Sphincters

Question 1

Sphincter

Answer 1

One way valve

Composed of specialised circular muscle

Question 2

UOS

Circopharyngeus

Answer 2

Skeletal muscle - under voluntary control
At level C6 
Closed during inspiration
Relaxes (opens) to allow swallowing
Anatomical sphincter

Question 3

LOS

Answer 3

Smooth muscle - not under voluntary control
Located at gastro-oesophageal junction
Relaxes (opens) to allow entry of food into stomach
Closes to prevent reflux of gastric contents
Relatively weak sphincter
Physiological sphincter

Question 4

Pyloric Sphincter

Answer 4

Smooth muscle - not under voluntary control
Located at gastro-duodenal junction
Keeps food in stomach until it is the correct consistency for digestion
Regulates gastric emptying
Relaxes (opens) to allow entry of chyme into duodenum
Closes to prevent undigested stomach contents from entering duodenum

Question 5

Internal anal sphincter

Answer 5

Smooth muscle - not under voluntary control
Superior 2/3 of anal canal
Contraction is stimulated by sympathetic nerves (i.e. sphincter is closed)
Contraction is inhibited by parasympathetic nerves (i.e. sphincter is open, relaxed)
Mainly closed, only opens (relaxes) in response to filling of rectal ampulla

Question 6

External anal sphincter

Answer 6

Skeletal muscle - under voluntary control
Inferior 2/3 of anal canal
Contraction is stimulated by pudendal nerve (S2,3,4)
Voluntarily contracted in response to rectal ampulla filling until safe to defecate

Question 7

Anatomical sphincters of the biliary system

Answer 7

Bile duct sphincter
Pancreatic duct sphincter
Sphincter of Oddi