PERISTALSIS

PERISTALSIS

Introduction:

·         Peristalsis was first discovered by Baylins and Starling as a type of motility in which there is contraction above and relaxation a segment being stimulated.

·         Peristalsis is a series of wave like muscle contractions that moves food to different processing stations in the digestive tract.

·         Peristalsis is a worm like movement by which alimentary canal with both longitudinal and circular muscle fibres propel their contents, consisting of a wave of contraction passing along the tube.

·         A coordinated succession of contractions and relaxations of the muscular wall of a tubular structure, such as oesophagous, small intestine or ureter, producing a wave like pattern whose effect is to move the contents along.

Mechanism of Peristalsis:

·         The process of peristalsis begins in the oesophagous, when a bolus of food is swallowed; the strong wave like motions of the smooth muscle in the oesophagous carry the food to the stomach, when it is churned into a liquid mixture called chyme.

·         Peristalsis continues in the small intestine when it mixes and shifts the chyme back and forth allowing nutrients to be absorbed into the bloodstream through the small intestine walls.

·         Peristalsis concludes in the large intestine when water from the undigested food material is absorbed into the bloodstream. Finally the remaining waste products are excreted from the body periodically.

Characteristics of peristaltic waves:

·         The wave of peristalsis are irregular, they are stronger at sometimes then at others. They are also weak in some people, notably in the elders.

·         Although the normal peristaltic wave is downward, it is sometimes reverse. Reverse peristaltic actions may be triggered by mild digestive upsets or more serious disorders such as obstruction in the stomach or intestine.

·         Peristalsis, involuntary movement of the longitudinal and circular muscles, primarily in the digestive tract but occasionally in other hollow tubes of the body, that occur in progressive wave like contraction.

·         Peristaltic waves occur in the oesophagous, stomach and intestine. The waves can be short, local reflexes.

·         In the oesophagous, peristaltic waves begin at the upper portion of the tube and travel the whole length pushing food ahead of the wave into the stomach.

·         Particles of food left behind in the oesophagous, initiate secondary peristaltic waves that remain left over substance.

·         The wave travels the full length of the tube in about seconds.

·         The peristaltic wave contraction in the oesophagous of humans is weak compared with those of most other mammals.

·         In cud chewing animals, such as cows, buffalows, reverse peristalsis can occur so that the food is brought back from the stomach to the mouth for rechewing.

·         When stomach is filled, peristaltic waves are diminished. The presence of fat in a meal can completely stop these movements for a short period until it is diluted with the gastric juice is removed from the stomach.

·         Peristaltic waves start as weak contractions at the beginning of the stomach and progressively become stronger as they near the distal stomach region.

·         The waves help to move the stomach contents and propel food to the small intestine. Usually, 2-3 waves are present at one time in different regions of the stomach and about 3 waves occur each minute.

·         In the small intestine, local stimulation of the intestinal smooth muscles by the presence of food particles cause contraction that tend to travel from the stimulated point in both direction.

·         Under normal circumstances, the progress of the contractions in an oral direction is quickly inhibited while contractions travelling away from the mouth tend to persist.

·         If the intestine is paralyzed by applying such as drugs and nicotine or cocaine to the intestinal wall.

·         The contraction initiated by local stimulations travels equally well in both direction.

Neural control of peristalsis:

·         Peristalsis is manifestation of two major flows within the enteric nervous system that are stimulated by bolus of foodstuffs in the lumen, mechanical distension and perhaps mucosal irritation afferent enteric neurons. These sensory neurons synapse with two sets of cholinergic interneurons which lead to two distinctive effects.

·         One group of interneurons activates excitatory motor neurons above the bolus. These neurons contain acetylcholine and substance P which stimulates contraction of smooth muscle above the bolus.

·         Another group of inter-neurons activates inhibitory motion neurons that stimulate relaxation of smooth muscle below the bolus. These inhibitors neurons appear to use nitric oxide, vasoactive intestinal peptide of ATP as neurotransmitters.

 

How does peristalsis works?

Our digestive tract is like one long tube from mouth to anus. Alimentary canal has muscles that squeeze the food along.

What is the mode of action of Peristalsis?

We swallow food and our mouth pushes the food into our oesophagous. Oesophagous has muscles that push the food down into the stomach like a peristaltic wave. Stomach squeezes the food around and mixes it with digestive juice and enzymes. Our small intestine does this same rhythmic squeezing continuing the peristaltic action to push the food along. The small intestine absorbs the nutrients from the food as the food moves along. Our large intestine absorbs the water from the left part of the food. This allows the body to keep the water, which it needs and turns the mostly liquid stool or faecal matter into more solid and easier form to excrete out.

What causes the problems with peristalsis?

·         There are number of different things that can cause problems with the peristalsis process. Caffeine, alcohol and cigratte smoking are all suspected of causing problems with peristalsis.

·         Some people have more nerve endings or pain receptors in their intestine; which can cause spasms in response to food irritants.

·         Caffeine is a stimulant and bowel irritant which can speed things up to the point of diarrhoea.

·         Some people have food intolerance which can cause abdominal pain, intestinal cramp and diarrhoea.

What helps peristalsis return to normal?

By using food elimination diet, we can overcome food intolerance.

Function of Peristalsis:

1.       Peristalsis is a series of contractions that pushes solids or liquids through tubes in certain parts of the body, primarily the digestive system.

2.       It is also used to push urine from the kidneys to the bladder and move bile from the gall bladder to the duodenum.

3.       In peristalsis, upper muscle contracts while the muscle below it relaxes to low food in liquid to pass through. This muscle then continues the process by contracting further pushing the substances through the system and also preventing anything from travelling back up the tube.

4.       When food enters the mouth, it is chewed into what is known as bolus, which then enters the oesophagous as to swallow. Peristalsis then forces the food down the oesophagous and into the stomach. The bolus is then turned into a liquid substance known as chyme as it is processed in the stomach and then it moves on to the small intestine. The chyme is pushed through the small intestine by peristalsis but a different type of contraction pushes it through the large intestine.

 

Peristalsis occurs in different parts of the alimentary canal as follows:

1.       From oesophagous to stomach:

 In this process, when water or food enters the GI tract the muscles in this tract relax and compress in a motion i.e. wave like to allow the content to pass through. For instance, when you swallow an apple, smooth muscles in oesophagous relax and contract to allow the food through. The contracted muscles allow the content to pass to the area with relaxed muscles lower in the oesophagous. This continues until the food reaches the stomach. The muscles above remain contracted to prevent the food from flowing back.

 

 

2.       From stomach to large intestine:

Once the food has moved from the oesophagous to the stomach, the stomach forces the content through the intestine. First the food is moved to the small intestine for digestion. This process facilitates the removal of gas from the digestive system to avoid build up. While there are several contractions in the small intestine, the large intestine only experience two or three contractions for relaxation, which enable faeces to be excreted from the body through the anus.

 

 

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