Fisiologi Sekresi&Absopsi-blok Digest12

7/28/2019 Fisiologi Sekresi&Absopsi-blok Digest12

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dr. Mustofa, M.ScLAB. FISIOLOGI FKIK UNSOED

FISIOLOGI SISTEMPENCERNAAN

Sekresi & Absorpsi


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1. Describe the secretion of the oral cavity juice.

2. Describe the secretion of gastric juice and the

roles of stomach in absorption.

3. Explain the functions of the intestinalsecretions, and discuss the regulation of

secretory activities.

4. Describe the secretion and regulation of theaccessory digestive organs.

5. Describe the intestinal absorptive processes

Learning Objective


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1. AN OVERVIEW OF THE STRUCTURE ANDFUNCTION OF THE DIGESTIVE TRACT

2. ORAL CAVITY AND ASSOCIATED GLANDULAR

ORGANS

3. THE STOMACH

4. THE SMALL INTESTINE AND ASSOCIATED

GLANDULAR ORGANS

5. THE LARGE INTESTINE

Outline


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Heart

Liver

ABSORPTION

SECRETION

Large intestine

Rectum

AnusMouth

Food andwater

StomachHepatic

Portal vein

Small intestineSalivary glands

MOTILIT

Y

FECES

enzim asam, dll

VitaminC, D, B2, B12, dll

ProteinMineral

Karbonhidrat

Lipid

Adapted by:Dr. Andreanyta Meliala, PhD.

Vitamin KAir, Elektrolit

AktifitasBAKTERI

PembentukanGas CO2, Metana, dll

FLATUS

Digestion


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Secretion: Includes both exocrine and endocrine

secretions. Exocrine:

HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin,

elastase, and histamine are secreted into the lumen of theGI tract.

Endocrine: Stomach and small intestine secrete hormones to help

regulate the GI system.

Gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, andsomatostatin.

Functions of the GI Tract (Continued)


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Absorption:

Process of the passage of digestion(chemical subunits) into the blood or

lymph.

Functions of the GI Tract (Continued)


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nutrients


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GIT Regulation


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GIT Regulation


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Composition and function of

saliva


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Major salivary components

Mucin 1 (MG1)

sIgA

Mucin 2 (MG2)

Lactoferrin

Peroxidases

AmylasesCarbonic anhydrases

Proline-rich proteins

Lysozyme

StatherinsHistatins

1 10 100 1000 10000

Size (kDa)


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Multifunctionality

Salivary

Families

Anti-

BacterialBuffering

Digestion

Mineral-

ization

Lubricat-

ion &Visco-

elasticity

Tissue

Coating

Anti-

Fungal

Anti-

Viral

Carbonic anhydrases,

Histatins

Amylases,

Mucins, Lipase

Cystatins,

Histatins, Proline-

rich proteins,

Statherins

Mucins, Statherins

Cystatins, Mucins,

Proline-rich proteins, Statherins

Histatins

Cystatins,

Mucins

Cystatins,

Histatins, Mucins,

Peroxidases

adapted from M.J. Levine, 1993


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Mucin Functions

Tissue Coating Protective coating about hard and soft tissues

Concentrates anti-microbial molecules at

mucosal interface

Lubrication


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Mucin Functions (contd)

Aggregation of bacterial cells

Bacterial adhere to mucins may result in

surface attachment, or Mucin-coated bacteria may be unable to

attach to surface

Bacterial adhesion

Mucin oligosaccharides mimic those on

mucosal cell surface

React with bacterial adhesins, thereby

blocking them


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Amylases

Hydrolyzes (1-4) bonds of starches

Maltose is the major end-product (20% is

glucose)


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Lingual Lipase

Secreted by von Ebners glands oftongue

Involved in first phase of fat digestion

Hydrolyzes medium- to long-chain

triglycerides

Important in digestion of milk fat in

new-born

Unlike other mammalian lipases, it is

highly hydrophobic and readily enters

fat globules


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Statherins

Calcium phosphate salts of dental enamelare soluble

Supersaturation of calcium phosphates

maintain enamel integrity Statherins prevent precipitation or

crystallization of supersaturated calcium

phosphate in ductal saliva and oral fluid


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Proline-rich Proteins (PRPs)

Inhibit calcium phosphate crystal growth


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Calculus formation

Calculus forms in plaque despite

inhibitory action of statherin and PRPs in

saliva Proteolytic enzymes of oral bacteria or

lysed leukocytes may destroy inhibitory

proteins Plaque bacteria may produce their own

inhibitors


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Lactoferrin

Nutritional immunity

Some microorganisms (e.g., E. coli) have

adapted to this mechanism by producingenterochelins.

bind iron more effectively than lactoferrin

iron-rich enterochelins are then reabsorbed by

bacteria

Lactoferrin, with or without iron, can be

degraded by some bacterial proteases.

In unbound state, a direct bactericidal effect


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Lysozyme

Present in numerous organs and most body fluids Sources of oral LZ:

major and minor salivary glands, phagocytic cells

Biological function

Classic concept of anti-microbial activity of LZ is based on

its muramidase activity (hydrolysis of(1-4) bondbetween N-acetylmuramic acid and N-acetylglucosamine

in the peptidoglycan layer.

Gram negative bacteria generally more resistant thangram positive because of outer LPS layer


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Other anti-microbial activities of

LZ Muramidase activity (lysis of peptidoglycan

layer)

Cationic-dependent activation of bacterial

autolysins disrupts membranes

Aggregation of bacteria

Inhibition of glucose uptake and acidproduction

De-chaining of streptococci


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Histatins

A group of small histidine-rich proteins

Potent inhibitors ofCandida albicans

growth


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Cystatins

Are inhibitors of cysteine-proteases Are ubiquitous in many body fluids

Considered to be protective against unwanted

proteolysis bacterial proteases

lysed leukocytes

May play inhibit proteases in periodontal

tissues

Also have an effect on calcium phosphate

precipitation


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CCK :

Cholecytokinin

GIP:

Gluc-dep. Insulino-

Tropic peptide

Each hormone:

Feedback

Multiple Targets

Major GIT hormone


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Mekanisme lokal:

Prostaglandin, histamin, dan bahan kimia

lain yg dilepaskan ke cairan interstitial dapat

berpengaruh pada sel sekitar

Mesenger lokal ini penting dalam kordinasi

tanggap terhadap perubahan pH lokal,rangsang fisik atau kimia lain.

GIT Regulation


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1.Chyme in the duodenum witha pH less than 2 or containingfat digestion products (lipids)

inhibits gastric secretions by

three mechanisms.

2.Sensory vagal action potentials

to the medulla oblongata(green arrow) inhibit motor

action potentials from the

medulla oblongata (pink arrow).

3.Local reflexes inhibit gastricsecretion (orange arrow s).

4.Secretin, gastric inhibitorypolypeptide, and cholecystokinin

produced by the duodenum

(brown arrows) inhibit gastric

secretions in the stomach.

Intestinal Phase

Secretin, gastric inhibitory

peptide, cholecystokininCirculation

pH


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Stomach (continued)Insert fig. 18.5

Stomach


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Secrete gastric juice:

Goblet cells: mucus.

Parietal cells: HCl and intrinsic factor.

Chief cells: pepsinogen.

Enterochromaffin-like cells (ECL):histamine and serotonin.

G cells: gastrin. D cells: somatostatin.

Stomach: ghrelin.

Gastric Glands


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HCl Production Parietal cells

secrete H+ intogastric lumen byprimary activetransport, throughH+/ K+ATPasepump.

Parietal cellsbasolateralmembrane takes

in Cl-

against itselectrochemicalgradient, bycoupling itstransport withHC03

-.

Insert fig. 18.8

HCl production


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HCl production is stimulated:

Indirectly by gastrin.

Indirectly by ACh. ACh and gastrin stimulate release of

histamine.

Histamine: Stimulates parietal cells to secrete HCl.

HCl production


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Makes gastricjuice very acidic. Denatures

ingested proteins

(alter tertiarystructure) sobecome moredigestible.

Activates

pepsinogen topepsin. Pepsin is more

active at pH of 2.0.

Insert fig. 18.9

HCl Function

Digestion and Absorption in the


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Proteins partially digested by pepsin.

Carbohydrate digestion by salivary

amylase is soon inactivated by acidity.

Alcohol and aspirin are the only

commonly ingested substances

absorbed.

Digestion and Absorption in the

Stomach


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Parietal and chief cells impermeable to

HCl.

Alkaline mucus contains HC03

-.

Tight junctions between adjacent

epithelial cells.

Rapid rate of cell division (entireepithelium replaced in 3 days).

Prostaglandins inhibit gastric secretions.

Protective Mechanisms of Stomach


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Usus halus

Getah pencernaan di Usus


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Getah Pankreas

Getah Empedu

Getah usus halus

Getah pencernaan di Usushalus


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1,8 L /hari1. Kelenjar Brunner: di mukosa duodenum,

merangsang sekresi:

Mukus: melindungi mukosa duodenum dari iritasi

HCl & pepsin

Buffer :me pH (khime dlm duodenum pH: 1-2 sp7-8)

2. Kripte Lieberkuhn

Produksi enzim, cairan isotonik dan alkalin

Getah Usus halus


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3. Enterosit vili

menghasilkan: amilase, enterokinase,

lipase, peptidase, disakaridase, yang

tidak dikeluarkan ke lumen namun akan

memecah lemak, protein, karbohidrat

begitu absorbsi dimulai

Getah Usus halus


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1500 cc / hari

Mengandung: bikarbonat, elektrolit: Na,K,Cl,enzim

Mempunyai 2 fungsi:

1. Endokrin: sel endokrin sekresi insulin & glukagon2. Eksokrin: berasal dari sel asinus dan epitel: keduanya

menghasilkan cairan disebut cairan pankreas

(pancreatic juice) yg dikeluarkan ke usus halus.

enzim yang dikeluarkan sel asinus berguna untuk memecah

khime menjadi molekul kecil yang mudah diabsorbsi.

Sel epitel mengeluarkan air & ion untuk mengencerkan

khime & sebagai buffer

Getah Pankreas


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Pengaturan sekresi melalui pengendalian

hormon. Bila khime masuk duodenum,

maka duodenum mengeluarkan hormon :

1. sekretin: memacu pankreas sekresi buffer

air dengan pH 7,5-8,8 dan buffer

bicarbonat serta fosfat

2. kolesistokinin: rangsang produksi dan

sekresi enzim pankreas


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Pengaturan sekresi


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Pengaturan sekresi


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digestive enzymes secreted as inactive precursors(zymogens) to prevent autodigestion

important proteolytic enzymes are t ryps in,chymotryps inandcarboxypept idases

other enzymes are-

panc reatic l ipase panc reatic amylase

t ryps inogenis activated byenteropeptidasewhichis secreted by intestinal mucosa in response to

chyme trypsin then activates the other proenzymes

t ryps ininh ib i torsecreted to delay activation oftrypsinogen

Enzim pankreatik


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F O O D

Aktifasi enzimatik


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cephal ic phase~15% mainly causes secretion ofenzymes into the acini - vagus mediated

gastr ic phase~15% gastric distension by means of

vago-vagal reflex evokes enzyme secretion

gastrin release by antral lumen causing more enzymerelease

intest inal phase~70% -pancreatic HCO3 secretion

strongly stimulated when duodenal pH is acid - S

cellssecrete secretin into the blood and thisstimluates pancreatic duct cells

chyme also causes I cellsto release CCKwhich

causes pancreatic enzymes to be secreted (mainly

due to peptones and fatty acids)

Fase sekresi pankreas


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Stimuli of Pancreatic Secretion

ACh - parasympathic vagus nerves as well as

myenteric cholinergics Gastrin - liberated during gastric phase ofstomach secretion

CCK (cholecystokinin) - secreted by duodenaland upper jejunal mucosa when food enters

small intestine these 3 all stimulate production of digestive

enzymes by the acini and act via IP3 to releaseintracellular Ca

Secretin - same duodenal and upper jejunalmucosa but secretin acts via cAMP on the ductalcells to increase HCO3 secretion

Ab b i h l


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Pengiriman nutrientdari saluran cerna ke

sirkulasi, terutama tjd di usus halus

permukaan yang luas.

Absopsi efisien bila:

1. Bentuk hasil pencernaan baik

2. Permukaan absorpsi adekuat

3. Kecepatan/ waktu transit nutrientdi usus halus

4. Kofaktor dan atau karier spesifik

Absorbsi usus halus

Ab b i h l


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1. Absorbsi air dan elektrolit

membranintestinalsangat permeabel

terhadap air

Air diserap menggunakan osmot ic gradient

Sebagian besarnutrientdiserap oleh

yeyunum

Absorbsi usus halus

Ab b i h l


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brush border

permukaan absorbsi Na via Na channeldan Na-nutrient

cotransporter

Na dipompa ke darah oleh Na-K ATPase

Absorbsi usus halus


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Ab b i h l


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2. Pencernaan & absorpsi karbohidrat

300g / hari

Polisakarida kompleks: 64% pati, 0.5%

glikogen

Disakarida: 26% sukrosa, 6.5% laktosa,

3% MALTOSA

Hidrolisis lengkap 80% glucosa, 14%fruktosa, 5% galaktosa kapiler

Absorbsi usus halus

C b h d t b ti


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Carbohydrate absorption

pancreatic juices cannot further hydrolyse

oligosaccharides brush borderoligosaccharidases

brush border lactase, sucrase-isomaltase andmaltase release monosaccharides (glucose,galactose and fructose)

glucose and galactose taken up by SGLT1 fructose by GLUT5

all three transported via GLUT2 out into theportal vein and to the liver


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In a normal diet, bulk is Carbs, 250-800 g (ex. Atkins)

+ 125 g protein, +25-160 g fat.


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Fat absorption

lipids- mainly triacylglycerols

1 - large oil droplets (shearing forces in gut)

2 - emulsified oil drops with bile salts

pancreatic lipase at oil-water interface

3 - formation of micelles

micelles come to the absorptive surface of gut

monoglycerides and free fatty acids are then

absorbed


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4. inside cells resynthesis of triacylglycerols, cholesterol

and phospholipids to chylomicrons

5. secreted into lacteal and to systemic circulation to

adipose tissue where the chylomicron is stripped of its

triacylglycerols and chylomicron remnant goes to liver -dietary cholesterol to liver. free fatty acids are also

synthesised to prostaglandins (can act as local gut

hormones)


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Product Absorption pathway

Carbohydrates Fru Facilitated diffusion

Glu/Gal Active Transport / Sodium

Protein Amino Acids Active transport / Sodium

Proteins (except.) endo-exocytosis

(infants mainly)

Fat Free Fatty Acids Diffusion

Monoglyc. Diffusion

Vitamins (fat) A, D, E, K Diffusion (via micelles)

Vitamins (water) B-12 Binds to Intrin. Factor.

Endocytosis

Iron Active Transport

then into ferritin

kolon


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kolon

kolon


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Sekresi:mukus yang diproduksi oleh sel goblet untuk

pelumas feses dan epitel

HCO3- , untuk menyeimbangkan asam produksi

bakteri

kolon

kolon


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Absorbsi :

airOsmosis

elektrolit

vitamin yg dihasilkan kerja bakteri:

Vitamin K: larut lemak, untuk pembekuan darahBiotin: larut air, penting untuk metabolisne glukosa

Vitamin B5: asam pantotenat: larut air, untuk membuat

hormon steroid & beberapa neurotransmiter

Bakteri mengubah bilirubin menjadi urobilinogen

(diabsorpsi ke sirkulasi, dibuang melalui urin) dan

sterkobilin

kolon

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Fisiologi Sekresi&Absopsi-blok Digest12