Lecture 1 - Purpose of the gut Flashcards
Mouth
Physical breakdown of food
Chemical breakdown - Contains salivary amylase and lipase
Infection control - Immunoglobulins
Features of the oesophagus
Rapid transport of bolus to the stomach
Contains an upper and lower oesophageal sphincter
Upper oesophageal sphinter
Prevents air from entering the GI tract
Lower oesophageal sphincter
Prevents oesophageal reflux
Stomach
Temporary storage of food
Produces chyme
Physical and chemical breakdown of food
Infection control (HCL) - innate immunity and acidic
Acidity activates trypsin
Secretes intrinsic factor via parietal cells
Secretes gastrin from chief cells of the gastric glands
Intrinsic factor
Binds to Vit B12
The complex binds to receptors in the terminal iluem
Chyme
Fluid that contain gastric secreteions and partially digested food that passes out of the stomach
3 parts of the small intestines
Duodenum
Jejunum
Ileum
Duodenum
Neutralises chyme via HCO3- rich secretions i.e. bile and pancreatic secretions
Absorbs iron
C shape of the duodenum
Where the head of the pancreas sits in
Sphincter of Oddi
Where the ampulla of Vater and pancreatic duct enters the duodenum
Functions of the jejunum and ileum
Nutrient absorption e.g sugars, AA and FAs - jejunum
Water and electrolyte absorption - ileum
Bile recirculation - ileum
B12 absorption - terminal ileum
Functions of the large bowel
Stores faeces
Final water absorption (small intestines absorb a greater volume)
Final electrolyte absorption
Some bile salt absorption
Structure of the large bowel and parts
Caecum Ascending colon Transverse colon Descending colon Sigmoid colon
The large intestines is wider and shorter than the small intestines
Rectum and anus purpose
Defaecation
What is synthesised in the large bowel
Produces mucus Vit K B12 Thiamine Riboflavine
ANS system of the GI tract
The preganglionic fibe synapses with an autonomic ganglia outside the CNS
The postganglionic fibre synapses on peripheral effector organs
All the preganglionic fibres secrete Ach
Post ganglionic fibres release Ach, neuropeptides or norepinephrine
Parasympathtic contron of GI system
Triggers digestion via:
- vagus nerve (oesphagus to transverse colon)
- splanchnic nerves [S2,3,4] (transverse colon to the anal canal)
= craniosacral outflow
Associated with the enteric nervous system:
- Myenteric plexus
- Submucosal plexus
What do parasympathetic postganglionic fibres release?
Acetylecholine
Peptides:
- Gastrin secreting petide
- Vaso-inhibitory peptide
What do the parasympathetic fibres innervate
Smooth muscle - contract
Endocrine cells
Secretory cells - G cells and parietal cells to release gastrin and HCL
Vertebral levels of sympathetic innervation to the gut
T5- L2
Role of sympathetic innervation in the GI system?
‘Off button’ - inhibition
Vasoconstriction
Presynaptic splanchnic nerves
Pass through the vertebral trunk without synapsing. The prevertebral neurones amalgamate to form the:
- Greater splanchnic nerve (T5-9)
- Lesser splanchnic nerve (T10-11)
- Least splanchnic nerve (T12)
The splanchnic nerves synapse with the prevertebral ganglia:
- coeliac
- superior mesenteric
inferior mesenteric
Enteric nervous system
Can operate independently from brain
Communicates with the parasympathetic and sympathetic NS
Meissner’s plexus - submucosal (Superficial)
Auerbach’s plexus - Myenteric
- In muscularis propria in between the circular and longitudinal muscle
What does the Meissner’s plexus control
Blood flow and secretions
What does the Auerbach’s plexus control?
Motility - contractions of muscles
