Flashcards in 12 - GI Secretion 1 Deck (36):
What are the two main types of GI secretions?
mucus: for lubrication
diestive: to digest proteins, fats, or starches/carbs
What are the four types of glands in the GI system? What is an example of each?
1. Epithelial glands: single cell goblet cells
2. Submucosal glands: sm. int. crypts of lieberkuhn
3. Deep tubular glands: glands in stomach producing acid and pepsinogen
4. Complex glands that empty products into GI tract: salivary glands, pancreas, liver.
What are some factors that cause glandular secretion?
Direct contact (mucus)
ENS: tactile stimulation, chemical irritation, gut distension (meissner's plexus).
ANS: para increases secretion, symp alone causes slight increase in secretion.
What are the two types of proteins produced by salivary glands?
Ptyalin (alpha amylase) that digests starches - any gland that makes ptyalin is called a serous gland
What are the three types of salivary glands and their products?
Submandibular: serous and mucus
Sublingual: serous and mucus
Describe the composition of saliva during maximal salivation?
There's less time for modification therefore its composition is closer to that of ECF.
Describe the nervous regulation of saliva production?
Parasympathetic control from salivatory nuclei in brainstem.
Taste stimuli, particularly acid, and tactile stimuli, particularly smooth objects.
What else does parasympathetic stimulation also lead to in salivary cells?
Production of kallikrein (precursor of bradykinin) which dilates blood vessels.
Describe esophageal secretions?
Mucous to lubricate the passage of food and prevent mucosal damage.
Mucous mainly secreted via single celled goblet cells.
What is the function of mucous glands of the stomach?
to lubricate and also protect gastric mucosa against the effects of acid.
Where are oxyntic glands located? Describe the different types of cells in these glands and their functions.
In the proximal stomach.
Oxyntic (parietal) cells: secrete acid and intrinsic factor
Chief cells: secrete pepsinogen
Enterochromaffin-like cells (ECL): secrete histamine
What happens to the pepsinogen secreted by chief cells?
It's activated to pepsin by HCL and begins protein digestion by hydrolyzing collagen.
What is the function of pyloric glands? Where are they located?
Located in the antrum; Secrete mucous and gastrin.
What type of cells in pyloric glands secrete gastrin? When does this occur? What inhibits this?
G cells produce gastrin in response to presence of proteins. Also helps to control gastric secretions.
Gastrin inhibited by D cells which produce somatostatin in response to low pH.
What are the stimuli for acid secretion in the stomach?
Histamine, gastrin, and acetylcholine from the vagus nerve and from ENS.
What are the stimuli for pepsinogen secretion?
Acetylcholine from the PNS or ENS.
What are some duodenal factors that inhibit gastric secretion?
ENS: gastric secretion inhibited by distension, irritation, and acidity in the duodenum.
Fat and protein breakdown products and altered osmolality in duodenum result in release of secretin which acts in pancrease and secondarily to decrease gastric secretion.
What is the total amount of gastric secretion in a day?
~1500 mL daily.
What are the phases of gastric secretion? What percent of the total gastric secretion does each account for?
1. Cephalic: 20%
2. Gastric: 70%
3. Intestinal: minimal
Describe the cephalic stage of gastric secretion. What does it occur in response to? Where does the stimuli originate?
Sight, smell, thought or taste of food.
Originates in cerebral cortex and appetite centers of amygdala and hypothalamus and transmitted to stomach via vagus nerve.
Describe the gastric stage of gastric secretion.
Local nerves secretory reflexes: enteric NS
Vagal reflexes: from stomach to brain and back to stomach
gastrin-histamine stimulation when food is in stomach
Describe the intestinal phase of gastric secretion.
Small amounts due to duodenal production of gastrin.
What inhibits gastric acid secretion?
Presence of food in the small intestine:
1. Enterogastric reflex through myenteric NS which is activated by acid, protein breakdown products, and local irritation.
2. Presence of acid, fat, protein breakdown products, hypoosmotic, hyperosmotic factors, local irritation in upper sm. intestine result in hormones that inhibit gastric secretion.
What are hormones that inhibit gastric acid secretion?
Gastric inhibitory peptide
Vasoactive intestinal peptide
What produces intrinsic factor and what is its function?
Parietal cells: necessary for vitamin B12 absorption in the terminal ileum.
What are the two components of a salivary gland? What is the function of each?
1. Acini - at tip of the gland; produces ptyalin or mucous which are similar in concentration to ECF.
2. Duct - Where sodium and chloride are absorbed and potassium and bicarbonate are secreted.
How is gastric acid produced by the parietal cells?
Cl moves from the ECF through parietal cell to the lumen of the canaliculus.
At the same time, Na is actively pumped out of the canaliculus into ECF in exchange for K.
Now KCl is in the lumen. Water in the parietal cell become H and OH and the H/K ATPase pumps K into the cell and H into the lumen.
H combines with Cl in the lumen to become HCl. (OH combines with CO2 to make bicarb that goes into the ECF.
Describe the three receptors on a parietal cell. What does binding of these receptors cause?
Muscarinic receptor: binds Ach which turns on acid production
Histamine receptor: histamine turns on acid production
CCK receptor: gastrin binds to promote acid production
Where does peptic ulcer disease occur? What are symptoms?
2/3 of ulcers are in the proximal small intestine and 1/3 are gastric ulcers in the antrum.
Can be non-symptomatic or show classical signs such as pain and life-threatening bleeding.
What are the first and second most common causes of peptic ulcers? What are other causes?
1. H. pylori
OThers: cocain, meth, smoking, viral infection, gastrinoma, Chron's. lymphoma, or ischemia.
What is Zollinger-Ellison syndrome?
Gastrinoma - tumor that produces gastrin and thus stimulates acid production and can cause peptic ulcers.
Describe helicobacter pylori
Has flagella and adhesions: makes a defect in the mucous layer to travel close to the epithelial surface and adhere to it.
Produces urease which makes urea into ammonia and CO2 and make a protective environment for itself.
How is H. pylori treated?
Combination of antibiotics and a proton pump inhibitor.
~10-14 day treatment
What is Barrett's Esophagus? What is an associated risk?
When the lower esophageal sphincter isn't good and acid comes up from the stomach.
If it occurs long enough the squamous cells of the esophagus start to become columnar.
Risk for adenocarcinoma.
What are the two types of cancers of the esophagus? Where are they located and what usually causes each?
Squamous cell carcinoma: proximal or mid-esophageal mass, related to tobacco use.
Adenocarcinoma: distal esophageal mass, related to acid.