Large Intestine Flashcards
What is the structure of the large intestine?
Four layered wall
What is the function of the large intestine?
Absorption (water and electrolytes out of colon into blood volume
Defecation
DIgestion (b vitamins and vitamin K)
What epithelium is the large intestine?
Stratified squamous epithelium
How is the large intestine unique?
Chief parietal cells
What is the enteric nerve supply of the large intestine?
Intrinsic nerves that supply the caecum -> anal canal
Consists of submucosal and myenteric plexuses
What is the parasympathetic nervous supply of the large intestine?
CNX vagus until the left colic flexure
Pelvic splanchnic nerves S2-4 supply the remainder
What is the sympathetic nervous supply of the large intestine?
Abdominopelvic splanchnic nerves T10-L2
Is the large intestine supplied by visceral afferent fibres?
Yes
What supplies the anal canal inferior to the pectinate line?
Somatic motor and sensory from pudendal nerve S2-S4
- Sensitive to pain, touch, temperature
What is the digestive role of the large intestine?
Enteric bacteria ferment some indigestible carbohydrates and mucin (component of mucus)
Produces short-chain fatty acids (absorbed)
Fermentation also produces gases (-500ml/day) e.g. CH4 dimethyl sulfide
Bacteria also involved in vitamin synthesis e.g. B, K
What is the role of the large intestine in absorption?
Most remaining water, electrolytes (largely NaCl) vitamins produced by bacteria
What is the role of the large intestine in propulsion?
Haustral contractions and mass movement propel faeces towards rectum
Passage eased by mucous (globlet cells)
What is the last role of the large intestine?
Defecation
What is the arterial supply of the large intestine?
Branches of the superior mesenteric artery
- Caecum and appendix
- Ascending colon
- Part of the transverse colon
Branches of the inferior mesenteric artery
- Part of the transverse colon
- Descending, sigmoid, rectum
What is the venus drainage of the large intestine?
70% via portal vein –> liver
Tributaries of the superior mesenteric vein
- Caecum and appendix
- Ascending and transverse colon
Tributaries of the inferior mesenteric vein -> splenic vein
- Descending, sigmoid colon, rectum
What are varicose veins in the rectum referred to?
Haemorrhoids
What are three features unique to the colon?
Teniae coli
- Longitudinal m. layer of the mscularis is arranged as three separate, thickened bands
- Extend from caecum to beginning of rectum
Haustra
- Muscular tone puckers colonic wall into pocket-like sacs called haustra (segmented appearance)
Omental (epiploic) appendices
- Small, fatty projections of the omentum that hang from the surface of the colin
What type of mucosa is found in the large intestine?
Simple columnar epithelium
What is the difference between large intestine and small intestine?
Large intestine does not have: circular folds, villi or brush border
What does the large intestine have that the small intestine and stomach do not?
Goblet cells
What is the role of goblet cells in the large intestine?
For protection against pathogens and helps faeces move through
Yellowy white and stringy
What is special about the stomach?
Inner oblique layer
What is special about the small intestine?
Villi and microvilli
What is special about the large intestine?
Goblet cells
What is dysbiosis?
Maladaptive imbalance of microbiome
What is a microbiome?
Genetic material of all the cells in the microbiota
What happens to the microbiota when the environment is too acidic?
Hard for biome to colonise in the stomach and small intestine
What is the relationship of mother to baby during birth and breastfeeding in regards to microbiome?
Natural birth passes on mother’s microbiome
Breast milk = microbiome from mother = antibodies
Where is the microbiome most abundant?
In large intestine
What factors impact the ability of microbiota to have stable colonisation?
Acidic environments
Bile
Pancreatic juice
Peristalsis
What are factors that contribute to an individual’s microbiota?
birth mother’s health
Birth vaginal/caesarean
Infant milk
Rural/urban living
Diet
Medications
Stress levels
Smoker
What constitutes a health gut microbiome?
Diverse range of good bacteria
Stability of microbiome = “good” bacteria keep “bad” bacteria in check
Resistance to stress related change (e.g. antibiotic, infections)
What vitamins are the gut microbiome important for digesting?
Synthesis of B vitamins and vitamin K
What are the main roles of microbiota?
Synthesising vitamins
Processing/digesting complex polysaccharides
Synthesis of essential amino acids
Glucose and cholesterol metabolism
Why has research exploring the gut microbiome and health grown in recent years?
Increased availability and decreased costs of gene sequencing
What diseases can be caused by disturbances/imbalances of the gut microbiome?
Inflammatory bowel disease
IBS
Diabetes
RA/AS/Psoriatic arthritis
