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Gastroenterology > Introduction > Flashcards

Introduction Flashcards

1
Q

Explain what catabolic enzymes do

A

they facilitate the chemical breakdown of large molecules into their subunits is performed by hydrolysis

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2
Q

What must carbohydrates be broken down into in order to be absorbed

A

monosaccharides

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3
Q

what must proteins be broken down into in order to be absorbed

A

amino acids

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4
Q

How do proteins get broken down into amino acids

A

proteases hydrolyze proteins into amino acids

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5
Q

What must lipid/fat be broken down into to be absorbed

A

free fatty acids and glycerol

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6
Q

What is meant by ‘mastication’

A

chewing

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7
Q

what is meant by ‘deglutition’

A

swallowing

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8
Q

define peristalsis

A

rhythmic wavelike contractions that move food in one direction towards the anus

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9
Q

define segmentation

A

strong rhythmic contractions that result in the mixing of digestive tract contents

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10
Q

Explain the exocrine secretions of the GIT

A

includes the secretions of water, enzymes, acid etc. into the lumen of the digestive tract to aid in digestion of ingested food

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11
Q

Explain the endocrine secretions of the GIT

A

hormones released into the blood that help regulate digestion

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12
Q

List the components of the GIT

A
  • oral cavity
  • pharynx
  • oesophagus
  • stomach
  • small intestine
  • large intestine (colon)
  • rectum
  • anal canal
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13
Q

List the accessory digestive organs

A
  • teeth
  • tongue
  • salivary glands
  • liver
  • gallbladder
  • pancreas
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14
Q

What is the mucosa of the GIT lumen comprised of

A

a single layer of simple columnar epithelial cells supported upon a thin layer of connective tissue

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15
Q

what is the thin layer of connective tissue of the GIT mucosa called

A

lamina propria

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16
Q

In what layer of GIT are lymph nodes found

A

lamina propria

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17
Q

What are the main functions of the mucosa

A
  • absorption of nutrients
  • secretes digestive juices
  • secretion of mucus
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18
Q

which cells secrete mucus

A

goblet cells

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19
Q

Explain the submucosa layer of the GIT

A
  • rich in blood and lymph vessels
  • absorbed nutrients from the gut lumen enter blood and lymph vessels
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20
Q

Explain the submucosal plexus of the GIT

A

this nerve plexus provides the nerve supply to the muscularis mucosae, regulates absorption and secretion

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21
Q

What is an alternative name for the submucosal plexus

A

Meissner’s plexus

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22
Q

Describe the muscularis layer of the GIT

A

composed of two layers of smooth muscle layers
- circular and longitudinal muscles layers- segmental contractions and peristatic movements

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23
Q

what neuronally regulates muscular contractions of the GIT

A

myenteric plexus (auerbach’s plexus)

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24
Q

Describe the serosa layer of GIT

A

the outer wall of the git and is composed of areolar connective tissue
the outer layer of serosa that is exposed to the abdominal cavity is also covered in simple squamous epithelium

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25
Q

What effect does activation of PNS have on digestive system

A

stimulates motility and secretions of the digestive system

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26
Q

What effect does activation of SNS have on digestive system

A

reduces motility and secretions of digestive tract

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27
Q

What is the ENS

A

enteric nervous system- contained completely within the digestive tract
contains sensory neurons, interneurons and motor neurons thus is capable of regulating various aspects of the digestive system independent of external influences

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28
Q

Describe the process of peristalsis

A

wavelike movement of luminal contents (bolus) through the GIT that is regulated by the ENS.
Movement of a bolus of food through the GIT occurs as the circular layer of smooth muscle contracts behind the bolus relaxes. This is followed by shortening of the tube as the longitudinal muscles contract encourages movements of the bolus forwards.

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29
Q

What leads to the contraction of smooth muscle behind a bolus in peristalsis

A

motor neurons which are excited by Ach and in turn release ACh and substance P stimulating smooth muscle contraction

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30
Q

What leads to relaxation of smooth muscle in front of the bolus in peristalsis

A

motor neurons in front release inhibitory neurotransmitters nitric oxide and vasoactive intestinal peptide (VIP) inducing smooth muscle relaxation

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31
Q

Name the enzyme in saliva and its role

A

amylase / pytalin - begins the process of breaking down starch (polysaccharide)

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32
Q

Name the three salivary glands

A
  • parotid gland
  • submandibular gland
  • sublingual gland
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33
Q

What are the three phases of deglutination

A
  1. oral
  2. pharyngeal
  3. oesophageal
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34
Q

describe the oral phase of swallowing

A

is voluntary
involves the movement of food to the back of the mouth by the tongue
Oropharyngeal receptors detecting the food bolus stimulate the pharyngeal phased

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35
Q

describe the pharyngeal phase of swallowing

A

is under reflex control
the soft palate lifts up to block the nasopharynx ensuring food does not enter the nasal cavity
to prevent choking/aspiration of food into the airways the vocal cords close off the opening of the larynx and the epiglottis folds down to cover the vocal cords.
the larynx is also physically moved away from the path of the food bolus. the upper esophageal sphincter also relax to accommodate the bolus of food…. all this occurs very rapidly in approx 1 second.

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36
Q

describe the esophageal phase of swallowing

A

the bolus of food is moved towards the stomach by peristaltic contractions
roughly 5-6 seconds
under autonomic control

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37
Q

What cells line the esophagus

A

stratified squamous epithelia

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38
Q

how does food move through the esophagus

A

peristalsis

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39
Q

What kind of movements are seen in the stomach

A

muscular contractions of stomach smooth muscle results in grinding / trituration

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40
Q

what is created in the stomach when contents are mixed together

A

chyme

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41
Q

what is the function of the stomach

A
  • store food
  • secrete digestive juices
  • initiate the digestion of proteins
  • kill bacteria with a low pH (less than 2)
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42
Q

What is the upper and lower section of the stomach called

A

upper- fundus
lower- body/corpus
most distal - pyloric region (antrum and pyloric sphincter)

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43
Q

what are the long folds on the inner surface of the stomach called

A

rugae

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44
Q

what do parietal cells secrete

A

hydrochloric acid (HCl) and intrinsic factor

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45
Q

what do chief cells secrete

A

inactive enzyme pepsinogen (active - pepsin- begins protein digestion)

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46
Q

what do ECL (enterochromaffin like cells) secrete

A

histamine and serotonin

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47
Q

what do G cells secrete

A

gastrin (hormone)

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48
Q

what do D cell secrete

A

somatostatin (hormone)

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49
Q

what hormone secreted in the stomach signals hunger to the brain

A

ghrelin

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50
Q

Explain HCl secretion on the luminal side

A
  • parietal cells pump H+ into lumen to reduce pH via active transport (H+/K+ ATPase pumps)
  • the K+/Cl- co transporter exchanges K+ for Cl-
  • in the lumen of the stomach H+ and Cl- are attracted to each other forming HCl.
  • structural changes on apical surface of parietal cells increase surface area to facilitate insertion of more H+/K+ pumps
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51
Q

What is the lowest pH value in gastric lumen

A

0.8

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52
Q

Explain HCl secretion on the basolateral membrane of the parietal cells

A
  • Cl- is taken into the cell against its electrochemical gradient by coupling it’s transport with bicarbonate using Cl-/HCO3- transporters
  • bicarbonate travels across the basolateral membrane in the opposite direction (alkaline tide)
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53
Q

What regulates HCl secretiomn

A
  • gastrin (stimulates parietal cells directly)
  • gastrin also stimulates ECL cells to release histamine the most potent stimulator of parietal cells.
  • the vagus nerve of the PNS also stimulates both parietal and ECL to increase HCl secretion
    –> synergistic effect
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54
Q

What happens in the acidic environment of the stomach

A
  1. destroys foreign pathogens
  2. denatures proteins
  3. converts pepsinogen into pepsin (active in acidic environment)
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55
Q

what does pepsin break down

A

ingested proteins into smaller peptides

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56
Q

how does the stomach protect itself from gastric juices and pepsin

A
  • thick layer of mucous
  • secretion of HCO3- from epithelial cells
  • tight junctions between epithelial cells prevent the leak of acid or pepsin into underlying submucosa
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57
Q

what substances are commonly absorbed across the gastric wall

A

alcohol and aspirin

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58
Q

List the three sections of the small intestine in order

A

duodenum
jejunum
ileum

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59
Q

describe the duodenum

A

starts at the pyloric sphincter and is approximately 20-30 cm long
responsible for the absorption of carbohydrates, lipids, amino acids, calcium and iron

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60
Q

describe the jejunum

A

takes up the next 2/5 of small intestine
absorbs similar nutrients to the duodenum

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61
Q

describe the ileum

A

primarily absorbs bile salts, vitamin B12, water and electrolytes
ends at ileocecal valve that opens into large intestine.

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62
Q

what are the large folds in the small intestine called

A

plicae circulares (circular folds) formed by the mucosa and submucosa

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63
Q

what are the microscopic folds in the small intestine called

A

villi

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64
Q

What are microvilli

A

epithelial cells of small intestine mucosa have numerous folding’s on their apical surface - brush border, which further increase the surface area of the small intestine facilitating absorption

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65
Q

What cell types cover villi

A
  • epithelial cells which absorb nutrients
  • goblet cells which secrete mucus
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66
Q

What supplies villus

A

blood and lymph - carry absorbed nutrients away

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67
Q

what is carried away by the blood supply of the villus

A

absorbed sugars and amino acids

68
Q

The _____ of the lymph system carry away absorbed fats in the villi

A

lacteals

69
Q

What is the name for the intestinal crypts found at the base of villi:

A

Crypts of Lieberkühn

70
Q

What role do paneth cells have in the intestinal crypts

A

secrete antibacterial lysozymes and defensins that protect against pathogens

71
Q

What is the role of intestinal stem cells

A

divide by mitosis to replenish themselves and to create new epithelial or goblet cells which then migrate up towards the villi

72
Q

Where do cells at the tip of the villus which undergo apoptosis go

A

they are shed into the lumen.

73
Q

how often is the intestinal epithelium renewed

A

every 5-7 days

74
Q

What is the role of microvilli

A

they increase the surface area of the mucosa for the absorption of nutrients and also contain digestive enzymes for carbohydrate and protein breakdown

75
Q

What is the role of enterokinase

A

converts an inactive protein digesting enzyme called trypsinogen into its active form trypsin

76
Q

what role does trypsin have

A

activates other inactive digestive enzymes that are released into the gut from the pancreas.

77
Q

What contraction/motility is seen in the small intestine

A
  • weak peristalsis
  • segmentation
78
Q

why is peristalsis weak and slow in the small intestine

A

slow motility provides adequate time for proper digestion and absorption of nutrients

79
Q

what cells are responsible for the rhythm of contraction in the small intestine

A

interstitial cells of cajal

80
Q

where are ICC found

A

in the muscularis layer

81
Q

what are the main functions of the large intestine / colon

A
  • absorb water
  • electrolytes
  • certain vitamins
82
Q

List the parts of the colon in order from when contents pass through

A
  • ascending colon
  • transverse colon
  • descending colon
  • sigmoid colon
  • rectum
  • anal canal
83
Q

what is the major difference between small and large intestine mucosa

A

no villi present in the large intestine

84
Q

What muscle is the internal anal sphincter composed of

A

smooth muscle (involuntary)

85
Q

what type of muscle is the external anal sphincter composed of

A

striated muscle (voluntary)

86
Q

How much bacteria is estimated to be in the gut microbiome

A

10 ^14

87
Q

What vitamins do we obtain from the bacteria

A

vitamin K and B

88
Q

what does bacteria in gut ferment

A

indigestible short chain fatty acids

89
Q

what does the breakdown of indigestible short chain fatty acids by the bacteria in the gut via fermentation provide

A

calories (up to 10% of total intake)

90
Q

Define diarrhoea

A

increase in stool frequency and/or volume
or
decrease in stool consistency`

91
Q

What is osmotic diarrhoea

A

unabsorbed dietary nutrient - fluid retained in intestine (e.g., lactase deficiency)

92
Q

what is secretory diarrhoea

A

endogenously triggered secretions of fluid and electrolytes (e.g., diarrheal diseases)
- this is a significant cause of morbidity and mortality in developing countries.

93
Q

Explain the use of ORS

A

oral rehydration solutions - contain various amounts of glucose, Na+, Cl- and HCO3- …. provides energy and drives water back into body

94
Q

What kind of gland is the pancreas

A

both an endocrine and exocrine

95
Q

what does the endocrine pancreas secrete

A

hormones (from cells of the islets of Langerhans) into the blood - primarily to regulate blood glucose levels.

96
Q

what does the exocrine pancreas do

A

secretes digestive pancreatic juices into the duodenum via the pancreatic duct

97
Q

what is an acini

A

the exocrine secretory unit of the pancreas which create the pancreatic juices

98
Q

what does the pancreatic juices contain

A
  1. bicarbonate for acid neutralization
  2. inactive enzymes to aid with digestion
99
Q

Explain acid neutralization by the pancreas (in detail)

A
  • The cells that line the ductules secrete a high concentration of bicarbonate into the lumen whilst absorbing Cl-. Water follows the movement of bicarbonate into the lumen and as a result, 1-2 litres of pancreatic juice is secreted per day.
  • Na+/HCO3- cotransporters on the basolateral membrane moves HCO3- into the cell. Bicarbonate is also synthesised in the cell (action of carbonic anhydrase).
  • Bicarbonate is released into the lumen of the ductule in exchange for a Cl- anion. Cl- leaks back into the ductule through cystic fibrosis transmembrane conductance regulator (CFTR).
  • Bicarbonate in pancreatic juice neutralises highly acidic chyme from the stomach.
100
Q

What digestive enzyme(s) from the pancreas digests carbohydrates

A

amylase

101
Q

What digestive enzyme(s) from the pancreas digests proteins

A
  • trypsin
  • chymotrypsin
  • elastase
  • carboxypeptidase
102
Q

What digestive enzyme(s) from the pancreas digests fatty acids from phospholipids

A

phospholipase

103
Q

What digestive enzyme(s) from the pancreas digests fatty acids from glycerol

A

lipase

104
Q

What digestive enzyme(s) from the pancreas releases cholesterol from other molecules

A

cholesterol esterases

105
Q

What digestive enzyme(s) from the pancreas digests RNA

A

ribonuclease

106
Q

What digestive enzyme(s) from the pancreas digests DNA

A

deoxyribonuclease

107
Q

what are pancreatic inactive enzymes called

A

zymogens

108
Q

How is trypsinogen (zymogen) activated

A

activated within the small intestine by the enzyme enterokinase that is found anchored to the brush boarder.
Enterokinase converts trypsinogen into trypsin, then trypsin activates other pancreatic zymogens.

109
Q

list mechanisms that protect pancreatic from self digestion

A
  • zymogens
  • stored at low pH in impermeable vesicles with trypsin inhibitors.
110
Q

what are the cells of the liver called

A

hepatocytes

111
Q

what separates hepatic plates

A

capillary spaces called sinusoids

112
Q

what is the role of fenestrae

A

increases permeability

113
Q

what effect does chronic exposure of toxins result in in terms of the liver

A

excessive collagen deposition causing liver fibrosis that alters liver function.

114
Q

What are the functions of the liver

A
  • synthesis and secretion of bile
  • detoxification
  • regulate blood glucose levels
  • synthesis of plasma proteins
115
Q

what is the function of bile

A

emulsifies the fats in the chyme - solubilizes lipids to increase the surface area available for fat digesting enzymes to act

116
Q

how does the liver detoxify

A

kupffer cells line the sinusoids of the liver and act via phagocytosis to remove foreign chemicals and debris

117
Q

what plasma proteins are synthesized in the liver

A

albumin, plasma globulins, fibrinogen, angiotensinogen and clotting factors

118
Q

what is glycogenesis

A

storage of energy as glycogen

119
Q

what is lipogenesis

A

storage of energy in the form of triglycerides

120
Q

what is glycogenolysis

A

breakdown of glycogen into glucose

121
Q

what is gluconeogenesis

A

the synthesis of glucose from non carbohydrate sources (e.g., amino acids)

122
Q

what does the liver convert free fatty acids into during fasting

A

ketone bodies

123
Q

What kind of blood is in the hepatic portal veins

A

nutrient rich but O2 poor

124
Q

where does the blood leaving the liver go

A

into the heart via vena cava

125
Q

what kind of blood is in the hepatic artery

A

O2 rich

126
Q

How is bile secreted from the liver

A

bile is secreted into bile canaliculi which is then drained by the bile ducts which converge to form hepatic ductts

127
Q

where is bile reabsorbed following use

A

terminal ileum, then returned to the liver via hepatic portal vein.

128
Q

what is a bile salt

A

bile acids conjugated with amino acids glycine or taurine

129
Q

what is a micelle in terms of bile salts

A

in aqueous solution bile salts form micelles - hydrophobic regions are located in the center and hydrophillic regions are face the water and surround the micelle

130
Q

what is emulsification

A

refers to the breakdown of large globules of fat into smaller globules

131
Q

where is bilirubin produced

A

spleen
liver
bone marroww

132
Q

what is bilirubin a breakdown product of

A

haemoglobin

133
Q

what is conjugated bilirubin converted to by intestinal bacteria

A

urobiliogen

134
Q

what does bilirubin conjugate with

A

glucuronic acid

135
Q

what happens to urobilinogen

A

reabsorbed by GIT - kidneys filter in to blood plasma where its derivatives produce the yellow colour associated with urine

136
Q

how does kupffer cells recognize blood borne bacteria

A

PAMPs (pattern associated molecular patterns)

137
Q

what is deamination

A

the breakdown of amino acids in the liver which produces toxic molecule ammonia. Liver contains enzymes which convert ammonia to urea which is then secreted into the blood and cleared by kidneys

138
Q

what is the role of the gallbladder

A

stores and concentrates bile by removing water (thus acidifies)

139
Q

how does bile get into gallbladder

A

bile drains from liver via hepatic ducts and into gallbladder via the cystic duct

140
Q

how does the bile duct deliver bile into the duodenum

A

via the duodenal papilla

141
Q

during fasting when there is no food to digest the __________ __ _____ at the end of the common bile duct closes which forces bile back up into the gallbladder for storage

A

sphincter of Oddi

142
Q

what is the major component of gallstones

A

cholesterol

143
Q

what procedure results in the removal of the gallbladder

A

laparoscopic cholecystectomy

144
Q

define the cephalic phase of digestion

A

The sight, smell or taste of food can reflexively stimulate secretions of the gastric system (e.g. saliva from the salivary glands, gastric juices from the stomach) via the autonomic nervous system. This primes the digestive system to deal with incoming food.

145
Q

define the gastric phase of digestion

A

Gastric distension and arrival of nutrients into the stomach stimulates neural and endocrine responses

146
Q

define the intestinal phase of digestion

A

the intestine response to the arrival of nutrients and acidic chyme from the stomach

147
Q

what nerve is responsible for the cephalic phase of digestion

A

vagus nerve

148
Q

what does activation of the vagus nerve stimulate specifically

A
  • chief cells to secrete pepsinogen
  • parietal cells to secrete HCl (directly and also indirectly via G cells)
  • Gastrin from G cells to stimulate ECL cells to release histamine (increases HCL secretion)
149
Q

what macronutrient in the stomach leads to increased gastrin secretion

A

protein

150
Q

what macronutrient in the stomach leads to inhibiting gastrin secretion

A

fats

151
Q

explain the positive feedback in the gastric phase

A

As more HCl and pepsinogen are produced, more proteins are digested and thus more short peptides and amino acids are made available to stimulate the G-cells. As a result, more gastrin is produced which in turn promotes the further production of pepsinogen and HCl

152
Q

explain the negative feedback in the gastric phase

A

As more H+ cations are secreted into the lumen of the stomach the pH of the gastric juice drops. Low pH inhibits G-cells and gastrin release. Low pH also stimulates D-cells release inhibitory somatostatin

153
Q

What does entry of chyme into the small intestine stimulate specifically

A
  • sensory receptors of vagus which are sensitive to osmolality and mechanical distension
  • the secretion of hormones such as cholecystokinin, somatostatin and GLP-1… these are inhibitory to gastric secretion
154
Q

What gastrointestinal hormones are responsible for the increase in the release of insulin

A

incretin
and glucose dependent insulinotropic peptide (GIP)

155
Q

Define the gastroileal reflex

A

Increased gastric activity causes increased motility of the ileum and increased movements of chyme through the ileocecal sphincter.

156
Q

what effect does insulin release have on blood glucose levels

A

lower blood glucose concentration

157
Q

define the ileogastric reflex

A

Distension of the ileum causes a decrease in gastric motility.

158
Q

Define the intestino-intestinal reflexes

A

Over distension of one intestinal segment causes relaxation throughout the rest of the intestine

159
Q

what stimulates the secretion of pancreatic juices

A

the arrival of chyme into the duodenum leads to the acinar cells being stimulated by ACh released from vagus nerve and cholecystokinin (CCK)

160
Q

What is the negative feedback in the regulation of pancreatic juice

A

duodenal hormone secretin produced in response to low pH within the duodenum on arrival of gastric chyme.
Secretin stimulates the secretion of bicarbonate and water from the pancreas - bicarbonate neutralizes the acidic chyme

161
Q

REGULATION OF BILE

A

neural - ACh
CCK
secretin - to secrete bicarbonate in the bile

162
Q

what is the role of brush border enzymes

A

form monosaccharides (glucose, galactose and fructose) which can be absorbed across the epithelial membrane by secondary active transport (SGLT1, GLUT5)

163
Q

What does the action of pepsin lead to

A

formation of polypeptides (v few free amino acids)

164
Q

what is the role of endopeptodases

A

digest polypeptides chains into smaller peptide by breaking bonds

165
Q

what is the role of exopeptidases

A

remove amino acids from the end of peptide chains

166
Q

what is the name of the structure formed when proteins are bound to the resynthesized triglycerides and phospholipids

A

chylomicrons

167
Q

how are chylomicrons absorbed

A

they are secreted by exocytosis and absorbed into the lacteal in villi

Gastroenterology (1 decks)

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