GI tract control Flashcards
How is maximum absorption of nutrients achieved?
- Regulating motility (rate at which food passes through the GI tract)
- Controlling secretion of digestive juices.
How does the small intestine sense lumen contents?
Distention- mechanoreceptors
Osmolality- osmoreceptors
Acidity- chemoreceptors
Digestive products- chemoreceptors
What does receptor activation of the small intestine cause?
- Neves= long and short reflexes
- Hormone release
- Paracrine transmission
What is the enteric nervous system?
100 million nerve cells in myenteric and submucosal plexus.
What is the enteric nervous system involved in and give an example?
Involved in short reflexes e.g. local distention leads to motility (muscle contraction).
What does the parasympathetic system do?
- inc motility
- inc secretion
- interact with the enteric nervous system
- e.g. long reflexes
- ACh
What does the sympathetic system do?
- decrease motility
- decrease blood flow
- noradrenaline
Features of GI hormones
- All short chain peptides
- Secreted by enteroendocrine cells found in the mucosa into the blood.
- Target various regions of GI and glands.
- May have effects on the CNS.
Examples of hormones acting in paracrine transmission.
Histamine (gastric secretion)
Prostagladin
Bradykinin
Saliva is 99% water. What is the protein and ion composition of saliva and what is their function?
Proteins:
- mucins
- a-amylase (digestion of carbohydrates)
- anti-bacterials (antibacterial drugs cause dry mouth)
- growth factors
Ions:
- Na, Cl, HCO3 (produce osmotic gradient)
- pH=7
What is the function of saliva?
lubrication
solvent
protect teeth and gums
What are the 3 salivary glands and what secretion are they involved in?
Parotid- watery secretion
Sublinguals- mucus secretion
Submandibular- mixed secretion
What is the structure of the salivary glands?
duct and acinus
What type of saliva does the parasympathetic system induce?
Watery saliva
Low enzyme conc
4ml/min
What type of saliva does the sympathetic system induce?
Small volume of saliva
Rich in enzymes
What is the fundus in the stomach important for?
Acid secretion
What is the antrum in the stomach important for?
Mixing food
What is gastrin produced by and what does it do?
Produced by G cells.
Increases acid secretion and gastric motility.
Secretes pepsin.
What is the composition of gastric juice?
- HCl (kills microbes, solubilisation)
- Pepsinogen-> pepsin (digestion)
- Intrinsic factor (absorption of vit B12)
- Mucus (protection, lubrication)
What do parietal cells release?
HCl and intrinsic factor
What is acid secretion stimulated by?
ACh
Gastrin
Histamine
Structurally, what happens during acid secretion?
Receptor activation activates ion channels which causes changes in parietal cell structure:
tubulovesicles-> canaliculus (inc surface area and number of pumps).
What are the three phases of gastric secretion control?
- Cephalic phase (stimulatory
- Gastric phase (stimulatory/ inhibitory)
- Intestinal phase (inhibitory)
Draw the gastric phase pathway
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