GI III & IV: Cephalic, Oral, and Esophageal Phases

Question 1

Does absorption happen in the mouth?

Answer 1

In general, no; the exception is alcohol and certain drugs

Question 2

What is xerostomia?

Answer 2

Also known as dry mouth, caused by impaired salivary secretion; can be congenital or autoimmune; decrease in secretion reduces pH in oral cavity (due to less bicarb), leading to tooth decay, esophageal erosions, and difficulty swallowing

Question 3

What are the most important muscles involved in chewing?

Answer 3

• Temporalis (most impt.)
• Masseters
• Lateral pterygoids
• Medial pterygoids

Question 4

What are secretions elicited by?

Answer 4

secretagogues, which are substances that act on secretory cells and stimulate secretion

Question 5

Secretions in the GI tract come from which 3 sources?

Answer 5

• Glands associated with the GI tract (salivary glands, pancreas, liver)
• Glands formed by the gut wall itself (Brunner’s glands in duodenum)
• Intestinal mucosa

(secretions include water, electrolytes, protein, and humoral agents)

Question 6

When does most stimulation of salivary secretion occur?

Answer 6

during cephalic and oral phases of a meal

Question 7

Where does digestion of carbs and starches begin?

Answer 7

oral cavity

Question 8

Which enzymes are present during the oral phase?

Answer 8

• salivary amylase (breakdown of carbohydrates)

- lingual lipase (breakdown of fats)

Question 9

What are the 3 pairs of major salivary glands?

Answer 9

• parotid: serous secretions
• submandibular: mixed secretions
• sublingual: mucous secretions

Question 10

What are the two types of secretions in the mouth?

Answer 10

-serous (water, electrolytes, enzymes)
-mucous (mucin glycoprotein)
(and then there are also mixed secretions that are 50/50 mucous and serous)

Question 11

Saliva is produced by the salivary glands at what rate?

Answer 11

1L per day (secretes its own weight)

Question 12

How is saliva formed?

Answer 12

2-step process:

1) Formation of isotonic plasma-like solution by acinar cells (primary secretion / initial saliva)
2) Modification of plasma-like solution by ductal cells (via complex transport mechanisms) to produce hypotonic final saliva

Question 13

How is salivary secretion regulated?

Answer 13

It is exclusively neural (except in the GI system itself…certain GI secretions are neural AND hormonal). Salivary secretion is stimulated by BOTH sympathetic and parasympathetic divisions, although parasympathetic is the most dominant.

Question 14

Stimulation of salivary cells results in which physiological effects?

Answer 14

• increased saliva production
• increased bicarbonate and enzyme secretions
• contraction of myoepithelial cells

Question 15

What accounts for final saliva being hypotonic?

Answer 15

1) Ductal cells are relatively water-impermeable, so water is not absorbed along with solute
2) There is net absorption of solute (because more NaCl is absorbed than KHCO3 is secreted)

Question 16

How does composition of saliva vary with flow rate?

Answer 16

• highest flow rates: final saliva almost similar to plasma (or initial secretion)
• lowest flow rates: final saliva most dissimilar to plasma (because ductal cells have more time to extract electrolytes=hypotonic)

Question 17

What is the exception to the general trend of ionic composition varying with flow rate?

Answer 17

HCO3-, for its secretion is selectively stimulated when saliva production is stimulated

Question 18

Where is the swallowing center located?

Answer 18

in the medulla and lower pons

Question 19

The swallowing reflex specifically inhibits which two processes?

Answer 19

respiration and food entrance into trachea while swallowing

Question 20

Digestion is under involuntary control after which point?

Answer 20

After bolus passes upper esophageal sphincter

Question 21

Motor impulses from the swallowing center travel to the pharynx and upper esophagus via ________ and to the remaining esophagus via _______.

Answer 21

cranial nerves; vagal motor neurons

Question 22

What is relaxation of the esophageal sphincters mediated by during the esophageal phase?

Answer 22

peptidergic fibers in the vagus nerve that release VIP

Question 23

What is receptive relaxation?

Answer 23

When the orad region of the stomach relaxes at the same time as the LES relaxes, which reduces pressure in the orad and helps movement of the bolus into the stomach

Question 24

What are the 2 main functions of the esophagus and esophageal sphincters?

Answer 24

1 ) Propel food from pharynx to stomach

2) Sphincters protect airway from swallowed material and esophagus from acidic gastric reflux

Question 25

What are the main functions of the UES and LES?

Answer 25

- UES keeps air out of upper end of esophagus (prevents us from taking in unwanted materials from the envt.) - LES keeps gastric acid contents out of lower end of esophagus (protects us from gastric reflux)

Question 26

Where is the vomiting center located?

Answer 26

reticular formation in the pons

Question 27

What are some of the stimuli that elicit the cephalic phase of the integrated response to a meal?

Answer 27

cognitive stimuli, including the idea of food, olfaction, visual stimuli, and auditory stimuli

Question 28

Olfactory stimuli increase salivary secretion via which nerve?

Answer 28

CN IX (glossopharyngeal)

Question 29

What is the secretory unit of the GI tract?

Answer 29

acinar cells (a type of specialized epithelial cell)

Question 30

Salivary glands are formed by 2 main anatomical structures:

Answer 30

1) Acinus (secretory unit) | 2) Network of collecting ducts (empty secretory juice into gut)

Question 31

What would happen if a patient had an adenoma in his or her parotid gland?

Answer 31

difficulty swallowing, chewing and speaking; poor salivation leading to dry mouth and bad breath

Question 32

What are the main functions of saliva?

Answer 32

- lubrication of ingested food w/ mucus to aid movement through esophagus - protection of oral cavity by diluting/buffering ingested foods and maintaining healthy tissue (contains lysozyme, which can lyse bacterial cell walls) - initial digestion of starches and lipids by salivary enzymes

Question 33

Describe the composition of saliva.

Answer 33

- inorganic constituents: water, bicarb, ions, fluoride (inorg. constit. entirely dependent upon stimulus and rate of salivary flow) - organic constituents: salivary amylase, lingual lipase, glycoprotein, lysozyme, kallikrein

Question 34

Salivary secretion is hypotonic, meaning it has...

Answer 34

-higher K+ and HCO3- concentrations -lower Na+ and Cl- concentrations (has lower osmolarity)

Question 35

The esophageal phase of swallowing is controlled by what?

Answer 35

swallowing reflex AND enteric nervous system

Question 36

During swallowing, how is the secondary peristaltic wave initiated?

Answer 36

by a primary peristaltic contraction, which propels food downs the esophagus and distends it

Question 37

What is the purpose of secondary peristalsis in swallowing?

Answer 37

Repetitive secondary peristalsis clears the esophagus of the bolus.

Question 38

Which pressure is lower - intraesophageal or abdominal?

Answer 38

intraesophageal

Question 39

What is the problem created by intraesophageal pressure being lower than abdominal pressure?

Answer 39

- must have a way to keep air out of upper end of esophagus (done by UES) - must have a way to keep gastric acid contents out of the lower end of the esophagus (done by LES)

Question 40

Does the muscularis mucosa get thicker or thinner in the small and large intestine?

Answer 40

thinner... this part of the GI tract does not have to handle food pieces that are quite as large as the ones being propelled through the esophagus

Question 41

True or false: patients with GERD have squamous epithelia absent close to the stomach.

Answer 41

True- the transition from squamous to columnar epithelium occurs higher up in patients with GERD.

Question 42

How is GERD treated?

Answer 42

- H2 receptor antagonists (ex: ranitidine) | - proton pump inhibitors (ex: omeprazole)

Question 43

What is achalasia?

Answer 43

A motility disorder of the esophagus in which the smooth muscle layer of the esophagus does not have normal peristalsis, and the LES does not relax normally in response to swallowing. Common symptoms include dysphagia, regurgitation, and chest pain.

Question 44

What are some characteristics of the vomiting act?

Answer 44

- reverse peristalsis of small intestine - relaxation of pyloric sphincter and stomach to receive intestinal contents - forced inspiration against closed glottis decreases intrathoracic pressure and increases intraabdnominal peressure

Question 45

What happens during retching (aka, dry heaving)?

Answer 45

The UES remains closed, so gastric contents are forced into the esophagus but do not enter the pharynx. It often precedes vomiting.