Verdauungssystem erklärt

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, Magen, small intеѕtinе, large intеѕtinе, аnd аnuѕ.

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

  • Einnahme; Essen essen
  • propulsion; moving the food from the mouth to the intestines for absorption or excretion
  • Verdauung; Chemischer und mechanischer Abbau von Lebensmitteln in kleinere Stücke
  • Absorption; Absorption von löslichen Molekülen und 
  • Secretion; production of enzymes and other solutions like acid, bicarbonate, etc.
  • defecation; discharge of stool from the body

Diese lebenswichtigen Funktionen sind notwendig, um eine gesunde Homöostase (Aufrechterhaltung einer konstanten inneren Umgebung) und das optimale Funktionieren des menschlichen Körpers aufrechtzuerhalten. 

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

Organe und ihre Funktionen

Der Gastrointestinale (GI) Trakt

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 Magen ist ein starker Muskelsack, der sich periodisch zusammenzieht, die Nahrung zersetzt und mit den Magensekreten vermischt; eine Mischung aus Wasser, Salzsäure und Proteasen (eiweißverdauende Enzyme). Es hat eine kleinere und eine größere Krümmung zusammen mit einem Antrum und einem Pylorus. Der Speisebrei, halbverdaute Nahrung gemischt mit Magensekret, wird durch Peristaltik (wellenartige Bewegungen) in den Darm befördert, wo der Rest der Nahrung verdaut und absorbiert wird. 

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.

Leber und Gallenblase

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 Gallengang. Galle emulgiert große Fettmoleküle in kleinere Fetttröpfchen, die von den Lipasen (fettverdauenden Enzymen) effektiv verdaut werden können. 

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.

Die exokrine Bauchspeicheldrüse

Die Bauchspeicheldrüse ist ein blattförmiges Organ und aufgrund ihrer Funktion in zwei Teile gegliedert: die exokrine und die endokrine (hormonproduzierende) Bauchspeicheldrüse. Die exokrine Bauchspeicheldrüse ist für die Produktion aller primären Verdauungsenzyme verantwortlich, die für den Abbau von Nahrung erforderlich sind. Das Pankreassekret ist eine Mischung aus:

  1. Kohlenhydrate 
  2. Proteasen 
  3. Lipasen 
  4. Bikarbonat und 
  5. Wasser
Macroscopic and microscopic view of the pancreas. Servier Medical Art by Servier, CC BY 3.0.

Die Speicheldrüsen

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 Unterkiefer (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.

Nerven und Gefäßversorgung

Die neurovaskuläre Versorgung bezieht sich auf die Blutversorgung und die Nervenversorgung, deren Verbindungen für die Aufrechterhaltung eines Organs lebenswichtig sind. Der Verdauungstrakt wird von einer Reihe verschiedener Nerven und Gefäße versorgt. 

Nervenversorgung

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. 

 Der untere Teil des Analkanals unterhalb der Kammlinie wird von somatischen (willkürlichen) Nerven, dem Pudendusnerv, abgeleitet. Dies gibt uns die Kontrolle über den Stuhlgang.  

Gefäßversorgung

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. 

Der Leber kommt eine besondere Bedeutung zu, da sie über die Pfortader, die die Leber mit nährstoffreichem Blut versorgt, mit dem Magen-Darm-Trakt verbunden ist. Das Leberparenchym (Gewebe) wird von den Leberarterien, die aus der Zöliakie stammen, versorgt und von den Lebervenen, Nebenflüssen der unteren, entwässert Hohlvene

Erfahren Sie mehr über die räumlichen Beziehungen von Verdauungsorganen in 3D mit diesem brillanten lebensgroßes anatomisches Modell.

Verweise
  1. Anatomie, Kopf und Hals, Lippen, Meghan A. Piccinin; Patrick M. Zito.
    https://www.ncbi.nlm.nih.gov/books/NBK507900/
  2. INNERVATION DES GASTROINTESTINAL TRACT: MUSTER DES ALTERNS; Robert J. Phillips und Terry L. Powley
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2045700/
  3. Drake, Richard L.; Vogl, Wayne; Mitchell, Adam WM (2005). Greys Anatomie für Studenten. Philadelphia, Pennsylvanien: Elsevier. S. 989–995. 
  4. Snells klinische Anatomie nach Regionen 10th Auflage; Lawrence E. Wineski. S. 279-500, S. 609-700.
  5. Klinisch orientierte Anatomie von Anne MR Agur, Arthur F Dalley und Keith L. Moore. Kopf und Hals, Bauch, Becken, Perinium.
  6. Lehre mich Anatomie; Bauch und Becken
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173558/#:~:text=The%20principal%20functions%20of%20the,or%20incapable%20of%20being%20digested.
  8. Ihr Verdauungssystem und wie es funktioniert; https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
  9. Vier Hauptfunktionen des Verdauungssystems; http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm

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