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Medical Physiology > Lecture 7: GI > Flashcards

Lecture 7: GI Flashcards

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USMLE® Step 1 flashcards
1
Q

What occurs in the alimentary tract?

A

Moving food through the tract
Secretion of digestive juices
Digestion of food
Absorption of water, electrolytes, vitamins, and digestive products
Circulation of blood through the GI organs to carry away absorbed substances

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2
Q

What kind of systems control the alimentary tract?

A

Local
Nervous
Hormonal

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3
Q

What does the smooth muscle of the GI tract function as? Why is it significant?

A

Syncytium.
Cytoplasms are connected, so they are electrically connected via gap junctions.

Allows for independent stimulation without CNS.

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4
Q

What is the enteric nervous system?

A

The nervous system of the gut, found in its walls in two separate layers.

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5
Q

What are the two plexuses of the enteric nervous system?

A

Myenteric plexus (Auerbach’s): GI movements

Submucosal (Meissner’s): GI secretions & local blood flow.

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6
Q

Which nerve plexus is more superficial?

A

Myenteric/Auerbach’s

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7
Q

What parasympathetic fibers innervate the GI tract?

A

Vagus nerves, going down until the proximal half of the colon.

Sacral segments 2-4, doing distal half of the colon all the way to the anus.

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8
Q

Which NT is responsible for GI excitation?

A

ACh

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9
Q

What sympathetic fibers innervate the GI tract?

A

T5-L2

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10
Q

What NT inhibits the GI tract?

A

NE

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11
Q

What are the two ways NE inhibits the GI tract?

A

Secreted NE can inhibit the GI tract’s smooth muscle.

The major effect is when NE inhibits the actual neurons of the enteric nervous system.

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12
Q

What is the main GI hormone secreted by the stomach?

A

Gastrin

Secreted by G cells of the antrum, duodenum, and jejunum.

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13
Q

When is gastrin secreted?

A

Protein
Distention
Nerves

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14
Q

What is the effect of gastrin?

A

Gastric acid secretion
Mucosal growth

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15
Q

What is the man GI hormone responsible for fat breakdown?

A

CCK, Cholecystokinin.

Released by I cells of the duodenum, jejunum, and ileum.

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16
Q

When is CCK secreted?

A

Mainly fats
Protein
Acid

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17
Q

What are the effects of CCK?

A

Pancreatic enzyme secretion (amylase and lipase)
Pancreatic bicarb secretion (fats are acidic)
Gallbladder contraction (releases bile)
Growth of exocrine pancreas

Inhibits gastric emptying.

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18
Q

What is secretin secreted by?

A

S cells of the duodenum, jejunum, and ileum.

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19
Q

What is the effect of secretin?

A

Pepsin secretion
Pancreatic bicarb secretion
Biliary bicarb secretion
Growth of exocrine pancrease

Inhibits gastric acid secretion

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20
Q

What stimulates the secretion of secretin?

A

Acid
Fat

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21
Q

What enzyme stimulates insulin release in the GI tract?

A

Gastric inhibitory peptide

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22
Q

What stimulates gastric inhibitory peptide to be released?

A

Protein
Fat
Carbs

K cells of the duodenum and jejunum

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23
Q

What enzyme stimulates gastric and intestinal motility?

A

Motilin

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24
Q

What stimulates the secretion of motilin?

A

Fats
Acids
Nerves

M cells of the duodenum and jejunum.

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25
Q

What circulation are GI hormones released into?

A

Portal circulation!

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26
Q

If the GI tract has no more nervous innervation, what happens to the hormonal effects?

A

They still persist.

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27
Q

What do we call the movement of the GI tract smooth muscle?

A

Peristalsis

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28
Q

Describe peristalsis.

A

Distension of the gut (usual stimulus) causes the previous section of gut 2-3cm behind to contract. This contractile ring then slowly moves forward, like a wave.

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29
Q

What stimulates peristalsis?

A

Distension of the gut (main)
Chemical/physical irritation
Strong parasympathetic stimulation

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30
Q

What happens when peristalsis gets stopped by a sphincter?

A

Churning of the food, causing local, intermittent constrictive contractions.

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31
Q

What circulation are the blood vessels of the GI specifically a part of?

A

Splanchnic circulation.

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32
Q

Where does blood from the splanchnic circulation go to?

A

Liver via portal vein

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33
Q

What does blood from the portal vein flow through in the liver?

A

Liver sinusoids, which can remove bacteria and other particulate matter.

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34
Q

How does blood leave the liver?

A

Hepatic vein to IVC.

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35
Q

How are carbs and proteins absorbed?

A

Gut absorption, transported in the portal venous blood to the liver.

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36
Q

How are fats absorbed?

A

They can be absorbed into intestinal lymphatics.
Into the thoracic duct
Bypassing the liver.

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37
Q

What is the functional unit of the liver called?

A

Liver lobule.

We have 50k-100k in the liver.

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38
Q

What do all the liver lobules empty into blood-wise?

A

Central veins

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39
Q

What is the largest organ in the body?

A

Liver

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40
Q

What kind of plates radiate from central veins?

A

Liver cellular plates

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41
Q

Where are bile canaliculi found?

A

In between liver cellular plates.

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42
Q

Where do bile canaliculi empty into?

A

Bile ducts

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43
Q

Where do portal veins empty into in a liver lobule?

A

Into the hepatic sinusoids, then into the central veins.

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44
Q

What do hepatic arterioles supply?

A

Tissues between the lobules, aka interlobar septas.

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45
Q

Where do lymphatics empty into the liver lobule?

A

Spaces of disse, found lateral to liver cell plates.

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46
Q

What two cells line a hepatic sinusoid?

A

Kupffer cells
Endothelial cells

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47
Q

What are kupffer cells?

A

AKA reticuloendothelial cells.

They are resident macrophages lining the sinusoids in order to phagocytize bacteria and other foreign matter.

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48
Q

Summarizing the liver lobule, what is leaving and what is entering it?

A

Bile and lymphatics are leaving
Hepatic arterioles and portal veins are entering

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49
Q

What are the two main arteries of the lower GI tract?

A

Superior and Inferior mesenterics

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50
Q

What 3 locations do the arteries of the GI tract go to?

A

Along muscle bundles
Into the intestinal villi
Into submucosal vessels

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51
Q

What are the functions of submucosal vessels in the gut?

A

Absorption
Secretion

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52
Q

What vasodilators are released from the mucosa of the intestinal tract during digestion?

A

CCK
Vasoactive intestinal peptide
Gastrin
Secretin

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53
Q

What vasodilators are released from GI glands?

A

Kallidin
Bradykinin

54
Q

What is the function of vasodilation in the GI tract?

A

Increasing blood flow in the presence of a decreased O2 concentration.

55
Q

How does blood flow work in the villus?

A

Arterial and venous are on opposite sides.
Blood diffuses across the middle.

56
Q

What kind of conditions can affect blood flow in the villus?

A

Circulatory shock
GI disease
Ischemic death of villus
Disintegration of villus
Diminished intestinal absorptive capacity

57
Q

What are the 3 main functions of the stomach?

A

Storing food
Mixing food with secretions
Emptying food into the GI

58
Q

What is chyme? Where do I find it?

A

Chyme is created in the stomach from the mixing of food and enzymes.

59
Q

What is the vagovagal reflex?

A

When food stretches the stomach.

It reduces the tone of the wall to accommodate larger amounts of food.

Stomach to brain to stomach.

60
Q

What are the two kinds of glands found in the stomach?

A

Gastric glands (mucus and chief cells)

Pyloric glands (mucus and pepsinogen and gastrin)

61
Q

What kind of cells do gastric glands contain?

A

Mucous neck cells
Chief cells
Parietal cells

62
Q

What do chief cells secrete?

A

Pepsinogen -> pepsin

63
Q

What do parietal/oxyntic cells secrete?

A

Secrete HCl & intrinsic factor

64
Q

What is intrinsic factor for? What happens if it is impaired?

A

Vit B12 absorption in the SI.

Lack thereof results in pernicious anemia.

65
Q

What do pyloric glands secrete?

A

Mucus
Pepsinogen
Gastrin (key difference!!)

66
Q

What are the 5 inhibitory nervous reflexes that inhibit stomach emptying relative to the duodenum?

A

The degree of distension of the duodenum
Presence of any degree of irritation of the duodenal mucosa
Degree of acidity of duodenal chyme
Degree of osmolality of the chyme
Presence of certain breakdown products in the chyme, mainly proteins and then fats.

67
Q

What is the main stimulus for release of inhibitory hormones from the duodenum?

A

Fats

68
Q

How do fats inhibit gastric emptying?

A

Decreasing pyloric pump (contractions)
Increasing pyloric sphincter contractions

69
Q

What are the two hormones associated with inhibiting gastric emptying?

A

CCK
Gastric inhibitory peptide

70
Q

What is the main cell of the pancreas?

A

Acini cells

71
Q

What do acini cells secrete?

A

Bicarb
Digestive enzymes for all 3 food types.

72
Q

What are the digestive enzymes associated with proteins?

A

Trypsin (Inactive - trypsinogen)
Chymotrypsin (Chymotrypsinogen)
Carboxypolypeptides (Carboxypolypeptidase)

73
Q

What are the digestive enzymes associated with carbs?

A

Pancreatic amylase

74
Q

What are the digestive enzymes associated with fat breakdown?

A

Pancreatic lipase
Cholesterol esterase
Phospholipase

75
Q

What are the 3 things in the SI that increase surface area?

A

Valvulae conniventes (3x)
Villi (10x)
Brush border microvilli (20x)

1000x increase in SA.

76
Q

What are the 3 monosaccharides?

A

Glucose
Fructose
Galactose

77
Q

What does fructose become?

A

Glucose, converted by the liver.

78
Q

What does galactose become?

A

Glucose, after it is broken down from lactose.
(Does not occur freely in nature)

79
Q

What are the disaccharides?

A

Sucrose (most common) (A-glucose+B-fructose)
Lactose (B-galactose+B-glucose)
Maltose (2x a-D-glucose)

80
Q

What kind of syrups is sucrose most commonly found?

A

Beet-cane-maple syrup

81
Q

Where is maltose most commonly found?

A

Beer, cereals, and germinating seeds.

82
Q

What is the process of combining polysaccharides?

A

Condensation

83
Q

What is the process of separating polysaccharides?

A

Hydrolysis

84
Q

What are the 3 main sources of carbs in a human diet?

A

Sucrose
Lactose
Starches

85
Q

How is sucrose broken down?

A

Sucrase in the intestine.

86
Q

How is lactose broken down?

A

Lactase in the intestine

87
Q

How is starch broken down?

A

Saliva + pancreatic amylase

Then

Maltase + alpha-dextrinase in the SI

88
Q

What does saliva contain?

A

Alpha-amylase, aka ptyalin (converts starch to maltose)

89
Q

What are the main 3 enzymes that the brush border microvilli secrete?

A

Sucrase
Lactase
Maltase

90
Q

What is the main monosaccharide present once digestion is done?

A

Glucose

91
Q

What is a triglyceride made up of?

A

3 Fatty Acids + Glycerol

92
Q

Where does most digestion of fats occur in?

A

SI, because it requires bile salts to emulsify them first.

93
Q

Describe the breakdown of fat.

A

TGs enter stomach and get broken down into slightly smaller molecules, which get emulsified by bile salts and phospholipids.

TGs get emulsified and broken down by pancreatic LIPASE into smaller fatty acids and monoglycerides.

They turn into micelles along with vitamins and minerals to get absorbed.

94
Q

What are the end products of a TG?

A

Free fatty acid and 2 monoglycerides.

95
Q

What is the chemical process that breaks apart polypeptides?

A

Hydrolysis

96
Q

Describe the breakdown of protein.

A

Proteins are broken down first by pepsin into Proteones, peptones, and polypeptides.

Next, trypsin, chymotrypsin, carboxypolypeptide, and proelastase break them down into just polypeptide and amino acids.

Lastly, peptidase breaks down the last polypeptides into just amino acids.

97
Q

Where is pepsin found?

A

Stomach

98
Q

What secretes trypsin, chymotrypsin, carboxypolypeptide, and proelastase?

A

Pancreas

99
Q

What secretes peptidases?

A

Brush border microvilli
Cytosol

100
Q

What are the types of peptidases?

A

Aminopolypeptidases
Dipeptidases

101
Q

What activates pepsinogen into pepsin?

A

Acid, aka HCl

102
Q

What are the functions of HCl in the stomach?

A

Activating pepsin
Kill pathogens
Improve iron/calcium absorption
Inactivating foreign hormones
Denaturing food proteins

103
Q

What can give plasma a yellow color?

A

Chylomicrons

104
Q

What breaks down a chylomicron?

A

Lipoprotein lipase

105
Q

Where do chylomicrons come from?

A

Intestine

106
Q

What remains in a chylomicron after the TG is removed?

A

Cholesterol

107
Q

Where do chylomicrons go once they’re mainly cholesterol?

A

They bind to liver receptors on endothelial cells in the liver sinusoids.

108
Q

What are the 4 types of lipoproteins?

A

VLDL (very low density lipoprotein)
IDL (intermediate density lipoprotein)
LDL (low-density lipoprotein)
HDL (high-density lipoprotein)

109
Q

If I have a lot of HDL, what is the primary thing is it composed of?

A

Proteins over fats.

Proteins are more dense, hence high-density.

Note:
This is why HDL is considered the “good one”

110
Q

What apoprotein mediate LDL?

A

B

111
Q

What apoprotein mediate HDL?

A

E

112
Q

What apoprotein mediates IDL?

A

E

113
Q

What 4 things are found within lipoproteins?

A

TGs
Cholesterol
Phospholipids
Proteins

114
Q

What lipoprotein has no TGs?

A

HDLs

115
Q

What progressively decreases as the lipoproteins increase in density?

A

TG concentration.

VLDL have a lot of TGs.
IDLs have some.
LDL have barely any.
HDL has none.

116
Q

Where is most fat in our body stored?

A

Adipose tissue
Liver

117
Q

What makes up the majority of a fat cell’s volume?

A

TGs

118
Q

When does the liver have high amounts of TGs?

A

Early stages of starvation
DM
Any condition when fat is being used for energy instead of carbs (think ketosis)

119
Q

What are fatty acids split into?

A

Acetyl-CoA

120
Q

What does Acetyl-CoA form when condensed?

A

Acetoacetic acid

121
Q

What is acetoacetic acid + 2 hydrogens broken down into?

A

Beta-hydroxybutyric acid

Acetone

Note:
These plus acetoacetic acid are known as the ketone bodies.

122
Q

What do the ketone bodies do?

A

THey all diffuse freely through liver cell membranes, can be reversed, and are eventually oxidized for energy.

123
Q

What happens if we have very high levels of ketones in our blood?

A

Ketosis.

124
Q

Why is ketosis potentially dangerous?

A

Our body requires oxaloacetate from carb metabolism in order to process acetyl-CoA.

Kreb’s Cycle (KC) is limited without oxaloacetate to use.

Can lead to ketoacidosis if we have enough ketones in our blood to drop our pH.

125
Q

How do we get rid of acetone?

A

Ventilation

126
Q

How long does it take to adapt to ketosis?

A

2 weeks

127
Q

What is cholesterol soluble in?

A

Fat

128
Q

What kind of diet/food type increases blood cholesterol?

A

High saturated fats

High fat = high liver acetyl-CoA = high cholesterol production

129
Q

What happens if i increase how much cholesterol I consume a day?

A

Not much change in blood cholesterol.
Negative feedback control in the liver that will regulate it.

130
Q

What happens to my blood cholesterol if I eat lots of UNsaturated fats?

A

Depression of blood cholesterol

131
Q

Lack of what hormones increases blood cholesterol?

A

Lack of insulin or thyroid hormone

132
Q

What are the 5 factors that affect blood cholesterol?

A

Ingestion of cholesterol = minor changes
Saturated fats = increased cholesterol
Unsaturated fats = decreased cholesterol
Lack of insulin/thyroid hormone = increased cholesterol
Genetic disorders

Medical Physiology (14 decks)

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