Intro to GI Physiology

Question 1

What are long GI reflexes? What is a classic example?

Answer 1

Question 2

The submucosal plexus is also known as […] plexus and it controls […] and […]

Answer 2

Meissner’s

GI secretion

Blood flow

Question 3

• What does it mean to say that the microvilli that line the gut are an example of countercurrent blood flow?
• How / when does this make the microvilli particulary susceptible to damage?

Answer 3

Question 4

What are the 3 parts of the small intestine, from proximal to distal.

Answer 4

Duodenum

Jejunum

Ileum

Question 5

What are the 4 main functions of the GI tract?

Answer 5

Question 6

What are the 3 parts of the large intestine, from proximal to distal.

Answer 6

Cecum

Colon

Rectum

Question 7

What are intrinsic gut reflexes? What’s a classic example?

Answer 7

Question 8

The enteric nervous system can be thought of as a sub-branch of the […] nervous system

Answer 8

Autonomic

Question 9

Answer 9

Question 10

What are the 3 main mechanisms that are used to regulate the GI tract?

Answer 10

Endocrine

Neurocrine

Paracrine

Question 11

The myenteric plexus is also known as […] plexus and it controls […]

Answer 11

Auerbach’s

GI motility

Question 12

True or false: substances that enter the GI tract are considered outside as long as they remain in the lumen.

Answer 12

True

Question 13

What is the peristaltic reflex?

Answer 13

Question 14

Explain what is seen in this image.

Answer 14

SNS (postganglionic) and PSNS (preganglionic) synapse on the plexi of the gut, which then affect the function of the gut wall cells. The gut wall also contains sensory neurons which can effect both the enteric plexi and/or send signals up to the prevertebral ganglia of SNS, the spinal cord, or the vagus nerve (up to brainstem).

Question 15

What is a longer GI reflex? What are some classic examples?

Answer 15

Question 16

Of the 4 main functions of the GI tract, which 2 are the most regulatable?

Answer 16

Motility

Secretion

Question 17

Describe the general path that is taken by anything that enters the mouth.

Answer 17

Question 18

IN GENERAL, how is blood flow regulated to the GI tract?

Answer 18

Same as what we learned for HLK

For intrinsic factors, pO₂ is a major regulator. As oxygen decreases, local factors like adenosine and NO are released to cause vasodilation.

For extrinsic factors, the sympathetic NS can regulate blood flow to gut (ex: during exercise, SNS vasoconstricts vessels to gut to reduce blood flow)

Question 19

What are the 4 main layers of tissue that make up the barrier between the abdominal cavity and the lumen of the GI tract?

Answer 19

From internal to external:

• Mucosa
• Submucosa
• Muscularis externa
• Serosa

Question 20

Answer 20

Question 21

Describe in VERY GENERAL terms the anatomy of the gut wall.

Answer 21

Will learn more about this in later lectures, but in general:

Mucosa

• Specialized epithelium with microvilli
• Lamina propria (capillaries, nerve endings, immune cells)
• Muscularis mucosa (circular and longitudinal muscle)

Submucosa

• Major blood vessels and lymph vessels as well as submucosal nerve plexus (secretion and vasomotion)

Muscularis externa

• Circular muscle and myenteric nerve plexus (gut motility)

Serosa

• Longitudinal muscle