motility in GI tract

Question 1

how does a skeletal muscle contact?

Answer 1

stimulated by neurons

Motor neurons innervate skeletal muscle via axon branching and forming junctions with the muscle

Question 2

what happens at the neuromuscular junction when a muscle is trying to contact?

Answer 2

action potential in motor neurone leads to ach release at cleft

ACh binds to receptors on the motor end plate opening ion channels and resulting in depolarisation

Question 3

what does action potential in the t-tubule trigger?

Answer 3

Ca2+ to enter and increased concentration

Ca2+ binds to troponin to allow force generation and contraction

Removal of Ca2+ from the cytosol is required for relaxation

Question 4

what is segmentation initiated by?

Answer 4

electrical activity of interstitial cells of cajal (pacemaker cells)

Question 5

what are varicosities?

Answer 5

bulbous swellings of nerve fibres which release NTs into a wide synaptic cleft

Question 6

How does E-C coupling occur in smooth muscle

Answer 6

No tropinin is involved

Contractile proteins are regulated by Ca2+/CaM activation of myosin light chain kinase resulting in phosphorylation of myosin which causes contraction

Question 7

why is cAMP important during E-C coupling of smooth muscle?

Answer 7

it’s a second messenger which inhibits MLCK

Question 8

what does exciting neurotransmitter that lead to contraction include?

Answer 8

ACh and 5-HT

Question 9

What does inhibitory neurotransmitters that lead to relaxation include?

Answer 9

VIP (vasoactive intestinal peptide) and NO (nitric oxide)

Question 10

what is rate of absorption and transit time slower in the ileum?

Answer 10

allow absorption of more slowly digested substances eg. fats , bile , fat soluble vitamins

Question 11

what activity occurs in the fasted state and what is it known as?

Answer 11

interdigestive peristaltic activity which is known as a the migrating myoelectric complex which begins in the stomach

Question 12

what happens during MMC once the complex reaches the ileum?

Answer 12

another starts in the stomach which moves undigested material towards the large intestine

Question 13

MMC is initiated by an increase of what hormone

Answer 13

Motilin (increases neuronal activity)

Question 14

what is the motility pattern in the fed state?

Answer 14

produces random activity of sequential contractions (segmentation)

solid foods included twice the amount of contractions to equicalorific liquid

Question 15

what are anti-spasmodic?

Answer 15

reduce smooth muscle contraction (anti-muscarinic antagonist)
eg. hyoscine butylbromide and mebeverine

Question 16

what is anti-motility therapy?

Answer 16

reduces transit through the GI tract by decreasing activity of myenteric plexus (eg loperamide)

Question 17

what is prokinetics therapy?

Answer 17

stimulates GI tract activity by increasing contraction by acting on the 5-HT receptors eg. metoclopramide

Question 18

how do laxatives work?

Answer 18

stimulate initestinal movement by increasing bulk, adding lubricant or acting as a local irritant to the mucosal layer