Physiology and Biochemistry of the GIT

Question 1

2 tasks of GIP and which cells is it in?

Answer 1

K cells signal Beta cells of pancreas to produce insulin - this is why oral insulin is faster and more robust than IV insulin. Second task is that it tells Parietal cells to shut down acid production - just like Secretin does.

Question 2

Which hormone is known for shutting things down globally in the GI? Which cells does it live in? What is its synthetic form?

Answer 2

Octreotide is the synthetic form of Somatostatin. Somatostatin never met a cell or a secretion it didn’t want to inhibit - including the alpha and beta cells of the pancreas.

Somatostatin is released from the Delta cells in both the intestine and the pancreas.

Question 3

Which hormones directly or indirectly increase the release of acid from Parietal cells?

Answer 3

Gastrin from G cells, Histamine from ECL cells.

Sidebar: Ach directly stimulates acid via the Vagus nerve.

Question 4

Which hormones decrease or inhibit the release of gastric acid from Parietal cells?

Answer 4

Secretin both releases bicarb and inhibits gastric acid. GIP from K cells inhibits gastric acid and signals beta cells in the pancreas to give the insulin. Somatostatin inhibits HCl from parietal cells.

Sidenote: Prostaglandins also inhibit parietal cells from their acid.

Question 5

How do Prostaglandins act on the stomach cells?

Answer 5

Prostaglandins increase mucous secretion and inhibit acid secretion.

Question 6

Pepsinogen is released from which cells and requires what for activation? What is Pepsin’s job?

Answer 6

Pepsinogen is released from Chief cells and activated by HCl as it requires very low pH. It cleaves peptide bonds.

Question 7

What medications are notorious for suppressing Prostaglandins, thereby messing up the balance of mucous and acid production.

Answer 7

NSAIDs damage stomach lining from its own proteases.

Question 8

B12 is primarily obtained from what? What chaperones it to the terminal ileum?

Answer 8

B12 is obtained from meat. Intrinsic Factor released from Parietal cells chaperones B12.

Question 9

If Parietal cells are destroyed and both acid and IF are lost, what problems will arise?

Answer 9

B12 deficiency –> Pernicious anemia. Lack of sufficient acid will lead to protein indigestion.

Question 10

Where are the SIK cells located and what do they produce?

Answer 10

Duodenum. Secretin, CCK, GIP respectively. Secretin protects wall with bicarb and shuts off the pylorus and inhibits acid secretion. CCK squeezes gall bladder bile out and relaxes sphincter of Oddi and is Iron Chef and releases the pancreatic enzymes. GIP alerts beta cells to release insulin and also inhibits gastric acid.

Question 11

Where are Delta cells found and what do they release? What is an analog of this substance?

Answer 11

Delta cells are in antrum of stomach and in pancreas. Octreotide is the analog of Somatostatin.

Sidebar: AcH is mean to Delta cells. It favors G cells, ECL, and Chief cells to promote digestion.

Question 12

Enterokinase on the intestinal epithelium activates what enzyme?

Answer 12

Trypsinogen to Trypsin.

Question 13

Lipase is inefficient without who bound to it in its active form?

Answer 13

Colipase which is cleaved to active form by Trypsin.

Question 14

Which transporter on the intestinal epithelium absorbs glucose and galactose? What special transporter takes up fructose? Which transporter brings them into the bloodstream?

Answer 14

SGLT-1 (sodium glucose transporter). GLUT-5 passively transports fructose. All 3 into bloodstream by GLUT-2.

Question 15

What is the D-Xylose test used for?

Answer 15

If you eat D-Xylose, in most cases you should pee D-Xylose.

Performed to Dx conditions of malabsorption of the proximal small intestine due to defects in the integrity of the gastrointestinal mucosa. D-xylose is a monosaccharide that does not require enzymes for digestion prior to absorption.

Question 16

Explain the use of the radio-contrast Schilling test.

Answer 16

Detection of Pernicious Anemia - determine how well the patient is able to absorb B12 from their intestinal tract.

Can help detect IF deficiency.

Question 17

Where are Iron and Folate picked up? Which type of iron is picked up from heme groups in meat?

Answer 17

Iron is picked up in the duodenum just like most minerals; Folate (B9) in the jejunum. Fe2+ is from meat, while Fe3+ is from supplements.

Question 18

Why do we even have an acronym for Dyspnea on Exertion?

Answer 18

DOE

Question 19

Where are fat soluble vitamins, including B12 absorbed?

Answer 19

ileum. A, D, K, E.

Question 20

What things can cause IDA?

Answer 20

Heavy menstruation, GI bleed, Crohn disease affecting the duodenum, resection of the duodenum, and plenty more.

Question 21

Which area of the colon is most responsible for water reabsorption?

Answer 21

Sigmoid colon!

Question 22

What are the lymph nodes of the GI called and where are they found?

Answer 22

Peyer Patches mount offense against bad things. Definitively part of ileum topography.

Question 23

Which cells begin most immune responses?

Answer 23

Dendritic cells take invaders to the lymph nodes to present to CD4 T-cells, beginning the cascade of drama, differentiation, and specialization. Including proliferation of B cells in germinal centers.

Question 24

antibodies found in the intestine/peyer’s patches, M cells are…

Answer 24

IgA. Found in mucus, sweat, tears, breast milk.

Question 25

Lead point for intusseception in children is where which immunological process occurs?

Answer 25

M cells contained within Peyer patches take up antigens and present them to B cells, which then form germinal centers. Following CD40L stimulation from T cells, B cells class switch to IgA, and differentiate into plasma cells.

Question 26

Bile is a surfactant. What is a surfactant?

Answer 26

Molecule which has both a polar and nonpolar end, allowing it to be a detergent.

Bile salts are made up of hydrophobic planar cholesterol.

Question 27

Steatorrhea can lead to loss of Calcium and Mg and what kind of stones?

Answer 27

Calcium oxalate stones. Think Crohns or anyone with a resected ileum.

Question 28

Macrophages convert Hb to what? Who chaperones Bilirubin to the liver?

Answer 28

Biliverdin –> Bilirubin. Albumin chaperones Bilirubin to make it more water-soluble.

Question 29

Describe the journey of bilirubin from the liver to the stercobilin.

What percentage of Urobilinogen gets sucked back into the gut without becoming Stercobilin?

Answer 29

Bilirubin conjugates with glucuronic acid and this water soluble form is excreted into the biliary tree –> hits up the gut bacteria becoming colorless Urobilinogen and then brown Stercobilin (color responsible for feces).

20% of Urobilinogen goes into the Enterohepatic circulation with the rest of the bile via Portal Vein,

Question 30

When urobilinogen is picked up by the kidneys and oxidized, what does it become?

Answer 30

Urobilin - the pigment responsible for the color of urine.

Question 31

The iconic coloring of blood, urine, stool are all derived from which molecule?

Answer 31

Hemoglobin –> Bilirubin –> Urobilinogen. And then either Stercobilin or Urobilin.

Question 32

If you don’t have bilirubin in your stool…what would they look like?

Answer 32

Pale clay colored stools.