Down the duodenum Flashcards
what glands produce a mixed mucous/serous secretion
submandiubular and sublingual
what gland produces a serous secretion only
parotid glands
what are the 4 major functions of saliva
lubrication, defence, buffering, digestion
describe the lubrication function
glycoproteins called mucins produced. solution of food products facilitates taste, speech, swallowing
what are the defence molecules found in saliva
lysozyme, lactoferrin and antibodies, proline rich proteins bind to and neutralise tannins
what is the buffering effect
bicarbonate ions raise the ph of saliva from acidic during basal secretion to ph8 during active secretion
what enzyme is responsible for the digestive function of saliva
salivary amylase breaks down starch to oligosaccharides but is inhibited by low ph in the stomach. it is protected by bolus of food
what cells produce primary secretion of saliva
acinar cells
what is the primary secretion composition
isotonic to plasma and high in nacl
what does the high conc of nacl in primary secretion do
draws water into the acinar lumen
what is the other function of acinar cells
secrete salivary enxymes and other proteins by exocytosis
what do myoepithelial cells do
contract to empty saliva into the ducts
what happens to the saliva as it proceeds through the ducts
becomes more hypotonic
what promotes ion exchange in the salivary ducts
aldosterone
salivation is controlled by the
ANS
what type of response is there to the prospect of food in the cephalic phase of digestion
anticipatory response
what do PS fibres do
secrete ach and VIP to promote vasodilation therefore increase blood supply, metabolism and growth
what does PS stimulation also do
cause contraction of myoepithelial cells and via ach open more of the acinar cell channels increasing vol of saliva secreted
what do sympathetic fibres do
promote vasoconstriction, myoepithelial cell contraction and via cAMP exocytosis
describe the swallowing process
bolus pushed back to mouth > touch receptors in the pharynx > initiate the swallowing reflex
where is the swallowing reflex coordinated
swallowing centre in the medulla and lower pons
what is the swallowing reflux called
deglutition
what is deglutition apnoea
the respiratory centre of the medulla is directly inhibited by the swallowing centre for a brief term.
how is inhalation of the food prevented
fine control of multiple striated muscles in the pharyngeal region
what is the upper oesophageal sphincter
consists of the striated cricopharyngeus muscle.
describe the layers of muscle in the human oesophagus
upper third: longituindal and circular layers of muscle are striated, middle third contains smooth and striated, lower third contains ENITRELY SMOOTH
where does the primary peristaltic wave begin
begins just below the UOS and sweeps the bolus downwards. if bolus fails to be moved all the way down the stomach»_space; secondary peristaltic wave is initiated
how is a secondary peristaltic wave initiated
persistent distension of the oesophagus
how is the secondary peristaltic wave also initiated
local reflex and part of vagovagal reflex
what is the lower oesophageal sphincter
region of specialized circular smooth muscle at the bottom of the oeseophagus
what controls the LOS
ENS fibres which receive input from the ANS
describe the action of the LOS
normally tonically contracted but relaxes due to NO before food has arrived
why does the LOS relax before food has arrived
feed forward vagal reflex
what is the gastro-oesophageal reflux
acidic contents of the stomach enter the oesophagus leading to heart burn
what is barretts oesphagus
when epithelium of oesophagus changes to that of the stomach
what happens in the achalasia
reflex relaxation of the spinchter is compromised therefore there is difficulty swallowing
how much mucus is secreted by the oesophagus and why
small amount to lubricate food during swallowing
what is emesis
vomiting coordinated in the vomiting centre of the medulla oblongata
what is the chemoreceptor trigger zone
receptors on the floor of the fourth ventricle of the brain, stim of this zone leads to vomiting
why can emetics stimulate vomiting
can interact with the chemoreceptor trigger zone as it lies outside the blood brain barrier
what is the 1st stage of vomitting
increased salivation,
what is the 2nd stage of vomitting
retroperistalsis (sweep contents up the digestive tract into small through pyloric sphincter)
3rd stage of vomitting
lowering of intrathroacic pressure coupled with an increase in abdominal pressure as the abdominal muscles contract. propels stomach contents into the oesophagus without retroperistalsis
4th stage of vomitting
upper oesophageal sphincter remains contracted, the person retches: the contents drain back into the stomach, eventually the spinchter may relax and allow vomiting
what can happen with bile?
bile can enter the vomit due to duodenal contraction in severe cases
what are the 4 main functions of the stomach
act as reservoir, facilitate digestion, destroy ingested microbes, regulate appetite through feedback effects on the brain aswell as feedforward mechanisms
what is the vagovagal reflex responsive to
oesophageal or stomach stretch which causes the fundus and body of the stomach to relax
what is a receptive relaxation
fundus and body of the stomach relax so food can be accommodated with little increase in pressure
what is the antrum
thicker muscular walls of the stomach and performs forceful contractions, leads into the pylorus
what is the pyloric sphincter
circular muscle, narrowly opening therefore limiting the rate of stomach emptying.
why do slow waves generated by ICCs in the stomach body stop at the pylorus
pyloric sphincter region lacks ICCs
What increases the duration and amplitude of the plateau and the increase of aps and contractions occuring?
ach and gastrin
what happens when the wave of contraction reaches the pylorus
the pyloric sphincter contracts to prevent passage of ingesta
what happens after the pyloric sphincter contracts
stomach contents are forced backwards towards the middle of the stomach in retropulsion
what is chyme
food mixed with gastric secretions
what happens to the pylorus between contractions
it relaxes then under the influence of tonic gastric pressure allowing contents to pass into the duodenum. large or tougher food particles tend to remain in the stomach for longer
what is the migrating myoelectric complex
the wave of contractile activity that sweep remaining food towards relaxed pylorus, into the duodenum and this continues down into the terminal ileum
what initiates the myoelectric complex
the hormone motilin
name the gastric glands
cardiac, oxyntic, pyloric
cardiac secretes
mucus
pyloric secretes
mucus and gastrin
oxyntic glands secrete
hcl, pepsiongens, chymosin, other enzymes, intrinsic factors, mucus
where are the cardiac glands
near entrance of oesophagus
where are oxyntic glands and what cell types are contained here 3
in the funus and body containing parietal, chief and mucus secreting cells
where are the pyloric glands and what cell types 2
antrum, contains mucus secreting and G cells which secrete gastrin
what do chief cells secrete
pepsinogens
how are chief cells stimulated
by vagal ACh and a cholinergic reflex in response to acidity
what does acidity do
cleavage of pepsinogens to form pepsins, cleavage of prochymosin to form chymosin/rennin
what does vitamin b12 first bind to
haptocorrin secreted in saliva protecting it from stomach acidity
what does vitb12 bind to in the small intestine
an intrinsic factor secreted by the stomach parietal cells to resist digestion by proteases.
role of gastric acid 6
delay gastric emptying, improve absorption of calcium + iron and release vit b12, activate pepsinogens, destroy ingested microbes
describe the composition of gastric juice
between meals = more nacl, low hcl. at stimulation = parietal cells active, isotonic solution of hcl.
what does acid secretion involve
proton pumps on luminal membranes of pariteal cells, stimulated by intracellular reaction of co2 with water, hco3- and cl0 exchanger
what is alkaline tide
gastric venous blood becomes more alkaline due hco3- added to plasma
name the 3 forms of control on acid secretion
endocrine, paracrine and neurocrine transmitter release
what is role of gastrin
role is to promote histamine production and release from ecl cells
what promotes release of gastrin
local stretch reflexes, bagal stimulation via GRP, peptides, AA and Ca2+ in the stomach lumen
what is the role of histamine
agonist of hcl secretion, released from enterochromaffin like cells, a paracrine transmitter
role of ach
promotes release of acid, histamine and gastrin and inhibits somatostatin release
what do ach and gastrin both do
increase free caclium within the parietal cell.
maximum secretion of hcl requires ….
activation of both ca2+ and camp pathways resulting in potentiation
how does histamine act
acts on h2 receptors to increase camp as a secondary messenger
what is the inhibition of acid secretion mediated by….. 3, give details
- somatostatin - paracrine released from D cells. prevents excessive acid secretion
- secretin - released from S cells, inhibits acid secretion by stim vagal afferent fibres, reduce gastrin release
- prostaglandins - paracrines promote bicarb and mucus prod
what is the first phase of acid secretion
cephalic phase - mediated by feedforward ach, acid secretion increases but negative feedback through somatostatin release limitis ph change
what is the second phase of acid secretion
gastric phase - due to presence of food, protons buffered by proteins in food, ph rises, secretory mechanisms from inhibition reduces changes in ph, stretch of stomach wall = vagovagal and local reflexes which increase gastrin/acid release, peptides and aa stim g cells to increase gastrin secretion
what is the third phase of acid secretion
intestinal phase - chyme enters duodenum. duodenal stretch triggers vagovagal reflexes increasing acid secretion and gastrin release. decrease in ph = decrease in acid secretion
what is the protection from acid and ulcer formation
stomach mucosa is protected by mucus and bicarb by epithelial lining of stomach and gastric glands (gastric mucosal barrier)
what is the gastric mucosal barrier
mucus and bicarb secreted by mucous cells forming epithelial lining of stomach and gastric glands = alkaline lining
describe how epithelial mucous cells are lost
they are lost from the stomach surface and replaced by mucous cells from the necks of the gastric glands which migrate upwards and over the surface
how are neck mucous cells replaced
replaced as stem cells deeper within the glands which divide and differentiate
if the gastric mucosal barrier is compromised what happens
gastric ulcer, treated with drugs to suppress acid secretion including h2-receptor antagonists and h+/k+ atpase proton pump inhibitors
what are predispositions to gastric ulcers
NSAID drugs e.g. asprin and gram negative helicobacter pylori (bacterium)
what is the control of gastric emptying
level of tone of the pyloric sphincter is carefully controlled by the body. ENS, ANS and hormones. Relaxation promoted by inhibitory fibres which release NO
what are neural and hormonal reflexes often involved in
slowing the emptying of stomach contents generally by inhibiting gastric motility/tightening the pyloric sphincter
what are enterogastric reflexes
slow gastric emptying when the distal gut is stretched
what are enterogastric reflexes in response to
excess acid, fat digestion products, peptides and amino acids
what substances are absorbed across the stomach wall
alcohol, ketamine and aspirin
what part of the pancreas is bicarbonate rich
exocrine section
pancreatic acinar cells secrete what
enzymes by exocytosis, the proteases as inactive zymogens
pancreatic secretory trypsin inhibitor is packaged in……. which helps to……
same zymogen granules as trypsinogen, helps protect acinar cells from activation of trypsin inappropriately
what do acinar cells secrete a small amount of
nacl rich solution into the lumen
what do pancreatic duct cells secrete a lot of
aqueous component of the pancreatic juice, bicarb solution
what nerves stimulate pancreatic secretion
parasympathetic
what does sympathetic stimulation do
vasoconstriction, decreasing secretion
enteric neurons pass where
from stomach and duodenum to pancreas
what is the main stimulus for CCK release
fat digestion products in duodenum
what does cck stimulate in the pancreas
enzyme secretion from acinar cells and potentiates the effect of secretin on duct cells
what do ach and cck increase in pancreatic cells
intracellular calcium
what do secretin and vip increase
intracellular [camp]
what does camp do in the acinar and duct cells
open the luminal chloride channels, increasing secretion
what is the luminal chloride channel in duct cells
cystic fibrosis transmembrane conductance regulator
what is the most common form of cystic fibrosis
impaired electrolyte and water secretion into the duct system > clogged ducts > maldigestion and nutrient deficiency
what is cholera toxin
results in high levels of camp > excessive secretion by the CFTR of cl-, na+ and water > diarrhoea
