Lecture 1 Flashcards
What does the GI tract add to a meal? Why?
Water, ions, enzymes to create an aqueous solution of molecules suitable for absorption and transport around the body.
How much does the daily oral intake, combined with salivary, gastric, biliary and pancreatic secretions contribute to the fluid that enters the upper gastrointestinal tract each day?
8.5L
What is the daily faecal fluid excretion amount?
Less than 150 mL
What is the net absorption of the GI tract?
> 8L per day
Where does 90% of the net absorption occur in the GI tract?
Small intestin
What is the max amount of water the colon can absorb?
2 to 3 L a day
What are gut commensal bacteria?
Bacteria that live in the gut and are important for gut health
How many bacteria are within the gut?
Trillions, large numbers diverse species
Describe the variation of the gut bacteria
Vary widely between individuals, but stay fairly constant within an individual unless exposed to various stresses in the gut.
What are the protective functions of gut bacteria?
Barrier:
- Competes against growth of pathogenic organisms
- Influences expression of genes on intestinal epithelium
- Regulates permeability of tight junctions
Immunity
- Drives IgA production
Describe the tolerance of the immune system to gut bacteria
The immune system is tolerant towards commensal bacteria and non-harmful antigens. Problems with this tolerance lead to allergies and inflammatory bowel disease.
What happens to the undigested carbs that enter the colon?
Fermented by commensal bacteria, producing short chain fatty acids. Flatus is a by-product.
What are short chain fatty acids an important source of?
Energy and nutrients
Why might some people suffer more from bloating and distension?
Certain types of gut flora will produce certain types of fatty acids, which produce gas as a by-product.
How can gut microbiota influence metabolism?
Certain compositions of gut microbiota may produce favourable SCFA’s that have a positive effect on metabolism, leading to increased chance of obesity and diabetes.
How can inflammation alter the normal flora balance?
An individual who has had severe gastroenteritis may develop post-infectious irritable bowel syndrome. This is when there is a disturbance in the balance of the gut flora and as a result, the individual is left with this imbalance after infection.
How can antibiotic use alter normal flora balance?
- Can lead to antibiotic associated diarrhoea
- Can cause Clostridium difficile infection
What are the two main causes of the alteration of normal flora balance?
Inflammation and antibiotics
Describe how Clostridium can infect the gut
Clostridium is a bacterium that in healthy people, does not tend to be pathogenic, but in people who are immunosuppressed or elderly, who then take courses of antibiotics, healthy bacteria is suppressed and Clostridium is allowed to proliferate, causing diarrhoea and infection.
What is the role of probiotics?
To restore the balance of gut flora
What does the gut have for physical protection?
- Tight junctions reduce the permeation of large molecules through the gut.
- Mucus secreted by goblet cells provide lubrication and a barrier.
How does the immune system protect the gut?
IgA IEL's Defensins/Paneth cells M cells and Peyer's patches Macrophages Mesenteric lymph nodes Innate immune system
How do Paneth cells protect the gut?
Secrete lysozymes that have anti-bacterial effect
What are the 2 roles of gastric acid?
Sterilise food
Initial digestion
What is achlorhydria?
Absence of acid
What is the only bacteria known to survive in the stomach?
Helicobacter pylori
What are the two ways in which the GI nervous system can work? What are the consequences of this?
Both independently and in conjunction with the brain. Symptoms such as bloating or diarrhoea may be linked to the brain (e.g. nervousness) but peristalsis is independent.
What do the sensory neurones in the GI tract sense?
Mechanical and chemical conditions
List the sensory neurones for the oesophagus, stomach, duodenum, and jejunum
Oesophagus: chemoreceptors
Stomach: release of 5HT
Duodenum: CCK - satiety/fullness
Jejunum: mechanoreceptors “stretch”
What do motor neurones in the gut control?
Motility, fluid exchange, gastric/pancreatic secretion, local blood flow
Describe the modulation of gut sensitivity.
- Hypersensitivity and hypervigilance
- Emotional state affects gut function
What does enhancement of the gastrocolic reflex lead to?
The urge to go to the bathroom after eating
How is food intake regulated?
Appetite and satiety
Ghrelin, Cholecystokinin, leptin
What does regulation of a meal require overall?
GI hormones and neural control
What GI hormones are required for regulation of a meal?
Endocrine - Enteroendocrine cells - gastrin, CCK, leptin - Apical portion of cells sampling lumen Paracrine - Somatostatin
How is the meal regulated by neural control?
- Vagal afferents and efferents
- Enteroenteric reflexes
- Cephalic, gastric and duodenal phases
What are the key gastointestinal functions?
Digestion - primary role of pancreatic and biliary secretions
Absorption - surface area increased by folds, villi, and microvilli
Excretion
What is the normal percentage of water in stool? What is the normal volume and weight?
65-80% water
Volume: less than 200mL
Weight: less than 200g
What is the central role of the liver?
Blood from the gut passes through liver before reaching systemic circulation
Detoxification role
Central role in metabolism (lipid metabolism, glucose homeostasis)
What is an endoscope?
Flexible telescope with camera, lens, and light. For visualising GI tract internally.
What are the changes that occur at the gastro-oesophageal junction? What irregularities can occur?
Squamous mucosa (white and pale) becomes columnar mucosa (darker). Normally, this gives a circular pattern. If it is not circular, this is irregular and could indicate Barrett’s oesophagus
How is the duodenum described endoscopically?
Duodenal cap and second part of the duodenum
What is the major duodenal ampulla?
WHere the bile duct and pancreatic duct drain into the small intestine to release biliary and pancreatic secretions
What sits next to the ileocecal valve?
Appendiceal orifice
What are diverticula of the colon? What can they cause?
Pockets that form in the colon wall as a result of wear and tear typically in older people. Can result in constipation which is called diverticulosis. If stool gets trapped in diverticula and causes infection and inflammation, diverticulitis occurs.
What do colonic polyps increase the risk of? What is done to reduce this risk?
Increase the risk of colon cancer. Can be removed at the time of endoscopy to prevent development of colon cancer.
What are the pathways to colon cancer?
Cumulative somatic mutations: APC
Hereditary nonpolyposis colorectal cancer
Hypermethylation
How is iron absorption tested for?
Test for CYS282. Abnormal iron levels may be caused by haemochromatosis.
How is coeliac disease tested for?
Tests for HLA susceptibility genes DQ2 and DQ8
