1.02 - Gut Secretions

Question 1

What are the factors of absorption

Answer 1

• blood and lymph flows
• Number and state of enterocytes
• Nutrients intake
• Gastric. Motility
• Intestinal motility increases absorption decreases

Question 2

The mechanism of absorption with no food

Answer 2

Pumping sodium out the cell via K/Na

Therefore low conc of. Na+ in cell and high conc of Na+ outside

Na+ can travel between cell

The proton/Na+ pump allows Na+ in cell

HCO3-/Cl- pump allows cl- in cell

Question 3

The mechanism of absorption of food

Answer 3

Pumping sodium out the cell

Therefore low conc of. Na+ in cell and high conc of Na+ outside

Na+ can travel between cell

The proton/Na+ pump allows Na+ in cell

HCO3-/Cl- pump allows cl- in cell

SGLT-1 → allows glucose and sodium into cell

→ doesn’t work without glucose

GLUT 2 allows glucose to be transported out the cell

AQP 10 and APQ3 allows water through the cell transcellular

Question 4

How are proteins absorbed

Answer 4

• Amino acids = by Na+ cotransporters then by facilitated diffusion Into blood
• Di and tri peptides = absorbed by brush border PepT1 (2nd active transport, Na+ moves down conc grad in exchange for H+ moving into lumen)

Question 5

How are carbohydrates absorbed

Answer 5

• glucose and galactose = enters cell via 2nd active transport with Na+ via SGLT1 an exits cell via GLUT2 into blood
• Fructose = enters cell by Facilitated diffusion with GLUT5 on apical membrane exit via GLUT2

Question 6

How are fats absorbed

Answer 6

diffusion into enterocyte packaged into chylomicron for passage into lacteals of blood

Question 7

How is iron absorbed

Answer 7

duodenum and proximal jejunum, heme iron/ferrous/Fe2+(animal) is more readily absorbed than non-heme iron/ferric/Fe3+(plant). → through DMT1

Question 8

How are vitamins absorbed

Answer 8

• Fat soluble vitamins (A,D,E,K) absorption via diffusion across brush border of enterocyte
• VitB12(+ intrinsic factor) absorbed from terminal ileum
• Vitamins (A,B,C,D,E and K) absorbed

Question 9

How are electrolytes secreted

Answer 9

1. K/Cl/Na transporter allows Cl- into cell
2. Aided by Na+/K ATPase as it decreases Na+ conc
3. Cl- moves into lumen via cystic fibrosis transmembrane (CFTR)
4. K+ exits leading to hyper polarisation
5. Promotes further Cl- secretion
6. Creates electronegative intestinal lumen
7. Na+ flow from intestinal fluid through tight junction
8. Movement of NaCl creates an osmotic gradient causing water to move into lumen via osmosis

Question 10

How does acetyl choline control intestinal secretions

Answer 10

1. AcH binds to muscarnic receptors made of G protein
2. Causes conformational change in G protein
3. Initiates IP3 to be produced
4. IP3 binds to IP3 receptors on the ER releasing Ca2+
5. Increases Ca2+ conc
   - directly activates calcium dependent chloride channels
   - May increase additional signal pathways
   - CFTR. → protein kinase modality by Ca2+

Question 11

How does VIP control intestinal secretions

Answer 11

1. VIP binds to VPAC receptors that are made of G proteins
2. Change in protein activating it
3. Activates Gproteins stimulate adenylate cyclase (enzyme makes ATP into cAMP)
4. Increase cAMP
5. Activates protein kinase A
6. Protein kinase A phosphorylates the CFTR chloride increasing Cl- secretion

Question 12

What hormones do the intestines secrete

Answer 12

• intestinal gastrin
• entero-oxyntin
• secretin
• CCK
• PYY
• Gastro inhibitory peptide

Question 13

What does intestinal gastrin do

Answer 13

1. Chyme enters the duodenum
2. If there is a high conc of peptones(partially digested proteins), this stimulates duodenal G cells
3. Duodenal G cells secrete intestinal gastrin
4. Travels through the blood and stimulates the parietal cell in stomach → H+ secreted out and HCL
5. Intestinal gastrin also binds to receptors on chief cells → pepsinogen released
6. H+ secreted from parietal contributes to pH 1.8 -3.5 pepsinogen converted into pepsin

Question 14

What does entero-oxyntin

Answer 14

1. Increased peptones in the duodenum stimulate endocrine cells
2. Endocrine cells release entero-oxyntin
3. Entero-oxyntin also binds to receptors on chief cells and parietal cell
4. Increasing HCL and pepsinogen secretion

Question 15

What does secretin do

Answer 15

1. S cells respond to increased conc of H+ and fatty acids
2. They secrete hormone secretin
3. Bind to receptors on antral G cell inhibiting gastrin
4. Decreasing HCL secretion and pepsinogen secretion
5. Secretin can stimulate cholesterol into bile acids in liver
6. Therefore bile can be released for lipid digestion
7. Secretin binds to pancreas ductal epithelial cells to stimulate HCO3- secretion in SI.

Question 16

What does CCK do

Answer 16

1. I cells respond to increased conc of fatty acids, peptones and oligosaccharides
2. I cells release CCK
3. CCK bind to receptors on parietal cells to inhibit the H+/K+ pump → less H+ released → less HCL
4. CCK binds to liver and increases the function of secretin → increasing bile
5. Binds to gall bladder so it contracts to release concentrated bile in small intestine
6. Binds to sphincter of oDDI to release bile
7. Binds to pancreas acinar cell to release pancreatic enzymes

Question 17

What does PYY and neurotensin

Answer 17

1. Stimulate endocrine cells to release PYY and neurotensin due to distension of chyme in SI
2. Act on pariteal cells which inhibit H+/K+ pump decreasing HCL secretion

Question 18

What is gastro inhibitory peptide

Answer 18

1. K cells responds to high conc of oligiosaachrides/polysaccharides and fatty acids
2. Release gastro inhibitory peptide
3. Binds to receptors on parietal cell and inhibit H+/K+ pump —> less HCL. Secretion
4. Bind to Islet of Langerhans beta cell → stimulate insulin secretion