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Hello wonderful fraturnity of the CS art,
DIGESTION, con`t
The pharynx, or throat.
This is the crossing over point between the digestive tract and the
respiratory tract. It it a common chamber for food on the way to the
esophagus and air on the way to the windpipe. At this point along the
line something can "go down the wrong way". Normally, A valve closes the
opening to the windpipe. You actually hold your breath for a second
while the ball of food is swallowed into the esophagus.
The esophagus, or gullet.
This is a collapsible, muscular tube about ten inches long. It passes
downward behind the windpipe, between the lungs and behind the heart. It
penetrates through the diaphragm and reaches the stomach. Food is moved
along the esophagus by waves of automatic muscular contractions
traveling downward along the tube. These contractions are known as
*peristaltic waves* and the process is called peristalsis. The
peristaltic waves push along before them any food that may be in the
tube. The point where the gullet leads into the stomach is guarded by a
muscular structure called the *cardiac sphincter*. This is a circular
muscule that is ordinarily contracted so the passage way is closed. When
food is swallowed the cardiac sphincter relaxes. An opening forms in the
center and the food is swept into the stomach. Then the muscle contracts
and the opening closes to prevent food from leaving the stomach, and
going back up the esophagus.
DEGLUTITION, or swallowing, is divided into three stages, which
correspond to the three regions--- mouth, pharynx, and
esophagus---through which food passes. The first stage consists of the
passage of the bolus of food through the fauces. The second stage
consists of the passage of the bolus through the pharynx. During this
stage, the respiratory opening into the larynx is closed by the
approximation of the vocal folds which close the glottis, by the
elevation of the larynx, and by contraction of the muscles of
deglutition. The parts are crowded together by the decent of the base of
the tongue, by the lifting of the larynx, and the coming together of the
vocal folds.
The third stage consists in the passage of the bolus through the
esophagus. Apparently the consistency of the food affects this stage of
the process. Solid or semisolid food is forced down the esophagus by a
peristaltic movement and requires from four to eight seconds for its
passage from the mouth to the stomach. About half of this time is taken
up in the passage through the esophagus, and the remainder is spent in
transit through the cardiac orifice of the stomach. Liquid or very soft
food is shot through the esophagus and arrives at the lower end in about
0.1 second. It may pass into the stomach at once or may be held in the
esophagus for some moments,depending on the condition of the cardiac
sphincter. When the stomach is empty,the cardiac sphincter is relaxed or
partially relaxed. On ingestion of food it becomes tonically contracted,
and as digestion continues, the sphincter becomes more tense. The
tension develops in response to the rise of acidity in the liquid just
within the cardiac portion of the stomach.
The food, after passing through the upper esophageal sphincter enters
the esophagus. No futher digestion takes place in the esophagus. Its
role is to move food down to the stomach. The lower two thirds of the
esophagus is enveloped in smooth muscle. Successive waves of contraction
of these muscles move food down to the stomach. Because of this
peristalsis, humans can swallow even if they are upside down, or in
space. With out peristalsis we could not leave the gravity field we live
in.
As the food passes the lower esophageal (cardiac) sphincter it enters
the stomach. If this sphincter does not close properly, the food backs
up into the esophagus, and the acid coating the food causes a burning
sensation called *heartburn* ( which has nothing to do with the heart).
This is a common problem during pregnancy, when the digestive organs are
displaced far upward. It also happens with overeating (stuffing
yourself).
During the process of mastication,insalivation, and deglutition the
food is reduced to a soft, pulpy condition,any starch it contains may
begin to be changed into sugar, and the food acquires a more or less
alkaline reaction.
Vomiting,
Under ordinary circumstances the contraction of the cardiac sphincter
prevents the regurgitation of food, but spasmodic contractions of the
abdominal muscles may, if the diaphragm is fixed, force the contents of
the stomach through the esophagus and mouth to the exterior. This is
called vomiting. It is usually preceded by a sensation of nausea and a
reflex flow of saliva and is itself a reflex act brought about by
mechanical irritation of the throat or by irritating substances in the
stomach and duodenum, or by pain,heart conditions, and certain emotions
as fear,worry,repulsion,etc.
STARCH,or carbohydrates:
Sugars are simple carbohydrates. Carbohydrates are a loosely defined
group of molecules that contain the elements carbon,hydrogen, and
oxygen. Because they contain many carbon hydrogen bonds, carbohydrates
are well suited for energy storage. Among the simplest of the
carbohydrates are the simple sugars or *monosaccharides*. The name
implies *taste sweet*. Simple sugars may have as few as three carbon
atoms, but the molecules that play the central role in energy storage
have six carbon atoms. Glucose is a six-carbon sugar with seven energy
storing CH bonds. Glucose circulates in the blood. It is converted to a
*transport form* before it is moved from place to place, and is less
readily consumed (metabolized) while it is being moved. The transport
form is made by linking two momosaccharide molecules to form
*disaccharide*. Sucrose (table sugar) is a disaccharide, formed by
linking glucose to fructose. If glucose is linked to galactose we have
lactose. Lactose is fed to babies in mothers milk. If two glucose are
linked together we get the sweet taste in the barley seeds that are
fermented into alcohol in the process of beer making.
Starches are chains of sugars. Sugars are made insoluble by joining
them into long polymers called *polysaccharides*, which are composed of
monosaccharide sugar subunits. Starches are polysaccharides formed from
glucose. Starch is a great way to store energy,but it has to be broken
down (digested) in order for the body to use it. The starch is broken
down into carbohydrates (sugars), which are further broken down into
molecules and atoms our bodies can use directly.Recall we often refer to
carbohydrates,fats and proteins. We could just as easyly say
starch,fats,and proteins. As we get further into digestion,link starch
and carbohydrates together in your minds as two forms of the samething.
Bless you Bob Lee
--
oozing on the muggy shore of the gulf coast
l...@fbtc.net
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