DSA: Intro to GI Physio

Question 1

What are the functions of the GI tract?

Answer 1

Digest and absorb nutrients.

Question 2

The functions of the GI tract are digestion and absorption of nutrients. To do these functions, the GI tract does 2 things:

Answer 2

1. Motility moves food we ingest from the mouth–> rectum and mixes and reduces the size of the food. The rate we move from the food is regulated so that we can digest and absorb properly.
2. Secretions help to digest and absorb as well.

Question 3

Name the GI sphincters?

Answer 3

1. UES,
2. LES,
3. Pylorus,
4. sphincter of oddi,
5. ileocecal valve
6. internal and external spincter

Question 4

What is the purpose of the GI sphincters?

Answer 4

Control the passage of GI contents in our intestine to help with digestion and absorption.

Question 5

Th wall of the GI tract has two surfaces:

Answer 5

mucosal surface, which faces the lumen, and the serosal surface, which faces the blood.

Question 6

Describe the mucosal layer of the GI tract

Answer 6

made up of epithelial cells, lamina propria and muscularis mucosae.

• Epithelial cells carry out absorptive and secretory functions.
• Lamina propria consists primarily of connective tissue, blood and lymph vessels.
• Muscularis mucosae consists of smooth muscle cells; contraction of the muscularis mucosae changes the shape and surface area of the epithelial cell layer

Question 7

What is the purpose of the muscularis externa?

Answer 7

control motility via the

• Inner circular smooth muscle
• Outer longitudinal smoothe muscle

Question 8

Where is the enteric NS located and what is its purpose?

Answer 8

• Located in ganglia in the myenteric and submucosal plexuses
• Controls the contraction, secretion, and endocrine functions of the GI tract.

Question 9

Describe the organization of the enteric NS.

Answer 9

ENS is located in ganglia in the myenteric and submucosal plexuses.

• Ganglia receive input from the parasympathetic and sympathetic NS, CNS and from mechanoreceptors and chemoreceptors in the mucosa.
• Motor information then goes to [smooth muscle, secretory, and endocrine cells]

Question 10

Does the ENS require info from the CNS?

Answer 10

ENS does not need input from the CNS. It can act without info from the brain.

Question 11

How do we relay information between ganglia in the enteric NS?

Answer 11

Interneurons

Question 12

Parasympathetic Innervation

Preganglionic nerve CB are located in ___________ and they are short/long.

Answer 12

Preganglionic nerve CB are located in: brainstem or sacral SC. Preganglionic nerves are long.

Question 13

Parasympathetic Innervation

Describe the path of the preganglionic parasympathetic nerves, whose CB are located in the brainstem or the sacral SC.

Answer 13

Preganglionic parasym nerves: vagus and pelvic splanchnic

• Vagus nerve innervates the upper GI tract (above the splenic fixture).
• Pelvic nerve innervates the lower GI tract (below splenic fixture)

Release ACh and onto nAChR in ganglia located in or near the target organ in the myenteric and submucosal plexus.

Postganglionic neurons are short and located near the effector (smooth muscle, endocrine, secretory cells) and release ACh onto mAChR.

Question 14

The CNS has important roles in regulating GI function. What is it?

Answer 14

The vago-vagal reflex (gastric receptive relaxation reflex) modulates ENS response.

Question 15

The vago-vagal reflex (gastric receptive relaxation reflex) modulates ENS response. What is it?

Answer 15

The vagus nerve is a mixed nerve, where 75% of the fibers are afferent and 25% are efferent.

• Vagal afferents deliver sensory information from the periphery [mechanoreceptors or chemoreceptors in the wall of the GI tract] àCNS (NTS in the brainstem)
• Vagal efferents send info from the CNS–>tissue in the periphery (smooth m, secretory or endocrine cells)

Thus, vago-vagal reflexes are those where the afferent and efferent limb are in the vagus nerve.

Question 16

Sympathetic innervation occurs via nerves that run from:

______–>_______–>_____

Answer 16

SC→ preverterbral gangia (celiac, SM, IM)→GI organs]

Question 17

Describe the path of sympathetic innervation

Answer 17

• Preganglionic fibers originate in the SC and are short–>
• Synapse on prevertebral ganglia outside the gastrointestinal tract and release ACh–>
• Postganglionic fibers go from [prevertebral ganglia–>myenteric and submucosal plexus and release NE onto ADR-alpha/beta.

Question 18

GI peptides can be what three things?

Answer 18

Paracrines

Hormones

Neurocrines

Question 19

GI peptides (paracrines, hormones and neurocrines) regulate the function of the GI tract.

We categorize the peptides based on what?

Answer 19

1. whether they are released from a endocrine cell or a neuron
2. route it takes to reach its target.

Question 20

What are the 3 types of regulation the GI system undergoes to release peptides?

Answer 20

• Paracrine regulation
• Endocrine regulation
• Neural regulation

Question 21

Paracrine regulation- __________ are released from ________ cells of the GI tract. How do they act?

Answer 21

• Paracrine regulation- paracrines are released from endocrine cells of the GI tract.
• They act locally and reach their target by diffusing short distances.

Question 22

What are examples of paracrines?

Answer 22

1. Somatostatins
2. Histamine

Question 23

Somatostatin

Site of secretion:

D/t:

Action:

Answer 23

Somatostatin is released by D cells in the GI mucosa when the pH of the lumen decreases. Thus, its functions are to

1. Inhibit H+ secretion
2. Inhibit secretion of other GI hormones.

Question 24

Is somatostatin only released by D cells of the GI mucosa?

Answer 24

No.

It is also secreted outside of the GI tract by the hypothalamus and g cells of the exocrine pancreas.

Question 25

**_Histamine_** ## Footnote Site of secretion: D/t: Action:

Answer 25

**Histamine** is released in the stomach by _ECL (enterochromaffin-like cells)_ in the gastric glands and targets _parietal cells_ to produce HCl (acid)

Question 26

**Endocrine regulation-** _______ are released from _____ cells in the GI tract. What is their track?

Answer 26

**hormones** are released from **endocrine cells** in the [GI tract--\> portal circulation--\> liver--\> enter systemic circulation] and binds to specific receptors on the target cell, which can be at the GI tract or somewhere else.

Question 27

**What are examples of 4 types of hormones?**

Answer 27

**1. Gastrin** **2. CCK** **3. Secritin** **4. GIP**

Question 28

What cells have granules filled with hormones that are release when they are stimulated?

Answer 28

**Enteroendocrine cells**

Question 29

**Gastrin** is released when?

Answer 29

**After eating a meal**

Question 30

**Gastrin** ## Footnote Site of secretion: D/t: Action:

Answer 30

**_G cells in the stomach_** d/t the presence of [**_small peptides_, _distention_ and _vagal stimulation_]** which occur after eating a meal. Action: 1. **_increases H+ secretion_** 2. **_the growth of the mucosa to protect the stomach lining_**

Question 31

**Generally, what does _CCK_ do?**

Answer 31

**Can be a paracrine signal that _promotes digestion and absorption of fat_**

Question 32

**_CCK (paracrine signal) promotes fat digestion and absorption_** ## Footnote Site of secretion: D/t: Action (4):

Answer 32

**_I cells in the [duodenum and jejunum of the SI]**_ release CCK when [_**small peptides**_ and _**FA_**] are sensed. Action: 1. Increase secretion of pancreatic enzyme and HCO3- (indirectly) 2. Contraction of the gallbladder and relaxation of the sphincter of oddi ejects bile to the lumen of SI 3. Growth of exocrine pancreas and gallbladder (trophic) (because major target organs) 4. Inhibits gastric emptying so that we can process digest and absorb the fat

Question 33

**Can _secretin_ be a paracrine signal?**

Answer 33

**Yes**

Question 34

**_Secretin (paracrine signal)_** ## Footnote Site of secretion: D/t: Action:

Answer 34

**S cells of the duodenum** when **[H+ or FA]** is sensed. ## Footnote Action: 1. Increase secretion from HCO3- _pancreas_ and _biliary_ 2. Decrease gastric H+ secretion 3. Inhibits trophic effect of gastrin on the mucosa of the stomach (bc we are decreasing H+ secretion)

Question 35

**What is _GIP_ called?**

Answer 35

**(glucose dependent insulinotropic peptide)**

Question 36

**_GIP_** ## Footnote Site of secretion: D/t: Action:

Answer 36

Released from **duodenum and jejunum** d/t **[FA, AA, oral glucose]** Actions: 1. Secrete insulin from the pancreatic B cells 2. Decrease gastric H+ secretion

Question 37

**What would be more effectin in increasing insulin secretion? Oral glucose or IV glucose? Why?**

Answer 37

Oral because it stimulates GIP which stimulates insulin secretion and has direct stimulatory effects on B cells... **Incretin effect**

Question 38

**_Neural regulation_- ________ are made in ______ of the GI tract and released via an AP. What is their track?**

Answer 38

Neural regulation- **_Neurocrines (NT’s)_** are made in **neurons** of the GI tract and released via an AP. They diffuse across the synapse and bind to the target cell.