sistem pencernaan (digestion system)
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Digestion
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Digestive Functions & Processes
Functions
ingestion = intake of food
digestion = breakdown of molecules
absorption = uptake of nutrients into blood orlymph
defecation = elimination of undigested material
Processes
motility = muscular contractions that break upfood, mix it with enzymes & move it along
secretion = digestive enzymes & hormones
membrane transport = absorption of nutrients
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Stages of Digestion
Mechanical digestion is physical breakdown of food intosmaller particles
teeth & churning action of stomach & intestines
Chemical digestion is series of hydrolysis reactions thatbreak macromolecules into their monomers
enzymes from saliva, stomach, pancreas & intestines
results
polysaccharides into monosaccharides
proteins into amino acids
fats into glycerol and fatty acids
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Saliva
Functions of saliva
moisten, begin starch & fat digestion, cleanse teeth,inhibit bacteria, bind food together into bolus
Hypotonic solutions of 99.5% water and solutes: amylase = begins starch digestion
lingual lipase = digests fat after reaches the stomach
mucus = aids in swallowing
lysozyme = enzyme that kills bacteria immunoglobulin A = inhibits bacterial growth
electrolytes = Na+, K+, Cl-, phosphate & bicarbonate
pH of 6.8 to 7.0
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Swallowing
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The esophagusSaliva contains salivary amylase. It hydrolyzes the glucose polymers starch andglycogen. The epiglottis blocks the top of the windpipe when we swallow. Peristalsismoves the bolus along the epiglottis.
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The stomachThe stomach can hold 2L of food and water. The lining of the stomach secretes
gastric acid. Gastric acid contains HCl and pepsin. Pepsin is an enzyme thathydrolyzes proteins. But it breaks proteins into smaller polypeptides.
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Functions of Hydrochloric Acid
Activates enzymes pepsin & linguallipase
Breaks up connective tissues & plant cellwalls
liquifying food to form chyme
Converts ingested ferric ions (Fe+3) toferrous ions (Fe+2) that can be absorbed& utilized for hemoglobin synthesis
Destroys ingested bacteria & pathogens
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Small Intestine
Nearly all chemical digestion and nutrient
absorption occurs in the small intestine
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Oral Cavity StomachSmall Intestine
Lumen Brush border
Carbohydrates
Salivary AmylasePolysaccharides ==>smaller Polysaccharides(starch,glycogen)(maltose)
Pancreatic AmylasePolysaccharides ==> disaccharides (maltose)
Disaccharidases==> monosaccharides
Proteins PepsinProteins ==> small polypeptide
Trypin, ChymotrypinPolypeptides ==> smal
ler polypeptides ==>aminopeptidase,carboxypeptidase==> Amino Acids
Dipeptidasessmall
polypeptides ==>Amino Acids
NucleicAcids
NucleasesDNA,RNA ==> Nucleotides ==>
Nucelotidases==> nuclesides ==>Nucelosidases==> Nitrogenousbases, sugars,phosphates
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Carbohydrates
Proteins
Fats
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The digestive enzymes in the table below are summarizedaccording to type of food that they digest.
FOOD TYPEENZYME SOURCE PRODUCTS
CARBOHYDRATES Salivary amylase
Pancreatic amylase
Maltase
Salivary glands
Pancreas
Small intestine
Maltose
Maltose
Glucose
PROTEINS PepsinTrypsin
Peptidases
Stomach mucosa
Pancreas
Intestinal mucosa
Peptides
Peptides
Amino acids
FATS Lipase Pancreas Fatty acidsand glycerol
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The table below shows digestive enzymes grouped by source of the enzyme.
SOURCEENZYME FOOD PRODUCT
MOUTH (salivary glands) Salivary amylase Polysaccharides Maltose
STOMACH Pepsin Proteins Peptides
PANCREAS Pancreatic amylaseTrypsin
Lipase
Polysaccharides
Proteins
Fats
Maltose
Peptides
Fatty acids
and glycerol
SMALL INTESTINE MaltasePeptidases
Maltose
Peptides
Glucose
Amino acids
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Digestive function is affected by hormonesproduced inmany endocrine glands, but the most profound control isexerted by hormones produced within thegastrointestinal tract. The gastrointestinal tract is thelargest endocrine organ in the body and the endocrinecells within it are referred to collectively as the entericendocrine system. Three of the best-studied enterichormones are:
Gastrin: Secreted from the stomach and plays animportant role in control of gastric acid secretion.
Cholecystokinin: A small intestinal hormone that
stimulates secretion of pancreatic enzymes and bile. Secretin: Another hormone secreted from small
intestinal epithelial cells; stimulates secretion of abicarbonate-rich fluids from the pancreas and liver.
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HORMONES
Major Activities Stimuli for Release
GastrinStimulates gastric acid secretion and proliferation of gastric
epitheliumPresence of peptides and amino acids in gastric lumen
Cholecystokinin
Stimulates secretion of pancreatic enzymes, and contraction andemptying of the gall bladder
Presence of fatty acids and amino acids in the smallintestine
SecretinStimulates secretion of water and bicarbonate from the pancreas
and bile ductsAcidic pH in the lumen of the small intestine
GhrelinAppears to be a strong stimulant for appetite and feeding; also a
potent stimulator of growth hormone secretion.Not clear, but secretion peaks prior to feeding and
diminishes with gastric filling
MotilinApparently involved in stimulating housekeeping patterns of motility
in the stomach and small intestineNot clear, but secretion is associated with fasting
Gastricinhibitorypolypeptide
Inhibits gastric secretion and motility and potentiates release ofinsulin from beta cells in response to elevated blood glucoseconcentration
Presence of fat and glucose in the small intestine
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gastrin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/parietal.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/secretin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/ghrelin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/gh.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/motilin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/mmcomplex.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/secretion.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/motility.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/motility.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/secretion.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gip.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/mmcomplex.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/motilin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/gh.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/ghrelin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/secretin.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bile.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/cck.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/parietal.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/gastrin.html -
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Hormones and Digestion:Feedback loops.The hormone Gastrin stimulates theproduction of gastric acid.The pyloric sphincter regulates the release of chyme (nutrientbroth) into the small intestine.Bile contains bile salts that aid digestion and absorption of
fats.
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Secretin hormone production is stimulated byacid chyme entering the duodenum. Thishormone stimulates the pancreas to releasebicarbonate to neutralize the acid.
CCK stimulates the gall bladder to release bileand the panceas to release pancreatic juices.
If the chyme is rich in fats causes the release ofenterogastrone. This hormone inhibitsperistalsis and the release of secretion of acid.
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The small intestine
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Essential Amino Acids
The human liver can synthesize 9 of the 20 amino acids
used in proteins. Those that cannot be synthesized arecalled the essential amino acids. They must be supplied
by diet.
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Bile Ducts and Gallbladder
Definition:
Bile is produced by the liver cells and collects in the small bile ducts betweenthe microscopic liver lobules which lead to the larger ducts. Outside the liver,two outflowing hepatic ducts unite to form the common hepatic duct. From herethe bile enters the cystic duct and the common bile duct . The common bile duct
joins the pancreatic duct to enter the duodenum. The opening is controlled by avalve which regulates the flow of gastric juices (bile, pancreatic enzymes) into
the duodenum.
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Function:
Bile is produced in the liver and aids the digestion of fattyfood substances. Between 250 and 1000 millilitres of bileare produced each day. The most important constituentsof bile are: water, bile salts, cholesterol , phospholipids .
Between meals, the bile is stored in the gallbladder,which contracts once or twice as food is taken. Thiscauses the bile to enter the duodenum via the commonbile duct. 80 to 90% of the bile acids are laterreabsorbed by the small intestine and re-enter the liver
via the bloodstream (portal system).
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Fat Digestion & Absorption
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Absorption and Motility
Transit time is 12 to 24 hours
reabsorbs water and electrolytes
Feces consist of water & solids (bacteria, mucus, undigested fiber,fat & sloughed epithelial cells
Haustral contractions occur every 30 minutes distension of a haustrum stimulates it to contract
Mass movements occur 1 to 3 times a day
triggered by gastrocolic and duodenocolic reflexes
filling of the stomach & duodenum stimulates motility
moves residue for several centimeters with each contraction
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Defecation
Stretching of the rectum stimulates defecation
intrinsic defecation reflex via the myenteric plexus
causes muscularis to contract & internal sphincter to relax
relatively weak contractions
defecation occurs only if external anal sphincter is voluntarily
relaxed parasympathetic defecation reflex involves spinal cord
stretching of rectum sends sensory signals to spinal cord
splanchnic nerves return signals intensifying peristalsis
Abdominal contractions increase abdominal pressure as levator ani liftsanal canal upwards
feces will fall away