GI V & VI Flashcards
Describe the major functions of the stomach.
2 main functions, secretions
The major functions of the stomach are: (storage and motility)
Storage: temporary storage of meal
Secretion of H+: killing microorganisms and conversion of pepsinogen → pepsin
Secretion of Intrinsic factor (IF): essential for the absorption of vitamin B12
Secretion of mucus and HCO3- : protection of gastric mucosa
Secretion of water: lubrication of bolus, suspension of nutrients in solution
Motor Activity: mixing secretions (H+ and pepsin) with bolus.
Coordination of motor activity of smooth muscle and emptying of stomach contents into duodenum.
Describe the importance of the following secretions in the stomach:
H+
Intrinsic factor
mucus and HCO3
water
Secretion of H+: killing microorganisms and conversion of pepsinogen → pepsin
Secretion of Intrinsic factor (IF): essential for the absorption of vitamin B12
Secretion of mucus and HCO3- : protection of gastric mucosa
Secretion of water: lubrication of bolus, suspension of nutrients in solution
What would happen if one underwent gastric surgery? What would be the effect (in regards to gastric secretions?)
intrinsic factor is req for vit. b12 absorption which really happens further in intestine but factor required for absorption is intrinsic factor (synthesized in stomach)
gastric surgery- lose intrinsic factor so bc not synthesized elsewhere in body, those ppl will have problems w vitamin b12 absorption.
Describe the regulation of motor and secretory responses in the stomach. Provide examples for neural, endocrine, and paracrine.
Regulation of both motor and secretory responses are via:
Neural: Intrinsic and extrinsic
Paracrine: histamine is a powerful stimulator of H+ secretion.
Endocrine:
gastrin (stomach and duodenum)- stimulates gastric acid secretion.
somatostatin (stomach, duodenum, and pancreas) - inhibits gastric secretion.
Describe the importance of somatostatin.
imp. negative regulator of acid secretion (negative feedback system) when pH drops, acid secretion, then drop of pH stimulates somatostatin which will inhibit further secretion. neg. feedback
Describe the functional anatomy of the LES and cardia.
What is the region? Luminal secretion? Motility?
LES and cardia (LES part of esophagus)
luminal secretion: mucus and bicarb
motility:
- prevention of reflux
- entry of food
- regulation of belching
Describe the functional anatomy of the fundus and body of stomach.
Luminal secretion? Motility?
Luminal secretion: H+ Intrinsic factor mucus HCO3- pepsinogens lipase
Motility:
- reservoir
- tonic force during emptying
Describe the functional anatomy of the antrum and pylorus.
Luminal secretion? Motility?
luminal secretion: mucus and HCO3-
motility: mixing, grinding, sieving, regulation of emptying
What are the three regions the stomach is divided into?
What are the 2 functional parts the stomach is divided into (to discuss physiology)?
The cardia
The corpus (or fundus, body)
The antrum
The proximal part (closer to mouth) (thin wall)
The distal part (further away from mouth). (thick wall)
Describe gastric pits and glands.
Slide 8
The lining of the stomach contains columnar epithelium – folded into gastric pits.
Each gastric pit is the opening where gastric glands empty.
Note in Pylorus:
Long pits and short
glands
gastric pit- columnar epithelial cells, in pits have openings where diff glands we find will empty their contents and now transported into lumen
surface epithelial cells -careful to protect those cells or else they are eroded (like we can see in esophagus)
The gastric mucosa is divided into three distinct regions based on the gland structure. Describe.
Small cardiac glandular region (below LES) – primarily mucus and HCO3- - secreting gland cells, that provide mechanical and chemical protection of the gastric mucosa
The remaining portion of the gastric mucosa is divided into:
Oxyntic or parietal gland region (fundus)
Pyloric gland region (antrum).
Describe the 6 types of secretory cells the fundus and antrum contain.
parietal or oxyntic cells
mucuous neck cells
peptic or chief cells
enterochromaffin-like cells
D cells
G cells
What do parietal or oxyntic cells secrete?
HCl: kills bacteria, allows activation of pepsin from pepsinogen, low pH for effective pepsin action.
HCl (hydrochloric acid): H+ activates pepsinogen into pepsins.
Intrinsic factor: glycoproteins that bind vitamin B12 making it absorbable by the ileum mucosa. It is an ESSENTIAL FACTOR!
Intrinsic Factor: glycoprotein, required for normal absorption of vitamin B12 in the ileum.
What do mucous neck cells secrete?
Mucus: protection of gastric mucosa.
Bicarbonate [HCO3]- + MUCUS : important for protection of gastric mucosa against acidic and peptic luminal environment.
What do Peptic or Chief cells secrete?
Pepsinogens: In acidic environment they are cleaved into pepsins (mixture of various proteases). Pepsins are only active in ACIDIC environments.
Pepsin initiates protein digestion in the stomach (20%) but that is not essential.
Pepsinogen: is the inactive proenzyme of pepsin.
What do ECL cells secrete?
Histamine (paracrine): most powerful stimulator of HCl secretion;
What do D cells secrete?
Somatostatin (endocrine) - powerful inhibitor of HCl secretion.
What do G cells (pyloric region) secrete?
Gastrin (endocrine): HCl secretagogue.
In the gastric juice (The cells of the gastric mucosa secrete a fluid called Gastric Juice) what is the only essential component?
In a healthy human, intrinsic factor is the only essential component of gastric juice, the functions of other components are redundant.
Describe how the parietal cell is different when resting vs active.
Slide 18
Resting parietal cell cytoplasm contains numerous tubules and vesicles – tubulovesicular system, their membranes contain transport proteins needed for secretion of H+ and Cl-. Intracellular secretory canaliculi are present.
Once activated, the tubulovesicular membranes fuse with the plasma membrane of the secretory canaliculi – (increases the number of H+-K+ antiporters on the secretory canaliculi membrane) – and opens to the lumen of the gland.
Describe the blood, lumen, and intracellular gastric parietal cell.
What is the combination of all events?
In the intracellular fluid: Carbonic anhydrase produces H2CO3 from CO2 + H2O.
-H2CO3 then dissociates into H+ and HCO3-.
In the Lumen (or apical membrane): H+ is secreted via the H+-K+ ATPase – active process that transports both H+ and K+ against electrochemical gradient (uphill).
- Cl- follows H+ by diffusing through Cl- channels.
- Increased intracellular Ca++ and cAMP increase luminal conduction of Cl- and K+.
In the basolateral membrane: HCO3- is absorbed into the blood via Cl- - HCO3- exchanger.
Combination of all these events leads to a net secretion of HCl and net absorption of HCO3-.
What does omeprazole do?
In the Lumen (or apical membrane): H+ is secreted via the H+-K+ ATPase – active process that transports both H+ and K+ against electrochemical gradient (uphill). This is inhibited by the drug omeprazole- used to treat ulcers to reduce H+ secretion.
