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Systems Physiology I > Absorption Processes of the Digestive Tract > Flashcards

Absorption Processes of the Digestive Tract Flashcards

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1
Q

Whats absorption?

A

Food biomolecules broken down into their component parts
(digestion) can be absorbed across the epithelial mucosa
and into the body proper.

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2
Q

where does absorption occur?

A

stomach
small intestine
largwe intestine

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3
Q

describe absorption in the stomach

A

no food stuffs, but lipid-soluble NSAIDS and alcohol can pass through the epithelia and
into the blood stream

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4
Q

describr absorption in the small intestine

A

the site of most absorption,
water and all digested nutrients derived from
food absorbed here.

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5
Q

describe absorption in the large intrstine

A

absorbs water and salt

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6
Q

how many litres per day are absorbed?

A

9 litres per day

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7
Q

where do all secretions come from?

A

All secretions come from plasma therefore secretion closely
parallels absorption!

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8
Q
  • 95 % of fluid is absorbed back ….
A

… the plasma

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9
Q

Only bilirubin is lost as

A

a waste product

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10
Q

slide 8

A
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11
Q

To absorb food molecules efficiently the small intestine has

A

3 main adaptations

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12
Q

To absorb food molecules efficiently the small intestine has which are

A

1) A large surface area
2) A thin wall (adapted epithelial cells with transporters)
3) Good blood supply

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13
Q

the different parts of the the small intestine

A

duodenum
jejunum
ileum

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14
Q

The small intestine is very

A

lon (6m long)

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15
Q

describe the small intestines large surface area

A
  • the small intestine is very long - 6m long
  • circular folds - inner mucosa surface is folded
  • have villi
  • microvilli
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16
Q

what is the small intestine covered with

A
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17
Q

epithelial cells on villi are covered with

A
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18
Q

villi and microvilli greatly increase

A
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19
Q

each villus hass an extremely thin

A

wall

  • only one cell thick
  • ## intestinal absorptive cells
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20
Q

simple columnar epithelial cells found in

A

the small intestines and colon

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21
Q

thin walls allow for

A

rapid absorption

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22
Q
A
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23
Q

each villus is uspplied with

A

blood vessels to receive the absorbed foods

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24
Q

whats abosorbed into blood capilleries

A

Glucose / amino acids / vitamins / minerals are absorbed into blood capillaries

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25
Products of fat digestion absorbed into
central lacteal
26
sodium absorption can be both...
... passive and active
27
describe aodium absorption through cells
- transcellular uptake - active process creasted by a basal membrane Na+ pump that pumps sodium out of the cells
28
14
29
15
30
amino acids absorption is us
secondary active trasport -
31
AA absorption is accomplished by
Na+ dependant symport
32
siyrces if protein
ingested food endogenous sources
33
what are endogenous sources of protein?
- Digestive enzymes secreted into lumen- - Proteins within cells shed from the villi into the lumen - Plasma proteins that leak from capillaries in
34
proteins are absorbed primarily as
amino acids and as a few small peptide fragments
35
transport proteins are selective for
different amino acidds
36
whats teritary active transport
proton (H+) gradient used to transport peptides against their concentration gradient.
37
Proton gradient maintained by
Na+ moving into the cell down its concentration gradient and pumping H+ out against its concentration gradient.
38
how is carbohydrate absorptiojn accomplished?
Secondary active transport – accomplished by Na+ - dependent symport
39
Carbohydrate arrives at the small intestine as
small disaccharides (maltose, lactose, sucrose)
40
* Carbohydrate arrives at the small intestine as small disaccharides (maltose, lactose, sucrose) what digests these disaccharides?
The integral enzymes (disaccharidases) of the microvilli digest these disaccharides into their component monosaccharides (glucose, galactose, fructose)
41
Glucose and galactose are absorbed by
secondary active transport / co-transport
42
Na+ and glucose or galactose are carried across
the membrane simultaneously (symport) by the SGLT transport protein.
43
Na+ and glucose or galactose are carried across the membrane simultaneously (symport) by the SGLT transport protein.. Is energy used here?
No energy is used here, we use the Na+ concentration gradient, which is created actively by the Na+ / K+ pump which uses ATP hydrolysis.
44
Fructose enters and leaves the cell only
passively by facilitated diffusion (GLUT5 / GLUT2)
45
once concentrated in the cell, the monosaccharides
leave the cell down their concentration gradients and into the villus by facilitated diffusion (GLUT2).
46
cholesterol and lecithin play important rolesin
fat absorption
47
in a micelle, the bile salts and lecithin aggregate in
small clusters with the fat-soluble parts in the middle to form a hydrophobic core and a hydrophilic surface.
48
Micelles are thus water soluble, but they...
... dissolve water insoluble substances in their hydrophobic cores
49
In addition cholesterol (water insoluble) dissolves in
the micelles core
50
portions of a phopholipid ?
Phospholipid: has both a lipid-soluble and water soluble component
51
Free Fatty Acids (FFA) can diffuse through
the plasma membrane
52
Monoglycerides and FFA can be
transported and enter the cells where they move to the endoplasmic reticulum
53
in th eER they are
re-synthesised into triglycerides
54
triglycerides coalesce into
droplets are are coated with a layer of lipoprotein
55
what are the different lipids?
hdl ldl idl vldl chylomicrons
56
what do chylomicrons pass through
the secretory pathway of the cell.
57
what are chylomicrons transported in
speciliased veciles to the golgi apparatus for further processing
58
what further processing do chylomicrons undergo in the golgi apparatus
protein coating - and are eventually secreted into the interstitial fluid via exocytosis
59
after chylomicroms are excreted from golgi into interstitial fluid, what then?
here the pass into the central lacteal of the villus
60
chylomicrons do not
enter the blood capillaries
61
why dont chylomicrons enter the blood cappilleries?
Chylomicrons do not enter the blood capillaries as the capillaries possess a basement membrane that prevents chylomicrons from entering. The lacteal does not have such a membrane
62
the amount of caclium absorbed in
regulated
63
calcium enters the cells down ints
concentration gradient through special channels (TRPV5/6) where it is bound by calbindin
64
calcium absorbtion is
passive transport
65
calbindin mediates the
transport of calcium across the enterocytes from the apical side to the basolateral site
66
calcium exits the cell by two active processes:
- Primary active transport Ca 2+– ATPase pump called PMCA1b - Secondary active transport: Na+ – Ca2+ anti-porter called NCX1
67
vitamin D is
active calcitriol
68
what does vitamin D regulate?
regulates the amount of calcium by increasing the expression of the genes that encode the above mentioned proteins for transport of Ca2+ into / out of the cells and also by increasing production of calbindin.
69
calbindin action is a
rate limited process
70
why is calbindin action a rate limited process?
The presence of calbindin increases the amount ofcalcium crossing the cell but does not raise the free concentration
71
iron absorption essential for
haemoglobin production
72
how much iron ingested inuk diet
5-20 mg per day ingested
73
how much iron absorbed per day
only 0.5 to 1 mg per day men 1-1.5 mg per day for women
74
haem iron is a
animal protein
75
non haem iron (aka elemental iron) are found in
plant based foods (less efficienct absorbtion than haem iron)
76
iron is absorbed into
the small intestine
77
iron is actively sborbed into
epithelial cells as either haem or elemental iron (non-haem)
78
the two types of iron
haem or non haem (elemental)
79
haem iron is absorbed more efficiently via the
haem carrier protein 1 - active transport)
80
Dietary iron is
oxidised Fe3+ form, but the divalent Fe2+ is more easily absorbed. Dietary Fe3+ reduced to Fe2+ by membrane-bound Dcytb protein. - Transported by divalent metal transporter (DMT1).
81
Fe within haem is converted to
Fe2+ by haem oxygenase and forms an Fe2+ iron pool wihth other Fe2+ from other sources
82
42+
83

Systems Physiology I (21 decks)

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