GI secretion, motility, digestion - Collins Flashcards

1
Q

Peristalsis through the tract orchestrated by ____ cells.

A

Cajal

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2
Q

What two types of movement are seen in the GI tract?

A

Peristalsis (movement) and segmentation (mixing).

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3
Q

Describe the biochemical cascade that leads to contraction when Ca levels rise in a smooth muscle cell.

A

High Ca binds calmodulin–> calmodulin binds myosin light chain kinase–> phosphorylates myosin with ATP –> actin binds–> contraction–> repeats until Ca levels drop, then the reverse happens.

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4
Q

Sympathetic innervation travels through which three ganglia to reach the GI tract?

A

Celiac, Superior Mesenteric, Inferior Mesenteric

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5
Q

Parasympathetic innervation to the GI tract travels through which two nerves?

A

Vagus, Pelvic

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6
Q

To reach the lumenal cell, vagal nerve impulses will have to travel through which structures, in order (3 muscles, 2 plexi)

A

Longitudinal muscle–> myenteric plexus–> circular muscle–> submucosal plexus–> muscularis mucosae–> target cell

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7
Q

Stomach BER = 3 cycles per minute
Duodenum BER = 12 cycles per minute

Why?

A

Because otherwise you get a “backlog.” haha

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8
Q

What is the purpose of the BER? What happens when Ach is added?

A

The BER establishes rhythm onto the Ach stimulation, so that you get coordinated contractions that can propel contents through the tract. Otherwise you would see more chaotic movement that would be ineffectual.

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9
Q

Define paracrine, endocrine, and neurocrine transmission. Which cell type can do them all?

A

Mast cells can.

Paracrine–> direct cell/cell
Endocrine–> through the blood
Neurocrine–> nerve to cell

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10
Q

Describe the three steps of swallowing. Which are voluntary/involuntary?

A

Stage 1: Voluntary–>oral to oropharynx. Kids have to learn this
Stage 2: Involuntary–>glottis covers trachea, UES relaxes)
Stage 3: Incoluntary–>esophageal peristalsis

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11
Q

Failure of the LES to relax due to damage/loss of the enteric nerves of the LES wall is called _____ and can make swallowing difficult

A

achalasia

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12
Q

____ in the stomach allow increased distension WITHOUT an increase in pressure.

A

Rugae

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13
Q

This structure facilitates size-dependent movement of food into the duodenum.

A

Pyloric sphincter –> facilitates size-dependent movement of food into the duodenum.

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14
Q

Describe the muscular activity of the stomach during digestion.

A

Wavelike contraction of the stomach down towards the pyloric sphincter. All else gets kicked up into the fundal region. (retropulsion). At the same time you are having receptive relaxation. This cycle repeats again and again until it all gets small enough to pass through.

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15
Q

Carbs, fat, and protein leave the stomach in which order?

A

Carbohydrate is fastest. Then protein. Then fat, which is the slowest. Takes a lot of time b/c the fat isn’t soluble in water.

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16
Q

Describe the four steps of vomiting.

A

Neuronally controlled.

1) Increased salivation is important for lubrication, and also secretion of bicarbonate to protect from the gastric acid.
2) Reverse peristalsis. UES/LES must both relax
3) Contraction of abdominal muscles
4) ejection

17
Q

Give two examples of neuronally-mediated “intestinal reflexes”

A

Gastrocecal–> food in stomach stimulates mass movement in the colon

Gastroileal–> food in stomach stimulates movement from the ileum into the colon (through the ileocecal sphincter)

EG when you eat you have to poop. Babies do this at the table, even.

18
Q

What initiates MMCs? What does that even stand for? Where do they occur? How long do they last?

A

Migrating Motor Complexes are initiated by motilin (and possible neuronally mediated as well). They last for 90 minutes. Occur from the BODY of the stomach to the ileocecal valve.

19
Q

Describe the three phases of an MMC.

A

Phase I–> quiescent (50%)
Phase II–> “irregular contractions” shake the rug to dislodge stuff from walls but don’t propel anything. (30%)
Phase III–>powerful contractions. Sphincters open. (20%)

20
Q

What are two stimuli that control the status of the ileocecal sphincter (local signals)?

A

Neutral state is closed.

Opened by distension of end of ileum (local reflex)
Closed by distension of proximal colon (local reflex)

21
Q

What types of movement are seen in the small intestine?

A

Segmentation
Peristalsis
MMC

22
Q

What types of mvmt are seen in the colon?

A

Haustration

Mass movement

23
Q

What is haustration?

A

Different sections of the bowel act to separate contents into discrete segments known as “haustra”. So you can poop in a reasonable amount of time. Remember the barium study–> not evenly distributed throughout the colon, but rather in several large chunks.

24
Q

How often do mass movements occur in the colon?

A

1-3x/day

25
Q

What is the rectoanal inhibitory reflex?

A

Filling of the rectum causes relaxation of the internal anal sphincter via release of VIP and NO from intrinsic nerves. At same time, the external anal sphincter contracts.

[Defecation (evacuation) occurs when the external anal sphincter is voluntarily relaxed and is enhanced by an increase in intra-abdominal pressure.]

26
Q

What is the purpose of the low pH in the stomach created by parietal cell excretion of HCL?

What else do parietal cells secrete into the stomach?

A

Denature proteins–> start digestion
Sterilize food at pH = 1
Activate pepsin from pepsinogen

Parietal cells also secrete Intrinsic Factor.

27
Q

What steps does the body take to protect against the acidity of the stomach?

A

1) Mucus and alkaline (HCO3) layer protect the cells of the stomach
2) Tight junctions prevent acid leakage
3) Rapid cell turnover ensures surface integrity.

28
Q

____ is the destruction of epithelial cells is due to them being “pushed” out into the lumen where they are degraded. This serves a protective function for the body.

A

Anoicus

29
Q

TO what is B12 bound in the stomach.

A

NOT Intrinsic factor. It is bound to salivary R protein. Pancreatic proteases remove this protein in the duodenum, where IF binds B12 for transport to the terminal ileum.

30
Q

What are four phases of gastric acid production, and what modulates each?

A

1) Interdigestive (basal) phase (aka the “fed” state): circadian based. Eg acid levels are highest in the evening, and lowest in the morning after the fast (pH 3-7)
2) Cephalic phase–> vagus nerve regulation (eg the “smell, sight, and taste of food initiate acid production)
3) Gastric phase–> Initiated by entry of food into the stomach.
4) Intestinal phase–> degraded proteins in the duodenum cause G cells to release Gastrin. [He seemed to contradict this in class, saying this phase was inhibitory…not sure what to make of that]

31
Q

Stimulation of the vagus nerve to initiate the cephalic phase of gastric acid production will cause a chain reaction of 4 steps. What are they?

A

1) Ach release
2) Histamine release from ECL cells
3) Release of Gastrin Releasing Peptide (GRP) from the vagal and enteric neurons
4) INhibition of somatostatin release from the delta cells

32
Q

LO4: In general terms discuss how the parietal cell secretagogues induce acid secretion.

A

x