Overview of GI Tract

Question 1

functions of GI tract

Answer 1

1. intake, digestion, and absorption of nutrients
2. immune and endocrine organ
3. regulates food intake and glucose homeostasis
4. establishes gut microbiome
5. largest interface between outside and inside world

Question 2

components of GI tract

Answer 2

• esophagus
• stomach
• small intestine
• large intestine
• rectum & anus
• accessory organs

Question 3

esophagus function

Answer 3

transport and protection

Question 4

stomach function

Answer 4

storage and controlled delivery of digests to small intestine

Question 5

small intestine function

Answer 5

mixing, digestion, and absorption

Question 6

large intestine function

Answer 6

reclaim water, site of gut microbiota, storage

Question 7

rectum & anus function

Answer 7

waste storage and defecation

Question 8

accessory GI organs

Answer 8

liver
pancreas
gallbladder

Question 9

layers of the GI tract

Answer 9

1. mucosa
2. submucosa
3. muscularis
4. serosa

Question 10

mucosa

Answer 10

innermost layer; surface lining of the GI tract lumen

Question 11

intestinal lumen

Answer 11

body cavity that communicates with the external environment

Question 12

components of the mucosa

Answer 12

1. epithelium
2. lamina propria

Question 13

mucosal epithelium

Answer 13

outer layer of absorptive and secretory cells

Question 14

mucosal lamina propria

Answer 14

inner layers containing blood vessels, nerves, and immune cells

Question 15

submucosa

Answer 15

loose connective tissue beneath the mucosa that provides support
- contains larger blood vessels, lymphatics, nerve plexus, and ganglion cells

Question 16

submucosal plexus

Answer 16

ganglia of nerves of the enteric nervous system

Question 17

muscularis

Answer 17

two layers of smooth muscle located beneath the submucosa
- extends from esophagus to anal canal

Question 18

layers of muscularis

Answer 18

outer longitudinal muscle
inner circular muscle

Question 19

myenteric plexus

Answer 19

enteric nerves located between muscle layers

Question 20

serosa

Answer 20

outermost layer of epithelium and connective tissue

Question 21

why does GI tract function need to be regulated

Answer 21

1. initiate postprandial and inter-meal periods
2. maximize nutrient absorption based on diet
3. allows for communication between proximal and distal regions and accessory organs

Question 22

control mechanisms of GI

Answer 22

1. endocrine
2. neural
3. paracrine

Question 23

enteroendocrine cells

Answer 23

process signals and respond to food intake
- have mechanoreceptors and chemoreceptors in lumen
- release peptides/hormones in response to changes in lumen environment

Question 24

GI hormones

Answer 24

hormones synthesized by enteroendocrine cells; must be:
- present in the gut
- released by appropriate physiological stimulus
- produce an appropriate response
- have identified structure
- blocked by an antagonist

Question 25

extrinsic nervous system

Answer 25

cell bodies are located outside of the gut wall

communicate with enteric nerves and CNS

• afferents: vagal and spinal
• efferents: vagus and pelvic nerves (parasympathetic)

Question 26

what portion of the gut does the vagus nerve innervate

Answer 26

innervates proximal portion of the gut

Question 27

what portion of the gut does the pelvic nerve innervate

Answer 27

innervates distal portion of the gut

Question 28

function of visceral afferents

Answer 28

transmit information from gut to CNS for REFLEXES only (no consciousness)

allows for homeostatic regulation in response to external stimuli

Question 29

enteric nervous system (ENS)

Answer 29

intrinsic; cell bodies are located inside the gut wall

most ENS nerves do NOT receive CNS input

contains neurotransmitters

Question 30

where are the nerves of the enteric nervous system located

Answer 30

submucosal and myenteric plexus

Question 31

function of submucosal plexus

Answer 31

regulates secretions and absorption

Question 32

function of myenteric plexus

Answer 32

regulates motility and contractility

Question 33

intrinsic primary afferent neurons (IPANs)

Answer 33

neurons that communicate afferent information within the ENS

cell bodies located in submucosal & myenteric plexus

Question 34

function of IPANs

Answer 34

regulates contraction and secretions of the gut WITHOUT CNS input
- activates local secretory cells
- regulates blood flow

Question 35

vago-vagal reflex

Answer 35

extrinsic reflex pathway that controls contraction of the GI muscle layer in response to distention by food
- regulates gut function
- vagal afferent stimulates vagal efferent to cause: receptive relaxation, acid/enzyme/hormone secretion/antral contraction