Flashcards in Digestion and Absorption Deck (55):
What are carbs broken down in to?
Monosaccharides such as glucose, galactose and fructose.
What are the enzymes used in the breakdown of carbs?
Amylase and disaccharidases
What are proteins broken down in to?
Peptide chains and amino acids
What are the enzymes used in the breakdown of proteins?
Proteases and dipeptideases
What are fats and lipids broken down in to ?
Fatty acids and monoglycerides
What is the enzyme used in the breakdown of lipids?
What is the digestive tract wall comprised of?
Mucosa, submucosa, muscularis externa, serosa
What are the constituents of the mucosa of the digestive tract wall?
Epithelial cells - Absorption
Exocrine cells - Secrete digestive juices
Endocrine gland cells - Secrete hormones
Lamina Propria - capillaries, enteric neurones and immune cells
What are the constituents of the submucosa of the digestive tract wall?
Larger blood and lymph vessels
Nerve network - Submucous plexus
What are the constituents of the muscularis externae of the digestive tract wall?
Circular muscle layer
Nerve network - myenteric plexus
Longitudinal muscle layer
What is the serosa of the digestive tract wall made of?
How do adjacent smooth muscle cells in the digestive tract contract at the same time?
Gap junctions electrically couple adjacent cells.
What are the pacemaker cells of the digestive tract called?
Interstitial cells of Cajal (ICCs)
Where would you find ICCs?
Between the longitudinal and circular muscle layers and in the submucosa
What is peristalsis?
A wave of contraction that normally proceeds along the gut towards the anus.
What happens to the muscles in the gut during peristalsis
Muscle before the lump of food/chyme/shit - Longitudinal muscle relaxes, circular muscle contracts
Muscle after - Longitudinal contracts, circular relaxes
What is segmentation?
Rhymthic contractions within the GI tract that mix and divide luminal contents.
This is called HAUSTRATION in the large intestine
What are tonic contractions?
Sustained contractions in the sphincters of the GI tract.`
What are the sphincters of the digestive tract?
Upper Oesophageal Sphincter = Skeletal
Lower Oesophageal Sphincter = Smooth muscle
Pyloric Sphincter = Smooth
Ileocaecal Sphincter = Smooth
Internal Sphincter = Smooth
External Sphincter = Skeletal
What closes off the trachea when you swallow?
What closes off the nasal passage when you swallow?
Name the salivary glands.
What are the 6 main functions of saliva?
Lubrication - (important for speech and swallowing)
Solvent - (important for taste)
Antibacterial - (contains lysozyme, lactoferrin and immunoglobulins)
Digestion of complex carbs - (contains amylase)
Neutralisation of acid - (contains bicarbonate)
Facilitates sucking by infants - (fluid seal)
What are the two stages in the formation of saliva?
Primary secretion - by the acinus
Secindary modification - by the duct cells
Explain primary secretion and secondary modification of saliva.
Cells in the acinus produce a secretion with Na+, K+, Cl-, HCO3-, H2O, mucus and amylase.
Duct cells modify the secretion by removing Na+ and Cl- (no salty taste) and adding little amounts of K+ and HCO3-. (No movement of H2O - hence diluting.)
How does flow rate of saliva affect the HCO3- content?
High flow, high content
Low flow, low content
Explain simple salivary reflex and its impulses.
Chemo/pressure receptors in the mouth are activated.
Impulses sent via AFFERENT NERVES to the salivary centre in medulla.
Impulses vie Extrinsic autonomic nerves (sympathetic and parasympathetic.)
Salivary glands increase production.
Explain acquired salivary reflex.
Think about/see/smell food. Cerebral cortex reacts and signals to the salivary centre in medulla.
Impulses via Extrinsic autonomic nerves (sympathetic and parasympathetic.)
Salivary glands increase production.
What does parasympathetic stimulation do to saliva?
Which nerves cause large volumes of saliva when stimulated?
What drugs can cause a dry mouth?
Muscarinic Receptor Antagonists (e.g atropine) and antidepressants that block M-receptors
What is secreted in the Fundus and Body areas of the stomach by the Oxyntic Mucosa?
HCl - Activates Pepsinogen to pepsin, denatures protein, kills mose micro-organisms.
Pepsinogen - Precurser of pepsin. (pepsin needed to activate.)
Intrinsic factor - binds vitamin B12 allowing absorption in terminal ileum.
Histamine - Stimulates HCl
Mucus - protective
What is secreted in the Atrum area of the stomach?
Gastrin - Stimulates HCl secretion
Somatostatin - Inhibits HCl secretion
Mucus - protective
What is a possible treatment for NSAID induced peptic ulcer?
PGE1 Analogue like Misoprostrol
What is zollinger-ellison syndrome?
Rare gastrin producing tumour
What is the sequence of carbohydrate digestion?
Starchh is broken down in to Oligosaccrharides by Amylases (Alpha) which is produced by the salivary glands and the pancreas.
Oligosaccharides are then further broken down in to monosaccharides via the action of ologosaccharidases
These monosaccharides are then absorbed.
Why does alpha amylase only break starch in to oligosaccharides?
It can't break down the terminal bonds between each monosaccharides.
What polymorphism is attributed Lactose intolerance?
What kind of breath test would you perform if you suspected a patient was lactose intolerant?`
Hydrogen breath test
What can undigested lactose cause?
Acidification of the colon and increased osmotic load which causes diarrhoea
What is an endopeptidase
A peptidase that acts to break down non-terminal peptide bonds
What is an exopeptidase?
A peptidase that acts to break down terminal peptide bonds, therefore producing amino acids
Where is the brush border?
How does peptide leave the Lumen to get into the interstium in the small intestine?
Via H+ dependant channels. It is then hydrolysed and the Amino Acids cross the basolateral border by Na+-independent channels
How are triglycerides broken down?
Lingual and then Gastric Lipase breaks them down into Diglyceride and Free fatty acids.
The Fatty Acids act as a surfactant and stimulate CCK release from duodenum and secretion of pancreatic lipase.
What 3 things in the duodenum are used in Lipid digestion?
Pancreatic Lipase - digestive enzyme
Bile salts from gallbladder
HCO3- - neutralises stomach acid providing optimal pH for enzymes
Failure to secrete bile salts would result in...?
Lipid malabsorption - (STEATORRHOEA)
Secondary vitamin (A, D, E and K) deficiency due to failure to absorb lipid vitamins
What is the difference between Gastric Lipase and Pancreatic Lipase?
Gastric Lipase breaks Triglyceride into a diglyceride and a free fatty acid.
Pancreatic Lipase breaks Triglyceride into 2-monoglyceride and 2 Free Fatty Acids
What drugs would you use in hypercholesterolaemia?
Statin and Ezetimibe (prevents cholesterol absorption by preventing internalisation)
If there is less than 5mM or Ca2+ in chyme, how is it transported out of the lumen?
Active transport, mainly in the duodenum and upper jejunum.
What are the fat soluble vitamins?
A D E and K
What vitamins are water soluble?
B vitamins (but not B12)
What is Vitamin B9?
What is Vitamin C?