DIGESTIVE SYSTEM

The digestive system is also known as the alimentary canal. Food contains a large amount of nutrients that function within the body for body building, growth and cell repair. This food material also provides energy within the body. The alimentary canal begins at the mouth and ends at the anus. We take food through the mouth and this food is digested and absorbed and the waste material comes out in the form of stool through the anus.

Digestion..

Digestion is the conversion of large molecules of food into smaller molecules which occurs in two ways.

Mechanical digestion..

It works to mechanically break down food mainly through the act of chewing food in the mouth in which large molecules of food are broken down into smaller molecules. Some extent of mechanical digestion also takes place in the stomach.

Chemical digestion…

In this digestion, food molecules are combined with chemicals and enzymes that help in digestion. In this chemical digestion, food is mixed with saliva and different enzymes.Food is mixed with different chemicals at different places in the digestive track and digested. In chemical digestion, secretions from the main organs of the digestive track and accessory organs also help in digestion.

Process of digestion…

Ingestion…

It is the first step in the process of deification. In which the food is placed in the mouth is called ingestion.

Propulsion…

It is the second step in the process of digestion. According to this step the food placed in the mouth moves slowly in the alimentary canal which is called propulsion.

Digestion…

This digestion is mainly seen in two types mechanical digestion and chemical digestion. It occurs in the mouth, stomach and intestines.

Absorption…

The digested small molecules are absorbed into the body as nutrients through the mucus membrane of the digestive track. All of them are carried out by the organs of the digestive track.

Elimination…

After the nutrient material digested in the digestive track has been absorbed, the residual material is called faeces or stool, which leaves the body through the action of defecation through the rectum and anus is called elimination.

Organs of the Digestive System…

Digestive tract also called alimentary tract is a hollow tube starting from mouth and extending to anus.

mouth

Fairings

Esophagus

Stomach

The small intestine consists of the duodenum, jejunum, and ileum.

Large intestine which includes cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal.

Accessory organs of the digestive tract…

These organs do not come in the main track of the digestive tract but are located in the side which pours its secretion into the alimentary canal and helps in the process of digestion so it is called accessory organ.

3 pairs of salivary glands

Liver and biliary tract

Goal Bladder

Pancreas.

Abdominal organs are accessory organs that help in digestion.

Basic structure of the alimentary canal…

The alimentary canal consists of four tissue layers continuous from the esophagus to the anus as follows:

mucosa

Sub mucosa

Muscular layer

Cirrhosis or adventitia

The above tissue layers are arranged from inner to outer side

Mucosa layer…

It is the innermost layer of the alimentary canal. It is in direct contact with food. Its wall is made up of columnar epithelium tissue. Its wall also contains goblet epithelium cells which secrete mucus. This mucus acts to lubricate the food. Mucus being a viscous fluid prevents food from rubbing against the inner wall of the alimentary track and acts to protect its wall. It is the layer associated with the action of protection secretion and absorption. Different glands secrete their secretions on this mucus layer like oral cavity, gastric juice is secreted in stomach. All these liquids help in chemical digestion which is in contact with the mucosal layer.

Submucosal layer…

This layer is composed of areolar connective tissue. Vascular layer contains blood vessels and nerves. These blood vessels and nerves function to control the functions of the digestive track. Nerve supply consists of sympathetic and parasympathetic nerve supply which control the movement of the mucosal layer.

Muscular layer…

The muscular layer consists of a double layer of smooth muscles in which the outer layer is composed of longitudinal muscles and the inner layer is composed of circular muscles. These muscles have invo voluntary control, the contraction of these muscles leads to the breakdown of food. This contraction and relaxation of the muscles causes the food to move along the track, this movement is called peristalsis movement. This movement causes the food to move forward and the sphincter valve prevents the food from moving backwards.

Adventasia…

This is the outer covering of the digestive track i.e. the superficial layer. It consists of loose fibrous tissue. This serous membrane covers the organ of the abdominal cavity called the peritoneum.

Peritoneum…

It is the covering of the organs of the abdominal cavity. It is a very large membrane. It is divided into two parts and forms a cavity in the middle called the peritoneum. This cavity contains a fluid called serous fluid. The outer layer of this cavity is the parietal. Serous fluid lies between the layer called the peritoneum and the inner layer called the visceral peritoneum.

Important folds of peritoneum include falciform ligament, lesser omentum and greater omentum.

The falsi firm ligament attaches the liver to the anterior abdominal wall and dia farm.

A fold of the lesser omentum attaches to the stomach and duodenum while the greater omentum is a large fold of peritoneum attached to the transverse colon and small intestine.

ORGANS OF THE DIGESTIVE TRACK

• mouth…

Mouth is also called oral or buccal cavity. The mouth is a cavity made of bone and muscles and the surrounding structure is as follows.

In front of it there is the opening of lips and mouth cavity.

Posteriorly, the mouth is connected to the oropharynges.

Its side wall is made of cheek muscle.

Above it lies the hard palate made up of bone and behind it lies the soft palette made up of muscles.

On the lower side of the mouth is the tongue. The lining of the cavity inside the mouth is known as the mucus membrane. It contains stratified squamous epithelium cells.

There is an arch-like structure at the back center of the oral cavity known as the uvula. On both the lateral sides of this uvula there are folds on both sides in which the folds on the anterior side are called palatoglossal arches and the folds on the posterior side are called palatopharyngeal arches. On either side of these arches are collections of lymphoid tissue called palatine tonsils.

• Tongue…

The tongue is made up of skeletal muscles with a layer of mucus membrane over it. It forms the floor of the oral cavity. which divides the oral cavity into two parts in the middle. The tongue is attached inferiorly to the hyoid bone at the back. The tongue is attached to a fold of the basal mucus membrane of the oral cavity called the frenulum.

The superior surface of the tongue is composed of stratified squamous epithelium cells. There are papillae on the upper and lateral sides of the tongue. These papillae are attached to the nerve endings and are also known as test birds. These papillae are of three types.

Filiform papillae..

These papillae are located in the anterior two-thirds of the tongue and do not contain testes.

Fungiform papillae..

They are located on the tip of the tongue and on its side. They are like tiny dots and are known as test birds for most taste buds.

Valette papilla…

They are arranged in a V shape on the posterior side of the tongue and are the largest of all the papillae.

Functions of the Tongue…

It plays an important role in the act of speaking and speech.

The test works for discrimination due to the presence of test birds on its surface.

Mastication means chewing. Both tongue and teeth complete the act of chewing. The tongue is important for the movement of food in the mouth.

Deglutition is the act of swallowing Ma Tong helps in pushing the food back down the throat.

• Teeth…

Teeth are useful parts for chewing. They are fixed with jaws. Teeth are replaced only once in humans.

The first teeth that appear in childhood are called milky teeth or deciduous teeth, followed by the second set of permanent teeth.

Deciduous teeth are 20 in number, each with 4 incisors, 2 canines and 4 molar teeth.

Permanent teeth are 32 in number including 4 incisors, 2 canines, 2 premolars and 3 molar teeth.

Structure of a tooth..

Each tooth has three parts.

The crown that appears above the gum.

The root is pressed into the jaw below the gum.

The neck is located between the crown and the root.

Other structures of the tooth include the following parts.

1 pulp..

It is a cavity of loose fibrous tissue in the middle which contains blood vessels and nerves.

2. Dentin..

The structure surrounding the pulp is called dentin and is made of calcified material.

3. Enamel…

The outer part of the tooth i.e. the crown or the part covering the dentin called enamel forms the hard part of the tooth.

4. Cementum..

The top layer of dentin at the root of the tooth is a bone-like structure called cementum.

5. Periodontal membrane..

This membrane is useful for holding the root of the tooth in its socket.

Functions of the Teeth…

A tooth’s function is sold based on its shape. Different shaped teeth perform different functions like..

The incisors and canine teeth are sharp which are important in cutting and breaking.

Premolar and molar teeth have flat surfaces so they are important for grinding.

Salivary glands…

Salivary glands are accessory structures. Which is located on the side of the wall of the mouth. It secretes a fluid called saliva. These salivary glands are among the three which are as follows.

Parotid glands..

It is a pyramid shape gland. It is a gland located between the skin and muscle mass in the lower part of the external ear.Each gland has a parotid duct and this duct opens near the second upper molar tooth in the upper jaw. This gland produces water called saliva which contains enzymes but no mucus.

2. Sub mandibular gland…

This gland is located below the angle of the mandible. It secretes both mucus and enzymes. Its submandibular duct i.e. the duct of Vertsion opens at the lingual frenulum.

3. Sublingual glands..

This is a small gland located on the opposite side of the submandibular gland. It opens into the floor of the mouth through the sublingual duct i.e. Duct of Revenus.

All the above glands have a fibrous capsule on their outer surface. It has a number of lobules and these lobules are made up of secretory cells which pour their secretion into small ducts and all these small ducts join and form a large duct which opens at the mouth.

Salaiva’s composition…

Saliva is secreted by the salivary gland. This gland is located in the oral cavity. The fluid secreted is called saliva. Its pH is slightly acidic. 6.35 to 6.85. An estimated one and a half liters of saliva is produced daily. Its structure includes water, mineral salts including sodium, potassium, chloride and some enzymes including salivary amylase and mucus organic substances like urea, uric acid, lysosome and some blood clotting factors.

The secretion of saliva is controlled by the autonomic nervous system in which the parasympathetic nervous system increases the production of saliva and the sympathetic nervous system decreases the production of saliva. The parotid gland secretes salivary amylase.

Function of the saliva…

When food is placed inside the mouth, saliva mixes with the food and acts as a lubricant so that the lining of the mucus membrane is not damaged.

Due to the presence of water in the composition of saliva, it keeps the mouth clean and due to the presence of mucus, it keeps the mouth lubricated so that the tissues of the mouth remain soft and moist.

Salivary amylase within saliva helps in the chemical digestion of polysaccharides and digests them into disaccharides or monosaccharides.

Due to the presence of lysosomes, immunoglobulins and clotting factors in the composition of saliva, it helps in destroying micro-organisms.

The food comes into contact with water by mixing with the liquid and it dissolves to give the test.

• Pharynx..

The pharyns are wide muscular tubes located at the back of the nose and mouth. Fairings are mainly divided into three parts

nasopharynx

oropharynx

Laringo Fairings..

The nasopharynx acts as a passageway for the action of respiration.

The oropharynx and laryngopharynges act as passages to the digestive system as well as passages to the respiratory system.

Food passes from the oral cavity to the esophagus through the pharyngs thus the pharyngs act as both a food passage and an air passage.

The structure of the pharyngs consists of layers similar to the basic structure of the digestive tract, with the mucosal layer being the innermost layer. Above it lies the sub-mucosal layer and above it lies the muscular layer. Which is discussed in detail in Basic Structure.

• Esophagus…

The esophagus is a thin muscular tube that lies between the pharynx and the stomach and acts as a food passage.It extends from the lower part of the neck to the stomach. Its length is 25 centimeters and width is two centimeters. The lumen of this tube is collapsing i.e. thickened and widens during swallowing. At the upper and lower ends of the esophagus are the sphincter muscles. Upper crico pharyngeal sphincter and lower isopharyngeal sphincter

A sphincter or cardiac sphincter is present which prevents the gastric contents from rising up into the stomach i.e. prevents reflux.

Esophagus has trachea in front and vertebral column in back and lungs on right and left.

Similar to the basic structure of the digestive tract, the structure of the esophagus consists of tissue layers, with an innermost mucosal layer, a submucosal layer, a muscular layer, and an outermost adventitia layer. Esophagus acts as a food passage.

• Stomach…

It is an organ of the digestive system. It is the organ of J shape. It forms the widest part of the alimentary canal. Mainly the stomach lies in the epigastric region and part of it lies in the left hypochondriac region.

A part of the liver is located in front of it, abdominal aorta, pancreas and spleen are located in the back. Above is the diaphragm and below is the intestine.

structure..

The structure of the stomach is divided into three parts

Fundash

body and

pylorus..

Fundus…

It forms the uppermost part of the stomach. It is found in dome shape. Above the level where the esophagus joins the stomach. It is sometimes filled with gas. Here the cardiac sphincter muscles lie between the junction of the esophagus and the stomach.

body…

The part below the fundus of the stomach is called the body, which extends to the lower narrow part of the stomach called the pylorus.

Pylorus…

The stomach consists of a descending portion after the body, which begins with the pyloric antrum, which is a narrow portion after the body, leading to the duodenum is a canal-like structure called the pyloric canal, which opens into the duodenum and is surrounded by sphincter muscles. is called the pyloric sphincter.

Apart from this, two curvatures are seen on the body portion of the stomach, a lesser curvature which forms the right side border of the stomach and a greater curvature which forms the left side border of the stomach.

Layers of the Stomach…

The wall of the stomach, similar to the basic structure of the digestive tract, is composed of four tissue layers, with the outermost layer being the peritoneum, also called the adventitia layer, which forms the serous lining.

Below it is a layer of muscles. In the stomach, this muscular layer is made up of three layers, one having longitunnel muscle fibers which are arranged superficially, the other circular muscle fibers which are arranged in a circular shape under the superficial layer and these fibers are also important for forming the sphincter muscles. Muscle fibers are mainly found in this layer stem which is not found in the basic structure. It is especially found in the stomach wall which is a very important layer for the movement and mechanical digestion of food in the stomach.

Below the muscular layer lies the submucosal layer which contains a network of blood vessels and lymph vessels.

The innermost layer of the stomach wall is called the mucosal layer. This layer is made up of columnar epithelium tissue. This layer secretes mucus and also acts as a lubricant. In this layer there are folds of mucus membrane which are especially visible when the stomach is empty, called rugai, when the stomach becomes swollen with food, this rugai disappears.

Functions of the Stomach…

Stomach performs the following functions.

Stomach serves to store food for a short period of time.There is also partial mechanical digestion of food before it moves through the intestinal track.

Stomach functions to secrete gastric juice. This gastric juice has an acidic content and the enzymes present in it help in the digestion of food.

The muscular layer in the wall of the stomach is specially arranged and its contraction causes a churning movement which helps in mechanical digestion of the food and breaks the food into small pieces and then the food moves into the duodenum.

Intrinsic factor is secreted from the inner wall of the stomach which is essential for the absorption of vitamin B.

Water, alcohol and some drugs are also absorbed to some extent from the wall of the stomach.

It also works to destroy bacteria or viruses inside the stomach. In which these bacteria reach the stomach through mucus and oral cavity, they are destroyed in acidic secretions and they stop moving in the interstitial track, thus it also acts as a protection for the body.

Digestion in Stomach:
Food taken by mouth reaches the stomach through the esophagus. Mechanical digestion of food begins due to the charming movement of the stomach due to the contraction of the muscular layer of the stomach. Here all the food is converted from large molecules to small molecules by mechanical digestion.
After this mechanical digestion has gone on for some time, hydrochloric acid is secreted with the food through the glands in the inner wall of the stomach.
Chemical digestion begins when the chemicals present in this juice of the stomach mix with the food.
In addition to hydrochloric acid, this gastric juice contains enzymes, mainly pepsin and renin. This pepsin digests large molecules of protein into smaller molecules. Digestion of protein begins here.
Renin in the gastric juice digests the protein casein in milk and converts it into paracasein. Thus, digestion of protein mainly takes place in the stomach.
Digestion of carbohydrates and fats does not take place in the stomach, only mechanical digestion takes place here. After partial digestion of this food in the stomach, it goes to the small intestine where complete digestion and absorption takes place.
As the food in the stomach mixes with gastric juice, the harmful bacteria and viruses in the food are destroyed due to the acidic property of HCL in it.

Gastric juice…

The stomach is an organ of the digestive system. It forms the largest part of the digestive system and has a capacity of approximately one and a half to two liters. Its innermost wall is made of mucus membrane. Glands below this membrane secrete a digestive juice called gastric juice.

The gastric juice is a clear and colorless liquid. When food reaches the stomach, these juices mix with it and help in digestion.

Salivary amylase present in saliva is mixed with gastric juice in the stomach, reducing its effect and reducing carbohydrate digestion.

The gastric glands secrete approximately two liters of gastric juice during the day.

The composition of gastric juice includes water, mineral salts, mucus, hydrochloric acid, intrinsic factor, pepsinogen, enzymes etc.

Function of the Gastric Juice..

Water acts to liquefy the food in the stomach.

Hydrochloric acid makes the food acidic and works to destroy the micro-organisms in the stomach thus having antiseptic and disinfectant properties and performing a protective function.

It also provides a medium for the digestion of protein which occurs due to the conversion of pepsinogen to pepsin.

Gastric lipase present in gastric juice helps in the digestion of fat to some extent.

Intrinsic factor is essential for the absorption of vitamin B12.

The mucus in the gastric juice acts as a lubricant and prevents friction between the stomach wall and the food.

• Small Intestine…

The small intestine is a tube-like structure in the gastrointestinal tract that begins in the stomach and extends to the ileocecal valve where it joins the large intestine.

Part of the small intestine lies in the abdominal cavity around the umbilical region, with the large intestine arranged around it. Its diameter is about an inch wide and its length is about 20 ft. It is arranged like a tangle in the abdominal cavity. Small Intestine

. Duodenum..

The duodenum is the initial part of the small intestine. It starts at the end of the stomach i.e. the pylorus and is approximately 25 cm long and arranged in a c shape.

2. Jejunum…

It is the post-duodenal part of the small intestine whose upper part joins the end part of the duodenum. From here these tube-like structures are arranged downwards in clusters. The length of the jejunum is approximately 8 feet. The jejunum joins the ileum at the bottom.

3. Ilium…

The ileum is the portion of the small intestine after the jejunum that joins the jejunum at the top and is approximately 12 feet in length. It connects to the large intestine through the ileosic sphincter.

Structure of the Small Intestine…

The small intestine is also made up of four tissue layers, similar to the basic structure of the digestive tract.

The outermost layer is the peritoneum. It is made up of serous membrane and is in double layer.

Below the peritoneum layer is the muscular layer. The lining of this track is composed of smooth muscles with an outer layer of longitudinal muscle fibers and an inner layer of circular muscle fibers. Due to the contraction of the muscles, peristalsis movement is observed and the content moves along the track.

Below the muscular layer is the submucosal layer which contains blood vessels, nerves etc. Some glands are also located in this layer.

The inner lining of the small intestine is made up of a mucus layer. Between this mucus layer and the submucous layer is a layer of plain muscles which is called the muscularis mucosa. Contractions of these muscle fibers empty the lactic acid.

In the lining of the mucosal layer are permanent fold-like structures called valvular cone vents. Due to this fold, the content remains there for a long time and maximum absorption can take place and the digestive juices can act on the food there for a long time so that proper digestion takes place.

Mucosal layer consists of villous structures that absorb the digested food.

In this layer there are some nodules of lymphatic tissue called Peyer’s patches which perform a protective function in the intestine.

Part of the small intestine is supplied with blood by the superior mesenteric artery. and venous return via the mesenteric vein.

The nerves are supplied by the sympathetic and parasympathetic nerves.

Intestinal juice…

Intestinal juice is clear yellow in color. Which is secreted as much as one to two liters per day. Its property is alkali. Its pH ranges from 7.6 to 8.0.

Its structure consists of water, mineral salts, mucus and enzymes like maltase, sucrase etc.

This intestinal juice also includes pancreatic juice and bile. All these juices are called permanent. Which is very important in the digestion of protein, fat and carbohydrates.

Functions of Small Intestine…

Pendulum movement occurs in the small intestine due to which the intestinal contents can be mixed.

The fluid in the intestine is called perineum which moves throughout the intestine through peristalsis movement and helps in digestion.

The small intestine secretes digestive juices.

Chemical digestion of protein, fat and carbohydrates takes place in it.

90% of the digested nutrients are absorbed through the wall of the small intestine.

The segments in the inner layer of the small intestine allow digestive juices and food time to mix, digest and absorb.

• Large Intestine…

The large interstyle begins at the ileocecal junction and extends to part of the anus.It has a total length of 1.5 meters and is divided into lower sections.

caecum

Colon

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

the rectum

Anal canal

Between cecum and ileum lies a narrow diverticulum known as appendix.

Sikkam…

Sikkim is the initial part of the Large Interstyle. It is five to eight centimeters long. It is a blind pouch and is located in the right lower abdominal quadrate.

colon..

A colon begins with an ascending colon. It is on right side in vertical position. From there it is seen upwards to the border of the liver. The ileum joins the ascending colon near the cecum where the ileocecal valve is located.which allows the content to enter the large intestine but does not allow the content to pass in the reverse direction.

The transverse colon is then positioned horizontally into the abdominal cavity. It passes through the liver, stomach and lower part of the spleen.

It extends from the hepatic flexure to the splenic flexure.

The descending colon is in a vertical position and lies in the abdomen on the left side. It is arranged in the lower part of the stomach and spleen.

The sigmoid colon is positioned below the iliac crest. It is the terminal part of the large intestine and is in an S shape.

Rectum…

It is approximately 20 cm long piece. It starts from the sigmoid colon and extends to the anal canal.

Anal canal…

The two to three centimeter portion of the rectum at the end of the large intestine is called the anal canal. The mucus membrane lining the anal canal is arranged in longitudinal folds.This is called the anal column.This part contains arteries and veins and two sphincter muscles are arranged around the anus.

Internal sphincter muscles are smooth muscles.Which is under the control of autonomic nervous system i.e. involuntary function. The external sphincter muscles are the skeletal muscles that are under our voluntary control.

Structure of the Large Intestine…

The structure of the large intestine also has 4 tissue layers similar to the basic structure of the digestive tract.

In which the innermost mucosal layer is found.This mucosal layer does not have a villi as in the small intestine. Epithelium tissue and goblet epithelium cells are present in that layer, which are responsible for absorbing water and secreting mucus.Some lymphatic nodules are also located in this layer.

The submucosal layer of the large intestine has the same characteristic as the basic structure.Above it is the muscular layer which is found in double layer outer layer is made up of longitudinal muscle fibers and inner layer is made up of circular muscle fibers.

At the outermost part is the cirrhotic layer.Which is part of visceral peritoneum.

The large intestine is supplied with blood by the inferior and superior mesenteric arteries and venous return by the superior and inferior mesenteric veins.

Functions of the Large Intestine…

Water and Electrolytes Absorption..

Most of the water absorption takes place in the small intestine, but some water absorption and some electrolytes also occur in the large interstitium.

Water absorption from the stool in the large intestine plays an important role in making the stool semi-solid.

Microbial activity..

Certain bacteria are present in the large intestine. These bacteria are important for the synthesis of vitamin K and folic acid. These bacteria can be harmful if they move to other body parts and can cause infection.

Due to the activity of these bacteria and the work of fermentation, gas is produced from the undigested food which comes out from the bowel in the form of flatus through the anus.

Mass Movement…

Peristalsis movement is seen in other parts of the intestine but this type of peristalsis movement is not seen in the large intestine.

In the large intestine there is a large strong peristalsis movement after a long time interval that moves the contents along the intestinal track towards the descending colon and sigmoid colon which is called mass movement.

Deification…

Due to the mass movement in the large intestine, the faecal material moves in the interstitium towards the sigmoid colon and the rectum due to which the stretch receptors in the rectal wall are stretched and the defecation reflex starts and the process of defecation begins.

In the defecation reflex, there is a stretch in the wall of the rectum, causing stimulation of the sensory nerve due to the stretching of its receptors. It transmits impulses to the sacrum in the spinal cord.Apart from this, due to the pressure of the diaphragm and abdominal cavity for the process of defecation, it helps in the process of defecation. Sitting position also helps in the defecation process. Finally, due to the stimulation of parasympathetic nervous, the internal sphincter relaxes and the stool comes out through it. Relaxation of the internal sphincter and external sphincter causes passing of stool.

Feces.

The feces is brown in color. This brown color is due to stercobilin present in it. It has semi-solid and solid properties. Approximately 60 to 70% of the body’s composition is water. Excess water is absorbed through the wall of the large intestine. The following are found in the structure of the feces.

Dead and Live Micro Organisms.

Dietary fibers.

Epithelium tissue of the wall of the intestine.

Mucus and undigested food. etc..

As mucus is secreted through the intestinal wall, stool can easily pass without wearing down the intestinal wall.