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Medicine Unit 8 > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

what are the stages of digestion and absorption

A

mouth
oesophagus
stomach
intestines

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2
Q

digestion definition

A

breakdown the large molecules into small/simpler molecules

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3
Q

absorption definition

A

small molecules pass through cell membranes into the blood or lymph capillaries

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4
Q

refresher for enzymes

A

typically proteins
increase the speed of most chemical reactions that take place within cells, catalyst
vital for life
important for digestion and metabolism
cleavage

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5
Q

what is cleavage

A

splitting of a large complex molecule into smaller or simpler molecules

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6
Q

models that demonstrate enzyme action

A

lock and key
induced fit

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7
Q

lock and key model

A

both enzyme and substrate have a specific configuration and unique shape that fit together

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8
Q

induced fit model

A

the substrate induces the enzyme to adopt the form of the substrate
enzymes are flexible and favour geometric adoption for binding and catalysis of the substrate

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9
Q

digestion product of proteins

A

amino acids

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10
Q

digestion product of fats

A

fatty acids and glycerol

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11
Q

digestion product of carbohydrates

A

monosaccharides

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12
Q

monosaccharides

A

glucose
galactose
fructose

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13
Q

where does digestion and absorption take place

A

mouth
oesophagus
stomach
small intestine
large instestine

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14
Q

components of the GI tract

A

mouth
oesphagus
stomach
small intestine
large intestine
anus

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15
Q

accessory organs associated with the alimentary tract

A

salivary glands
liver
gall bladder
pancreas

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16
Q

another word for chewing

A

mastication

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17
Q

types of digestion in the mouth

A

mechanical
chemical

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18
Q

mechanical digestion in the mouth

A

3 main functions
reduces the size of ingested particles
mixes food with saliva, lubricating it and exposing the food to digestive enzymes
increasing the surface area of ingested material

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19
Q

increasing the surface area of ingested material

A

increases the rate it can be digested

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20
Q

chemical digestion in the mouth

A

salvia contains 2 enzymes with fat and carb targets
salivary amylase
lingual lipase

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21
Q

starch chemical digestion in the mouth

A

alpha amylase (ptyalin) cleaves internal alpha-1,4-glycosidic bonds present in starch
produces maltose, maltotriose and alpha limit dextrins

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22
Q

fat chemical digestion in the mouth

A

lingual lipase
plays role in hydrolysis of dietary lipids

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23
Q

ph of saliva

A

6.2-7.6
eliminates acids from food, drink and bacteria

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24
Q

clinical importance of salivary amylase

A

infants have low levels of pancreatic enzymes in the first year
pancreatic insufficiency e.g. cystic fibrosis

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25
Q

what does lipase hydrolyse

A

triglycerides
uses 3 molecules of water to break 3 ester bonds
forms 1 glycerol molecule
3 fatty acid molecules

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26
Q

what does amylase break down

A

starch at alpha 1,4 linkages into polysaccharides and maltose by addition of water

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27
Q

maltose

A

2 glucose molecules

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28
Q

R group

A

any group in which a carbon or hydrogen atom is attached to the rest of the molecule

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29
Q

oesophagus

A

connection between the mouth and the stomach
25-30cm
divided into cervical,thoracic and abdominal parts
uses peristalsis to pass food to stomach
upper and lower oesphageal sphincters control the movement of food into and out of the oesophagus

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30
Q

production and secretion of gastric juice in stomach daily

A

2L per day

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31
Q

stomach ph

A

1-3.5
break down food
activates enzymes
denatures proteins
kills bacteria

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32
Q

how much can stomach hold

A

2-4L of food

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33
Q

what Lines the stomach walls

A

mucus
acts primarily as a lubricant
protects mucosa from injury
with bicarbonate mucus will neutralise acid and maintain the surface of the mucosa at nearly neutral ph
this is part of gastric mucosal barrier that protects stomach from acid and pepsin digestion

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34
Q

water in stomach

A

acts as the medium for the action of acid and enzymes
and solubilises many of the constituents of a meal

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35
Q

what is intrinsic factor

A

glycoprotein produced by the parietal cells in the stomach
vitamin B12 binds to IF to form IF-Cbl complex
needed for absorption in the small intestine
plays crucial role in transportation and absorption of the vital vitamin B12 by terminal ileum

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36
Q

what is vitamin b12 needed for

A

mature red blood cells
neurological functioning

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37
Q

5 constituents of gastric juice

A

intrinsic factor
hydrogen ion
pepsin
mucus
water

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38
Q

stomach acid secretion

A

enterochromaffin-like cells ECL
gastrin and acetylcholine activate phospholipase C
PLC catalyses the formation of inositol triphosphate, IP3
IP# causes release of intracellular calcium ions and activates calmodulin kinase
calmodulin kinases phosphorylate variety of proteins
leading to H+ secretion
ECL cells have cholecystokinin-2 CCK-2 receptors for gastrin
gastrin stimulates ECL cells to release histamine
histamine activates adenylate cyclase to form cyclic AMP
cyclic AMP activates protein kinase A
protein kinase A phosphorylate a variety of proteins leading to H+ secretion

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39
Q

acetylcholine

A

key neurotransmitter of parasympathetic nervous system

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40
Q

gastrin

A

peptide hormone secreted by G cells

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41
Q

phospholipase C

A

enzyme that produced second messengers

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42
Q

IP3

A

intracellular messenger
mediating hormonal mobilisation of intracellular calcium

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43
Q

calmodulin kinase enzymes

A

involved in phosphorylation
substrate-level phosphorylation is the direct production of ATP during the enzymatic oxidation of a substance
involves transfer of a phosphate group from a substrate to an ADP molecule

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44
Q

what type of receptors do ECL cells have for gastrin

A

colcecystokinin 2 receptors, CCK-2
don’t have acetylcholine receptors

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45
Q

transport processes involved in the secretion of Hal

A

H+ is pumped actively into the lumen by the H+, K+-ATPase,
Cl- enters the cell across the basolateral membrane In exchange for HCO3-

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46
Q

inhibition of proton pump

A

totally blocks gastric acid secretion
PPI’s are activated at low pH
bind irreversibly to sulfhydryl (Thiol) groups of pump
and inactivate the enzyme
leads to acid secretory inhibition
therefore omeprazole is useful in peptic ulcer treatment

47
Q

inhibition of carbonic anhydrase CA enzyme

A

decreases rate of acid secretion but doesnt prevent
metabolism produces much of the CO2 used to neutralise OH- but CO2 from blood is also required

48
Q

HCO3-diffusing into the blood

A

gastric venous blood has a higher pH than that of the arterial blood when the stomach is secreting

49
Q

protein digestion in the stomach

A

protein stimulates G cells= enteroendocrine cells
they release gastrin into the blood
gastrin stimulates the enterochromafin-like cells to release histamine
histamine then stimulates acid producing parietal cells (oxynitic cells)
gastrin also stimulates parietal cells to release Hal and chief cells to release pepsinogen
pepsinogen converted to pepsin to cleave protein (by HCl)

50
Q

what stimulates gastrin release

A

acetylcholine

51
Q

where are ECL cells

A

lamina proprietor of gastric glands

52
Q

what do parietal cells secrete

A

hydrochloric acid and intrinsic factor

53
Q

pepsin ph efficacy

A

optimum 1-3
denatured higher than 5

54
Q

pepsin information

A

endopeptidase with specificity for peptide bonds involving aromatic L amino acids

55
Q

what is the gastric mucosa composed of

A

pits and glands
pits and surface are lined with mucous or surface epithelial cells
base of pits are openings of glands which project into the mucosa towards outside or serosa

56
Q

oxyntic glands

A

contain parietal cells and peptic or chief cells
secrete enzyme precursor pepsinogen

57
Q

pyloric glands

A

contain gastrin producing G cells and mucous cells
whcih also produce pepsinogen

58
Q

mucous neck cells

A

present where glands open into the pits

59
Q

gastric pits and glands

A
60
Q

negative feedback of protein digestion in stomach

A

low antral pH means D cells release somatostatin
inhibits g cells
prevents over secretion of acid

61
Q

cell types in gastric pit and their functions

A
62
Q

digestion of dietary fats

A

gastric lipase is produced by chief cells of the fundus
stimulated by the neurohormonal stimuli, gastrin and cholinergic mechanisms
inhibited by cholecystokinin CCK
and glucagon like peptide ! GLP1

63
Q

cholinergic neurons

A

synthesis, release,metabolise acetylcholine

64
Q

digestion of carbohydrates stomach

A

salivary amylase inactivates due to low ph so there is little chemical digestion of carbohydrates in the stomach
mechanical breakdown of carbohydrates is ongoing
strong peristaltic contractions of stomach mix carbohydrates into more uniform mixture of chyme

65
Q

mechanical digestion in the stomach

A

food is mixed with gastric juices and churned by contractions in stomach wall
mixing waves
propulsion
retropulsion
break food into smaller pieces

66
Q

mixing was

A

unique style of peristalsis that mixes and softens the food with gastric juices to create chyme

67
Q

chyme

A

acidic fluid mixture of gastric juices and partly digested food which passes from stomach to small intestine

68
Q

propulsion q

A

forward movement

69
Q

retropulsion

A

backwards movement

70
Q

gastric emptying in the stomach

A

holds food for 4-6 hours
absorbs some non polar substances like alcohol and aspirin
pylorus acts as filter to duodenum

71
Q

what actually is gastric emptying

A

as peristaltic contractions become stronger
some of liquid chyme travels past pyloric sphincter as it has decreased its muscle tone
and into the duodenum
carbohydrates empty the fasters after liquids

72
Q

small intestine

A

connects with pylorus and leads to osmium ileale in the colon

73
Q

3 sections of small intestine

A

duodenum
jejunum
ileum

74
Q

duodenum

A

continuous with gastric pylorus
common bile duct and pancreatic duct lead into duodenum

75
Q

jejunum

A

middle section constituting about 2/5s of small intestine

76
Q

ileum

A

terminal section ending in right iliac fossa in colon

77
Q

main cells types in the small intestine

A

enterocytes
goblet cells
enteroendocrine cells
paneth cells

78
Q

enteroendocrine small intestine

A

release signalling molecules
hormones like CCK, motilin
they coordinate and regulate the activities of the digestive system

79
Q

paneth cells small intestine

A

release bacteriotoxic peptides and some growth factors
integral part of innate immune system

80
Q

enterocytes small intestine

A

absorptive cells
complete enzymatic digestion of nutrients in their brush border
release absorbed materials to the serosal/internal side

81
Q

goblet cells small intestine

A

secrete mucus to the lumenal/external side
acts as protective barrier

82
Q

when chyme enters the duodenum what occurs

A

intestinal receptors in the duodenum are activated
then triggers mechanisms inhibiting gastric emptying

83
Q

mechanisms triggered to inhibit gastric emptying

A

CCK increases distentibilityof the orad stomach
acid inhibits motility and emptying
other hormones such as secretin and gastric inhibitory peptide also inhibit emptying

84
Q

regulation of emptying

A

results from presence of receptors in the duodenum
respond to physical properties such as osmotic pressure
and chemical compotiiosn such as H+ and lipids of the intestinal contents

85
Q

small intestine chemical digestion of carbohydrates

A

pancreatic amylase is released following the stimulus of secretin and CCK
starch is digested into maltose, maltotriose and alpha limit dextrins
oligosaccharides and disaccharides are digested at the brush border

86
Q

brush border enzymes

A

lactase
sucrase
isomaltase
maltase

87
Q

lactase function

A

lactose to glucose and galactose

88
Q

sucrase function

A

sucrose to glucose and fructose

89
Q

isomaltase function

A

alpha 1,6 bonds of limit dextrins

90
Q

maltase function

A

maltose to glucose and glucose

91
Q

alpha limit dextrin

A

branched amylopectin remnants

92
Q

small intestine chemical digestion of fats

A

bile acts as an emulsifier to increase the surface area
lipase action= lipids to fatty acids and glycerides
bile salts envelop the fatty acids and monoglycerides to micelles
as the brush border of the small intestine the fatty acids and monoglycerides diffuse out of the micelle into the absorptive cells

93
Q

small intestine chemical digestion of protein

A

proteases such as trypsin and chymotrypsin
brush border peptidases hydrolyses to dipeptides and amino acids for absorption

94
Q

mechanical digestion small intestine

A

mechanical digestion: segmentation and peristalsis mix chyme with secretions

95
Q

absorption small intestine

A

folds called place circulares
villi
microvilli
increase surface area
which is approx 300 m2

96
Q

how do absorbed nutrients move into circulation

A

by blood capillaries and laterals
or lymph channels

97
Q

absorption across the intestinal wall of monosaccharides

A

SGLT1 needed for glucose uptake
energised by the electrochemical Na+ gradient
maintained by the extrusion of Na+ by the Na-K pump by secondary active transport
facilitated diffusion mediated by GLUT5 is for fructose absorption
facilitated diffusion GLUT2

98
Q

active transport

A

influx occurs against concentration gradient
uses ATP

99
Q

secondary active transport

A

concentration gradient of one molecule provides energy for transport of another molecule against concentration gradient
therefore energy from moving first molecule is enough to move second molecule against its concentration gradient

100
Q

absence of sodium transport through intestinal membrane

A

virtually no glucose can be absorbed because glucose absorption occurs in a co-transport mode with active transport of sodium.
Inhibition of the Na-K pump reduces active glucose absorption by decreasing the apical membrane Na + gradient and thus effecting facilitated diffusion and decreasing the driving force for glucose entry.
Therefore, it is the initial active transport of sodium through the basolateral membranes of the intestinal epithelial cells that provides the eventual force for moving glucose through the membranes as well.

101
Q

galactose transport mechanic m

A

almost the same as glucose

102
Q

fructose transport mechanism

A

by facilitated fission down concentration gradient
through intestinal epithelium
isn’t coupled with sodium transport
much of fructose upon entering cell becomes phosphorylated
then converted to glucose
transported in form of glucose through blood

103
Q

examples of transport proteins

A

SGLT1
GLUT5
GLUT2

104
Q

SGLT1

A

sodium ion coupled transporter that mediates the uptake of glucose or galactose
involved in secondary active transport

105
Q

GLUT5

A

mediates facilitated diffusion of fructose into the enterocyte

106
Q

GLUT2

A

mediates their efflux across the basolateral membrane into the interstitial space

107
Q

large intestine general

A

produces no digestive enzymes
reclaiming water and maintaining water balance
recovery of electrolytes
storage/elimination of remaining waste
peristalsis pushes the waste material toward canal end of the tract
can take 36 hours for food to move through the entire colon

108
Q

what occurs in the large intestine

A

non-digestible carbohydrates: bacterial flora aids in digestion
limited mainly to anaerobic fermentation by essential colonic bacteria
methane and hydrogen also produced= flatus
bacteria manufacture vitamin K which is absorbed
adequate dietary fibres

109
Q

how does bacterial flora aid in digestion

A

digestion of dietary fibres and undigested carbohydrates to short chain fatty acids
10% starches, cellulose and hemicellulose form fruit and vegetables and monosaccharides lactulose sorbitol and surculose

110
Q

vitamin K

A

importance for clotting

111
Q

adequate dietary fibres

A

soluble, slows down transit time such as pectins from fruit/veg, hemicelluloses from cereals
insoluble: draws water into stool= soften and increase faecel weight= improved obwel movement consistency snd speed up transit time such as cellulose form plant material

112
Q

GI health

A

fluids, low fluid= dry stools= constipation
optimal bacterial flora fibre helps
avoidance of antibiotics
regular movement- physical activity

113
Q

common problems of large intestine

A

constipation
diarrhoea
diverticulitis
chrons
colon cancer

Medicine Unit 8 (24 decks)

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