed fibrous feeds is not to just slow the feed down, but also so that during regurgitation, more saliva can be produced. Thus, we avoid the "sour stomach" or rumen acidosis condition found in feeding a ration short on fiber.

Finally, the tongue, as an organ, weighs about 8 pounds in the adult cow. While it is just about all muscle tissue, at its tip there are some very small papillae. These projection from the tongue are highly enervated, thus they serve the role of sense organs, helping determine what tastes good, what is alright to lick, and what is very cold or too hot. The nerves carry the sense signal to the brain for interpretation, and then the tongue is moved as per the brain directs. Certainly licking on a molasses block is pleasurable, but so can a cow find certain soils desirable to the taste.

Very near these papillae are taste buds that aid in determining what foods are desirable. These receptor cells in the taste buds are similarly highly enervated and therefore connected to the brain.

The base of the tongue is rooted in the throat, where connective tissue hold the back end of the tongue to the floor mouth and the juncture of the neck area.

Next month, and subsequent months, we will move into the area of nerves. I have found the subject of nerves to be more difficult of study than, say, the digestive or musculature system. So I have waited two and a half years before taking them on!

So I am a bit nervous about the nerves. But that is OK, for we will, together, study the nervous system and learn the topic.