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GI Exam 1 > DSA: Intro to GI Physio > Flashcards

DSA: Intro to GI Physio Flashcards

1
Q

What are the functions of the GI tract?

A

Digest and absorb nutrients.

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2
Q

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

A
  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.
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3
Q

Name the GI sphincters?

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

What is the purpose of the GI sphincters?

A

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

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5
Q

Th wall of the GI tract has two surfaces:

A

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

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6
Q

Describe the mucosal layer of the GI tract

A

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
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7
Q

What is the purpose of the muscularis externa?

A

control motility via the

  • Inner circular smooth muscle
  • Outer longitudinal smoothe muscle
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8
Q

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

A
  • Located in ganglia in the myenteric and submucosal plexuses
  • Controls the contraction, secretion, and endocrine functions of the GI tract.
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9
Q

Describe the organization of the enteric NS.

A

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]
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10
Q

Does the ENS require info from the CNS?

A

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

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11
Q

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

A

Interneurons

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12
Q

Parasympathetic Innervation

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

A

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

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13
Q

Parasympathetic Innervation

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

A

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.

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14
Q

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

A

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

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15
Q

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

A

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.

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16
Q

Sympathetic innervation occurs via nerves that run from:

______–>_______–>_____

A

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

17
Q

Describe the path of sympathetic innervation

A
  • 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.
18
Q

GI peptides can be what three things?

A

Paracrines

Hormones

Neurocrines

19
Q

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

We categorize the peptides based on what?

A
  1. whether they are released from a endocrine cell or a neuron
  2. route it takes to reach its target.
20
Q

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

A
  • Paracrine regulation
  • Endocrine regulation
  • Neural regulation
21
Q

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

A
  • Paracrine regulation- paracrines are released from endocrine cells of the GI tract.
  • They act locally and reach their target by diffusing short distances.
22
Q

What are examples of paracrines?

A
  1. Somatostatins
  2. Histamine
23
Q

Somatostatin

Site of secretion:

D/t:

Action:

A

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.
24
Q

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

A

No.

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

25
Q

Histamine

Site of secretion:

D/t:

Action:

A

Histamine is released in the stomach by ECL (enterochromaffin-like cells) in the gastric glands and targets parietal cells to produce HCl (acid)

26
Q

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

A

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.

27
Q

What are examples of 4 types of hormones?

A

1. Gastrin

2. CCK

3. Secritin

4. GIP

28
Q

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

A

Enteroendocrine cells

29
Q

Gastrin is released when?

A

After eating a meal

30
Q

Gastrin

Site of secretion:

D/t:

Action:

A

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
31
Q

Generally, what does CCK do?

A

Can be a paracrine signal that promotes digestion and absorption of fat

32
Q

CCK (paracrine signal) promotes fat digestion and absorption

Site of secretion:

D/t:

Action (4):

A

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
33
Q

Can secretin be a paracrine signal?

A

Yes

34
Q

Secretin (paracrine signal)

Site of secretion:

D/t:

Action:

A

S cells of the duodenum when [H+ or FA] is sensed.

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)
35
Q

What is GIP called?

A

(glucose dependent insulinotropic peptide)

36
Q

GIP

Site of secretion:

D/t:

Action:

A

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
37
Q

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

A

Oral because it stimulates GIP which stimulates insulin secretion and has direct stimulatory effects on B cells…

Incretin effect

38
Q

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

A

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.

39
Q
A

GI Exam 1 (13 decks)

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