Lecture 15: Digestion and its neural control Flashcards
How is food broken down in the body?
separated chemically (and physically) into different nutrients that can be absorbed
What happens to byproducts of the digestive process?
transported along the intestinal tract for further processing and recovery of key materials
What does digestion involve?
enzymatic breakdown of foods
What are proteins, sugars and starches and lipids broken down to?
proteins to amino acids
sugars and starches to simple sugars such as glucose and fructose
lipids to fatty acids and glycerol
What is the role of bacterial fermentation?
breaks down oligosaccharides
What are short chain fatty acids important for?
energy metabolism of mucosa in colon of humans and important signalling molecules
What do animals with active lifestyles tend to depend on?
foods high in simple sugars and protein
What is the role of the somatic nervous system in digestion?
chewing, swallowing, peristalsis in oesophagus and opening key sphincters
What is the role of visceral neurons in digestion?
salivation, secondary peristalsis
include sympathetic and parasympathetic nervous systems and the ENS
What happens when we see or smell food?
initiates the cephalic phase of digestion -> no food needs to be ingested for this to occur
What is the cephalic phase of digestion?
salivation, gastric relaxation and gastric acid secretion via parasympathetic nervous system (vagus) in particular
What increases the response of the cephalic phase?
the food being more palatable
also depends on hunger and appetite
What does chewing depend on?
motor pattern generator in brain stem
Is chewing, movement of the tongue and swallowing involuntary or voluntary?
voluntary
What happens in the oesophagus during swallowing and what are these actions controlled by?
primary peristalsis controlled by CNS via vagus
secondary peristalsis controlled by the ENS
What type of muscle is the oesophagus?
striated muscle
What are upper and lower esophageal sphincters important to regulate?
reflux
What is the stomach controlled by?
major peripheral control network which is controlled by the vagus nerve
also has important control system via non-neural pacemaker cells in antrum (interstitial cells of Cajal)
Where does digestion occur in the GI tract?
in the duodenum and the jejunum
Where does absorption occur in the GI tract?
nutrients are absorbed in the duodenum and the jejunum
water is absorbed in the ileum and the colon
How does chemical refinery occur in the small and large intestines?
mixes food with enzymes and water, neutralises acids, separates nutrients and transports them to place of use, recovers reactants, disposes of waste products
What controls the small and large intestines?
the enteric nervous system (largely peripheral)
Where is the ENS contained?
entirely within the intestinal wall and runs its full length
Can the ENS operate without the CNS?
yes, but it is modulated by input from the brain, spinal cord and SNS
What does tetrodotoxin block?
blocks nerve action potentials but not smooth muscle action potentials
How does the GI tract mix food?
utilises segmenting (mixing contractions) and propulsive contractions (peristalsis)
What does the ENS contain?
all neurons needed for complex behaviours like mixing and propulsion
What does secretion and absorption of water and salt require?
secretomotor neurons
