Intestines Flashcards
Describe teh dirences between jejune my and illumise
SVS
Describe the SMA
SMA - branch of aort a- comes of anteriorly - abt 1cm below CT - appears underneath body of pancreas - pancreas folded around it - gives off jejune and ideal branches -branches anastomoses together, plexus of vessels
Describe the IMV
Venous drainage for midgut is smv - similar arcades in mesentery of small bowl - all vessels are retroperitoneal - thru double layer of peritoneum (mesentery). SMV joins up with splenetic vein and IMV - into portal vein - then goes into liver. Hepatic veins drain into IVC
Describe chyme in the small ntestin
Now conditioned
• Isotonic
• Neutral
• Digestion nearly complete
Describe the SA of teh small intestine
Folds are permanent (Plicae Circulares) unlike rugae - small bowel does not distend unless in pathology. Then there is villi . On top of villi - enterocytes which have microvilli
Needs large surface area
• Mucosa folded into villi
• Surface is covered in micro villi (brush border) Slow movement of contents
• Precise control required
Describe intestinal epithelia and crypts
Epithelial cells –
• Enterocytes (most of the cells in the small intestine)- absorptive cells
• Tall columnar cells
• Goblet cells- mucus producing
• Enteroendocrine cells- produce hormones
Intestinal gland (crypts of Lieberkuhn) Stem cells at base • Migrate to surface • Maturing as they migrate into variety of cell types - as chyme passes through it sloughs off cells - every 3-6 days mucosa is shed - so stem cells necessary Paneth cells at base (innate mucosal defence cells) • Produce antimicrobial peptides - keep stem cells and local area healthy and free of bacteria aMucosa is constantly shed (3-6 days)
Briefly describe harbs
Key points
• Carbohydrates are chains of sugars
• Polysaccharides, disaccharides, monosaccharides
• Only monosaccharides can be absorbed
• Glucose can only enter with Na+
• There are carbohydrates of plant origin that cannot be digested in small intestine
• These are utilised and partially digested by bacteria in the colon (providing nutrients for colonic mucosa)
The goal is to get monosaccharides
• Glucose, galactose, fructose
• End products of carbohydrate metabolism (these can move out of the lumen)
What re common dietary carbohydrates
- Starch (polysaccharide)
- Lactose (disaccharide)
- Sucrose (disaccharide)
Wha are 2 forms of chains of starch
Starch consists of:
• Straight chains of glucose- Amylose
• Branched chains of glucose-Amylopectin
• In Amylose the chains have alpha 1-4 bonds • In amylopectin the branched bits are alpha 1-6 bonds
Describe digestion of 1,4 bonds
- Salivary and pancreatic amylase breaks the Alpha 1-4 bonds in amylose……
- ……Producing the disaccharide maltose (glucose + glucose)
- When amylase breaks the alpha 1-4 in amylopectin you liberate shorter (but still branched) chains of glucose (called alpha dextrins)
How are 1,6 bonds broken
• Isomaltase is required to break the branched alpha 1-6 bonds
- found in brush border
What are 2 brush border enzymes
- Maltose (maltase) = Glucose + Glucose
- Alpha dextrins (isomaltase) = Glucose
- Lactose (lactase) = glucose + galactose (a lot present in newbors) - later on in life can get lactose intolerance
- Sucrose (sucrase) = glucose + fructose
Describe monosaccharide absorption
glucose./galactose can only be absorbed with Na+ in SgLT1
Fructose gets absorbed hogue Glut1.
All products absorbed on basolateral membrane via GLUT2
Gradient generated by sodium potassium ATPase
Describe the first stage o protein digestion (stomach)
In stomach • Pepsinogen released from chief cell • gets converted to pepsin • By HCl • Pepsin acts on protein • Oligopeptides/amino acids • Move to small intestine
Describe the role of the pancreas in protein igtesion
Pancreas releases proteases as zymogens (move into intestinal lumen to be activated)
• Trypsinogen is important
- trypsin is a catalyst for the other proenzymes to their active forms
• Converted to trypsin by enteropeptidase (enterokinase - brush border enzyme)
• Trypsin then activates other proteases (see slide for list. They break don chains o peptides into shorter ones or AAs)
What are endo and exopeptidases
Major proteases- released from pancreas • Endopeptidases (produce shorter polypeptides - break bonds in the middle of the chain) • Trypsin • Chymotrypsin • Elastase
- Exopeptidases (produce dipeptides or amino acids - work at end of polypeptides)
- Carboxypeptidase (A & B)
Describe how peptides and AAs are absorbed
Brush border- also contains proteases
• The enterocytes express peptidases in their brush border •Sometimes cannot completely digest proteins down to amino acids
• However intestine can absorb short peptides (as well as amino acids) by Peptide transporter 1 (PepT1)- co strasport with H+ ions
•Amino acids are transported into cell (similar to glucose)
• Na+-amino acid co-transporters
Cytosol of enterocyte
• The small peptides are then acted on by cytosolic peptidases (broken down to amino
acids) •Certain di- and tri-peptides can also be absorbed into blood
Describe the uptake of water
Absorption driven by movement of sodium into enterocytes • Na+ moved by active transport out of cell on basolateral membrane
• Na+ diffuses into epithelial cells
• Water can also move into intercellular space *Osmotic gradient from all absorption leads to uptake of water
◦ Fluid absorbed is isosmotic
What is teh basis of electrolyte/water uptake
Small intestine vs large intestine
• Both have Na+-k+ ATPase on basolateral membrane
• Apical membrane
• Small intestine- Na+ is co-transported with (glucose, amino acids…)
• Large intestine- Na+ channels
• Induced by aldosterone
Wat is included in oral rehydration fluid
Mixture of glucose and salt will stimulate maximum water uptake
• As contained in oral rehydration fluid
• Uptake of Na+ generates osmotic gradient
• Water follows
• Glucose uptake stimulates Na+ uptake
What is water secretion driven by
Secretion is driven by chloride movement (predominantly)
- chloride ions can be moved down channels
What are causes o vit b12 deficiency
Vitamin B12 (cobalamin) Deficiency can lead to megaloblastic anaemia and neurological symptoms
Causes
• Lack of intrinsic factor by (parietal cells)means (B12 cant bind in the stomach- pernicious anaemia)
•Hypochlorhydria (inadequate stomach acid)
• Gastric atrophy, PPIs
•Inadequate intake in food (strict vegetarians)
•Inflammatory disorders of ileum (where it is absorbed)
• Crohn’s disease
What causes lactose intolerance and what are the elects
Caused by deficiency of the enzyme lactase (brush border enzyme)
• After the age of 2 years the enzyme is expressed less
•When lactose is consumed in quantity it cannot be absorbed
• Remains in gut lumen created high osmotic effect
• Water is not absorbed resulting in diarrhoea
• Lactose is fermented in gut producing flatus/bloating
What is I s
In the absence of documented abnormalities, IBS is a common GI disorder
• Affects 10-15% of adults
•Symptoms include:
• Abdominal pain (often cramping, sometimes relieved by defaecation)
• Bloating
• Flatulence
• Diarrhoea/constipation (sometimes alternating)
• Rectal urgency
Causes are multifactorial
•More common in females vs males (2:1)
•20s-40s most affected age range
•More common in association with psychological disorders
What is coeliac disease and what are teh symptoms
Coeliac disease arises from an immunological response to the gliadin fraction of gluten • Found in wheat, rye and barley • Damages mucosa of intestines • Absence of intestinal villi • Lengthening of intestinal crypts • Lymphocytes infiltrate epithelium • Impaired digestion/malabsorption
- Genetic factors (high concordance monozygotic twins (75%)
- Very common (underdiagnosed) estimates of 1% of western population affected
Surface area down as villi flattened - enzymes less effective - high osmotic pressure in gut
Symptoms
• Majority related to malabsorption (diarrhoea, weight loss, flatulence, abdo pain)
• Anaemia (impaired iron absorption), neurological symptoms (hypocalcaemia)
What are the investigation and treatment for Ofelia disassembled
Investigations • Bloods- Immunoglobulin A (IgA) antibodies to smooth muscle endomysium and tissue
transglutaminase • Upper GI endoscopy + biopsies (duodenum)
• Mucosal pathology • Villi are reduced or absent
Treatment •Diet- strict gluten free diet
• Clinical improvement quite quick (days/ weeks)
• Histological improvement (weeks/months
