The Gut

Question 1

What are the five main functions of the gut?

Answer 1

1) Motility–moves food and waste
2) Digestion
3) Absorption
4) Immune function
5) Secretion and excretion

Question 2

How is the gut controlled neurologically?

Answer 2

Some conscious effort is involved in chewing, swallowing, and defecation; otherwise autonomic control modulated via acetylcholine

Question 3

What is the main paracrine hormone in the stomach?

Answer 3

Histamine from ECF cells

Question 4

What is the role of motilin in the GI tract?

Answer 4

It promotes smooth muscle contractions from the esophageal sphincter to the duodenum

Question 5

What is the role of vasoactive intestinal peptide?

Answer 5

It increases secretions by the liver and small intestine and decreases relaxation in the smooth muscle of the intestines

Question 6

What types of nerves make up the enteric nervous system?

Answer 6

1) Intrinsic primary afferent neurons (sensory for stretch, osmolar changes, and pH changes)
2) interneurons (process IPAN signals)
3) Motor neurons–muscle motor and secretomotor

Question 7

What nerves are involved in parasympathetic innervation of the gut?

Answer 7

Mostly vagus; oral cavity has some involvement by glossopharyngeal (and motor by hypoglossal and mandibular), pelvic splanchnics involved in hindgut.

Question 8

How does the sympathetic nervous system interact with the gut?

Answer 8

Postganglionic fibers can innervate tissues directly or interact with the CNS fibers; they decrease motility and secretions

Question 9

What is the role of phasic contractions in gut smooth muscle?

Answer 9

The rapid contractions and relaxations of the gut help mix and churn the gut contents; the movement of contents helps promote exposure to epithelium and absorption of nutrients

Question 10

What is the role of tonic contractions in gut smooth muscle tissue?

Answer 10

Sustained contractions at sphincters regulate flow of chyme and promotes reservoir function

Question 11

What is the basic means by which peristalsis occurs?

Answer 11

Muscle downstream of a bolus relaxes and muscles at a bolus site contract to force the bolus forward

Question 12

How do phasic contractions propagate through the body?

Answer 12

Smooth muscle cells tend to be simultaneously activated and are engaged by slow-wave activity. The enteric nervous system largely controls it.

Question 13

Which cells set pacemaker activity for the gut?

Answer 13

The interstitial cells of Caja;

Question 14

What are the six sphincters of the gut?

Answer 14

1) upper esophageal
2) lower esophageal
3) pyloric
4) ileocecal
5) internal anal
6) external anal

Question 15

What are the voluntary components of the esophageal phase of digestion?

Answer 15

1) Mastication

2) Initial voluntary swallowing

Question 16

What are the automatic components of the esophageal phase of digestion?

Answer 16

1) soft palate elevates and seals nasopharynx
2) pharyngeal folds contract and form a conduit; epiglottis shuts
3) Upper esophageal sphincter relaxes
4) Pharyngeal contractions push food into the esophagus

Question 17

What is the difference between primary and secondary peristalsis in the esophagus?

Answer 17

Primary is the wave of peristaltic contractions initiated by swallowing
Secondary is the response by the esophagus to stretching from retained food or GER

Question 18

What is the sequence of esophageal peristalsis once the bolus reaches the upper sphincter?

Answer 18

As the upper sphincter closes, the lower sphincter opens. The lower sphincter closes as food passes to prevent reflux of the gastric contents

Question 19

What are the roles of gastric motility?

Answer 19

1) mechanical breakdown of food
2) Regulate output of chyme into small intestine
3) Reservoir function
4) housekeeping role during fasting to help expel contents regularly

Question 20

Where are the interstitial cells of Cajal located and at what rate do they depolarize?

Answer 20

In the greater curvature of the stomach; rate=3 contractions per minute

Question 21

How does gastric pressure respond to changes in gastric volume?

Answer 21

Muscle cells around the stomach relax with increasing volume, so the pressure of the stomach decreases

Question 22

What is the role of vigorous contractions at the pylorus of the stomach?

Answer 22

Forces food back towards the body of the stomach to mix with acid and promote further breakdown of food

Question 23

What size do particles need to reach to enter the duodenum and what types of particles enter first?

Answer 23

Usually they must be 1-2 mm in size; emptying is promoted with liquids and slowest with high calorie foods

Question 24

What are the phases of the migrating motor complex?

Answer 24

Phase 1–quiescence/no muscle activity
Phase 2–intermittent, brief contractions; most are mixing in nature but some may be propulsatory
Phase 3–brief 5-10 minute bursts of high-amplitude contractions that move downstream

Question 25

How does the motor complex of the digestive system change with feeding?

Answer 25

Strong irregular contractions predominate; highest motility is in the duodenum, lowest is in the ileum

Question 26

What are the goals of colonic phase of digestion?

Answer 26

Fluids and electrolytes are absorbed short-chain fatty acids absorbed stool is retained and eliminated

Question 27

What type of contractions does the colon exhibit?

Answer 27

Mass peristalsis in haustra---high amplitude propagating. Stimulated by food in the stomach

Question 28

What are the brief components of defecation?

Answer 28

Stool reaches the rectum and promotes relaxation of the internal anal sphincter; signals go to brain as rectum fills that defecation necessary. Voluntary control of external anal sphincter helps determine when it will occur

Question 29

What are the four main functions of the stomach?

Answer 29

1) Food accommodation (ingestion is faster than digestion) 2-mechanical breakdown of food 3-secretion of H+, HCO3-, electrolytes, and fluids 4-digestion (by pepsin)

Question 30

What are the functions of gastric acids?

Answer 30

1-activate pepsinogen 2-innate immunological protection from bacteria 3-promotes food breakdown

Question 31

What is the process of secretion in parietal cells?

Answer 31

1) at rest, H/K pumps are in vesicles; stimulation will promote fusion of the vesicles with canalicular membranes 2) Carbonic anhydrase makes protons 3) Passive K+ pumps are activated as well to prevent intracellular hyperkalemia 4) Chloride ions flow as well to prevent electrochemical changes 5) Water follows ionic flow

Question 32

What compounds promote secretion of acids and where do they come from?

Answer 32

Acetylcholine from nervous system Gastrin from G-cells Histamine from ECL cells (strongest activator)

Question 33

What triggers promote gastrin release?

Answer 33

1) Stomach distension | 2) Presence of proteins and peptides in the stomach

Question 34

What factors inhibit gastrin release?

Answer 34

1) somatostatin release from D-cells 2) presence of fats, acids, and hyperosmolar chyme in duodenum 3) Secretin. CCK, VIP

Question 35

What are the phases of acid secretion and what are the triggers for each stage?

Answer 35

1) Basal--lowest at waking, highest in evening 2) Cephalic--thinking about or seeing feed increases acid secretion; vagally modulated 3) Gastric phase--stomach wall stretching, proteins present in gut (most important factor) 4) Intestinal--proteins in duodenum promote G cells and an entero-oxyntin hormone

Question 36

How does the stomach create barriers to protect itself from the acids it secretes?

Answer 36

1) Tight junctions between cells prevent leakage 2) The mucus layer has a significant role and requires constant recreation 3) Cells secrete bicarbonate in layer under mucus, irreversibly can knock out pepsin

Question 37

What are the two main receptors for regulators of pancreatic acinar secretions?

Answer 37

muscarinic ACh receptors and CCKb receptor; both are G-protein coupled

Question 38

What else do pancreatic acinar cells secrete to help the digestive process?

Answer 38

Serum highly enriched in Na, Cl, and H20 to help hydrate proteins and flow in the ducts

Question 39

What is the predominate goal of the pancreatic duct cells and what are the main mechanisms by which they achieve this?

Answer 39

Production of a fluid rich in HCO3; dependent on Cl/HCO3 exchanger and CFTR; Na and H20 are pulled along as well

Question 40

What compounds promote secretions from the pancreatic duct?

Answer 40

Acetylcholine and secretin; chloride channels are typically the target for these compounds

Question 41

How are pancreatic zymogens activated?

Answer 41

Enterokinase in the small bowel activates trypsinogen, which activates other proteases (chymotrypsin, protease, carboxypeptidases, etc.)

Question 42

What other compounds are secreted by the pancreatic acinar cells and which are most likely to be shut off first in case of damage?

Answer 42

Amylase, Lipase (first to shut off), nucleases, lithostatin, pancreatitis-associated protein

Question 43

What are the phases of pancreatic activation?

Answer 43

1) cephalic--conscious encounters with food promote secretion via vagus nerve 2) Gastric--gastrin activates CCK receptors 3) Intestinal--acids in duodenum promote secretin; fats in duodenum promote CCK

Question 44

What are the main mechanisms of control of the salivary glands?

Answer 44

acteylcholine is a parasympathetic activator norepinephrine is a sympathetic inhibitor no hormonal control over glands

Question 45

What are the main secretions in the saliva?

Answer 45

Amylase, mucus, HCO3 and K; but if secretions are very high, will also release Na

Question 46

What are the functions of saliva?

Answer 46

1) Lubrication for mastication and swallowing 2) Hydration of oral mucosa 3) Wash away residual food; antibacterial 4) Very minor starch digestion with salivary amylase