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PHSL 233 > L32 > Flashcards

L32 Flashcards

1
Q

what are the Sites of absorption

A

 mouth and esophagus
 stomach
 intestine

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2
Q

what is the small intestine responasabele for in absorbtion

A

 bulk absorption of isosmotic fluid and nutrients

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3
Q

what is the role of the proximal colon of the large intestine responsible for in absorption

A

 absorption of products of fermentation

 fluid and electrolytes

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4
Q

what is the role of the distal colon (large intestine) in absorption

A

 selective absorption of fluid and electrolyte

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5
Q

what if the differnce in epithelia between the large and small intestine

A

small = leaky

large = mostly tight

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6
Q

there are 2 ways of Na absorption. what are they

A

nutrient dependent

nutrient independent

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7
Q

describe nutrient dependent absorption in the small intestine

A

 Na+ is coupled to solute absorption of monosaccharides and amino acids

it is also specialised for the absorption of..
 bile salts
 vitamin

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8
Q

describe nutrient dependent absorption of Na in the proximal colon (large intestine)

A

 Na+ dependent absorption of short chain fatty acids

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9
Q

nutrient dependent of Na happens throughout the small intestine. where does it specify happen in the large intestine

A

in the proximal colon

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10
Q

where does nutrient independent absorption of Na happen

A

in both the large and small intestine

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11
Q

how does nutrient dependent absorption of Na happen in the small intestine

A

through SGLT1 and coupled with amino acids

don’t need to know the amino acid transporter names

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12
Q

what SGLT’s are found in the GI tract

A

only SGLT1

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13
Q

describe nutrient independent absorption on Na in the small intestine

A

this happens in the apical membrane through NHE3 (Na/H exchanger) and a Cl/HCO3 exchanger

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14
Q

what is important to note about the proximal and distal colon

A

they are functionally distinct

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15
Q

what happens at the proximal colon (not Na)

A

 fermentation of indigestible sugars and proteins

 generation of short chain fatty acids

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16
Q

describe Na absorption in the proximal colon

A

fermentation of indigestible sugars and proteins and generation of short chain fatty acids is coupled to Na+ absorption

this happens through electroneutral NaCl absorption
 paired Na+/H+ and Cl-/HCO3- exchangers as in small intestine
 Na+ absorption is associated with absorption of short chain fatty acid

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17
Q

Na in the proximal colon is absorbed through a Small chain fatty acid Na coupled transporter

what is the name of this transporter

A

 Sodium monocarboxylate

transporter

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18
Q

There is 7L of water that we need to reabsorbe

Bulk reabsorption of water happens in the small intestine and then small part in the colon

A

g

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19
Q

what is the role of the distal colon

A

 regulation of composition of faeces

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20
Q

describe Na absorption in the distal colon

A

 Na+ absorption varies depending on fluid and electrolyte status and aldosterone (when you are dehydrated ENaC causes more Na to be reabsorbed)

 salt depleted condition → high levels of plasma aldosterone
 salt replete condition → low levels of plasma aldosterone

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21
Q

how many L of fluid do we secrete per day (usually)

A

1-2 L

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22
Q

absorption of Na depends on location. what is it dependent on at different locations in the GI tract

A

duodenum
 Cl secretion
 HCO3- secretion

jejunum
 Cl secretion

ileum and proximal colon
 Cl secretion
 HCO3- secretion

distal colon
 Cl secretion

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23
Q

what do we secrete water in the intestine

A

We are still secreting water in the intestine to absorb that last bit of nutrients

24
Q

describe absorptive diarrhea

A

Glucogolactase (an example) causes absorptive diarrhea because you are not absorbing glucose therefore you are not absorbing Na and therefore not absorbing water

25
Q

what is the difference between absorptive and secretory diarrhea

A

absorptive = you are not absorbing water from the intestine

secretory = you are actively secreting water from the intestine (more than normal and happens through too high levels of cAMP)

26
Q

the main mechanism that causes water secretion in the small intestine and colon is what

A

electrogenic Cl secretion

27
Q

explain the mechanisms that cause electrogenic Cl secretion in the small intestine and colon that cause water screation

A

 active Cl secretion drives movement
of Na+ and water

 result – isotonic solution of NaCl

the NKCC1 cotransporter causes an accumulation of Cl in the cell above
electrochemical equilibrium

 Cl- channel = CFTR which is activated by cAMP
and is the exit pathway for Cl

28
Q

what can cause secretory diarrhea

A

 Vibrio cholerae

29
Q

describe how Vibrio cholerae can cause secretory diarrhea

A

Vibrio cholerae is a bacteria that multiplies in the small intestine

Vibrio cholerae produces cholera toxin which stimulates adenyl cyclase which causes more cAMP to be made which stimulates CFTR leading to more secretion of Cl leading to more secretion of bicarbonate and therefore of water

30
Q

what happens when vibrio cholerae secretes cholera toxin

A

the toxin binds to intestine, enters villous and crypt cells and stimulates adenylate cyclase irreversibly

this causes elevation of cAMP
which stimulates Cl- secretion in crypts
and inhibits nutrient-independent Na+
absorption in villi

this causes secretory diarrhea
 loss of isotonic fluid

31
Q

secretory diarrhea = loss of isotonic fluid

A

k

32
Q

The absorption of Na+ and water in the small intestine

A. is mainly facilitated by channels.

B. is nutrient dependent.

C. is entirely nutrient independent.

D. is facilitated by CFTR.

A

A. These are characteristics of tight epithelium and the small intestine is leaky epithelium

C. It is both dependent and independent

D. Na has nothing to do with the CFTR receptor itself

B is correct

33
Q

how much sugar do we inject per day

A

200-300g

 western Diet - 40 - 50% energy intake
 developing world - 90% of energy intake

34
Q

polysaccharides, disaccharides and monosaccharides are the sugars we ingest

without breaking them down what % of each one is found in our diet

A

 polysaccharides (45 -60%) - glycogen and starch

 disaccharides (30 – 40%) = sucrose, lactose and maltose

monosaccharides (10%) – glucose, fructose

35
Q

what sugars are we able to absorb

A

monosaccharides

these make up only 10% of you sugar intake therefore we need to break down the sugars we ingest

36
Q

what are the main monosaccharides absorbed and how

A

 glucose and galactose absorbed by Na+
-dependent mechanism (SGLT1)

 fructose absorbed by Na+
-independent mechanism (GLUT5)

37
Q

digestion of sugars to release monosaccharides is a 2-step process. describe it

A

luminal digestion
 mouth - a amylase
 small intestine – pancreatic amylase

the products of luminal digestion are
 a-limit dextrins
 short oligosaccharides and some disaccharides

 contact or brush border digestion = enzymes attached to apical membrane of epithelial cells which release monosaccharides
such as
glucose, galactose, fructose

38
Q

what are the products of luminal digestion

A

the products of luminal digestion are
 a-limit dextrins
 short oligosaccharides and some disaccharides

39
Q

Contact digestion because the components need to make contact with the plasma membrane so that they can be further broken down

This happens on the brush border membrane

A

j

40
Q

Lumanal digestion is starch with amalse, everything is soluable therefore you get pre digestion of suggars

They then they come into contact with the brush border membrane

Lactase breaks down lactose into glucose and galactose which BOTH can be transported couped to Na through SGLT1

Sucrase breaks down sucrose into frutose and glucose

Frotose is reabsorbed through GULT5

These are enzymes tha are membrane bound

A

k

41
Q

what does absorption of glucose, galactose and fructose result in

A

absorption of isosmotic fluid (parracellular)

42
Q

The absorption of glucose via SGLT1 is against the
concentration gradient,

BECAUSE

basolateral glucose
absorption is mediated by facilitated diffusion.

A

both statements are true and causally related

down the concentration gradient because although sugar might be high in the diet it is diluted in the cyme

idk why it is causal

43
Q

proteins are not a source of energy but are required for amino acids

what are our sources of protein

A

 50% diet
 25% sloughed cells
 25% digestive enzymes

44
Q

digestion of proteins happens in a 2 steep process. what is this

A

 luminal

 contac

45
Q

describe the digestion of proteins

A

luminal
proteins get broken down by H and pepsin in the stomach (gastric lumen) which leaves you with proteins and oligopeptides. then in the intestinal lumen these proteins broken down by trypsin, chymotrypsin, carboxypeptidase and elastases into oligopeptides

contact
oligopeptides then get broken down by enzymes in the membrane into amino acids and then are absorbed through amino acid transport proteins

NOTE di and tripeptides can be absorbed through peptide transport proteins and are then broken down into amino acids in the cytoplasum by peptidases, prolidase, dipeptidase and trypeptidase

46
Q

what does Na dependent amion acid (and peptide) absorption result in

A

absorption of isosmotic fluid

47
Q

fat digestion and absorption is very efficient, therefore if the system is so efficient how much fat is excreated per day

A

ONLY 5g

48
Q

fat and products of digestion insoluble in water therefore they have several stages to digestion & absorption. what are they

theres 7

A

 emulsification and stabilization (bile acids)

 digestion (via lipase)

 formation of micelles

 absorption

 re-esterification – synthesis of triglycerides

 formation of chylomicrons

Absorption into the lymphatic system

49
Q

what is the purpose of Emulsification and stabilization of fats with bile acids

A

 reduction in size to droplets
 motility
 important as it increases the surface area available for
digestion

50
Q

where does Emulsification and stabilization happen

A

stomach
 crude emulsion, through motitty (mechanical digestion)

small intestine
 emulsion stabilized by emulsification agents such as bile salts, phospholipids, cholesterol, lecithin

51
Q

what are Emulsification agents

A

 bile salts and phospholipids, cholesterol, lecithin

bile salts are amphipathic compounds

52
Q

what digestive enzymes are involved in fat digestion

A

minor Enzymes
 gastric and lingual lipases
 minor role

main enzymes
 pancreatic lipase/colipase
 secreted by the pancreas into the small intestine

53
Q

describe fat absorption

A

bile salts surround fat droplets to form emulsification droplets

bile salts + pancreatic lipase = micelles (smaller)

fat inside micelles gets broken down into FFA and monoglycerides which can diffuse through the cell membrane.

when inside the cell FFA and monoglyceride is resynthesized by enzymes in the ER and then packaged into vesicles bound for the basolateral membrane. these vesicles are called chylomicrons

the chylomicrons enter the lacteal and go into the lymphatic system

54
Q

what are some fat soluble vitamins

A

A, D and E therefore they are absorbed in the same way as fats

55
Q

water soluable vitamins have specific transport processes. what are some examples of this

A

 Na+
-dependent e.g., vitamin C

 vitamin B12
 intrinsic factor is released in stomach
 in duodenum B12 binds to intrinsic factor
 intrinsic factor/B12 complex attaches to specific receptors in terminal ileum
 complex absorbed by endocytosis and degraded to release B12 into portal
blood

56
Q

You have a pool,of VB12 in the liver and when you cant absorb it this pool is depleted and then you end up with anemia

A

j

57
Q

Protein

A. digestion starts in the mouth.

B. digestion occurs mainly in the stomach.

C. digestion is reduced during the gastric phase.

D. absorption is facilitated by brush border membrane peptidases

A

A. starts in stomach with pepsin

B. protein digestion MAINLY occurs at the brush border

D. is correct

PHSL 233 (31 decks)

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