week 10 Flashcards
Digestive system
Steps in digestion
- Ingestion 2.Mechanicalprocessing 3.Digestion
- Secretion
- Absorption
- Excretion
Mechanical digestion
- Segmentation
* Constantstirringandmixing •NBforwardmovementviaperistalsis(weakerandslowerhere
Chemical digestion
- ENZYMES!!!
- Catabolicprocess–itisnecessarytobreakthe fooddowninto‘bits’smallenoughtobe absorbedacrosstheintestinalepithelium
Enzyme
“Aproteinthatcatalysesaspecificbiochemicalreaction”
Large interstine
- Reabsorptionofwater
- Reabsorptionofbilesalts •Absorptionofvitaminsproducedbybacteria •Absorptionoforganicwastes(generatedbybacteria)
- Peristalticwaves
Thedefecationreflex
Two positivefeedback loops
1.Short reflex (local)
•Triggers peristaltic contractions in rectum
2.Long reflex (PSNS –reflex through spinal cord) •Coordinated by sacral parasympathetic system •Stimulates mass movement
Digestive tract
- Digestivetractakagastrointestinal(GI) tractoralimentarycanal
- Musculartube
- Extendsfromoralcavitytoanus •Passesthroughpharynx,esophagus,stomach,andsmallandlargeintestines
Role of the GIT
- Largeorganic masses
- smallerparticles
- fuel
- Digestsand absorbsfood
- ACATABOLICprocess
Functions of the GIT
- Ingestion–foodintomouth
- Digestion–breakingfoodintoeversmallerbits •Mechanical(chewing,mixing,churning,segmentation) •Chemical(enzymes…catabolism)
- Secretion–intotheGIT
- Absorption–endproductintobloodorlymph
- Defecation–elimination/excretion
- Motility/Propulsion‐movingthingsalong
- Defence–againstGITcontents,mechanicalstress,potential pathogens
Movement of digestive materials
- By muscular layers of digestive tract
- Along digestive tract –Rhythmic cycles of activity –Controlled by pacesetter cells
- Cells undergo spontaneous depolarization –Triggering wave of contraction through entire muscular sheet
Peristalsis
– Consists of waves of muscular contractions
– Moves a bolus along the length of the digestive tract
Segmentation
– Cycles of contraction
•Churn and fragment the bolus
•Mix contents with intestinal secretions
–Does not follow a set pattern
•Does not push materials in any one direction
Functions of oral cavity
•Sensoryanalysis
–Ofmaterialbeforeswallowing
•Mechanicalprocessing
–Throughactionsofteeth,tongue,andpalatalsurfaces •Lubrication
–Mixingwithmucusandsalivaryglandsecretions •Limiteddigestion
–Ofcarbohydratesandlipids
Saliva
Composition
- 99.4%water
- 0.6%includeselectrolytes(Na+,Cl‐,andHCO3‐),buffers,glycoproteins (mucins),antibodies,enzymes,wasteproducts
Functions
–Cleaning‐continuouslyflushesoralsurfaces
–Protection
–buffers,antibodies,lysozyme
–Lubricatingthemouth
–Moisteningandlubricatingmaterialsinthemouth
–Dissolvingchemicalsthatstimulatetastebudsandprovidesensory information
–Initiatingdigestion‐salivaryamylase,linguallipase(?)
Oesophagus
•Fromlaryngopharynxtostomach •Piercesdiaphragm“oesophagealhiatus” •Joinsstomachatthecardiacorifice •Glandsinsubmucosasecretemucus
•Muscularis
–skeletal‐superiorly
–smooth‐inferiorly