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Medicine yr1 > GI-breakdown/ absorption/ secretion/ taste > Flashcards

GI-breakdown/ absorption/ secretion/ taste Flashcards

1
Q

what are starch/ glycogen examples of?

A

polysaccharides

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2
Q

what are starch/ glycogen broken down into and by what?

A
  • maltose

- by amylase

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3
Q

give 3 examples of disaccharides

A
  • maltose
  • sucrose
  • lactose
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4
Q

what is maltose broken down into and by what?

A
  • glucose

- by maltase

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5
Q

what is sucrose broken down into and by what?

A
  • glucose and fructose

- by sucrase

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6
Q

what is lactose broken down into and by what?

A
  • glucose and galactose

- lactase

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7
Q

how are glucose and galactose absorbed?

A

Glucose and galactose are taken into the cell by co-transport with Na+

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8
Q

how is fructose absorbed?

A

Fructose is taken into the cell via GLUT5 receptors in the jejunum

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9
Q

how do glucose/ galactose/ fructose exit the cell?

A

via GLUT2 receptor on the basolateral membrane → into bloodstream → liver

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10
Q

which stomach enzyme breaks down proteins into dipeptides/ tripeptides and amino acids?

A

pepsin

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11
Q

what are examples of pancreatic proteases which break down proteins?

A

trypsin
chymotrypsin
carboxypeptidase
elastase

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12
Q

where are pepsidases and what do they break down?

A

in the brush-border break down peptides into single amino acids

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13
Q

how are zymogens activated?

A
  • Trypsinogen -> converted to trypsin via enterokinase (brush border enzyme in duodenum)
  • Trypsin -> activates zymogens, e.g. converts pancreatic chymotrypsinogen to chymotrypsin, procarboxypeptidase to carboxypeptidase
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14
Q

how can di/ tripeptides pass through the apical membrane?

A

via PEPT1 channels

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15
Q

how are amino acids transported across the apical membrane?

A
  • via active transport or

- via Na+ dependent transporters

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16
Q

how are micelles formed?

A

when bile salts mix with large lipid droplets

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17
Q

what is the main feature of micelles?

A

have increased SA

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18
Q

how does pancreatic lipase act on micelles and what happens next?

A
  • breaks fats into fatty acids and monoglycerides
  • Fatty acids & monoglycerides diffuse across the phospholipid bilayer and into the mucosal cell’s ER
  • Triglycerides are synthesised in ER and chylomicrons form, which are exocytosed into the lymph system
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19
Q

where are vitamins A/D/E/K (FAT SOLUBLE) absorbed?

A

mainly in jejunum (but also duodenum)

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20
Q

where is calcium, iron and magnesium absorbed?

A

in the duodenum

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21
Q

where are bile salts and vitamin B12 absorbed?

A

in the (terminal) ileum

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22
Q

what are SCFAs?

A

short chain fatty acids

eg butyrate

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23
Q

where are SCFAs absorbed?

A

are absorbed in the colon

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24
Q

how are SCFAs made?

A

made by bacteria fermenting high-fibre food

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25
Q

what does absorption of Vitamin B12 require?

A

intrinsic factor (released by parietal cells of stomach)

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26
Q

which process requires vitamin B12?

A

erythropoesis

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27
Q

what is calcium absorption associated with?

A

vitamin D

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28
Q

in what form is iron ingested and how does this change?

A

ingested as Fe3+ but must be converted to Fe2+ to be transported through cells; it is then converted back to Fe3+ once it is in the blood

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29
Q

what must Fe3+ bind to in order to travel in the blood?

A

transferrin

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30
Q 
Fructose is taken into the cell via:
A-GLUT1 receptors
B-GLUT2 receptors
C-GLUT3 receptors
D-GLUT4 receptors
E-GLUT5 receptors
A

E

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31
Q 
Glucose & galactose exit the cell via:
A-SGLT2 receptors
B-GLUT2 receptors
C-SGLT1 receptors
D-GLUT5 receptors
E-AQP10 receptors
A

B

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32
Q 
What converts chymotrypsinogen to chymotrypsin?
A-Carboxypeptidase
B-Enterokinase
C-HCl
D-Trypsin
E-Trypsinogen
A

D

33
Q 
Where is magnesium absorbed?
A-Duodenum
B-Jejunum
C-Terminal ileum
D-Colon
E-Appendix
A

A

34
Q

what are the 2 ways water is absorbed along the GI tract?

A

paracellularly (via osmosis) & transcellularly (aquaporins)

35
Q

which method is water secreted by?

A

only occurs paracellularly

36
Q

what is the secretion of water stimulated by?

A

ACh & VIP by increasing Cl- output into the lumen

37
Q

outline the steps in which water is absorbed paracellularly in the GI tract.

A

1-glucose-Na+ co-transport into the epithelial cell via SGLT-1 receptor

2-glucose enters blood via GLUT-2 receptor on the basolateral membrane

3-Na+ enters blood via Na+/K+ ATPase

4-water follows the movement of Na+ by moving in a para-cellular mechanism

38
Q

outline the steps in which water is absorbed transcellularly in the GI tract.

A

1-CO2 +H2OH2CO3H+ + HCO3- occurs inside cell

2-H+ exchanged for Na+
HCO3- exchanged for Cl-

3-NaCl formed inside the cell and enters the blood

4-water follows using AQP10 on apical surface and AQP3 on basolateral surface to enter the blood

39
Q

outline the steps in which water is secreted paracellularly in the GI tract.

A

1-Na+/ K+/ Cl- are drawn from blood and into the cell using various transporters -they are cycled in and out

2-some Cl- does not return to the blood, instead it enters gut lumen

3-some Na+ also enters lumen para-cellularly

4-NaCl is formed in the lumen

5-water follows into the lumen (intestinal secretion)

40
Q

through which aquaporin on the apical membrane is water absorbed transcellularly?

A

AQP10

41
Q

through which aquaporin on the basolateral membrane is water absorbed transcellularly?

A

AQP3

42
Q

through which receptor does glucose enter the cell paracellularly?

A

SGLT-1

glucose-Na+ co-transport

43
Q

How much water enters the small intestine each day?

A

approx 9L enters s. intestine

44
Q

how much water entering GI tract is from ingested food/ drink?

A

2L

45
Q

how much water entering GI tract is from gastrointestinal secretions?

A

7L

46
Q

How much of the water entering the GI tract is absorbed?

A
  • > The small intestine absorbs around 8 litres of this
  • > Colon absorbs the rest
  • > around 0.1 litres of water is secreted as faeces per day
47
Q

which part of the GI tract absorbs the most water?

A

small intestine

48
Q

what is mucus part made by?

A

glycoproteins called mucins

49
Q

what is bicarbonate released by and where does it sit?

A
  • epithelial cells

- sits in mucous

50
Q

where are prostaglandins synthesised from?

A

arachidonic acid

51
Q

what is the role of prostaglandins in the mucous-bicarbonate barrier?

A
  • encourage the release of bicarbonate
  • inhibit histamine & HCl release

(maintain mucosal blood flow)

52
Q

what is restitution in terms of the GI tract defence?

A

healing of damaged mucousa

53
Q

what happens if HCl does penetrate the mucous-bicarbonate barrier?

A
  • the underlying GI tract tissue will be damaged (e.g. gastric/duodenal ulcers)
  • CN X (vagal afferent fibres) sense the pain and send this information to the CNS
  • CN X (vagal efferent fibres) release NO and CGRP -> cause local vasodilation to increase local blood flow (hyperaemia) and carry away the acid (prevent it from causing more damage)
  • Gastrin, prostaglandins and growth factors help to heal the broken mucosa (restitution)
54
Q

what is released by vagal efferent fibres in response to damaged mucosa?

A

NO and CGRP-causing vasodilation-increasing blood flow

55
Q

what are Peyer’s patches made up of?

A

M cells-which aggregate into lymphoid tissue-patches

56
Q

where are Peyer’s patches found?

A

ileum

57
Q

what is the role of M cells?

A
  • M cells take up antigens of infectious agents from the lumen of the small intestine
  • > they deliver these antigens on their basolateral membrane to immune cells (mast cells, macrophages, T cells)
  • > promotes an immune response- releasing factors into the blood (via cytokines) and stimulating the adaptive immune response
58
Q

what is the response to IgA being released into the gut lumen in GI defence?

A

Activates innervation in the gut wall → increases mucous production and peristalsis (to protect and clear away other pathogens in the gut)

59
Q

what are some of the causes of vomiting?

A

taste of the food, irritation of the buccal cavity, bloating, inflammation by the food contents and toxins

60
Q

what are toxins in the GI tract sensed by?

A

vagal afferent (CN X) fibres -> nucleus tractus solitarius (and area postrema) in the medulla oblangata- the vomiting centre

61
Q

what is the role of the phrenic nerve in emesis (vomiting) in GI defence?

A

Phrenic nerve causes contraction of the diaphragm → increasing abdominal pressure

62
Q

what is the role of the vagus nerve in emesis (vomiting) in GI defence?

A

The vagus nerve causes contraction of the duodenum and pylorus (so food doesn’t pass into the bowel for absorption) & contraction of the antrum
This pressure forces food out of the stomach upwards

63
Q

which structures have to relax in order for vomit to leave?

A

reflex relaxation of the LOS and the UOS

64
Q

what is the name for lingual epithelium taste receptors?

A

GPCRs- ‘Gustducin’

65
Q

what are lingual taste receptors involved in?

A

sweet, bitter, and umami taste transduction

66
Q

what are the 3 types of taste receptor?

A

T1R1, T1R2 and T1R3

67
Q

which combination of taste receptors allows the taste of umami?

A

T1R1 + T1R3

-detects L-amino acids, monosodium glutamate (found in high protein foods)

68
Q

which combination of taste receptors allows sweet taste?

A

T1R2 + T1R3

69
Q

which taste receptor is responsible for bitter taste?

A

Taste receptor 2 family (T2Rs)

70
Q

what other component is found in taste receptors which plays an important role in saltiness perception?

A

ENaC

71
Q

what is the role of gut microbiota?

A

synthesise vitamin K and ferment dietary fibre to for SCFAs

72
Q

how are SCFAs generated?

A

Microbiota fermentation of dietary fibre generates SCFAs

73
Q

which GI structure absorbs SCFAs?

A

colon

74
Q

what happens to SCFAs entering the portal vein?

A

undergoes first-pass metabolism by the liver

75
Q

what are the 3 metabolic pathways SCFAs may enter?

A
  • acetate and butyrate may be converted to acetyl CoA. and utilised to form lipids and ketone bodies
  • SCFA may enter citric acid cycle-utilised for glucose production via gluconeogenesis
  • acetate may pass through into peripheral circulation and can be detected in peripheral blood
76
Q 
During transcellular water absorption, water leaves the cell via which channels on the basolateral membrane?
A-AQP2
B-AQP3
C-AQP4
D-AQP5
E-AQP10
A

B

77
Q 
In the process of restitution, vagal efferent fibres release…
A-CO & NGRP
B-ACh
C-VIP
D-NO & CGRP
E-NO & ACh
A

D

78
Q 
Which one of the following food components is detected by the umami taste receptor pathway?
A-Citric acid
B-Glycine
C-Fructose
D-Saccharin
E-Quinine
A

B

79
Q

Concerning fluid and electrolyte shifts in the normal gastrointestinal tract, which of the following statements is true?
A-Colorectal reabsorption is usually about 2.5L

B-Fluid re-absorption in the small intestine is normally about 2.5L or less

C-Faecal water output is less than 250ml

D-Fluid consumption is 250ml

E-Gastric secretion is 250ml

A

C

Medicine yr1 (55 decks)

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