GI Physiology Document notes Flashcards
What are the 4 layers of the digestive tract
Mucosa
Submucosa
Muscularis Externa
Serosa (bock)
What 5 things are in the mucosal layer
epithelial cells, exocrine cells, endocrine cells, lamina propria, muscularis mucosa
What 3 things are in the submucosal layer
connective tissue,
lymph tissue,
submucous (meissner’s) plexus
What 3 things are in the muscularis externa layer
circular muscle,
myenteric (Auerbach’s) plexus,
longitudinal muscle
What is in the serosa bock
connective tissue
The mucosa is the outermost layer
True or False
False
that would be the serosa bock
Where does the primary salivary secretion come from
Acinar cells
Which cells are responsible for the secondary modification of the primary saliva secretion
Ducts cells
What do the duct cells do to the primary secretion
Remove Na & Cl
Add K & HCO3
Parasympathetic saliva is…
Large volume
Watery
Enzyme rich
Sympathetic saliva is…
Low volume
Thick
Mucus rich
Parasympathetic control of saliva is mediated by which receptors and which NT
M1/M3 Ach receptors
VIP
Sympathetic control of saliva is mediated by which receptors and which NT
α and B1-adrenoceptors
Doesn’t say but probes noradrenaline?
What is the unconditioned (simple) salivary reflex
Activation of chemo/pressure receptors when food is in mouth leads to saliva production
What is the conditioned (acquired) reflex
Saliva production due to thinking of, seeing or smelling food
Which organ stores food before passing it to the small intestine
The stomach obviously
What is chyme
The mixture of gastric secretions and partially digested food - formed in the stomach
What gastric factors favour gastric emptying
Increased volume of chyme.
Finely divided chyme.
What duodenal factors go against gastric emptying
High volume of fat in duodenum.
High volume of acid in duodenum.
Distension of duodenum.
Lots of products of carbohydrate/protein breakdown in duodenum.
Which cells secrete HCL and where are they located
Parietal cells located in oxyntic mucosa
What, apart from, HCl do parietal cells secrete and what is it’s function
Intrinsic factor
Binds to B12 to allow absorption in terminal ileum
What are the 3 functions of HCL
Denatures proteins
Activates pepsinogen to pepsin
Kills micro-organisms
Which cells secrete pepsinogen and where are they found
Chief cells
oxyntic mucosa
What is pepsinogen
Inactive precursor of pepsin, activated by HCL
Which cells secrete histamine and where are they located
Enterochromaffin like cell
Oxyntic mucosa
What is the function of histamine
Stimulates HCL production
Which cells secrete gastrin and where are they located
Secreted by G cells (duh)
Pyloric Gland Area
What is the function of gastrin
Stimulates HCL production
Which cells secrete somatostatin and where are they located
Secreted by D cells
Pyloric Gland Area
What is the function of somatostatin
Inhibits HCL production
What does vagal stimulation do in terms of acid secretion
Increases secretion of substances which stimulate acid production
Name 4 mechanisms protecting mucosa from HCL and pepsin
Hydrophobic monolayer
Bicarbonate secretion
Elimination of H+ in exchange for Na+
Locally produced prostaglandins which reduce acid secretion
How do NSAIDs cause gastric ulceration and bleeding
NSAID’s reduce prostaglandin formation by COX 1 INHIBITION; can lead to gastric ulceration and bleeding
Name 2 drugs which affect acid secretion
Protein Pump Inhibitors (PPI’s)
H2 receptor antagonists
How do PPI’s work and give an example
Inhibit active (membrane inserted) proton pumps omeprazole
How do H2 receptor antagonists work and give an example
Competitively antagonise H2 receptors
Completely block histamine mediated acid secretion
Ranitidine
Name the two types of pancreatic secretions
Endocrine
Exocrine
well done
Name the 2 endocrine secretions and where they are secreted
Insulin
Glucagon
secreted into bloodstream
Name the 2 exocrine secretions and where they are secreted to
Digestive enzymes
Sodium bicarbonate
Secreted into duodenum as pancreatic juice
Where are pancreatic digestive enzymes secreted from
Acinar cells
Where is sodium bicarbonate secreted from
Duct cells
What is the function of the sodium bicarbonate that is secreted from pancreatic duct cells
Neutralises acid chyme thus protecting mucosa and providing optimum pH for pancreatic enzymes
Which cells secrete secretin and what does it do
S cells funnily enough
Increases secretion of aqueous NaHCO3 solution into duodenum
What cells secrete CCK and what does it do
i cells (not C cells) Increases secretion of digestive enzymes into duodenum
Where is bile secreted from
Bile duct cells
Hepatocytes
The presence of what stimulates gallbladder SM to contract
Presence of chyme in the duodenum
What is the function of bile
Aids in the digestion of fat
Name 3 features of the small intestine which make it well adapted for absorption
Circular folds
Villi
Microvilli
What are the two types of starch
Amylose
Amylopectin
What is the difference between the two types of starch
Amylose only has α 1-4 bonds
Amylopectin has α 1-6 and α 1-4 bonds
Does glycogen have α 1-6 bonds
Yes
but more commonly than amylopectin (1 in 10 rather than 1 in 30 like amylopectin)
What does salivary α amylase do
attacks 1-4 glycosidic links
What breaks down sucrose
Sucrase
wow
What breaks down lactose
Lactase
na wa
What is sucrose made up of
GLUCOSE + FRUCTOSE
What is lactose made up of
GLUCOSE + GALACTOSE
How are proteins broken down in the stomach
HCl denatures proteins, pepsin cleaves proteins into peptides.
How are proteins broken down in duodenum
pancreatic enzymes split peptide bonds between amino acids, brush border enzymes cleave amino acids from amino end of molecule.
Hydrophilic amino acids are absorbed by passive diffusion
True or False
False
HydroPHOBIC amino acids are absorbed by passive diffusion
How does bile affect lipids
Emulsifies them to allow a larger surface area for pancreatic lipase to act
What is the co-factor that allows pancreatic lipase to do it’s job
Co-lipase
incredible
What are free fatty acids and how are they absorbed
Short-medium length chains
Absorbed by passive diffusion
How are long chain fatty acids and mono-glycerides absorbed
Resynthesised into triglycerides in the ER and incorporated into chylomicrons
What are lacteals
lymphatic vessels of the small intestine
Which protein surrounds a chylomicron before it is incorporated into a lacteal
Apolipoprotein
ApoB-48
What is a chylomicron that isnt bound to ApoB-48 called
Nascent chylomicron
Where do chylomicrons drain to and via which vessel
Left venous angle
via thoracic duct
