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GI Physiology > GI physiology > Flashcards

GI physiology Flashcards

1
Q

Role of mouth and pharynx

A

chops and lubricates food, starts carb digestion, delivers food to oesophagus

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2
Q

Where is saliva secreted from

A

Salivary glands

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3
Q

Role of oesophagus

A

propels food to stomach using peristalsis

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4
Q

role of stomach

A

stores/churns food, carb digestion, initiates protein digestion using protease and pepsin, regulates chyme delivery to duodenum

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5
Q

small intestine

A

principle site of digestion and absorption of nutrients

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6
Q

large intestine role

A

reabsorb fluids and electrolytes, stores faecal matter before delivery to rectum

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7
Q

rectum and anus role

A

regulated expulsion of faeces

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8
Q

4 main roles of the alimentary canal

A

motility, secretion, digestion, absorption

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9
Q

what are layers of mucosa

A

1) mucus membrane
2) lamina propria
3) muscularis mucosae

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10
Q

layers of submucosa

A

1) connective tissue
2) larger blood and lymph vessels
3) glands
4) submucous plexus - neurone network

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11
Q

layers of muscularis externa

A

1) circular muscle layer
2) myenteric plexus - between two muscle layers
3) longitudinal muscle layer

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12
Q

Layers of serosa

A

connective tissue

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13
Q

Explain the electrical activity in smooth muscle cells

A

The small intestine(don’t need an action potential in the stomach) smooth muscle cells are all connected by gap junctions which allows current to flow between all the cells called the interstitial cells of Cajal (ICCs). These act as pacemakers and together form action potentials modulated by neuronal, hormonal and mechanical stimuli. Once the action potential is reach a slow and synchronous wave goes between all the cell. There will only be a contraction if the slow wave amplitude is high enough to reach threshold. The longer it maintains threshold, the longer the contraction

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14
Q

excitatory influences vs inhibitory influence

A

These are part of the parasympathetic system. Excitatory lead to increased gastric, pancreatic and small intestinal secretion and increase blood flow and smooth muscle contraction whereas inhibitory influences stop digestion by relaxing sphincters and stomach

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15
Q

What does the myenteric plexus regulate

A

motility and sphincters

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16
Q

what does the submucous plexus regulate and where is it found

A

epithelia and blood vessels and in the submucosa

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17
Q

what is a short reflex

A

Involves the ANS and stimulates a post-ganglionic fibre which then sends a signal right back to the GI wall. For example distension will cause inhibition of muscle activity in adjacent areas

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18
Q

What is a long reflex

A

a long reflex involves the CNS like a vago-vagal reflex that has both sensory and motor neurones. The gastroileal reflex is where in increase in gastric activity then increases propulsive activity towards the terminal ileum

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19
Q

What is released when longitudinal muscle relaxes and when does it relax

A

relaxes behind the food bolus and releases VIP and NO

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20
Q

What is released when longitudinal muscle contracts

A

Ach and substance P

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21
Q

what is release when circular muscle relaxes

A

VIP and NO

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22
Q

what is released when circular muscle contracts and when does it

A

it contracts after the food bolus and released Ach and substance P

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23
Q

What is segmentation

A

rhythmic contractions of the circular muscle layer found in the muscularis externa

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24
Q

colonic mass movement

A

powerful sweeping contraction forcing faeces into rectum

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25
Q

migrating motor complex

A

sweeping contraction from stomach to terminal ileum a few times an hour

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26
Q

tonic contractions

A

sustained contractions like sphincters are at high pressures

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27
Q

how do sphincters work

A

usually a higher pressure in the distal organ keeps the sphincter closed and it will emit tonic contraction

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28
Q

what is luminal digestion mediated by

A

pancreatic enzymes into the duodenum

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29
Q

what is membrane digestion mediated by

A

enzymes situated at the brush border of epithelial cells

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30
Q

what are the two types of digestion

A

luminal and membrane

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31
Q

assimilation

A

overall process of digestion and absorption

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32
Q

what is the limitation to alpha-amylase

A

It cannot break down terminal alpha-4 linkages, and branch alpha-6 linkages or alpha-4 linkages that area adjacent to branch points

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33
Q

in the apical membrane, which monosaccharides need active transport and which need facilitated diffusion? and which mediators are used?

A

facilitated diffusion - fructose by GLUT5

active transport - glucose and galactose by SGLT1

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34
Q

How do monosaccharides exit the cell into the blood

A

through the basolateral membrane through facilitated diffusion through GLUT2

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35
Q

How is SGLT1 involved in rehydration therapy

A

Sodium is needed to work the SGLT1 so it moves into the cytosol so that glucose can move in as well and this attracts water into the cell since water follows sodium

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36
Q

What are the two enzymes that breakdown protein and where are they found

A

pepsin - in the stomach works best at low PH

pancreatic proteases- released from pancreas and activated in the duodenum

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37
Q

What do brush border proteases do?

A

further break down oligopeptides at the brush border

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38
Q

What do cytoplasmic peptidases do?

A

break down oligopeptides once they are in the cytoplasm

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39
Q

Difference between endopeptidase and exopeptidase

A

Digestive enzymes in the duodenum and endopeptidases break proteins down into oligopeptides whereas exopeptidase break down into single amino acids

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40
Q

How are do amino acids enter the cell?

A

Through difference amino acid transporters, some of which require sodium and some that don’t

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41
Q

how do oligopeptides enter the cell?

A

through H+ dependent co-transporters and are then further broken down in the cytoplasm

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42
Q

how do amino acids leave the basolateral membrane?

A

through Na+ dependent transporters

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43
Q

Which type of diabetes are you more at risk for if you are overweight

A

type 2

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44
Q

What are the different satiation signals?

A

CCK, peptide YY (PYY3-36), glucagon-like peptide 1 (GLP-1), Oxyntomodulin (OXM), obestatin

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45
Q

What are satiation signals released in response to?

A

Eating a meal to indicate to slow eating

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46
Q

Which satiation signals are released from the small intestine?

A

CCK, OXM, Obestatin

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47
Q

Which satiation signals are released from L cells?

A

PYY-36, GLP-1

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48
Q

What happens to insulin and leptin with obesity?

A

they stop telling the body to increase energy burn and to eat less

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49
Q

where is ghrelin released

A

released from the oxyntic cells in the stomach

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50
Q

What is bariatric surgery?

A

surgery that can be used for obesity treatment. A gastric-bypass surgery that allows up to 50% weight loss in a year and it is sustainable since less caloric intake

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51
Q

What causes the stomach to relax to accommodate for food?

A

the vagus nerve

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52
Q

which part of the stomach is food stored and which part is it churned

A

Stored in the fundus and ground in the antrum

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53
Q

what is secreted from the gastric glands?

A

gastric juice and they are in the gastric mucosa

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54
Q

Explain journey of food through stomach

A

1) relaxation of stomach by vagus nerve to accomodate for extra food
2) food enters the orad region where it starts being broken down by pepsin, HCL and salivary amylase
3) stomach contents are slowly propelled to caudad region with weak tonic contractions to allow time for HCL to work
4) gastrin contractions also slowed
5) minimal mixing as it moves down so that the salivary amylase can stay inside the food particles since when expose to HCl will be denatured
6) slow peristaltic contraction driven by slow waves moved the food towards the pylorus and some chyme gets through to duodenum
7) Then chyme rebounds because of velocity of contraction and goes back into body of stomach which mixes food - retropulsion
8) small particles mixed with chyme then move through every time

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55
Q

increase of vagus nerve activity and gastrin release do what to stomach

A

increase stomach emptying

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56
Q

how does the duodenum delay stomach emptying

A

neuronal and hormonal response

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57
Q

how does the hormonal response work

A

enterogastrones like CCK inhibit stomach contractions

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58
Q

what kinds of things influence the neuronal and hormonal response (3)?

A

fat - takes long to digest so would need to delay gastric emptying

acid- acid needs to be neutralised first so takes time for pancreas to produce the bicarbonate (if it is not neutralised the enzymes will not be working as well)

hypertonicity - need to be released slowly since if too much carb and proteins products they will draw water into the lumen instead of water being absorbed and can cause low bp

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59
Q

Where are glands in the stomach found?

A

In the gastric mucosa at the bottom of the pits in the surface

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60
Q

how deep do pits go?

A

from mucosa to submucosa

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61
Q

What does HCL do?

A

Activates pepsinogen to pepsin, denatures proteins and kills most organisms that are ingested with food

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62
Q

What is pepsinogen?

A

Precursor of the peptidase, pepsin and once pepsin is formed it can activated pepsinogen

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63
Q

What does gastroferrin do?

A

Bind Fe2+ so doesn’t become salt

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64
Q

What are the two ways that secretagogues work?

A

Direct – stimulate the parietal cell to secrete more hydrogen into lumen. Indirect – Ach and gastrin can stimulate histamine which will then act on parietal cell

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65
Q

Which pathway do Ach and gastrin use when acting on parietal?

A

PLC pathway

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66
Q

Which pathway does histamine and somatostatin act on

A

AC and cAMP

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67
Q

Which receptors does Ach act on for acid secretion?

A

M3 receptors

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68
Q

Which receptors does gastrin act on?

A

G cell receptors

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69
Q

What changes occur during the cephalic phase?

A

Vagus nerve stimulated to release Ach which directly activates parietal cells. Ach also stimulates gastrin and histamine release and it decreases the inhibitory effect of somatostatin on G cells by inhibiting D cells

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70
Q

How does food in stomach increase digestion?

A

Food buffers the PH so D cells are inhibited and amino acids stimulate G cells

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71
Q

Which cells stimulate histamine and gastrin respectively?

A

Enterochromaffin cells and G cells

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72
Q

How is acid secretion inhibited in the stomach after digestion?

A

Antral PH falls as food exits stomach so D cells starts again. Prostaglandin is secreted which reduces histamine and gastrin

73
Q

Why is the digestion of fats difficult?

A

Because most fats like TAGs and cholesterol esters are insoluble or poorly soluble

74
Q

What is the first step to breaking down fats before bile salts are involved?

A

Mechanical disruption by chewing and mixing in the stomach and small intestine break down the liquids into smaller droplets so that there is more surface area for lipases to act. These droplets are then coated in a multilamellar layer so that they do not join up again

75
Q

What do bile salts do in fat digestion

A

Bile salts further digest these droplets and make them smaller and smaller. First turning them a unilamellar vesicle and then into a mixed micelle

76
Q

What enzyme works in the stomach against fats?

A

Gastric lipase – breaks down some fats since short and medium chains are absorbed in the stomach

77
Q

What stimulates both bile salt and pancreatic lipase release?

A

CCK

78
Q

What could failure to release bile salts result in?

A

lipid malabsorption and vitamin deficiency of fat soluble vitamins

79
Q

How is procolipase activated?

A

By trypsin

80
Q

What does colipase do?

A

Binds to bile salts so that they do not block the lipase attaching to the TAGs

81
Q

How do free fatty acids and monoacylglycerols enter the enterocytes?

A

They are first made neutral by adding a hydrogen and then can diffuse across the membrane

82
Q

Where do chylomicrons drain back into the venous system?

A

At the left venous angle

83
Q

Where is cholesterol picked up when it is absorbed?

A

It is picked up in clatherin coated pits where it attaches to NPC1L1 and then undergoes endocytosis

84
Q

When calcium concentration is high, how is it absorbed?

A

It diffuses through gap junctions into blood

85
Q

How much iron does the body contain

A

Approximately 3-5 grams

86
Q

What does too little iron cause?

A

Microcytic anaemia

87
Q

What does too much iron cause?

A

Excess iron can result in the production of hydroxyl radicals and hydroxide ions which are toxic for liver, pancreas and heart

88
Q

What is the reduced state of iron called?

A

Fe 2+

89
Q

What encourages the reduction of iron?

A

HCl, Vitamin C, gastroferrin from parietal cells, duodenal cytochrome B

90
Q

How is iron transported across the cell?

A

Chaperone protein

91
Q

Where is iron stored and what is it stored as?

A

Iron is stored in the cytoplasm as Fe3+ which is called ferritin

92
Q

After iron leaves the cell, what enzyme oxidizes the iron back to Fe3+?

A

Ferroxidase

93
Q

What causes hereditary chromatosis?

A

A defect in the HFE protein since that is what stops iron being transported to body if there is already too much

94
Q

Where is B12 found and what is the recommended daily amount?

A

In food bound to proteins and daily amount is 6micrograms

95
Q

Why does vitamin B12 have a complex absorbing pathway?

A

It needs to be efficient because it is only present in small amounts in the diet

96
Q

Where is B12 ultimately absorbed and how?

A

Terminal ileum by endocytosis

97
Q

How are fat soluble vitamins absorbed?

A

They passively diffuse into enterocytes where they are incorporated into chylomicrons and released into the lymph system and then venous system

98
Q

Where are fat soluble vitamins stored?

A

Adipose tissue

99
Q

How are water soluble vitamins absorbed?

A

Transport across membrane via Na+ dependent and independent transporters

100
Q

what parts make up the large colon?

A

caecum, appendix, colon, rectum

101
Q

what are the taeniae coli

A

longitudinal smooth muscle layer that is split into three parts

102
Q

how are haustra formed

A

the activity of the taeniae coli and circular muscle layers that are slowly moving

103
Q

what is the difference between the internal and external anal sphincter

A

the internal anal sphincter is thick and is controlled by the autonomic nervous system while the external one is surrounded by the skeletal muscle and is regulated by the somatic system

104
Q

why is it important that the ileocaecal valve is one way

A

it is important that it prevents colonic contents like bacteria coming into the small intestine

105
Q

where is the ileocaecal sphincter

A

several cm proximal to the valve

106
Q

what controls the ileocaecal sphincter

A

positive resting pressure that relaxes when duodenum is distended and contracts when the ascending colon is distended

It is also under control from vagus nerve, sympathetic nerves and hormonal signals

107
Q

where is the appendix attached to the colon

A

at the caecum via the appendiceal orifice

108
Q

what three actions does the gastroileal reflex involve

A
  • relaxation of ileocaecal sphincter
  • increased contraction of ileum
  • delivery of chyme from ileum to caecum
109
Q

What are the main functions of the ascending and transverse colon?

A

absorbing sodium, chlorine, water and short chain fatty acids AFTER they have been fermented by the flora

secreting potassium, bicarbonate and mucus

110
Q

what is the primary function of the descending colon

A

reservoir for storing contents, final drying stage before defeacation

111
Q

What are the three types of cell in the large colon

A

surface epithelial cells (colonocytes), crypt cells and goblet cells

112
Q

What is the function of epithelial cells?

A

absorb electrolytes and therefore also aid in water absorption

113
Q

What is the function of crypt cells

A

secrete ions

114
Q

What is the function of goblet cells in the large colon

A

secrete mucus to form a slippery surface gel and trefoil proteins which help stabilises mucus and help in host defense

115
Q

describe haustration

A

haustration is the movement of the circular muscle which slowly (less frequent than segmentation) mixes content back and forward in the intestine allowing time for absorption

116
Q

Describe mass movement, how often it occurs and what triggers it

A

simultanesous contractions of a large stretch of circular muscle throughout ascending and transverse colon that powerfully drives faeces to the rectum

It occurs 1-3 times per day

usually triggered by a meal with the gastrocolic response

117
Q

how is the internal anal sphincter triggered to open

A

as the rectum fills, it stretches which activates the mechanoreceptors in the rectal wall and causes the sphincter to relax

118
Q

How does the urge to defaecate reach the brain?

A

through afferents to the brain making it aware

119
Q

how do we control the external anal sphincter

A

if it is acceptable to defaecate, the brain sends signals via the pudenal nerve to relax the skeletal muscle but if it is not then the muscle will be contracted

120
Q

What helps stool come out of rectum

A

increasing the intra-abdominal pressure

121
Q

difference between afferent and efferent

A

afferent is towards the CNS and efferent is away from the CNS

122
Q

name some benefits of the flora in colon (4)

A
  • increase intestinal immunity since can compete with pathogens
  • promote motility
  • make vitamin K2 and free fatty acids to be absorbed
  • activate certain drugs
123
Q

describe the differences between nausea, retching and emesis

A

nausea is just an unpleasant sensation in the throat or stomach but there are no muscular contraction. Retching involves rythmic reverse peristaltic contractions but there is no vomit and emesis is when gastric expulsions come out of the mouth

124
Q

Process of vomiting

A
  1. Intestinal slow wave activity stops
  2. contraction from ileum to stomach (opposite of what it should be)
  3. glottis closes so no aspiration
  4. diaphragm and abdo muscles contract
  5. contents ejected
125
Q

What is the largest endocrine organ of the body?

A

small intestine

126
Q

what does the small intestine receive and secrete

A

receive: chyme, pancreatic juice, bile
secrete: intestinal juice

127
Q

What is segmentation? How often does it happen and what controls it?

A

It is the alternating contraction of circular muscle in the small intestine which moves chyme back and forth

it occurs about 12 times per minute; it is more frequent in duodenum but net movement is slow to allow for absorption

initiated by pacemaker cells but the strength is controlled by the parasympathetic system (the more involved the stronger)

128
Q

what is the gastroileal reflex

A

segmentation on an empty stomach that is triggered by gastrin

129
Q

when does peristalsis in small intestine occur and what does it do?

A

peristalsis of the small intestine occurs during fasting times every 90-120 minutes and is a strong contraction that moves through the whole length of intestine to clear any debris and mucus

130
Q

what is role of secretin

A

promotes secretion of pancreatic and biliary bicarbonate

131
Q

What does CCK do?

A

Inhibits gastric emptying

activates secretion of pancreatic enzyme for digestions

relaxes sphincter of Oddi and contraction of gall bladder

enhances secretin action

132
Q

What kind of receptors fo peptide hormones act on?

A

G-protein coupled receptors

133
Q

Where is it released and what does it do GLP-1

A

released from L cells in ileum and stimulates insulin secretion, inhibits glucagon secretion, gastric acid secretion, and emptying

134
Q

Where is GIP or gastric inhibitory peptide released from

A

K cells of duodenum and jejunum

135
Q

List the secretions of the small intestine?

A 
Gastrin
secretin
CCK
GIP
GLP-1
Motilin
Ghrelin
Succus entericus
136
Q

What is the role of bicarbonate secreted by the pancreas?

A

Pancreatic duct cells secrete 1-2L of aqueous NaHCO3- per day. The bicarbonate is important in being able to neutralise acidic chyme so that the enzymes are at optimal PH and it protects the mucosa

137
Q

What are the endocrine secretions of the pancreas

A

insulin, glucagon and somatostatin

138
Q

What are the exocrine secretions of the pancreas?

A

digestive enzymes and NaHCO3- solution

139
Q

Which cells release digestive enzymes and which ones release NaHCO3- solution

A

acinar cells and duct cells

140
Q

What are the 5 main pancreatic enzymes?

A

trypsinogen, chymotrypsinogen, procarboxypeptidase A and B, Pancreatic amylase, Pancreatic Lipase

141
Q

Why are the pancreatic enzymes stored in an inactive form?

A

To prevent self-digestion

142
Q

enzymes are released in response to what being elevated

A

Ca2+

143
Q

what are the three phases of gastric and pancreatic secretion?

A

cepahlic, gastric, intestinal

144
Q

What is the intestinal pathway that leads to digestive enzyme secretion?

A

fat and protein in the duodenum leads to CCK release from I cells which is carried to the pancreatic acinar cells and activates secretion

145
Q

How is secretion of bicarbonate activated in the intestinal phase?

A

acid in the duodenal lumen activates secretin release from S cells which is then carried to the pancreatic duct cells and results in bicarbonate secretion

146
Q

What are the 4 main roles of the liver?

A

metabolism, activation and deactivation of hormones, storage, protection

147
Q

what are the three types of metabolism

A

carbohydrate, fat, protein

148
Q

what does carbohydrate metabolism in the liver involve?

A

gluconeogenesis (produce glucose from amino acids)

glycolysis (form pyruvate and then either lactate or acetyl-coA)

glycogenesis (store glucose as glycogen)

glycogenlysis (release glucose, as required)

149
Q

What does fat metabolism in the liver involve?

A

synthesis of lipoproteins and cholesterol

ketogenesis

processing chylomicron remnants

150
Q

what is cholesterol involved in?

A

needed to make bile acids and steroid hormones

151
Q

what does protein metabolism in the liver involve?

A

synthesis of plasma proteins

converting ammonia to urea

transamination and deamination of amino acids

152
Q

What are some proteins the liver synthesizes

A

coagulation factors
albumin
apolipoproteins

153
Q

what does the liver store?

A
  • fat soluble vitamins
  • iron
  • water soluble B12
  • copper
  • glycogen
154
Q

what does protection of the liver function involve?

A

kupferr cells are liver phagocytes that destroy particulate matter like bacteria and old enterocytes like haemoglobin. They also produce immune factors

155
Q

what substance does the liver detoxify?

A

bilirubin, drugs, ethanol

156
Q

where is bile stored between meals?

A

gall bladder

157
Q

What happens during a meal with bile?

A

during a meal the chyme in the duodenum stimulates CCK and vagal impulses to contract the gall bladder smooth muscle to release bile

The sphincter of Oddi opens so that bile can leave

158
Q

What drains the primary juice into the biliary ductules and ducts

A

canaliculi

159
Q

how are bile salts modified when before they are put into the duodenum?

A

Bicarbonate and water is added by the pancreatic ducts

160
Q

What is bile juice made of?

A

primary biliary acids, water, electrolytes, lipids, phopholipids, cholesterol, IgA, bilirubin, metabolic wastes

161
Q

Why could morphine worsen biliary colic pain?

A

Since it can cause sphincter of Oddi constriction and increase the intrabiliary pressure

162
Q

Where are bile salts reabsorbed to go back to the liver?

A

at the ileum

163
Q

What is added to secondary bile salts in the liver so that they can be reused?

A

glycine and taurine

164
Q

What is the main function of drug metabolism in the liver

A

The liver converts parent drugs to less pharmacologically active, polar metabolites that are not absorbed by the kidneys so that they can then be excreted

165
Q

What is an example of a drug that GAINS activity in the liver?

A

codeine turns into morphine

166
Q

What happens during a phase 1 reaction?

A

drugs are made more polar by adding a chemically reactive group

167
Q

what happens during phase 2 reactions in drug metabolism?

A

add an endogenous compound like glucoronic acid (glucoronidation) which usually results in an inactive product

168
Q

what happens in hepatic failure that could cause encephalopathy

A

detoxification of ammonia fails and is then absorbed into the blood stream

169
Q

Where is most water absobed?

A

small intestine

170
Q

what are the main ways that water moves out of the lumen?

A

transcellular through aquaporins or paracellular through the gap junction in the epithelium

171
Q

what are the main mechanisms of sodium absorption in the postprandial period and where does it occur

A

Na+/glucose co-transport or Na+/amino acid co-transport (both go into the cell) and occurs in the jejunum

172
Q

What is the main mechanism for sodium absorption in the interdigestive period and where does it occur?

A

parallel Na+/H+ and Cl-/HCO3- and occurs in the ileum and colon ( Na and Cl move in and H and HCO3 move out)

173
Q

what causes the Cl- to be absorbed in the small intestine

A

the sodium going into the cell from the Na+ glucose and amino acid transporters leaves a negative lumen so the Cl wants to leave

174
Q

What is a method for sodium absorption in the distal colon?

A

epithelial sodium channels which are increased by aldosterone and are NOT regulated by cAMP like the other methods(which reduces NaCl absorption)

175
Q

what causes Cl to be absorbed in the large intestine?

A

the negative lumen created by epithelial sodium channels

176
Q

where does Cl- secretion occur

A

crypt cells

177
Q

what is the role of CFTR

A

it is how Cl- exits the cell into the lumen if the concentration is too high

178
Q

What activates CFTR

A
  • bacterial endotoxins
  • hormones and neurotransmitters
  • immune cell products
  • some laxatives
179
Q

What are some causes of diarrhoea

A
  • hypermotility
  • reduction in NaCl absorption
  • excessive secretion (increased cAMP and CFTR)
  • poorly absorbed solutes in lumen

GI Physiology (1 decks)

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