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Rest and digest physiology part 2 Flashcards

1
Q

What is hydrolysis

A

splitting of a chemical bond by the insertion of a water molecule

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2
Q

what are glycosidic linkages in

A

carbohydrates

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3
Q

what are peptide bonds in

A

proteins

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4
Q

what molecule are ester bonds in

A

fats

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5
Q

what are 2 general classes of digestive enzymes

A

those that act within lumen of the gut
those that act at the membrane surface of the epithelium

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6
Q

Where do enzymes acting within the lumen originate from

A

major GI glands, including salivary glands, and especially the pancreas

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7
Q

What is the luminal phase of digestion

A

incomplete hydrolysis of nutrients and the formation of short chain polymers from the original macromolecule

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8
Q

What completes the hydrolytic process (membranous phase)

A

enzymes chemically bound to surface epithelium of small intestine

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9
Q

What is the membranous phase

A

enzymes break the short chain polymers from the luminal phase digestion into monomers that can be absorbed across the epithelium

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10
Q

What follows the membranous phase of digestion

A

absorption

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11
Q

3 phase of digestion

A

luminal phase
membranous phase
absorption

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12
Q

What elements are in carbohydrates

A

carbon, hydrogen adn oxygen

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13
Q

What are polysaccharides

A

long chain carbohydrates

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14
Q

what are oligosaccharides

A

medium sized molecules carbohydrates

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15
Q

what are disaccharides

A

2 molecule carbohydrates

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16
Q

what are monosaccharides

A

simple sugar molecule carbohydrate

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17
Q

3 main types of carbohydrates

A

fibers, sugars and starches

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18
Q

What is starch

A

energy storage carbohydrate of plants

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19
Q

What is glycogen

A

energy storage carbohydrate of animals

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20
Q

Name 3 most important simple sugars in animals diets

A

glucose, fructose and galactose

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21
Q

What form do carbohydrates need to be in to be absorbed

A

monosaccharide form

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22
Q

Name enzyme in luminal phase for carbohydrates

A

amylase

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23
Q

name some enzymes used in membranous phase to break down disaccharide into monosaccharide

A

Lactase, maltase, isomaltase, sucrase

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24
Q

Where is final step of carbohydrate digestion

A

apical surface of small intestinal epithelial cells

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25
what makes up lactose
glucose and galactose
26
what makes up sucrose
glucose and fructose
27
How are glucose and galactose absorbed
secondary active transport through a co-transport or process ( sodium symporter)
28
How is fructose absorbed
transported across apical membrane via facilitated diffusion
29
Where are proteolytic enzymes secreted from and in what form
secreted from stomach glands and pancreas in form of inactive zymogens(precusors of enzymes)
30
Where does luminal phase happen for proteins
begins in stomach facilitated by gastric enzymes and HCL, completed in small intestine by action of pancreatic enzymes
31
What happens in stomach for protein digestion
acid denatures proteins and pepsinogen is activated to become pepsin jumpstarting chemical digestion proteins
32
What does pepsin do
cleaves covalent bonds in proteins to form shorter polypeptide chains
33
What happens in small intestine for protein digestion
polypeptide chains are broken down further into small peptide chains by pancreatic enzymes including trypsin, chymotripsin and carboxypeptidase
34
What form can proteins be absorbed as
tripeptides, dipeptides and simple amino acids
35
How are acidic and most neutral amino acids absorbed
transported via sodium symporters on apical surface of enterocytes like glucose and galactose
36
How are alkali amino acids absorbed
facilitated diffusion route like fructose
37
Most common dietary lipid/ fats
triglycerides which also include sterols and phospholipids
38
Why is it more complicated for digestion of lipids and why
hydrophobic nature so aggregate the aqueous environment of GI lumen makes more difficult for enzymes to access molecules
39
4 phases of lipid assimilation
emulsification, hydrolysis, micelle formation and absorption
40
Describe emulsification for lipids
churning action of stomach helps disperse lipids into smaller droplets and also addition of bile when they reach the small intestine
41
What does Bile contain to help to interact to lipids
salts with hydrophilic and hydrophobic regions allowing them to interact with both lipids and the GI environment
42
Describe hydrolysis for lipids
bile/ bile salts break large fat globules down into smaller droplets and interact with a co-enzyme to allow pancreatic anzymes to digest the lipid molecules
43
Describe micelle formation for lipids
products of hydrolytic lipid digestion combine with bile acids and phospholipids to form micelles
44
Describe absorption for lipids
micelles are considerably smaller and diffuse through the gut lumen into the apical membrane of the enterocytes
45
What part of the micelle doesn't diffuse into enterocytes
bile acids
46
What happens to lipids once inside enterocytes
Major lipids re-esterified to form triglycerides and phospholipids repackaged with cholesterol and proteins to form chylomicrons Chylomicrons too large for basolateral membrane Expelled via exocytosis too large and hydrophobic so cannot absorb by blood circulation taken up by lymphatic system then drains back into venous bloodstream
47
What enzyme digests triglycerides
pancreatic lipase
48
what enzyme digests phospholipids
phospholipase
49
what enzyme digests lipid esters
cholesterol esterase
50
Where does most lipid digestion occur and where does small amounts of lipid digestion occur
most in small intestine some in mouth via lingual lipases and stomach via gastric lipase
51
Do vitamins require digestion
no but vary chemical compositions so absorbed in different ways
52
How are fat soluble vitamins (A,D,E and K) absorbed
same absorption route as lipids and transport via micelles as they are entirely hydrophobic so would unlikely make it to the enterocyte alone
53
How are water soluble vitamins like C and B absorbed
diffusion or by passive and active transporters
54
How is water soluble vitamin C and B1 transported in by
c- sodium dependent transport b1- sodium dependent transporter at low concentration passive diffusion at high concs
55
How are other water soluble vitamins like B2 absorbed and B6
B2- facilitated transport B6- simple diffusion
56
How does water absorption happen
osmosis and driven by concentration gradient conc of solute in epithelial cells higher than chyme remaining water absorbed in colon
57
What tells us that water is absorbed across tight junctions between enterocytes
hydrostatic and osmotic pressures in both small and large intestines
58
What do osmotic pressures arise from
nutrients such as glucose, ions like sodium, chloride, potassium, calcium, magnesium, phosphate disruptions or genetic mutations to ion transporters can lead to diarrhea or constipation
59
How is mineral absorption controlled
It is not- minerals that enter intestine are absorbed whether needed or not Iron and calcium are exceptions as absorbed in amount of bodys current requirements
60
How is calcium absorption controlled
blood levels of ionic calcium determine dietary calcium and regulated by hormones normally passively absorbed by paracellular diffusion lower luminal levels additional transcellular absorption process mediated by calcium channels in apical membrane Calcium leaves basolateral membrane via sodium/calcium exchange and calcium ATPase regulated by vitamin D3
61
What can calcium absorption be affected by
number of factors eg lactose enhance calcium absorption dietary fiber can inhibit it amount of soluble calcium available to be absorbed affected by pH
62
How is ionic iron absorbed and used
absorbed into mucosal cells via active transport once inside mucosal cells it binds to protein ferritin creating iron-ferritin complexes that store iron until needed store iron is lost when epithelial cells slough off when needed increase uptake of iron from intestine and accelerated release of iron into blood stream
63
How are most ions absorbed
active transport in small intestine but absorption mechanisms can be conc dependent and vary in different parts of GI tract
64
How is sodium absorption
coupled to absorption of nutrients such as amino acids and glucose
65
How is chloride absorbed
cross epithelial barrier via both paracellular and transcellular routes absored passiveley in proximal region of small intestine following + charged soidum
66
How is chloride absorbed in ileum and colon
actively via electroneutral route
67
What type of absorption do phosphate and magnesium also exhibit
both paracellular and transcellular
68
What happens due to the sodium and chloride absorption
results in sodium and chloride influx and hydrogen and bicarbonate efflux from the cell
69
What is the name of the chemical process responsible for breaking down macromolecules during digestion
hydrolysis
70
why does the stomach secrete zymogens
to avoid autodigestion
71
The mixing of bile with broken down smaller particles of food in the small intestine is part of which phase of lipid assimilation
emulsification
72
Why is the digestion of lipids arguably more complicated than that of carbohydrates and proteins
due to their hydrophobic nature
73
what is the main function of insulin
to drive glucose into cells to be used or stored
74

GI (9 decks)

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