Physiology & anatomy of the GI tract Flashcards
What are the main roles of the GI tract?
absorption of nutrients
excretion of waste products
What is required in the GI tract to preform its function?
1) breakdown of large molecules
2) secretion of enzymes
3) transport mechanisms
4) secretion of compounds to aid absorption
What is peristalsis?
cyclical contraction & relaxation of sheets of smooth muscle
What is the role of the myenteric plexus?
co-ordinates contraction-relaxation cycle between the 2 layers of muscle
What are the two smooth muscle types used in peristalsis?
Cyclical and longitudinal
What are the 5 muscarinic receptor subtypes used in?
M1 - CNS, salivary gland, gastric glands
M2 - heart- rate of contraction, GI smooth muscle contraction, CNS
M3 - salivary glands, smooth muscle (GI, airways)
M4 - CNS
M5 - CNS
How can GI motility be controlled therapeutically?
1) antagonism or stimulation of muscarinic receptor
2) stimulation or antagonism of pre-synpatic receptors
- D2 receptor antagonist (bloating)
- opioid receptor agonist (diarrhoea )
- 5 - HT receptor agonist (constipation)
What are the 4 functions of the stomach?
1) food storage
2) start digesting proteins & CHO
3) kill ingested bacteria
4) chyme formation
What is the role of the small intestines?
digestion of nutrients and absorption
Why do some diabetics suffer from delayed gastric emptying?
caused by vagal neuropathy - impaired pyloric sphincter function
What does the duodenum receive from the stomach?
chyme
What do the following enzymes breakdown: lipase, amylase, protease, nuclease, HCO3
Lipase - fats Amylase - carbs Protease - trypsin, chymotrypsin, carboxypeptidase nuclease - nucleic acid HCO3 - neutralises acid
Where does most nutrient absorption occur?
duodenum and jejunum
What absorption occurs in the terminal ileum?
bit B-12 and bile absorption
What is bile made from? synthesised in? stored in? and secreted into?
cholesterol
liver
gall bladder
duodenum
What is the role of Bile?
emulsifies fats and helps form micelles to aid fat absorption
What is enteroheptic recycling?
re-uptake of bile into liver
How are carbs and proteins absorbed?
Protein to AA then transporter
Polysaccharides (Carbs) to glucose then symporter with sodium
For each vitamin what mechanism is used to absorb it: fat soluble vits, vit C, Vit B1, Vit B6, folic acid, vit B12
fat soluble - micelle
vit C - sodium dependent active transport
vit B1 - active transport in jejunum
vit B6 - simple diffusion
folic - facilitated transport
vit B12 - binds to intrinsic factor and absorbed in ileum
How is calcium uptake?
passive diffusion through calcium channel
What is the ileocecal juncture?
prevents bacteria in large intestines from infecting small intestines
