Motility of the gut

Question 1

Describe the GI muscle

Answer 1

Single unit- its a visceral muscle
GAP junctions that couples the cells- so acts as one unit

The Latch- bridge mechanism operates in this muscle
decreasing the use of ATP

The myosin actin arrangements =not highly structured

Peristalsis- requires both longitudinal and circular muscle

Interstitial cells of Cajal act as pacemakers- shows rhythmic cycles of activity

Question 2

Vagal Stimulation

Answer 2

increases gastric motility

Question 3

CCK

Answer 3

Decreases gastric motility

stimulates gall bladder contraction

Question 4

GIP

Answer 4

decreases gastric motility

Question 5

Secretin

Answer 5

decreases gastric motility

stimulates the HCO3- secretion

Question 6

what are the functions of gastric motility

Answer 6

Mixing and propulsion

Question 7

What are the interactions between in gastric motility

Answer 7

Smooth muscle
Enteric NS
Autonomic NS
Hormones

Question 8

What are the types of motility

Answer 8

Peristalsis- waves that move the bolus
Segmentation- churn and fragment a bolus
Sphincter tone and relaxation

Question 9

Factors affecting the GI motility

Answer 9

Smooth muscle functional synctium contracts due to either
NEURAL CONTROL
HORMONAL CONTROL

Question 10

Neural control

Answer 10

Autonomic and Enteric NS

Parasympathetic (Vagus):
Excitatory fibres ACH
Inhibatory (VIP/ADH)

Sympathetic 
    Inhibitory effects (noradrenaline)

Question 11

Hormonal Control

Answer 11

Endocrine (CCK, gastrin, motilin)

Local (paracrine)

Question 12

Muscle Layer DEEP-SUPERFICIAL

Answer 12

Oblique Muscle layer
Circular Muscle Layer
Longitudinal Muscle Layer

Act together in moving food backwards and forwards whilst pepsinogen and HCl being secreted

Question 13

What happens when the stomach starts to fill

Answer 13

Stomach pressure remains constant until 1L ingested
This is done due to the intrinsic ability of the smooth muscle to exhibit plasticity

Basic electrical rhythm initiated by pacemaker cells- initiate the peristaltic waves which move towards the pylorus (3mL/min)

Question 14

Where is the most vigorous activity by the pylorus

Answer 14

Mixing occurs mostly here- chyme is either

delivered in small amounts to duodenum
forced backwards into stomach for further mixing

NB Pyloric valve is important in preventing leakage

Question 15

How is the gastric emptying controlled?

Answer 15

Neural enterogastric reflex
Hormonal mechanisms

Inhibit gastric secretion and duodenal filling

Question 16

Motilin

Answer 16

increases gastric and intestinal

Question 17

Presence of fatty, hypertonic, acidic chyme in duodenum leads to

Answer 17

duodenal entero-endocrine cells secrete secretin CCK and gastrin which inhibits the contractile forced rate of stomach emptying

This leads to the decrease in Presence of fatty, hypertonic, acidic chyme in duodenum which leads leads to decrease in secretion of hormones.
( NEGATIVE FEEDBACK)

Question 18

The enteric nervous system

Answer 18

2 interconnected plexuses- myenteric and submosaic

Separate divisions of ANS as it contains complete reflex pathways- sensory, motor, interneurons

regulates GI system indapendantly of CNS

Question 19

Local and Central reflex pathways in the GI system

Answer 19

Local efferents from chemoreceptors and mecanoreceptors to the plexus regulate the cells of the GI systems

Chemoreceptors and mechanoreceptors send impulses to the CNS vis splanchnic and vagal efferents

CNS via sympathetic and parasympathetic efferents also regulate the cells fo GI system