What is probiotic bacteria?
- bacteria that can get through the stomach to the colon -stomach is a big barrier
What is the gut-brain axis?
-brain and gut communicate= 2 directional communication
What happens in the digestive process, simply?
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
How is fat important in digestion?
--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)
What os vomiting for?
-if take in something noxious= vomit -evolved to be used for purposes of getting rid of noxius material in as short time as possible
What components are proteins, sugars and fats broken down into?
-proteins= amino acids -sugars and starches into simple sugars= glucose, fructose and galactose -lipids into fatty acids and glycerol
Where does most of the compounds breakdown happens?
-the breakdown happens mostly in upper duodenum and distal stomach, very little elsewhere (mouth)
What is the fermentation in animals used for?
-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
Where in humans do the short chain fatty acids play an important role?
-in the energy metabolism of mucosa in the ascending colon
What is the diet of animals with active life-styles like?
-tend to depend on foods high in simple sugars and protein= as those are easy to digest
What neurons are involved in digestion?
-both somatic and visceral -also endocrine system! (gut is the biggest endocrine organ)
What does the somatic nervous system control in digestion?
-conscious control -chewing, swallowing, peristalsis in esophagus and opening key sphincters -as soon as you get to oesophagus= mostly visceral control
What do the visceral neurons control in digestion?
-involved in salivation, primary peristalsis, all functions from stomach to anus
What visceral neurons are involved in digestion?
-sympathetic and parasympathetic nervous systems, many types of visceral afferents and the enteric nervous system
What happens when we see or smell food?
-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
How does the palatability of the food effect cephalic phase?
- more palatable the food, the greater the response (use memory as part of the process) -partly determined by nature of food previously eaten
What does hypothalamus do?
What happens when food is in the mouth?
-chewing -movement of tongue -swallowing
How is chewing controlled?
-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
How is tongue movement controlled?
-voluntary set of muscles, controlled via motor cortex -huge number of muscles, not grounded much
How is swallowing controlled?
-voluntary process, motor pattern generator in the brain stem -you'll gag if you don't swallow properly -swallowing center
What happens in the oesophagus?
-primary peristalsis= CNS -secondary peristalsis=ENS -upper and lower sphincters important to regulate reflux
What happens in primary peristalsis in the oesophagus?
-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.
What happens in secondary peristalsis in the oesophagus?
-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.
What is the importance of the upper and lower oesophageal sphincters?
-upper= involved in gag reflex -lower= so acid from stomach doesn't get into oesophagus= then achalasia (human disease)
What is special about ruminants and reflux?
-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
How is the stomach innervated?
-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
What does parasympathetic mean?
-end target close to origin
What do the interstitial cells of Cajal do?
-pacemaker cells, in the antrum of the stomach, start the contractions of the stomach
What happens in the small and large intestine?
-where the action is! -digestion -absorption -propulsion
Where in the small and large intestine does digestion occur?
-duodenum and jejunum
Where in the small and large intestine does absorption occur?
Where in the small and large intestine does propulsion occur?
How long is the small and large intestine in humans?
-6m small intestine -1m large intestine (guinea pigs= about 1m for small intestine)
What do the small and large intestines do as chemical refineries?
-mixing food (converted to slurry by stomach) with enzymes and water -neutralizing acid -allowing for absorption -recovering reactants -disposing of waste products
What are the small and large intestines mainly controlled by?
-mainly peripheral control= enteric nervous system (ENS)
Where is the enteric nervous system?
-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
How many neuron cell bodies are in the ENS?
-more than the spinal cord -about 300 million in humans
How does the ENS operate?
-can operate without CNS, but modulated by input from brain via sympathetic nervous system
What do the segmentation movements do?
What does peristalsis do?
-propulsive contraction -moving matter forwards
What does the ENS contain?
-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)
What does secretion and absorption of water and salt require? (ENS)
-secretomotor neurons -also directly regulates part of the nutrient process(the ENS)
What are the neuron circuits controlling intestinal motility like?
-very complex, all this is repeated over and over again
What can happen with excitatory sensory neurons in the gut?
-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
How are gastrointestinal functions regulated?
-all are under neural control, but brain modulates local nervous system rather than programming details