GI10 - The Intestines

Question 1

4 parts of the duodenum

Answer 1

1. ) 1st Part - superior division aka the cap (L1 spinal level)
   - most common site of duodenal ulceration
2. ) 2nd Part - descending division (L1-L3)
   - contains the ampulla of vater
3. ) 3rd Part - inferior division (L3)
   - crosses over the IVC and aorta

4.) 4th Part - ascending division (L3-L2)

Question 2

5 characteristic differences between the jejunum and ileum

Location
Intestinal Wall
Vasa Recta
Arcades
Colour

Answer 2

1. ) Location - jejunum is in the LUQ whilst ileum is RLQ
2. ) Intestinal Wall - jejunum has a thicker intestinal wall
3. ) Vasa Recta - jejunum has longer straight arteries
4. ) Arcades (arterial loops) - more in the ileum
5. ) Colour - jejunum is red whilst ileum is more pink

Question 3

6 features of the blood supply to the intestines

Main Branch
Transverse Colon
Ascending Colon
Terminal Ileum and Caecum
Marginal Artery
Jejunum and Ileum

Answer 3

1. ) Main Branch - superior mesenteric artery coming out just inferior to the celiac trunk at L1 level
2. ) Middle Colic - supplies transverse colon
3. ) Right Colic - supplies ascending colon
4. ) Ileocolic - supplies terminal ileum and caecum
5. ) Marginal Artery - formed by the anastomoses of the terminal branches of the above arteries
6. ) Branches to Jejunum and Ileum - come directly off the SMA

Question 4

4 features of intestinal epithelia

Epithelial Cells
Intestinal Gland
Paneth Cells
Shedding

Answer 4

1.) Epithelial Cells - enterocytes (simple columnar), goblet cells, enteroendocrine cells

2. ) Intestinal Gland - crypts of Lieberkuhn
   - stem cells at the base migrate to surface, maturing as they migrate into variety of cell types
3. ) Paneth Cells - part of innate mucosal defence
   - produce antimicrobial peptides

4.) Shedding - mucosa is constantly shed every 3-6 days

Question 5

3 features of starch digestion

Amylose
Amylopectin
End Products x3

Answer 5

1. ) Amylose - straight chains of glucose
   - held by alpha 1-4 bonds
   - broken down by salivary and pancreatic amylase
2. ) Amylopectin - branched chains of glucose
   - branched sections held by alpha 1-6 bonds
   - when broken down by amylase, left with shorter but still branched alpha dextrins
   - isomaltase required to break the alpha 1-6 bonds

3.) End Products - glucose, maltose, alpha dextrins

Question 6

Digestion of 2 other carbohydrates

Lactose
Sucrose

Answer 6

1. ) Lactase - lactose –> glucose + galactose
   - glucose and galactose use SGLT-1 for co-transport and GLUT2 for facilitated diffusion
2. ) Sucrase - sucrose –> glucose + fructose
   - fructose uses GLUT5 transporter to enter the cell and GLUT2 to enter the blood

Question 7

4 features/location of protein digestion

Stomach
Intestinal Lumen
Brush Border
Enterocyte Cystosol

Answer 7

1. ) Stomach - pepsin
   - pepsinogen converted to pepsin in presence of HCl
   - produces oligopeptides and AAs
2. ) Intestinal Lumen - trypsin and other proteases
   - trypsinogen converted to trypsin by enteropeptidase
   - trypsin then activates other proteases
   - endopeptidases produce shorter polypeptides
   - exopeptidases produces dipepties or AAs
3. ) Brush Border - enterocytes express peptidases
   - if not broken down to AAs, intestine can absorb short peptides and AAs by PepT1 (transporter)
   - AAs absorbed using co-transport
4. ) Enterocyte Cytosol - small peptides broken down into AAs by cytosolic peptidases
   - certain di- and tripeptides can be absorbed into blood

Question 8

4 causes of vitamin B12 (cobalamin) deficiency

Answer 8

1.) Lack of Intrinsic Factor - B12 cannot bind to IF in the SI to be transported to the distal ileum

2. ) Hypochlorhydria - inadequate stomach acid
   - acid is important for the initial release of B12
   - caused by gastric atrophy or PPIs

3.) Inadequate Dietary Intake - esp vegetarians due to lack of meat

4. ) Inflammatory Diseases of the Ileum - affects absorption of B12
   - e.g. Crohn’s disease

Question 9

5 features of coeliac’s disease

Definition
4 Effects
6 Symptoms
2 Investigation
Treatment

Answer 9

1.) Definition - immunological response to the gliadin fraction of gluten (found in wheat, rye, and barley)

2. ) Effects - reversible damages to mucosa of intestines:
   - absence of intestinal villi
   - hypertrophy of intestinal crypts
   - lymphocytes infiltrate epithelium and lamina propria
   - impaired digestion/malabsorption
3. ) Symptoms - often due to malabsorption
   - diarrhoea (water), weight loss (nutrients)
   - flatulence: more food products in LI so bacteria ferment to produce gases (methane, hydrogen, CO2)
   - abdominal pain
   - anaemia (impaired iron absorption), neurological symptoms (hypocalcaemia)
4. ) Investigations
   - blood tests: IgA antibodies to smooth muscle endomysium and tissue transglutaminase
   - biopsies: mucosal pathology, reduced or absent villi

5.) Treatment - gluten free diet