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ANATOMO

FISIOLOGI SISTEM

GASTROINTESTINAL

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Fungsi

4 activities dari GI tract

1. Motility

Propel ingested food from mouth toward rectum

2. Secretion

Aid in digestion and absorption

3. Digestion

Food broken down into absorbable molecules

4. Absorption

Nutrients, electrolytes, and water are absorbed

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Structure of GI Tract

Arranged linearly in following sequence

Mouth, esophagus, stomach, small intestine, large

intestine, and anus

Other structures of GI tract

Salivary glands, pancreas, liver, and gallbladder

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Structure of GI Tract

Lapisan dinding GI tract1. Mucosa

Innermost layer (faces lumen) Layer of epithelial cells specialized for absorption

and secretion2. Submucosa

Consists of collagen, elastin, glands, and bloodvessels

3. Circular and Longitudinal Smooth Muscle Provides motility for GI tract

4. Serosa Faces the blood

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STRUKTUR GI Tract

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Autonomic Nervous Systemhas an extrinsic

and an intrinsic component

Extrinsic

Sympathetic and Parasympathetic innervation of GI

tract

Intrinsic

Called Enteric Nervous System Contained within wall of GI tract

Communicates with Extrinsic component

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Intrinsic Innervation

Can direct all functions of GI in absence ofextrinsic innervation

Controls contractile, secretory, and endocrine

functions of GI tract Receives input from

1. Parasympathetic and sympathetic nervous systems

2. Mechanoreceptors and chemoreceptors in mucosa

Sends information directly tosmooth muscle,secretory, and endocrine cells

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Oral Cavity Mouth or oral cavity

Lips (labia)

Orbicularis oris

Cheeks

Buccinator

Palate: Oral cavity roof

Hard and soft

Palatine tonsils

Tongue Involved in speech,

taste, mastication,

swallowing

Skeletal muscles

Upper lip

Palatine tonsil

Salivary duct orifices

SublingualSubmandibular

Lower lip

Hard palate

Soft palate

Uvula

Tongue

Teeth

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Salivary Glands

Produce saliva Prevents bacterial

infection

Lubrication

Contains salivaryamylase Breaks down starch

Three pairs

Parotid: Largest

Submandibular

Sublingual: Smallest

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Pharynx and Esophagus

Pharynx Food passes through

the oropharynx and

laryngopharynxPharynx

Internal nares

Opening of auditory tube

Nasopharynx

OropharynxLaryngopharynx

Esophagus

Trachea

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Pharynx and Esophagus

Esophagus

Transports food from pharynx

to stomach

Passes through esophageal

hiatus (opening) of diaphragm

and ends at stomach

Hiatal hernia

Sphincters

Circular muscles

Upper

Lower

Liver

Oral cavity

Pharynx

Esophagus

Stomach

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Esophagus

Muscular tube that conveys food from

pharynx to stomach

Inner circular muscle

Outer longitudinal muscle

Food passes through quickly because of

peristalsis

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Esophagus

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Esophagus

Pyrosis(heartburn)common esophageal discomfort

Result of regurgitation of food and gastric fluid into

lower esophagus Acid reflux can cause esophagitis

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Stomach

Specialized for accumulation of food

Capable of considerable expansion (can hold 2-3L)

Gastric juice converts food into semiliquid

called chyme 4 Parts

Cardia

Fundus

Body

Pylorus

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Stomach AnatomyFig. 26.12

Openings

Gastroesophageal: to esophagus

Pyloric: to duodenumParts

CardiaFundusBodyPyloric

Three layers of

smooth

muscle

Longi-

tudinal

layer

(outer)

Circular

layer

(middle)

Oblique layer(inner)

BodyGastric folds

Pylorus

Duodenum

Pyloric

orifice Pyloric

sphincter

Cardia

Esophagus

Fundus

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Stomach

Gastric mucosa has numerous openings calledgastric pits

Gastric glandsempty into bottom of pits

4 functionally different cell types composeglands

Mucous cells

Chief cells Parietal cells

Enteroendocrine cells

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Stomach Histology

Layers

Three layers of

muscles Outer longitudinal

Middle circular

Inner oblique

24-19

Fig. 26.13

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Stomach Histology

Rugae: Folds instomach when empty

Gastric pits: Openings

for gastric glands

Contain cells

Mucous cells: Mucus

along surface and in

pits

Parietal cells:

Hydrochloric acid

Chief cells:

Pepsinogen

24-20Fig. 26.13

Fig. 26.12

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Stomach

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Small Intestine

3 Parts

1. Duodenum

2. Jejunum

3. Ileum

Primary site for digestion and absorption of

nutrients

Bile duct and pancreatic duct empty into

duodenum

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Small Intestine

Site of greatest amount of digestionand absorption Divisions

Duodenum

Jejunum

Ileum

Duodenum

Jejunum

Ileocecal valve

Ileum

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Small Intestine Secretions

Mucus

Protects against digestive enzymes and

stomach acids

Digestive enzymes

Disaccharidases: Break down disaccharides to

monosaccharides

Peptidases: Hydrolyze peptide bonds

Nucleases: Break down nucleic acids

24-24

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Small Intestine

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Small Intestine

Intestinal lining increases absorptive surfacearea

Villi

Finger-like projections of the mucosa

Microvilli

Tiny projections on luminal membrane of each

intestinal cell Give the apical region striated appearance called

brush border

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Histology of Small Intestine

Circular folds,villiand microvilliincrease surface areaEpithelial cells produced by intestinal glands

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Villi

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Microvilli

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Large Intestine

Cecum, ascending colon, transverse colon,descending colon, sigmoid colon, rectum, analcanal

Reabsorbs water and electrolytes Eliminates waste

NO Villi

Mucosa contains numerous tubular glandscalled crypts

Responsible for mucus secretion

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Large Intestine

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Large Intestine

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Movement in Large Intestine

Mass movements Common after meals

Defecation reflex Distension of the rectal wall by

feces

Defecation Usually accompanied by voluntary

movements to expel feces through

abdominal cavity pressure caused

by inspiration (breathing in) and

contraction of abdominal wall

muscles

Rectal valve

Anal canal

Veins

Internal

anal sphincter

External

anal sphincter

Anus

Rectum

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Liver

Largest internal organ

Receives major blood supply from hepatic

portal vein

Brings venous blood rich in nutrients from

digestive tract

Hepatocytes

Livers cells

Capable of regeneration

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Liver

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Liver

Functions

1. Protein synthesis (albumin, prothrombin)

2. Bile formation and secretion

3. Detoxification of drugs and steroids

4. Lipoprotein synthesis

5. Carbohydrate metabolism

6. Urea formation from ammonium

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Gallbladder

Attached to surface of the liver

Blind pouch that stores bile

Ducts

Hepatic Duct

Cystic Duct

Common Bile Duct

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Gallbladder

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Pancreas

Exocrine and Endocrine Gland

1. ExocrineAcinar Cells

Secretes essential digestive enzymes through

pancreatic duct into duodenum

2. EndocrineIslets of Langerhans

Secretes insulin and glucagon into blood stream

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Duodenum and Pancreas

Duodenum25cm in adultAccessory glands empty secretions into duodenum

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Pancreas

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Pancreas

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GI Peptides

Includes hormones, neurocrines, andparacrines

Regulate functions of GI tract

Contraction and relaxation of smooth muscle walland sphincters

Secretion of enzymes for digestion

Secretion of fluid and electrolytes

Trophic (growth) effects

Some regulate secretion of otherGI peptides

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GI Peptides

Hormones Peptides released from endocrine cells of GI tract Secreted into portal circulation and enter systemic

circulation Target cells may be in GI tract or may be located

elsewhere in body Gastrin, Cholecystokinin, Secretin, and Gastric Inhibitory Peptide

Paracrines Secreted by endocrine cells of GI tract Act locallywithin same tissue that secretes them

Somatostatin (inhibitory actions)

Neurocrines Released by neurons of GI tract following an AP

ACh, norepinephrine, Vasoactive Intestinal Peptide (VIP), Gastrin-Releasing Peptide (GRP), Neuropeptide Y, and Substance P

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GI Hormones

Gastrin

Secreted by G cells in stomach in response to

eating

Stimuli include proteins, distention of stomach, andvagal stimulation

Gastrin-releasing peptide (GRP) is released from vagal nerve

endings onto G cells

Secretion is inhibitedby low pH in stomach Promotes H+secretionby gastric parietal cells

Stimulates growth of gastric mucosa

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GI Hormones

Cholecystokinin

Secreted by I cells of small intestine in response to fatty acids andsmall peptides

5 Actions:

1. Contraction of gallbladder Eject bile from gallbladder into small intestine necessary for

emulsification lipids

2. Secretion of pancreatic enzymes

Digest lipids, carbohydrates, and proteins

3. Secretion of bicarbonate (HCO3-) from pancreas4. Growth of exocrine pancreas and gallbladder

5. Inhibition of gastric emptying

Ensures adequate time for digestive and absorptive

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GI Hormones

Secretin Secreted by S cellsof duodenum in response to H+

and fatty acids

Promotes secretion of pancreatic HCO3- Neutralizing H+allows for pancreatic enzymes to digest fats

Inhibits effects of gastrin on parietal cells (H+secretion and growth)

Gastric Inhibitory Peptide (GIP)

Secreted by small intestine in response to all 3types of nutrients

Stimulates insulin secretionby pancreas

Inhibits gastric H+secretion

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GI Paracrines

Somatostatin

Secreted by endocrine cells in response todecreased luminal pH

Inhibitssecretion of other GI hormones Inhibitsgastric H+secretion

Histamine

Secreted in H+-secreting region of stomach

Stimulates H+secretion by gastric parietal cells(along with gastrin and ACh)

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GI Neurocrines

Synthesized in cell bodies of GI neurons

AP causes release of neurocrine which

interacts with receptors on postsynaptic cell

ACh (released from cholinergic neurons)

Norepinephrine (released from adrenergic

neurons)

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Motility

Contraction and relaxation of walls and sphincters ofGI tract

Mixes ingested food to prepare it for digestion andabsorption

Propels food along GI tract

Contractile tissue of GI tract is Smooth Muscle

Exceptpharynx, upper 1/3 esophagus, and

external anal sphincter are striated muscle Smooth muscle cells coupled via gap junctions

Permits rapid spread of APs for coordinated,smooth contraction

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Motility

Segmentation Contraction

Circular muscle contracts sending chyme in bothorad and caudad directions

Intestine then relaxes allowing chyme to mergeback together

Peristaltic Contractions

Longitudinal muscle contracts orad to bolus

propeling chyme along small intestine Simultaneously, portion of intestine caudad to

bolus relaxes

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Motility

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Secretion

Addition of fluids, enzymes, and mucus to

lumen of GI tract

Secretions produced by

Salivary glands (saliva)

Gastric mucosal cells (gastric secretion)

Pancreatic exocrine cells (pancreatic secretion)

Liver (bile)

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Salivary Secretion

Salivary glands produce 1 L/day of saliva

Functions of saliva

Initial digestion of starches and lipids by salivaryenzymes

Dilution and buffering of ingested foods

Lubrication of ingested food to aid its movement

Structure of Salivary Glands

Parotid glands, submandibular glands, and sublingualglands

Each gland delivers saliva to mouth through a duct

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Salivary Glands

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Gastric Secretion

Gastric mucosal cells secrete gastric juice

HCland pepsinogeninitiate protein digestion

Intrinsic factorrequired for absorption of vitamin B12

Mucusprotects gastric mucosa from HCl

Cell Types of Gastric Mucosa

Bodyof stomach contains oxyntic glands Parietal cells HCl and Intrinsic Factor

Chief cells Pepsinogen

Antrumof stomach contains pyloric glands G cells Gastrin into the circulation

Mucous neck cells Mucus, HCO3-, and Pepsinogen

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Gastric Secretion

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Gastric Gland

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HCl Secretion

Parietal cellssecrete HCl which converts inactivepepsinogen to pepsin

1. Within cell, CO2combines with H2O to form H+and

HCO3

-

2. At apical membrane,H+secreted into lumen ofstomach via H+-K+ATPase Cl-follows H+into the lumen by diffusing through

Cl-channels

3. At basolateral membrane,HCO3-

absorbed intoblood via a Cl--HCO3-exchanger

Eventually HCO3-secreted back into GI tract by

pancreas

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HCl Secretion

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Regulation of HCl Secretion

ACh Released from vagus nerve

Binds to receptors on parietal cells

Produces H+secretion by parietal cells

Atropineblocks muscarinic receptors on parietal cells

Histamine

Released from mastlike cells in gastric mucosa

Binds to H2receptorson parietal cells

Produces H+secretion by parietal cells

Cimetidineblocks H2receptors

Gastrin

Released into circulation by G cellsof stomach antrum

Binds to receptors on parietal cells

Stimulates H+secretion

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Ulcers

Gastric Ulcers

Mucosal barrier is defective allowing H+and

pepsin to digest portion of mucosa

Helicobacter pyloriproduces NH4+from urea NH4

+breaks down mucosal barrier to H+

Duodenal Ulcers

More common H+secretory rates are higher than normal

Excess H+damages duodenal mucosa

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Pancreatic Secretion

Exocrine pancreas secretes ~1 L/day into duodenum Fluid consists of HCO3

-and enzymes HCO3

-neutralizes H+delivered to duodenum from stomach Enzymatic portiondigests carbohydrates, proteins, and lipids into

absorbable molecules

Structure of Pancreatic Exocrine GlandsComprises ~90% of pancreas

Rest of pancreatic tissue is endocrine pancreas and blood vessels

Acinar Cells Line blind end of branching duct system

Secrete enzymatic portionDuctal Cells

Line the ducts Secrete aqueous HCO3

-component

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HCO3-Secretion

Apical membrane of ductal cells contains a Cl--HCO3-exchanger

Basolateral membrane contains Na+-K+ ATPase and aNa+-H+exchanger

1. CO2and H2O combine in cells to form H+ and HCO3-

2. HCO3-is secreted into pancreatic juice by Cl--HCO3

-exchanger

3. H+

is transported into blood by Na+

-H+

exchanger Absorption of H+causes acidification of pancreatic venous blood

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Regulation of Pancreatic Secretion

Acinar cells (enzymatic secretion)

Receptors for CCK and muscarinic receptors forACh

CCKis most important stimulant I cells secrete CCK in presence of amino acids and fatty acids in

intestinal lumen

AChalso stimulates enzyme secretion

Ductal cells (aqueous secretion of HCO3-)

Receptors for CCK, ACh, and secretin

Secretin(from S cells of duodenum) is majorstimulant

Secreted in response to H+in intestine

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Bile Secretion

Necessary for digestion and absorption of

lipidsin small intestine

Mixture of bile salts, bile pigments, and

cholesterol

Bile salts emulsify lipids to prepare them for

digestion

Solubilize products of lipid digestion in packets

called micelles

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Bile Secretion and Recycling

1. Produced and secreted by liver2. Stored in gallbladder

3. Ejected into small intestine when gallbladder contracts

4. After lipids absorbed, bile salts are recirculated to livervia enterohepatic circulation

Absorption of bile salts from ileum into portalcirculation

Delivery back to liver

5. Extraction of bile salts from the portal blood byhepatocytes

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Bile Secretion and Recycling