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Flashcards in Lecture 1 Deck (22):

Luminal organs

Small and Large intestine


Hepato-bilary system

Gall bladder


Reffered pain

GI tract, depending on where pain originates from, it is referred to different areas because visceral pain felt by gut, is often is same pathway as somatic nerves.
-often tend to correlate with dermatomes
-generally tends to be felt in the Upper, Mid or Lower Abdomen


T8-9 Referred Pain

Heart + Aorta



Small bowel
Ascending colon to mid transverse Testis
Renal Tract


T12-L1 Referred Pain

Large Bowel
Prostate (male) or Uterus+Adnexa (female)


Gut Barrier function

barrier against foreign invaders (bacteria, pathogen)
Lubrication - goblet cells release mucous (barrier/prevent bacterial permeation)
Immune cells form gut barrier
Epithelial cells: Goblet-mucous secretion, Paneth cells-protective enzymes. Tight junction-less permeation of large molecules through.
Deeper: Immune cells (T and B) + Lymphoid follicles


Role of gastric acid

1. Sterilize food (gut exposed to external triggers/factors that are potentially harmful)
2. Initial digestion
3. Only bacteria known to survive in stomach (Helicobacter Pylori-pathogen causing stomach ulcers)


Gut Microbiota

Commensal Bacteria/Gut flora- live in gut and good for gut health- probiotics
Large numbers(trillions), diverse species
Most cannot be cultured/identified (due to be so diverse)
Vary widely between individuals (dont have identical type of gut bacteria) , but stay fairly constant within an individual (unless exposed to gut stresses)
Stomach + DJI (proximal+distal) + Colon


Order and Distribution of Gut Microbiota

Stomach: 0-10^2 (fairly sterile)
Duodenum: 10^2
Jejunum: 10^3
Prox. Ileum: 10^3
Dist. Ileum: 10^7 -10^9
Colon: 10^11-10^12 (highly populated w. bacteria)
-gut bacteria predominantly lives in colon. has regulation in determining symptoms in some people


Protection against pathogens re barrier function

1. Competes against growth of pathogenic organisms (important as gut is exposed to large number of pathogens, therefore needs to be able to protect itself)
2. Influences expression of genes on intestinal epithelium (certain cells promoted to increase, depending on state of gut flora)
3. Regulates permeability of tight junctions (selective permeability)
-mucosal barrier
-has gut flora, which protects invasion of foreign organisms (competes against foreign pathogens)


Protection against pathogens re balance of both Immunity + Tolerance

1. Complex inter-relationship
2. Multiple components of the gut and systemic immune system
3. Drives IgA production
4. Tolerance to commensal bacteria and to non-harmful antigens (allergies, inflammatory bowel disease) (exposed to a number of foreign pathogens, but doesn't illicit immune response against all these organisms)
-degree of tolerance important, w. loss of tolerance develop diseases (inflammatory bowel disease) and allergies (celiac disease) (must protect and tolerate BOTH otherwise will be constant state of inflammation - Immunity and Tolerance balance)
-balance of immunity and tolerance is an important driver of diseases


Effects on Metabolism

Undigested carbohydrates that enter colon are fermented by commensal bacteria, producing short-chain fatty acids (acetate, propionate, butyrate)
-Flatus is a bi-product (gas) --> driver of irritable bowel syndrome (component driven by gut bacteria)
SCFAs source of energy/nutrients for bowel
-gut flora from obese mouse put into skinny mouse will make skinny mouse obese
Certain compositions of gut microbiota may produce favourable SCFAs that have positive effects on metabolism (obesity, diabetes) - individuals produce different SCFA, hence why some people suffer from certain symptoms (bloating and distention) whilst other people dont


Alterations in normal flora balance

1. Inflammation: e.g. patient w severe gastroenteritis may develop post-infectious irritable bowel syndrome- inflammation has disturbed balance of gut flora, even after infection, causing persistent symptoms
2. Antibiotic use: (esp chronic use)
-Antibiotic-associated diarrhoea (can cause a number of GI symtoms including diarrhoea)
-Clostridium difficile infection. Clostridium is bacteria that isnt normally pathogenic in healthy people. But in the elderly or immunosuppressed people who take antibiotic courses, antibiotics suppress normal healthy gut flora, clostridium proliferates, causing diarohea and infection
Role of Probiotics: reintroduction of health bacteria to cure these disturbances


Key GI functions

Absorption: min, nutrients and vitamins
Role of Liver



rough break down of food into small molecules
Gastric acid
Pancreatic and Biliary secretions



Nutrients need to be absorbed into gut so can enter/transported into circulation
Small intestine's prominent role
Surface of small bowel increased by:
1. Folds
2. Villi (finger like projections)
-eptihelial cells
3. Microvilli



Waste products + Fluid
Normal stool is 65-80% water
Normal stool volume


Fluid Balance

alot of the fluid is produced by the gut, but is reabsorbed again, otherwise would have diarohea
GI tract adds water, ions, enzymes to a meal
Creates (the meal into )an aqueous solution of molecules suitable for absorption (more easily) and transport around the body
-after absoprtion, must be inbalance with what is secreted (what gut releases has to be mostly absorbed, otherwise is manifested as diarohea)
-Daily oral intake combined with salivary, gastric, biliary and pancreatic secretions contribute a total of approx. 8.5L of fluid that enters the upper gastrointestinal tract each day (all has to ba absorbed as only exretion is 150ml)
-Daily faecal fluid excretion is normally less than 150mL
-NEt absorption >8L/day (mainly occurs in small bowel, even though Colons main role is to absorb fluid)
-More than 90% of this net absorption occurs in the small bowel
-Colon unable to absorb >2 to 3L/day (instead majority of fluid absorption occurs in small intestine)


Normal situation

1. Fluids IN (mL)
– Oral ingestion 2000 (1/4 ingestion)
– Salivary 1000
– Gastric acid 1500
– Pancreatic 1500
– Biliary 1500
– Intestinal 2000
• TOTAL 8500 (8.5L)

2.Absorption (mL)
– Small bowel 7000-8000
– Colon 600-1000

3. Fluids OUT (mL)
– Stool volume 100-150


GI tract as highly integrative process

Integrae rpocess- things working simultaneously
Enteric nervous system (sophisitically)
– Can work both independently and in conjunction with the brain - drive symptoms in Functional conditions (IVF: bloating abdominal cramps. Anxious or nervous tend to have more GI symptoms: butterflies in tummy/diarrhea before public speaking- shows how brain can effect gut function)
-Independant peristalsis for food propogation
– Sensory neurons
• Sense mechanical (stretch) and chemical conditions (changes)
-doesnt sense pain traditionally. stretching of bowel/bile duct causes pain, basis of diseases such as biliary colic
– Motor neurons
• Motility
• Fluid exchange
• Gastric / pancreatic secretion
• Local blood flow (regulates blood flow and secretions of various hormones)
1. Enhanced Gastrocolic reflex: e.g. of enteric communicating with gut. toilet after meal. stomach is distended by meal and sends reflex to colon stimulating colon to move
2. Gut-brain connection


Integrate response to meal - GI hormones and vagal nerve

Regulation of food intake - appetite and safety
– ghrelin,CCK,leptin
• Regulation of meal requires
– GIhormones
• Apical portion of cells
sampling lumen
• e.g. gastrin, CCK, somatostatin
– Neural pathways
• Vagal afferents and
• Enteroenteric reflexes
• Cephalic, gastric and duodenal phases