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Gastrointestinal system
02 April 2017

21:14

Function
Primary functions:
• Regulate intake of food and h2o - partly by gut- appetite, thirst
• Conversion food -> nutrients - strut of gut -break -> components absorbed across gut wall
• Absorptions of nutrients & h20- across gut wall -> circulation
• Energy store- intermittent eating- store as can't digest all at once
• Excretion of waste products- substances don’t want - out body ->bile -> GI tract -> faeces
• Protect against bact & toxins- stomach 1st line defence
Processes:
 Sensory inputs: appeptitie, taste, smell, sight - from food in GI tract & b4
...
Across gut
 Secretion, absorption & excretion - across lining GI tract
 Regulation by nerves hormones (by ANS, by GI tract) & local factors (reflexes)

Enteric Nervous System
- Subdivision of ANS
- Self-contained NS
 Autonomic nerves w/in gut, w/ ganglia (collection nerve cell bodies) @ myenteric & submucosal
plexus
 Control smooth musc contraction & exocrine/endocrine gland secretions
 Regulated by symp & para nerves & sensory reflexes- baroreceptors - feedback using stretch ->
enteric NS - can signal to symp & para
Sensory reflexes-higher p
...
funct
...
Externa
Submucosal plexus - nerve cell bod - nerves control secretion from submucosa-> lumen of GI tract

Control gut motility
 Interstitial cells of Cajal (pace-setter cells) - can depolarize -> change memb pot
...
To
smooth muscle cells next to it, smooth muscle cells joined by gap junctions - if dep 1/2 - will
spread to all connected
 Specialised smooth muscle cells
 Pace maker activity
 Det
...
of slow waves of gut contraction - imp as Irritable bowel syndrome if cells abnormal
Stim para NS -ots spikes, stronger signal
Pace setter cells give small dep
...
AP
If get up to threshold for AP - spike pot
...
Oral cavity, teeth, tounge- mechanical processing,
some chem
...

2
...
Oesophagus- transp mat-> stomach- deliver bolus food
down
4
...
down mat via acid &enz
...
Small intestine- enz digest & absorp
...
Large intestine- dehydration and compaction of
indigestible mat in prep for elimination -cecum, colon
Accessory Organs of Digestive Tract
Facilitate digestion food- food not pass through it
1
...
Liver
3
...
Pancreas - make enz
...
Tiss
...
Around outsidecontact & change SA
Submucosa
❖ Loose conn
...

❖ Exocrine glands- make enz
...


Initial stages of digestion
 Mechanical b
...
down food- amylase (breakdown carbs) and lipase (breakdown fats to trigly) in saliva
 Swallowing reflex to move bolus -> pharynx and oesophagus - voluntary w/ skeletal musc

Gastric- when food in stomach
 Sensory input from -stretch, chem, Ph change , peptides
from food
 Mediated by parasym & enteric nerve reflexes , hormones
(gastric)

Sensory input from food- provide cephalic phase
 Chem stim of olfactory receptors in nose and taste buds in tounge

Intestinal Food in intestines
 Sensory input from food- strech, chem
 Mediated by para and enteric nerve reflexes, hormones
(secretin, cck)
- Try to inhibit gastric acid production

Food and air pass at pharynx - food then to oesophagus

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Nasal cavity and olfaction
Olfaction- sensation of smell
Detect odorant prot produced by food
• Cilia embedded in mucus
• Olfactory epithelium - end of axons into brain
• Sensory receptors - constantly regen
...

• Stem cells
• Only nerve cells to regenerate
Salivary Glands
Sensory inputs cause saliva production
Functions of saliva

- Try to inhibit gastric acid production
- Change mot & secret so intestinal not stomach

Tongue and gustation
○ Gustation - sensation of taste
○ Primary taste sensations- sweet, salty, sour, bitter, umami (detecting glutamate), water -taste
buds
○ Secretion of lingual lipase- breakdown fat
○ All papilla recognise all tastes
○ Lots regions rough surfaces
○ Thick epithelium
○ Papilla have diff anatomies/clusters of taste buds
• Short form receptors embedded in stratified epithelium of papilla- respond to molec in food
• Taste nerves detect neurotransmitters

1
...
down cell wall bact
Lactoferrin- attach iron bact need to function
Thiocyanate
Antibodies (lgA)

2
...
a
...
Facilitates speech and taste - dissolve substance-> saliva to get to taste
buds

Help mucous drain ->
ducts

produced by diff cell types
Serous: watery secretion cont
...
mucous & other glycoproteins- sticky

Submandibular: 70% serous & mucous, mostly serous - under jaw
Parotid: 25% entirely serous -in cheeks
Sublingual: 5% mucous & serous, mostly mucous -under tongue
Lots of tiny glands all over body
Secretions->oral cavity
Duct where secretions empty out

Acini drain -> duct -> bigger ducts -> oral cavity
Primary secretion:
• Na, K, Cl, HCO3 - actively transport from blood across cell -> lumen
• Iso-osmotic to plasma - water can follow the electrolytes

Control Saliva Secretion
Entirely Nervous control- ANS

Para nerves
○ Cephalic phase, sensory inputs b4 & during eating
○ Large vol aqueous saliva rich in amylase
○ ↑ rate primary secretion via ion transport & enz release
○ Contrac of myoepithelial cells (outside acini)
○ ↑ salivary blood flow by vasodilation- deliver more substrates
Symp nerves
○ Anxiety, fear, exercising
○ Small vol viscous saliva rich in mucous -sticky
○ Cont myoepithelial
○ ↓ salivary blood flow by vasoconstriction - blood needed elsewhere

Oesophagus
❖ Transport food oral cavity -> stomach
❖ Mucosa & sub-mucosa folds to accommodate bolu
❖ Stratified squamous epothelium to protect oesophagus- don’t damage it
from rough food , lots layers to protect (more than 1 cell thick unlike
others)
❖ Skeletal muscle (upper regions) in muscularis propria layer to facilitate
swallowing- voluntary
❖ Need have ability distend & expand

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Don’t want lose Nacl here so reabsorbed further down (ductal cells) and khco3 is
secreted to give more alkaline pH
Vesicles of enz - release on primary activation
Final Secretion
• Less Na & Cl, more K & HCO3
• Hypo-osmotic to plasma (more dilute)
Pavlov
 Anticipatory response
 Classical conditioning
 Feed-forward mechanism
 Saliva response to presence food
 -> introduce ringing bell (association)
 -> saliva response to ringing bell alone - para nerves stim by bell now
 Conditioned reflexes in absence food
 Efficient way get ready for food



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