Gastrointestinal Tract

Question 1

What is the overall function of the GI Tract

Answer 1

Digestion and absorption of nutrients

Question 2

What are the major organs of the GI Tract

Answer 2

Oral Cavity (mouth)
Pharynx (throat)
Oesophagus
Stomach
Small Intestine
Large Intestine
rectum lol

Question 3

What is the mucosa

Answer 3

The luminal lining of the trac

Question 4

What are the 4 layers of the GI tract from inside to out

Answer 4

Mucosa
Submucosa
Muscularis
Serosa - squamous epithelial cells, separated from muscularis by loose CT.

Question 5

What are the 3 layers of the mucosa

Answer 5

Epithelium
Lamina Propria - loose CT
Muscularis Mucosae - thin layer of smooth muscle that supports the mucosa and provides it with the ability to move and fold.

Question 6

What are the roles of the epithelium in the mucosa

Answer 6

Mainly protective in the mouth, oesophagus and anal canal

Secretion and Absorption in the stomach/intestines

Question 7

What is the role of the lamina propria

Answer 7

Contains blood and lymphatic vessels - loose CT between muscualris mucosae and epithelium

Question 8

What is the muscularis mucosae and what is its role

Answer 8

Thin layer of smooth muscle fibres pull mucosa into folds to increase the absorptive surface area

Question 9

Describe the neuronal networks in the highly vascular submucosa

Answer 9

Has a submucosal plexus AKA Meissner’s plexus - part of the enteric nervous system

Question 10

What do the neuronal networks of the highly vascular submucosa control

Answer 10

Primarily secretions but also the smooth muscle and blood vessel tone

Question 11

What parts of the muscularis are skeletal muscle and under voluntary control

Answer 11

Muscularis of the mouth, upper oesophagus and external anal sphincter - these are skeletal muscles

Question 12

What is the rest of the muscularis, that is not under voluntary control controlled by

Answer 12

Contains intrinsic nerve supply - myenteric plexus AKA auerbach’s plexus
This part is smooth muscle btw

Question 13

What does the intrinsic nerve supply in the muscularis control

Answer 13

Controls the GI tract motility

Question 14

What is the serosa

Answer 14

It is the superficial layer of those portions of the GI tract suspended in the abdominopelvic cavity

Question 15

What are the 2 distinct nervous systems that control GI tract activity

Answer 15

Autonomic nervous system

Enteric/internal nervous system

Question 16

What effect do the SNS and PNS have on GI tract activity

Answer 16

SNS - inhibitory action on GI tract activity

PNS - excitatory

Question 17

What plexuses make up the enteric nervous system

Answer 17

Myenteric plexus (Auerbach's)
Submucosal plexus (Meissner's)

Question 18

Describe the myenteric plexus and what it mainly controls

Answer 18

Situated between the longitudinal and circular muscle of the muscularis. Consists of a linear chain of interconnecting neurones and extends the full length of the GI tract.
Mainly controls motor activity along length of GI tract.

Question 19

Where is the submucosal plexus and what does it mainly control

Answer 19

Lies in the submucosa

Mainly controls secretions and local absorption function within the inner wall of each segment of the gut.

Question 20

What is mastication

Answer 20

The breakdown of food mechanically and initial enzymatic digestion of ptyalin (alpha-amylase)

Question 21

What is another word for swallowing

Answer 21

Deglutition

Question 22

What are the stages of swallowing

Answer 22

1. Oral stage - bolus to the back of the oral cavity
2. Pharyngeal stage (involuntary)
3. Oesophageal phase (involuntary)

Question 23

What are the main muscles involved in chewing

Answer 23

Masseter
Temporalis
Pterygoids

Question 24

What innervates the main muscle of mastication

Answer 24

The mandibular division of the trigeminal nerve

Question 25

What innervates the tongue

Answer 25

Hypoglossal nerve

Question 26

What nerve mainly supplies the buccinator and orbicularis iris muscles

Answer 26

Facial

Question 27

What does the bolus pass through in the pharyngeal stage

Answer 27

Oropharynx Cricopharynx Into the upper oesophagus

Question 28

What prevents nasal regurgitation of masticated food

Answer 28

The nasopharynx is shut off from the oropharynx in the pharyngeal stage by the contraction of muscles of the soft palate and posterior pharyngeal wall.

Question 29

Where does food pass to in the oesophageal stage

Answer 29

Propels food bolus down the oesophagus.

Question 30

What nerves mediate the oesophageal stage

Answer 30

The vagus nerve and sympathetic nerves

Question 31

What is the primary peristaltic wave

Answer 31

The positive pressure peristaltic wave that coincides with the entry of the bolus into the oesophagus

Question 32

What is the stripping wave

Answer 32

This is the smaller positive wave that clears the left over food material from the oesophagus.

Question 33

What are secondary peristaltic waves

Answer 33

Waves generated in the oesophagus in response to dilation of the oesophagus

Question 34

Describe tertiary peristaltic waves

Answer 34

Irregular, non-propulsive contractions involving large segments of oesophagus, that occur during emotional stress

Question 35

How does the rate of progression of peristaltic wave vary in different portions of the oesophagus

Answer 35

- upper part of oesophagus, the peristaltic wave progresses rapidly - Waves are more sluggish in the lower third of the oesophagus

Question 36

Why is there a difference in the rate of progression of peristaltic waves in different portions of the oesophagus

Answer 36

Due to the musculature being striated in the upper portion of the oesophagus and smooth at the lower 1/3 of the oesophagus

Question 37

What are the 3 layers of the smooth muscle in the muscularis

Answer 37

- Outer longitudinal - Middle circular - inner oblique

Question 38

What are the 3 types of exocrine gland cells in the gastric glands

Answer 38

Mucous Neck cells Chief (zymogenic) cells Parietal (oxyntic) cells

Question 39

What do mucous neck cells secrete

Answer 39

Mucus and HCO3-

Question 40

What do chief (zymogenic) cells secrete

Answer 40

The principal gastric enzyme precursor - pepsinogen

Question 41

What do parietal (oxyntic) cells secrete

Answer 41

HCl and an intrinsic factor involved in the absorption of Vit. B12

Question 42

What is gastric juice

Answer 42

This is the combined secretions of the 3 types of exocrine gland cells

Question 43

What are G cells (enteroendocrine) and what do they do

Answer 43

In mucosa, secrete gastrin

Question 44

What are the 4 major digestive secreted by enteroendocrine cells

Answer 44

Gastrin Secretin Choleocystokinin (CCK) Gastric Inhibitory Peptide (GIP)

Question 45

What does gastrin do

Answer 45

stimulates G cells of stomach to secrete gastric juice, a mix of HCl and pepsinogen

Question 46

What does CCK act on and what reaction does it cause

Answer 46

Acts on gall bladder Simulates it to contract and release bile Acts on pancreas to release pancreatic digestive enzymes into the pancreatic fluid

Question 47

When is secretin released

Answer 47

Secreted by cells in the duodenum when exposed to acidic contents of the emptying stomach (causes bicarbonate release to neutralise acid)

Question 48

What does secretin stimulate

Answer 48

Stimulates the pancreas to secrete bicarbonate into the pancreatic fluid (neutralising the acidity of the intestinal contents)

Question 49

What are the phases of gastric secretion

Answer 49

Cephalic Gastric Intestinal

Question 50

What is the cephalic phase of gastric secretion

Answer 50

Sight/sound/smell initiates reface via medulla, hypothalamus and vagal output to stimulate submucosa plexus to increase gastrin release, gastric peristalsis and HCl release

Question 51

What is the gastric phase of gastric secretion

Answer 51

Food stretches stomach wall, stretch receptors and chemoreceptors increase submucosal plexus activity that increases gastric juice secretion Increased myenteric plexus activity increases stomach peristalsis. Increased parasympathetic = release of gastrin by enteroendocrine cells

Question 52

What is the intestinal phase of gastric secretion

Answer 52

Activation of receptors in duodenum results in hormonal/neuronal reflexes that are inhibitory on gastric motility and gastric acid secretion. 3 hormones, Secretin inhibits gastric juice secretion, CCK inhibits motility and GIP inhibits both.

Question 53

What is the submucosa

Answer 53

The submucosa is a thick connective tissue layer that contains arteries, veins, lymphatics, and nerves.