L28 - Digestion 1 Flashcards
Which is not a major function of the human digestive system?
fermentation of food
What is the role of the gastrointestinal system?
digestion, absorption, motility, secretion, protect body from pathogens from the external environment, excrete waste
Which part of the GI tract has a major role in excretion?
colon
Which part of the GI tract has a major role in absorption of nutrients?
duodenum / jejunum, ileum
What are the four layers of the digestive tract?
- mucosa: epithelial cells, lamina propria, muscularis mucosae, modifications ↑ SA
- submucosa
- muscularis externa
- serosa
layers are mostly constant the whole way through the GI tract
What is the role of the muscularis mucosae?
regulates the mucosa as it enables villi to sway back and forth
this is important as it helps modify SA and induces mixing action so that food particles are exposed to the villi
What is the role of the submucosa?
elastic and allows distension in the gut
houses blood vessels and lymph vessels as well as the submucosal plexus
What is the role of muscularis externa?
manages gut motility which is mediated by squeezing movements and peristalsis
What is the role of the serosa?
layer which holds everything together
lubricated to minimise friction
What are the characteristics of the enteric nervous system?
entirely contained within walls of digestive tract
independent of CNS
What is the role of the submucosal plexus?
regulates submucosa (epithelium and muscularis mucosae)
What is the role of the myenteric plexus?
regulates muscularis externa (motility)
What are the two types of contractions that GI motility utilises?
- tonic (sustained) contractions
2. phasic or rhythmic contractions
Where do tonic (sustained) contractions occur?
occur in some smooth muscle sphincters
sphincters separate some organs and can make reservoirs e.g. stomach
What is the role of sphincters in the stomach?
provides time for digestion and absorption
What are the three different types of phasic contraction patterns?
- peristaltic contractions
- segmental contractions
- migrating motor complex
What type of movement do peristaltic contractions provide and where do they occur?
propulsive movement
in the oesophagus
What type of movement do segmental contractions provide?
non-propulsive movement (mixing)
enhances digestion and absorption
What is the migrating motor complex?
housekeeping function which appears in fasted state
sweeps food remnants and bacteria out of the upper GI tract and into the large intestine
Which factors could affect GI motility?
sympathetic nervous system, parasympathetic nervous system, enteric nervous system, local hormones and paracrines, presence of food in the gut
What is the role of the vagus nerve?
- anticipatory response triggered by stimuli received in the brain e.g. sight, smell of food 2. salivary secretion (regulated by facial nerve) 3. swallowing 4. initiates peristalsis 5. relaxes gastro-oesophageal sphincter 6. controls stomach propulsion 7. stimulates gastric acid secretion 8. controls small intestine peristalsis
What are the characteristics of long reflexes?
integrated in CNS
include ‘cephalic phase’: feedforward
originate completely outside GIT e.g. sight, smell, anticipation
prepare to receive and process food
What are local stimuli of long reflexes?
pH, stretch, osmolarity, products of digestion stimulate sensory receptors and neurons in the gut which provide feedback to the cephalic integrating centre
What are local stimuli of long reflexes?
pH, stretch, osmolarity, products of digestion stimulate sensory receptors and neurons in the gut which provide feedback to the cephalic integrating centre
What are the characteristics of short reflexes?
integrated in ENS submucosal and myenteric plexus "little brain" complex reflex circuit (sensory, integration, response) motility, secretion, growth coordinates with ANS (both SNS and PNS)
What does local stimuli in short reflex provide feedback to?
sensory receptors and neurons which provide feedback to interneurons -> neurons of myenteric and submucosal plexuses -> smooth muscles or secretory cells -> digestive system responses
What is cholecystokinin?
hormone secreted into the blood by specific cells of small intestine
target stomach, gallbladder and pancreas
What is histamine?
paracrine secreted into interstitial fluid by specific cells in gastric gland
target other cell type in gastric gland
