[Biology Class Notes] on Human Digestive System Pdf for EXAM

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The Four Mains Functions of the Digestive System:

Digestion and absorption is the main function of the digestive system. Digestion is the breakdown of food into smaller molecules, which are absorbed into the body. The alimentary canal is a continuous tube with two holes: the mouth and anus. It includes the mouth, pharynx, oesophagus, stomach, small intestines, and large intestines. The food passed in the digestive tract or lumen technically does not enter the body until when it enters the walls of the digestive tract and hence passes through the blood or lymphatic arteries.  Key Functions of the digestive system include:

• Motility- Food moves through the digestive canal, due to a process known as peristalsis, which involves the action of muscles in the GI tract that transport food to the digestive system. Through the evacuation of undigested waste from the body, incoming nutrients are broken down and mixed.

• Secretion- It is the release of enzymes, hormones, and other chemicals that aid in the digestion of food by the body. Hormones signal the body to generate digestive juices and notify the brain whether you’re on an empty stomach or full.

• Digestion- Proteins, lipids, carbs, vitamins, minerals, and water are all broken down into molecules small enough to pass through the digestive fluid and into the bloodstream during digestion. The digestive juices that we consume for energy, development, and cell repair break down the meal.

• Amino acids are formed when proteins are broken down.

• When fats are broken down, fatty acids and glycerol are produced.

• Simple sugars are formed when carbohydrates are broken down.

• Absorption- Digested carbohydrates travel from the gut to the circulation, where they are transported by the circulatory or lymphatic systems throughout the body for usage or storage.

• The lymphatic system absorbs fatty acids and vitamins.

• The blood transports simple carbohydrates, amino acids, glycerol, and some vitamins and minerals to the liver.

• When these nutrients are needed, the liver stores metabolizes, and delivers them to the body.

More About the Topic

The food that you eat makes a long journey through your body. It moves from the top of your mouth to the bottom of your anus. You may want to refer to the digestive system diagram to understand the complete route. Along its incredible journey, the beneficial parts of your food get absorbed. This helps to give your body the necessary energy and essential nutrients.

The digestive system is uniquely designed to do its job, which is to turn the food into energy and nutrients that are essential for survival. Once the body absorbs the essential substances, it packages the solid waste for disposal through a bowel movement. Many organs work in complete harmony to let the digestive system function. 

Here is the Complete Human Digestive System Diagram:

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Mouth 

The digestive system diagram labeled starts from the mouth. In fact, your body starts the digestive process before even you take your first bite of food. The salivary glands get active as you see or smell food. When you start to eat, you chew the food into small pieces so that it gets digested easily. The saliva gets mixed with the food which helps to break down the food into a form that the body can absorb. When you swallow the food, the tongue passes the food into the throat, and then the food moves to the esophagus.

Esophagus

The esophagus is located in the throat, and it is placed near the windpipe or the trachea. The esophagus receives the food that you swallow. Many muscular contractions occur within the esophagus that delivers the food to the stomach. There is also a ring-like muscle or the lower esophageal sphincter that lets the food into the esophagus. When the sphincter contracts it prevents the food from flowing back from the stomach to the esophagus.

Stomach

The stomach is a hollow container in the digestive system labeled diagram, and it holds the food that gets passed down from the esophagus. This is where the food gets mixed with the enzymes in the stomach. The enzyme breaks the food down into a form that can be used.

There are cells in the stomach lining that secrete a powerful and strong acidic enzyme that is responsible for breaking down the food. When the food contents in the stomach get processed, then these get released and move to the small intestine.

Small Intestine

The small intestine is a muscular tissue 22 feet long, and it is divided into three segments. These are the duodenum, jejunum, and ileum. Here food is broken down further with the enzymes that are released from the pancreas and bile that is released by the liver. The food also gets mixed with the digestive juices that get released by the liver and the pancreas. The duodenum segment is responsible for breaking down the food continuously. The jejunum and the ileum are present in the lower intestine and are responsible for nutrient absorption into the bloodstream. After the nutrient from food gets absorbed, the leftover residue of food passes through the small intestine and into the colon or the large intestine.

Pancreas

Digestive enzymes get secreted from the pancreas into the duodenum. This helps in breaking down fat, protein, and carbohydrates. The pancreases are also responsible for making insulin that gets passed into the bloodstream. Insulin is a hormone that helps to mobilize the sugar in your body.

Liver

There are many functions that the liver performs in the digestive process, but its main role is to process the nutrients that get absorbed by the small intestine. The bile that gets secreted from the liver into the small intestine helps to digest fat and other vitamins. The liver also detoxifies any harmful chemicals in food.

Gallbladder

The gallbladder is the place where the bile released from the liver is stored and concentrated. This is released into the duodenum present in the small intestine which helps to absorb and digest the fat.

Colon (Large Intestine)

The colon or the large intestine is responsible for processing the waste to make it easy to empty your bowel. The colon is a muscular tube that is 6 feet long and connects the small intestine and the rectum. When the colon is full of stool, it then empties all the contents in the rectum where the bowel movement begins.

Rectum

The rectum is 8-inch long and straight, and it connects the colon to the anus. The rectum receives the stool, and it holds on to it until the process of evacuation. 

 

Anus

The anus is the final part of the digestive tract, which is 2 inches in length. The lining in the upper anus detects any content in the rectal. The anus has the sphincter muscles that let you control the stool. When there is an urge to go to the bathroom, the external sphincter holds on to the stool till you reach the bathroom where it relaxes and releases the contents.

When you draw and label a diagram of the digestive system, you will be able to visualize these clearly.