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physiology 2 > GIT physiology 4 > Flashcards

GIT physiology 4 Flashcards

1
Q

paracellular absorption

A

movement of solute is passive and the permeability is inverse to resistance and is dependant on the structure of tight junctions

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2
Q

transcellular absorption

A

movement of solute across two cell membranes (apical and basal) so will often have contrasting concentration gradients

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3
Q

transcellular absorption is driven cy

A

2 degree active transport

drives passive transport by setting up an electrochemical gradient

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4
Q

paracellular through tight junctions

A

TJs occlude paracellular passage of water and solutes

‘tightness’ varies and determined whether/how much paracellular route is used

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5
Q

colon TJs

A

tight

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6
Q

small intestine TJs

A

leaky

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7
Q

carbohydrates that are absorbed

A

only monosaccharides

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8
Q

monosaccharides

A

fructose
galactose
glucose

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9
Q

starch is made up of

A

glucose

broken down by saliva and pancreatic juices into subunits maltoses

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10
Q

maltoses are brown down by

A

maltase and a-dextinase

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11
Q

maltoses brown down into

A

glucose

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12
Q

lactose broken down into

A

galactose

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13
Q

lactose broken down by

A

lactase

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14
Q

lactose broken down in

A

the intestine

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15
Q

sucrose broken down to

A

fructose

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16
Q

sucrose broken down by

A

sucrase

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17
Q

sucrase

A

break sucrose down into fructose

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18
Q

lactase

A

breaks lactose down into galactose

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19
Q

maltase and a-dextrinase

A

breaks maltose down into glucose

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20
Q

GLUT5

A

transports fructose

depends on driving gradient of fructose

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21
Q

SGLT1

A

sodium dependant transport of glucose/galactose

able to scavenge

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22
Q

GLUT2

A

allows glucose and galactose to diffuse out if there is enough in the cell

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23
Q

disaccharides

A

broken down into monosaccharides

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24
Q

lactase deficiency

A

causes lactose to go straight through the digestive system without being absorbed unchanged

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25
Q

consequence of not absorbing lactose

A

osmotically active
creates osmotic drag and water will follow
bacteria anaerobically metabolise lactose creating gas
gas and water overpresent in stool

26
Q

protein digestion

A

pepsin digests some proteins
pancreatic proteases convert most luminal orcein to oligopeptides and amino acids
peptidases liberate free amino acids

27
Q

apical AA transporters

A

present on apical membrane

  • distinct transporters for differently charged AAs
  • Na co-transport
  • scavenger transporter
28
Q

basal AA transporters

A

Na-independent

29
Q

pepT1

A

peptide transporter

requires a proton gradient

30
Q

3 classes of lipids

A
  • triglycerides
  • phospholipids
  • cholesterol
31
Q

triglycerides

A

glycerol with 3 fatty acids
storage and transformation form of energy
fast deposits for insulation and protection

32
Q

phospholipids

A

lecithins, cephalins, sphingomyelins
glycerol and 2 fatty acids
phosphorous group

33
Q

cholesterol

A 
synthesised from acetyl-CoA
structural role in membranes 
precursor for 
- bile salts 
- steroid hormones 
- vitamin D
34
Q

digestion of triglycerides

A

lingual lipase and gastric lipase (less important)
mainly pancreatic lipase

gives 2 fatty acids and monoglyceride

35
Q

fat absorption

A

can diffuse through bilayer
also cavoelae-mediated uptake and carrier-mediated transport eg. fatty acid translocase
packed into lipoprotein complexes that carry lipids from small intestine through circulation
- chylomicrons
- exocytosed into lacteals (SI lymphatic vessels), then secreted into bloodstream

36
Q

water is mostly absorbed in

A

small intestine

37
Q

water is absorbed by

A

osmotic gradient

38
Q

electrolytes and minerals

A

active or passive (requires electrochemical gradient)

used to set up the osmotic gradient required to move water across membranes

39
Q

Chloride is absorbed via

A

passive diffusion and Na, H, Cl, HCO3 exchange

40
Q

chloride is secreted via

A

Cl- channels

-CTFR

41
Q

-CFTR

A

cystic fibrosis transmembrane conductive regulator

regulated by cell volume or signalling

42
Q

CFTR gating

A

CL- diffuses out down its concentration gradient

water follows

43
Q

CTFR is regulated by

A

cAMP

when cAMP goes up chloride goes out

44
Q

bioavailability of minerals depends on

A

pH
redox state of the metal
dietary complexes with enhance and diminish solubility

45
Q

dietary complexes which enhance solubility

A

organic acids - ascorbate (fruit juice), lactate (fermented milk), pyruvate/cysteine/histidine

46
Q

dietary complexes which diminish absorption

A

phytates (in cereals), tannins (in tea), oxalates (rhubarb, greens), carbonates (Perth)

47
Q

daily calcium absorption

A

1g of Ca ingested
mostly most bioavailable
absorbed transcellularly or paracellularly
leaky tight junctions allow calcium to pass through
TRPV6 calcium pump

calbindin binds systolic Ca2+ - prevents pree Ca2+ from blocking TRPV6

48
Q

TRPM6

A

transports magnesium

49
Q

dietary iron is eaten in 2 forms

A

haem iron

non-haem iron

50
Q

haem iron

A

iron in meat, blood, muscle
bound to haem
more readily absorbed
taken up as Fe-porphyrin complex by haem transporter HT

51
Q

non-haem iron

A

iron in vegetables
either ferrous or ferric
ferric iron is completely insoluble
divalent metal transporter (DMT)

52
Q

ferric iron

A

completely insoluble and must be reduced first

53
Q

DMT

A

divalent metal transporter
can only pick up ferrous iron
ferric iron must first be reduced but this is not an efficient process and most will be lost

54
Q

iron inside the cell

A

very reactive

needs to be bound to ferritin for storage

55
Q

basal iron transporter

A

IREG1 - ferroportin

56
Q

iron the the blood

A

bound to transferrin for transport

57
Q

Haem-Fe transporter

A

more efficient

enzyme used to break it apart

58
Q

if cells with iron die

A

iron is lost from the system

hepcidin regulates plasma iron levels

59
Q

when there is too much iron in the system

A

hepcidin is secreted
hepcidin switches off all ferroportin channels (IREG1)
iron enters cells but is all stored as ferritin which is toxic to the cell so the cell dies and the iron is lost to the system

60
Q

hepcidin

A

regulates plasma iron levels

secreted from the liver

61
Q

when ferroportin is switched off by hepcidin

A

iron is still take up by the cell and stored as ferritin
too much ferritin is toxic to the cell
cell dies and iron is lost

physiology 2 (21 decks)

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