The Intestines And Inflammatory Bowel Disease Flashcards
What are the main roles of the intestines?
Absorb nutrients
Water
Electrolytes
What are the basic cells of the intestine?
Enterocytes
What are plicae circulares?
Valvular flaps projecting into the lumen of the small intestine
Why is mucus in the gut important?
Keeps the bacteria away from the cells
How often is mucosa shed in the gut?
3-6 days
Describe the cells in intestinal glands
Stem cells at the base - migrate to surface as they mature
Enteroendocrine - release hormones
Paneth cells - protection against infection
What types of carbohydrates can be absorbed?
Monosaccharides
Where does the final breakdown of carbohydrates occur?
In the brush border of the gut
What are the monosaccharides?
Fructose
Galactose
Glucose
What are the common dietary carbohydrates?
Starch
Lactose
Sucrose
What are the 2 parts of starch?
Amylose (20%)
Amylopectin (80%)
What type of bonds make the straight chains in starch?
Alpha 1, 4 glycosidic
What type of bonds make the branching chains in starch?
Alpha 1, 6 glycosidic
Which bonds does amylase break?
Alpha 1, 4 glycosidic
Usually cleaves at the ends of straight chains
What are alpha dextrins?
Smaller units from starch that still contain branches
Which enzyme breaks alpha 1,6 glycosidic bonds?
Isomaltase
This enzyme has many different names
Which enzymes are found in the brush border?
Maltase
Isomaltase
Lactase
Sucrase
Describe SGLT-1
Sodium glucose transporter
Na/K/ATPase sets up the gradient
On apical membrane
Cotransports glucose or galactose with Na+ into enterocyte
Describe GLUT-5
On the apical membrane
Transports fructose into the enterocytes
Describe GLUT-2
Basolateral membrane
All the monosaccharides pass through this into the blood
Down their concentration gradients
Describe the idea behind oral rehydration methods
Uptake of Na+ generates osmotic gradient so water follows
Glucose uptake stimulates Na+ uptake
A mixture of glucose and salt will stimulate maximum water uptake
What kinds of peptides can be absorbed in the gut?
Amino acids
Dipeptides
Tripeptides
Describe the first part of protein digestion
In the stomach, acid unravels proteins
Pepsinogen secreted from chief cells
Converted to pepsin by HCl
Pepsin breaks down proteins
Trypsinogen is converted to trypsin by …
Enteropeptidase (on brush border)
Which pancreatic protease activates all the other proteases?
Trypsin
How do exopeptidases work?
Break bonds at ends of polypeptides
Produces dipeptides/amino acids
How do endopeptidases work?
Break bonds in middle of polypeptides
Produce shorter polypeptides
Name an exopeptidase
Carboxypeptidase
Name 3 endopeptidases
Trypsin
Chymotrypsin
Elastase
Why can newborns absorb whole proteins?
Needed to help immunity etc when breast feeding
How are amino acids transported into cells?
Na+ amino acid transporter
How are most protein products absorbed?
As dipeptides or tripeptides
Via H+ co-transporter
(PepT 1)
Inside the cells, further broken down into amino acids
Which hormone induces the Na+ channels in the large intestine?
Aldosterone
What is the difference in absorption when calcium is normal/high and when it is low?
Normal/high = calcium absorbed passively paracellular Low = active transcellular absorption (facilitated diffusion apical and pumped out of basolateral by Ca-ATPase)
How is iron absorbed?
Haem/Fe2+
Cotransported with H+ (why gastric acid is important to this)
What happens to iron when iron levels are low?
Binds to transferrin
Transported to stores
What happens to iron when levels are high?
Contained in ferritin complexes
Trapped inside enterocyte
Can be transported out if we need it
Lost when enterocyte is shed
How is iron stored in the body?
Approx 1/2 is in Hb
Approx 1/2 stored in ferritin complexes in bone marrow, liver and spleen
How are water soluble vitamins absorbed?
Via Na+ cotransport
How is vitamin B12 absorbed?
In the terminal ileum
Bound to intrinsic factor (secreted by parietal cells)
B12 deficiency leads to …
Megaloblastic anaemia
How does the small intestine ensure caudal drive of contents?
Intestinal pacemakers have higher frequencies proximally
Intestinal gradient set up
Drives the contents caudally
Peristaltic contractions
What is segmentation?
Contents move back and forth on a particular area
Shuttling to increase the contact time
Aid absorption
What is mass movement?
Occurs 1-3 times a day
Contents move rapidly from transverse colon to rectum
Often triggered by eating (gastro-colic reflex)
What are haustra?
In the large intestine
Formed because the longitudinal muscle (taenia coli) is not the complete length
Forms pouches
When do we get the urge to defaecate?
Stretch receptors activated
When rectum is 25% full
Describe the internal and external anal sphincters
Internal - smooth muscle, PNS control
External - striated/skeletal muscle, voluntary control
How do we defaecate?
Relax both the internal and external anal sphincters
Increase intra-abdominal pressure
What are inflammatory bowel diseases?
A group of conditions characterised by idiopathic inflammation of the GI tract (affecting the function of the gut)
What are the 2 most common IBDs?
Crohn’s disease
Ulcerative colitis
What are the peak ages for Crohn’s disease?
15-30 years
60 years
What is the peak age for UC?
Young adults
What is diversion colitis?
Inflammation distal to a surgical cut through the bowel
What is microscopic colitis?
Can only see the inflammatory changes on histology
Where does Crohn’s affect?
Anywhere in the GI tract
Ileum involved in most cases
Which IBD is more likely to be transmural?
Crohn’s
Through all layers of bowel wall
Which IBD presents with skip lesions?
Crohn’s
Where does UC commonly affect?
Begins in rectum
Can extend to involve entire colon
Which IBD is found in a continuous pattern?
UC
Which IBD usually just has mucosal (superifical) inflammation?
UC
Name some extra-intestinal problems linked to IBDs
MSK pain - arthritis
Erythemanodosum, pyoderma gangrenosum, psoriasis
Primary sclerosing cholangitis
Eye problems
What things can trigger the start of an IBD?
Antibiotics
Infections
Smoking
Diet
Describe Crohn’s and the affect on the body
Inflammation in area that would normally absorb nutrients
More water left in the gut lumen - diarrhoea
Weight loss due to not absorbing enough
Terminal ileum involvement - vita B12 deficiency - megaloblastic anaemia
Hyperaemia
Mucosal oedema
Which IBD is more likely to present with strictures?
Crohn’s
Which IBD can give a cobblestone appearance?
Crohn’s
What is a cobblestone appearance?
Areas of oedema surrounded by ulceration
Where can the bowel form fistulae to?
Other parts of bowel
Bladder
Vagina
Skin
What microscopic evidence signifies Crohn’s disease?
Granulomata
How would we investigate for Crohn’s disease?
Bloods - anaemia
CT/MRI - bowel wall thickness, obstruction, extramural problems
Barium enema (less likely) and xray
Colonoscopy - biopsy - histology
Is UC more common in males or females?
Females
Describe some general features of UC
Pain tends to be less localised than Crohn’s
Always in rectum
Inflammatory infiltrate of lamina propria
Crypt abscesses and distortion
Decreased goblet cells - less mucus so loss of protection
Loss of haustra
Which IBD is more likely to have crypt distortion?
UC
Which IBD has a decreased production of mucus?
UC
Describe the investigations for UC
Bloods - anaemia, serum markers Stool cultures Plain abdominal x-ray CT/MRI Colonoscopy Barium enema
What do we call cases that cannot be classed as either Crohn’s or UC?
Indeterminate colitis
In which IBD is bleeding more common?
UC
Which IBD is more likely to present with perianal disease?
Crohn’s
In which IBD is fibrosis more common?
Crohn’s
In which IBD is the mucosa friable? (Delicate)
UC
What would you see using radiology for Crohn’s?
Lots of narrowing in the lumen of gut
Lots of distortion due to inflammation and healing
‘String sign of Cantour’
What would you see in the radiology for UC?
Lead pipe colon (featureless bowel - no haustra)
Contrast medium may adhere to walls of bowel - see the continuous ulceration
What are the treatment options for IBDs?
Stepwise
- Aminosalicylates for flares and remission
- Corticosteroids for flares only (avoid long term)
- Immunomodulators for extreme cases, fistulae and maintenance of remission
- Surgery
Describe the surgery for Crohn’s
Not curative
Fix strictures/fistulae
Remove as little bowel as possible
Describe the surgery for UC
Can be curable
Colectomy usually
Dramatically reduces/eradicates disease process
