Regulation of gut function

Question 1

What ganglia innervate the stomach, small intestine and colon?

Answer 1

coeliac ganglion - Stomach
superior mesenteric ganglion - Small intestine + ascending large intestine
inferior mesenteric and pelvic ganglion - Transverse colon to rectum

Question 2

What is the neurotransmitter used in the sympathetic NS innervating the GI tract?

Answer 2

Norepinephrine-Only at effector organs

Question 3

Where do the pre-ganglionic sympathetic neurones arise from in the spinal cord that innervate the stomach and colon?

Answer 3

Thoracic and lumbar spinal cord
Stomach (T6-9)
Colon (L2-5)

Question 4

What does activation of the sympathetic NS do to the GI tract?

Answer 4

Inhibits its activities

Question 5

What are the divisions of the GI tract NS?

Answer 5

Question 6

How is the stomach, small intestine and proximal colon parasympathetically innervated?

Answer 6

Vagus nerve

Question 7

What NT is used in the parasympathetic innervation of the stomach, small intestine and the proximal colon and where do the preganglionic neurones originate from?

Answer 7

ACh

Preganglionic neurons originate in dorsal vagal complex within brainstem from sacral spinal cord.

Question 8

What does activation of the parasympathetic NS do to the GI tract?

Answer 8

Stimulates its activities

Question 9

In the GI sympathetic NS, are the ganglia close or far from the effector organs?

Answer 9

Far

Question 10

In the GI parasympathetic NS, are the ganglia close or far from the effector organs?

Answer 10

Close

Question 11

What are the NTs in the GI NS?

Answer 11

ACh everywhere apart from sympathetic target organs

Question 12

Where are neurones myelinated/unmyelinated in the GI NS?

Answer 12

Myelinated pre-ganglionically, Unmyelinated post-ganglionically

Question 13

What is a plexus?

Answer 13

A network of interconnecting nerves

Question 14

Where are the plexuses of the GI tract enteric(intrinsic) NS and which intestinal layers are they in?

Answer 14

Meissner’s plexus-Submucosa

Auerbach’s plexus-Muscularis Propria

Question 15

What is the general function of the enteric NS?

Answer 15

“The 2nd brain”
Autonomous
Can also interact with sympathetic and parasympathetic nervous system
The wall of the gastrointestinal tract contains many neurons – 2nd only to the brain

Question 16

What is the function of Meissner’s(Submucosal) plexus?

Answer 16

Senses the local environment (gut lumen)

Controls secretion, blood flow, epithelial and endocrine cell function

Question 17

What is the function of Auerbach’s(Myenteric) plexus?

Answer 17

Controls activity of muscularis propria

Controls gut motor (motility) function
tone, velocity of contraction and intensity of contraction.

Question 18

Describe the pathway of the local enteric reflex

Answer 18

1. Food enters gut and stretches smooth muscle
2. Distension activates neurones in the myenteric plexus, chemicals in food stimulate submucosal plexus
3. Sequential contraction/relaxation of circular+longitudinal muscles causes peristalsis

Question 19

What are the actions of the circular and longitudinal muscles in peristalsis

Answer 19

Circular muscles contract behind the bolus
Longitudinal muscles contract in front of the bolus(Lumen widens)

Question 20

What are the effects of the sympathetic nervous system on the enteric NS?

Answer 20

Reduces peristalsis
Reduces absorption
Reduces secretion
Reduces blood flow (via enteric nervous system and also directly)

Question 21

What are the effects of the parasympathetic nervous system on the enteric NS?

Answer 21

Increases peristalsis
Increases absorption
Increases secretion
Increases blood flow

Question 22

What is the cause and mechanism of Hirschsprung’s Disease?

Answer 22

Congenital absence of ganglion of myenteric and submucosal-No enteric NS

Tonal contraction without reciprocal relaxation

Intestinal distension proximal to a-ganglionic segment of bowel

Most will require surgery

Question 23

What are enteroendocrine cells and what is their function?

Answer 23

Specialised epithelial cells located at the base of intestinal crypts throughout the GI tract, from stomach to colon

Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries, that secrete their hormone in response to a wide range of stimuli

Question 24

What molecules are secreted in the stomach?

Answer 24

gastrin, ghrelin, somatostatin and histamine

Question 24

What moelcules are secreted in the pancreas?

Answer 24

insulin, glucagon, somatostatin and pancreatic polypeptide

Question 25

What molecules are secreted in the duodenum?

Answer 25

secretin, CCK and somatostatin

Question 26

What molecules are secreted in the colon?

Answer 26

PYY, GLP-1, Oxyntomodulin, neurotensin and somatostatin

Question 27

What molecules are secreted in the small intestine?

Answer 27

PYY, GIP, GLP-1+2, Oxyntomodulin, neurotensin and somatostatin

Question 28

What is the: function, place of production requirements for secretion of gastrin?

Answer 28

Stimulates **gastric acid secretion** by parietal cells in stomach Synthesised in **gastric antrum and upper small intestine** Release stimulated by:- **amino acids and peptides in the lumen of the stomach gastric distension vagus nerve Release inhibited when pH of stomach falls below pH 3**

Question 29

What is the: Place of secretion function, requirements for secretion of secretin?

Answer 29

Secreted by the **S cells of the upper duodenum and jejunum** **Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)** Function: **stimulates pancreatic bicarbonate secretion** (effect potentiated by CCK) inhibition of gastric acid and gastric emptying inhibits gastrin, acid secretion, and growth of stomach mucosa stimulates biliary secretion of bicarbonate and fluid trophic effect on the exocrine pancreas

Question 30

What is the: function, requirements for secretion, place of secretion for cholecystokinin?

Answer 30

**Secreted by cells most densely located in the small intestine** **Release stimulated by fat and peptides in the upper small intestine** **stimulates pancreatic enzyme release (lipase, amylase, proteases)** stimulates gallbladder contraction and relaxation of the sphincter of Oddi delays gastric emptying decreases food intake and meal size trophic effects on the exocrine pancreas and gallbladder

Question 31

Function of motilin?

Answer 31

Increases GI motility

Question 32

What is the: place of secretion, function, requirements for secretion of GIP? (glucose-dependent insulinotropic peptide)

Answer 32

Also known as Gastric inhibitory polypeptide **Secreted by mucosal K cells** (predominant in the duodenum and jejunum) GIP released **following ingestion of a mixed meal** **The only hormone with a response to all 3 macronutrient types (glucose, amino acid, fatty acids)** Likely stimulated by change in intraluminal osmolarity **Stimulates insulin secretion**

Question 33

What is the: place of secretion function requirements for secretion for GLP-1?

Answer 33

**Produced in the small intestine and secreted from L cells** Release stimulated by the presence of **hexose and fat** Induces satiety **Increases sensitivity of pancreatic beta-cells to glucose**

Question 33

What is the: place of synthesis requirements for secretion function for pancreatic polypeptide

Answer 33

Secreted by PP cells in the pancreas Secretion stimulated by fat **Potential role in satiety**

Question 34

What is the: place of synthesis, function requirements for secretion of somatostatin

Answer 34

Synthesized in endocrine **D cells of the gastric and duodenal mucosa, pancreas** Somatostatin is a universal inhibitor (Endocrine Cyanide) **Release in response to a mixed meal** Inhibition of **gastric secretion motility intestinal and pancreatic secretions release of gut hormones intestinal nutrient and electrolyte transport growth and proliferation**

Question 35

What is the: place of secretion function of peptide YY?

Answer 35

Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum Released from **L cells post- prandially (particularly protein)** **Reduces intestinal motility**, gallbladder contraction and pancreatic exocrine secretion

Question 36

What are the functions of the neuroendocrine hormones *and* where are they located? (VIP, GRP, enkephalins)

Answer 36

Located within nerves in the gut Vasoactive intestinal peptide (VIP) → relaxation of gut smooth muscle Gastrin releasing peptide (GRP) → induces gastrin release Enkephalins → increase smooth muscle tone

Question 37

Where are neuroendocrine tumours found and give an example of one type and 2 ways to treat them?

Answer 37

Tumours of the **neuroendocrine cells (which are found predominantly in the gastrointestinal tract and pancreas)** For example, *Zollinger Ellison syndrome – tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration* **- treatment with proton pump inhibitor to inhibit acid secretion - role for somatostatin analogues to halt tumour growth and reduce secretion**

Question 38

What occurs in the gastric phase of gastric secretion?

Answer 38

Food causes distension in stomach, causing vagus nerve to innervate the brainstem, in turn stimulating more stomach secretion **-Stomach distension and food chemicals activate enteric(intrinsic) NS to stimulate secretions**

Question 38

What occurs in the cephalic phase of gastric secretion?

Answer 38

Smell, thought of food stimulates brainstem, **PS NS via vagus nerve** innervates enteric plexus, Post-ganglionic neurones **stimulate secretion of gastrin, acid- and digestive enzymes**

Question 39

What occurs in the intestinal phase of gastric secretion?

Answer 39

**Chyme in duodenum with pH<2 causes brainstem stimulation, inhibiting gastric secretions** Local acid/lipid reflexes also work on the enteric NS, reducing secretions **Secretin, GIP and cholecystokinin, released by the duodenum inhibit gastric secretions.**