Digestive System Our Digestive System

 Digestive System, Our Digestive System

Digestive System

 Digestive System, Our Digestive System

Energy is required for vital activities in the body. This energy is provided by food. Foods must be digested in order to be usable in the body. Digestion; It is the breakdown of nutrients down to their building blocks.

 

Foods that are broken down to building blocks are easily taken into the cell and used in respiratory reactions. Thus, the energy required for vital activities is produced. There are two types of digestion: mechanical digestion and chemical digestion. Mechanical digestion is the physical breakdown of food into small pieces. Chemical digestion is the breakdown of nutrients into building blocks by enzymes.

 

Structure, Task and Functioning of the Digestive System

1.       Mouth

2.       Swallow

3.       Esophagus

4.       Stomach

5.       Small intestine

6.       Large bowel

 

Structure, Task and Functioning of the Digestive System

The digestive system consists of the digestive tract and the organs that aid digestion that shed their secretions into this channel.

 

Mouth

Digestion of food begins in the mouth. Mouth; It is a space surrounded by lips, cheeks, palate and pharynx. There is saliva secreted from the tongue, teeth and salivary glands in the oral cavity. Teeth break down nutrients and physically break them into small pieces. Thus, it increases the action surface of digestive enzymes.

Milk teeth start to appear in humans from the 6th month. At the age of 6-7, the milk teeth fall off and leave their place to permanent teeth. An adult human has a total of 32 teeth, 8 incisors, 4 canines, 8 premolars and 12 molars in the lower and upper jaw. The incisors are used to cut food, to split canines, and molars to grind. Language is the organ of taste. It helps chew food, push the chewed food into the throat and talk. Saliva secretion both facilitates digestion by softening foods and provides digestion of food thanks to the digestive enzymes it contains.

 

Swallow

Swallow; The oral cavity is the section between the nasal cavity, food and trachea. It ensures that the foods chewed in the mouth are transmitted to the esophagus. This event is called swallowing. During swallowing, the cap of the larynx (epiglottis) closes the windpipe. Thus, food is prevented from getting into the windpipe.

 

Oesophagus

The oesophagus is located between the pharynx and the stomach. It is a muscular tube about 25 cm long, 2 cm in diameter. The oesophagus consists of connective tissue, smooth muscle and mucous layers from the outside to the inside. The secretory cells in the mucous layer produce a secretion called mucus. This secretion makes the inner surface of the oesophagus slippery, making it easier for food to move through the oesophagus.

 

Since the muscles at the beginning of the oesophagus are striated muscles, swallowing occurs voluntarily. The muscles in the continuation of the oesophagus are smooth muscles. For this reason, foods are conveyed to the stomach by peristaltic contraction movements of these muscles that work involuntarily. In the case of vomiting, peristaltic movements occur from the stomach to the mouth.

 

Stomach

The stomach is the part of the digestive canal between the oesophagus and the small intestine. The place where the stomach meets the oesophagus is called the stomach (cardia), and the place where it meets the small intestine is called the stomach gate (pylorus). Kardia prevents the food in the stomach from passing into the oesophagus and the food in the pyloric small intestine into the stomach. Stomach from outside to inside; It consists of connective tissue, smooth muscles and mucous membranes.

 

The outermost connective tissue provides protection of the stomach. It is covered with a thin membrane called the peritoneum. The liquid secreted by this membrane protects the stomach against friction by making the stomach slippery on the outside. Smooth muscles are located transverse, longitudinally and diagonally. In this way, it regularly contracts and relaxes, allowing the food to be mixed with gastric juice and mechanically digested. Foods that become slurry by mixing with gastric juice are called chums. Partially digested chyme in the stomach passes into the small intestine. The cells of the innermost mucous layer secrete a secretion made up of digestive enzymes and mucus. This secretion is called gastric juice. The gastric juice contains HCl (hydrochloric acid), mucus and pepsinogen. HCl is a strong acid and its pH is about 2. It activates the pepsinogen enzyme, allowing it to become pepsin. Mucus forms a layer on the inner surface of the stomach, preventing the stomach cells from being damaged by HCl and protecting the stomach cells against the enzyme pepsin, which digests proteins. Pepsinogen; It is the inactive state of the pepsin enzyme that digests proteins. When the pepsin enzyme is not involved indigestion, it is in the form of pepsinogen, which is its inactive form. Thus, the stomach tissue is prevented from being damaged by pepsin.

 

The work of the stomach is regulated by the vagus nerve and gastrin hormone. Seeing, smelling, or touching the stomach wall stimulates the vagus nerve. The vagus nerve also stimulates the stomach glands and releases the gastrin hormone. Gastrin hormone also increases gastric juice secretion.

 

Small intestine

Small intestine; k with stomach It is an organ about 3 cm in diameter and 7.5 m in length, located between the forehead and intestine. Chemical digestion of food is completed in the small intestine. Chemical digestion is completed and the foods broken down to the building block are absorbed in the small intestine and mixed into the blood.

The first part of the small intestine that comes after the stomach is called the duodenum (duodenum), the middle part is called the empty intestine (jejunum), and the last part is called the folded intestine (ileum). Secretions from the liver and pancreas are poured here. The empty intestine is the part of small intestine after the duodenum. Most of the food that is digested is absorbed here. The curved intestine is the last part of the small intestine. Nutrients and digestive residues that are not absorbed in the small intestine are transmitted to the large intestine by peristaltic movements.

Like the stomach, the small intestine consists of connective tissue, smooth muscle tissue and mucous layers from the outside to the inside. Connective tissue is located outermost and protects the small intestine. The smooth muscle tissue under the connective tissue allows the chyme coming from the stomach to move through the small intestine with peristaltic movements. Cells in the mucous layer covering the inner surface of the small intestine secrete mucus and small intestine sap. Mucus covers the inner surface of the stomach and prevents the acidic environment in the stomach from damaging the stomach wall. Enzymes in small intestine juice provide digestion of nutrients.

Absorption of digested food takes place in the mucous layer. The mucous layer creates folds towards the intestinal cavity to increase the absorption surface of nutrients. These folds are called villi. The epithelial cells on the edges of the villi facing the intestinal cavity are covered with cytoplasmic extensions called microvilli. Thanks to the villi and microvilli, the absorption surface of the small intestine increases approximately 600 times. The nutrient monomers formed as a result of digestion are absorbed by the blood and lymph capillaries in the villi and pass into the circulatory system.

 

The chyme coming from the stomach to the duodenum is acidic as it mixes with gastric secretions. The acidity of chyme is reduced by pouring secretions from the liver and pancreas into the duodenum. With the arrival of chyme in the duodenum, secretin and cholecystokinin hormones are secreted from here.

 

Large bowel

The large intestine, the last part of the digestive tract, comes after the small intestine. It is 1-1.5 m long and consists of three parts. The first part that joins the small intestine is called the cecum (cecum), the middle part is called the colon, and the last part is called the rectum (smooth intestine). The rectum is the part that opens to the outside with the anus. The part of the large intestine called the colon; Ascending colon, horizontal colon and descending colon and small intestine surrounds.

 

The functions of the large intestine are generally as follows:

• It absorbs the water, bile salts and B and K vitamins synthesized by the bacteria in the intestines and ensures their passage into the blood.

• It becomes a living environment for beneficial bacteria that produce B and K vitamins.

• It temporarily stores digestive wastes and allows them to be expelled from the anus as feces by peristaltic movements.

 

In the large intestine, unlike the small intestine, there are no villi and enzyme producing cells in the mucous layer. Therefore, chemical digestion does not occur in the large intestine. There is a structure that acts as a valve at the junction of the large intestine and small intestine. Thanks to this structure, bacteria and waste materials in the large intestine are prevented from returning to the small intestine.