12 - GI Secretion 1

Question 1

What are the two main types of GI secretions?

Answer 1

mucus: for lubrication
diestive: to digest proteins, fats, or starches/carbs

Question 2

What are the four types of glands in the GI system? What is an example of each?

Answer 2

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.

Question 3

What are some factors that cause glandular secretion?

Answer 3

Direct contact (mucus)

ENS: tactile stimulation, chemical irritation, gut distension (meissner’s plexus).

ANS: para increases secretion, symp alone causes slight increase in secretion.

Question 4

What are the two types of proteins produced by salivary glands?

Answer 4

Ptyalin (alpha amylase) that digests starches - any gland that makes ptyalin is called a serous gland

and mucus

Question 5

What are the three types of salivary glands and their products?

Answer 5

Parotid: serous

Submandibular: serous and mucus

Sublingual: serous and mucus

Question 6

Describe the composition of saliva during maximal salivation?

Answer 6

There’s less time for modification therefore its composition is closer to that of ECF.

Question 7

Describe the nervous regulation of saliva production?

Answer 7

Parasympathetic control from salivatory nuclei in brainstem.

Taste stimuli, particularly acid, and tactile stimuli, particularly smooth objects.

Question 8

What else does parasympathetic stimulation also lead to in salivary cells?

Answer 8

Production of kallikrein (precursor of bradykinin) which dilates blood vessels.

Question 9

Describe esophageal secretions?

Answer 9

Mucous to lubricate the passage of food and prevent mucosal damage.

Mucous mainly secreted via single celled goblet cells.

Question 10

What is the function of mucous glands of the stomach?

Answer 10

to lubricate and also protect gastric mucosa against the effects of acid.

Question 11

Where are oxyntic glands located? Describe the different types of cells in these glands and their functions.

Answer 11

In the proximal stomach.

Oxyntic (parietal) cells: secrete acid and intrinsic factor

Chief cells: secrete pepsinogen

Enterochromaffin-like cells (ECL): secrete histamine

Question 12

What happens to the pepsinogen secreted by chief cells?

Answer 12

It’s activated to pepsin by HCL and begins protein digestion by hydrolyzing collagen.

Question 13

What is the function of pyloric glands? Where are they located?

Answer 13

Located in the antrum; Secrete mucous and gastrin.

Question 14

What type of cells in pyloric glands secrete gastrin? When does this occur? What inhibits this?

Answer 14

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.

Question 15

What are the stimuli for acid secretion in the stomach?

Answer 15

Histamine, gastrin, and acetylcholine from the vagus nerve and from ENS.

Question 16

What are the stimuli for pepsinogen secretion?

Answer 16

Acetylcholine from the PNS or ENS.

Gastric acid.

Question 17

What are some duodenal factors that inhibit gastric secretion?

Answer 17

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.

Question 18

What is the total amount of gastric secretion in a day?

Answer 18

~1500 mL daily.

Question 19

What are the phases of gastric secretion? What percent of the total gastric secretion does each account for?

Answer 19

1. Cephalic: 20%
2. Gastric: 70%
3. Intestinal: minimal

Question 20

Describe the cephalic stage of gastric secretion. What does it occur in response to? Where does the stimuli originate?

Answer 20

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.

Question 21

Describe the gastric stage of gastric secretion.

Answer 21

Local nerves secretory reflexes: enteric NS

Vagal reflexes: from stomach to brain and back to stomach

gastrin-histamine stimulation when food is in stomach

Question 22

Describe the intestinal phase of gastric secretion.

Answer 22

Small amounts due to duodenal production of gastrin.

Question 23

What inhibits gastric acid secretion?

Answer 23

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.

Question 24

What are hormones that inhibit gastric acid secretion?

Answer 24

Secretin

Gastric inhibitory peptide

Vasoactive intestinal peptide

Somatostatin

Question 25

What produces intrinsic factor and what is its function?

Answer 25

Parietal cells: necessary for vitamin B12 absorption in the terminal ileum.

Question 26

What are the two components of a salivary gland? What is the function of each?

Answer 26

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.

Question 27

How is gastric acid produced by the parietal cells?

Answer 27

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.

Question 28

Describe the three receptors on a parietal cell. What does binding of these receptors cause?

Answer 28

Muscarinic receptor: binds Ach which turns on acid production Histamine receptor: histamine turns on acid production CCK receptor: gastrin binds to promote acid production

Question 29

Where does peptic ulcer disease occur? What are symptoms?

Answer 29

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.

Question 30

What are the first and second most common causes of peptic ulcers? What are other causes?

Answer 30

1. H. pylori 2. NSAIDs OThers: cocain, meth, smoking, viral infection, gastrinoma, Chron's. lymphoma, or ischemia.

Question 31

What is Zollinger-Ellison syndrome?

Answer 31

Gastrinoma - tumor that produces gastrin and thus stimulates acid production and can cause peptic ulcers.

Question 32

Describe helicobacter pylori

Answer 32

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.

Question 33

How is H. pylori treated?

Answer 33

Combination of antibiotics and a proton pump inhibitor. ~10-14 day treatment

Question 34

What is Barrett's Esophagus? What is an associated risk?

Answer 34

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.

Question 35

What are the two types of cancers of the esophagus? Where are they located and what usually causes each?

Answer 35

Squamous cell carcinoma: proximal or mid-esophageal mass, related to tobacco use. Adenocarcinoma: distal esophageal mass, related to acid.

Question 36

What are the four steps involved in vitamin B12 (cobalamine) absorption?

Answer 36

1. It comes into contact with stomach acid and breaks it off of food. 2. R factor from salivary glands binds to free B12. 3. In small intestine, pancreas releases enzymes to separate R-factor from B12. 4. Intrinsic factor from parietal cells binds free B12 and absorption occurs in the terminal ileum.