Lecture 5 - Motility

Question 1

How is feed procured?

Answer 1

lips, tongue, incisors

Question 2

Molars

Answer 2

grind the feed
- vary in use depending on diet and species

Question 3

Vertical vs lateral chewing

Answer 3

• vertical = carnivores and omnivores
• lateral = herbivores (better for grinding plant matter)

Question 4

Floating

Answer 4

• teeth wear unevenly due to grinding and continue to erupt

Question 5

Indications for floating

Answer 5

1. dropping feed
2. dropping wt
3. head tossing
4. balls of chewed hay coughed out

Question 6

2 swallowing phases

Answer 6

1. oropharyngeal phase
2. oesophageal phase

Question 7

Oropharyngeal swallowing phase

Answer 7

• bolus pushed back by tongue and triggers pressure receptors
• uvula blocks nose
• glottis and epiglottis blocks lung access
• swallowing center in medulla coordinates and inhibits respiratory center
• pharyngoesophageal sphincter opens

Question 8

Oesophageal swallowing phase

Answer 8

• peristaltic waves
• skeletal muscle
• cardiac sphincter opens

Question 9

Peristalsis motility

Answer 9

• waves of contraction
• peristaltic reflex (duodenum) programmed by enteric nervous system
• relaxation/contraction of longitudinal muscle and circular muscle

Question 10

Gastric motility steps

Answer 10

1. Fundus
   - receptive relaxation = making room
   - NO and VIP induced by ACh to induce relaxation
2. Corpus
   - mixing vat for saliva, food, and gastric secretions
3. Antrum
   - propulsion of food through pyloric sphincter to the duodenum
   - controlled by distension and parasympathetic

Question 11

Gastric emptying

Answer 11

• peristalsis
• pyloric sphincter opens and chyme enters duodenum
• regulated by force of contractions and signals from duodenum; rate dependent on physical and chemical state
• vagal component: vagotomy decreases contractions, stimulation of vagal nerve increats contrations

Question 12

Factors increasing gastric emptying

Answer 12

1. neural control
   - distension of gastric wall
   - increased parasympathetic
2. endocrine control
   - gastrin

Question 13

Factors decreasing gastric emptying

Answer 13

1. neural control
   - chemoreceptor, osmoreceptor, mechanoreceptor at duodenum
   - increased sympathetic
2. endocrine control
   - CCK, GIP, secretin

Question 14

Most common form of motility

Answer 14

Segmentation

Question 15

Segmentation

Answer 15

contraction of circular muscle where digesta is not propagated in one direction; alternating contractions for mixing
- frequency decreases distally

Question 16

Segmentation in the colon

Answer 16

• haustration = clearing

Question 17

Motility regulation duodenum

Answer 17

• stimulus = chyme distending duodenum
• sensors = stretch receptors in duodenal wall
• signal = nervous
• effector smooth muscle
• response = vigorous segmentation in duodenum
• effect = removal of chyme

Question 18

Motility regulation in ileum/colon

Answer 18

• stimulus = protein/digesta causing gastrin release
• response =
  1. gastro-ileal reflex: stimulates segmentation in ileum, gastrin inhibits the ileo-caecal sphincter so it opens
  2. gastro-colic reflex: mass movements in colon

Question 19

Tonic contraction

Answer 19

sustained contraction of muscle

Question 20

Mechanism for contraction

Answer 20

Interstitial Cells of Cajal (ICC)
- pacemakers in circular and longitudinal muscle layers that set a constant pulse of depolarization/repolarization in ssmooth muscle cells

Question 21

Basic electrical rhythm

Answer 21

smooth muscle cells have an intrinsic rhythm of depolarization/ repolarization frequency

Question 22

When does contraction occur?

Answer 22

When depolarization goes above threshold to cause action potential
- Ach (parasympathetic) increases the basal membrane potential to stimulate APs and contraction
- Norepinephrine (sympathetic) decreases resting basal membrane potential and prevents generation of APs and contraction

Question 23

small intestine motility in fed state

Answer 23

Segmentation reflex
- major type of motility
- mix luminal content
- regulated by ENS

Question 24

small intestine motility in fasting state

Answer 24

Migrating Myoelectric Complex - to push things along

Question 25

3 phases of migrating myoelectric complex

Answer 25

Phase 1: quiescent period Phase 2: intermittent contraction Phase 3: powerful propulsions to sweep intestinal content out

Question 26

Motilin

Answer 26

stimulates stomach and duodenum - intrinsic nerves stimulate distal duodenum and jejunum

Question 27

large intestine motility

Answer 27

Fxns: - microbial digestion - reabsorption of H2O and electrolytes Haustral contractions for mixing Peristaltic contractions to clear Antiperistaltic movement to fill cecum Aboral mass movement

Question 28

Antiperistaltic movement

Answer 28

motlilty in large intestine to fill cecum

Question 29

Stomach worms

Answer 29

increase gastric emptying

Question 30

vomiting center in the medulla

Answer 30

- activated by visceral afferents anywhere in GI; blockage or mucosal irritation = stimulus - vestibular stimulation = motion sickness; signal from perception - efferent nerves activate upper GI, diaphragm, and abdominal muscles - closes glottis, LES relations, stops respiration, somatomotor signals, abdominal pressure

Question 31

2 concerns with vomiting

Answer 31

1. significant fluid and electrolyte 2. acid-base imbalance

Question 32

How are most signals sent in the gut?

Answer 32

- interneurons; not being sent up the spinal cord to the brain

Question 33

Sympathetic effects

Answer 33

- inhibits digestion - postganglionic neurons release norepinephrine to decrease: 1. GI tract smooth m. motility 2. exocrine secretion 3. endocrine secretion

Question 34

Parasympathetic effects

Answer 34

- promote digestion - postganglionic neurons release acetylcholine to increase: 1. GI tract smooth m. motility 2. Exocrine secretion 3. Endocrine secretion

Question 35

Long reflex

Answer 35

1. stimulus: distention, osmolarity, food, pH 2. receptor cells: mechano and chemoreceptors 3. CNS 4. Ach (+) or Norep (-) released 5. effector cells: smooth muscle and endocrine cells 6. motility and secretion OR 1. Stimulus: smell, taste, sight 2. activates CNS 3. to enteric nervous system 4. effector cells: smooth muscle and endocrine cells 5. motility and secretion

Question 36

Short reflex

Answer 36

1. stimulus: distention, osmolarity, food, pH 2. receptor cells: mechano and chemoreceptors 3. enteric nervous system: myenteric plexus (sym and para) and Submucosal plexus (para) 4. effector cells: smooth muscle and endocrine cells 5. motility and secretion

Question 37

Ileus

Answer 37

- caused by inhibition of motor activity - increase activity upstream and decrease activity downstream - if blocked too long = distention then sympathetic reflex enters CNS = pain - common complication of inhibiting motor neuron activity