Alimentary canal also known as the digestive tract or gastrointestinal (GI) tract is a long muscular tube that extends from the mouth to the anus. It is around 8 to 10 meters long and has openings at both ends, with the mouth at the front (anterior) and the anus located at the end (posterior). It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. It is responsible for digestion, nutrient absorption, and waste elimination. Accessory structures like the tongue and teeth aid in the digestive process. The alimentary canal plays a vital role in the digestive process and is essential for maintaining proper nutrition and overall health.
What is the Alimentary Canal?
The alimentary canal, or gastrointestinal tract, is a vital organ system in the human body. In an average adult human, the alimentary canal can be approximately 5 to 7 meters (16 to 23 feet) long, from the mouth to the anus. It is responsible for the digestion and absorption of nutrients. The process begins with mastication in the mouth, where saliva, initiates the breakdown of carbohydrates. The food then travels down the esophagus, and reach the stomach where protein digestion takes place. In the small intestine, the majority of digestion and nutrient absorption occurs. The large intestine's primary role is water absorption and the formation of feces. The rectum stores feces until they eliminated through the anus. This process is essential for breaking down food into its basic components, which enables nutrient uptake for energy and body function.
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Organs of the Alimentary Canal
The alimentary canal is composed of different organs, including the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. All these organs work together to break down food into smaller particles and molecules that can be absorbed into the bloodstream.
Mouth
The process of digestion begins in the mouth, where food is mechanically broken down by chewing and chemically through the action of saliva. Enzymes like amylase are present in the saliva that start to break down carbohydrates. Mouth is divided in two parts: the vestibule and the oral cavity.
Oral Cavity
The oral cavity, commonly known as the mouth, is the entry point for food and air. The oral cavity includes the lips, teeth, tongue, and the hard and soft palates. The components and functions of the oral cavity are as follows:
- Lips and Cheeks: The lips and cheeks form the walls of the oral cavity. It provides support and containment for food and saliva and also help in producing speech sounds.
- Tongue: The movement of the tongue help food enters the mouth. In the mouth the digestive process starts. The tongue is attached to the base of the oral cavity. The taste buds on the papillae are sensory organs. Three types of lingual papillae are present those are: Circumvallate, filiform, and fungiform.
- Palate: The palate is divided into the hard palate (front) and soft palate (rear). The hard palate assists in chewing, and the soft palate closes off the nasal passages during swallowing to prevent food and liquid from entering the nose.
- Salivary Glands: Salivary glands in and around the oral cavity produce saliva, which contains enzymes like amylase to initiate the breakdown of carbohydrates. Saliva also lubricates food, making it easier to swallow. The parotid, submandibular (submaxillary), and sublingual glands are the three principal pairs of salivary glands.
Teeth
Teeth are composed of dentin, a substance similar to bone, which is covered with enamel, the body's toughest tissue. To carry various mastication process that are used to chew food into small pieces, oral cavity contains teeth of different types that are as follows:
| Type | Function |
| Incisor | Used for biting |
| Canines | Used for tearing |
| Premolars | Tearing and grinding food |
| Molars | Chewing and grinding food |
A soft bolus is created when the meal is masticated with the aid of saliva and mucus, which can then be swallowed to allow it to pass through the upper gastrointestinal tract and into the stomach. Saliva's digestive enzymes assist in keeping teeth clean by dissolving any food particles that may have become lodged in the teeth.
Esophagus
The esophagus is a muscular tube that extends approximately 10 to 13 inches in length. It connects the throat, or pharynx, to the stomach. Its primary function is to allow the movement of food and liquids from the mouth to the stomach for digestion. The muscles in the esophagus contract in coordinated manner, the movement is called peristalsis, which propels food downward. During swallowing, the epiglottis, a flap-like structure in the throat, ensures that food and liquids enter the esophagus and not the windpipe.
Stomach
It is located in the upper abdomen, just below the diaphragm. An empty stomach resembles a J-shaped bag. Gastric glands found in the stomach secretes gastric juice, which aids in digestion and killing microorganisms. The stomach is differentiated into four parts:
- Cardiac: Cardiac forms the first part where the stomach starts and is present near the heart. It is responsible for receiving food from the esophagus and allows it to enter the stomach.
- Fundus: The fundus is the upper portion of the stomach, and its primary role is to store and collect gases produced during digestion. This area expands as the stomach fills with food and gas.
- Body: In the body most of the digestive processes occur and forms the central region. It contains gastric glands that secrete gastric juices, including hydrochloric acid and digestive enzymes. These substances are important for breaking down food.
- Pyloric: The pylorus forms the lower part of the stomach and is responsible for regulating the release of partially digested food (chyme) into the small intestine.
Small Intestine
The stomach's lowest part pyloric opens into the duodenum. The small intestine is the longest part of the alimentary canal. On the inner surface it is covered with villi which increases the surface area of the intestine. The small intestine is further divided into three parts those are:
- Duodenum: It is the connection between the stomach and the intestine, it is S-shaped. It is where partially digested food, known as chyme, is mixed with digestive enzymes from the pancreas and bile from the liver (via the common bile duct). These enzymes and bile aid in the breakdown of carbohydrates, proteins, and fats, allowing for better absorption of nutrients.
- Jejnum: The jejunum follows the duodenum and is the middle portion of the small intestine. It's the primary site for nutrient absorption, particularly of carbohydrates and proteins. The walls of the jejunum are lined with finger-like projections called villi and microvilli, which increase the surface area for nutrient absorption into the bloodstream.
- Ileum: The ileum is the final section of the small intestine, connecting to the large intestine at the ileocecal valve. It continues the absorption process, primarily focusing on bile salts, vitamin B12, and any remaining nutrients.
Large Intestine
The large intestine, also known as the colon, is primarily responsible for the final stages of digestion, water absorption, and the elimination of waste products. It follows the small intestine in the digestive tract and consists of several parts including the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The large intestine is further divided into 3 parts those are:
- Caecum: The caecum is the beginning of the large intestine and is a pouch-like structure that receives material from the ileum (the last part of the small intestine). It contains the vermiform appendix, a small, finger-like projection that has unclear but potential roles in the immune system. It contains microorganism which shows a symbiotic relationship. Caecum is the part from which the vestigial organ is attached i.e., the vermiform appendix.
- Colon: The colon is the longest part of the large intestine and is further divided into several regions: the ascending colon, transverse colon, descending colon, and sigmoid colon. The colon is responsible for water absorption and the formation of feces.
- Rectum: The rectum is the final portion of the large intestine before the anus. It stores feces until they can be eliminated from the body.
Function of Alimentary Canal
The alimentary canal, also known as the digestive tract or gastrointestinal tract, is responsible for various essential functions in the human body. These functions include:
- Ingestion: The process of taking in food and liquids through the mouth for further processing.
- Mastication: Chewing food in the mouth and breaking it down into smaller particles for easier digestion.
- Digestion: It breaks down food into smaller, absorbable molecules through both mechanical and chemical processes.
- Absorption: The uptake of nutrients (e.g., glucose, amino acids, fatty acids, vitamins, and minerals) from the digested food into the bloodstream. It distribute the same to the body's cells and tissues. This process occurs in the small intestine.
- Secretion: The release of digestive enzymes, acids, and other substances from various accessory organs, including the salivary glands, stomach, liver (bile production), and pancreas (enzyme production).
- Mixing and Churning: Mechanical mixing of food and digestive fluids in the stomach and intestines. It further breaks down food particles and aids in digestion.
- Excretion: The undigested waste, indigestible food materials, and other metabolic byproducts is eliminated from the body through the rectum and anus.
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