Le système digestif expliqué

The digestive system аllоwѕ uѕ to break dоwn the food wе еаt tо оbtаin energy аnd nourishment. It is usually divided into thе gаѕtrоintеѕtinаl tract (also called thе GI tract оr digеѕtivе tract), the liver, pancreas, and gallbladder. The GI trасt iѕ a ѕеriеѕ of hоllоw оrgаnѕ jоinеd in a lоng, twisting tubе frоm thе mоuth to thе аnuѕ. Thе hоllоw organs that mаkе uр the GI trасt аrе the mоuth, esophagus, estomac, small intеѕtinе, large intеѕtinе, аnd аnuѕ.

Thеѕе оrgаnѕ соmbinе tо реrfоrm six tаѕkѕ: ingеѕtiоn, ѕесrеtiоn, рrорulѕiоn, digestion, аbѕоrрtiоn, аnd defecation.

  • Ingestion; manger des aliments
  • propulsion; moving the food from the mouth to the intestines for absorption or excretion
  • Digestion; décomposition chimique et mécanique des aliments en petits morceaux
  • Absorption; absorption des molécules solubles et 
  • Secretion; production of enzymes and other solutions like acid, bicarbonate, etc.
  • defecation; discharge of stool from the body

Ces fonctions vitales sont nécessaires au maintien d'une homéostasie saine (maintien d'un environnement interne constant) et au fonctionnement optimal du corps humain. 

Illustration of the digestive system. Servier Medical Art by Servier, CC BY 3.0.

Les organes et leurs fonctions

Le tractus gastro-intestinal (GI)

The mouth is the starting point of the GI tract. A significant amount of mechanical digestion (physical breakdown of food into smaller pieces) occurs in the mouth. The mouth also helps lubricate the food with the saliva helping it move along the pharynx and the esophagus. Speaking of which, the esophagus is a muscular tube that connects the mouth with the stomach and provides a passageway for the bolus (a semi-solid ball of food that has been chewed and mixed with the saliva). 

Teeth in adults and children are involved in the mechanical digestion of food. Servier Medical Art by Servier, CC BY 3.0.

Food reaching the stomach is stored and digested, both mechanically and chemically. Chemical digestion refers to a process by which the body breaks down complex insoluble food molecules e.g., starch into smaller soluble molecules i.e., glucose, amino acids, and fatty acids. The estomac est un sac musculaire puissant qui se contracte périodiquement, décomposant et mélangeant les aliments avec les sécrétions gastriques ; un mélange d'eau, d'acide chlorhydrique et de protéases (enzymes digérant les protéines). Il a une petite et une grande courbure avec un antre et un pylore. Le chyme, aliment semi-digéré mélangé à la sécrétion gastrique, est propulsé par le péristaltisme (mouvements ondulatoires) dans les intestins où le reste de la nourriture est digéré et absorbé. 

The peristaltic movement of pre-digested food (bolus) through the esophagus. Servier Medical Art by Servier, CC BY 3.0.

The small intestine starts from the pylorus of the stomach and is divided into three portions; duodenum, jejunum, and ileum. Most of the digestion occurs in the duodenum and initial jejunum. It is a 5-meter-long luminal structure with a specialized epithelium— the brush border.

Small intestine and villi. Servier Medical Art by Servier, CC BY 3.0.

This epithelium contains numerous villi and microvilli across its surface. Villi and microvilli are small finger-like projections that increase the surface area (area available for absorption) greatly. These microvilli also give the intestine a towel-like appearance. After most of the soluble nutrients i.e., amino acids, glucose, fructose, fatty acids glycerol are absorbed the food is propelled towards the anus in the large intestine.

Microscopic view of the intestinal villi. Servier Medical Art by Servier, CC BY 3.0.

The large intestine i.e., the colon starts from the ileocecal junction and extends to the rectum. Ascending, transverse, descending, and the sigmoid colon are all part of the large intestine. The primary function of the colon is to absorb water and electrolytes from the remaining undigested food. The colon also has a series of muscular band loops called tinea-coli which contract to produce bulk movements throughout the colon and help push the feces into the rectum.

Ascending, transverse, and descendant colon. Servier Medical Art by Servier, CC BY 3.0.

The Rectum connects the sigmoid colon to the anus. The feces are temporarily stored in the rectum until it is expelled out of the body through the anus by a process called defecation.

Le foie et la vésicule biliaire

The liver plays a vital function in maintaining a healthy body. In most people, it is located in the upper right abdominal region, below the right dome of the diaphragm and the right lung.

Macroscopic view of the liver and gallbladder from the back (left) and the front (right). Servier Medical Art by Servier, CC BY 3.0.

Apart from its numerous other functions like detoxification of exogenous toxic substances, storing nutrients, and synthesis of proteins and triglycerides (fats), the liver also produces bile. Bile is temporarily stored in the gallbladder (attached to the liver) and secreted into the small intestine through the voies biliaires. La bile émulsionne les grosses molécules de graisse en gouttelettes de graisse plus petites qui peuvent être efficacement digérées par les lipases (enzymes digérant les graisses). 

Microscopic view of the liver and gallbladder with the bile ducts and bile canaliculi that collect the bile produced by the hepatocytes. Servier Medical Art by Servier, CC BY 3.0.

Le pancréas exocrine

Le pancréas est un organe en forme de feuille et, en fonction de sa fonction, il est divisé en deux parties : le pancréas exocrine et le pancréas endocrine (produisant des hormones). Le pancréas exocrine est responsable de la production de toutes les enzymes digestives primaires nécessaires à la décomposition des aliments. La sécrétion pancréatique est un mélange de :

  1. Carbohydrases 
  2. Protéases 
  3. Lipases 
  4. Bicarbonate, et 
  5. L'eau
Macroscopic and microscopic view of the pancreas. Servier Medical Art by Servier, CC BY 3.0.

Les glandes salivaires

Saliva is a watery secretion, produced by glandular structures in the buccal cavity, mixed with enzymes e.g., carbohydrases (carbohydrate digesting enzymes) and lipases. It helps to soften the food bolus and partially digests the food, especially starch (carbohydrates) present in the food. There are three bilateral (present on both sides) sets of salivary glands present in our body. The parotid gland, submandibular gland, and sublingual glands. The parotid glands, present below the ears, are the major salivary glands. As their names suggest, the submandibular glands are located under the mandibule (jaw bone) and the sublingual glands below the tongue. 

Position of the parotid, sublingual, and submaxillary glands in the head. Servier Medical Art by Servier, CC BY 3.0.

Nerfs et vascularisation

L'approvisionnement neurovasculaire fait référence à l'apport sanguin et à l'apport nerveux, dont les connexions sont essentielles pour maintenir un organe en vie. Le digestif est alimenté par un ensemble de nerfs et de vaisseaux différents. 

Approvisionnement nerveux

The buccal Cavity and the structures in it are innervated by cranial nerves (CN), nerves originating directly from the brain or brain stem. Most of the innervation is by CN V (5th), the trigeminal nerve, along with CN IX (9th) and CN X (10th). The 10th CN, the Vagus nerve, supplies most of the GI tract. Stimulation through CN X enhances peristalsis and secretion in the entire GI tract. Another key feature to be noted is that the innervation of most of the digestive system is from the autonomic nervous system, i.e., it is not under voluntary control. The liver and pancreas are innervated by the vagal and splanchnic (sympathetic) nerves. 

 La partie inférieure du canal anal, sous la ligne pectinée, est dérivée des nerfs somatiques (volontaires), le nerf pudendal. Cela nous donne le contrôle sur la défécation.  

Alimentation vasculaire

The mouth’s vascular supply involves different branches of the External Carotid Artery (ECA) e.g., the lingual artery to the tongue. The venous drainage of the mouth is through a series of small veins which eventually drain into the internal jugular vein. The esophagus, stomach, and the proximal (upper) part of the duodenum are supplied by branches of the Celiac (branch of abdominal aorta) artery and drained by adjacent veins back into the celiac vein. The distal part of the duodenum, jejunum, ileum and two-thirds of the transverse colon are all supplied by the Superior Mesenteric Artery (branch of abdominal aorta). The last one-third of the transverse colon, the descending and sigmoid colon, and the anal canal up to the pectinate line are supplied by the Inferior Mesenteric Artery (branch of the abdominal aorta). Below the pectinate line, the anal canal is supplied by the Pudendal Artery. The venous drainage of these structures is through the veins of the corresponding arteries. Most of the pancreas is supplied by the branches of the Splenic artery (branch of Celiac Artery) and drained by the splenic vein. 

Le foie revêt une importance particulière car il est relié au tractus gastro-intestinal par la veine porte hépatique qui alimente le foie en sang riche en nutriments. Le parenchyme (tissu) hépatique est alimenté par les artères hépatiques, qui proviennent de l'artère cœliaque, et est drainé par les veines hépatiques : affluents de l'inférieure veine cave

En savoir plus sur les relations spatiales 3D des organes digestifs avec ce brillant modèle anatomique grandeur nature.

Les références
  1. Anatomie, Tête et cou, Lèvres, Meghan A. Piccinin ; Patrick M. Zito.
    https://www.ncbi.nlm.nih.gov/books/NBK507900/
  2. INNERVATION DU TRACTUS GASTRO-INTESTINAL : MODÈLES DE VIEILLISSEMENT ; Robert J. Phillips et Terry L. Powley
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2045700/
  3. Drake, Richard L.; Vogl, Wayne; Mitchell, Adam WM (2005). L'anatomie de Gray pour les étudiants. Philadelphie, Pennsylvanie : Elsevier. p. 989–995. 
  4. Anatomie clinique de Snell par régions 10e Édition; Lawrence E. Wineski. pages 279-500, pages 609-700.
  5. Anatomie à orientation clinique par Anne MR Agur, Arthur F Dalley et Keith L. Moore. Tête et Cou, Abdomen, Bassin, Périnium.
  6. Apprends-moi l'anatomie ; Abdomen et Bassin
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173558/#:~:text=The%20principal%20functions%20of%20the,or%20incapable%20of%20being%20digested.
  8. Votre système digestif et son fonctionnement ; https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
  9. Quatre fonctions principales du système digestif ; http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm

Le contenu partagé sur le site Web Health Literacy Hub est fourni à titre informatif uniquement et n'est pas destiné à remplacer les conseils, diagnostics ou traitements proposés par des professionnels de la santé qualifiés dans votre État ou votre pays. Les lecteurs sont encouragés à confirmer les informations fournies par d'autres sources et à demander l'avis d'un médecin qualifié pour toute question qu'ils pourraient avoir concernant leur santé. Le Health Literacy Hub n'est pas responsable des conséquences directes ou indirectes découlant de l'application du matériel fourni.

fr_FRFrench