pancreatic exocrine secretions and control Flashcards
what are the functional units of the pancreas ?
Exocrine Tissue:
* This part of the pancreas is responsible for producing digestive enzymes. These enzymes (amylase, lipase, proteases, etc.) are secreted into the small intestine via the pancreatic duct to help break down food. The exocrine tissue is made up of clusters of cells called acini (singular: acinus) that secrete these enzymes.
Endocrine Tissue:
* The endocrine part of the pancreas consists of clusters of cells known as islets of Langerhans. These cells are responsible for producing hormones that regulate blood sugar levels:
- Alpha cells produce glucagon, which increases blood glucose levels.
- Beta cells produce insulin, which lowers blood glucose levels.
- Delta cells produce somatostatin, which regulates the secretion of both insulin and glucagon.
- PP cells produce pancreatic polypeptide, which regulates the release of digestive enzymes.
what are acinar cells ?
- Acinar cells: These are specialized cells in the pancreas that produce digestive enzymes like amylase, lipase, and proteases. These enzymes help break down food in the small intestine.
- Acini: These are small clusters of acinar cells that form sacs. These sacs are connected to a network of ducts (like tubes) that carry the digestive enzymes to the small intestine (duodenum).
how are digestive enzymes produced by acinar cells transported to the duodenum ?
- Ducts: As the digestive enzymes travel through the ducts, the ducts have different types of cells lining them:
- Intercalated ducts: The smallest ducts, lined with squamous (flat) or cuboidal (cube-shaped) cells.
- Intralobular ducts: Located within the lobes of the pancreas, lined with cuboidal or low columnar cells.
- Extralobular ducts: Larger ducts outside the lobes, lined with columnar (taller) cells.
- Interlobular ducts: Found between the lobes, lined with columnar cells and sometimes goblet cells (which secrete mucus).
- Pancreatic duct: This is the main duct where all the smaller ducts converge. It’s lined with columnar cells and carries the digestive enzymes into the duodenum, where they help with digestion. The pancreatic duct joins with the common bile duct (from the liver) to empty into the duodenum.
what are the pancreatic exocrine functions ?
- Secretes 1.5L of fluid/day (containing, e.g. sodium and HCO3–rich juice, albumin, globulin and digestive enzymes)
- Acinar cells secrete digestive enzymes which breakdown carbohydrates, fats, proteins, and nucleic acids
- Enzymes secreted in inactive form (as zymogens) to prevent auto-digestion
- Activation of enzymes occurs in the duodenum
- The anions that are secreted in the pancreatic juice:
HCO3-, Cl-, SO42-, HPO42- - The cations that are secreted in the pancreatic juice:
Na+, K+, Ca2+, Mg2+
What is the process by which the pancreas neutralizes stomach acid and modifies its secreted juice?
- The pancreas secretes a bicarbonate (HCO3-) rich fluid to neutralize stomach acid and raise pH to 6-7.
- As the fluid travels through the ducts:
- Cl-/HCO3- exchange occurs in epithelial cells.
- H+ is actively pumped out via Na+/H+ exchanger.
- H+ is exchanged for K+ using Na+/K+ ATPase.
- H+ neutralizes HCO3-, forming carbonic acid (H2CO3).
- H2CO3 dissociates into CO2 and HCO3-, helping maintain pH balance.
what are the effects of secretin on the composition and volume of pancreatic juice in humans ?
- Secretin, a hormone released when acidic chyme enters the small intestine, increases the secretion of bicarbonate-rich pancreatic juice.
- It stimulates the pancreas to produce a larger volume of fluid that is high in bicarbonate (HCO3-).
- The bicarbonate helps neutralize the acid from the stomach, creating a better environment for digestion in the small intestine.
- Secretin does not significantly increase enzyme secretion, but it makes the juice more alkaline to neutralize stomach acid.
describe the main enzymes secreted by the pancreas (no need to memorise fully just get the general points)
describe the proteolytic enzymes secreted by the pancreas
what is the fate of pancreatic enzymes in the duodenum
- Digestive enzymes survive different lengths of time in the small intestine
- Percentage of secreted enzymes that reach the small intestine
- Amylase: 75%
- Trypsin: 20%
- Lipase: 1%
how are pancreatic secretions controlled ?
Neural control:
* Vagus nerve stimulation increases pancreatic secretion during digestion.
* The parasympathetic nervous system triggers the release of digestive enzymes and bicarbonate-rich fluid.
Hormonal control:
* Secretin: Released when acidic chyme enters the small intestine. It stimulates the pancreas to secrete bicarbonate-rich fluid to neutralize stomach acid.
* Cholecystokinin (CCK): Released in response to fats and proteins in the duodenum. It stimulates the pancreas to release digestive enzymes (like amylase, lipase, and proteases).
* Gastrin: Stimulates both acid and enzyme secretion from the pancreas during the early stages of digestion.
Feedback mechanisms:
* Positive feedback: Secretin and CCK enhance each other’s effects, increasing enzyme and bicarbonate secretion.
* Negative feedback: As pH increases in the duodenum, secretin secretion is reduced, regulating the amount of bicarbonate released.
describe the control of pancreatic secretions in the cephalic , gastric and intestinal phases
what are the Effects of cystic fibrosis on pancreatic secretions ?
- Thickened mucus: In cystic fibrosis, the body produces thick and sticky mucus, which affects the pancreatic ducts.
- Blocked ducts: The thickened mucus blocks the pancreatic ducts, preventing the normal flow of pancreatic enzymes and bicarbonate-rich fluid to the small intestine.
- Reduced enzyme secretion: Due to the blockage, the pancreas cannot effectively release digestive enzymes (amylase, lipase, proteases) into the small intestine, leading to impaired digestion of food, especially fats and proteins.
- Increased risk of malnutrition: The inability to properly digest food results in malabsorption of nutrients, leading to weight loss and malnutrition.
- Damage to pancreatic tissue: The blocked ducts can lead to pancreatic tissue damage and eventual pancreatic insufficiency, where the pancreas is unable to produce enough digestive enzymes.
- Excessive bicarbonate secretion: The pancreas may try to compensate by producing excessive amounts of bicarbonate, but the thick mucus still prevents it from reaching the small intestine effectively.
What is steatorrhoea characterised by?
The voiding of oily, smelly faeces.
Which pancreatic enzyme can cause steatorrhoea?
Pancreatic lipase.
What is the basic unit of the pancreas that has tubule-acinar glands?
Acinus.
Name two digestive enzymes of the pancreas.
- Trypsinogen * Pancreatic lipase
What activates trypsinogen?
Enterokinase or enteropeptidase, and subsequently by trypsin.
Which pancreatic enzyme is secreted in its active form?
Pancreatic lipase.
What enhances the activity of pancreatic lipase?
Bile salts.
What is the role of secretin in pancreatic function?
It promotes the secretion of pancreatic juice.
What is one exocrine secretion of the pancreas whose secretion is increased by secretin?
HCO3-.
What are the three main triggers for the control of pancreatic secretions?
- Cephalic phase * Gastric phase * Intestinal phase
What effect does the cephalic phase have on pancreatic juice secretion?
Stimulates secretion of protein-rich pancreatic juice through vagal innervation.
What stimulates gastrin release during the gastric phase?
Distension of stomach and contents of the chyme.
What are the two key players in the intestinal phase of pancreatic secretion?
- Secretin * CCK
What is the effect of sympathetic stimulation on the exocrine secretions of the pancreas?
Inhibits the exocrine secretions.
Which pancreatic exocrine secretion reaches the small intestine at higher levels?
Amylase.
Which enzyme converts trypsinogen to trypsin?
Enterokinase or enteropeptidase.
What is the best enhancer of pancreatic lipase activity?
Bile salts.
Fill in the blank: The sympathetic nervous system ______ digestion.
inhibits
