D2 Digestion Flashcards
WHat is the role of exocrine glands?
Exocrine glands produce and secrete substances via a duct onto an epithelial surface
What 2 places do exocrine glands secrete substances into/onto?
The surface of the body (e.g. sweat glands, sebaceous glands)
The lumen of the digestive tract / gut (e.g. digestive glands)
What are 4 examples of digestive glands?
salivary
gastric
pancreatic
intestinal glands
What is the role of salivary glands?
Salivary glands – secrete saliva which contains amylase (breaks down starch)
What is the role of gastric glands?
secretes gastric juices which includes hydrochloric acid and proteases (breaks down protein)
What is the role of pancreatic glands?
secretes pancreatic juices which include lipase, protease and amylase
What is the role of intestinal glands?
secretes intestinal juices via crypts of Lieberkuhn in the intestinal wall
What are exocrine glands composed of?
Exocrine glands are composed of a cluster of secretory cells which collectively form an acinus (plural = acini)
What are acini surrounded by?
The acini are surrounded by a basement membrane and are held together by tight junctions between secretory cells
WHat do the secretory cells possess ? (organelles)
The secretory cells possess a highly developed ER and golgi network for material secretion and are rich in mitochondria
How are exocrine products secreted?
Exocrine products are released (via secretory vesicles) into a duct, which connects to an epithelial surface
How may ducts arise? (from what are they formed)
These ducts may arise from a convergence of smaller ductules (each connected to an acinus) in order to enhance secretion
What is the secretion of digestive uices controlled by?
The secretion of digestive juices is controlled by both nervous and hormonal mechanisms
What do nervous and hormonal mechanisms control?
These mechanisms control both the volume of secretions produced and the specific content (e.g. enzymes, acids, etc.)
What does the sight and smell of food do?
The sight and smell of food triggers an immediate response by which gastric juice is secreted by the stomach pre-ingestion
What happens when food enters the stomach? (nervous mechanism)
When food enters the stomach it causes distension, which is detected by stretch receptors in the stomach lining
What does the stretching of the stomach lining cause?
Signals are sent to the brain, which triggers the release of digestive hormones to achieve sustained gastric stimulation
nervous mechanism
What secretes gastrin?
Gastrin is secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids
What happens to gastrin when stomach pH is too low?
If stomach pH drops too low (becomes too acidic), gastrin secretion is inhibited by gut hormones (secretin and somatostatin)
What stimulates the small intestine to secrete hormones?
When digested food (chyme) passes into the small intestine, the duodenum also releases digestive hormones:
What is the role of secretin and CCK?
Secretin and cholecystokinin (CCK) stimulate the pancreas and liver to release digestive juices
What is the role of pancreatic juices?
Pancreatic juices contain bicarbonate ions which neutralise stomach acids, while the liver produces bile to emulsify fats
What do the gastric glands secrete apart from hormones?
The gastric glands that line the stomach wall secrete an acidic solution that creates a low pH environment within the stomach
What is the normal pH of the stomach and why?
The normal pH of the stomach is roughly 1.5 – 2.0, which is the optimum pH for hydrolysis reactions by stomach enzymes
What are the 3 functions of the acid conditions of the stomach?
Assists in the digestion of food
Activates stomach proteases
Prevents pathogenic infection
How do the acidic conditions in the stomach help the digestion of food?
by dissolving chemical bonds within food molecules
How do the acidic conditions of the stomach help activate stomach proteases?
e.g. pepsin is activated when pepsinogen is proteolytically cleaved in acid conditions
How do the acidic conditions of the stomach help prevent pathogenic infections?
stomach acids destroy microorganisms in ingested food
What is the stomach wall lined by and why?
The stomach wall is lined by a layer of mucus, which protects the stomach lining from being damaged by the acid conditions
What does the pancreas release in relation to pH?
The pancreas releases bicarbonate ions into the duodenum which neutralises the stomach pH (intestinal pH ~7.0 – 8.0)
What may also neutralise stomach pH?
Certain foods (e.g. antacids) may also neutralise stomach acids, impairing digestion and increasing chances of infection
What maintains low pH environment of stomach?
The low pH environment of the stomach is maintained by proton pumps in the parietal cells of the gastric pits
How do proton pumps maintain acidic conditions in stomach?
These proton pumps secrete H+ ions (via active transport), which combine with Cl– ions to form hydrochloric acid