Gastric Motility and Pancreatic Function Flashcards
What is gastric motility?
Peristaltic waves from the body of the stomach to the antrum (contractions)
How does contractions strength vary across the stomach?
Is different in different areas
What is the contraction strength like in the body of the stomach?
Weak because it has a thin muscle
What is the contraction strength like in the antrum of the stomach?
Powerful because has a thick muscle
Where in the stomach does mixing occur?
Antrum
What happens when the pyloric sphincter is contracted?
Small quantitiy of gastric contents (chyme) enters the duodenum, further mixing occurs as antrul contents are forced back towards the body
What is gastric contents known as?
Chyme
What is the gastric peristaltic wave produced by?
Peristaltic rhythm
What is the peristaltic rhythm generated by?
Pacemaker cells in the longitudinal muscle layer
What is the rate of the peristaltic rhythm?
About 3/min
How does the signal from the peristaltic rhythm travel through the longitudinal muscle layer?
Gap junctions
What must be reached for the stomach to contract?
Action potential must reach threshold
What is the slow wave rhythm of the peristaltic rhythm known as?
Basic electrical rhythm (BER)
What is the action potential size proportional to?
Tension on the stomach wall
Explain the hormonal/neural control of contractions?
Gastrin increases contraction
Distension of stomach wall causes long/short reflexes which increases contraction
Fat/acid/amino acid/hypertonicity in duodenum inhibits motility (contraction)
How does gastrin impact contraction?
Increases
How does distension of stomach wall impact contraction?
Increases
How does the presence of fat, acid, amino acid, or hypertonicity in the duodenum impact contraction?
Decreases
What controls the force of contractions?
Frequency of action potentials
What secretes bicarbonate?
Brunner’s glands duct cells
In what layer are Brunner’s glands found?
Submucosal
What is neutralisation of acid in the duodenum done by?
Bicarbonate
What happens to the water and carbon dioxide produced during acid neutralisation?
Water flows down the gut and carbon dioxide diffuses away
Why is it important that the duodenum is not acidic?
It would denature enzymes from the pancreas and damage the duodenum epithelium which needs to absorb things such as iron
What does acid in the duodenum trigger?
Long (vagal) and short (ENS) reflexes causing HCO3 secretion
Release of secretin from S cells causing HCO3 secreiton
What are long reflexes controlled by?
Vagas nerve
What are short reflexes controlled by?
ENS reflexes
What does secretin cause?
Bicarbonate to be secreted from the pancreas and liver which will end up in the duodenum as well as from Brunner’s glands in the duodenum
How does acid neutralisation impact secretin release?
Inhibitis secretin release (negative feedback control)
What are the 3 parts of the pancreas?
Head (located within curvature of duodenum)
Body
Tail (extends to spleen)
What are the 2 classes of glands contained in the pancreas?
Endocrine
Exocrine
Where do endocrine glands secrete into?
The blood
Where do exocrine glands secrete into?
Surrounding tissues
What is the endocrine portion of the pancreas?
Islets of Langerhans
What do islets of Langerhans produce?
Insulin, glucogon and somatostatin
What are the functions of insulin and glucagon?
Control [glucose]blood
What is the function of somatostatin?
Control secretion of insulin and glucagon
What are the exocrine portions of the pancreas?
Acinar cells found in lobules which are connected by intercalated ducts
Explain the pathway exocrine hormones from the pancreas take?
Intralobular ducts -> interlobular ducts -> main pancreatic duct -> common bile duct -> hepatopancreatic ampulla -> duodenum
What controls the hepatopancreatic ampullar?
Sphincter of Oddi
What pancreatic duct is present other than the main one?
Accessory pancreatic duct that is closed unless the other duct becomes blocked, then it would open
What does the sphincter of Oddi control?
Delivery of pancreatic juice and bile into the duodenum
Which of the exocrine and endocrine pancreas is responsible for the digestive functions of the pancreas?
Exocrine
Where are the exocrine hormones of the pancreas produced?
Acini
What are functions of the exocrine pancreas?
Secretion of bicarbonate by duct cells
Secretion of digestive enzymes by acinar cells
What is the classification of duct cells of the pancreas?
Cuboidal
What is the shape of acinar?
Triangular to form bulb like structures
What are digestive enzymes stored as in the acinar cells?
Zyogen granules
Why are digestive enzymes stored in accini as zymogen granules?
Prevents autodigestion of the pancreas
What converts all zymogens to their active form?
Trypsin
What is the zymogen of trypsin?
Trypsinogen
What converts trypsinogen into trypsin?
Enterokinase
Where is enterokinase found?
Bound to brush border of duodenal enterocytes
What are some categories of pancreatic enzymes?
Proteases
Nucleases
Elastases
Phospholipases
Lipases
a-Amylase
What is the function of proteases?
Cleave peptide bonds
What is the function of nucleases?
Hydrolyse DNA/RNA
What is the function of elastases?
Collagen digestion
What is the function of phospholipases?
Converts phospholipids to fatty acids
What is the function of lipases?
Converts triacylglycerides to fatty acids and glycerol
What is the function of a-Amylase?
Convert starch to maltose and glucose
What is the mechanism for controlling bicarbonate secretion from the pancreas?
1) Secretin released in response to acid in duodenum
2) Bicarbonate secretion stimulated by secretin
What is the mechanism for controlling zymogen secretion?`
1) Cholecystokinin (CCK) released in response to fat/amino acids in duodenum
2) Zymogen secretion stimulated by CCK
3) Also under neural control (vagal/local reflexes), triggered by arrival of organ nutrients in duodenum
