Intestinal development and homeostasis

Question 1

What tissue layer (gastrulation) creates the intestine?

Answer 1

The endoderm

Question 2

What are the functions of the intestine?

Answer 2

The intestine functions in absorption of nutrients, wast disposal, immunologic defense, hosting the microbiome and the endocrine coodination of systemic nutrition levels.

Question 3

How is the epithelial layer of the gut structured?

Answer 3

Into crypts and vili

Question 4

How are vili formed in the intestinal epithelial layer?

Answer 4

The vili are formed during development, due to the rapidly expanding endothelial layer, not being able to fit inside of the surrounding muscle tissue. This causes a zigzag pattern and ridges, which ultimately allows the selective growth pattern of the epithelium.

Question 5

Where are the stem cells of the intestine located?

Answer 5

In the crypts next to paneth cells

Question 6

What types of cells, will intestinal stem cells create?

Answer 6

Absorptive enterocytes or secretory cells (goblet cells, tuft cells, enteroendocrine cells) and paneth cells

Question 7

What is the most common marker of stem cells in the intestine

Answer 7

LGR5.
It activates the Wnt pathway and keeps stem cells proliferating

Question 8

Activation of what pathway keeps intestinal stem cells proliferating?

Answer 8

The Wnt pathway.
(It is activated by LGR5)

Question 9

What decides, if intestinal stem cells become adsorptive or secretory cells?

Answer 9

Delta/Notch and lateral inhibition

Question 10

What is the Wnt signal amplifyer? What is it’s receptor?

Answer 10

Rspondin.
It’s receptor is LGR5

Question 11

How does Wnt, Rspondin and LGR5 work together and what do they do?

Answer 11

Wnt signalling keeps stem cell indentity (proliferating), and the cells respons to Wnt is increased by Rspondin, whose receptor is LGR5

Question 12

What signals does Paneth cells in the gut epithelial layer secrete?

Answer 12

Wnt and Egf.
They inhibit differentiation in stem cells

Question 13

What causes self-organization in the gut vili?

Answer 13

Ephrine signals.
Wnt will increase EphB expession → this is expressed by stem cells → stem cells repulse other cells from their area, and are themselves repulsed by other cells (not paneth cells)

Question 14

What 3 signals are required when creating an intestinal organoid?

Answer 14

EGF, Noggin and R-spondin

Question 15

What drives crypt formation in the intestinal epithelial layer?

Answer 15

Rapid cell division.
Cells are organized by eprine signalling and Notch will not allow paneth cells to touch.

Question 16

What cells maintain the intestine during homeostasis? and during injury?

Answer 16

Homeostasis: (LGR5) stem cells
Injury: Progenitor cells can rescue the LGR5 cell pool

Question 17

What happens to the gut epithelial layer, when you consume less food?

Answer 17

The vili will get smaller, due to less cell differentiation, stem cells will instead self renew

Question 18

What signalling pathway mediates the epithelial layers respons to calorie restriction?

Answer 18

mTOR signalling

Question 19

What mediates the stem cell respons to calorie restrictions in the epithelial layer of the gut?

Answer 19

The Paneth cell niche