S6.2 The Intestines

Question 1

What factors allow substances to be absorbed in the bowel?

Answer 1

Large surface area: villi, microvilli

Plicae circulares: slow down movement of contents.

Question 2

Briefly describe the cells in the intestines

Answer 2

Simple columnar epithelium.
Enterocytes (main), goblet cells, intestinal crypt with stem cells at base, enteroendocrine cells (secretin) and Paneth cells (innate immunity).

Question 3

Describe the digestion of lactose and sucrose

Answer 3

Lactose into glucose and galactose (lactase)
Sucrose into glucose and fructose (sucrase)

Question 4

Describe the digestion of starch

Answer 4

Amylase breaks alpha-1,4 bond in amylose producing dextrins.
Isomaltase breaks alpha-1,6 bonds in amylopectin producing glucose and maltose

Question 5

On the luminal membrane of the enterocyte, what is the role of SGLT1?

Answer 5

Na+ glucose cotransport

Question 6

On the luminal membrane of the enterocyte, what is the role of GLUT5?

Answer 6

Fructose absorption

Question 7

On the apical membrane of the enterocyte, what is the role of GLUT2?

Answer 7

Glucose and fructose enter the blood

Question 8

How does the stomach cause protein digestion?

Answer 8

Pepsinogen released by chief cells gets converted to pepsin by HCL.
Pepsin breaks proteins into amino acids for absorption via Na+/aa cotransport

Question 9

How does the pancreas cause protein digestion?

Answer 9

Pancreas releases proteases as zymogens which later get activated eg trypsinogen to trypsin

Question 10

Describe the uptake of water and electrolytes in the intestines

Answer 10

NaKATPase on BLM creates gradient for Na+ movement into the cell
In small intestine this is via Na+ cotransporters, in large it is via Na+ channels

Na+ entering increases the osmotic gradient leading to water uptake - isosmotic fluid uptake

Question 11

How is calcium absorbed in the small intestine?

Answer 11

Enters via facilitated diffusion, requires calbindin

Can also occur via paracellular reabsorption

Question 12

How is iron absorbed in the small intestine?

Answer 12

In the form of haem, H+ cotransport
Low iron binds to transferrin and stored
High iron is contained in ferritin complexes

Question 13

How is Vit B12 absorbed?

Answer 13

In the terminal ileum bound to intrinsic factor (secreted by parietal cells).

Question 14

What is the effect of B12 deficiency?

Answer 14

Can lead to megaloblastic anaemia

Caused by lack of intrinsic factor (causing pernicious anaemia), poor diet and Crohns

Question 15

What is lactose intolerance?

Answer 15

Deficiency of lactase prevents lactose breakdown, which remains in the gut, so water is not absorbed causing diarrhoea.

Question 16

What are the symptoms of IBS?

Answer 16

Abdominal pain, bloating, flatulence

Question 17

What is coeliacs disease?

Answer 17

Intolerance of the gliadin fraction of gluten, found in wheat, rye and barley.
Results in damaged mucosa of intestines causing absence of villi and reduced absorption

Question 18

What are the symptoms of coeliacs disease?

Answer 18

Diarrhoea, weight loss, anaemia (reduced iron absorption)

Question 19

What are the investigations and treatments for coeliacs disease?

Answer 19

Endoscopy, blood (IgA)

Gluten free diet

Question 20

How does the SMA supply the colon?

Answer 20

Via the ileocolic, right colic and middle colic

All of these anastomoses to form the marginal artery

Question 21

Hows does the IMA supply the colon?

Answer 21

Left colic artery supplies the descending colon

As the IMA passes into the pelvis, it becomes the superior rectal artery

Question 22

What is the venous drainage of he gut?

Answer 22

All of the gut drains into the portal vein