Chapter 18Chapter 18

The Digestive SystemThe Digestive System

MotilityMotility::

Movement of food through the GI Movement of food through the GI tract.tract. Ingestion:Ingestion:

Taking food into the _______________.Taking food into the _______________. Mastication:Mastication:

Chewing the food and mixing it with Chewing the food and mixing it with saliva.saliva.

_______________________:_______________________: Swallowing the food.Swallowing the food.

Peristalsis:Peristalsis: Rhythmic wave-like contractions that Rhythmic wave-like contractions that

move food through GI tract.move food through GI tract.

Functions of the GI TractFunctions of the GI Tract

Secretion:Secretion: Includes both _____________ and Includes both _____________ and

endocrine secretions.endocrine secretions. Exocrine:Exocrine:

HCl, HHCl, H220, HC00, HC033--, bile, lipase, pepsin, , bile, lipase, pepsin,

amylase, trypsin, elastase, and amylase, trypsin, elastase, and histamine are secreted into the lumen of histamine are secreted into the lumen of the GI tract.the GI tract.

Endocrine:Endocrine: Stomach and small intestine secrete Stomach and small intestine secrete

hormones to help regulate the GI hormones to help regulate the GI system.system.

Gastrin, secretin, CCK, GIP, GLP-1, Gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, and somatostatin.guanylin, VIP, and somatostatin.

Functions of the GI Tract Functions of the GI Tract (continued)(continued)

Digestion:Digestion: Breakdown of food particles into Breakdown of food particles into

subunits (__________________ structure subunits (__________________ structure change).change).

Absorption:Absorption: Process of the passage of digestion Process of the passage of digestion

(chemical subunits) into the blood or (chemical subunits) into the blood or lymph.lymph.

Storage and elimination:Storage and elimination: Temporary storage and elimination of Temporary storage and elimination of

indigestible food.indigestible food.

Functions of the GI Tract Functions of the GI Tract (continued)(continued)

Digestive System (GI)Digestive System (GI)

GI tract divided into:GI tract divided into: Alimentary canal.Alimentary canal. Accessory digestive Accessory digestive

organs.organs. GI tract is ______ft long and GI tract is ______ft long and

extends from mouth to extends from mouth to anus.anus.

Crop found in birds and other lower animals

Layers of GI TractLayers of GI Tract Composed of 4 tunics:Composed of 4 tunics:

Mucosa.Mucosa. Submucosa.Submucosa.

Muscularis.Serosa.

Lines the lumen of GI tract.Lines the lumen of GI tract. Contains:Contains:

Connective tissue & lymph nodules.Connective tissue & lymph nodules. Thin layer of smooth muscle responsible Thin layer of smooth muscle responsible

for the folds.for the folds. Goblet cells:Goblet cells:

Secrete _______________.Secrete _______________.

MucosaMucosa

Contains blood vessels, lymph, and Contains blood vessels, lymph, and nerve fibers nerve fibers

Absorbed molecules enter the Absorbed molecules enter the blood and lymphatic vessels.blood and lymphatic vessels.

Submucosal plexus (Meissner’s Submucosal plexus (Meissner’s plexus):plexus): Provide autonomic nerve supply to the Provide autonomic nerve supply to the

muscularis mucosae. muscularis mucosae.

SubmucosaSubmucosa

Responsible for segmental contractions Responsible for segmental contractions and peristaltic movement through the GI and peristaltic movement through the GI tract.tract. Inner circular layer of _________ muscle.Inner circular layer of _________ muscle. Outer longitudinal layer of smooth muscle.Outer longitudinal layer of smooth muscle.

Contractions of these layers move food Contractions of these layers move food through the tract; pulverize and mix the through the tract; pulverize and mix the food.food. Major nerve supply to GI tract. Major nerve supply to GI tract.

Fibers and ganglia from both sympathetic Fibers and ganglia from both sympathetic and parasympathetic nervous systems.and parasympathetic nervous systems.

Enterogastric Reflex: (_____________)Enterogastric Reflex: (_____________)

MuscularisMuscularis

Enterogastric Reflex: Enterogastric Reflex: (pacemaker)(pacemaker)

Type of food determines rate of passage Type of food determines rate of passage in gutin gut

High fat meal – may be in GIT ____ or High fat meal – may be in GIT ____ or more hoursmore hours

High COH – may be out by ____ hoursHigh COH – may be out by ____ hours

SerosaSerosa

Binding and protective outer layer.Binding and protective outer layer.

Extrinsic innervation:Extrinsic innervation: Parasympathetic nervous system:Parasympathetic nervous system:

Vagus and spinal nerves:Vagus and spinal nerves: Stimulate motility and GI secretions.Stimulate motility and GI secretions.

Sympathetic nervous system:Sympathetic nervous system: Reduce peristalsis and secretory activity.Reduce peristalsis and secretory activity.

Regulation of the GI TractRegulation of the GI Tract

_______________: constriction of the guy at _______________: constriction of the guy at one point on its length initiates constriction one point on its length initiates constriction at a neighboring point – wave at a neighboring point – wave

_______________: constrictions of circular _______________: constrictions of circular muscles appear and disappear in patterns muscles appear and disappear in patterns that push the contents back and forththat push the contents back and forth

Submucosal and myenteric plexuses:Submucosal and myenteric plexuses: Local regulation of the GI tract.Local regulation of the GI tract.

Paracrine secretion:Paracrine secretion: Molecules acting locally.Molecules acting locally.

Hormonal secretion:Hormonal secretion: Secreted by the mucosa.Secreted by the mucosa.

Regulation of the GI Tract Regulation of the GI Tract (continued)(continued)

From Mouth to StomachFrom Mouth to Stomach

Tongue: in herbivores, tongue Tongue: in herbivores, tongue grasps food and brings it ingrasps food and brings it in Rough surface: papillae, providing Rough surface: papillae, providing

traction for moving foodtraction for moving food Bringing food into mouth is voluntary Bringing food into mouth is voluntary

MouthMouth

MouthMouth

________________:________________: decreases particle size and decreases particle size and mixes with saliva which contains salivary mixes with saliva which contains salivary amylase.amylase. Enzyme that can catalyze the partial digestion of Enzyme that can catalyze the partial digestion of

starch.starch. Makes food into a bolusMakes food into a bolus

________________:________________: important in ruminants- important in ruminants- (regurgitation)(regurgitation) Ruminants take in large amounts of food in a Ruminants take in large amounts of food in a

short period of time short period of time

SalivaSaliva

Glands: 3 major paired glands in mammalsGlands: 3 major paired glands in mammals 1. Parotid: below and front of ear1. Parotid: below and front of ear 2. Mandibular – under jaw2. Mandibular – under jaw 3. Sublingual – under tongue3. Sublingual – under tongue

Ruminants have 4th: Inferior molarRuminants have 4th: Inferior molar ____________ – small glands____________ – small glands

Saliva – pH = 6-7 Saliva – pH = 6-7 Functions: LubricantFunctions: Lubricant Dissolves some foodDissolves some food TasteTaste

SalivaSaliva

Composition of saliva:Composition of saliva: 1. Water: 98-99%1. Water: 98-99% 2. ______________2. ______________ 3. ______________________ – starch splitting3. ______________________ – starch splitting

found in humans, horses, swine and dogs (not found in humans, horses, swine and dogs (not ruminants)ruminants)

Starts COH digestionStarts COH digestion 4. Sodium bicarbonate, phosphate4. Sodium bicarbonate, phosphate

buffers stomachbuffers stomach

Ruminants: large amount of salivaRuminants: large amount of saliva Important in ___________________recyclingImportant in ___________________recycling

Saliva formation

From Mouth to StomachFrom Mouth to Stomach

__________________ (swallowing):__________________ (swallowing): Begins as a voluntary activity.Begins as a voluntary activity. Cannot be stopped.Cannot be stopped. Larynx is raised.Larynx is raised. Epiglottis covers the entrance to Epiglottis covers the entrance to

respiratory tract.respiratory tract.

Esophagus:Esophagus: Muscular tube – passes through Muscular tube – passes through

thoracic cavity and diaphragm to the thoracic cavity and diaphragm to the ________ of the stomach________ of the stomach

Normally closed, stretches open when a Normally closed, stretches open when a bolus of food passes throughbolus of food passes through

Sits on the _________ side of the tracheaSits on the _________ side of the trachea Connects pharynx to the stomachConnects pharynx to the stomach Can observe bolus transport in cattleCan observe bolus transport in cattle

From Mouth to Stomach From Mouth to Stomach (continued)(continued)

EsophagusEsophagus

Peristalsis: Peristalsis: Wave-like muscular Wave-like muscular

contractions:contractions: Circular smooth muscle Circular smooth muscle

contract behind, relaxes contract behind, relaxes in front of the bolus.in front of the bolus.

_______________ Sphincter:_______________ Sphincter: muscle that opens and muscle that opens and closescloses Physiological barrier Physiological barrier

between esophagus and between esophagus and stomachstomach

Insert 18.4a

Ruminant StomachRuminant Stomach

________________ animals________________ animals Digestive systemDigestive system

Large, lots of space for processing large Large, lots of space for processing large quantities of bulky foragequantities of bulky forage

4 chambers of stomach:4 chambers of stomach: ____________________________________________________________________

4-compartments of ruminant; only one stomach

Ruminant StomachRuminant Stomach Reticulorumen Reticulorumen

@ 1 billion bacteria & 1 million protozoa per @ 1 billion bacteria & 1 million protozoa per millilitermilliliter

Large structure for fermentation of celluloseLarge structure for fermentation of cellulose ________________% of total digestion occurs here________________% of total digestion occurs here

______________________ secretory function secretory function Does have _________________ functionDoes have _________________ function Composed of smooth muscle with Composed of smooth muscle with vagus vagus

innervationinnervation Blood from reticulorumen Blood from reticulorumen

portal vein – liverportal vein – liver

Digestion in ruminantDigestion in ruminant

Carbohydrates – celluloseCarbohydrates – cellulose Microbe population Microbe population

volatile fatty acids (_______________________________) volatile fatty acids (_______________________________) absorbed across rumen wallabsorbed across rumen wall

Proteins – digested by _____________Proteins – digested by _____________ Lipids – also broken downLipids – also broken down Microbes in rumen synthesize all Microbes in rumen synthesize all

______complex vitamins and all ______complex vitamins and all ____________ amino acids____________ amino acids

Ruminant StomachRuminant Stomach

____________________ – common to both the rumen – common to both the rumen and reticulum (where they sort of meet)and reticulum (where they sort of meet) esophageal grooveesophageal groove Extends from the cardia to the omasumExtends from the cardia to the omasum Formed by two heavy musclesFormed by two heavy muscles Can close to allow food to go directly from Can close to allow food to go directly from

the esophagus to the _______________the esophagus to the _______________ ____________________________________

OmasumOmasum

Epithelium has leaflike foldsEpithelium has leaflike folds Enormous ________________ abilityEnormous ________________ ability

AbomasumAbomasum

True stomach True stomach similar to monogastric stomach with similar to monogastric stomach with

some secretory ability some secretory ability Has a _______________ sphincter Has a _______________ sphincter

Most distensible part of GI tract.Most distensible part of GI tract. Empties into the duodenum.Empties into the duodenum.

Functions of the stomach:Functions of the stomach: ____________________.____________________. Initiates digestion of ____________.Initiates digestion of ____________. Kills bacteria.Kills bacteria. Moves food (chyme) into Moves food (chyme) into

intestine.intestine.

Non- Ruminant StomachNon- Ruminant Stomach

Stomach Stomach (continued)(continued)

ContractionContractions of the s of the stomach stomach churn churn chyme.chyme. Mix chyme Mix chyme

with with gastric gastric secretions.secretions.

Push food Push food into into intestine.intestine.

Insert fig. 18.5

Stomach Stomach (continued)(continued)

Gastric Gastric mucosa has mucosa has gastric pits in gastric pits in the folds.the folds.

Cells that line Cells that line the folds the folds deeper in the deeper in the mucosa, are mucosa, are gastric gastric glands.glands.

Insert fig. 18.7

Stomach Stomach (continued)(continued)

Non Ruminant Stomach (_________) Non Ruminant Stomach (_________) Exterior Subdivided into:Exterior Subdivided into: 1. Cardia (entrance)1. Cardia (entrance) 2. Fundus2. Fundus 3. Body3. Body 4. Pylorus (termination) (aka: antrum; 4. Pylorus (termination) (aka: antrum;

constricted part) joins to duodenumconstricted part) joins to duodenum Cardia and pylorus act as sphincters to Cardia and pylorus act as sphincters to

control passage of foodcontrol passage of food

Stomach Stomach (continued)(continued)

Interior Subdivided into: Interior Subdivided into: 1. Esophageal Region (non glandular; 1. Esophageal Region (non glandular;

compares to fore-stomaches in rum)compares to fore-stomaches in rum) large in horse, small in piglarge in horse, small in pig

2. Cardiac-gland region (sometimes 2. Cardiac-gland region (sometimes called gastric gland region)called gastric gland region)

large in pig, smaller in horselarge in pig, smaller in horse 3. ________________-gland region3. ________________-gland region 4. Pyloric-gland region4. Pyloric-gland region

Surface is folded into depressions or Surface is folded into depressions or gastric pits, increases surface areagastric pits, increases surface area

Horse Rabbit

Hindgut FermentersHindgut Fermenters Both Rabbit and horse are monogastricsBoth Rabbit and horse are monogastrics

Rabbit – Produce “hard” and “soft” fecesRabbit – Produce “hard” and “soft” feces Hard – “rabbit pellets”Hard – “rabbit pellets” Soft – material from _________ this is enclosed Soft – material from _________ this is enclosed

in mucous membrane that passes through the in mucous membrane that passes through the hindgut and is eaten by the rabbit as it hindgut and is eaten by the rabbit as it emerges from the anusemerges from the anus

Secrete gastric juice:Secrete gastric juice: Goblet cellsGoblet cells:: mucus. mucus. Parietal cellsParietal cells:: _____________________. _____________________. Chief cellsChief cells:: pepsinogen. pepsinogen. Pyloric (G cells):Pyloric (G cells): gastrin. gastrin. Stomach:Stomach: ______________________. ______________________.

Gastric GlandsGastric Glands

Chief cells secrete___________

Parietal cells secrete ________

HCl production is stimulated:HCl production is stimulated: Indirectly by ____________Indirectly by ____________

Makes gastric juice very acidic.Makes gastric juice very acidic. Makes proteins become more Makes proteins become more

digestible.digestible. Activates pepsinogen to pepsin.Activates pepsinogen to pepsin.

Pepsin is more active at pH of 2.0.Pepsin is more active at pH of 2.0.

HCl Production HCl Production (continued)(continued)

HCl FunctionsHCl Functions

Insert fig. 18.9

Digestion and Absorption in the Digestion and Absorption in the StomachStomach

Proteins partially digested by______.Proteins partially digested by______. Carbohydrate digestion by salivary Carbohydrate digestion by salivary

amylase is soon inactivated by acidity.amylase is soon inactivated by acidity. _______________________ are the only _______________________ are the only

commonly ingested substances commonly ingested substances absorbed.absorbed.

Parietal and chief cells impermeable Parietal and chief cells impermeable to ____.to ____.

Alkaline mucus contains HC0Alkaline mucus contains HC033--..

Tight junctions between adjacent Tight junctions between adjacent epithelial cells.epithelial cells.

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

___________________ inhibit gastric ___________________ inhibit gastric secretions.secretions.

Protective Mechanisms of Protective Mechanisms of StomachStomach

Small IntestineSmall Intestine Each villus is a fold in Each villus is a fold in

the mucosa.the mucosa. Covered with columnar Covered with columnar

epithelial cells epithelial cells interspersed with interspersed with goblet cells.goblet cells.

Epithelial cells at the Epithelial cells at the tips of villi are tips of villi are exfoliated and replaced exfoliated and replaced in crypt of Lieberkuhn.in crypt of Lieberkuhn.

Lamina propria contain Lamina propria contain lymphocytes, lymphocytes, capillaries, and central capillaries, and central lacteal.lacteal.

Insert fig. 18.12

Duodenum and jejunum:Duodenum and jejunum: Carbohydrates, amino acids, lipids, iron, Carbohydrates, amino acids, lipids, iron,

and Caand Ca2+2+.. Ileum:Ileum:

Bile salts, vitamin BBile salts, vitamin B1212, electrolytes, and , electrolytes, and HH220.0.

Absorption in Small IntestineAbsorption in Small Intestine(most absorption occurs here)(most absorption occurs here)

Small intestine

Microvilli contain brush border enzymes Microvilli contain brush border enzymes that are not secreted into the lumen.that are not secreted into the lumen.

Absorption requires both brush border Absorption requires both brush border enzymes and pancreatic enzymes.enzymes and pancreatic enzymes.

Intestinal EnzymesIntestinal Enzymes

Small intestine

Small intestine

PancreasPancreas

In close proximity to DuodenumIn close proximity to Duodenum Release proteases (__________ enzymes)Release proteases (__________ enzymes) __________________ (starch spitting)__________________ (starch spitting) Lipases (fat breakdown) + bicarbonate Lipases (fat breakdown) + bicarbonate

(buffer)(buffer) Opens into duodenum near the common Opens into duodenum near the common

bile ductbile duct

Outer surface bulges outward to form Outer surface bulges outward to form ____________..

Little absorptive function.Little absorptive function. Absorbs HAbsorbs H220, electrolytes, several vitamin B 0, electrolytes, several vitamin B

complexes, vitamin K, and folic acid.complexes, vitamin K, and folic acid. Intestinal microbiota produce significant Intestinal microbiota produce significant

amounts of folic acid and _________________.amounts of folic acid and _________________. Bacteria ferment indigestible molecules to Bacteria ferment indigestible molecules to

produce short-chain fatty acids. produce short-chain fatty acids. Does not contain villi.Does not contain villi.

Secretes __________, via active transport of Secretes __________, via active transport of NaCl into intestinal lumen.NaCl into intestinal lumen.

Large IntestineLarge Intestine

Small intestine:Small intestine: Most of the fluid and electrolytes are absorbed Most of the fluid and electrolytes are absorbed

by small intestine.by small intestine. Absorbs about 90% of the remaining volume.Absorbs about 90% of the remaining volume.

Absorption of Absorption of HH220 0 occurs passively as a result of occurs passively as a result of the osmotic gradient created by active transport.the osmotic gradient created by active transport.

Aldosterone stimulates NaCl and HAldosterone stimulates NaCl and H220 0 absorption in the ileum.absorption in the ileum.

Large intestine:Large intestine: Absorbs about ________ of the remaining volume.Absorbs about ________ of the remaining volume.

Absorption of HAbsorption of H220 occurs passively as a result 0 occurs passively as a result of the osmotic gradient created by active of the osmotic gradient created by active transport of Natransport of Na++ and Cl and Cl--..

Fluid and Electrolyte Absorption in Fluid and Electrolyte Absorption in the Intestinethe Intestine

DefecationDefecation

Waste material passes to the rectum.Waste material passes to the rectum. Occurs when rectal pressure _________ Occurs when rectal pressure _________

and external anal sphincter relaxes. and external anal sphincter relaxes. Defecation reflex:Defecation reflex:

Longitudinal rectal muscles contract to Longitudinal rectal muscles contract to increase rectal pressure.increase rectal pressure.

Relaxation of internal anal sphincter.Relaxation of internal anal sphincter. Excretion is aided by contractions of Excretion is aided by contractions of

abdominal and pelvic skeletal muscles.abdominal and pelvic skeletal muscles. Push feces from the rectum.Push feces from the rectum.

Structure of LiverStructure of Liver

Liver Liver __________________ internal organ. internal organ. Arranged into functional units Arranged into functional units

called called lobules.lobules. Plates separated by Plates separated by sinusoidssinusoids.. Secretes Secretes ________ ________ into bile canaliculi, into bile canaliculi,

which are drained by bile ducts.which are drained by bile ducts.

Structure of LiverStructure of Liver (continued) (continued)

Insert fig. 18.20

Products of digestion that are Products of digestion that are absorbed are delivered to the liver.absorbed are delivered to the liver.

Capillaries drain into the hepatic Capillaries drain into the hepatic portal vein, which carries blood to portal vein, which carries blood to liver.liver. ¾ blood is deoxygenated.¾ blood is deoxygenated. _____________ _____________ vein drains liver.vein drains liver.

Hepatic Portal SystemHepatic Portal System

Enterohepatic CirculationEnterohepatic Circulation

Compounds that Compounds that recirculate recirculate between liver between liver and intestine.and intestine. Many Many

compounds can compounds can be absorbed be absorbed through small through small intestine and intestine and enter hepatic enter hepatic portal blood.portal blood.

Insert fig. 18.22

Major Categories of Liver Function

The liver produces and secretes 250–1500 ml of The liver produces and secretes 250–1500 ml of bile/day.bile/day.

Major constituents of bile areMajor constituents of bile are Bile pigment (bilirubin) - also produced in the spleen and Bile pigment (bilirubin) - also produced in the spleen and

bone marrowbone marrow Bile saltsBile salts PhosholipidsPhosholipids __________________________________________________ Inorganic ionsInorganic ions

Bile Production and SecretionBile Production and Secretion

Metabolism of Heme and Metabolism of Heme and BilirubinBilirubin

Free ____________is not water solubleFree ____________is not water soluble Must be carried by______________________Must be carried by______________________ Bound cannot be filtered by kidneys or excreted Bound cannot be filtered by kidneys or excreted

by liver in bileby liver in bile Conjugated bilirubin – combined with Conjugated bilirubin – combined with

glucuronic acidglucuronic acid Enters intestine and converted by bacteria to Enters intestine and converted by bacteria to

urobilinogenurobilinogen Brown color to_____________________Brown color to_____________________ Absorbed by circulation = __________________ color to Absorbed by circulation = __________________ color to

urineurine

Metabolism of Heme and Metabolism of Heme and BilirubinBilirubin

Insert fig. 18.23

Jaundice

Bile Production and Secretion Bile Production and Secretion (continued)(continued)

Bile acids are Bile acids are derivatives ofderivatives of ___________.___________. Major pathway of Major pathway of

cholesterol cholesterol breakdown in the breakdown in the body.body.

Bile salts Bile salts micells micells FFA, FFA, monoglycerides, monoglycerides, cholesterolcholesterol diffuse across diffuse across

membrane.membrane.

Insert fig. 18.25

Major bile salts

BileBile Bile congregates to form Bile congregates to form ____________________

Nonpolar = central area – away from Nonpolar = central area – away from waterwater

Polar = outer area – loves waterPolar = outer area – loves water

Emulsify and allow for transport of Emulsify and allow for transport of cholesterol and other lipidscholesterol and other lipids

Production of bile from cholesterol is Production of bile from cholesterol is ________________ pathway of cholesterol pathway of cholesterol breakdown breakdown

Detoxification of the BloodDetoxification of the Blood

Liver can remove hormones, drugs, Liver can remove hormones, drugs, and other biologically active and other biologically active molecules from the blood by:molecules from the blood by: Excretion into the Excretion into the ________.________. Chemical alteration of the molecules.Chemical alteration of the molecules.

___________________is produced by ___________________is produced by deamination deamination of amino acids in the liver.of amino acids in the liver.

Liver converts it into urea.Liver converts it into urea. Excreted in urine.Excreted in urine.

Detoxification of the Blood Detoxification of the Blood (continued)(continued)

Inactivation of steroid hormones Inactivation of steroid hormones and drugs.and drugs.

Hydroxylation (addition of OH-) Hydroxylation (addition of OH-) groupsgroups Makes hormones more polar-excreted Makes hormones more polar-excreted

in urinein urine

Bile Production and Secretion Bile Production and Secretion (continued)(continued)

Triglycerides formed in epithelial Triglycerides formed in epithelial cells – encased in protein coat cells – encased in protein coat (chylomicrons) – enter lacteals(chylomicrons) – enter lacteals

All _________ is digested/absorbed in All _________ is digested/absorbed in upper part of small intestine.upper part of small intestine.

Secretion of Glucose, Secretion of Glucose, Triglycerides and KetonesTriglycerides and Ketones

Liver helps regulate blood glucose Liver helps regulate blood glucose concentration by:concentration by: Glycogenesis and lipogenesis.Glycogenesis and lipogenesis. Glycogenolysis and gluconeogenesis.Glycogenolysis and gluconeogenesis.

Contains enzymes required to Contains enzymes required to convert free fatty acids into _________ convert free fatty acids into _________ bodies.bodies.

Production of Plasma ProteinsProduction of Plasma Proteins

Albumin and most of the plasma Albumin and most of the plasma globulins (except immunoglobulins) globulins (except immunoglobulins) are produced by the liver.are produced by the liver.

Albumin:Albumin: Constitutes 70% of the total plasma Constitutes 70% of the total plasma

protein.protein. Contributes most to the ___________ osmotic Contributes most to the ___________ osmotic

pressure in the blood.pressure in the blood. Globulins:Globulins:

Transport cholesterol and hormones.Transport cholesterol and hormones. Inhibit trypsin.Inhibit trypsin. Produce blood clotting factorsProduce blood clotting factors

Sac-like organ attached to the Sac-like organ attached to the inferior surface of the liver.inferior surface of the liver.

Stores and concentrates bile.Stores and concentrates bile. When gallbladder fills with bile, it When gallbladder fills with bile, it

expands.expands.

GallbladderGallbladder

PancreasPancreas Exocrine:Exocrine:

Acini:Acini: Secrete Secrete

pancreatic pancreatic juice.juice.

Endocrine:Endocrine: Islets of Islets of

LangerhansLangerhans::

Secrete Secrete insulin and insulin and glucagon.glucagon.

Insert fig. 18.26

Contains HContains H220, HC00, HC033- - and digestive enzymes. and digestive enzymes.

Pancreatic JuicePancreatic Juice

Pancreatic JuicePancreatic Juice Complete Complete

digestion of food digestion of food requires action of requires action of both pancreatic both pancreatic and brush border and brush border enzymes.enzymes. Most pancreatic Most pancreatic

enzymes are enzymes are produced as produced as zymogenszymogens..

Trypsin (when Trypsin (when activated by activated by enterokinase) enterokinase) triggers the triggers the activation of other activation of other pancreatic pancreatic enzymes.enzymes.

Pancreatic trypsin Pancreatic trypsin inhibitor attaches inhibitor attaches to trypsin.to trypsin. Inhibits its activity Inhibits its activity

in the pancreas.in the pancreas.

Fig. 18.29

Neural and endocrine mechanisms Neural and endocrine mechanisms modify the activity of the GI system.modify the activity of the GI system.

GI tract is both an GI tract is both an ________________________ gland, gland, and a and a target target for the action of for the action of hormones.hormones.

Neural and Endocrine RegulationNeural and Endocrine Regulation

Gastric motility and secretion are Gastric motility and secretion are automatic.automatic.

Waves of contraction are initiated Waves of contraction are initiated spontaneously by pacesetter cells.spontaneously by pacesetter cells.

Extrinsic control of gastric function is Extrinsic control of gastric function is divided into 3 phases:divided into 3 phases: Cephalic phase.Cephalic phase. Gastric phase.Gastric phase. Intestinal phase.Intestinal phase.

Regulation of Gastric FunctionRegulation of Gastric Function

Cephalic PhaseCephalic Phase

Stimulated by sight, smell, and taste of Stimulated by sight, smell, and taste of food. food.

Activation of vagus:Activation of vagus: Stimulates chief cells to secrete Stimulates chief cells to secrete

__________________.. Directly stimulates G cells to secrete Directly stimulates G cells to secrete

gastringastrin.. Directly stimulates ECL cells to secrete Directly stimulates ECL cells to secrete

________________________________________ Indirectly stimulates parietal cells to Indirectly stimulates parietal cells to

secrete secrete HClHCl..

Arrival of food in stomach stimulates the Arrival of food in stomach stimulates the gastric phase.gastric phase.

Gastric secretion stimulated by:Gastric secretion stimulated by: Distension.Distension. Chemical nature of ___________(amino acids and Chemical nature of ___________(amino acids and

short polypeptides).short polypeptides). Stimulates G cells to secrete gastrin.Stimulates G cells to secrete gastrin. Stimulates chief cells to secrete pepsinogen.Stimulates chief cells to secrete pepsinogen.

Positive feedback effect.Positive feedback effect. As more HCl and pepsinogen are secreted, As more HCl and pepsinogen are secreted,

more polypeptides and amino acids are more polypeptides and amino acids are released.released.

Gastric PhaseGastric Phase

Gastric Phase Gastric Phase (continued)(continued)

Secretion of HCl is Secretion of HCl is also regulated by a also regulated by a negative feedback negative feedback effect:effect: HCl secretion HCl secretion

decreases if pH < decreases if pH < 2.5.2.5.

At pH of 1.0, At pH of 1.0, gastrin secretion gastrin secretion ceases. ceases.

Insert. Fig. 18.30

Inhibits gastric activity when Inhibits gastric activity when chyme enters the small intestine.chyme enters the small intestine.

Activates sensory neurons of Activates sensory neurons of _________ and produces an _________ and produces an inhibitory neural reflex:inhibitory neural reflex:

Inhibits gastric motility and secretion.Inhibits gastric motility and secretion. In the presence of fat, enterogasterone In the presence of fat, enterogasterone

inhibits gastric motility and secretion.inhibits gastric motility and secretion. Hormone secretion:Hormone secretion:

Inhibit gastric activity:Inhibit gastric activity: Somatostatin, CCK, and GLP-1.Somatostatin, CCK, and GLP-1.

Intestinal PhaseIntestinal Phase

Submucosal and myenteric plexuses Submucosal and myenteric plexuses contain 100 million neurons.contain 100 million neurons.

Include preganglionic Include preganglionic parasympathetic axons, ganglion cell parasympathetic axons, ganglion cell bodies, postganglionic sympathetic bodies, postganglionic sympathetic axons; and afferent intrinsic and axons; and afferent intrinsic and extrinsic sensory neurons.extrinsic sensory neurons.

Controls peristalsis and Controls peristalsis and segmentationsegmentation

Enteric Nervous SystemEnteric Nervous System

Paracrine Regulators of the Paracrine Regulators of the IntestineIntestine

Serotonin (5-HT):Serotonin (5-HT): Stimulates intrinsic afferents, which send impulses Stimulates intrinsic afferents, which send impulses

into intrinsic nervous system; and activates motor into intrinsic nervous system; and activates motor neurons.neurons.

Motilin:Motilin: Stimulates contraction of the duodenum and Stimulates contraction of the duodenum and

stomach antrum.stomach antrum. Guanylin:Guanylin:

Activates guanylate cyclase, stimulating the Activates guanylate cyclase, stimulating the production of cGMP.production of cGMP.

cGMP stimulates the intestinal cells to secrete ClcGMP stimulates the intestinal cells to secrete Cl-- and H and H220.0. Inhibits the absorption of NaInhibits the absorption of Na++..

___________________:___________________: May stimulate kidneys to secrete salt in urine.May stimulate kidneys to secrete salt in urine.

Intestinal ReflexesIntestinal Reflexes

Intrinsic and extrinsic regulation controlled Intrinsic and extrinsic regulation controlled by intrinsic and paracrine regulators.by intrinsic and paracrine regulators.

Gastroileal reflex: Gastroileal reflex: Increased gastric activity causes increased Increased gastric activity causes increased

motility of ileum and movement of chyme motility of ileum and movement of chyme through ileocecal sphincter.through ileocecal sphincter.

_____________________ reflex:_____________________ reflex: Distension of ileum, decreases gastric motility.Distension of ileum, decreases gastric motility.

Secretion of pancreatic juice and bile is stimulated by:Secretion of pancreatic juice and bile is stimulated by: ___________________:___________________:

Occurs in response to duodenal pH < 4.5.Occurs in response to duodenal pH < 4.5. Stimulates production of HC0Stimulates production of HC033

-- by pancreas. by pancreas. Stimulates the liver to secrete HC0Stimulates the liver to secrete HC033

-- into the bile. into the bile. __________________:__________________:

Occurs in response to fat and protein content of Occurs in response to fat and protein content of chyme in duodenum.chyme in duodenum.

Stimulates the production of pancreatic enzymes.Stimulates the production of pancreatic enzymes. Enhances secretin.Enhances secretin. Stimulates contraction of the sphincter of Oddi.Stimulates contraction of the sphincter of Oddi.

Secretion of Pancreatic JuiceSecretion of Pancreatic Juice

Digestion and Absorption of Digestion and Absorption of CarbohydratesCarbohydrates

Salivary amylase:Salivary amylase: Begins starch Begins starch

digestion.digestion. Pancreatic amylase:Pancreatic amylase:

Digests starch to Digests starch to oligosaccharides.oligosaccharides.

Oligosaccharides Oligosaccharides hydrolyzed by brush hydrolyzed by brush border enzymes.border enzymes.

Glucose is Glucose is transported by transported by secondary active secondary active transport with Natransport with Na+ +

into the capillaries.into the capillaries.

Insert fig. 18.32

Digestion begins in the stomach when pepsin Digestion begins in the stomach when pepsin digests proteins to form polypeptides.digests proteins to form polypeptides.

In the duodenum and jejunum:In the duodenum and jejunum: ____________________________________cleave peptide bonds in the cleave peptide bonds in the

interior of the polypeptide:interior of the polypeptide: Trypsin.Trypsin. Chymotrypsin.Chymotrypsin. Elastase.Elastase.

______________________________________cleave peptide bonds from the cleave peptide bonds from the ends of the polypeptide:ends of the polypeptide:

Carboxypeptidase.Carboxypeptidase. Aminopeptidase.Aminopeptidase.

Digestion and Absorption of Digestion and Absorption of ProteinProtein

Digestion and Absorption of Digestion and Absorption of Protein Protein (continued)(continued)

Free amino Free amino acids acids absorbed by absorbed by _____________________________with _____with NaNa++..

Insert fig. 18.33

Arrival of lipids in the duodenum Arrival of lipids in the duodenum serves as a stimulus for secretion serves as a stimulus for secretion of bile.of bile.

__________________________:__________________________: Bile salt micelles are secreted into Bile salt micelles are secreted into

duodenum to break up fat droplets.duodenum to break up fat droplets. Pancreatic lipase and colipase Pancreatic lipase and colipase

hydrolyze triglycerides to free fatty hydrolyze triglycerides to free fatty acids and monglycerides.acids and monglycerides.

Digestion and Absorption of Digestion and Absorption of LipidsLipids

Free fatty acids, monoglycerides, and Free fatty acids, monoglycerides, and lysolecithin leave micelles and enter lysolecithin leave micelles and enter into epithelial cells.into epithelial cells. Resynthesize triglycerides and Resynthesize triglycerides and

phospholipids within cell.phospholipids within cell. Combine with a protein to form Combine with a protein to form

chylomicrons.chylomicrons.

Digestion and Absorption of Digestion and Absorption of Lipids Lipids (continued)(continued)

In blood, lipoprotein lipase hydrolyzes In blood, lipoprotein lipase hydrolyzes triglycerides to free fatty acids and triglycerides to free fatty acids and glycerol for use in cells.glycerol for use in cells.

Remnants containing cholesterol are Remnants containing cholesterol are taken to the liver. taken to the liver. Form VLDLs which take triglycerides to cells.Form VLDLs which take triglycerides to cells. Once triglycerides are removed, VLDLs are Once triglycerides are removed, VLDLs are

converted to LDLs.converted to LDLs. LDLs transport cholesterol to organs and blood LDLs transport cholesterol to organs and blood

vessels.vessels. HDLs transport excess cholesterol back HDLs transport excess cholesterol back

to liver.to liver.

Transport of LipidsTransport of Lipids

Absorption of FatAbsorption of Fat

Insert fig. 18.36