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Intestines Flashcards

1
Q

Describe teh dirences between jejune my and illumise

A

SVS

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2
Q

Describe the SMA

A

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

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3
Q

Describe the IMV

A

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

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4
Q

Describe chyme in the small ntestin

A

Now conditioned
• Isotonic
• Neutral
• Digestion nearly complete

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5
Q

Describe the SA of teh small intestine

A

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

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6
Q

Describe intestinal epithelia and crypts

A

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)
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7
Q

Briefly describe harbs

A

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)

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8
Q

What re common dietary carbohydrates

A
  1. Starch (polysaccharide)
  2. Lactose (disaccharide)
  3. Sucrose (disaccharide)
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9
Q

Wha are 2 forms of chains of starch

A

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

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10
Q

Describe digestion of 1,4 bonds

A
  • 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)
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11
Q

How are 1,6 bonds broken

A

• Isomaltase is required to break the branched alpha 1-6 bonds
- found in brush border

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12
Q

What are 2 brush border enzymes

A
  • 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
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13
Q

Describe monosaccharide absorption

A

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

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14
Q

Describe the first stage o protein digestion (stomach)

A 
In stomach
• Pepsinogen released from chief cell
• gets converted to pepsin
• By HCl
• Pepsin acts on protein
• Oligopeptides/amino acids
• Move to small intestine
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15
Q

Describe the role of the pancreas in protein igtesion

A

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)

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16
Q

What are endo and exopeptidases

A 
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)
17
Q

Describe how peptides and AAs are absorbed

A

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

18
Q

Describe the uptake of water

A

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

19
Q

What is teh basis of electrolyte/water uptake

A

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

20
Q

Wat is included in oral rehydration fluid

A

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

21
Q

What is water secretion driven by

A

Secretion is driven by chloride movement (predominantly)

- chloride ions can be moved down channels

22
Q

What are causes o vit b12 deficiency

A

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

23
Q

What causes lactose intolerance and what are the elects

A

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

24
Q

What is I s

A

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

25
Q

What is coeliac disease and what are teh symptoms

A 
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)

26
Q

What are the investigation and treatment for Ofelia disassembled

A

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

Gi (15 decks)

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