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GI > Rest and digest physiology part 2 > Flashcards

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
Q

what makes up lactose

A

glucose and galactose

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26
Q

what makes up sucrose

A

glucose and fructose

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27
Q

How are glucose and galactose absorbed

A

secondary active transport through a co-transport or process ( sodium symporter)

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28
Q

How is fructose absorbed

A

transported across apical membrane via facilitated diffusion

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29
Q

Where are proteolytic enzymes secreted from and in what form

A

secreted from stomach glands and pancreas in form of inactive zymogens(precusors of enzymes)

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30
Q

Where does luminal phase happen for proteins

A

begins in stomach facilitated by gastric enzymes and HCL, completed in small intestine by action of pancreatic enzymes

31
Q

What happens in stomach for protein digestion

A

acid denatures proteins and pepsinogen is activated to become pepsin jumpstarting chemical digestion proteins

32
Q

What does pepsin do

A

cleaves covalent bonds in proteins to form shorter polypeptide chains

33
Q

What happens in small intestine for protein digestion

A

polypeptide chains are broken down further into small peptide chains by pancreatic enzymes including trypsin, chymotripsin and carboxypeptidase

34
Q

What form can proteins be absorbed as

A

tripeptides, dipeptides and simple amino acids

35
Q

How are acidic and most neutral amino acids absorbed

A

transported via sodium symporters on apical surface of enterocytes like glucose and galactose

36
Q

How are alkali amino acids absorbed

A

facilitated diffusion route like fructose

37
Q

Most common dietary lipid/ fats

A

triglycerides which also include sterols and phospholipids

38
Q

Why is it more complicated for digestion of lipids and why

A

hydrophobic nature so aggregate the aqueous environment of GI lumen makes more difficult for enzymes to access molecules

39
Q

4 phases of lipid assimilation

A

emulsification, hydrolysis, micelle formation and absorption

40
Q

Describe emulsification for lipids

A

churning action of stomach helps disperse lipids into smaller droplets and also addition of bile when they reach the small intestine

41
Q

What does Bile contain to help to interact to lipids

A

salts with hydrophilic and hydrophobic regions allowing them to interact with both lipids and the GI environment

42
Q

Describe hydrolysis for lipids

A

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
Q

Describe micelle formation for lipids

A

products of hydrolytic lipid digestion combine with bile acids and phospholipids to form micelles

44
Q

Describe absorption for lipids

A

micelles are considerably smaller and diffuse through the gut lumen into the apical membrane of the enterocytes

45
Q

What part of the micelle doesn’t diffuse into enterocytes

A

bile acids

46
Q

What happens to lipids once inside enterocytes

A

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
Q

What enzyme digests triglycerides

A

pancreatic lipase

48
Q

what enzyme digests phospholipids

A

phospholipase

49
Q

what enzyme digests lipid esters

A

cholesterol esterase

50
Q

Where does most lipid digestion occur and where does small amounts of lipid digestion occur

A

most in small intestine
some in mouth via lingual lipases and stomach via gastric lipase

51
Q

Do vitamins require digestion

A

no but vary chemical compositions so absorbed in different ways

52
Q

How are fat soluble vitamins (A,D,E and K) absorbed

A

same absorption route as lipids and transport via micelles as they are entirely hydrophobic so would unlikely make it to the enterocyte alone

53
Q

How are water soluble vitamins like C and B absorbed

A

diffusion or by passive and active transporters

54
Q

How is water soluble vitamin C and B1 transported in by

A

c- sodium dependent transport
b1- sodium dependent transporter at low concentration
passive diffusion at high concs

55
Q

How are other water soluble vitamins like B2 absorbed and B6

A

B2- facilitated transport
B6- simple diffusion

56
Q

How does water absorption happen

A

osmosis and driven by concentration gradient
conc of solute in epithelial cells higher than chyme
remaining water absorbed in colon

57
Q

What tells us that water is absorbed across tight junctions between enterocytes

A

hydrostatic and osmotic pressures in both small and large intestines

58
Q

What do osmotic pressures arise from

A

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
Q

How is mineral absorption controlled

A

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
Q

How is calcium absorption controlled

A

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
Q

What can calcium absorption be affected by

A

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
Q

How is ionic iron absorbed and used

A

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
Q

How are most ions absorbed

A

active transport in small intestine but absorption mechanisms can be conc dependent and vary in different parts of GI tract

64
Q

How is sodium absorption

A

coupled to absorption of nutrients such as amino acids and glucose

65
Q

How is chloride absorbed

A

cross epithelial barrier via both paracellular and transcellular routes
absored passiveley in proximal region of small intestine following + charged soidum

66
Q

How is chloride absorbed in ileum and colon

A

actively via electroneutral route

67
Q

What type of absorption do phosphate and magnesium also exhibit

A

both paracellular and transcellular

68
Q

What happens due to the sodium and chloride absorption

A

results in sodium and chloride influx and hydrogen and bicarbonate efflux from the cell

69
Q

What is the name of the chemical process responsible for breaking down macromolecules during digestion

A

hydrolysis

70
Q

why does the stomach secrete zymogens

A

to avoid autodigestion

71
Q

The mixing of bile with broken down smaller particles of food in the small intestine is part of which phase of lipid assimilation

A

emulsification

72
Q

Why is the digestion of lipids arguably more complicated than that of carbohydrates and proteins

A

due to their hydrophobic nature

73
Q

what is the main function of insulin

A

to drive glucose into cells to be used or stored

74
Q
A

GI (7 decks)

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