GI-breakdown/ absorption/ secretion/ taste Flashcards
1
Q
what are starch/ glycogen examples of?
A
polysaccharides
2
Q
what are starch/ glycogen broken down into and by what?
A
- maltose
- by amylase
3
Q
give 3 examples of disaccharides
A
- maltose
- sucrose
- lactose
4
Q
what is maltose broken down into and by what?
A
- glucose
- by maltase
5
Q
what is sucrose broken down into and by what?
A
- glucose and fructose
- by sucrase
6
Q
what is lactose broken down into and by what?
A
- glucose and galactose
- lactase
7
Q
how are glucose and galactose absorbed?
A
Glucose and galactose are taken into the cell by co-transport with Na+
8
Q
how is fructose absorbed?
A
Fructose is taken into the cell via GLUT5 receptors in the jejunum
9
Q
how do glucose/ galactose/ fructose exit the cell?
A
via GLUT2 receptor on the basolateral membrane → into bloodstream → liver
10
Q
which stomach enzyme breaks down proteins into dipeptides/ tripeptides and amino acids?
A
pepsin
11
Q
what are examples of pancreatic proteases which break down proteins?
A
trypsin
chymotrypsin
carboxypeptidase
elastase
12
Q
where are pepsidases and what do they break down?
A
in the brush-border break down peptides into single amino acids
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
14
Q
how can di/ tripeptides pass through the apical membrane?
A
via PEPT1 channels
15
Q
how are amino acids transported across the apical membrane?
A
- via active transport or
- via Na+ dependent transporters
16
Q
how are micelles formed?
A
when bile salts mix with large lipid droplets
17
Q
what is the main feature of micelles?
A
have increased SA
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
19
Q
where are vitamins A/D/E/K (FAT SOLUBLE) absorbed?
A
mainly in jejunum (but also duodenum)
20
Q
where is calcium, iron and magnesium absorbed?
A
in the duodenum
21
Q
where are bile salts and vitamin B12 absorbed?
A
in the (terminal) ileum
22
Q
what are SCFAs?
A
short chain fatty acids
eg butyrate
23
Q
where are SCFAs absorbed?
A
are absorbed in the colon
24
Q
how are SCFAs made?
A
made by bacteria fermenting high-fibre food
25
what does absorption of Vitamin B12 require?
intrinsic factor (released by parietal cells of stomach)
26
which process requires vitamin B12?
erythropoesis
27
what is calcium absorption associated with?
vitamin D
28
in what form is iron ingested and how does this change?
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
29
what must Fe3+ bind to in order to travel in the blood?
transferrin
30
```
Fructose is taken into the cell via:
A-GLUT1 receptors
B-GLUT2 receptors
C-GLUT3 receptors
D-GLUT4 receptors
E-GLUT5 receptors
```
E
31
```
Glucose & galactose exit the cell via:
A-SGLT2 receptors
B-GLUT2 receptors
C-SGLT1 receptors
D-GLUT5 receptors
E-AQP10 receptors
```
B
32
```
What converts chymotrypsinogen to chymotrypsin?
A-Carboxypeptidase
B-Enterokinase
C-HCl
D-Trypsin
E-Trypsinogen
```
D
33
```
Where is magnesium absorbed?
A-Duodenum
B-Jejunum
C-Terminal ileum
D-Colon
E-Appendix
```
A
34
what are the 2 ways water is absorbed along the GI tract?
paracellularly (via osmosis) & transcellularly (aquaporins)
35
which method is water secreted by?
only occurs paracellularly
36
what is the secretion of water stimulated by?
ACh & VIP by increasing Cl- output into the lumen
37
outline the steps in which water is absorbed paracellularly in the GI tract.
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
outline the steps in which water is absorbed transcellularly in the GI tract.
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
outline the steps in which water is secreted paracellularly in the GI tract.
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
through which aquaporin on the apical membrane is water absorbed transcellularly?
AQP10
41
through which aquaporin on the basolateral membrane is water absorbed transcellularly?
AQP3
42
through which receptor does glucose enter the cell paracellularly?
SGLT-1
| glucose-Na+ co-transport
43
How much water enters the small intestine each day?
approx 9L enters s. intestine
44
how much water entering GI tract is from ingested food/ drink?
2L
45
how much water entering GI tract is from gastrointestinal secretions?
7L
46
How much of the water entering the GI tract is absorbed?
- >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
which part of the GI tract absorbs the most water?
small intestine
48
what is mucus part made by?
glycoproteins called mucins
49
what is bicarbonate released by and where does it sit?
- epithelial cells
| - sits in mucous
50
where are prostaglandins synthesised from?
arachidonic acid
51
what is the role of prostaglandins in the mucous-bicarbonate barrier?
- encourage the release of bicarbonate
- inhibit histamine & HCl release
(maintain mucosal blood flow)
52
what is restitution in terms of the GI tract defence?
healing of damaged mucousa
53
what happens if HCl does penetrate the mucous-bicarbonate barrier?
- 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
what is released by vagal efferent fibres in response to damaged mucosa?
NO and CGRP-causing vasodilation-increasing blood flow
55
what are Peyer's patches made up of?
M cells-which aggregate into lymphoid tissue-patches
56
where are Peyer's patches found?
ileum
57
what is the role of M cells?
- 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
what is the response to IgA being released into the gut lumen in GI defence?
Activates innervation in the gut wall → increases mucous production and peristalsis (to protect and clear away other pathogens in the gut)
59
what are some of the causes of vomiting?
taste of the food, irritation of the buccal cavity, bloating, inflammation by the food contents and toxins
60
what are toxins in the GI tract sensed by?
vagal afferent (CN X) fibres -> nucleus tractus solitarius (and area postrema) in the medulla oblangata- the vomiting centre
61
what is the role of the phrenic nerve in emesis (vomiting) in GI defence?
Phrenic nerve causes contraction of the diaphragm → increasing abdominal pressure
62
what is the role of the vagus nerve in emesis (vomiting) in GI defence?
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
which structures have to relax in order for vomit to leave?
reflex relaxation of the LOS and the UOS
64
what is the name for lingual epithelium taste receptors?
GPCRs- 'Gustducin'
65
what are lingual taste receptors involved in?
sweet, bitter, and umami taste transduction
66
what are the 3 types of taste receptor?
T1R1, T1R2 and T1R3
67
which combination of taste receptors allows the taste of umami?
T1R1 + T1R3
| -detects L-amino acids, monosodium glutamate (found in high protein foods)
68
which combination of taste receptors allows sweet taste?
T1R2 + T1R3
69
which taste receptor is responsible for bitter taste?
Taste receptor 2 family (T2Rs)
70
what other component is found in taste receptors which plays an important role in saltiness perception?
ENaC
71
what is the role of gut microbiota?
synthesise vitamin K and ferment dietary fibre to for SCFAs
72
how are SCFAs generated?
Microbiota fermentation of dietary fibre generates SCFAs
73
which GI structure absorbs SCFAs?
colon
74
what happens to SCFAs entering the portal vein?
undergoes first-pass metabolism by the liver
75
what are the 3 metabolic pathways SCFAs may enter?
- 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
```
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
```
B
77
```
In the process of restitution, vagal efferent fibres release…
A-CO & NGRP
B-ACh
C-VIP
D-NO & CGRP
E-NO & ACh
```
D
78
```
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
```
B
79
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
C
