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GI System > The Gut > Flashcards

The Gut Flashcards

1
Q

What are the five main functions of the gut?

A

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

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2
Q

How is the gut controlled neurologically?

A

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

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3
Q

What is the main paracrine hormone in the stomach?

A

Histamine from ECF cells

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4
Q

What is the role of motilin in the GI tract?

A

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

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5
Q

What is the role of vasoactive intestinal peptide?

A

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

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6
Q

What types of nerves make up the enteric nervous system?

A

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

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7
Q

What nerves are involved in parasympathetic innervation of the gut?

A

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

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8
Q

How does the sympathetic nervous system interact with the gut?

A

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

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

What is the basic means by which peristalsis occurs?

A

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

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12
Q

How do phasic contractions propagate through the body?

A

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

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13
Q

Which cells set pacemaker activity for the gut?

A

The interstitial cells of Caja;

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14
Q

What are the six sphincters of the gut?

A

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

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15
Q

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

A

1) Mastication

2) Initial voluntary swallowing

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16
Q

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

A

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

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17
Q

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

A

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

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18
Q

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

A

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

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19
Q

What are the roles of gastric motility?

A

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

20
Q

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

A

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

21
Q

How does gastric pressure respond to changes in gastric volume?

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

What are the phases of the migrating motor complex?

A

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

25
Q

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

A

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

26
Q

What are the goals of colonic phase of digestion?

A

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

27
Q

What type of contractions does the colon exhibit?

A

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

28
Q

What are the brief components of defecation?

A

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

29
Q

What are the four main functions of the stomach?

A

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)

30
Q

What are the functions of gastric acids?

A

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

31
Q

What is the process of secretion in parietal cells?

A

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

32
Q

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

A

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

33
Q

What triggers promote gastrin release?

A

1) Stomach distension

2) Presence of proteins and peptides in the stomach

34
Q

What factors inhibit gastrin release?

A

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

35
Q

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

A

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

36
Q

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

A

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

37
Q

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

A

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

38
Q

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

A

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

39
Q

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

A

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

40
Q

What compounds promote secretions from the pancreatic duct?

A

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

41
Q

How are pancreatic zymogens activated?

A

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

42
Q

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

A

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

43
Q

What are the phases of pancreatic activation?

A

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

44
Q

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

A

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

45
Q

What are the main secretions in the saliva?

A

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

46
Q

What are the functions of saliva?

A

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

GI System (6 decks)

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