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GI Year 2 > Basic Science > Flashcards

Basic Science Flashcards

1
Q

Describe the stages of HCl formation

A

CO2 from blood>H2CO3 (unstable carbonic acid)
H2CO3<> H2 + HCO3
H2 for H/K pump + HCO3/Cl pump (HCO3 out, HCl in)
HCl + H2O @basolateral membrane

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2
Q

What controls ACh, gastrin and histamine secretion?

A

ACh=neurocrine
Gastrin=endocrine
Histamine=paracrine

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3
Q

What stimulates acid secretion?

A

Sight
Smell
Taste
Thought of food

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4
Q

3 phases of gastric acid secretion

A

Cephalic
-stopping eating=dec. vagal activity

Gastric phase

  • dec. phase (inc. HCl)= dec. gastrin
  • -ve feedback

Intestinal phase
-acid in duodenum> secretin release>dec. gastrin + dec. gastrin stim of parietal cells

Fat/CHO in duodenum > GIP release>gastrin and parietal HCl sec.

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5
Q

Role of intrinsic factor in B12 absorption

A

B12 cannot cross the membrane as its a charged molecule with intrinsic factor
If there’s no IF then B12 will pass right through and lead to pernicious anemia
No B12=RBCs can’t mature

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6
Q

Role of gastric secretions

A

Produced by surface epithelium cells and mucous neck cells
Cytoprotective role
-protects from mechanical injury
-neutral pH (HCO3)=projects against gastric acid corrosion and pepsin digestion

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7
Q

Role of enterogasterones

A

Act collectively to prevent more acid build up in duodenum

  • inhib gastric secretion
  • reduce gastric emptying
    • inhib mobility/ contract pyloric sphincter
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8
Q

What’re the enterogastrones?

A

Secretin
CCK
GIP

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9
Q

Pepsinogen secretion formation

A

Pepsinogen= the zymogen=secreted by chief cells
Low pH (< 3) converts it
Pepsinogen promotes more pepsin making
Pepsins inactivated at neutral pH

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10
Q

What’re the 6 components of bile?

A 
Bile acids 
Lecithin
Cholesterol
Bile pigments 
-bilirubin from haemoglobin
Toxic metals 
-detoxify by adding proteins 
Bicarb
-neutralisation of the acid chyme
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11
Q

What is bilirubin?

A

The predominant bile pigment, extracted from blood by hepatocytes and secreted into bile=bile is yellow

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12
Q

Why is urine yellow and faeces brown?

A

Reabsorbed bilirubin excreted in urine=yellow urine

Bilirubin modified by bacterial squash enzymes=brown faeces

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13
Q

What’re bile acids synthesised from and where are they synthesised?

A

In liver from cholesterol

Before secretion bile acids are conjugated with glycine or taurine= increased solubility of bile salts

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14
Q

What’re the 3 layers of the gallbladder wall?

A 
Mucosa
-folded=ruggae=expansion
Muscularis
-smooth muscle=contraction 
Serosa
-connective tissue
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15
Q

How does the gallbladder concentrate bile?

A

Absorbs the Na and H2O

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16
Q

What effect does CCK have of on the sphincter of Oddi and what causes CCK release?

A

Fat in duodenum=CCK release
CCK=sphincter of Oddi relaxes, gallbladder contracts to squeeze out bile
Discharge of bile into duodenum=fat solubilisation

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17
Q

Summarise the action of CCK

A 
Fat/amino acids in duodenum=CCK release
CCK=decreases gastric emptying 
CCK=increases pancreatic enzyme secretion
Gallbladder contraction
DIGESTION
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18
Q

Summary of actions of secretin

A 
Acid in duodenum=secretin 
Decreases gastric acid 
Decreases gastric emptying 
Increases duodenal HCO3 secretion 
Increases pancreatic HCO3 secretion
Increases HCO3 secretion 
NEUTRALIZATION
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19
Q

What’s the function of the duodenum, ileum and jejunum?

A

Duodenum=gastric acid neuralization, digestion and iron absorption
Jejunum=95% of nutrient absorption
Ileum=NaCl/H2O absorption=chyme dehydration

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20
Q

What does a virus cell absorb?

A 
NaCl
Monosaccharides 
Amino acids
Peptides 
Fats 
Vitamins 
Minerals 
Water
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21
Q

What does a crypt cell secrete?

A

Cl

Water

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22
Q

Where is intestinal fluid secreted from?

A

~1500ml/day from epithelial cells lining crypts of Lieberkuhn

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23
Q

Why’s H2O secretion important for nutrient digestion?

A

Maintain contents in a lumenal state
Promotes mixing of nutrients
Aids nutrient presentation to absorbing surface
Dilated and washes away potentially injurious substances

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24
Q

How are K, Na + 2x Cl transported?

A

Co transported using an electrical gradient

25
Q

Where is the chloride channel located and what does the Cl do?

A

Apical membrane

Makes an osmotic gradient so water can passively move through the cell

26
Q

What’re the events that lead to the Cl Chanel opening?

A

ATP>cAMP> phosphorylation of PKA>Cl channel opens

27
Q

What is the purpose of segmentation?

A

Primary mechanism during digestion
Contraction then relaxation of short segments
Mixes contents with enzymes
Chyme comes into contact with absorbing surface

28
Q

How are segmentation contractions generated?

A

Pacemaker cells in longitudinal muscle
Intestinal basic electrical rhythm (BER) produces oscillations in membrane= potential>threshold>AP>contraction

AP determines strength of contraction
BER decreases as you go down the pathway

29
Q

What does parasympathetic, sympathetic and autonomic stimulation do to gut contraction?

A

Parasympathetic=vagus=increases
Sympathetic=decreases
Autonomic=no effect

30
Q

What is the migrating motility complex?

A

Pattern of peristalsis from antrum to ileum

As one wave ends, another begins

31
Q

What does the arrival of food mean for the MMC?

A

=stops MMC and initiation of segmentation

32
Q

What does the MMC act to?

A

Move undigested food into the large intestine

Limit bacterial colonisation of small intestine

33
Q

What hormone is involved in the initiation of the MMC?

A

Motilin

34
Q

How is intestinal movement mediated?

A

Myenteric plexus

35
Q

Describe the gastroileal reflex

A

Gastric emptying=increase in segmentation activity in ileum

  • opening of ileocaecal sphincter
  • entry of chyme into large intestine
  • distension of colon
  • reflex contraction of ileocaecal sphincter
  • -prevents backflux into small intestine
36
Q

What’s the 2 muscular layers of the colon?

A

Circular layer= complete

Longitudinal layer=incomplete

37
Q

Where is the muscularis externae thicker than in the rectum?

A

Anal canal

38
Q

What’s the epithelium in the anal canal?

A

Simple columnar

39
Q

How are chymes dehydrated?

A

Actively transports Na from lumen into blood>osmotic absorption of water>dehydration of chyme>solid faecal pellets

40
Q

What is fermented by bacteria in the large intestine?

A

Short chain FA’s=energy source in ruminants

Vit K=blood clotting

41
Q

Describe the mechanisms controlling defeacation

A

Wave of intense contraction towards rectum

Distension of rectal wall made by mass movements of faecal matter into rectum>defaecation reflex>urge to defaecate

42
Q

What is the innervation of the defaecation reflex?

A

Parasympathetic via pelvic splanchnic nerves

No sympathetic

43
Q

Transit time to mouth, oesophagus, stomach, small intestine and colon

A 
Mouth=1 min
Oesophagus= 4-8s
Stomach=2-4hrs
Small intestine=2-4hrs
Colon=10hrs-several days
44
Q

PH of mouth, stomach, small intestine and colon

A

Mouth=6.5-7.5
Stomach=1.5-4
Small intestine=7-8.5
Colon=5.5-6.5

45
Q

In what conditions can a facultative anaerobes grow

A

Can grow with or without O2 but may not thrive

46
Q

In which conditions can obligate grow?

A

Can’t survive in O2

47
Q

Is gut microbiota higher or lower in western individuals?

A

Lower

48
Q

Do fatty diets have more or less diversity?

A

Less

49
Q

Jobs of bacterial diversity?

A 
Metabolism of dietary components 
Produce essential metabolites 
Defence against:
-competition 
-barrier function 
-PH inhibition 
-immune system priming 
Grow in fibre
Can use host derived (endogenous) substrate for growth
50
Q

Why should fibre be included in diets?

A 
Contain phytochemicals, anti-oxidants and vitamins
Increases bacterial fermentation:
-more phytochemicals
-maintain pH
-increase commensal population
-supply of short chain FAs
51
Q

What’re the 3 main FAs and their functions?

A

Butyrate
-epithelial growth and regreneration

Propionate

  • gluconeogenesis in liver
  • satiety signalling

Acetate

  • transported in pheripheral tissues
  • lipogenesis
52
Q

Why’s re the products of/ presence of bacteria important for a healthy gut?

A

Barrier effect

  • large numbers prevent colonisation of ingested pathogens
  • inhibit overgrowth of pathogenic bacteria

Active competition exclusion

PH inhibition

53
Q

What must the immune system be able to do?

A

Respond to foreign/pathogenic agents

Actively down-regulate immune responses to self proteins, dietary antigens and commensal microbiota

54
Q

Functions of the SI with regards to digestion?

A

Breaking food down to its components
Decontaminated dirty food
Controlled hydrolysis to avoid fluid shifts
Absorption against nutrients

55
Q

What digests proteins in the SI?

A

Trypsin

Chromotrypsin

56
Q

How is fat digested in the SI?

A

Pancreatic lipase

  • absorbs glycerol and free FAs
  • via lacteal and lymphatic system
57
Q

How’re carbs digested in the SI?

A

Pancreatic amylase

  • breakdown to disaccharides
  • final digestion by brush border disaccharides
58
Q

How does the SI achieve its barrier function?

A 
Regulating what gets in and out
Low bacterial populations 
It’s a toxic environment 
-digestive enzymes 
-bile salts
-presence of IgA
59
Q

How does is the barrier of the SI maintained?

A

Immune sampling
Monitoring the presence of pathogens
Translocation of bacteria
Gut associated lymphoid tissue (GALT)

GI Year 2 (22 decks)

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