L11 - Intestines Flashcards
Jejunual artery
Located in left upper quadrant
Thick intestinal walls
Longer vasa recta (straight arteries)
Less arcades (arterial loops)
Ileal artery
Located in lower right quadrant
Thin intestinal walls
Shorter vasa recta
More arcades
Right colic artery
Ascending colon
Middle colic artery
Transverse colon
Ileocolic artery
In the right iliac fossa
Appendix
Terminal ileum and caecum
Marginal artery
Sum of all the distal branches of the SMA where they anastamose
Venous drainage of git
The IMV joins the splenic vein
Where the SMV and splenic vein meet, forms the portal vein that drains into the IVC
Chyme in intestines
Isotonic
Neutral
Digestion nearly complete
Adaptations of the small intestines
Villi
Microvilli - brush border
Plicae circulares
Segmentation shuttling - controlled segment contraction
Intestinal epithelia
Enterocytes- tall columnar (absorption)
Goblet cells - produces mucus
Enteroendocrine cells - produce hormones
Crypts of Lieberkuhn (gland)
- stem cells
Crypts of Lieberkuhn
- stem cells at base - mature as they migrate to surface - high turnover of epithelial cells
- Paneth cells at base - prodeuce antimicrobial peptides and protects stem cells
Monosaccharides
Only monoasaccharides can be absorbed
- Glucose - only enters with Na+
- Galactose
- Fructose
Fibre
Binds to bile salts so they are excreted.
Therefore, more bile salts must be made from bile acids in the liver using cholesterol
Partially digested by bacteria in the colon providing nutrients
Common dietary carbhydrates
Starch
Lactose - milk
Sucrose - cane sugar
Amylose
Straight chains of glucose
alpha 1-4 glycosidic bonds only
Amylopectin
Branched chains of glucose
alpha 1-4 glycosidic bonds and alpha 1-6 glycosidic bonds (branched)
Starch digestion
Starch is made of amylose and amylopectin.
Alpha 1-4 glycosidic bonds broken down by salivary and pancreatic amylase producing:
- maltose in amylose
- alpha dextrins in amylopectins
Isolmaltase breaks the brnachedalpha 1-6 glycosidic bonds
Maltose
glucose + glucose
Alpha dextrins
Branched sub unit containing 4 glucose
Lactose
Glucose + galactose
Broken down by lactase
Lactose intolerant
Not enough lactase when older
Lactose remains in gut drawing water in to the gut causing diarrhoea
Lactose is fermented in the gut producing gas - flatulence and bloating
Sucrose
Glucose + fructose
Broken down by sucrase
Enterocyte Na+/K+ ATPase
On the basolateral surface of the enterocyte.
Maintains a low Na+ conc inside the cell establishing a conc gradient
Monosaccharide absorption
SGLT1 :
On lumenal surface
Absorbs Na+ and glucose/ galcatose into the enterocyte from the lumen
SGLT2 - Transports monosaccharides into the blood from the enterocyte
GLUT5 - Transports fructose from the lumen t the enterocyte via facilitated diffusion
Pepsin
Pepsinogen released from chief cells
Activated in the stomach at pH 2-3 to pepsin
Pepsin breaks down proteins into oligopeptides which are transported to the small intestines
Protein digestion in the small intestines
Pancreas releases protease zymogens:
- trypsinogen
- chymotrypsinogen
- proelastase
- procarboxypeptidase A and B
Enterokinase
Converts trypsinogen to trypsin
Exopeptidases
Produce dipeptides or amino acids
Break bonds at the end of polypeptides
- procarboxypeptidase A and B
Endopeptidases
Produce shorter polypeptidases
Break bonds in the middle of polypeptidases
- trypsinogen
- chymotrypsinogen
- proelastase
Trypsin
Trypsinogen is converted to trypsin by enterokinase on epithelial cells
Trypsin activates other zymogens in gut lumen
Brush border
- Partially digested polypeptides can be absorbed by the enterocyte via the peptide transporter 1
- Amino acids are absorbed from the lumen into the enterocyte using an Na+/ amino acid co transporter
- The dipeptides in the enterocyte are broken down by cytosolic peptidases into amino acids
- Amino acids are transported out of the cell into the blood
Water uptake in large intestines
Large intestines contain Na+ channels induced by aldosterone
Osmosis
Occurs paracellularly via tight junctions and transcellularly
Oral rehydration
MIxture of glucose and salt for maximum water uptake
Water secretion
Driven by chloride movement predominantly
- Chloride enters the crypt epithelial cell from blood via the NKCC1
- cAMP levels increases inside the cell
- cAMP activates CFTR so Cl- are secreted into the lumen
- Na+ is driven into the lumen via tight junctions
- Osmotic gradient is created so water flows into the lumen
vit B12 deficiency causes
Pernicious anaemia
Hypochlorhydria - inadequate stomach acid
Veganism
Inflammatory disorders of the ileum e.g. Chron’s
Irritable bowel syndrome
Abdominal pain Bloating Flatulence Diarrhoea Constipation Rectal urgency
Who does IBS affect commonly
Females 2:1
Young adults 20 - 40s
People with psychological disorders such as depression and anxiety
Coeliac disease
Immunological response to the gliadin fraction of gluten
- Damages mucosa of intestines
- Absence of intestinal villi
- Hypertrophy and lengthening of crypts
- Lymphocyte infiltration of epithelium and lamina propria
- Impaired digestion and malabsorption
Where is gluten found
Wheat
Rye
Barley
Coeliac synptoms
Diarrhoea
Weight loss
Flatulence
Abdominal pain
Anaemia - impaired iron absorption
Neurological symptoms - hypocalcaemia
Investigations for coeliac’s
Bloods
- IgA to endomysium
- tissue transglutaminase
Upper GI endoscopy and biopsy (duodenum)
- reduced villi
- mucosal pathology
Treatment of coeliac disease
Strict gluten free diet
