Smooth Muscle

Question 1

where in the GI tract is skeletal muscle found?

Answer 1

pharynx , top 1/3 of the oesophagus and the anal sphincter

Question 2

what are the 2 types of smooth muscle present in the GI tract?

Answer 2

phasic and tonic

Question 3

where is tonic muscle found?

Answer 3

sphincters e.g. lower oesophageal, ileocecal (between large and small intestine), internal anal and orad (upper stomach)

Question 4

where is phasic muscle found?

Answer 4

rapid contraction and relaxation, this is present in the body of the oesophagus, stomach antrum and small/ large intestines (e.g. peristalsis)

Question 5

what is the role of myenteric plexus?

Answer 5

Involved in tonic contractions, can increase their rhythm and intensity for peristalsis

Question 6

what is the role of the submucosal plexus?

Answer 6

Submucosal plexus has more of a sensory function and it modulates intestinal absorption

Question 7

Give an example of a GI reflex?

Answer 7

Gastro-colic reflex, when stretch is detected in the stomach motor activity increases in the colon to provide space for the new chyme

Question 8

explain Hirschsprung’s disease

Answer 8

(causes megacolon)- congenital lack of nerve cells in the lower colon, this makes the area become aperistaltic and it becomes tightly wound leading to megacolon before the point where the nerves are missing

Question 9

explain chagas disease

Answer 9

infectious disease of a parasitic nature, resulting in a reduction in the number of ganglionic cells

Question 10

explain achalasia

Answer 10

dramatic reduction in the number of neuronal cells in the lower esophagus

Question 11

what is the vago-vagal reflex?

Answer 11

The vago-vagal reflex relaxes the fundus (upper area of the stomach) when there is stretching in the oesophagus, this is known as receptive relaxation

Question 12

how is stomach pressure prevented from greatly increasing during digestion?

Answer 12

highly folded structure that flattens out and relaxes in response to vagus stimulation

Question 13

explain the cephalic phase of gastric motility?

Answer 13

Inhibitory fibres stimulated in vagus nerve to allow large volume to enter stomach

Question 14

explain the gastric phase of gastric motility?

Answer 14

• Excitatory phase where the stomach empties at rate proportional to volume in it
• Activation of pressure receptors and release of gastrin stimulates activity
• Myogenic reflex - stretching smooth muscle causes reflex contraction

Question 15

explain the intestinal phase of gastric motility?

Answer 15

• Mainly an inhibitory phase to prevent overloading of the small intestine
• Hormones and paracrine systems regulate the phase
• e.g. high levels of fat = release of CCK which inhibits gastric motility

Question 16

what are the 3 main functions of gastric motility?

Answer 16

• Peristaltic contractions- propulsion allowing propagated movement of food to be absorbed and eliminate waste products at the end
  
  • Produces segmental contractions- not related to propulsion that increase churning / mixing of food to aid absorption of nutrients
    Allows organs such as the stomach and large intestine to act as revisors, made possible by the sphincters

Question 17

how often does the MMC occur?

Answer 17

every 90-120mins

Question 18

what is the function of the MMC?

Answer 18

• Has a nutritional and cleansing function
  
  • Removes undigested squamous cells (from desquamation), bile and pancreatic secretions and undigested food
  • It also keeps bacteria populations in check e.g. prevents the migration of colonic bacteria into the terminal ileum

Question 19

what are the 2 types of motility in the colon?

Answer 19

colonic rhythmic phasic and giant migrating contractions