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
