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Physiology 214 > Section 8 : GI physiology > Flashcards

Section 8 : GI physiology Flashcards

1
Q

Four functions of the gastrointestinal system

A

Motility Secretion Digestion Apsorption

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2
Q

4 main layers of GI tract

A

mucosa submucosa muscularis externa serosa

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3
Q

How fast is the turnover of the intestine ?

A

repopulation every 4-5 days

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4
Q

Where are the stem cells in the small intestine ?

A

The stem cells are at the base of the crypt and push the epethilium upwards at it replicates. The cells at the top of the villi are the oldest and shed into the lumen

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5
Q

What is a primary stem cell marker in the gut ?

A

Lgr5

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6
Q

What happens to Lgr5+ cells cultured in vitro ?

A

Lgr5 is the marker for gut stem cells.

When left to culture in vitro they will form a small version of the GI tract with visible lumen, villus, and crypt domains

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7
Q

What does GALT stand for ?

A

gut associated lymphgoid tissue

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8
Q

What role does the GI tract play in the immune system ?

A

It exists in a state of constant inflamation, as it has to combat antigens, bacteria, and physical damage (and viruses ?)

It has to maintain protection while tolerating commensal microbes

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9
Q

What are the parts of the stomach?

A

Fundus, body, antrum,

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10
Q

What are the three phases of digestion

A

Cephalic, oral, an esophaegeal

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11
Q

What is the cephalic phase of digestion ?

A

It is the activation of GI function in antisipation of a meal

cognative, olfactory, and visual stimuli contribute
Auditory stimulus can be paired (Pavlov)

Dorsal motor nucleus in the brainstem activates, and stimulates Vagus nerve

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12
Q

What do acinar cells secrete ?

A

They secrete saliva, containing electrolytes and amylase

It is approximately isotonic to plasma

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13
Q

What is the 2 stage model of salavary secretion

A

In the endpieces of the duct make the amylase containing primary secretion (nearly isotonic)

As it exits through the tubule, it reabsorbs NaCl and secretes KHCO3-

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14
Q

What happens to the lower esophageal sphincter during swallowing ?

A

It opens at the same time as the upper esophegeal sphincter and remains open until food passes through

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15
Q

What is GERD ?

A

gastroesophegael reflux disease also called heartburn

It is treated by acid inhibitors

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16
Q

3 functions of the stomach

A

Store food
Secrete HCl
begin protein digestion

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17
Q

What is secreted by the fundus and body of the stomach ?

(6)

A

H+
Intrinsic factor
Mucus
HCO3-
pepsinogen
Lipases

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18
Q

What is secreted by the chief cells ?

A

Pepsinogen

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19
Q

What is secreted by the parietal (oxynitic) cells ?

A

HCl and intrinsic factor

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20
Q

What are the 3 phases of gastric secretion ?

A

Cephalic:
HCl and pepsinogen increase in prep ration

Gastric:
Food reacts in stomach
Food increases gastric secretion

intestinal (inhibitory)
the gastric juices shut down as chyme empties into intestines

21
Q

What are the stomach epithelial cells called ?

A

Parietal cells

22
Q

What is the secretion of the enterichromaffin-like cells ?

A

Histamine

23
Q

What is secreted by the D cells ?

A

Somatostatin

24
Q

What is secreted by the G cells ?

A

Gastrin

25
Q

4 steps of gastric secretion:

A

1) Food or cephallic reflex
2) Gastrin stimulates acid through direct action on parietal cells or through histamine
3) Acid stimulates release of pepsinogen
4) Somatostatin release by H+ provides a negative feedback

26
Q

What neurotransmitter stimulates the secretion in the GI

A

ACh

27
Q

Define:

Deglutition
Eructation
Flatulence
Borborygmi
​Chyme

A 
Deglutition= swallowing
Eructation= burping
Flatulence= intestinal gas
Borborygmi= rumbling noises in GI tract from intestinal gas
Chyme= bolus mixed with gastric and pancreatic secretions
28
Q

What is the negative feedback for gastric secretion ?

A

Increased H+ triggers somatostatin release, which inhibits the whole thing`

29
Q

How does acid go through mucin without burning the epitielium ?

A

Viscous fingering:
When a low viscosity fluid is injected into a highly viscous fluid, it spreads out in a finger-like protrusion, instead of mixing with the fluid

30
Q

Four aspects of gastric motility in the stomach:

A

Filling (relaxation of the sphincters, mediated by vagus nerve)
Storage (body of the stomach)
Mixing (antrum)
Emptying (regulated by factors in the duodenum)

31
Q

What are the “pacemaker cells” in the intestine ?

A

The interstitial cells of Cajal,
They mediate peristalsis

32
Q

How is food mixed in the stomach ?

A

The antrum squeases food back into the body of the stomach

33
Q

Factors controlling stomach emptying into duodenum (4)

A

Fat in duodenum (inhibits emptying until it can be absorbed)

Acid in duodenum (inhibits emptying until it can be neutralised)

Hypertonicity of duodenum (inhibits emptying when osmolarity rises, as it is hard to absorb when its already pumping at max)

Distention in duodenum (too much chyme prevents further emptying into small intestine)

34
Q

Factors outside GI that influence motility of chyme (2)

A

Emotion : stress can stimulate or inhibit motility and emptying

Pain: increases sympathetic activity and inhibits motility and emptying

35
Q

Acid, saline, oleate meals,

Which will empty first ?

A

The saline meal will empty first, followed by acid, then oleate

36
Q

What part of the brain mediates vomiting / emesis ?

A

The medulla of the brain stem

37
Q

Endocrine function of the pancreas

A

The islets of langerhans secrete insulin and glucagon

38
Q

The exocrine function of the pancreas

A

secretes pancreatic enzymes (proteolytic, amylase, and lipases) and alkali substances to neutralise acid

39
Q

Proteolytic enzymes secreted by pancreas

A

tripsinogen (pro-trypsin)

chymotrypsinogen (pro-chymotrypsin)

procarboxypeptidase

40
Q

exocrine secretion in the GI regulated by (2):

A

secretin, CCK

41
Q

When are macromoleules broken down into their constitutive components ?

A

Enterokinase, Disaccharidases, & Aminopeptidases are contained in the brush border.

(enterokinase catalyses trypsinogen -> trypsin)

42
Q

Where do the nutrients go after absorption by the gut?

A

Sugars and proteins go into the blood

fats go into the lymph

43
Q

How does glucose pass through the epethilium of the small intestine ?

A

Luminal glucose enters through SGLT transporters (secondary Na/glucose transporters) and exits into the blood via Glut2 transporters (or less commonly, exocytosis).

44
Q

How do luminal cells of the small intestine regulate size?

A

The size of the cells are dependant on pH,
to combat, it will adjust the tight junctions

45
Q

How much is fluid load in humans ?

A

approx 9L/diem

98% is absorbed

46
Q

Why is ORS successful?

A

ORS- Oral rehydration solutions
•In most diarrhea caused by bacterial toxins, there is an inhibition of NaCl absorption AND stimulation of Cl secretion
•SGLT1 is not affected by cAMP/toxins so the Na+ (and water) which enters because of D-glucose absorption compensates for the anti-absorption of NaCl

47
Q

What is ghrelin?

A

It stimulates hunger through the hypothalamic NPY- secreting neurons

48
Q

How does CCK stimulate satiety?

A
  • Inhibition of gastric emptying
  • Rats lacking CCK1R show increased meal size and become obese
  • CCK will stimulate short-acting satiation
  • CCK works with Leptin- which increases vagal-afferent responsiveness to CCK from I cells.

Physiology 214 (8 decks)

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