GI Motility

Question 1

What are the functions of the GI tract?

Answer 1

• digestion and absorption
• secretion
• storage
• defecation
• motility
• defence (immunity)

Question 2

What is GI Motility

Answer 2

It is the muscular contractions that mix and move the contents to the appropriate sites for digestion and absorption.

Question 3

What are the 2 patterns of motility?

Answer 3

• Peristalsis- moves food anally in response to wall stretch
• segmentation- mixes lumen content

Question 4

What are the 3 ways of regulating GI motility?

Answer 4

1. Reflexes that originate outside the digestive system (called long reflexes) - Extrinsic
2. Reflexes that originate inside the digestive system (called the enteric nervous system or short reflexes) - Intrinsic
3. Gastrointestinal (GI) Peptides

Question 5

What is the extrinsic nervous system composed of?

Answer 5

parasympathetic and sympathetic

Question 6

Role of the Sympathetic nervous system on GI Motility?

Answer 6

• in the GI tract they originate between T5 & L2 of spinal cord
• Innervates all of GI tract
• nerve endings secrete mainly NE and epinephrine
• stimulation inhibits GI activity

Question 7

Role of Parasympathetic Nervous system on GI Motility?

Answer 7

• in the gut it is divided into cranial and sacral
• cranial PN fibres are almost in the vagus nerves, except to mouth & pharyngeal.
• sacral originate from 2-4 sacral segment of spinal cord
• it passes through pelvic nerve to distal half of large intestine
• stimulation causes increased activity.

Question 8

Function of GI polypeptides:

Answer 8

Endocrine regulation of GI tract are mediated by release of hormones by triggers associated with food.

Active polypeptides are secreted by nerve cells and glands in the mucosa.

many types of hormone-secreting enteroendocrine cells have been identified in gut mucosa.

they are identified by letters (G cells, I cells etc), and release hormones such as gastrin, CCK, secretin, GIP, and Motilin:

they inhibit / increase gastric motility to maximise digestion & absorption.

Question 9

The function of cholecystokinin:

Answer 9

• produced by I cells in duodenum and jejunum
• also secreted by neurons in the brain
• stimulates contraction of gall bladder for bile release
• Stimulation of pancreatic enzyme release
• relaxes Sphincter of Oddi
• inhibits gastric emptying by slowing contraction,
• promotes intestinal motility

Question 10

The function of secretin:

Answer 10

• produced by S cells of upper small intestine mucosa.
• mildly affects gastric emptying,
• promotes pancreatic secretion of HCO3

Question 11

Function of GIP:

Answer 11

GIP
- secreted by “K cells” mainly in duodenum
- slows the rate of stomach emptying when SI is overloaded.

Question 12

Function of GLP-1

Answer 12

GLP-1
- produced by “L cells” in distal small intestine mucosa.
- delays gastric emptying

Question 13

Function of Gastrin

Answer 13

Gastrin
- released from the gastric antrum G cells by stomach distension.
- increases motility in the stomach.

Question 14

Function of Motilin:

Answer 14

Motilin
- secreted by “M-cells” in the upper small intestine.
- secreted during fasting, and the only known function of this hormone is to increase gastrointestinal motility - migrating motor complex

Question 15

What are the 3 segments of the oesophagus and its innervation?

Answer 15

3 segments are cervical, thoracic and abdominal

• The proximal one-third (1/3) is striated muscle
  innervated by somatic motor neurons of vagus nerve without interruption
• The distal two-third (2/3) part is smooth muscles.
  innervated by visceral motor neurons of vagus nerve with interruptions (-synapse with postganglionic neurons; cell bodies in oesophagus)