Lecture 15: Digestion and its neural control

Question 1

How is food broken down in the body?

Answer 1

separated chemically (and physically) into different nutrients that can be absorbed

Question 2

What happens to byproducts of the digestive process?

Answer 2

transported along the intestinal tract for further processing and recovery of key materials

Question 3

What does digestion involve?

Answer 3

enzymatic breakdown of foods

Question 4

What are proteins, sugars and starches and lipids broken down to?

Answer 4

proteins to amino acids
sugars and starches to simple sugars such as glucose and fructose
lipids to fatty acids and glycerol

Question 5

What is the role of bacterial fermentation?

Answer 5

breaks down oligosaccharides

Question 6

What are short chain fatty acids important for?

Answer 6

energy metabolism of mucosa in colon of humans and important signalling molecules

Question 7

What do animals with active lifestyles tend to depend on?

Answer 7

foods high in simple sugars and protein

Question 8

What is the role of the somatic nervous system in digestion?

Answer 8

chewing, swallowing, peristalsis in oesophagus and opening key sphincters

Question 9

What is the role of visceral neurons in digestion?

Answer 9

salivation, secondary peristalsis

include sympathetic and parasympathetic nervous systems and the ENS

Question 10

What happens when we see or smell food?

Answer 10

initiates the cephalic phase of digestion -> no food needs to be ingested for this to occur

Question 11

What is the cephalic phase of digestion?

Answer 11

salivation, gastric relaxation and gastric acid secretion via parasympathetic nervous system (vagus) in particular

Question 12

What increases the response of the cephalic phase?

Answer 12

the food being more palatable

also depends on hunger and appetite

Question 13

What does chewing depend on?

Answer 13

motor pattern generator in brain stem

Question 14

Is chewing, movement of the tongue and swallowing involuntary or voluntary?

Answer 14

voluntary

Question 15

What happens in the oesophagus during swallowing and what are these actions controlled by?

Answer 15

primary peristalsis controlled by CNS via vagus

secondary peristalsis controlled by the ENS

Question 16

What type of muscle is the oesophagus?

Answer 16

striated muscle

Question 17

What are upper and lower esophageal sphincters important to regulate?

Answer 17

reflux

Question 18

What is the stomach controlled by?

Answer 18

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)

Question 19

Where does digestion occur in the GI tract?

Answer 19

in the duodenum and the jejunum

Question 20

Where does absorption occur in the GI tract?

Answer 20

nutrients are absorbed in the duodenum and the jejunum

water is absorbed in the ileum and the colon

Question 21

How does chemical refinery occur in the small and large intestines?

Answer 21

mixes food with enzymes and water, neutralises acids, separates nutrients and transports them to place of use, recovers reactants, disposes of waste products

Question 22

What controls the small and large intestines?

Answer 22

the enteric nervous system (largely peripheral)

Question 23

Where is the ENS contained?

Answer 23

entirely within the intestinal wall and runs its full length

Question 24

Can the ENS operate without the CNS?

Answer 24

yes, but it is modulated by input from the brain, spinal cord and SNS

Question 25

What does tetrodotoxin block?

Answer 25

blocks nerve action potentials but not smooth muscle action potentials

Question 26

How does the GI tract mix food?

Answer 26

utilises segmenting (mixing contractions) and propulsive contractions (peristalsis)

Question 27

What does the ENS contain?

Answer 27

all neurons needed for complex behaviours like mixing and propulsion

Question 28

What does secretion and absorption of water and salt require?

Answer 28

secretomotor neurons