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Physiology Block 3 > 10 - Overview of GI physiology > Flashcards

10 - Overview of GI physiology Flashcards

1
Q

What are the relative lengths (in percentages) of the parts of the small intestine?

A

Duodenum - 5%
Jejunum - 40%
Ileum - 55%

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2
Q

Name the sphincters and valves of the GI tract? (hint-there’s 6)

A
  1. Upper esophageal sphincter (UES)
  2. Lower esophageal sphincter (LES)
  3. Pyloric sphincter
  4. Sphincter of oddi (from pancreas and liver to the small intestine)
  5. Internal anal sphincter
  6. External anal sphincter
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3
Q

What are the four layers of the GI tract?

A

Mucosa

Submucosa

Muscularis propria

Serosa or adventitia

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4
Q

What are the layers of the GI mucosa?

A

Epithelium, lamino propria, and the muscularis muscosa.

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5
Q

What’s located in the submucosa of the GI tract?

A

Meissner’s submucosal plexus.

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6
Q

What are the layers of the muscularis propria?

A

Circular muscle and longitudinal muscle.

Auerbach’s (myenteric) plexus located between the two.

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7
Q

What makes up the enteric NS?

A

The myenteric plexus and submucosal plexus.

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8
Q

What is the function of the myenteric nerve plexus (Auerbach’s plexus)? What is its location?

A

Motility.

Located between longitudinal and circular muscle layers in the muscularis propria.

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9
Q

What is the function of the submucosal nerve plexus (Meissner’s plexus)?

A

Absorption, secretion, and local blood flow.

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10
Q

What causes GI motility?

A

Muscle units function as a unit in that action potential in 1 muscle fiber is easily transmitted to adjacent fibers, allowing multiple fibers to function as a syncytium.

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11
Q

What are the contraction rate s caused by electrical activity in the stomach, duodenum, and ileum? What is the rate determined by?

A

Stomach: 3/min

Duodenum: 12/min

Ileum: 8/min

Rate dictated by interstitial cells of cajal (pacemaker cells).

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12
Q

Describe resting membrane potential in the GI tract?

A

There’s baseline slow waves that vary by location and (with the exception of the stomach) do not cause contraction.

Slow waves are NOT action potentials.

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13
Q

What are spikes in membrane potential? What are they caused by?

A

Depolarization of the membrane (less negative, more excitable). Spikes occur on top of slow waves and cause contractions (PHASIC) only when threshold is reached.

  1. Stretch
  2. Acetylcholine
  3. Parasympathetics
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14
Q

What causes the membrane potential to be more negative? What is this called?

A

Called hyperpolarization, less excitable.

Caused by norepinephrine (fight or flight) and the sympathetic NS.

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15
Q

How long will spikes in membrane potential occur? What makes contraction strength increase?

A

As long as the membrane potential is at threshold potential.

The more APs, the stronger the smooth muscle contraction.

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16
Q

The influx of what ion causes contractions? Compare GI contractions compared to skeletal muscle contractions?

A

Due to the influx of calcium.

Longer lasting than skeletal muscle contractions.

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17
Q

What is the function of the sympathetic NS in the GI tract? Where does it originate, describe the pre and post ganglionic fibers?

A

Inhibits GI function: constricts blood vessels to GI tract and diverts blood in times of stress.

Originates between T5 and L2.

  • pregang enter sympathetic chain
  • postgang innervate entire gut
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18
Q

What are the components of the parasympathetic NS of the GI tract? What does each innervate?

A

Cranial division via the vagus nerve, that innervates esophagus, stomach, pancreas, sm intestine, and proximal lg intestine.

Sacral division via the 2nd,3rd, and 4th sacral segments to the pelvic nerves and then to the distal colon (includes rectum and anus).

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19
Q

What is the function of the parasympathetic NS in the GI tract? Where do postganglionic fibers go?

A

Increases GI activity and function.

Post-ganglionic fibers end in ENS (myenteric and meissner).

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20
Q

What are the stimulatory substances produced by the myenteric plexus?

A

Acetylcholine and substance P.

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21
Q

What are the inhibitory substances produced by the myenteric plexus?

A

Vasoactive intestinal peptide (VIP) and nitric oxide (NO).

22
Q

Describe and explain the cause of the propulsive movement of the gut? What is required for this movement to occur?

A

Forward movement of a contractile ring around the gut wall, at appropriate rate for digestion/absorption.

Stimulus is distension of the wall (chemical, irritation), via ENS, ring forms and peristaltic movement is initiated.

Intact, active myenteric plexus is mandatory. Response is

23
Q

Describe the mixing movements of the gut?

A

Peristaltic against closed sphincter.

Constrictive.

Continual mixing of GI contents with enzymes. Serves to shear and chop contents.

24
Q

Describe segmentation?

A

Mixes contents over a short length of intestine.

25
Q

Define peristalsis?

A

Contraction and relaxation, properls the luminal contents aborally.

26
Q

How do isolated contractions move substances?

A

Both orally and aborally.

27
Q

Where is cholecystokinin (CCK) from and what does it get released in response to?

A

Released by cells in the duodenum and jejunum in response to fats being present.

28
Q

What is the function of cholecystokinin (CCK)?

A

Causes gallbladder to contract, resulting in release of bile to emulsify fats.

Slows down gastric motility so what is present in the small intestine can be addressed.

29
Q

Where is secretin released from and what is it released in response to?

A

From the duodenum in response to acidic gastric contents being present.

30
Q

What is the function of secretin?

A

Slows down gastric motility.

31
Q

Where is gastric inhibitory peptide (GIP) released from and what is it released in response to?

A

From the upper small intestine in response to presence of fatty acids, amino acids, and carbohydrates.

32
Q

What does gastric inhibitory peptide (GIP) do?

A

Slows down gastric motility.

33
Q

Describe the villi in the small intestine? What is their function?

A

Used for reabsorption.

Villus tip and crypt.

Cells originate at the crypt and migrate towards tip for absorption. Crypt secretes things like fluid to help spread out intestinal contents.

34
Q

Describe the microvasculature of the villus?

A

Has countercurrent flow, 80% of oxygen diffuses from artery to vein.

Villus is vulnerable to ischemia.

35
Q

Describe the splanchnic venous circulation of the GI tract?

A

Blood flows from spleen and intestinal veins to the hepatic portal vein, into the livers, and out of the liver through the hepatic veins to the vena cava.

36
Q

How does neural control impact GI blood flow (ie. sympathetic and parasympathetic)?

A

Parasympathetic NS increases flow and glandular activity.

Sympathetic NS causes vasoconstriction and decreases flow. Blood shunted away from GI tract during heavy exercise, circulatory shock, need to mobilize blood.

37
Q

How does local metabolic control impact GI blood flow?

A

Causes increased flow to intestinal wall and villi during absorption.

Returns to normal flow between meals.

38
Q

What factors are responsible for increased GI blood flow?

A

Dilators: CCK, VIP, gastrin, and secretin.

Release of kinins (kallidin, bradykinin) which as a whole induce vasodilation.

39
Q

Describe the three types of GI reflexes? What part of the nervous system is involved in each?

A
  1. Intra-gut reflexes (ENS): have effect on contraction and secretion
  2. Entero-gastric and colo-ileal reflex: gut to pre-vertebral sympathetic ganglia and back to another portion of the gut. (sympathetic)
  3. Defecatory reflex: gut to CNS (spine or brain). (parasympathetic)
40
Q

Describe the function of intra-gut reflexes (ENS)?

A

Duodenal distension slows gastric emptying.

41
Q

Describe the function of the entero-gastric and colo-ileal reflexes?

A

Sympathetic.

Duodenal distension inhibits gastric emptying

Cecal distension slows ileal emptying.

42
Q

Describe the gut to CNS and defacatory reflex?

A

Parasympathetic

Sensory nerves go from stomach to brain via vagus and back to stomach via vagus.

Rectum to spinal cord (S2-S4) and back to rectum to control the internal anal sphincter.

43
Q

What is celiac sprue?

A

Severe damage to intestinal villi caused by eating gluten - individuals can die from this.

Causes diarrhea from malabsorption and weight loss.

Cannot have wheat, barely, rye, and some vitamins/medications.

44
Q

What are the two ways by which blood is delivered to the liver? How much of the total blood comes from each?

A

3/4 through portal vein

1/4 through hepatic artery

45
Q

Does the colon have villi?

A

NO.

Villi are for absorption, and the colon does not absorb things.

The colon does have crypts though.

46
Q

What does the term “ileus” describe? What can cause this?

A

Decreased small bowel motility; weak waves make it harder to move contents forward.

No obstruction.

May be post-op, from medications, electrolyte disorders, or severe illness.

47
Q

How is the gut innervated by the parasympathetic NS? What is released from the pre and post synaptic fibers?

A

Vagus innervates ~90% of the GI tract

Remaining 10% (descending colon to rectum) is from S2-S4

Presynaptic: release Ach
Postsynaptic: release Ach

48
Q

What does the presynaptic and post synaptic sympathetic fibers release?

A

T5-L2

Presynaptic: release Ach

Postsynaptic: release norepi

49
Q

What is Ulcerative Colitis (UC)? What are common symptoms?

A

Inflammatory condition of the colon involving the mucosa and submucosa.

Continuous, starting in rectum.

Pain, fevers, blood per rectum, weight loss, increased risk of colon cancer.

50
Q

What is Crohn’s Disease (CD)? What are common symptoms?

A

Condition affecting any portion of the GI tract, mouth to anus (most commonly affected are terminal ilium and R colon). May skip areas.

Involving ALL layers of the GI tract.

Pain, fevers, weight loss, strictures, fistulas.

Physiology Block 3 (17 decks)

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