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HOM > Small intestine onwards > Flashcards

Small intestine onwards Flashcards

1
Q

how long does chyme take to pass through the small intestine

A

2-5 hours

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2
Q

what controls motility

A

slow wave activity

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3
Q

what does contraction require

A

slow waves must be large enough to generate action potentials

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4
Q

segmentation contractions

A

commonest form of motility but are only weakly propulsive

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5
Q

what is peristaltic activity increased by

A

stretch of the gut wall

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6
Q

what is the ileocaecal valve

A

the junction of the caecum and colon where the lips are reffered to as the ileocaecal valve

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7
Q

what does high pressure in the colon do to the iloecaecal valve

A

reduce movement through the valve

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8
Q

what is the iloecaecal sphincter formed of

A

smooth muscle

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9
Q

what happens when the terminal ileum is distended

A

a peristaltic reflex is coordinated by the ENS and pushes intestinal contents onwards

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10
Q

what is the gastroileal reflex

A

ileal motility enhanced in response to signals from a full stomach

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11
Q

what is the colonoileal reflex

A

inhibits movement through the sphincter when colon is full

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12
Q

approximation of nutrient ratios absorbed everyday

A

carbs>fat>amino acids>ions>water

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13
Q

what do mucosal folds of kerckring do

A

increase the surface area of the small intestine

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14
Q

what else increase the surface area

A

vili and microvilli on the epithelial cells forming a brush border

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15
Q

what do the crypts of lieberkuhn do

A

found between the villi and secrete fluid and contain stem cells for the replacement of desquamated epithelial cells lost from gut

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16
Q

difference between folds of kerckring and crypts of lieburkuhn

A

Folds are on the surface of the small intestine whereas the crypts are found between the vili

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17
Q

what does stomach acid help do in regard to proteins

A

denature it, therefore making it vulnerable to attack by pepsins e.g. digesting collagen

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18
Q

what is the most important enzyme type in protein digestion

A

pancreatic proteases

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19
Q

inactive zymogen trypsinogen is converted to….

A

trypsin by enteropeptidase on the brush border of the upper small intestine

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20
Q

what is the brush border

A

villi and microvilli on the epithelial cells of the small intestine

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21
Q

what does trypsin activate

A

trypsinogen, chymotrypsin, elastase and carboxypeptidases

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22
Q

what do these enzymes do

A

digest proteins to peptides

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23
Q

what happens after the proteins are digested to peptides

A

they are further digested by brush border peptidases

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24
Q

what happens to the products of digestion

A

they are taken up into the cells by facilitated diffusion or secondary active transport.

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25
Q

what happens to some amino acids within the cells

A

glutamine oxidised for energy within the rapidly dividing intestinal cells

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26
Q

what does the salivary and pancreatic amylase do to starch

A

cleave the internal a-1,4 bonds but cannot touch the a-1,6 branching liinks or the a-1,4 bonds next to them

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27
Q

what is the result of salivary and pancreatic amylase

A

smaller chains of glucose molecules (oligosaccharides) mostly maltose

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28
Q

what are the enzymes on the brush border of the duodenum and jejunum

A

glucoamylase and a-dextrinase, lactase, sucrase and trehalase

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29
Q

what do glucoamylase and a-dextrinase do

A

break down the a-1,4 and 1,6 bonds respectively within oligosaccharides

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30
Q

what do lactase, sucrase and trehalase do

A

digest lactose, sucrose and trehalose respectively

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31
Q

how is glucose and galactose is taken up by

A

SGLT1 on the apical membrane of epithelial cells in the duodenal and jejunal villi

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32
Q

fructose is taken up by

A

GLUT5 a facilitated diffusion transporter

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33
Q

how is fructose exported

A

glut2 on basolateral membrane

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34
Q

where is sodium absorption the highest

A

in the small intestine, its movement into cells is down electrochemical gradient

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35
Q

what is sodium absorption coupled to

A

movement of monosaccharides via SGLT-1 and some amino acids

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36
Q

when does potassium become concentrated

A

as water is absorbed and this provides driving force for paracellular uptake by the small intestine

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37
Q

where is there net secretion

A

from the colon via apical potassium channels

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38
Q

where and when is chloride absorbed

A

throughout digestive tract via paracellular pathway and exchange with bicarbs

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39
Q

what is the absorption of water

A

throughout the digestive tract both through ingesta and gastrointestinal secretions e.g. saliva

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40
Q

what is the reserve capacity

A

the gut can take up two or three times more water than 7.5litres if needed

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41
Q

what is the standing gradient model

A

water uptake across an epithelium holds that sodium is pumped into the intercellular clefts by primary active transport involving the na+/k+ ATPases, anions follow

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42
Q

what happens in the standing gradient model when the anions follow

A

a solute gradient is set up, highest near the tight junctions, decreasing towards the open ends where it becomes equal to the concentration in the bulk phase

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43
Q

what happens as a result of the high solute concentration within the intercellular clefts

A

water enters from the adjacent cells and from the lumen via leaky tight junctions, putting up the pressure in the clefts, driving flow across the basement membrane and removed by blood capillaries

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44
Q

what happens as a result of the small intestinal epithelium being leaky

A

absorption is isosmotic, much less water is absorbed in the colon but this can be against a larger osmotic gradient since tight junctions are tighter

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45
Q

what helps improve solubility of calcium and iron

A

gastric acid

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46
Q

what helps reduce insoluble fe3+ to fe2+

A

vitamin c in the stomach

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47
Q

what are the mechanisms for calcium absorption

A

draw this . lol .

include paracellular uptake which is important if calcium intake is high.

active form of vitamin d3 can upregulate the expression of several proteins involved in transcellular uptake INCLUDING CALBINDIN

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48
Q

what is the role of iron reductase and where is it located

A

on duodenal brush border, reduces fe3+ to fe2+ which is taken up via the proton fe2+ cotransporter

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49
Q

what is the proton fe2+ cotransporter called

A

DMT1

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50
Q

how else is iron taken up

A

as haem

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51
Q

how is iron transported out of the cell

A

via ferroportin

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52
Q

how does iron transport around the blood

A

bound to the protein transferrin

53
Q

in the presence of hepcidin from the liver what happens

A

efflux is reduced and excess iron is trapped in the cell bound to the protein ferritin

54
Q

when is ferritin lost

A

when epithelial cell is shed

55
Q

how are vitamins absorbed

A

transported in lymph, most water soluble ones taken up in small intestine by diffusion or active transport.

56
Q

how is vitamin b12 transported

A

absorbed via receptor mediated endocytosis in the ileum and exported from the cells, vitamin b12 travels bound to protein transcobalamin II

57
Q

structure of the liver

A

thousands of lobules, between this are portal triads. mixed blood from hepatic artery and portal vein drains via hepatic sinusoids towards central vein which empties into the hepatic vein

58
Q

what lines the sinusoids

A

hepatocytes

59
Q

what are bile canaliculi

A

tiny channels which drain the bile produced by hepatocytes towards the branches of the bile duct

60
Q

bile flows…. to the blood

A

countercurrent

61
Q

outline the functions of the liver

A

carb, protein and lipid metabolism, bile formation, storage of vitamins, destruction and detoxification of some hormones, filtration of blood, blood reservoir

62
Q

describe the destruction and detoxification of hormones by the liver

A

the first pass metabolism of toxins absorbed by the gut ensures that they do not reach the rest of the circulation

63
Q

what is important about the filtration of blood by the liver

A

removal of effete erythrocytes and any gut bacteria which have entered the hepatic portal vein

64
Q

describe carb metabolism by the liver

A

liver takes up monosaccharides from the portal vein by facilitated diffusion using GLUT2

65
Q

what happens to glucose?

A

converted to glycogen which accumulates in the liver and in the muscle (much more)

66
Q

can muscle export glucose directly

A

no

67
Q

what happens to excess glucose

A

converted to triglycerides by the liver and exported as lipoproteins, stored as fat in adipocytes

68
Q

can long chain fatty acids be made into glucose

A

no, but short chain fatty acid propionate can

69
Q

how can intracellular proteins be metabolised by the liver

A

intracellular proteins can be decomposed via lysosomal enzymes and returned as amino acids to the blood

70
Q

how can extracellular proteins be metabolised by the liver

A

digested by macrophages

71
Q

what does the process of transamination allow for

A

interconvert amino acids, pyruvate, and TCA cycle intermediates by the process of transamination allowing for non essential amino acids to be synthesized

72
Q

what are essential amino acids

A

must be included in the diet

73
Q

what happens to excess amino acids

A

oxidised for energy directly or converted to glucose or ketone bodies

74
Q

what is the exception for urea and glutamine

A

produced and exported directly

75
Q

what is bile

A

an excretory product of the liver

76
Q

what does bile contain

A

bile acids, phospholipids, cholesterol and bile pigments

77
Q

roles of bile 3

A

1 promotion of fat absorption as bile acids are surfactants therefore used with phospholipids. 2 excretion of waste esp cholesterol and heavy metals. 3 protection as IgA, mucus and tocopherol have protective roles

78
Q

what are primary and secondary bile acids

A

primary are made from cholesterol in the liver whereas secondary bile acids by gut bacteria

79
Q

what is the role of the gall bladder

A

bile is collected and concentrated before expulsion into the digestive tract

80
Q

where is the sphincter of oddi

A

at the entrance of the duodenum

81
Q

what happens between meals in the gall bladder

A

sphincter of oddi contracts and bile is diverted into the gall bladder

82
Q

what happens during a meal

A

cck promotes gall bladder contraction and the relaxation of the oddi sphincter emptying the bile into the duodenum

83
Q

what happens to bile once it enters the duodenum

A

epithelial cells in terminal ileum take them up by secondary active transport, rest absorbed passively in the colon

84
Q

how are bile acids returned to the liver

A

via the hepatic portal vein, in hepatocytes some secondary bile acids are re-converted to primary

85
Q

how can cholesterol be controlled with bile acids

A

as bile is made of cholesterol, inhibition of bile acid up take by the gut can be a strategy for reducing cholesterol levels

86
Q

what is the bile pigment

A

bilirubin is yellow coloured breakdown product of haem made in the spleen, bone marrow and liver

87
Q

how is bilirubin transported

A

bound to albumin and is taken up by the liver where it is rendered soluble by conjugation with glucuronic acid

88
Q

how is bilirubin broken down

A

bacteria in colon and ileum convert it into urobilinogen

89
Q

what happens to urobilinogen

A

some reabsorbed into the blood and either resecreted in bile or secreted in the urine, rest lost in faeces

90
Q

urobilinogen can be converted into …

A

yellow urobilin if oxidised on exposure to air in urine or brown stercobilin which is responsible for colour of faeces

91
Q

why are bile salts amphiphatic

A

hydrophobic domains bind to surface of a fat globule while the hydrophilic domains face outwards as stabilization

92
Q

what happens to triglycerides and lipids in the duodenum

A

they are emulsified into emulsion droplets which increases the surface area for attack by lipases

93
Q

what enzyme is responsible for the hydrolysis of triglyceride within an emulsion droplet

A

pancreatic lipase

94
Q

what does pancreatic lipase do

A

with the helper protein colipase it forms two free fatty acids and one 2-monoglyceride

95
Q

what are mixed micelles

A

tiny aggregates of long chain fatty acids, monoglycerides, phospholipids and cholesterol, they are produced as a result of the action of lipases

96
Q

what do mixed micelles do

A

ferry the products of fat digestion to the brush border, these enter the epithelial cells by diffusion or transport protein, dietary fat almost completely absorbed by the end of the ileum

97
Q

how does cholesterol enter enterocytes

A

via special transporters, its absorption can be reduced by plant sterols

98
Q

how is fat exported from the gut epithelial cells

A

fat digestion products and cholesterol bind to fatty acid binding proteins FABP within the epithelial cells of the small intestine, they then go to the ER where they are converted back to triglycerides

99
Q

what happens to the triglycerides at the ER

A

combined with apolipoproteins phospholipids and cholesterol to form CHYLOMICRONS a lipoprotein particle

100
Q

what happens to chylomicrons

A

exported from the golgi apparatus and released via exocytosis to enter the central lacteals of the villi. the chylomicrons within lymph enter the venous circulation via the thoracic duct

101
Q

outline fat metabolism

A

lipoprotein lipase bound to capillary walls catalyzes the hydrolysis of triglycerides within chylomicrons

102
Q

what happens to the fatty acids after they were produced by lipoprotein lipase

A

transported across endothelium and diffuse into the cells where they are resynthesized to triglycerides

103
Q

when are VLDLs secreted

A

secreted by the liver when fasting as a means of exporting triglyceride and hepatic cholesterol to tissues. they contain phospholipids and apoplioproteins too

104
Q

what are the ketone bodies

A

collectively they are the three products: the ketoacids acetoactate and b hydroxybutyrate or acetone

105
Q

what is the longitudinal muscle layer of the colon gathered into

A

three bands, the taeniae coli

106
Q

what are haustra

A

regular but non permanent divisions along the colon which arise from contractions of the circular smooth muscle

107
Q

does the colon have villi

A

no

108
Q

where are faeces stored

A

transverse colon

109
Q

what are the roles of the large intestine

A

store mix and process contents. expose contents to mircobes. expel waste as faeces

110
Q

what is the large intestine motility

A

ICCs within the circular muscle of the colon generate slow waves which can be prolonged by ACh

111
Q

what is transit time through the colon

A

may be 1-2 days as colonic movements are low amplitude contractions to allow fluid absorption

112
Q

how can forwards movement of contents be accelerated

A

through high amplitude propagating contractions allowing mass movements promoted by gastrocolic reflex

113
Q

what is the internal anal sphincter

A

thickening of circular smooth muscle just inside the anus, has its own myogenic tone

114
Q

what is the external anal sphincter

A

made of striated muscle therefore under somatic motor control. it is tonically contracted

115
Q

what happens when the sigmoid colon is filled by a mass movement

A

Sensory nerves from the rectum send signals to the sacral
spinal cord, which responds via autonomic fibres in the
pelvic nerves, resulting in highly propulsive movements.
- The internal anal sphincter relaxes, a reflex that seems to
involve both intrinsic and extrinsic neurons.
- The external sphincter may be voluntarily relaxed.
- Relaxation of pelvic floor muscles lowers the anus, which
straightens the angle between rectum and anal canal.
- Defaecation is aided by the Valsalva manoeuvre

116
Q

what is hirschsprung disease

A

ens ganglion cells are lacking in descending colon and internal anal sphincter&raquo_space;> colon dilates to a large size and may perforate = congential megacolon

117
Q

diarrhoea or constipation?

A

the consistency of the stool reflects the balance between overall GI secretion, ability of gut to hold water and absorption.

118
Q

what are opioid receptors

A

in gastrointestinal tract which are stimulated by endogenous transmitters and promote decreased propulsion, decreased secretion and increased sphincter toner

119
Q

what are the gut flora

A

bacteroides, bifidobacterium and eubacterium species.

120
Q

describe gut bacterial metabolism

A

bacteria will metabolise and carbs in the colon to produce volatile fatty acids which are energy source for colonic cells

121
Q

what is a high fibre diet believed to do

A

provide substrate for the metabolism of beneficial gut bacteria, relieve constipation, promote satiety, protect against bowel cancer

122
Q

what happens to lactose in those that are lactose intolerant

A

undigested lactose gets through the colon, colonic bacteria thrive on it producing metabolites leading to excess gas, water retention and diarrhoea

123
Q

what is the breath hydrogen test for lactose intolerance

A

hydorgen is some of the gas produced by the colonic bacteria

124
Q

what is the importance of gut microbes

A

normal intestinal bacteria help maintain health digestive immune system

125
Q

how are normal healthy gut microbes restored after diarrhoea or antibiotics

A

vermiform appendix may be a store of benefical microbes . the mucosal walls of the appendix contain masses of gut associated lymphoid tissue as a local defence against infection.

126
Q

what is flatus

A

gas in the digestive tract, it contributes to borborygmi

127
Q

what are the proportions of gases in flatus

A

50% n2, small amount of o2 and 25% h2, 15% co2 and 10% methane

128
Q

how much faeces is produced per day

A

120 grams of which 75% is water > bacteria > fat/protein> inorganic matter and remainder is indigestible fibre

HOM (8 decks)

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