Lecture 11-Control of digestion

Question 1

What is probiotic bacteria?

Answer 1

• bacteria that can get through the stomach to the colon -stomach is a big barrier

Question 2

What is the gut-brain axis?

Answer 2

-brain and gut communicate= 2 directional communication

Question 3

What happens in the digestive process, simply?

Answer 3

1. Food taken into mouth 2. Broken down into ever smaller components, eventually into individual molecules 3. Separated chemically( and physically= as fat rises to the top in the stomach as it is lighter and gets emptied into the intestine last) into different nutrients that can be absorbed 4. Bi-products transported along the intestinal tract for further processing and recovery of key materials 5. Waste products excreted

Question 4

How is fat important in digestion?

Answer 4

–fat activates lot of receptors in the mucosa -and the overall satisfaction with the food is dependent on fat -enough nutrients= duodenum= says that -we can overcome that= by apetite (thalamus)

Question 5

What os vomiting for?

Answer 5

-if take in something noxious= vomit -evolved to be used for purposes of getting rid of noxius material in as short time as possible

Question 6

What components are proteins, sugars and fats broken down into?

Answer 6

-proteins= amino acids -sugars and starches into simple sugars= glucose, fructose and galactose -lipids into fatty acids and glycerol

Question 7

Where does most of the compounds breakdown happens?

Answer 7

-the breakdown happens mostly in upper duodenum and distal stomach, very little elsewhere (mouth)

Question 8

What is the fermentation in animals used for?

Answer 8

-many species use bacterial fermentation to breakdown cellulose-into short chain fatty acids and sugars -if you’re a herbivore= deal with food that is indigestible, cellulose in plants -plants and leaves make their way through the duodenum, reach distal gut= process of fermetation occurs (not breaking down the food, it is converting it to sth else) = into short fatty acids)= extremely inefficient, herbivores are larger due to this -even humans use cellulose breakdown, the production of short chained fatty acids, = these activate things in the brain -represent about 30% of energy requirement in the distal gut

Question 9

Where in humans do the short chain fatty acids play an important role?

Answer 9

-in the energy metabolism of mucosa in the ascending colon

Question 10

What is the diet of animals with active life-styles like?

Answer 10

-tend to depend on foods high in simple sugars and protein= as those are easy to digest

Question 11

What neurons are involved in digestion?

Answer 11

-both somatic and visceral -also endocrine system! (gut is the biggest endocrine organ)

Question 12

What does the somatic nervous system control in digestion?

Answer 12

-conscious control -chewing, swallowing, peristalsis in esophagus and opening key sphincters -as soon as you get to oesophagus= mostly visceral control

Question 13

What do the visceral neurons control in digestion?

Answer 13

-involved in salivation, primary peristalsis, all functions from stomach to anus

Question 14

What visceral neurons are involved in digestion?

Answer 14

-sympathetic and parasympathetic nervous systems, many types of visceral afferents and the enteric nervous system

Question 15

What happens when we see or smell food?

Answer 15

-cephalic phase of digestion -salivation, gastric relaxation, gastric acid secretion -happens via NS (vagus) in particular -no food needs to be digested -depends on hunger and appetite (depends on the hypothalamic regions of hunger) -food in mouth gives same behaviours=but also activates gustation and olfaction

Question 16

How does the palatability of the food effect cephalic phase?

Answer 16

• more palatable the food, the greater the response (use memory as part of the process) -partly determined by nature of food previously eaten

Question 17

What does hypothalamus do?

Answer 17

-regulates hunger

Question 18

What happens when food is in the mouth?

Answer 18

-chewing -movement of tongue -swallowing

Question 19

How is chewing controlled?

Answer 19

-it is a rhythmic activity -depends on motor pattern generator in brain stem -has a hedonic component (nice to do) -under voluntary control thus cortical involvement -sucking is essential for early survival-seems to have hedonistic component

Question 20

How is tongue movement controlled?

Answer 20

-voluntary set of muscles, controlled via motor cortex -huge number of muscles, not grounded much

Question 21

How is swallowing controlled?

Answer 21

-voluntary process, motor pattern generator in the brain stem -you’ll gag if you don’t swallow properly -swallowing center

Question 22

What happens in the oesophagus?

Answer 22

-primary peristalsis= CNS -secondary peristalsis=ENS -upper and lower sphincters important to regulate reflux

Question 23

What happens in primary peristalsis in the oesophagus?

Answer 23

-controlled by the CNS via vagus, differs from species to species -in humans much of oesophagus is striated muscle,as more distal= smooth muscle then still controlled by vagus but part of the enteric nervous system -primary peristaltic wave, which occurs when the bolus enters the esophagus during swallowing. The primary peristaltic wave forces the bolus down the esophagus and into the stomach in a wave lasting about 8–9 seconds. The wave travels down to the stomach even if the bolus of food descends at a greater rate than the wave itself, and will continue even if for some reason the bolus gets stuck further up the esophagus.

Question 24

What happens in secondary peristalsis in the oesophagus?

Answer 24

-controlled by the enteric nervous system -In the event that the bolus gets stuck or moves slower than the primary peristaltic wave (as can happen when it is poorly lubricated), stretch receptors in the esophageal lining are stimulated and a local reflex response causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus, and these secondary waves will continue indefinitely until the bolus enters the stomach. The process of peristalsis is controlled by medulla oblongata.

Question 25

What is the importance of the upper and lower oesophageal sphincters?

Answer 25

-upper= involved in gag reflex -lower= so acid from stomach doesn’t get into oesophagus= then achalasia (human disease)

Question 26

What is special about ruminants and reflux?

Answer 26

-vomiting is important part of normal digestive function in ruminants, like cows, sheep, antelope, giraffes -the rumination = vomit back to mouth -so there the vomiting is actually part of the normal digestion process

Question 27

How is the stomach innervated?

Answer 27

-major peripheral control network under substantial central regulation via vagus -lesser role for sympathetic nervous system -has important control system via pacemaker cells in antrum(the beginning of the stomach) (intersitial cells of Cajal ICC) -ENS less well studied than vagal control systems-may act like a parasympathetic ganglion with some autonomy

Question 28

What does parasympathetic mean?

Answer 28

-end target close to origin

Question 29

What do the interstitial cells of Cajal do?

Answer 29

-pacemaker cells, in the antrum of the stomach, start the contractions of the stomach

Question 30

What happens in the small and large intestine?

Answer 30

-where the action is! -digestion -absorption -propulsion

Question 31

Where in the small and large intestine does digestion occur?

Answer 31

-duodenum and jejunum

Question 32

Where in the small and large intestine does absorption occur?

Answer 32

-nutrients=duodenum,jejunum -water=ileum,colon

Question 33

Where in the small and large intestine does propulsion occur?

Answer 33

-whole length

Question 34

How long is the small and large intestine in humans?

Answer 34

-6m small intestine -1m large intestine (guinea pigs= about 1m for small intestine)

Question 35

What do the small and large intestines do as chemical refineries?

Answer 35

-mixing food (converted to slurry by stomach) with enzymes and water -neutralizing acid -allowing for absorption -recovering reactants -disposing of waste products

Question 36

What are the small and large intestines mainly controlled by?

Answer 36

-mainly peripheral control= enteric nervous system (ENS)

Question 37

Where is the enteric nervous system?

Answer 37

-contained entirely within the intestinal wall and running its full length -starts at the mouth all the way to the anus -once you get past stomach the enetric system operates on its own -do not need connection to the brain -GI tract the only organ with its own complete nervous system

Question 38

How many neuron cell bodies are in the ENS?

Answer 38

-more than the spinal cord -about 300 million in humans

Question 39

How does the ENS operate?

Answer 39

-can operate without CNS, but modulated by input from brain via sympathetic nervous system

Question 40

What do the segmentation movements do?

Answer 40

-mixing contraction

Question 41

What does peristalsis do?

Answer 41

-propulsive contraction -moving matter forwards

Question 42

What does the ENS contain?

Answer 42

-all neurons needed for complex behviours like mixing and propulsion -also has an immune function –intrinsic sensory neurons (to detect what is where) –excitatory and inhibitory motor neurons (to make muscles contract, it is smooth muscle here so active contraction= latch mechanism) –interneurons (to integrate the whole thing and communication)

Question 43

What does secretion and absorption of water and salt require? (ENS)

Answer 43

-secretomotor neurons -also directly regulates part of the nutrient process(the ENS)

Question 44

What are the neuron circuits controlling intestinal motility like?

Answer 44

-very complex, all this is repeated over and over again

Question 45

What can happen with excitatory sensory neurons in the gut?

Answer 45

-sensory neurons make synapse with each other, can get positive feedback= produces excitation in the neighbouring neuron -this required intrinsic inhibition to prevent spasm! -there are also other excitatory circuits present

Question 46

How are gastrointestinal functions regulated?

Answer 46

-all are under neural control, but brain modulates local nervous system rather than programming details