1a.) Purpose of Gut Flashcards
Describe the passage of food through the alimentary canal
Describe approximate locations of viscera in abdomen
State generic purpose of the gut
Ingest, digest and absorb what’s needed and egest what we don’t
State 3 functions of mouth in digestion
- Physical breakdown of food
- Digestive enzymes released
- Infection control (if you don’t produce enough saliva there is high risk of infection)
State the main function of the oesophagus in digestion
Rapid transport of bolus to stomach
There is an upper and lower oesophageal sphincter; state the role of each
- Upper: prevent air entering GI tract
- Lower: help prevent reflux into oesophagus
State 4 functions of stomach in digestion
- Storage
- Produce chyme (involves physical breakdown, chemical breakdown, storage)
- Infection control (acidic environment kills some bacteria)
- Secrete intrinsic factor (absorption of vitamin B12)
Label the following image of the stomach
What is chyme?
Fluid that passes out of stomach that consists of gastric secretions and partially digested food
State 3 functions of the duodenum
- Neutralisation/osmotic stabilisation of chyme (chyme is acidic and hypotonic)- duodenum has HCO3 rich secretions
- Digestion- pancreatic secretions & bile
Describe the anatomical relationship between liver and pancreas with duodenum
Both connect to second part of the duodenum thorugh common entrance
State the 4 functions of teh jejunum and ileum in digestion
- Nutrient absorption (mainly jejunum)
- Water/electrolyte absorption (mainly ileum)
- Bile recirculation (ileum)
- B12 absorption (terminal ileum)
State the 3 functions of the large bowel
- Final water absorption
- Temporary storage
- Electrolyte absorption (some bile salt absorption and production of some short chain fatty acids)
State the role of the rectum
Defaecation
Where is more water absorbed, the small or large bowel?
Although one of main funtion of large bowel is water absorption the small bowel actually absorbs more water as water absorption is easier in small bowel due to e.g. water potential gradients being larger
Label the image of the large bowel
What two nervous systems control the gut?
- Autonomic nervous system (parasympathetic and sympathetic)
- Enteric nervous system
Which nervous system is the ‘on’ button for the gut?
Parasympathetic
Which nervous system is the ‘off’ button for the gut?
Sympathetic
The parsympathetic system which controls the gut has what we call a craniosacral output?
Vagus nerve originates in brain
Pelvic splanchnic nerve originates in sacral spine
What do parasympathetic post ganglionic fibres release?
- ACh
- Peptides
- Gastrin releasing peptide
- Vaso-inhibitory peptide
What are the spinal roots for the pelvic splanchnic nerves?
S2-S4
Describe how the sympthetic nervous system acts a the ‘off’ button for the digestive system
Vasoconstriction to divert blood flow away from digestive tract. This is why heart rate can increase when eating.
Which nerves does sympathetic nervous system use to communicate with GI? What is special about these sympathetic nerve fibres?
Pre-ganglionic fibres pass thorugh sympathetic chain without synapsing and then join with other pre-gnaglioni fibres to form splanchnic nerves: Greater (T5-T9), Lesser (T10-T11) and Least (T12) splanchnic nerves.
State the roots which make up the 3 abdominopelvic presynaptic splanchnic nerves
- Greater: T5-T9
- Lesser: T10-T11
- Least: T12
The sympathetic splanchnic nerves that communicate with GI tract synapse with which prevertebral ganglia? (4)
- Coeliac
- Renal
- Superior mesenteric
- Inferior mesenteric
- Others
What do the sympathetic splanchnic nerves innervate mainly?
Blood vessels
What areas does vagus nerve innervate?
- Oesophagus
- Transverse colon
What area do splanchnic pelvic nerves innervate?
- Transverse colon
- Anal canal
Long pre-ganglionic fibres of parasympathetic nervous system extend to viscera in GI system; to which plexuses of the enteric nervous system do they extend?
Myenteric and submucosal plexuses
Describe and compare pathway of pre- and post-ganglionic fibres for parasympathetic and sympaethetic nervous system to GI tract
Parasympathetic
- Long pre-ganglionic fibres synapse with in viscera often to myenteric and submucosal plexuses of the enteric nervous system
- Release Ach or neuropeptide
Sympathetic
- Pre-ganglionic fibres pass through sympathetic chain without synapsing and combine with other pre-ganglionic fibres to form splanchnic nerves which then synapse with prevertebral ganglia (coeliac, superior mesenteric and inferior mesenteric, renal). Post-ganglionic fibres extend from prevertebral ganglia to viscera and synapse with myenteric and submucosal plexuses of enteric nervous system
Can the enteric nervous system operate independently?
Yes but has extensive connections with ANS
Where does enteric nervous system exist from and to?
Oesophagus to anus
State the two main enteric plexuses and where they exist
- Submucosal (Meissner’s)- submucosa
- Myenteric (Auerbach’s)- between circular and longitudinal muscle of muscularis propria
State what the submucosal (Meissner’s) and myenteric (Auerbach’s) plexus are responsible for?
Meissner’s
- Secretions
- Blood flow
Myenteric
- Motility
State some roles of enteric nervous system
- Motor function
- Blood flow
- Secretions
- Transport across mucosa
- Immune function of gut
Describe how the gut is divided into regions and the benefit of this
Divided into regions by sphincters; allows different parts to have different functions
