gastric motility and the pancreas Flashcards
where do peristaltic waves travel from in the stomach and what occurs at each area
from the body to antrum
body - thin muscle so weak contractions (no mixing)
antrum - thick muscle so powerful contractions (mixing occurs)
what happens when the peristaltic wave reaches the antrum
contraction of the pyloric sphincter
what does contraction of the pyloric sphincter allow
- only a small quantity of gastric content (chyme) enters the duodenum
- rest of contents pushed back up to body so allows of further mixing/grinding with acid
what produces gastric peristaltic waves
peristaltic rhythm (~3/min) is generated by pacemaker cells in the longitudinal muscle
they are SLOW waves
briefly describe how the pacemaker cells make the slow peristaltic waves
slow waves:
- occur from spontaneous depolarisation/repolarisation
- conducted through gap junctions along longitudinal muscle layer
- depolarisation is sub-threshold so require further depolarisation to induce action potentials and contractions
slow wave rhythm is from basic electrical rhythm (BER)
what determines the strength of contractions
number of action potentials
what determines the frequency of the contractions
basic electrical rhythm (BER)
what neural/hormonal controls can affect gastric peristalsis and how
gastrin - increases contractions
distension of stomach wall - long/short reflexes - increases contractions
fat/amino acid/hypertonicity in duodenum - inhibits motility
what neutralises the acid in the duodenum
bicarbonate (HCO3) secretions from brunners gland duct cells (submucosal glands)
bicarb rises up from the duodenum to meet the acid coming in from the stomach
what is the reaction for neutralisation of the acid
H+ + HCO3- = H2CO3 = H2O + CO2
what are the two controls for duodenal HCO3 secretion that are triggered by the presence of acid
- long (vagal) and short (ENS) reflexes - increases HCO3 secretion
- release of secretin from S cells - increases HCO3 secretion
what does secretin also cause
HCO3 secretion from the pancreas and liver
how is secretin secretion controlled
self limiting negative feedback loop - when acid neutralisation occurs - secretin release inhibited
what are the three main parts of the pancreas
Head (located within curvature of duodenum),
body,
tail (extends to spleen)
what comprises the endocrine portion of the pancreas (i.e. material into circulatory system)
pancreatic islets (islets of Langerhans)
islet cells produce:
- insulin
- glucagon (control [glucose]blood )
- somatostatin (controls secretion of insulin and glucagon)
what comprises the exocrine portion of the pancreas (i.e. material to outside the body)
acinar cells that contain lobules
what is the primary exocrine route out of the pancreas
- acinar cells
- lobules connected by intercalated ducts
- interlobular ducts
- main pancreatic duct
- common bile duct
- hepatopancreatic ampulla (SPHINCTER OF ODDI)
- duodenum
what is the secondary exocrine route out of the pancreas
the accessory pancreatic duct - also goes to the duodenum
what is the function of the exocrine pancreas
digestive fucntion
- secretion of bicarbonate by duct cells
- secretion of digestive ezymes by acinar cells
what is the basic anatomical structure of the exocrine pancreas
acini - ducts - pancreatic duct
what kind of cells make up duct cells
cuboidal epithelium
why is nothing digested by the secreted enzymes as it goes down the pancreatic ducts
if it did pancreas would essentially be digesting itself
what are zymogens and where are they stored
digestive enzymes that are stored as inactive granules (zymogens)
stored in the acinar cells
what does having inactive forms of the enzymes prevent
autodigestion of the pancreas
what converts zymogens to their active forms
trypsin
what does trypsin come from
trypsinogen
what converts trypsinogen into trypsin
enterokinase bound to the brush border of the duodenum
what are the 6 categories of pancreatic enzymes
- proteases
- nucleases
- elastases
- phospholipases
- lipases
- a-amylse
what do each of the categories of pancreatic enzymes do
- proteases - cleave peptide bonds
- nucleases - hydrplyse DNA/RNA
- elastases - collagen digestion
- phospholipases - phospholipids to fatty acids
- lipases - triglycerides to fatty acids + glycerol
- a-amylse - starch to maltose and glucose
what stimulates secretion of bicarbonate
secretin
what is secretin rekeased in response to
acid in the duodenum
what stimulates secretion of zymogens
cholecystokinin (CCK)
what is CCK released in response to
fat/amino acids in the duodenum
also under neural control (vagal/local reflexes) - triggered by arrival of organic nutrients in the duodenum
summarise the negative feedback loop of secretin secretion
- increased acid in stomach
- increased secretin secretion in small intestine
- increased plasma secretin
- increased bicarbonate secretion in pancreas
- increased flow of bicarbonate to small intestine
- increased neutralisation of intestinal acid in small intestine
- TIGGERS NEGATIVE FEEDBACK TO REDUCE SECRETIN SECRETION AT STEP 2
summarise the negative feedback loop of cholecystokinin secretion
- increased fatty acids and amino acids
- increased CCK secretion in small intestine
- increased plasma CCK
- increased enzyme secretion in pancreas
- increased flow of enzymes to small intestine
- increased digestion of fats and proteins in small intestine
- TRIGGERS NEGATIVE FEEDBACK TO REDUCE CCK SECRETION AT STEP 2
