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Chapter: 12th Nursing : Chapter 1 : Human Anatomy and Physiology

Gastro Intestinal System

The alimentary canal, is a continuous hollow tube from the mouth to the rectum.

Gastro Intestinal System


The alimentary canal, is a continuous hollow tube from the mouth to the rectum. The alimentary canal along with the associated organs like the salivary glands, liver, pancreas and the gallbladder is called the digestive or gastrointestinal system. The primary role of the digestive system is to supply blood stream with nutrients that can be used by the body for its fuel, energy and fluid needs.

The organs that contribute to digestion are the tongue, salivary glands, the liver, the gallbladder, and the pancreas. The gallbladder and the pancreas secrete and deposit bile and digestive enzymes, respectively through the common bile duct to the duodenum of the small intestine.


The cheeks,tongue and palate frame the mouth, which is also called oral cavity .its boundaries are defined by the lips, cheeks, soft palate and epiglottis. It is divided in to two sections.

They are

·              The vestibule- the area between the cheeks and the teeth.

·              The oral cavity- filled by the tongue

The mouth is the opening through which the person ingests food and fluids. Incisors, canines, premolar and molars are the types of teeth helps in mastication


Tongue is one among the five sensory organ. It is a muscular structure used for moving food in the mouth and to swallow fluid and food. Taste buds are found on the upper surface of the tongue and the salivary glands.

Salivary glands

Salivary glands produce saliva which contains the digestive enzyme amylase. Amylase digests and breaks down starch into glucose and maltose.


The pharynx receives air from the nares or the mouth and it also receives food from the mouth. When people say that their food has gone down the wrong pipe, they are experiencing an abnormal small amount of food moving from the pharynx to the trachea.


The epiglottis is the flap like projection in the back of the mouth attached to the larynx. It goes up during breathing to allow the air to enter into the trachea and it moves down during the swallowing of food and drinking fluids to allow the food to enter the oesophagus.


The oesophagus is a long straight hollow structure that starts at the pharynx and ends at the stomach. The upper portion of the oesophagus has skeletal muscles and the lower portion has smooth muscles. Oesophagus has a sphincter at the top of pharynx end and it has a sphincter at the bottom of the stomach which prevent food from flowing back into the pharynx from oesophagus and backing up from the stomach into the oesophagus. The primary role of the oesophagus is peristalsis, wave like movements that move and propel food and fluids along the digestive tract with the help of muscles.


The stomach is a hollow organ on the left side of the abdomen that collects and processes food and fluids. The stomach has the fundus, body and antrum. The stomach secretes digestive enzymes, such as pepsin, hydrochloric acid and gastric acid to facilitate the digestive process. As the food and fluids are processed in the stomach, a partially digested chyme is formed. Pepsin digests proteins; and hydrochloric acid provides the pH of acidity that is necessary for digestion. Minimal absorption of water soluble vitamins and some medications such as aspirin takes places at stomach.


The liver is an abdominal organ and gland on the right side of the abdominal cavity and near the center of the body. The liver produces bile which is then transported to the gallbladder through the common bile duct and then to the small intestine. Bile is used for the breakdown and digestion of fats.

Small Intestine

The chyme from the stomach is mostly absorbed in the small intestine as usable minerals and nutrients. The small intestine also receives bile and the pancreatic enzymes from the bile ducts. These pancreatic enzymes break down carbohydrates, fats and proteins for absorption. The small intestine is also a hollow abdominal tube that connects to the stomach at its upper end and to the large intestine at its lower end which sphincter prevents back flow.

The three parts of the small intestine are the duodenum, jejunum and ileum

Iron is absorbed in the duodenum, jejunum absorbs all of the products of digestion and the ileum absorbs any remaining nutrients that has left behind.

Large Intestine

The large intestine is involved in the absorption of water and the removal of by products of digestion through defecation. The two major parts of the large intestine are the cecum and sigmoid colon.

The caecum is connected to the appendix which has an unknown role and the colon absorbs water and propels waste to the rectum.


The rectum is a part of the lower gastro intestinal tract. It is a continuation of a sigmoid colon and connects to the anus. The key role of the rectum is to act as a storehouse for feces.


The anus is the last part of the digestive tract. The lining of the upper anus is specialized to detect rectal contents. It knows whether the contents are liquid, gas or solid.

The stages of digestion are:


Digestion of the food starts by the action of mastication(chewing) aided by teeth, a form of mechanical digestion.

Saliva secreted by the salivary glands which contains the following:

Salivary Amylase - Starts the digestion of starch

Mucus - Lubricates the food

Hydrogen carbonate - Maintains the ideal condition of PH (Alkaline) for Amylase to work


Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules. So that they can be absorbed into the watery blood plasma. Digestion is a form of catabolism that is divided into mechanical and chemical digestion. The term mechanical digestion refers to the stepwise physical breakdown of large pieces of food into smaller pieces. In chemical digestion, enzymes break down food into the small molecules the body can use.


95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed by the colon .

Diseases related to digestive system

·              Poisonings

·              Diarrhea

·              Constipation

·              Diverticulitis

·              Gastric Eosophageal Reflux Disorder (GERD)

·              Peptic ulcers

·              Cholelithiasis

·              Cirrhosis of liver

·               Hepatitis

·              Colitis

·              Irritable Bowel Syndrome (IBS)

·              Cancer


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12th Nursing : Chapter 1 : Human Anatomy and Physiology : Gastro Intestinal System |

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