Sistem Pencernaan Dijelaskan

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, perut, small intеѕtinе, large intеѕtinе, аnd аnuѕ.

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

  • Proses menelan; memakan makanan
  • propulsion; moving the food from the mouth to the intestines for absorption or excretion
  • Pencernaan; penguraian makanan secara kimiawi dan mekanis menjadi potongan-potongan yang lebih kecil
  • Penyerapan; penyerapan molekul terlarut dan 
  • Secretion; production of enzymes and other solutions like acid, bicarbonate, etc.
  • defecation; discharge of stool from the body

Fungsi-fungsi vital ini diperlukan untuk menjaga homeostasis yang sehat (pemeliharaan lingkungan internal yang konstan) dan untuk fungsi optimal tubuh manusia. 

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

Organ dan fungsinya

Saluran Gastrointestinal (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.

Makanan yang mencapai lambung disimpan dan dicerna, baik secara mekanis maupun kimiawi. Pencernaan kimiawi mengacu pada proses di mana tubuh memecah molekul makanan kompleks yang tidak larut seperti pati menjadi molekul larut yang lebih kecil yaitu glukosa, asam amino, dan asam lemak. Itu perut adalah kantong berotot kuat yang berkontraksi secara berkala, memecah dan mencampur makanan dengan sekresi lambung; campuran air, asam klorida, dan protease (enzim pencerna protein). Ini memiliki kelengkungan yang lebih kecil dan lebih besar bersama dengan antrum dan pilorus. Kimus, makanan setengah cerna yang bercampur dengan sekresi lambung, didorong oleh peristaltik (gerakan seperti gelombang) ke dalam usus di mana sisa makanan akan dicerna dan diserap. 

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.

Hati dan Kandung Empedu

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 saluran empedu. Empedu mengemulsi molekul lemak besar menjadi tetesan lemak yang lebih kecil yang dapat dicerna secara efektif oleh lipase (enzim pencerna lemak). 

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.

Pankreas Eksokrin

Pankreas adalah organ berbentuk daun dan berdasarkan fungsinya dibagi menjadi dua bagian: pankreas eksokrin dan endokrin (penghasil hormon). Pankreas eksokrin bertanggung jawab untuk memproduksi semua enzim pencernaan utama yang diperlukan untuk pemecahan makanan. Sekresi pankreas adalah campuran dari:

  1. Karbohidrase 
  2. protease 
  3. Lipase 
  4. bikarbonat, dan 
  5. Air
Macroscopic and microscopic view of the pancreas. Servier Medical Art by Servier, CC BY 3.0.

Kelenjar ludah

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 rahang bawah (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.

Saraf dan Pasokan Vaskular

Pasokan neurovaskular mengacu pada suplai darah dan suplai saraf, koneksi yang sangat penting untuk menjaga organ tetap hidup. Pencernaan disuplai oleh satu set saraf dan pembuluh darah yang berbeda. 

Pasokan saraf

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. 

 Bagian bawah kanalis analis, di bawah garis pectinate, berasal dari saraf somatik (volunter), saraf pudendal. Ini memberi kita kendali atas buang air besar.  

Pasokan Vaskular

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. 

Hati memiliki kepentingan khusus karena terhubung ke saluran GI oleh vena Portal Hepatik yang memasok darah yang kaya nutrisi ke hati. Parenkim hati (jaringan) disuplai oleh arteri hepatika, yang berasal dari arteri Celiac, dan dialirkan oleh vena hepatik: cabang-cabang inferior vena cava

Pelajari lebih lanjut tentang hubungan spasial 3D organ pencernaan dengan brilian ini model anatomi seukuran manusia.

Referensi
  1. Anatomi, Kepala dan Leher, Bibir, Meghan A. Piccinin; Patrick M.Zito.
    https://www.ncbi.nlm.nih.gov/books/NBK507900/
  2. INNERVASI SALURAN GASTROINTESTINAL: POLA PENUAAN; Robert J. Phillips dan Terry L. Powley
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2045700/
  3. Drake, Richard L.; Vogl, Wayne; Mitchell, Adam WM (2005). Anatomi Gray untuk siswa. Philadelphia, Pennsylvania: Elsevier. hal. 989–995. 
  4. Anatomi Klinis Snell Berdasarkan Wilayah 10th Edisi; Lawrence E. Wineski. hal.279-500, hal.609-700.
  5. Anatomi Berorientasi Klinis oleh Anne MR Agur, Arthur F Dalley, dan Keith L. Moore. Kepala dan Leher, Perut, Panggul, Perinium.
  6. Ajari Saya Anatomi; Perut dan Panggul
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173558/#:~:text=The%20principal%20functions%20of%20the,or%20incapable%20of%20being%20digested.
  8. Sistem Pencernaan Anda dan Cara Kerjanya; https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
  9. Empat Fungsi Utama Sistem Pencernaan; http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm

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