GI physiology Flashcards
1
Q
Role of mouth and pharynx
A
chops and lubricates food, starts carb digestion, delivers food to oesophagus
2
Q
Where is saliva secreted from
A
Salivary glands
3
Q
Role of oesophagus
A
propels food to stomach using peristalsis
4
Q
role of stomach
A
stores/churns food, carb digestion, initiates protein digestion using protease and pepsin, regulates chyme delivery to duodenum
5
Q
small intestine
A
principle site of digestion and absorption of nutrients
6
Q
large intestine role
A
reabsorb fluids and electrolytes, stores faecal matter before delivery to rectum
7
Q
rectum and anus role
A
regulated expulsion of faeces
8
Q
4 main roles of the alimentary canal
A
motility, secretion, digestion, absorption
9
Q
what are layers of mucosa
A
1) mucus membrane
2) lamina propria
3) muscularis mucosae
10
Q
layers of submucosa
A
1) connective tissue
2) larger blood and lymph vessels
3) glands
4) submucous plexus - neurone network
11
Q
layers of muscularis externa
A
1) circular muscle layer
2) myenteric plexus - between two muscle layers
3) longitudinal muscle layer
12
Q
Layers of serosa
A
connective tissue
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
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
15
Q
What does the myenteric plexus regulate
A
motility and sphincters
16
Q
what does the submucous plexus regulate and where is it found
A
epithelia and blood vessels and in the submucosa
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
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
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
20
Q
What is released when longitudinal muscle contracts
A
Ach and substance P
21
Q
what is release when circular muscle relaxes
A
VIP and NO
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
23
Q
What is segmentation
A
rhythmic contractions of the circular muscle layer found in the muscularis externa
24
Q
colonic mass movement
A
powerful sweeping contraction forcing faeces into rectum
25
migrating motor complex
sweeping contraction from stomach to terminal ileum a few times an hour
26
tonic contractions
sustained contractions like sphincters are at high pressures
27
how do sphincters work
usually a higher pressure in the distal organ keeps the sphincter closed and it will emit tonic contraction
28
what is luminal digestion mediated by
pancreatic enzymes into the duodenum
29
what is membrane digestion mediated by
enzymes situated at the brush border of epithelial cells
30
what are the two types of digestion
luminal and membrane
31
assimilation
overall process of digestion and absorption
32
what is the limitation to alpha-amylase
It cannot break down terminal alpha-4 linkages, and branch alpha-6 linkages or alpha-4 linkages that area adjacent to branch points
33
in the apical membrane, which monosaccharides need active transport and which need facilitated diffusion? and which mediators are used?
facilitated diffusion - fructose by GLUT5
| active transport - glucose and galactose by SGLT1
34
How do monosaccharides exit the cell into the blood
through the basolateral membrane through facilitated diffusion through GLUT2
35
How is SGLT1 involved in rehydration therapy
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
36
What are the two enzymes that breakdown protein and where are they found
pepsin - in the stomach works best at low PH
| pancreatic proteases- released from pancreas and activated in the duodenum
37
What do brush border proteases do?
further break down oligopeptides at the brush border
38
What do cytoplasmic peptidases do?
break down oligopeptides once they are in the cytoplasm
39
Difference between endopeptidase and exopeptidase
Digestive enzymes in the duodenum and endopeptidases break proteins down into oligopeptides whereas exopeptidase break down into single amino acids
40
How are do amino acids enter the cell?
Through difference amino acid transporters, some of which require sodium and some that don't
41
how do oligopeptides enter the cell?
through H+ dependent co-transporters and are then further broken down in the cytoplasm
42
how do amino acids leave the basolateral membrane?
through Na+ dependent transporters
43
Which type of diabetes are you more at risk for if you are overweight
type 2
44
What are the different satiation signals?
CCK, peptide YY (PYY3-36), glucagon-like peptide 1 (GLP-1), Oxyntomodulin (OXM), obestatin
45
What are satiation signals released in response to?
Eating a meal to indicate to slow eating
46
Which satiation signals are released from the small intestine?
CCK, OXM, Obestatin
47
Which satiation signals are released from L cells?
PYY-36, GLP-1
48
What happens to insulin and leptin with obesity?
they stop telling the body to increase energy burn and to eat less
49
where is ghrelin released
released from the oxyntic cells in the stomach
50
What is bariatric surgery?
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
51
What causes the stomach to relax to accommodate for food?
the vagus nerve
52
which part of the stomach is food stored and which part is it churned
Stored in the fundus and ground in the antrum
53
what is secreted from the gastric glands?
gastric juice and they are in the gastric mucosa
54
Explain journey of food through stomach
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
55
increase of vagus nerve activity and gastrin release do what to stomach
increase stomach emptying
56
how does the duodenum delay stomach emptying
neuronal and hormonal response
57
how does the hormonal response work
enterogastrones like CCK inhibit stomach contractions
58
what kinds of things influence the neuronal and hormonal response (3)?
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
59
Where are glands in the stomach found?
In the gastric mucosa at the bottom of the pits in the surface
60
how deep do pits go?
from mucosa to submucosa
61
What does HCL do?
Activates pepsinogen to pepsin, denatures proteins and kills most organisms that are ingested with food
62
What is pepsinogen?
Precursor of the peptidase, pepsin and once pepsin is formed it can activated pepsinogen
63
What does gastroferrin do?
Bind Fe2+ so doesn't become salt
64
What are the two ways that secretagogues work?
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
65
Which pathway do Ach and gastrin use when acting on parietal?
PLC pathway
66
Which pathway does histamine and somatostatin act on
AC and cAMP
67
Which receptors does Ach act on for acid secretion?
M3 receptors
68
Which receptors does gastrin act on?
G cell receptors
69
What changes occur during the cephalic phase?
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
70
How does food in stomach increase digestion?
Food buffers the PH so D cells are inhibited and amino acids stimulate G cells
71
Which cells stimulate histamine and gastrin respectively?
Enterochromaffin cells and G cells
72
How is acid secretion inhibited in the stomach after digestion?
Antral PH falls as food exits stomach so D cells starts again. Prostaglandin is secreted which reduces histamine and gastrin
73
Why is the digestion of fats difficult?
Because most fats like TAGs and cholesterol esters are insoluble or poorly soluble
74
What is the first step to breaking down fats before bile salts are involved?
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
What do bile salts do in fat digestion
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
What enzyme works in the stomach against fats?
Gastric lipase – breaks down some fats since short and medium chains are absorbed in the stomach
77
What stimulates both bile salt and pancreatic lipase release?
CCK
78
What could failure to release bile salts result in?
lipid malabsorption and vitamin deficiency of fat soluble vitamins
79
How is procolipase activated?
By trypsin
80
What does colipase do?
Binds to bile salts so that they do not block the lipase attaching to the TAGs
81
How do free fatty acids and monoacylglycerols enter the enterocytes?
They are first made neutral by adding a hydrogen and then can diffuse across the membrane
82
Where do chylomicrons drain back into the venous system?
At the left venous angle
83
Where is cholesterol picked up when it is absorbed?
It is picked up in clatherin coated pits where it attaches to NPC1L1 and then undergoes endocytosis
84
When calcium concentration is high, how is it absorbed?
It diffuses through gap junctions into blood
85
How much iron does the body contain
Approximately 3-5 grams
86
What does too little iron cause?
Microcytic anaemia
87
What does too much iron cause?
Excess iron can result in the production of hydroxyl radicals and hydroxide ions which are toxic for liver, pancreas and heart
88
What is the reduced state of iron called?
Fe 2+
89
What encourages the reduction of iron?
HCl, Vitamin C, gastroferrin from parietal cells, duodenal cytochrome B
90
How is iron transported across the cell?
Chaperone protein
91
Where is iron stored and what is it stored as?
Iron is stored in the cytoplasm as Fe3+ which is called ferritin
92
After iron leaves the cell, what enzyme oxidizes the iron back to Fe3+?
Ferroxidase
93
What causes hereditary chromatosis?
A defect in the HFE protein since that is what stops iron being transported to body if there is already too much
94
Where is B12 found and what is the recommended daily amount?
In food bound to proteins and daily amount is 6micrograms
95
Why does vitamin B12 have a complex absorbing pathway?
It needs to be efficient because it is only present in small amounts in the diet
96
Where is B12 ultimately absorbed and how?
Terminal ileum by endocytosis
97
How are fat soluble vitamins absorbed?
They passively diffuse into enterocytes where they are incorporated into chylomicrons and released into the lymph system and then venous system
98
Where are fat soluble vitamins stored?
Adipose tissue
99
How are water soluble vitamins absorbed?
Transport across membrane via Na+ dependent and independent transporters
100
what parts make up the large colon?
caecum, appendix, colon, rectum
101
what are the taeniae coli
longitudinal smooth muscle layer that is split into three parts
102
how are haustra formed
the activity of the taeniae coli and circular muscle layers that are slowly moving
103
what is the difference between the internal and external anal sphincter
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
why is it important that the ileocaecal valve is one way
it is important that it prevents colonic contents like bacteria coming into the small intestine
105
where is the ileocaecal sphincter
several cm proximal to the valve
106
what controls the ileocaecal sphincter
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
where is the appendix attached to the colon
at the caecum via the appendiceal orifice
108
what three actions does the gastroileal reflex involve
- relaxation of ileocaecal sphincter
- increased contraction of ileum
- delivery of chyme from ileum to caecum
109
What are the main functions of the ascending and transverse colon?
absorbing sodium, chlorine, water and short chain fatty acids AFTER they have been fermented by the flora
secreting potassium, bicarbonate and mucus
110
what is the primary function of the descending colon
reservoir for storing contents, final drying stage before defeacation
111
What are the three types of cell in the large colon
surface epithelial cells (colonocytes), crypt cells and goblet cells
112
What is the function of epithelial cells?
absorb electrolytes and therefore also aid in water absorption
113
What is the function of crypt cells
secrete ions
114
What is the function of goblet cells in the large colon
secrete mucus to form a slippery surface gel and trefoil proteins which help stabilises mucus and help in host defense
115
describe haustration
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
Describe mass movement, how often it occurs and what triggers it
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
how is the internal anal sphincter triggered to open
as the rectum fills, it stretches which activates the mechanoreceptors in the rectal wall and causes the sphincter to relax
118
How does the urge to defaecate reach the brain?
through afferents to the brain making it aware
119
how do we control the external anal sphincter
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
What helps stool come out of rectum
increasing the intra-abdominal pressure
121
difference between afferent and efferent
afferent is towards the CNS and efferent is away from the CNS
122
name some benefits of the flora in colon (4)
- increase intestinal immunity since can compete with pathogens
- promote motility
- make vitamin K2 and free fatty acids to be absorbed
- activate certain drugs
123
describe the differences between nausea, retching and emesis
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
Process of vomiting
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
What is the largest endocrine organ of the body?
small intestine
126
what does the small intestine receive and secrete
receive: chyme, pancreatic juice, bile
secrete: intestinal juice
127
What is segmentation? How often does it happen and what controls it?
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
what is the gastroileal reflex
segmentation on an empty stomach that is triggered by gastrin
129
when does peristalsis in small intestine occur and what does it do?
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
what is role of secretin
promotes secretion of pancreatic and biliary bicarbonate
131
What does CCK do?
Inhibits gastric emptying
activates secretion of pancreatic enzyme for digestions
relaxes sphincter of Oddi and contraction of gall bladder
enhances secretin action
132
What kind of receptors fo peptide hormones act on?
G-protein coupled receptors
133
Where is it released and what does it do GLP-1
released from L cells in ileum and stimulates insulin secretion, inhibits glucagon secretion, gastric acid secretion, and emptying
134
Where is GIP or gastric inhibitory peptide released from
K cells of duodenum and jejunum
135
List the secretions of the small intestine?
```
Gastrin
secretin
CCK
GIP
GLP-1
Motilin
Ghrelin
Succus entericus
```
136
What is the role of bicarbonate secreted by the pancreas?
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
What are the endocrine secretions of the pancreas
insulin, glucagon and somatostatin
138
What are the exocrine secretions of the pancreas?
digestive enzymes and NaHCO3- solution
139
Which cells release digestive enzymes and which ones release NaHCO3- solution
acinar cells and duct cells
140
What are the 5 main pancreatic enzymes?
trypsinogen, chymotrypsinogen, procarboxypeptidase A and B, Pancreatic amylase, Pancreatic Lipase
141
Why are the pancreatic enzymes stored in an inactive form?
To prevent self-digestion
142
enzymes are released in response to what being elevated
Ca2+
143
what are the three phases of gastric and pancreatic secretion?
cepahlic, gastric, intestinal
144
What is the intestinal pathway that leads to digestive enzyme secretion?
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
How is secretion of bicarbonate activated in the intestinal phase?
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
What are the 4 main roles of the liver?
metabolism, activation and deactivation of hormones, storage, protection
147
what are the three types of metabolism
carbohydrate, fat, protein
148
what does carbohydrate metabolism in the liver involve?
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
What does fat metabolism in the liver involve?
synthesis of lipoproteins and cholesterol
ketogenesis
processing chylomicron remnants
150
what is cholesterol involved in?
needed to make bile acids and steroid hormones
151
what does protein metabolism in the liver involve?
synthesis of plasma proteins
converting ammonia to urea
transamination and deamination of amino acids
152
What are some proteins the liver synthesizes
coagulation factors
albumin
apolipoproteins
153
what does the liver store?
- fat soluble vitamins
- iron
- water soluble B12
- copper
- glycogen
154
what does protection of the liver function involve?
kupferr cells are liver phagocytes that destroy particulate matter like bacteria and old enterocytes like haemoglobin. They also produce immune factors
155
what substance does the liver detoxify?
bilirubin, drugs, ethanol
156
where is bile stored between meals?
gall bladder
157
What happens during a meal with bile?
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
What drains the primary juice into the biliary ductules and ducts
canaliculi
159
how are bile salts modified when before they are put into the duodenum?
Bicarbonate and water is added by the pancreatic ducts
160
What is bile juice made of?
primary biliary acids, water, electrolytes, lipids, phopholipids, cholesterol, IgA, bilirubin, metabolic wastes
161
Why could morphine worsen biliary colic pain?
Since it can cause sphincter of Oddi constriction and increase the intrabiliary pressure
162
Where are bile salts reabsorbed to go back to the liver?
at the ileum
163
What is added to secondary bile salts in the liver so that they can be reused?
glycine and taurine
164
What is the main function of drug metabolism in the liver
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
What is an example of a drug that GAINS activity in the liver?
codeine turns into morphine
166
What happens during a phase 1 reaction?
drugs are made more polar by adding a chemically reactive group
167
what happens during phase 2 reactions in drug metabolism?
add an endogenous compound like glucoronic acid (glucoronidation) which usually results in an inactive product
168
what happens in hepatic failure that could cause encephalopathy
detoxification of ammonia fails and is then absorbed into the blood stream
169
Where is most water absobed?
small intestine
170
what are the main ways that water moves out of the lumen?
transcellular through aquaporins or paracellular through the gap junction in the epithelium
171
what are the main mechanisms of sodium absorption in the postprandial period and where does it occur
Na+/glucose co-transport or Na+/amino acid co-transport (both go into the cell) and occurs in the jejunum
172
What is the main mechanism for sodium absorption in the interdigestive period and where does it occur?
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
what causes the Cl- to be absorbed in the small intestine
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
What is a method for sodium absorption in the distal colon?
epithelial sodium channels which are increased by aldosterone and are NOT regulated by cAMP like the other methods(which reduces NaCl absorption)
175
what causes Cl to be absorbed in the large intestine?
the negative lumen created by epithelial sodium channels
176
where does Cl- secretion occur
crypt cells
177
what is the role of CFTR
it is how Cl- exits the cell into the lumen if the concentration is too high
178
What activates CFTR
- bacterial endotoxins
- hormones and neurotransmitters
- immune cell products
- some laxatives
179
What are some causes of diarrhoea
- hypermotility
- reduction in NaCl absorption
- excessive secretion (increased cAMP and CFTR)
- poorly absorbed solutes in lumen
