[Biology Class Notes] on Peristalsis Pdf for Exam

Peristalsis Definition

Peristalsis could be defined as a series of involuntary movements of the longitudinal and circular muscles that are involved in the movement of food and other liquid particles in the digestive tract to various processing organs that are located in the digestive system. 

The movements occur in progressive wavelike contractions and take place in the esophagus, stomach and the intestines.  They can be short, local reflexes or long, continuous contractions that travel the whole length of the organ. The nature of the wave depends on the location of the organs and what triggers their action.

Peristalsis in the Digestive system

Peristalsis in the digestive system takes place in four organs. These are the esophagus, the stomach and the small and large intestines. Below is the summary of how the entire process is carried out in each of the organs.

Esophageal Peristalsis

Peristaltic waves in this organ start at the upper portion of the esophageal tube and pass through the complete length before driving food particles into the stomach. If there are leftover food particles in the tube then a secondary wave takes care of that. The entire process is defined as esophageal peristalsis. A single wave moves along the entire length of the esophageal tube and disappears once the stomach is filled. The excess fat present in food particles also plays a role in stopping the movement until it is dissolved or diluted in gastric juices.

It should be mentioned that in cud-chewing animals such as giraffes, camels and cattle, reverse peristalsis takes place where food is brought again in the mouth for chewing.

Peristalsis in Stomach

After esophageal peristalsis, the stomach receives a ball of food which is also called a bolus. Through stomach peristalsis, stomach muscles compress and break down the bolus even more which is followed by a certain degree of hydrolysis of the food particles. It is observed that peristaltic waves start as weak contractions at the beginning of the stomach and then become stronger at the distal regions.

This hydrolysis of food particles is assisted by pepsin which is an enzyme. After hydrolysis, all food particles are partially digested and it is known as chyme. The chyme or partially digested food will stay in the stomach for a while until further peristaltic movement propels it into the duodenum, the first part of the small intestine for further processing. Our stomach plays a major role in the storage of food and can store up to 4 litres of food at a time. That is why the partially digested food stays in the stomach for a small amount of time.

Intestinal Peristalsis

Intestinal peristalsis takes place in two locations

• Small intestine

• And the large intestine

Small Intestine: Once the chyme reaches the small intestine, one peristaltic movement lasts only a couple of seconds and travels a few centimetres per second. The primary purpose of the small intestinal peristaltic movement is to continue the digestion of food and absorb nutrients. Once that is done, the chyme makes its way through the small intestine to the large intestine.

Large Intestine: The peristaltic movement in the large intestine is the same as the small intestine. General contractions called mass movements to take place one to three times a day to propel the chyme which is now faeces or bodily waste towards the rectum so it could be expelled from the body.  These contractions are often triggered by meals as the presence of chyme in the stomach and duodenum prompts them.

Reverse Peristalsis

Reverse peristalsis can be defined as a wave of intestinal contraction which takes place in the opposite direction of the normal wave in which content present in the tube is driven in a backward direction. It generally occurs as a precursor to vomiting. Food poisoning or stomach irritation activates the emetic centre of the brain which signals for this type of intestinal contractions and food moves from the duodenum to the stomach. Reverse peristalsis is also known as retro peristalsis.

Peristalsis function

Peristalsis is a phenomenon that brings about the movement of food and liquid particles through muscle contractions to multiple organs of the digestive system. These organs are the esophagus, stomach and the large and small intestines.

• Oesophagus: Peristalsis pushes the food down the esophagus and into the stomach.

• Stomach: In the stomach, this process helps in storage of food and breaking down the food particles and mixing them with gastric juices secreted from the stomach lining. It also assists in partial digestion of food which is called chyme.

• Small Intestine: Peristalsis pushes the partially digested food through the small intestine and helps in the digestive process. It also assists in absorbing nutrients from the digesting food into the bloodstream.

• Large Intestine: In the large intestine, these movements propel bodily waste along the organ through the colon and into the rectum for expulsion from the body.