Physiology - upper GI + liver + gallbladder Flashcards
What is the chewing reflex
As jaw contracts, pressure created from food moving against gums and tongue –> pressure sensed by mechanoreceptors which then initiate a reflex which inhibits jaw muscles thus relaxing them –> and so on until food is chewed enough to swallow
Saliva is secreted by what 3 glands
Parotid
Submandibular
Sublingual
What kind of glands are exocrine glands + description
Exocrine - means they secrete into ducts to outside of body or on a surface
4 components of saliva
Water
Mucins
a-amylase
Lysozyme
Function of water as a component of saliva
Softens and dilutes particles thus reducing osmolarity
Function of mucins as a component of saliva
Combines with water to form mucus allows lubrication of food down the oesophagus
Function of a-amylase as a component of saliva
Is an enzyme that breaks down polysaccharides (starch, glycogen)
Function of lysozyme as a component of saliva
It kills bacteria in mouth by cleaving polysaccharide component of cell wall of bacteria
Salivary secretion is stimulated by what system
Autonomic - parasympathetic + sympathetic
What parasympathetic nerves control saliva secretion
Cranial nerves VII (facial nerve) + IX (glossopharyngeal nerve)
What type of salivary secretion is produced by parasympathetic system stimulation
- volume
- consistency
Lots of WATERY saliva
What type of salivary secretion is produced by sympathetic system stimulation
- volume
- consistency
- mucus content
- amylase content
Small volume, high protein THICK saliva
High mucus content (due to a1 adrenoceptors)
High amylase content (due to b2 adrenoceptors)
What is reflex control of salivary secretion
Food in mouth will be sensed my mechanoreceptors and cause salivary glands to become more active
Oesophagus vertebral level
C6 - T11/12
Types of muscle in oesophagus
Upper oesophagus is skeletal muscle
Remainder is smooth muscle
4 layers of oesophageal wall
Mucosa
Submucosa
Muscularis externa
Adventitia
Oesophageal mucosa is lined by what kind of epithelium
Stratified squamous non- keratinised
Where are submucosal glands (just means glands present in submucosa) found in the GI tract
Oesophagus and duodenum
What kind of glands are the submucosal glands in the oesophagus
Mucous secreting glands –> secrete into ducts –> lubricating oesophagus
Oesophagus function + peristalsis within oesophagus is produced by which layer of the muscularis externa
Transports food/liquid into stomach
Peristalsis produced by inner circular muscle of muscularis externa
What nerve innervating oesophagus controls contraction and relaxation of LOS
Vagus nerve
Stomach functions (5)
Temporary store of ingested food
Dissolves food particles
Controls delivery of food to small intestine
Sterilise ingested food (gastric acid kills micro-organisms)
Produce intrinsic factor
What function of the stomach is not compensatable by the body
Intrinsic factor production because it is essential for vitamin b12 absorption
What sphincter controls delivery of contents from stomach to SI
Pyloric
What is the opening of the top end of the stomach called (3 different names)
Cardiac/gastro-oesophageal opening
Lower oesophageal sphincter or cardiac sphincter
Stomach components from start to end
Cardiac opening/sphincter Cardiac region Fundus Body (greater/lesser curvature) Antrum Pyloric region Pyloric opening/sphincter
How many layers in the muscularis externa of the stomach (different to oesophagus)
3
What are the 3 layers of the muscularis externae of the stomach
Outer - longitudinal muscle
Middle - circular muscle
Inner - oblique muscle, doesn’t appear until antrum area
The mucosa and submucosa of the stomach fold to give what
Rugae
What cells form the lumens surface of the stomach
Flat surface mucus cells
What are gastric pits
Invaginations in the lumens surface of the stomach that lead down to gastric glands
Gastric glands composed of what 3 cells
Mucus neck cells
Parietal cells
Chief cells
Function of mucus neck cells (component of gastric glands)
Secrete mucous to protect stomach from gastric acid
Function of parietal cells (component of gastric glands)
Secrete HCl and intrinsic factor
Function of chief cells (component of gastric glands)
Secrete pepsinogens
What happens in the bolus phase of swallowing
Bolus (food) pushed to back of mouth by tongue
What happens in pharyngeal phase of swallowing
Bolus triggers reflex contractions of pharyngeal muscles
Soft palate reflected backward and upward so closing off nasopharynx to prevent regurgitation through nose
What happens as bolus approaches oesophagus
UOS relaxes and opens
Epiglottis covers larynx to prevent food entering trachea
What happens once food has entered oesophagus
UOS contracts to prevent reflux
What happens in oesophageal phase of swallowing
Peristaltic wave (muscle behind bolus contracts and muscle ahead relaxes), propelling bolus down to stomach
How long does it take to propel bolus down oesophagus into stomach
10 secs
When is receptive relaxation of the stomach initiated
Following receptive relaxation of LOS and entry of bolus into stomach
What is receptive relaxation of the stomach + what nerve is it mediated by
Relaxation of the fundus and body following relaxation of LOS, increasing stomach volume from 50ml to 1500ml
CN X
Function of the fundus of stomach
Storage
Function of body of stomach (5)
-secretion of 4 things
Storage Mucus secretion HCl secretion Pepsinogen secretion Intrinsic factor secretion
Function of pepsinogen (Secreted by chief cells)
Inactive precursor form of pepsin as pepsin would cause autodigestion of stomach
-pepsin breaks down proteins
Functions of antrum of stomach (2)
Mixing/grinding food (as contraction strongest here due to prominent inner oblique muscle)
Gastrin secretion by G cells
What is pepsin and how is it formed
Protein digestive enzyme
Pepsinogen gets cleaved chemically to form pepsin (Active form)
Describe gastric acid secretion process (7)
- what compound diffuses into parietal cell from blood and combines with water
- what does this then form and what enzyme is the reaction catalysed by
- the substance formed is not stable so dissociates into what 2 ions
- one of these ions gets pumped out apical membrane of parietal cell into the stomach lumen via a transporter
- the other ion gets pumped out basolateral membrane into blood in exchange for a different ion
- this exchanged ion then comes into parietal cell from the blood then what happens to it
- gastric acid is then finally formed by combination of what 3 things
- CO2 from blood diffuses into parietal cells and combines with water present in the cytoplasm, catalysed by carbonic anhydrase expressed by the parietal cells to form CARBONIC ACID
- Carbonic acid not stable so dissociates into hydrogen and bicarbonate ions immediately
- The hydrogen ions then pumped out apical membrane via H/K ATPase into stomach lumen
- Bicarbonate ions pumped out across basolateral membrane into blood in exchange for Cl ions coming in via chloride/bicarbonate exchanger
- Cl ions that have come into cell subsequently leave cell across apical membrane via a chloride shunt
- Now have H+ and Cl- inside stomach lumen, creating an osmotic gradient which water will follow
- Water then combines with H+ and Cl- –> HCl
Name the 2 hormones that control gastric acid secretion and what produces them
Gastrin (hormone) is produced by G cells
Histamine produced by local gland and only acts in the vicinity of where it’s secreted (so not within circulation)
Describe hormonal control of gastric acid secretion (describe gastrin specifically - how it stimulates gastric acid secretion) (5)
Gastrin binds to its receptor in the parietal cell basolateral membrane
- -> This increases Ca2+ conc. inside the cell
- -> which activates protein kinases
- -> which stimulates H/K ATPase
- -> Increased activity of H/K ATPase pumps more H+ into stomach lumen
Describe hormonal control of gastric acid secretion (describe histamine specifically - how it stimulates gastric acid secretion) (5)
Histamine acts on its G-protein coupled receptor on the basolateral membrane of the parietal cell
- ->which activates the AC protein the G protein is coupled to, stimulating it to convert ATP to cAMP
- -> cAMP then stimulates protein kinases
- -> which stimulate H/K ATPase
- -> Increased activity of H/K ATPase pumps more H+ into stomach lumen for HCl production
When the AC protein is activated, it stimulates the conversion of ATP to what (relating to gastric acid secretion)
cAMP
Describe neural control of gastric acid secretion (5)
-think what neurotransmitter stimulates gastric acid secretion
ACh released by parasympathetic fibres of CN X innervating stomach binds to muscarinic/cholinergic receptor in basolateral membrane of parietal cells
- -> causes rise in calcium inside cell
- -> increased Ca2+ conc. activates protein kinases
- -> which then stimulates H/K ATPase
- -> Increased activity of H/K ATPase pumps more H+ into stomach lumen for HCl production
What does H/K ATPase do (Relating to gastric acid secretion)
Uses ATP to pump 1 H+ out of cell into stomach lumen in exchange for 1 K+
What hormone like substance inhibits HCl production
-unlike gastrin, histamine and ACh (which all stimulate HCl production)
Prostaglandin
How does prostaglandin inhibit HCl production (5)
It binds to inhibitory G protein coupled receptors on the basolateral membrane of the parietal cell
- -> inhibiting the AC protein the G protein is coupled to
- -> so inhibiting conversion of ATP to cAMP
- -> thus inhibiting protein kinase stimulation
- -> therefore inhibiting H/K ATPase activity
The CEPHALIC PHASE of digestion (first phase of digestion followed by gastric then intestinal phase) is the gastric secretion that occurs even before food enters the mouth
-it results from the sight/smell/taste of the food so the brain induces an anticipatory response to prepare the GI tract for digestion
What nerve is the cephalic phase mediated by + what 2 mechanisms does this nerve stimulate HCl secretion
- Increased vagal activity –> increasing release of ACh –> stimulating parietal cells to produce HCl
- Increased vagal activity –> stimulates G cells to produce gastrin –> gastrin then stimulates parietal cells to produce HCl
3 things happen in the GASTRIC PHASE* that stimulate gastric acid secretion
*period in which swallowed food and semi-digested proteins activate gastric activity; 2nd phase of digestion; preceded by cephalic phase, proceeded by intestinal phase
- Stomach wall distends –> mechanoreceptors sense distension and trigger vagal/enteric reflexes –> triggering increase in ACh release –> stimulating parietal cells to make HCl
- Peptides in stomach lumen –> trigger G cells to produce gastrin –> stimulating parietal cells
- Local gastrin/ACh stimulates ECL cells which triggers them to release histamine –> which then stimulates parietal cells
In which 2 out of 3 phases of digestion can you stimulate gastric acid secretion
Cephalic and gastric
NOT INTESTINAL
In which phases of digestion (there are 3 phases) can you inhibit gastric acid secretion
All of them - cephalic, gastric + intestinal
What can you physically do in the cephalic phase of digestion (there are 3 phases of digestion) that can inhibit gastric acid secretion
Stop looking/thinking/smelling/eating –> decreased vagal activity –> decreased stimulation of parietal cells by ACh or gastrin
What negative feedback mechanism in the gastric phase of digestion (there are 3 phases of digestion) can inhibit gastric acid secretion
By decreasing pH (by increasing HCl conc.) –> triggers decreased gastrin production (NEGATIVE FEEDBACK - enough HCl so don’t need to make more)
What 2 things occur in the intestinal phase (there are 3 phases of digestion) that inhibits gastric acid secretion
- Acid in duodenum triggers enterogastric (splanchnic) reflex + release of secretin –> decrease gastrin secretion –> decreased parietal stimulation
- Fat in duodenum –> triggers GIP (gastroinhibitory polypeptide) release –> decreases gastrin secretion –> decreased parietal stimulation
What are enterogastrones + 3 examples of enterogastrones
Hormones released from glands in duodenal mucosa
- Secretin
- Cholecystokinin (CCK)
- Gastroinhinitory polypeptide (GIP)
Function of enterogastrones
Prevent further acid build up in duodenum by either INHIBITING GASTRIC ACID SECRETION or REDUCING GASTRIC EMPTYING
What is a zymogen + why are they produced
Inactive form of enzymes (inactive precursor) that undergoes acid hydrolysis to form the active form
Storing enzymes as zymogens prevents autodigestion
2 cytoprotective roles of gastric mucus
- protects mucosal surface from mechanical injury
2. HCO3 in mucus neutralises acidic pH –> protecting against gastric acid corrosion and pepsin digestion
Why is intrinsic factor important in vitamin B12 absorption
Intrinsic factor is needed to form a complex with vitamin B12 to allow it to be absorbed in the ileum
What does intrinsic factor deficiency cause
Pernicious anaemia - failure of RBC maturation because vit. B12 needed for RBC maturation
Stomach body v antrum motility
Body has thin muscle –> so weak contraction –> so no mixing
Antrum has thick muscle –> so powerful contraction –> allowing MIXING OF FOOD & CONTRACTION OF PYLORIC SPHINCTER
How is the peristaltic rhythm generated
By pacemaker cells in the longitudinal muscle layer
How many peristaltic waves are there per min
3
Slow peristaltic waves are due to what + description about AP threshold
Spontaneous depolarisation/repolarisation (intrinsic rhythm)
Slow wave depolarisation is sub-threshold so requires further depolarisation to induce APs
What determines the strength of contraction in peristalsis
Number of APs
What 4 things inhibit motility of GI tract
Fat
acid
amino acids
hypertonicity
in the duodenum
What neutralises gastric acid in the duodenum
Bicarbonate secretion from Brunner’s gland duct cells in the submucosa
What are the submucosal glands called in the duodenum
Brunner’s glands
When acid arrives in duodenum, it triggers what 2 things + what do these 2 things subsequently cause
- Long (vagal) and short (ENS) reflexes -
- Release of secretin from S cells
CAUSE HCO3 SECRETION
What is the main trigger for Brunner’s glands to make bicarbonate
Secretin from s cells
Secretin stimulates bicarbonate secretion from Brunner’s glands and what other 2 places
Pancreas (specifically the duct cells in the exocrine pancreas)
Liver
Bicarbonate ions bind with hydrogen ions from gastric acid to form what
Carbonic acid
Pancreas has 2 portions called what
Endocrine and exocrine
Function of endocrine portion of pancreas (made of what cells + produces what 3 hormones)
Made of islet of langerhans cells
- beta cells produce insulin
- alpha cells produce glucagon
- delta cells produce somastatin
What is somatostatin
A hormone that controls secretion of insulin and glucagon, and other hormones in the body
Function of exocrine pancreas + made of what 2 types of cells + what do these cells produce)
DIGESTIVE FUNCTION
Made of ACINAR cells which secrete pancreatic (digestive) enzymes
and DUCT cells which secrete bicarbonate
Individual acinar cells of exocrine pancreas join together to form what structure
Lobules
The point of joining of the main pancreatic duct with the common bile duct is called what
Hepatopancreatic ampulla (ampulla of vater)
Relation of sphincter of oddi + ampulla of vater
Sphincter of oddi is the actual muscular valve that surrounds the ampulla of water and controls the flow of bile and pancreatic juices through the ampulla of vater into duodenum
Where does bile and pancreatic juice enter duodenum
Major duodenal papilla in 2nd part of duodenum
What cells in exocrine pancreas secrete bicarbonate and digestive enzymes
Duct cells - secrete bicarbonate
Acinar cells - secrete digestive enzymes
Digestive enzymes secreted by acinar cells of pancreas are secreted in what form
Zymogens - inactive
What 2 organs produce zymogens
Chief cells in stomach
Acinar cells in pancreas
What zymogen produced by the pancreas is activated a different way from other digestive zymogens
Trypsinogen
How is trypsinogen (produced by the pancreas) activated differently from other digestive enzymes
Enterkinase (a membrane bound enzyme of the duodenum) converts trypsinogen to trypsin when trypsinogen comes into contact with it
Zymogen secretion in the pancreas is stimulated by what hormone/enterogastrone
Cholecystokinin
What secretes CCK + what physiological stimuli causes CCK to be released
Secreted by gland cells in duodenal mucosa
Fatty acids + amino acids in duodenum triggers CCK release
As well as fatty + amino acid trigger for CCK stimulation, what else controls CCK release
Neural control - vagus nerve
ENS - local reflexes
List 6 pancreatic enzymes + their respective functions
Proteases - cleave peptide bond
Nucleases - hydrolyse dna/rna
Elastases - digest collagen
Phospholipases - breakdown phospholipids to fatty acids
Lipases - break down TAG to monoglyceride + 2 fatty acids
A-amylase - break down starch/glycogen
Physiological stimuli for secretin release from S cells
Acid in duodenum
Functions of secretin (5)
Stimulates duct cells in pancreas to secrete bicarbonate
Stimulates Brunner’s gland in duodenal mucosa to secrete bicarbonate
Stimulates bile duct to secrete bicarbonate
Decreases gastric acid secretion
Decreases gastric emptying
Functions of CCK (4)
Stimulates pancreatic acinar cells to secrete zymogens (inactive digestive enzymes)
Relaxes sphincter of oddi - increasing pancreatic flow into duodenum
Contracts gallbladder to release more bile into duodenum
Increases tone of pylorus - decreasing gastric emptying
4 lobes of liver (major + minor)
Major - right and left
Minor - caudate and quadrate
What is the porta of the liver + where is it located
Where vessels enter and exit the liver
On the inferior surface of liver
Name the 3 main vessels at the porta
+ other vessels
Hepatic artery
Hepatic portal vein (just means portal vein inside liver)
Hepatic duct
Lymphatic vessels, nerves
How is common bile duct formed
Common hepatic duct joins with cystic duct (from GB)
What ligament attaches liver to underside of diaphragm
Coronary ligament
What area of the liver isn’t covered by connective tissue capsule and visceral peritoneum + where is it on the liver
Bare area
- Diaphragmatic surface on the right lobe
What structures within the liver are the functional units
Hexagonal LOBULES
What is the portal triad + where is it located
A branch of the portal vein, hepatic artery and hepatic duct
Located at each corner of a hexagonal lobule
What does each component of the portal triad carry (specify the thing being carried) + differentiate if each component is carrying into or out of the liver
Hepatic portal vein - carries nutrient rich, deoxygenated blood from GI tract INTO LIVER
Hepatic artery - carries oxygenated,, nutrientless blood from left side of circulation INTO LIVER
Hepatic duct - carries bile OUT OF LIVER
What vein exists at the centre of each hexagonal liver lobule and what is the subsequent pathway of venous blood through this vein
Central vein –> hepatic veins –> IVC
Hepatocytes (functional liver cells in the lobule) form what things that radiate out from the central vein
Hepatic cords
What are hepatic sinusoids + where are they in the liver + function
They are discontinuous, fenestrated open capillaries found between hepatic cords (line of hepatocytes)
Blood flowing through these sinusoids leaks into hepatocytes allowing them to process the blood so damaged/old RBCs can be removed from circulation
Direction of flow of blood from hepatic artery at the corner of a lobule
Hepatic artery –> hepatic sinusoid –> central vein –> hepatic veins
Direction of flow of blood from the hepatic portal vein at the corner of a lobule
Hepatic portal vein –> hepatic sinusoids –> central vein –> hepatic veins
4 functions of hepatocytes
Produce bile
Store nutrients
Nutrient interconversion - when nutrient deprived, liver will convert other nutrients into what’s needed
Detoxification - takes out harmful substances and puts it into bile, converts ammonia to urea
What nutrients does the liver store
Glycogen
Vit B12, A, D, E, K
Cu, Fe
6 components of bile
Bile acids Lecithin Cholesterol Bile pigments Toxic metals Bicarbonate
What 3 components of bile are made in liver and can solubilise fat
Bile acids
Lecithin
Cholesterol
What are bile pigments
Breakdown products of haemoglobin from old/damaged erythrocytes
What is the predominant bile pigment called
Bilirubin - breakdown product of haem
How does yellow bile form
Bilirubin is extracted from blood by hepatocytes and secreted into bile, giving it a yellow colour (bilirubin gives yellow colour)
How do faeces get its brown colour
Bilirubin is modified by bacterial enzymes in LI creating brown pigments
How does urine get its yellow colour
Bilirubin that’s not secreted into bile gets reabsorbed and excreted in urine, giving it a yellow colour
How are bile acids made
Made in liver from cholesterol
Before bile acids are secreted into bile to go to duodenum, what happens to them
Bile acids are conjugated (chemically combined) with glycine/taurine to form BILE SALTS
What are bile canaliculi + where are they found
Thin vessels that collect bile secreted by hepatocytes, lie between hepatocytes within a hepatic cord
Bile that gets secreted into canaliculi flows into what
Hepatic duct
How are bile salts recycled + where are they recycled
Recycled in ileum via a BILE SALT TRANSPORTER into the hepatic portal vein then back into the liver
Path of bile acid/salts from liver (recycled so ends up in liver again)
Liver –> common bile duct –> duodenum –> ileum –> hepatic portal vein –> liver
What surface of liver is the gallbladder on
Inferior
3 layers of the wall of the gallbladder
Mucosa - folded into rugae
Muscularis - contractile
Serosa - connective tissue
2 functions of gallbladder
Stores bile by active absorption of Na+
Concentrates bile 5-20 times by absorbing Na and H2O from it
What does gallbladder do if you keep eating lots of fatty food
Releases more bile out of it so less time to concentrate it
What is the trigger for gallbladder to release bile
Fat in duodenum
The stimuli for hydrochloric acid secretion by the parietal cells in the cephalic phase include
tasting/smelling/chewing
The major inhibitory mechanism for hydrochloric acid secretion by parietal cells is through what hormone
somatostatin (GHIH)
Presence of fat in stomach increases or decreases gastric emptying time
increases
3 phases of swallowing
Oral (voluntary)
Pharyngeal (involuntary)
Oesophageal (involuntary)
In which phase of swallowing is the back of the tongue is elevated and the soft palate pulled anteriorly against it
-this keeps the food within the oral cavity and allows the airway to remain open
Oral (voluntary) phase
