fisiologi saluran pencernaan

1. FAAL PENCERNAAN
(GASTROINTESTINAL)
Gastrointestinal Physiology

2. Berbagai tantangan fungsi saluran GI
The many challenges of the gastrointestinal tract
• FUNGSI utama saluran GI adalah mencerna (digesti)
dan menyerap (absorpsi) zat gizi.
• Secara teknis saluran GI berada di luar tubuh dan
mengandung banyak populasi mikroba.
• Bagaimana mencegah mikroba itu tidak menginfeksi
tubuh? (>2/3 sel imun tubuh ada di saluran GI).
• Bagaimana saluran GI mengatur motilitas dan fungsi
digesti dan absorpsinya? (banyak pasokan saraf – “otak
mini”, hormon dan zat lain)
• The major function of the GI tract is to digest and absorb nutrients.
• The GI tract is technically outside the body and contains a large population of microorganisms.
• How does the GI tract defend against the potential infection of the body by these microorganism? (>2/3 of the
immune cells in the body are in the GI tract)
• How does the GI tract coordinate it’s motility and digestive and absorptive functions? (The GI tract has a very
large nerve supply – “the little brain” - and numerous hormones and signaling peptides.

3. Rongga
mulut/ Oral cavity
Lambung/
Stomach
Usus kecil/
Small intestine
Kolon/
Colon
Motitlias
Motility
Menelan,
mengunyah
Swallowing, chewing
Peristalsis,
mencampur,
propulsi
Peristalsis, mixing,
Propulsion
Segmentasi,
mencampur,
propulsi Segmentation,
mixing, propulsion,
Mencampur
segmental,
gerakan massa
Segmental mixing, mass
movement
Sekresi
Secretion
Amylase,
lipase, peptides
HCl,
pepsinogen,
HCO3
Enzim pankreas,
empedu, enzim
epitel usus. Pancreatic
enzymes, bile, brush border
enzymes
Lendir/ Mucus
Digesti Digestion
Karbohidrat,
lemak (minimal)
Carbohydrates fats (minimal)
Protein,
lemak Proteins, fats
Karbohidrat,
protein, asam
nukleat Carbohydrates,
fats, proteins nucleic acids
None
bacteria only
Absorpsi
Absorption
None Alcohol Monosakarida,
asam amino, lipid,
vitamin, elektrolit
Monosaccharides,amino acids,
lipids, vitamins, electrolytes
Elektrolit, asam
lemak pendek,
vitamin Electrolytes,
short chain fatty acids, vitamins
Rangkuman fungsi saluran GI
Summary of the functions of the GI tract

4. Kendali fungsi GI: neural dan humoral
Control of GI function – neural and humoral

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Aktivitas otot polos saluran cerna disebabkan oleh irama naik-turun
aktivitas pompa Na-K sel otot polos. Jika terjadi depolarisasi, timbul
potensial aksi berantai, tonus usus naik.
Smooth muscle slow wave activity caused by the rhythmic increasing and decreasing of the smooth muscle electrogenic
Na,K-pump. When the waves depolarize the membrane to threshold, trains of action potentials occur, increasing tone.
Kontraksi ritmis saluran cerna paling cepat di duodenum, paling lambat di
kolon. Kontraksi ini dikendalikan oleh aktivitas bergelombang lambat di
otot polosnya. Sel Cajal intestinal bertindak sebagai alat pacu gelombang
lambat sel otot polos viseral itu.
The GI tract has rhythmic waves of contractions, fastest in the duodenum, slowest in the colon. These contractions are controlled by
slow wave activity in the muscles. Interstitial cells of Cajal act as pacemakers for the slow wave activity of the visceral smooth muscle
cells.
Kendali saraf terhadap motilitas/ Neural control of motility

6. Sistem saraf enterik memiliki refleks lokal (refleks pendek), tapi dipengaruhi dan dikendalikan oleh
otak dan sumsum tulang belakang (refleks panjang). Keduanya menuju ke pleksus saraf di
dinding usus (mienterik dan submukosa), mengatur motilitas dan sekresi usus.
Refleks panjang mempersiapkan saluran GI terhadap apa yang akan timbul, sedangkan refleks pendek
mempersiapkan saluran GI terhadap apa yang sudah timbul.
Long reflexes prepare the GI tract for what is coming, e.g. gastrocholic reflex –emptying the colon when the stomach is full. Other similar examples are the duodenocolic, gastroileal and enterogastric
reflexes where distension or chemical signals upstream increase inhibit peristalsis and secretion upstream. Short reflexes allow the GI tract to respond to what has arrived, e.g. distension or chemical
peristalsis and secretion downstream, or where distension or chemical signals downstream signals in one place initiates a reflex that increases secretion or motility at that location.
The enteric nervous system can operate local reflexes (short reflexes), but it is influenced and controlled by the brain and spinal cord (long reflexes). The final
pathway for neural control is found in the gut wall, primarily in the myenteric plexus (between longitudinal and circular smooth muscle) and the submucosal
plexus (between circular smooth muscle and the mucosa). Local and long reflexes acting through these plexi control motility and secretion.The tone of
gastrointestinal smooth muscles is constantly being modified by inhibitory (VIP and NO) and excitatory (ACh and substance P) interneurons.

8. Selain refleks mengontrol motilitas, digesti,
absorpsi, dan sekresi, ada berbagai hormon
dan peptida turut dalam regulasi refleks
secara kimiawi.
In addition to the long and short neural reflexes controlling motility, digestion, absorption and
secretion, there are several true hormones and many other peptides making up chemical
reflexes.
Motilitas saluran cerna:
Mengatur isi lumen untuk proses digesti dan absorpsi optimal.
Peristalsis adalah gerakan mendorong isi lumen menjauhi mulut (aboral).
Otot sirkular di depan relaksasi, di belakang kontraksi.
Segmentasi adalah gerakan mencampur isi lumen dan enzim pencernaan di
satu lokasi.
Katup atau sfinkter ileosekal terletak di antara usus kecil (ileum) dan usus
besar (sekum). Sfinkter itu akan relaksasi (terbuka) jika menerima sinyal
distensi, pasta makanan (chyme), atau sinyal kimiawi di distal ileum. Jika
sekum sudah penuh (terdistensi), sfinkter itu menutup dan peristalsis ileum
berkurang, membatasi kima yang masuk ke usus besar.
The ileocecal valve (sphincter) is characteristic of a gating mechanism in the GI tract controlling what gets into the next segment. Distension, liquid chyme or
chemical signals in the distal ileum relax the ileocecal sphincter, allowing the ileal content into the large intestine. If the cecum is already full (distended) the
sphincter is kept closed and ileal peristlasis is decreased, limiting the amount of chyme entering the already-full colon.
Peristalsis is the aboral (away from the mouth) movement of chyme. Circular muscle relaxation in front, contraction behind.
Segmentation is the mixing of chyme and digestive enzymes in one place. In general, motility is coordinated to move food (chyme) through
the GI tract at a rate that allows for optimal digestion and absorption.

9. Hormon utama saluran cerna
Major hormones of the GI tract
• Gastrin: memacu sekresi HCl lambung.
• Kolesistokinin: memacu sekresi enzim pankreas dan pengosongan
kandung empedu, menghambat pengosongan lambung.
• Sekretin: memacu sekresi bikarbonat oleh pankreas dan hati,
menghambat pengosongan lambung.
• Motilin: memacu motilitas saluran GI superior.
• GIP: menghambat sekresi HCl dan motilitas gaster pada
konsentrasi tinggi, memacu sekresi insulin.
• GLP-1: memacu sekresi insulin, menghambat sekresi glukagon oleh
pankreas, memperlambat pengosongan lambung.
• Gastrin - stimulates gastric HCl secretion and mucosal growth.
• Cholecyctokinin (CCK) - stimulates pancreatic enzyme secretion and gallbladder emptying. Inhibits gastric
emptying.
• Secretin - stimulates HCO3 secretion by the pancreas and liver. Inhibits gastric emptying.
• Gastric inhibitory peptide (GIP) - inhibits HCl secretion and gastric motility at high concentrations and
stimulates insulin secretion.
• Motilin - Stimulates motility in the upper GI tract.
• Glucagon-like peptide 1 (GLP-1) - stimulates insulin release, inhibits glucagon release by pancreas, slows
gastric emptying.

10. Air liur/ Saliva
• Terutama diproduksi 3 kelenjar liur: kel. parotid (20%),
submandibular (70%), dan sublingual (5%).
• Bersifat hipotonik, mengandung amilase, faktor pertumbuhan,
antibodi sekretorik, peptida antimikroba.
• Berfungsi melindungi mulut dan gigi, melumasi pita suara,
membantu menelan bolus makanan.
• Parasimpatis memacu produksi banyak saliva cair; simpatis
menghasilkan produksi saliva sedikit dan kental.
• Kendali utama oleh N. fasial (VII), glosofaringeal (IX), parasimpatis.
• Mainly produced by three pairs of glands.
Parotid – watery, 20%.
Submandibular (submaxillary) – moderately viscous, 70%.
Sublingual – viscous, 5%.
• Hypotonic, salivary amylase, some growth factors, secretory antibodies, antimicrobial peptides.
• Protects the mouth and teeth, lubricates the vocal cords.
• Lubricates bolus of food for swallowing.
• Parasympathetic stimulation results in copious salivary
secretion. Sympathetic secretion results in a small volume of a viscous saliva.
• The facial and glossopharyngeal cranial, parasympathetic nerves
provide the major neural control for the salivary glands.
• All exocrine glands (e.g. salivary glands, exocrine pancreas) have a primary secretion produced by acinar cells,
which is modified by secretion and absorption in the ducts.

11. ADA dua fase utama menelan: fase orofaring dan fase esofagal. Hanya
sebagian dari fase orofaring yang bersifat volunter.
Saat peristalsis menuruni esofagus, sfinkter inferior esofagus relaksasi
sehingga bolus makanan dapat memasuki gaster.
Akalasia esofagus: penyakit sfinkter esofagus inferior yang tak dapat
relaksasi saat menelan. Problemnya terletak pada saraf pleksus mienterik.
There are two major phases of swallowing, the oropharyngeal phase and the esophageal Phase. Only part of the
oropharyngeal phase is voluntary.
As peristalsis moves down the esophagus the lower esophageal sphincter (LES) relaxes. It is tonically contracted to prevent
gastroesophagealreflux.
With swallowing, the cardiac portion of the stomach also relaxes so as to accept the bolus of food.
There are also secondary waves of peristalsis if food is left in the esophagus.
The pharynx acts as an upper esophageal sphincter.
ACHALASIA – LES fails to relax on swallowing. Myenteric plexus problem, insufficient NO and VIP-ergic activity.
MENELAN/ SWALLOWING

12. Profil utama lambung
Main features of the stomach
• Penting untuk pencernaan protein (pepsin dan pH rendah).
• Isinya asam (pH rendah) untuk melindungi saluran GI dari
pertumbuhan bakteri.
• Menghasilkan faktor intrinsik untuk absorpsi vit. B12.
• Tidak berfungsi absorpsi (kecuali alkohol).
• Important for digestion of proteins (pepsin and low pH).
• Importance of the low pH in protecting the GI tract against bacterial overgrowth.
• Produces intrinsic factor necessary for vitamin B12 absorption.
• Some storage function (limited).
• Not much absorption (except alcohol).

13. Sel gaster dan sekretnya
Cells of the stomach and what they secrete.
• Sel parietal di kelenjar pilorus memproduksi asam
klorida (HCl) dan faktor intrinsik.
• Sel peptik (chief cell) gaster memproduksi pepsinogen.
• Sel G menghasilkan gastrin.
• Sel S menghasilkan somatostatin.
• Sel ECL menghasilkan histamin.
• Parietal (oxyntic) cells in pyloric gland of stomach – secrete HCl and intrinsic factor.
• Chief cells – secrete pepsinogen.
• G cells, mostly in the antrum, secrete gastrin
• S cells –secrete somatostatin.
• ECL (enterochromaffin like) cells secrete histamine.

14. Fase sekresi gastrik
Phases of gastric secretion
• Sefalik: dipicu pandangan dan penciuman, refleks panjang via N.
vagus. Timbul sekresi gastrin, histamin, HCl, pepsinogen.
• Gastrik: dipicu bolus makanan dalam gaster, melibatkan refleks
pendek dan hormon, khususnya gastrin (memacu), somatostatin
(menghambat). Asam menghambat sekresi HCl tapi memacu
sekresi pepsinogen (menjadi pepsin yang aktif dalam pH asam).
• Intestinal: dipicu isi gastrik yang memasuki duodenum, dimediasi
gastrin duodenal dan mekanisme persarafan.
• Cephalic – stimulated by sight and smell – involves long reflexes in vagus nerve: stimulates gastrin release which
stimulates the ECL cells to release histamine and stimulate parietal cell HC secretion. Vagal stimulation also
stimulates pepsinogen secretion.
• Gastric – stimulated by chyme in the stomach – involves short reflexes and hormones, notably gastrin
(stimulates), somatostatin (paracrine - inhibits). Acid in the stomach inhibits HCl secretion (somatostatin
mediated) but stimulates pepsinogen secretion. The pepsinogen is activated to pepsin by the acidic environment.
Controlled by long vaso-vagal reflexes, local enteric reflexes and gastrin-histamine mechanism.
• Intestinal – stimulated by gastric content entering the duodenum. Probably mediated by duodenal gastrin and
neural mechanisms.

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In the parietal cells H+
secretion by the gastric parietal cells involves an
H,K-ATPase that secretes H+
into the canaliculi. H+
is exchanged for
K+
which then leaks back out into the canaliculi lumen. Cl-
follows the H+
via an active transport mechanism. Carbonic anhydrase is necessary to
hydrate CO2 and produce the H+
. The HCO3
-
that is left behind diffuses
out of the cell via the basolateral membrane into the blood.
Three major classes of drugs used in controlling gastric acid.
• Antacids. Oldest. Work to neutralize gastric acid. May be a rebound effect.
• Histamine receptor blockers. Histamine receptors in the stomach are of the
H2 subtype. H2 receptor blockers are currently very popular.
• H,K-ATPase inhibitors. Very effective. Particularly for short term use to allow
ulcer repair, etc.

16. Bagaimana gaster melindungi dirinya tidak tercerna? Mukosa gaster
memiliki barier terdiri atas lapisan mukus dan sekresi bikarbonat
(HCO3), membentuk barier pH netral yang mantap.
Duodenum (usus 12 jari) tidak memiliki proteksi demikian terhadap
asam. Tapi getah pankreas dan cairan empedu yang mengalir ke
duodenum (melalui sfinkter Oddi) mengandung bikarbonat yang dapat
melawan efek asam.
How does the stomach avoid digesting itself? The gastric mucosal barrier relies on the mucus blanket and HCO3
secretion. Mucus neck cells secrete mucus to form an unstirred layer over the gastric mucosa. They also secrete
HCO3
-
into the unstirred layer forming a standing pH gradient, neutral near the mucosa to acidic in the gastric lumen.
While the stomach has protection against gastric acid and pepsin, the duodenum does not. That is why
it is very important that the stomach does not empty too much acidic content too fast into the small
intestine.
The major protection for the small intestine against gastric acid is the secretion of HCO3 in the
pancreatic juice and, to a lesser extent, bile.
In humans both pancreatic juice and bile enter the duodenum through the
same sphincter (the sphincter of Oddi).

17. When acidic chyme leaves the stomach there is a release of a high [HCO3-], enzyme and bile - rich fluid into the
duodenum through the common bile duct.
Pengosongan lambung dengan makanan tinggi karbohidrat terjadi dalam
sekitar 4 jam. Lebih lambat jika makanan tinggi lemak.
Refleks enterogastrik: makanan yang masuk duodenum memberi sinyal
umpan balik menghambat pengosongan gastrik, terutama kima yang
asam dan kaya asam amino.
Gastric emptying depends on the content of the stomach. A high fat meal leaves the stomach very slowly, a high protein
meal leaves more quickly and a high carbohydrate meal leaves in about 4 hours. High osmotic pressure chyme entering
the duodenum slows gastric emptying – due to duodenal osmoreceptors?
Enterogastric reflex – feedback from food entering the duodenum inhibiting gastric emptying, particularly for low pH and amino
acid – rich chyme.
May have both a neural and humoral component to this reflex. Duodenal distension delays gastric emptying – neural.
Several duodenal hormones slow gastric secretion and motility –secretin, CCK, GIP, GLP-1.

18. Sekresi pankreas
Pancreatic secretion
Pankreas memproduksi berbagai enzim pencerna protein,
lemak, karbohidrat, dalam bentuk nonaktif. Saluran keluar dari
pankreas (duktus pankreatikus) menghasilkan sekret kaya akan
bikarbonat (HCO3
-
). Semakin cepat sekresinya, kadar
bikarbonat makin tinggi.
In the pancreas the acinar cells produce several enzymes, inactive forms of several proteolytic enzymes and phospholipase A2,
lipase, colipase, amylase. The inactive forms of these enzymes are activated by trypsin, so if they are activated in the pancreas
the pancreas will be severely damaged. Protected by anti-trypsin.
The pancreatic ducts produce a HCO3
-
-rich secretion. The faster the rate
of secretion, the greater the [HCO3
-
].

19. Getah pankreas sangat penting mencerna protein,
lemak, karbohidrat
Pancreatic juice is very important for the digestion of carbohydrates, fats and proteins
Protease Amylolytic
enzyme
Lipase Nuclease Others
Trypsinogen Amylase Lipase DNAase Pro-
colipase
Chymo-
trypsinogen
Nonspecific
esterase
RNAase Trypsin
Inhibitors
Pro-
elastase
Phospho-
lipase A2
Procarboxy-
peptidase A
Procarboxy-
peptidase B

20. Enzim-enzim proteolitik pankreas masuk ke
duodenum, tripsinogen diaktifkan oleh enteropeptidase
(atau enterokinase) di epitel duodenal menjadi tripsin.
Tripsin memulai serangkaian reaksi untuk
mengaktifkan semua pro-enzim lain.
When the inactive proteolytic enzymes enter the duodenum trypsinogen is activated by an enteropeptidase in
the duodenal epithelium. The resulting trypsin sets off a chain reaction, activating all the other pro-enzymes.
The enteropeptidase is also called enterokinase.

21. A general model for a cell that secretes HCO3
-
is one that has a
HCO3
-
- Cl-
exchange pump (carrier) on the apical membrane. The Cl-
that enters the cell when the HCO3
-
leaves has to go back out of the cell.
This happens through a CFTR (cystic fibrosis transmembrane conductance
regulator) channel. This is a major channel in the gut for Cl-
secretion.
The HCO3
-
in the cell is produced by the hydration of CO2 catalyzed by
carbonic anhydrase. The remaining H+
leaves the cell at the basolateral
border in exchange for Na+
entering. The Cl-
for the CFTR channel enters
through the basolateral membrane Na,K,2Cl symporter.
Bicarbonate secretion

22. Apa yang terjadi di duodenum?
What happens in the duodenum when the stomach empties?
• Beberapa cm awal duodenum terdapat kelenjar Brunner yang
memproduksi mukus dan bikarbonat, melindungi duodenum dari
asam lambung. Produksinya dipicu saraf vagus dan sekretin.
• In the fist few centimeters of the duodenum there are glands – Brunner glands – that secrete heavy mucus and a HCO3
-
-
rich fluid. Important in protecting the duodenum from gastric contents. Secretion stimulated by vagus and secretin.
• Bolus asam dari lambung merangsang mukosa duodenal
mensekresi hormon sekretin. Sekretin memicu sekresi pankreas.
• Lemak dan asam amino di duodenum memicu sekresi kolesistokinin
(memicu sekresi pankreas, relaksasi sfinkter Oddi, kontraksi
kandung empedu).
• Stimulasi vagal memperkuat sekresi pankreas dan kontraksi
kandung empedu.
• The acidic chyme stimulates secretin release from the duodenal mucosa, Secretin travels in bloodstream to stimulate
pancreatic and bile duct HCO3
-
release (pancreas more important).
• Fats and amino acids in the duodenum stimulate cholecyctokinin release from the duodenal mucosa, travels in bloodstream
and stimulates pancreatic enzyme secretion, relaxation of sphincter of Oddi and contraction of gallbladder.
• Vagal stimulation backs up the pancreatic enzyme secretion and gallbladder contraction

23. © 2005 Elsevier
* Dinding dalam usus kecil terdiri atas jonjot-jonjot (villi). Morfologi villi dan
mikrovilli (brush-border) memaksimalkan permukaan absorpsi nutrisi ke
dalam darah menuju hati, dan lipid masuk ke dalam saluran limfe.
* Permukaan mikrovilli juga mengandung enzim pencernaan a.l. laktase.
Kekurangan enzim laktase  intoleransi laktosa/ produk susu (diare
osmotik).
* Kripta villiaris (ceruk jonjot usus) mengandung sel Paneth penghasil
peptida antimikroba untuk melindungi sel punca epitel usus. Juga terdapat
sel globlet penghasil mukus untuk proteksi dan pelumas.
* Sel epitel usus diganti setiap 3-5 hari.
The crypts contain Paneth cells at their base that secrete antimicrobial peptides to protect the stem cells. These stem cell
produce the epithelial cells that migrate up the villi, differentiating as they go to become better able to absorb nutrients. The
crypts also produce goblet cells that provide the mucus that protects the crypts themselves and protects and lubricates the
mucosal epithelium of the villi.
The morphology of the villus maximizes absorptive surface area and removal of nutrients, carbohydrates and amino acids
directly to the liver, and lipids mostly into the circulation via the lymph.
Epithelial cells turn over every 3 – 5 days.
Brush border maximizes surface area for absorption and also contains some digestive enzymes, a few exopeptidases,
lactase, sucrase, maltase and isomaltase. There is also a minor amount of lipase on the brush border.
Lactase deficiency leads to dairy products intolerance – osmotic diarrhea.

24. Hati adalah organ multifungsi, esensial untuk metabolisme dan pengolahan
senyawa esensial. Produknya garam empedu esensial bagi pencernaan
lemak di usus kecil. Ia juga organ utama untuk detoksifikasi. Jika sebagian
dibedah, dengan cepat akan tumbuh kembali.
Pada saat empedu tak terpakai, ia disimpan di kandung empedu, mengalami
pemekatan sampai 20 kali.
Kandung empedu berkontraksi lemah dengan stimulasi vagal dan sfinkter
Oddi relaksasi. Kolesistokinin adalah hormon pemicu terkuat kontraksi
kandung empedu.
The liver is a multifunctional organ, essential for metabolic functions and processing essential compounds. The bile salts it produces are
essential for lipid digestion in the intestine. It is the major organ for detoxification. If sections are surgically removed it can grow back
rapidly.
Bile is made up two parts, the first coming from the hepatocytes contains bile salts and bile pigments. The ducts this bile passes through
(terminal bile ducts and hepatic duct) adds a HCO3
-
- rich fluid which is stimulated by secretin, just as in the pancreas. In the interdigestive
period the sphincter of Oddi is closed and bile is diverted into the gallbladder where it is concentrated up to 20 fold.
The gallbladder contracts weakly with vagal stimulation (ACh) and the sphincter of Oddi relaxes (VIP, NO) CCK is the strongest stimulant
for galbladder contraction.
Hati dan kandung empedu
The liver and gallbladder

25. Drainasi vena saluran cerna langsung ke hati
melalui vena porta, membawa nutrisi untuk
disimpan dan diolah di hati.
Pada gagal jantung kanan, darah terbendung
di vena hepatika dan hati, membuat hati
membengkak.
With right heart failure blood backs up in the hepatic vein and liver, causing the very
distensible liver to swell. Distension of the liver below the border of the ribs is a sign of
heart failure.
The venous drainage of the GI tract goes directly to the liver via the hepatic
portal vein, carrying absorbed nutrients for storage and processing.
Hati diperdarahai oleh arteri hepatika dan vena porta hepatika.
The liver has two incoming blood supplies, one the heptic artery carrying arterial blood and the other in the larger hepatic vein carrying splanchnic
venous drainage.

26. Pencernaan karbohidrat dimulai di rongga mulut oleh amilase
air liur, tapi yang lebih penting adalah amilase getah pankreas.
Selain itu terdapat enzim disakaridase di jonjot usus kecil.
Carbohydrate digestion starts with salivary amylase, but pancreatic amylase is more important. The disaccharidases,
maltase, sucrase, isomaltase and lactase are located on the epithelial cell brush border. Thus there is some digestion in the
mouth, much more in the duodenal lumen, and finally some at the brush border, next to the hexase carriers.
Glukosa (sekitar 80% karbohidrat makanan) dan galaktosa masuk sel lewat
transportasi aktif, sedangkan fruktosa masuk sel lewat difusi difasilitasi.
Sebagian besar fruktosa diubah menjadi glukosa dalam sel epitel usus.
Glucose (about 80% of dietary carbohydrate) and galactose use the same secondary active transport system at the apical
membrane (SGLT1) and pass out the basolateral membrane by facilitated diffusion (GLUT2), while fructose transport at the
apical membrane is not Na+
dependent, using a facilitated diffusion carrier. Most fructose is converted to glucose in the
epithelial cell
Digesti dan absorpsi karbohidrat
Carbohydrate digestion and absorption

27. Pencernaan protein terutama oleh enzim proteolitik getah
pankreas. Sebagian eksopeptidase terdapat di “brush border”
(mikrovilli).
Penyerapan protein (asam amino dan peptida) terjadi secara
transportasi aktif dan difusi difasilitasi.
Sebagian kecil absorpsi protein melalui transitosis, ini masalah
bagi timbulnya alergi.
Pepsin and pancreatic proteolytic enzymes are the major factors in protein digestion, but some exopeptidases are also attached to the brush border.
There are at least 5 transport proteins for amino acids on the brush border membrane. Most transport across the apical membrane is of single amino
acids and is secondary active transport. There is also facilitated diffusion and H+
coupled cotransporters for di and even tripeptides.
Some very small amount of protein is absorbed by transcytosis – a problem for allergies.
Digesti dan absorpsi protein
Protein digestion and absorption

28. Digesti dan absorpsi lemak
Digestion and absorption of fats
Sangat rumit, membutuhkan:
Memerlukan enzim lipase dan kolipase pankreas untuk digesti.
Memerlukan garam empedu untuk emulsifikasi (lemak “melarut” dalam air) agar
mudah dicerna dan diserap.
Malabsorpsi atau maldigesti lemak  steatore (feses berlemak, pucat, dan
mengambang).
Very complex. Requires:
• Pancreatic lipase and colipase for digestion.
• Bile salts to emulsify fats for digestion.
• Adequate surface area and slow enough transit time for absorption.
• Malabsorption or maldigestion results in steatorrhea (fatty stool – light colored and floating).
Lemak makanan umumnya berupa senyawa
trigliserida. Trigliserida dipecah oleh enzim lipase
menjadi monogliserida dan asam lemak yang siap
diserap dalam bentuk misel (micelles),
Much of our dietary fat is in the form of triglyceride, which must be broken down to free fatty
acids and monoglycerides for absorption. But lipase and colipase cannot function in a solid lipid
phase. They need an emulsion with a large lipid-water interface. Bile salts act as detergents
and produce the emulsion so that lipase can digest fatty acids.
Emulsion eventually decreases in size to micelles. Lipids are absorbed as micelles.

29. Monogliserida dan asam lemak setelah diserap lalu dibentuk lagi menjadi
trigliserida dalam sel epitel usus. Lipid itu lalu dibungkus selapis protein dan
disalurkan ke saluran limfe dalam bentuk kilomikron. Asam lemak berantai
pendek dapat langsung masuk ke kapiler darah dan menuju ke hati.
Monoglycerides and fatty acids are absorbed in micelles.Triglycerides are reassembled in the epithelial cell. The lipids are
then covered with a layer of protein and exported into the lymph as chylomicrons. Short chain fatty acids can go into the
capillaries and directly to the liver.
Garam empedu di ileum diserap
kembali (95%) ke darah, menuju ke
hati (lewat vena porta) untuk
kembali dikeluarkan dalam empedu
untuk emulsifikasi lemak. Siklus ini
disebut sirkulasi enterohepatik.
Bile salts are taken back up in the ileum and recycled through
the liver into the bile – ENTEROHEPATIC CIRCULATION. Bile
salts in the blood are taken up by the liver and stimulate more
bile production.

30. Keseimbangan cairan di saluran cerna
Fluid balance in the gastrointestinal tract is the result of absorption and secretion
• Sekresi/ masukan
• Secretion/intake
Konsumsi/ Consumption, 2.0L
Air liur/ Saliva, 1.5L
Getah lambung/ Gastric juice, 2.0L
Getah pankreas/ Pancreatic juice, 1.5L
Empedu/ Bile, 0.5L
Sekresi usus/ Intestinal secretion, 1.5L
Total, 9.0L
• Absorpsi/ absorption
Dari usus kecil/ From the small intestine,
7.5L
Dari usus besar/ From the large intestine,
1.4L
Total , 8.9L
Ekskresi dalam feses/ Excreted in
stool, 0.1L

31. Absorpsi dan sekresi di usus kecil
Absorption and secretion in the small intestine
• Absorpsi terbesar air dan elektrolit terjadi di sel epitel dekat puncak villi. Air
mengikut elektrolit dan non-elektrolit yang ditransportasi aktif.
• Sekresi air dan elektrolit terjadi di kripti. Saluran CFTR dapat ditambah atau
dikurangi untuk menambah atau mengurangi sekresi.
• Differentiated epithelial cells near the villus tips do most of the absorption of water and electrolytes. Water follows
electrolytes and non-electrolytes transported by secondary active transport.
• Standing osmotic pressure established between cells by the Na+
pump.
• Secretion of water and electrolytes occurs in the crypts. A CFTR (cystic fibrosis transmembrane regulator)
channel in the apical surface can be increased or decreased to increase or decrease secretion.

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Usus besar (kolon)
The large intestine
• Mengandung banyak bakteri.
• Tiap hari dapat menyerap 5-8 L air dan elektrolit, jika
beban melebihi itu, akan timbul diare.
• Isinya semakin padat dari kolon asenden hingga ke
rektum.
• Huge bacterial load.
• Can absorb up to 5 to 8 L of water and electrolyte per day. If load exceeds this the individual will have diarrhea.
• Content gets less fluid going from ascending colon to rectum.

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Refleks defekasi
Defecation reflex
Distensi rektum mencetuskan peristalsis lokal di kolon desenden dan
sigmoid dan rektum, serta merelaksasi sfinkter anal internal. Untuk
defekasi volunter masih perlu merelaksasi sfinkter anal eksternal,
menahan napas, mengedan untuk menaikkan tekanan intraabdominal.
Distension of the rectum causes local peristalsis of descending and sigmoid colon and rectum and relaxes internal anal
sphincter (weak, myenteric plexus). Periodically get defecation reflex, mediated In the sacral cord, to increase movement
(pelvic n. efferents). For voluntary defecation need to also relax external anal sphincter, hold breath, strain to increase
intraabdominal pressure.

34. Terapi diare sekretorik dengan Oralit
Treatment of secretory diarrhea using ORT – the rationale
Pada kolera, dan diare sekretorik lain, transporter aktif Na-glukosa
dan Na-asam amino masih intak.
Cairan pengganti oral (Oralit) berisi glukosa dan asam amino,
elektrolit dan basa telah menolong jutaan jiwa di seluruh dunia.
In cholera, and other the secretory diarrheas, sodium-glucose and sodium-amino acid co-transporters are preserved.
Oral replacement fluids containing glucose and amino acids, electrolytes and a base have saved millions of lives
worldwide.