The Intestines

Question 1

Main differences between jejunum and ileum

Answer 1

Jejunum:
Upper left quadrant 
Thick wall
Longer vasa recta (straight arteries) 
Less arcades (arterial loops)

Ileum:
Lower right quadrant 
Thin wall
Shorter vasa recta 
More arcades

Question 2

What supplies Blood to the colon?

Answer 2

Caecum - ileocolic artery (SMA)

Ascending colon- right colic artery (SMA)

Transverse colon - middle colic artery (branch of superior mesenteric a)

Descending colon - left colic artery (IMA)

Question 3

What supplies blood to the small intestine?

Answer 3

Jejunum and ileal arteries
(Anastomoses of SMA)

Duodenum proximal- gastroduodenal a and superior pancreaticoduodenal a
Distal- SMA and inferior pancreaticoduodenal a

Question 4

Venous drainage of the intestines?

Answer 4

Veins -> superior mesenteric vein -> portal vein (-> behind neck of pancreas-> liver)

• portal vein, splenic vein, SMV, Srectal vein -> IMV all join within liver

Question 5

What do all the terminal branches of the superior mesenteric artery anastomoses to become?

Answer 5

Marginal artery (right and left)

Question 6

What 2 factors are important for absorption in the gut?

Answer 6

Large surface area - mucosa folded into villi, enterocytes covered in micro villi (brush border). Permanent folds in mucosal membrane SI - pilcae circulares

Slow movements of contents in peristalsis - precise control required. Segmentation - contraction distal and proximal (back and forth in gut)

Question 7

Epithelial cells of the intestine

Answer 7

Enterocytes (most of cells) - absorptive cells, tall, columnar

Goblet cells -> mucus

Enteroendercrine cells -> peptide hormones

Question 8

What are the crypts of Lieberkuhn? What cells are they made up of?

Answer 8

Intestinal gland

Stem cells at base - migrate to surface, maturing as they migrate into various cell types -> transit amplifying cells, goblet cells, enteroendocrine cells, enterocytes

Paneth cells at base (innate mucosal defence cells) - produce antmicrobial peptides

Mucosa is constantly shed 3-6 days

Question 9

Carbohydrates of plant origin can’t be digested in small intestine so what are they used for?

Answer 9

Dietary fibre - binds bile salts (uses cholesterol so lowers serum cholesterol) and provides nutrients for bacteria in the colon

Question 10

What does starch consist of?

Answer 10

Straight chain of glucose (amylose polysaccharide)
Alpha 1-4

and branched glucose chains (amylopectin) alpha 1-4 + alpha 1-6

Question 11

How is starch broken down?

Answer 11

Amylase breaks straight glucose chains into maltose (disaccharide)
And branches chains into alpha-dextrins (disaccharide) alpha 1-4

The chain alpha 1-6 bonds are broken by isomaltase -> maltose

-Maltase breaks down maltose -> glucose

Question 12

What is lactose made from, what happens if you are lactose intolerant?

Answer 12

Glucose + galactose

If lack lactase can’t break down lactose -> moves into colon & is used by bacteria which produce H2 (fermented-> flatulence) or lactose acts as an osmotic molecule and draws water in -> diarrhoea

After the age of 2 enzyme expressed less

Question 13

What’s sucrose made from, what breaks it down?

Answer 13

Glucose + fructose

Sucrase

Question 14

How are monosaccharides absorbed?

Answer 14

Mostly in duodenum and jejunum enterocytes

Basolateral membrane:
-Na+/K+ ATPase maintains low intracellular [Na]

Brush border/ apical:
- SGLT-1 binds Na+ with glucose/ galactose into cell

Basolateral:
-GLUT2 glucose/ galactose/ fructose out into capillary

(Fructose uses GlUT5 to enter celll facilitated transport and can leave by 2 channels)

Question 15

Locations in order for protein digestion

Answer 15

Stomach (pepsin) -> intestinal lumen (trypsin main) -> brush border of enterocytes -> cytosol of enterocyte (cytosolic peptidases)

Question 16

What protein digestion occurs in the stomach?

Answer 16

Chief cells -> pepsinogen -> pepsin (by HcL) -> turns proteins into oligopeptides/ AAs -> small intestine

Question 17

What does the pancreas release that’s important for protein digestion?

Answer 17

Pancreas releases proteases as zymogens (activated in intestinal lumen) e.g. trypsinogen (converted to trypsin by enteropeptidase), trypsin activates: (chymotrypsinogen-> chymotrypsin, proelastase-> elastase, procarboxypeptidase A and B)

Question 18

What are endopeltidases and exopeptidases, give some examples?

Answer 18

Endopeptidases produce shorter polypeptides by breaking bonds in the middle of polypeptide e.g. trypsin, chymotrypsin, elastase

Exopeptidases produce dipeptides or AAs by breaking bonds at ends of polypeptides e.g. carboxypeptidase A and B

Question 19

What occurs at the brush border Of enterocytes for protein digestion?

Answer 19

Contains proteases

Intestine can absorb short peptides by peptide transporter 1 (PepT1) co-transporter with H+

Amino acids can be co-transported into cell and then into blood with Na+

Question 20

What digestion occurs at cytosol of enterocytes?

Answer 20

Small peptides acted on by cytosolic peptidases -> AAs

Certain di/ trip peptidases can be absorbed into blood

Question 21

How is water absorbed in the intestines?

Answer 21

Driven by movement of sodium into enterocytes

NA/ K ATPase moves sodium out basolateral

• Na diffuses in apical (H+ antiport/ glucose/ AAs co-transporter) small intestine
• Na channels large intestine (ENaC) induced by aldosterone

Isoosmotic Water follows either transcellularly diffuses or paracellularly (through tight junctions) from osmotic gradient

Malabsorption-> diarrhoea

Question 22

Why is oral rehydration fluid a mixture of water, glucose and salt rather than just water?

Answer 22

Maximum water uptake

Na+ uptake generates osmotic gradient

Glucose uptake stimulates Na uptake

Question 23

How is water secreted in the intestinal lumen?

Answer 23

Driven predominately by chloride movement

Chloride enters crypts of epithelial cell co-transported with Na and K (NaK2CL) -> increase cAMP levels -> activates CFTR (cystic fibrosis transmembrane conductance regulator) which secretes chloride into lumen (infection can also activate)

Na can be drawn into lumen across tight junctions

NaCl secretion creates osmotic gradient so water moves into lumen

Question 24

What are some causes of B12 deficiency? What are the consequences?

Answer 24

Lack of intrinsic factor -> pernicious anaemia (B12 binds to in small intestine and then transported to distal ileum)

Hypochlorhydria (inadequate stomach acid) acid initially helps release cobalamin(B12)

Inadequate food intake (veggies)

Inflammatory disorders of ileum e.g. chrohn’s

-megoblastic anaemia, neurological symptoms

Question 25

What are the symptoms of irritable bowel syndrome, how common is it, risk factors?

Answer 25

Abdo pain, bloating, flatulence, diarrhoea, constipation, rectal urgency

Affects 10-15% adults

More common females (2:1) 20s-40s, more common in association with psychological disorder (poss serotonin lack)

In Absence of documented abnormalities

Question 26

What is coeliac disease. What foods should be avoided? What are the consequences and symptoms?

Answer 26

Immunological response to gliadin fraction of gluten (wheat, rye, barley)

Fermented sugars in intestine-> damages mucosa of intestines -> absence of intestinal villi, hypertrophy/ lengthening of crypts, lymphocytes infiltrate epithelium and lamina propria, impaired digestion/ malabsorption

Genetic factors

Diarrhoea, weight loss, flatulence, abdo pain, anaemia, neurological symptoms

Question 27

How to investigate and treat coeliac disease

Answer 27

Bloods: immunoglobulin A (IgA) antibodies to smooth muscle endomysium and tissue transglutaminase

Upper Gi endoscopy and biopsies (duodenum) - mucosal pathology like presence of immune cells, villi reduced/ absent

✅ strict gluten free diet (can affect growth of children), clinical improvement days/ weeks, histological weeks/ months