The Digestive System

 (How foods are processed and absorbed)

The essential energy for the functioning of our body is provided by food. A dozen organs, which make up the digestive system, combine to break down food, absorb nutrients and reject waste. The series of conduits and bags through which food travels before being evacuated as feces forms the digestive tract, a nine meter long canal. We subsequently distinguish the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus

The auxiliary organs participate in digestion without belonging to the digestive tract. Teeth and tongue facilitate food processing in a bowl. The salivary glands, liver, pancreas and gallbladder produce or store digestive substances (especially enzymes) and release them into the digestive tract

Functions of the digestive system

• Ingestion: the oral cavity allows food to penetrate the digestive tract and rumination occurs (bite) and the subsequent food bolus is ingested

• Digestion:
Mechanical digestion: the strong development of the digestive tract (mainly in the oral cavity and stomach) physically divides food into smaller particles

Digestion of substances: the hydrolysis responses aided by proteins (mainly in the stomach and in the small digestive tract) synthetically divide the food particles into additional atoms, sufficient to be consumed

• Secretion: enzymes and digestive fluids secreted by the digestive tract and its accessory organs promote chemical assimilation

• Absorption: final section: elements (supplements) of chemical assimilation from the digestive tract to blood or lymph for diffusion to tissue cells

• Elimination: undigested material will be discharged through the rectum and back with the poop

Overview of the digestive system

The organs of the Digestive System are classified into two major parts: 
• Gastrointestinal tract (GI tract): it is a continuous tube that extends through the ventral cavity from the mouth to the anus (mouth, oral cavity, oropharynx, esophagus, stomach, small intestine, large intestine, rectum and anus)
• Accessory structures :( teeth, tongue (in the oral cavity), salivary glands, liver, gallbladder and pancreas)

Regulation of the digestive system

Nervous control of the gastrointestinal tract: (autonomic nervous system)

Part of the nerve control is local and occurs as a result of local reflexes within the enteric plexus, and part is more general, largely mediated by the parasympathetic division of the ANS through the vagus nerve. Local neuronal control of the digestive tract is within the enteric nervous system (ENS). There are three main types of enteric neurons: (1) Enteric sensory neurons detect changes in the chemical composition of the digestive tract (2) Enteric motor neurons stimulate or inhibit smooth muscle contraction and glandular secretion in the digestive tract. system. (3) Enteric interneurons connect sensory and enteric motor neurons

Chemical regulation of the digestive system: (hormonal control)

The digestive tract produces a series of hormones, such as gastrin, secretin and others, which are secreted by the endocrine cells of the digestive system. These hormones help regulate many functions of the gastrointestinal tract (liver and pancreas) and other paracrine chemicals, such as histamine, are released locally within the digestive tract and affect the activity of nearby cells

Reflex mechanism

The regions of the gastrointestinal tract (especially the stomach and small intestine) use reflexes to stimulate or inhibit each other

The path of food in the digestive system

The digestive system consists of: mouth (oral cavity); pharynx; esophagus; stomach; small intestine; colon and blind; straight ahead; anal canal; and the liver, pancreas and salivary glands

The food we eat begins to turn into the mouth, where it is crushed by the teeth, compacted by the tongue and moistened with saliva. Amylase, a digestive enzyme contained in saliva, initiates the processing sugars. In less than a minute, the sting turned into a "bowl of food", that is, a soft, moist speck

Swallowing requires perfect coordination of the different muscles of the mouth and pharynx. The bolus is directed to the back of the oral cavity by the tongue and enters the pharynx. The tongue is raised against the soft palate, this obstructs the nasal cavity and prevents the bowl from flowing backwards. The food dish slides into the pharynx and pushes the epiglottis downwards, closing the entrance at the same time as the trachea. Under the combined action of the pharynx and tongue, the bolus descends into the esophagus

Once ingested, the bowl of food falls from the esophagus in seconds and reaches the stomach. It is mixed with gastric juices, whose enzymes begin to break down sugars and proteins. This phase, which lasts from 2 to 4 hours, transforms the plate of food into a chimo. Most of the digestion and absorption take place in the small intestine, where the chyme remains for 1-4 hours. Under the action of bile and pancreatic juices, the food is completely broken down and the nutrients are absorbed by the intestinal lining. In the large intestine, where part of the water and ions are absorbed, the waste is transformed into feces and then stored for at least 10 hours, waiting to be evacuated from the anus

Gastrointestinal Organs

Mouth and oral cavity

The oral cavity, or mouth, is the part of the digestive tract limited by the lips at the top, and it is lined with moist stratified squamous epithelium, which provides protection against abrasion

Teeth: (the first step of digestion)
Before being decomposed by the gastric and intestinal juices, the food undergoes a first transformation in the mouth. Teeth, 20 in children and 32 in adults, have played a crucial role since then

Let the bolus prepare before swallowing. Therefore, chewing is the first step in digestion

Salivary glands:
Around the oral cavity, there are numerous minor salivary glands scattered. 3 pairs of salivary glands called the parotid, submandibular and sublingual glands secrete most of the saliva into the oral cavity, using the salivary ducts. Saliva helps to moisten food during chewing, dissolves food in the formation of the bolus and helps to clean the teeth. Saliva is composed of 99.5% of water, the remaining 0.5% consists of enzyme amylase, bicarbonate ion (HCO3 -; maintains the pH of saliva at 6.5-7.5) and many electrolytes

Pharynx:
The adult pharynx is a common respiratory-digestive chamber, located (directly anterior to the vertebral column, posterior to: nasal cavity, mouth, continuing with the larynx and esophagus), the pharynx is composed of three parts: the nasopharynx, the oropharynx, and laryngopharynx. Normally, only the oropharynx and laryngopharynx transmit food. The oropharynx communicates with the nasopharynx superiorly, the larynx and the laryngopharynx inferiorly and the mouth anteriorly

Organ type
• A conical fibromuscular tube, without the anterior wall
• It is the crossroads between the gastrointestinal and respiratory tracts
• Its main function is to connect the nasal cavity to the larynx so that air can enter and exit the lungs
• Connect the oral cavity with the esophagus so that a food bolus can be ingested and passed to the stomach for further digestion

Esophagus:
Duct 25 cm long, it is that part of the digestive tract that extends between the pharynx and the stomach, passes through the esophageal break (opening) of the diaphragm and ends in the stomach, the esophagus pushes the food dish towards the stomach. thanks to an involuntary muscle contraction mechanism called peristalsis

Organ type
• Part of the digestive system
• Fibromuscular tubular hollow organ

The stomach:

                       (An acid pouch)

From the esophagus, the plate of food passes to the stomach, an elastic bag about 25 cm long which secretes extremely acidic juices. Prepared by the unceasing movements of the muscular layers of the stomach, the food gradually turns into a porridge, called chyme, which is expelled in small quantities into the duodenum

The lining of the stomach:
The internal lining of the stomach consists of an epithelium that invades to form many folds. The gastric glands found there release various substances (hydrochloric acid, enzymes, mucus, hormones ...) which enter the composition of the gastric juices. The mucosa rests on a vascularized submucosa, which covers three muscle layers. The different orientation of the fibers of these muscles ensures effective mixing of food

Stomach anatomy:
The opening from the throat to the stomach is the gastroesophageal or cardiac opening (located near the heart) and the region of the stomach around the cardiac opening is the cardiac region. The lower esophageal sphincter, also called the cardiac sphincter, includes the cardiac opening. Verify that, although it is a significant structure in the normal capacity of the stomach, it is a fair physiological constrictor and cannot be seen anatomically

A part of the stomach on one side of the heart region, the bottom (the base of a round-bottomed calfskin bottle), is actually better than the heart opening. The largest part of the stomach is the body, which swings to one side, thus forming a more prominent curvature and a lesser curvature. The close of the body to frame the (watchful) pyloric region, which joins the small digestive system. The opening between the stomach

In addition, the small digestive tract is the pyloric opening, which is surrounded by a moderately thick ring of smooth muscle called the pyloric sphincter

The gastric cycle:
Once in the stomach, the food dish is mixed and mixed with gastric juices. It becomes whitish broth: chyme. Regular contractions of the stomach push the chyme towards the closed pylorus. The repetitive opening of the pyloric sphincter passes small amounts of chyme in the duodenum

 Functions:
• Storage: Rugae allows the stomach to expand and retain food until it can be digested
• Digestion: the digestion of proteins begins following the action of hydrochloric acid and pepsin. The intrinsic factor prevents the breakdown of vitamin B12 by stomach acid
• Absorption: with the exception of some substances (e.g. water, alcohol, aspirin), poor absorption occurs in the stomach
• Mixing and propulsion: the mixing waves stir the ingested materials and stomach secretions in the chyme. Peristaltic waves move chyme into the small intestine
• Protection: mucus provides lubrication and protects digestion of the stomach wall. Stomach acid kills most microorganisms

Intestine:

                        (Pipes in a row)
After being kneaded in the stomach, chyme enters the intestine, a long sequence of tubes in which most of the digestion takes place. We distinguish the small intestine, which absorbs nutrients, and the large intestine, where chyme is transformed into feces. The contractions of the muscular intestine discharge waste through the anus

Small intestine:
Composed of duodenum, jejunum and ileum, the small intestine is a very long tube folded in on itself. It provides most of the digestion thanks to intestinal secretions secreted by its mucous membrane, pancreatic enzymes and bile. It is also in the small intestine where absorption occurs via epithelial cells. The numerous villi of the inner wall considerably increase the absorption surface

The large intestine:
The chyme of the ileum is poured into the blind, the first part of the large intestine. Then it enters the colon, where bacteria complete its degradation. As it advances, the water is absorbed by the lining of the colon, the chime solidifies and turns into feces. Colon movements push these feces into the rectum, triggering the reflex opening of the internal anal sphincters. External sphincters, whose contraction is voluntary, help to hold back defecation

Liver, Pancreas and Gallbladder:

                                         (Biochemical laboratories)
The digestive tract could not play its full role without the help of the auxiliary organs of the digestive system. The liver, pancreas and gallbladder develop many digestive substances, store them and then release them into the duodenum

Liver:
The liver, which weighs almost 1.5 kg, is the largest gland in the human body. Located on the right side of the abdomen, it consists of two asymmetrical lobes, separated by the ligament of the sickle. Truly a biochemical laboratory, the liver participates in more than 500 different chemical reactions thanks to the large amount of blood supplied by the hepatic artery from the heart and the hepatic portal vein from the hail intestine (1.5 liters of blood per minute). In particular, it produces bile, cholesterol and proteins, stores glucose, iron and vitamins and breaks down some toxic products in the blood, such as alcohol

The liver has the incredible ability to regenerate if one of its parts is amputated

The gallbladder:
The liver synthesizes almost a liter of bile every day. This greenish-yellow liquid is temporarily stored in the gallbladder. This 7-10 cm organ concentrates the bile and releases it into the duodenum during meals. The gills of the salts contained in the bile emulsify the fats (i.e. break them down into small drops), which facilitates their digestion

The pancreas:
Located behind the stomach, the pancreas is an elongated gland that secretes two types of substances. Acinar cells produce pancreatic juice, rich in enzymes (amylase, lipase), which is distributed through the pancreatic duct to the duodenum, where it participates in digestion. Far fewer islands of Langerhan produce hormones (insulin, glucagon) and belong to the endocrine system

Diseases of Digestive System 

• Gastroesophageal Reflux Disease (GERD)

• Gallstones

• Celiac Disease

• Crohn’s Disease

• Ulcerative Colitis

• Irritable Bowel Syndrome

• Hemorrhoids

• Diverticulitis

• Anal Fissure