Overview of the Physiology of the GI Tract

Question 1

What are the two main layers of smooth muscle that can move material within the lumen of the digestive tract?

Answer 1

1. Muscularis mucosae
2. Muscularis externa

Question 2

What are the 4 main layers of the digestive tract wall?

Answer 2

1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa

Question 3

What is the mucosa comprised of?

Answer 3

• Epithelial cells
• Exocrine cells
• Endocrine glands
• Lamina propria
• Muscularis mucosae

Question 4

What is the name given to epithelial cells in the mucosa?

Answer 4

Enterocytes

Question 5

Exocrine glands in the mucosa will release what?

Answer 5

Regulatory peptides and amines

Question 6

What is the submucosa composed of?

Answer 6

Loose connective tissue

Largery lymph and blood vessels

Glands

Nerve network - submucosal plxus

Question 7

What is the name of the nervous system associated with the GI tract?

Answer 7

Enteric nervous system

Question 8

What is the enteric nervosu system composed of?

Answer 8

Submucosal plexus

Myenteric plexus (of the muscularis externa)

Question 9

What is the muscularis externa composed of?

Answer 9

1. A circular muscle layer
2. Nerve network - myenteric plexus
3. Longitudinal muscle layer

Question 10

What is the nerve network associated with the muscularis externa?

Answer 10

Myenteric plexus

Question 11

Where is the myenteric plexus found?

Answer 11

Between the two layers of smooth muscle

(circular layer and longitudinal layer)

Question 12

What is the serosa?

Answer 12

Connective tissue, part of the mesentery

This is the outermost layer

Question 13

What allows for GI motility?

Answer 13

Mainly - joint action of the circular and longitudinal layers of muscle

Also - action of the muscularis mucosae

Question 14

What is the collective name of the three bands of muscle that make up the longitudinal muscle?

Answer 14

Teniae coli

Question 15

What is the main purpose of the muscularis mucosae?

Answer 15

Change absoptive and secretory area

Also aids mixing

Question 16

What connects smooth muscle cells allowing from spread of electric current?

Answer 16

Gap junctions

Question 17

In the stomach, small and large intestines how does the electrical activity present?

Answer 17

Slow waves

Question 18

What are the pacemaker cells that given rise to the slow waves called?

Answer 18

Interstitial cells of Cajal

Question 19

What mediates the upstroke and downstroke of action potentials for the slow waves?

Answer 19

Upstroke - voltage activated calcium channels

Downstroke - volateg activated potassium channels

Question 20

The force of contraction of the muscularis externa is directly related to what?

Answer 20

The number of action potentials released by the interstitial cells of Cajal

Question 21

How many slow wave normally occur per minute in:

a) Stomach
b) Small intestine
c) Large intestine

Answer 21

a) 3
b) 12 in duodenum, 8 in terminal ileum
c) 8 in proximal colon and 16 in the distal colon

Question 22

Which factors act to inhibit slow wave activity?

Answer 22

Vasoactive internal polypeptides (VIP)

Nitric oxide

Question 23

What is the function for the myenteric plexus?

Answer 23

Regulates motility and sphincters

Question 24

In terms of function, what is special about the enteric nervous system?

Answer 24

It can function independently to the brain

(yet, it will respond to cues from the autonomic nervous system and hormones)

Question 25

What are the 3 main roles of the enteric nervous system?

Answer 25

1. Coordinate muscular activity 2. Control secretory action 3. Coordinate absorptive action

Question 26

How does the enteric nervous system achieve its roles?

Answer 26

* Sensory neurones - mechano, chemo and thermoreceptors * Inter-neurones - makes up majority of receptors, co-ordinatign reflexes, motor programs * Effector neurones - excitory and inhibitory motor neurones supply both muscle layers, secretory epithelium, endocrine cells and blood vessels

Question 27

Why are there no parasympathetic post ganglion neurones in gut?

Answer 27

Pre-synaptic neurones synapse with the ganglia in the enteric nervous system instead

Question 28

During peristalsis, which substances cause contraction of either the longitudinal or circular smooth muscle?

Answer 28

Acetylcholine and substance P | (from excitory neurone)

Question 29

During peristalsis, which substances cause inhibition of either the longitudinal or circular smooth muscle?

Answer 29

Vasoactive internal polypeptide (VIP) and nitric oxide (released from inhibitory neurone)

Question 30

The mixing/churning movements of the intestine have different names based on whether they occur in the small or large intestines, what are these?

Answer 30

Small intestine - segmentation Large intestine - haustration

Question 31

Name the 6 sphincters of the **_MAIN_** GI tract pathway

Answer 31

1. Upper oesophageal 2. Lower oesophageal 3. Pyloric 4. Ileocaecal 5. Internal anal 6. External anal

Question 32

As well as the 6 main sphincters, what is the other sphincter related to the main GI tract?

Answer 32

Sphincter of oddi (controls release of bile and pancreatic enzymes into duodenum)

Question 33

Which three phases are involved in swallowing?

Answer 33

1. Oral 2. Pharyngeal 3. Oesophageal

Question 34

Which is the voluntary phase in swallowing?

Answer 34

Oral phase

Question 35

By stimulating mechanoreceptors (as food is pushed towards oropharynx during swallowing) afferent nerve impulses are sent where, by which nerves?

Answer 35

CN IX and CNX Pons and medulla

Question 36

The pharyngeal phase of swallowing consists of inhibition of what whilst the food bolus passes?

Answer 36

Ventilation | (breathing)

Question 37

In the oesophageal phase of swallowing, the swallowing centre within the pons and medulla will trigger what?

Answer 37

* Closure of the upper oesophgeal sphincter * Initiate primary peristaltic wave (via CN X)

Question 38

If food becomes lodged in the oesophagus, what is the response from the body?

Answer 38

Local pressure receptors are stimulated Secondary peristaltic waves are stimulated for a more forceful contraction Saliva production also increases

Question 39

What controls peristalsis?

Answer 39

Enteric nervous system

Question 40

Why does the lower oesophageal sphicter close after the food bolus passes?

Answer 40

To prevent gastro-oesopheal reflux