Gastrointestinal tract and its motility

1. MOVEMENT OF GIT AND MOTILITY
CONTENTS
• Movement of GIT
• Oral cavity
• Esophagus
• Peristalsis
• Stomach
• Small intestine
• Large intestine
• Motiliy of GIT
• Propulsion movement
• Mixing movement
Movements of GastrointestinalTract
The digestive and absorptive functions of the gastrointestinal tract (GIT) include chewing of
food and mixing it with saliva (mastication and salivation), swallowing, and its movement

2. through esophagus and stomach, where digestion begins, to the small intestine (the site of
further digestion and absorption). From the small intestine the food mass moves into the large
intestine and into the rectum where undigested matter and feces are expelled. The structure and
function of these parts must be such as to propel and move food (motility) from one end of the
tract to the other.
Gut motility is the term given to the stretching and contractions of the muscles in the
gastrointestinal (GI) tract. The synchronized contraction of these muscles is called peristalsis.
These movements enable food to progress along the digestive tract while, at the same time,
ensuring the absorption of the important nutrients.
Techniques of measuring these movements of the gut enable us to recognize the normal patterns
of contraction in each of the regions. The types of contraction in the gut differ depending on the
region and the type of food which has been eaten. Some contractions cause onward movement of
the food, others cause mixing and grinding.
The esophagus, stomach, small intestine, and large intestine are the main regions of the GI tract.
They are separated from each other by special muscles, called sphincters, which regulate the
movement of ingested material from one part to another. Each part of the GI tract has a unique
function to perform in digestion, and each has a distinct type of motility and sensation.
ORAL CAVITY

3. Digestion begins in the mouth where food is chewed, mixed with saliva, and swallowed. Oral
cavity deals with food selection, grinding and partial digestion of food. Grinding of food is also
termed as mastication. It lubricates and start chemical digestion food by action of enzyme
slivary amylase, which help semi digestion of starch. The pieces of food are then converted into
spherical mass called bolus.
PHARYNX AND ESOPHAGUS
Once the food is swallowed, the esophagus propels food from the mouth to the stomach. It does
not contribute to digestion and digestive action of saliva continue.

4. Peristalsis is the wave of contraction and relaxation in smooth muscles of alimentary canal wall.
It moves food from oral cavity to rectum.
STOMACH
The stomach is large enough to temporarily store the food eaten at each meal. Solid food is
gradually broken down by powerful muscle contractions in the lower end of the stomach. This
muscular activity produces small food particles suitable to enter the small bowel, where
processes of nutrient absorption begin.

5. Different types of food empty from the stomach at different rates; for example, fatty foods take
longer to leave the stomach than other foods. Beverages are handled differently by the stomach,
emptying more quickly into the small bowel and not requiring break-down into smaller particles.
Normally, most of an average-sized meal has left the stomach after about 2 hours.
In the stomach the food stimulates the release of digestive juices (secretions) like hydrochloric
acid and digestive enzymes e.g. pepsinogen (converted into active form pepsin by HCL) that
chemically further break down and mix with the food. The mixture is referred to as chyme.
Small Intestine
The chyme then passes, in a regulated controlled manner, out of the stomach into the small
bowel/intestine. In the small intestine, the muscular contractions occur irregularly, varying in
strength and type. Here also, the different nutrients in food affect the type of contractions
generated. After an average sized meal, the contractions continue for several hours, mixing the
food and moving it along the intestine. These types of contractions last until most of the meal
residues enter the large intestine. Different foods travel at different rates along the small
intestine; for example, foods high in fat travel more slowly than fiber-rich foods.
After most of the food has left the small intestine, a different pattern of contractions appears.
Bursts of powerful contraction, occurring about every 90 minutes during fasting and particularly
at night, progress slowly down the intestine. These bursts clear residual food and secretions from
the upper intestine, and thus act as a "housekeeper" in the intestine.
The average total length of the normal small bowel in adults is about 7 meters/22 feet. The small
intestine has 3 segments:
• the duodenum
• the jejunum
• the ileum
Each part or section performs an important role in nutrient absorption.
Duodenum – The chyme first enters into the duodenum where it is exposed to secretions that aid
digestion. The secretions include bile salts, enzymes, and bicarbonate. The bile salts from the
liver help digest fats and fat soluble vitamins (Vitamin A, D, E, and K). Pancreatic enzymes help

6. digest carbohydrates and fats. Bicarbonate from the pancreas neutralizes the acid from the
stomach.
Jejunum – The chyme is then further transited down into the second or middle part of the small
intestine, the jejunum. Mainly in the first half of the jejunum, the majority (about 90%) of
nutrient absorption occurs involving proteins, carbohydrates, vitamins, and minerals.
Ileum – The ileum is the last section of the small intestine and leads to the large intestine or
colon. The ileum mainly absorbs water, bile salts, and vitamin B12.
The ileocecal valve is a one way valve located between the ileum and the cecum, which is the
first portion of the colon. This valve helps control the passage of contents into the colon and
increases the contact time of nutrients and electrolytes (essential minerals) with the small
intestine. It also prevents back-flow (reflux) from the colon up into the ileum, and minimizes the
movement of bacteria from the large intestine up into the small bowel.
Large Intestine
The first portion of the large intestine, the cecum, is shaped like a pouch, and is the area of
storage for the contents arriving from the ileum. The primary function of the large intestine or
colon is to absorb fluids and electrolytes, particularly sodium and potassium, and to convert
remaining luminal contents into more solid stool. The colon absorbs on average 1-1.5 liters
(about 1-1.5 quarts) of fluid every day and has a capacity to adapt its fluid absorption to as much
as 5 liters/quarts per day if needed. Another function of the colon is to break down (ferment)

7. dietary fiber to produce short chain fatty acids – substances that can be absorbed and provide
added nutrition.
The patterns of contraction in the colon are not as well understood as those in the small intestine.
It is known, however, that eating a meal stimulates contractions in the colon – the larger the meal
the greater is the response.
Stretching of the rectum by stool produces relaxation of the muscles of the anus and surrounding
structures. The rectal contents can then be discharged voluntarily.
Gastrointestinalmotility
The term motility is defined as involuntary mobility of human tubular organs. To ensure the
efficient digestion of food is necessary not only the presence of active enzymes, but also a shift
and mixing of chyme during passage through the digestive tube. For this purpose, there are two
types of movements in the GIT:
1) Propulsion movements
2) Mixing movements
This division is artificial, because, in fact, both types of movements use the same mechanisms
and often one can convert to the other.
Propulsion movements

8. Propulsion movements are movements that provide movement of chyme in the digestive tract.
And a rate that is proportional to the rate of absorption and digestion.
Peristalsis
Basic propulsion movement is called peristalsis. Its principle is simple: circular muscle layer in
a certain place contracts and creates contractile ring, which is further shifted in
the aboral direction. Thus it slowly pushes chyme ahead. Distension of the intestine is often an
impulse for the formation of the contractile ring – and thus for the initiation of peristalsis. Larger
quantity of the chyme causes distention and thereby stimulating the enteric nervous system.
This triggers the contraction of the circular muscle segment that is a few inches orally from the
place of maximal distension of the tube. Peristalsis is also triggered by certain chemical stimuli
or strong parasympathetic activation. It also occurs automatically at certain intervals. In addition
to the contraction orally of the distended segment, occurs so called receptive relaxation aborally
from the distended segment of the tube. This facilitates the movement of the chyme, as relaxed
tube brings less resistance to the moving chyme. This whole process is
controlled by Auerbach’s plexus (or myenteric plexus) and is called the peristaltic reflex.
Propulsion movements can be experimentally cause also in oral direction, but they disappear
after few millimeters. The peristaltic movements are therefore unidirectional, although the
physiological basis for this phenomenon is not yet completely understood.
Mixing movements
Mixing movement ensures constant mixing of chyme, so that the entire volume of the
nutritionally important components is exposed to enzymes and came into a contact with the
lining of the intestine to be absorbed. These movements have different forms and varies
throughout the digestive tract.
Segmentation

9. Segmentation is well understood mixing movement. We can imagine it as repeated contractions
of several centimeters distant sections of circular smooth muscle. Contracted regions differ after
each segmentation cycle. Thus is the chyme segmented – formation of separated portions of
the chyme, which are subsequently again divided and one half is combined with a portion of the
previous one and second portions with the following. Number of portions gradually increases
and their volume on the other hand decreases, as one half of the two outer portions always has
nowhere to attach and form a new portion.
_