Introduction To The Funcions And Control Of The Alimentary Tract Flashcards
What inhibits smooth muscle tone mechanoreceptors?
Vagal reflex (Vasoactive intestinal peptide and nitric oxide)
What does the antral region of the stomach body do?
Mixes/grinds food with gastric secretions
How much gastric juice does the stomach store in 24 hours?
2-3 litres
What is included in gastric juice?
Mucus, Pepsinogen, intrinsic factor and lipase
What does gastric juice help with?
Digestion and absorption of food
What is the function of mucus in the stomach?
Lubricant that protects stomach and colon from gastric acid
What does lipase do?
TGs -> fatty acids and glycerol
What is mucus secreted by?
Goblet cells and mucus neck cells
What is pepsin secreted by?
Chief cells or peptic cells as pepsinogen
What is pepsinogen?
Inactive enzyme that forms pepsin in an acidic environment
What is pepsins function?
Protein digestion
What is HCLs function?
Important in defence and conversion of pepsinogen -> pepsin
What is HCL secreted by?
Parietal cells
What are intrinsic factors secreted by?
Parietal cells
What is intrinsics function?
Vit B12 absorption
Where are paracrine secretions secreted from?
Cells in the mucosa
Where do paracrine secretions act?
Locally on adjacent cells via interstitial fluid
What is an example of a paracrine secretion?
Somatostatin
What does somatostatin do?
Acts on g cells that inhibit gastrin release in the stomach
Where are the 4 places that exocrine secretions happen?
Salivary glands, gastric glands, pancreas, liver
What do the salivary glands secrete?
Mucus and lipase
What do gastric glands secrete?
HCL, pepsin, mucus
What does the pancreas secrete?
Bicarbonate ions, enzymes (amylase, lipase, carboxypeptidase)
What does the liver secrete?
Bile salts, bile acids
What are endocrine secretions and where are they synthesised?
Hormones, synthesised by ductless glands
How do endocrine secretions elicit a response?
Enter the bloodstream and travel to the target tissues where they bind to specific receptors
Where is gastrins target?
Stomach (specifically G cells in the antrum)
Where is secretins target?
Duodenal mucosa
What does secretin do?
Balances the acidity from the stomach by telling the pancreas to secrete bicarbonate rich secretions
Where is cholecystokinin targeted?
Duodenal mucosa
What is insulin secreted by?
Pancreas (beta cells)
What do endo, exo and paracrine secretions allow?
Active digestion and control of digestion, gastric motility and energy homeostasis
What food types are transported across the intestinal epithelium into the blood?
Glucose and amino acids
What food types are transported into the lymph via lacteals?
Fats and lipids
Where does absorption mainly take place?
Small intestine
What does the colon do?
Absorbs 90% of the water
How may drugs and some products of normal metabolism leave the body?
Saliva, bile, faeces and vomit
How do indigestible food particle leave the body?
Faeces
What are the 7 defence mechanisms in the gut?
- sight, smell and taste
- vomit reflex
- acid in stomach
- mucus secretions
- natural bacteria flora
- aggregation of lymphoid tissues
- peyer’s patches
How does acid in the stomach help in defence?
Kills most harmful bacteria
How does natural flora help in defence?
Prevents colonisation of harmful bacteria
How does aggregation of lymphoid tissue help in defence?
Analyse and respond to pathogenic microbes
Where are peyers patches located?
In the lamina propria layer of mucosa and extending into the submucosa of the ileum
What are the metabolic functions of the liver?
Involved in the carb, nitrate and lipoprotein metabolism
Also production of bile and excretion of bilirubin
What are the factors and mechanisms involved in the storage and digestion of the gut?
Mastication, swallowing, enzymatic digestion, absorption
What are the factors and mechanisms involved in the motility of the gut?
Peristalsis, mass movement, ACh, motility, NO and VIP
What are the factors and mechanisms involved in the defence of the gut?
Smell, sight, taste, gastric acid, vomit reflex, mucus, immune response (IgA)
What is the name of the nerves that go from the gut muscle to the spinal cords?
Splanchnic nerves
What is the name of the nerves that go from the gut muscle to the brain and ENS?
Afferent and efferent vagal nerves
What chemicals mediate contraction in the GI tract?
ACh and substance p
How does the ANS enable movement of food in the duodenum?
Ripples of contraction move the food towards the antrum.
When does the pyloric sphincter close?
When a peristaltic wave arrives
What causes the opening of the pyloric sphincter?
Repulsion of chyme
What allows mixing/grinding in the duodenum?
Repulsion of antral contents backwards towards the body
What is the sieving effect?
Viscous and solid matter (bigger than 2mm) being retained in the stomach
What happens in the fundus?
Pacemaker zone, spontaneous depolarisation and BER and peristalsis
Where can gastrin act?
Either directly on the cells that need to secrete acid
Or bind to histamine secreting ECL cells that act on parietal cells
How do ECL cells act on parietal cells?
H2
What effect does ACh have on parietal cells?
Secrete HCl via muscarinic receptors
What does ECL cell stand for?
Enterochromaffin cell
What does hyperacidity do to d cells?
Stimulates them to release somatostatin
What does the vagovagal reflex describe?
The reflex in which both the afferent and efferent axons are in the vagal nerve trunk
Where does the vagovagal reflex travel from?
Brain stem (medulla)
When is the vagovagal reflex active?
Receptive relaxation in response to swallowing
What does the vagovagal reflex promote?
Motility and acid secretion
What does DMVN stand for?
Dorsal vagal complex nucleus
What is the DMVN?
Main site of origin of vagal efferents supplying the gut
What are the two nerve fibres in the enteric nervous system that are intrinsic to the gut?
Myenteric plexus (Auerbachs) Submucosal plexus (meissners)
What does the myenteric plexus do?
Motor function
What does meissners plexus do?
Intestinal secretions
How are the nerve fibres connected to the CNS?
By parasympathetic fibres
Do the myenteric and submucosal plexus’ need to be connected to the CNS to work?
No- it can be mediated entirely by the ENS
What are the 6 neurotransmitters involved in the myenteric and submucosal plexus’?
ACh, NO, NA, 5HT, GABA, ATP
Where are the two plexuses found?
In the wall of the colon
Where do the plexuses receive input from?
PNS and SNS
What effect does the parasympathetic nervous system have on the gut?
Increases contraction of proximal colon
What effect does the sympathetic nervous system have on the gut?
Decreases colonic movement
What is the colocolonic reflex?
Food products that increase motility
Which is the most prominent plexus?
Myenteric
What effect does cholinergic stimulation have on the myenteric plexus?
Increases gastric motility and secretion
What effect does adrenergic stimulation have on the myenteric plexus?
Decreases gastric motility and secretion
What is the timeline of how fast materials ability to be absorbed?
Fatty acids> proteins> carbs
How do fatty acids in the duodenum decrease gastric emptying?
Increasing the contractility of the pyloric sphincter
What is peristalsis?
A wave of propulsive contractions that moves the contents of the gut towards the anus
What initiates contraction?
Distension
What controls peristalsis?
Vagal inhibitory and excitatory fibres
What causes relaxation in peristalsis?
When NO or VIP is released
