Sistem Pencernaan (Digestion System)

8/2/2019 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

Sistem Pencernaan (Digestion System)

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