The digestive system of humans is composed of the alimentary canal and the other associated glands. Let’s have a brief look at structures associated with the digestive system.
The alimentary canal begins with the mouth and posteriorly opens through the anus. This passage is also known as the gastrointestinal tract. This tract consists of all major digestive organs like the oesophagus, intestine and stomach. Additionally, they also have accessory organs like the liver, salivary glands, gall bladder, etc.
The mouth leads to the oral or buccal cavity. It is the anterior opening that aids in the intake of food. This oral cavity is anteriorly bounded by the lips. Also, the muscular tongue and teeth are important components of this oral cavity. The vestibule area of the mouth encompasses the lips, teeth and cheeks. Furthermore, there is a mucous membrane lining the tongue and aiding in the digestion process. This cavity receives secretions from the salivary glands.
Teeth help in the crushing and cutting of food particles. They break down the food and start the digestion process. The four types (Heterodont) of teeth structure in humans are:
The incisors and canines help in the cutting and tearing of food, respectively. The molars and premolars aid the crushing of food. Most mammals, including humans, develop two sets of teeth in their lifespan. One is the milk teeth, and the other is the permanent teeth. This type of dentition is called diphyodont.
The oral cavity leads to the pharynx, which serves as a common passage for air as well as food. This pharynx is found above the oesophagus (food pipe) and the trachea (windpipe). The food pipe is a fibromuscular tube that is approximately 10 inches long. This pipe empties into the upper surface of the stomach.
It is a hollow muscular organ that is vital for digestion. The stomach usually performs the chemical breakdown of food. It is located between the food pipe and the duodenum. There is a valve (pyloric sphincter) that helps in the passage of food from the stomach to the small intestine (duodenum).
Most of the nutrients are absorbed in the small intestine. It is approximately 18 feet long and comprises three regions called the – duodenum, jejunum and the ileum. These structures, along with the intestinal secretions, help in the chemical digestion of food. The ileum opens into the large intestine.
It is the large and also the last part of the alimentary canal. It is most important for the absorption of water. The final waste material is stored as faeces in the human rectum. This waste is removed by the final process of digestion which is also termed defecation.
The gastrointestinal tract includes accessory glands that aid in digestion. The major digestive glands associated with the human digestive system are the liver, pancreas and salivary glands. The cheeks, lower jaw and lower tongue surface, have salivary glands that secrete saliva. It helps to chew and swallow the food. The liver is the largest gland that secretes biochemicals like bile that aid in digestion. The pancreas is an elongated compound that acts as both endocrines as well as an exocrine gland. The exocrine portion secretes pancreatic juice, and the endocrine part secretes insulin, glucagon and hormones.
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