Motility of the lower GIT

Question 1

In the GIT which organs are accessory organs?

Answer 1

• those involved in secretion purposes
• liver
• pancrease
• gallbladder
• oral salivary glands and the tongue

Question 2

What is the classification of the lower GIT?

Answer 2

• inferior to the suspensory muscle of the duodenum
• ligament of Treitz

Question 3

What are the 4 main components of the lower GIT?

Answer 3

1 - small intestines

2 - large intestines

3 - rectum

4 - anus

Question 4

What are the 3 parts of the small intestines, from top to bottom?

Answer 4

1 - duodenum = shortest

2 - jejunum = medium

3 - ileum = longest

Question 5

Generally how long does digestion in the small intestines take?

Answer 5

• 3-5 hours

Question 6

The small intestines (SI) has adapted and evolved to maximise digestion and absorption. How has the surface of the SI adapted to increase its surface area and this absorption?

Answer 6

• brush border micro villi

Question 7

There are 2 types of motility in the small intestines, what are they?

Answer 7

1 - segmentation which is mixing and circulation providing maximum exposure to villi

2 - peristaltic contractions to propel chyme

Question 8

During segmentation contractions of the GIT, what happens?

Answer 8

• mixing of chyme
• stretch receptors trigger myenteric muscle contraction

Question 9

During segmentation contractions of the GIT, is there any net movement or is segmentation just to mix digesta?

Answer 9

• no net movement
• mixing only

Question 10

During propulsive peristalsis of the GIT, is there any net movement or is segmentation just to mix digesta?

Answer 10

• movement of chyme through the digestive tract

Question 11

During propulsive peristalsis how does the GIT know to contract and move chyme?

Answer 11

• stretch receptors trigger myenteric plexus stimulation of muscle contraction
• net movement forwards

Question 12

In addition to stretch receptors activiting propulsive peristalsis, what else can contribute to GIT motility?

Answer 12

• hormones
• excitation via gastrin, CCK, insulin, motilin
• inhibition via secretin and glucagon

Question 13

There are a number of propulsive peristalsis reflexes that are triggered once chyme enters the lower GIT, stretches the GIT and stimulates the mysenteric plexus. Gastroenteric reflex is one of those reflexes, what is this?

Answer 13

• gastric distention activates myenteric plexus
• this promotes peristalsis with small intestine

Question 14

There are a number of propulsive peristalsis reflexes that are triggered once chyme enters the lower GIT, stretches the GIT and stimulates the mysenteric plexus. Gastroileal reflex is one of those reflexes, what is this?

Answer 14

• food in the stomach is recognised
• causes peristalsis in the ileum
• ileocecal valve opens and contents enter the large intestine

Question 15

There are a number of propulsive peristalsis reflexes that are triggered once chyme enters the lower GIT, stretches the GIT and stimulates the mysenteric plexus. The migrating motor complex s one of those reflexes, what is this?

Answer 15

• a pattern of electrical activity in the lower GIT
• purpose is to move SI contents
• occur between meals (around every 90 minutes)

Question 16

There are a number of propulsive peristalsis reflexes that are triggered once chyme enters the lower GIT, stretches the GIT and stimulates the mysenteric plexus. The migrating motor complex (MMC) is one of those reflexes. How is the MMC contriolled?

Answer 16

• intrinsic enteric control (no external stimulus needed)
• hormone motilin can also contribute

Question 17

There are a number of propulsive peristalsis reflexes that are triggered once chyme enters the lower GIT, stretches the GIT and stimulates the mysenteric plexus. The migrating motor complex (MMC) is one of those reflexes. The MMC is not only important for movement of chyme, but it also has another important purpose, what is this?

Answer 17

• ensure there is no bacterial overgrowth

Question 18

The enteric nervous system (ENS) is the intrinsic nervous system of the GIT and ensure mixing and peristalsis contractions. What are 2 alternative pathways that are able to module the mixing and peristaltic contractions of the large intestines?

Answer 18

1 - neural via autonomic nervous system

2 - hormonal secretions

Question 19

How often does the large intestine have mass movement peristaltic contractions per day?

Answer 19

• 2-3 times per day
• moves stool into rectum

Question 20

As the chyme moves through the large intestines, what is the large intestines doing to the properties of the chyme?

Answer 20

• extracting H2O
• changes chyme from liquid to faeces

Question 21

What strutctural aspect of the large intestines are involved in the mixing of the chyme?

Answer 21

• haustra bulges

Question 22

If there is poor motility of too much motility what can this do to the stool and symptoms for the patient?

Answer 22

• poor motility = constipation
• fast motility = diarrhea

Question 23

Mass movements of the large intestines (LI) are facilitated by reflexes in the upper GIT. What 2 reflexes, that are triggered by stretch receptors in the upper GIT contribute to mass movements every 2-3 hours in the large intestines?

Answer 23

1 - gastro-colic reflexes

• food stretches stomach and initiates contraction of LI

2 - duodeno-colic reflexes

• duodenum is stretched with food and signals the LI

Question 24

What is the defecation reflex?

Answer 24

• movement of faeces into the rectum (normally empty)
• rectum is stretched and activates the enteric nervous system (submucosa and myenteric plexus)
• stretch receptors also signal parasympathetic nervous system

Question 25

Once the stretch receptors of the rectum are activated due to the prescence of faeces, is it efferent or afferent nerve fibres that feed this information to the parasympathetic nervous system?

Answer 25

- afferent nerve fibres are sensory - efferent nerve fibres elicit an effect

Question 26

Once the stretch receptors of the rectum are activated due to the prescence of faeces, afferent nerve fibres feed this information to the parasympathetic nervous system, and then what happens?

Answer 26

- efferent nerve fibres of parasympathetic nervous system are stimulated - they provide stimulus for the internal anal sphincter

Question 27

There is the internal and external anal sphincter, which one comes under voluntary and involuntary control?

Answer 27

- internal = involuntary - external = voluntary

Question 28

The internal anal sphincter is under involuntary control, but what stops us from losing control of our defacation?

Answer 28

- external anal sphincter - skeletal muscle under voluntary control - relaxing of this allows control of defacation

Question 29

What is the prupose of emesis, more commonly known as vomiting?

Answer 29

- removal of dangerous ingested toxins from the GIT

Question 30

How many phases of emesis (vomiting) are there, and what are they called?

Answer 30

1 - nausea phase 2 - retching phase 3 - expulsive phase

Question 31

The first phase of emesis (vomiting) is nausea, what is this?

Answer 31

- unpleasant feelings, unease, and distress - feeling of the need to vomit.

Question 32

The second phase of emesis (vomiting) is retching, which normally elicits the act of vomiting, what is this?

Answer 32

- laboured respiratory movements - abdominal, thoracic and diaphram muscle (s) contract - diaphragm contraction downwards generates a pressure gradient to permit emesis

Question 33

The third phase of emesis (vomiting) is expulsion, which normally, what is this?

Answer 33

- involuntary emptying of gastric contents - emptying is due to pressure gradient caused by diaphragm - lower oesophageal sphincter

Question 34

In the final phase of vomitting, what happens to ensure, or at least minimise vomit entering the trachea or nasopharynx?

Answer 34

- epiglottis covers trachea - soft palate cover nasopharynx

Question 35

Where is the vomiting centre in the brain located and are adrenoreceptors or muscarinic receptors able to stimulate this?

Answer 35

- medulla oblongata - muscarinic as its involuntary (parasympathetic)

Question 36

What is the chemoreceptor trigger zone?

Answer 36

- area of the medulla oblongata - located ventrally to 4th ventricle - receives inputs from blood-borne drugs or hormones, and communicates with other structures in the vomiting center to initiate vomiting

Question 37

What is able to innervate the chemoreceptor trigger zone?

Answer 37

- dopamine - serotonin (5HT) receptors

Question 38

In addition to receiving inputs from blood-borne drugs or hormones, and communicates with other structures in the vomiting center to initiate vomiting, motion sickness is also able to eleicti vomiting. How does this work?

Answer 38

- labyrinth (inner ear-vestibular system) balance centre - innervates the chemoreceptor trigger zone (via cranial nerve 8) - 5HT innervates via serotonin