physiology gi 1

8/8/2019 Physiology GI 1

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PHYSIOLOGY

GI SYSTEM


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Food composition

Proximateprinciples

Carbohydrates

Lipids

Proteins

Water

Otheressential components

Vitamins

Minerals


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Food composition

Carbohydrates

Lipids

Proteins


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Total Energy Requirement

Basal Metabolic rate+

Typeofwork


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Basal Metabolic Rate

BMR isthetotalnumberofcalories body requiresfor

normal bodilyfunctions (excluding activityfactors).

Thisincludes keeping heart beating, inhaling andexhaling

air, digesting food, making new blood cells, maintaining

bodytemperatureandeveryothermetabolic processin

the body.


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CalculateBMR

Harris-Benedictformula (BMR basedontotal body weight)

Men BMR = 66 + (13.7 X wtin kg)+ (5 X htin cm)- (6.8 X ageinyears)

Women

BMR = 655 + (9.6 X wtin kg)+ (1.8 X htin cm)- (4.7 X ageinyears)


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Activity Multiplier

1. Sedentary = BMR X 1.2 (littleornoexercise, desk job)

2. Lightlyactive = BMR X 1.375 (lightexercise/sports 1-3 days/wk)

3. Mod.active = BMR X 1.55 (moderateexercise/sports 3-5days/wk)

4. Veryactive = BMR X 1.725 (hardexercise/sports 6-7days/wk)

5. Extr.active = BMR X 1.9 (harddailyexercise/sports & physicaljob or2X daytraining, i.emarathon, contestetc.)


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Whatisyourobjective?

Fatloss : - 500

Maintenance : Keepsame

Weight gain: + 500


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Digestion

Digestionisaprocess wherebythe complexfood

materialis brokentosimplerformssothatit can

beabsorbedandutilized bythe body.

Food

material

Simpler

forms


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FunctionsofdigestivesystemFunctionsofdigestivesystemFunctionsofdigestivesystemFunctionsofdigestivesystem

Ingestion: getting foodintothe GI tract (eating)

Propulsion- moving foodalong thetracte.g.

swallowing andperistalsis (wave-likemotion)

Secretion: keysubstanceslikeacidetc


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Mechanicaldigestion- physical grinding and

churning offoodstuffsto breakdownand

exposetoenzymesandthesurfaceofthe GI

tract

Chemicaldigestion- breakdownoflarger

moleculesintoabsorbableparts byenzymaticaction


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Absorption- transportofdigestedmolecules,

vitamins, minerals, water, into blood

Defecation- eliminationofunusedfoodstuff

(feces)


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Four Major LayersofGI Tract

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa


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FourmajorlayersofGI Tract

Mucosa

Innermostlayer, whichlinesthelumen

Functionsincludeabsorption, secretion

Consistsofepithelium, typicallysimple columnar, often withgoblet cells

Submucosa

Deeptothemucosa

Madeupofconnectivetissue containing bloodandlymphatic vessels, lymphoidnodules, andnervefibres

Providesvascularsupplytomoststructuresofthe GI tractwall


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Four Major LayersofGI Tract

Muscularismucosa

Deeptothesubmucosa

Smoothmusclelayer responsibleforperistalsisandsegmentation

Aninner circularlayerandanouterlongitudinallayer

Serosa

Outermostlayeroftheintraperitonealorgans

Also know asthevisceralperitoneum


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PartsofD

igestivesystemKey parts

Mouth

Pharynx

Esophagus

Stomach

Small intestine Large intestine

Anus


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PartsofD

igestivesystem

Accessory organs

Teeth

Tongue

Salivary glands

Gallbladder Liver

Pancreas


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Mouth, Pharynx,

Esophagus


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Teeth

Humans usually have 20 primary teeth (also called deciduous,baby, or milk teeth) and 32 permanent teeth. Among primaryteeth, 10 are found in the (upper) maxilla and the other 10 in the

(lower) mandible.

Teeth are classified as incisors, canines, and molars.

In the primary set of teeth, there are two types of incisors,

centrals and laterals, and two types of molars, first and second.

All primary teeth are replaced with permanent counterpartsexcept for molars, which are replaced by permanent premolars.


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Teeth

Among permanent teeth, 16 are found in the maxilla with theother 16 in the mandible.

Central incisor

Lateral incisor Canine

First premolar

Second premolar

First molar

Second molar

Third molar: wisdom teeth

If any additional teeth form, for example, fourth and fifth molars,which are rare, they are referred to as supernumerary teeth.


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Teeth


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Salivary Glands

Threepairsofsalivary

glandssecretesalivainto

theoral cavity, where itismixed withfoodduring

mastication.

Parotid

Sub-mandibular

Sublingual


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CompositionofSaliva

Water (97-99.5%)

Electrolytes: Na+, K+, Cl-

Mucin- proteinthatformsthick, slimy

mucus

Salivaryamylase- starts breakdownof

carbohydrates

Other: IgAantibodies, Lysozyme


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Tongue

Coating ofsensors (dorsalsurface)fortaste, heat, pain,andtactileinformation

Muscularorgan

Tonguemusclesinsidethetongue, whichmakeupmostofthetonguemass, includethe Lingualisinferior,superior, transverse, andvertical.

Tonguemuscleslike Styloglossus, the Hyoglossus,Palatoglossus, Pharyngoglossus, and Genioglossusbeginoutsidethetongue withonlyterminalfibersinsideit, and controlitsmovement.


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Mechanical Processes

Mastication (chewing)

Cheeks, tongue, andteethinvolvedin both

voluntaryandinvoluntary grinding and

tearing offoodstuffs


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Mechanical Processes

Deglutition (swallowing)

Buccalphase (voluntary) Bolusforcedintooropharynx bytongue

Pharyngeal-esophagealphase (involuntary)

Tongue blocksoffmouth, softpalate blocksoff

nasopharyxandepiglottis blocksofftrachea Foodpropelledintoesophagus


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Roleofesophagus

Esophagus

Movesfoodtothestomach by Peristalsis


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Ifchewing notpossible

Rylestubefeeding

Parenteralfeeding: IVfluids

Gastrostomyfeeds: feedingtubethroughtheskinandthe

stomach wall, directlyintothestomach.


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Collectinformation


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Roleofstomach


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Gastric Movements

Proper

digestion

requires

coordinated

movements

ofthe

stomachandintestines


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Gastric Movements

Loweresophagealsphincter (LES /Cardiac sphincter)

Junctionofesophagusandthestomach

Mainfunctionofthesphincteristhepreventionof

refluxfromthestomachintotheesophagus.


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Gastric Movements

Peristalsis: Theperistaltic waves beginhighupon

thefundus, aboutthreetimesaminuteandpassinggentlytowardsthepylorus. Peristalsishelpsin

propelling thefoodahead.

Churning: Processofmixing offood


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Gastric Movements

Pyloric Sphincter (Pylorus)

Junctionofstomachandduodenum

Thedistinctivefeaturesofthepylorusisverynarrow

lumen whichensuresthatonlysmallsizeparticlesleavethestomach.


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Gastric Movements

Gastric emptying

Gastric emptying requires coordination between

theantralperistaltic wavesandduodenalmotility

toensureefficientmovementofthenutrientsinto

theduodenum.


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ACID SECRETION

AT A GLANCE


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Acidsecretion

Typesofsecretoryepithelial cellsinstomach

Mucous cells

Parietal cells

Chiefcells

G cells


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Acidsecretion

Typesofsecretoryepithelial cellsinstomach

Mucous cells Secreteanalkalinemucusthat

protectstheepitheliumagainstshearstressandacid

Parietal cells Secretehydrochloric acid

Chiefcells Secretepepsin, aproteolytic enzyme

G cells Secretethehormone gastrin


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Stimulusforacid release

Histamine Acetyl choline Gastrin

Parietal cell

Acid release


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Stepsinacidsecretion

STEP 1: Hydrogenionsare generated withinthe

parietal cellfromdissociationofwater. Thehydroxylionsformedinthisprocess rapidly

combine with carbondioxidetoform bicarbonate

ion, a reaction cataylzed by carbonic anhydrase.


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STEP 2: Bicarbonateistransportedoutofthe

basolateralmembraneinexchangefor chloride.

ThisprocessservestomaintainintracellularpH

intheparietal cell.


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STEP 3: Chlorideandpotassiumionsaretransportedintothelumenofthe cannaliculus byconductance channels, whichisnecessaryforsecretionofacid.


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STEP 4: Hydrogenionispumpedoutofthecell, intothelumen, inexchangeforpotassiumthroughtheactionoftheprotonpump;potassiumisthuseffectively recycled.


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Gastric

lumen

Basolateral

Membrane

Histamine Acetyl cholineGastrin

Parietal

cell H2O + CO2= H+ + HCO3-

K+

HCO3-

Cl-

Cl-H+

Cl-

H+K+ ATPase (Protonpump)

HCO3-

Cl-

H+K+


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Acidsecretion

Fasting stomachsecretes gastric juiceatthe rateof10-60 mlperhour (Basal Output).

Mealtimesecretionof500 mlto 1000 ml- startsimmediatelyafterfood; reachesitsmaximumafter 1 to2hours, and graduallydeclinestofasting levelafter 3 to 4 hours. (Maximal Output).

Gastric juiceisacidic;itspH ranges between 0.9 to1.5.


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Canstomach bearthisacid?

Theepitheliumofthestomachisintrinsically resistant

tothedamaging effectsofgastric acidandotherinsults.

+

Mucinproduction (Protective)


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Neurological controlof GIT

Autonomic

nervoussystem

Parasympathetic nerves

Sympathetic nerves

Enteric nervous

system

Nervoussystemofgastrointestinal

tract

Central control Centers withinthemedullaoblongata

Higher brain centers

Gastrointestinalmotilityandsecretionsare

controlled bythenerves withinthe GIT.


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Autonomic Nervous System

Parasympathetic nerves: Role

Stimulationofnerve causessmoothmusclecontractionandthesecretionofdigestive juices.

Sympathetic nerves: Role

Reducessmoothmuscle contractionand

glandularsecretion.


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Enteric Nervous System

Liesentirelyinthe wallofthe gastro-intestinaltract,

beginning intheesophagusandextending allthe

waytotheanus.

Control

Movements

Control

Secretions


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Roleof Neurotransmitters

Acetylcholinemostoftenexcites gastrointestinal

activity.

Norepinephrinealwaysinhibits gastrointestinal

activity.

Other keyneurotransmittersin GIT include

dopamine.


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Thank You.

physiology gi 1

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