GI better deck Flashcards
1
Q
what are the embryological boundaries of the foregut
A
mouth to common bile duct
2
Q
what are the embryological boundaries of the midgut
A
common bile duct to 2/3rds transverse colon
3
Q
what are the embryological boundaries of the hindgut
A
2/3rds transverse colon to anal canal
4
Q
what develops from the endoderm
A
bowel epitheliumhepatocytes of liverendo/exocrine cells of pancreas
5
Q
what develops from the visceral mesoderm
A
muscle wallconnective tissue of wall/pacreas/livervisceral peritoneum
6
Q
what is the primitive gut derived from
A
endoderm + visceral mesoderm
7
Q
what is the oropharyngeal membrane
A
at cranial end of embryo at head of foregut4th week = ruptures to form the mouth
8
Q
what is the cloacal membrane
A
at end of hindgut at caudal end 7th week = ruptures to form the anus
9
Q
what are the pharyngeal arches
A
extensions of foregut from oropharyngeal membrane to respiratory diverticulum = 5 arches (no no.4)
10
Q
what are pharyngeal arches made of
A
mass of mesenchymal tissue invaded by cranial neural crest cellsexternally covered by endoderm = cleftsinternally covered by ectoderm = pouches
11
Q
bones and innervation of 1st arch
A
maxilla/mandible/incus/malleus= mandibular nerve
12
Q
bones and innervation of 2nd arch
A
stapes/styloid/lesser horn hyoid cartilage = facial nerve
13
Q
bones and innervation of 3rd arch
A
body and greater horn of hyoid cartilage = glossopharyngeal nerve
14
Q
bones and innervation of 4th arch
A
thyroid cartilage/epiglottic cartilage = superior laryngeal nerve of vagus
15
Q
bones and innervation of 6th arch
A
cricoid cartilage/arytenoid cartilages/corniculate/cuneiform cartilage= recurrent laryngeal nerve of vagus
16
Q
describe the development of the oesophagus
A
- 4th week = respiratory diverticulum form
- trancheosophageal septum develops = separates respiratory diverticulum form dorsal foregut = separated into respiratory primordium and dorsal oesophagus
- initially short oesophagus = lengthen with descent of heart and lungs
17
Q
describe the development of the stomach at the 4th week
A
- appears as fusiform dilation of foregut2. attached to body wall by dorsal/ventral mesenteries3. L/R vagus on L/R side of stomach4. dorsal wall grows faster = greater curvature
18
Q
describe the development of the stomach at the 7th week
A
- stomach rotates 90 degrees clockwise = produces lesser sac behind2. lesser curvature facing R greater facing L3. L vagus of anterior, R on posterior
19
Q
describe the development of the stomach at the 8th week
A
- stomach/duodenum rotate upwards = C shaped duodenum 2. = thinning of dorsal mesentery = becomes greater omentum3. ventral mesentery attach to liver = lesser omentum= produce distinct spaces of peritoneal cavity = greater/lesser sac
20
Q
how is the 4 layers of greater omentum formed
A
during foetal period anterior/posterior greater omentum fuse = one thick sheet of 4 layers
21
Q
name the stages of midgut development
A
- elongation
- physiological herniation
- rotation
- retraction
- fixation
22
Q
describe physiological herniation
A
during 6th week
- loop of midgut elongates rapidly
- liver enlargement = abdominal cavity too small
- = midgut pushed out into extraembryonic cavity
23
Q
describe stage 3: rotation
A
loop of midgut rotates 270 anticlockwise around axis of superior mesenteric artery jejunum and ileum form a number of coiled loops
24
Q
describe stage 4: retraction
A
during 10th weekherniated midgut return to abdominal cavityjejunum return first
25
describe stage 5: fixation
some of gut mesenteries lie against back of abdomen = parts of bowel fixed to wall with single anterior layer of peritoneum = retroperitoneal
26
what structures in the abdomen are fixed
duodenum except cap
ascending colon
descending colon
rectum
27
what structures in the abdomen are mobile
```
stomach
jejunum/ileum
appendix
transverse colon
sigmoid colon
```
28
describe the formation of the anorectal canal
urorectal septum divides the cloacal membrane = into urogenital sinus and anorectal canal
29
what happens in stage 1 swallowing
= voluntary - food compressed against mouth roof and pushed towards oropharynx by tongue- buccinator/suprahyoid muscles manipulate food
30
what happens in stage 2 swallowing
= involuntary nasopharynx closed off by soft palate and pharynx shortened/widened by hyoid bone elevation
31
what happens in stage 3 swallowing
= involuntary - sequential contraction of constrictor muscle then depression of hyoid bone/pharynx- upper oesophageal sphincter relax- peristalsis until through lower oesophageal sphincter into stomach
32
describe peristalsis in the oesophagus
sequential contractions of constrictor muscles behind bolus
33
what is the gag reflex
reflex elevation of the pharynx often followed by vomiting caused by irritation of oropharynx/back of tongue
34
what is responsible for the gag reflex
reflex arc between glossopharyngeal (sensory/afferent nerve) and vagus (effector/efferent nerve)
35
name 3 functions of saliva
1. lubricant for mastication
2. maintaining oral pH (6.2-7.4)
3. release digestive enzymes - salivary alpha amylase
36
what type of gland is the parotid gland
serous
37
what innervates the parotid gland
sympathetic = mandibular branch of trigeminalparasympathetic = glossopharyngeal
38
what type of gland is submandibular gland
mixed mucous and serous
39
what innervates the submandibular gland
parasympathetic = lingual nerve = chorda tympani branch of facial nerve
40
what type of gland is sublingual gland
mixed mucous and serous but mainly mucous
41
what innervates the sublingual gland
same as submandibular
42
what is the action of parasympathetic innervation of the salivary glands
stimulates saliva secretion
43
what is the action of sympathetic innervation of the salivary glands
inhibits saliva secretion
44
describe the structure of salivary glands
1. acinar cells - serous and mucous
| 2. ducts
45
describe serous acinus
dark nucleus in basal thirdsmall central ductsecrete water and alpha amylase
46
describe mucous acinus
pale staining 'foamy'nucleus at baselarge central ductsecrete mucous
47
describe the structure of intralobular ducts
1. intercalated ducts
| 2. striated ducts
48
describe intercalated ducts
short narrow cuboidal cells = connect acini to larger striated ducts
49
describe striated ducts
= striated, basal membrane has microvillimajor site for reabsoprtion of NaCl
50
describe ion transport across the ducts
secrete = K+ and HCO3-reabsorb = Na+ and Cl- and H2O so saliva is hypotonic
51
what is BMR
basal metabolic rate = minimum amount of energy required to keep the body alive
52
how do you calculate BMI
weight/height squared
53
energy requirement at skeletal muscle and fuels used
40% body mass
22% BMR
triglycerides/glucose
54
energy requirement at liver and fuels used
2.6% body mass
21% BMR
triglycerides/amino acids
55
energy requirement at brain and fuels used
2% body mass
20% BMR
glucose
56
energy requirement at heart and fuels used
0.5% body mass
9% BMR
triglycerides/other lipids
57
energy requirement at kidneys and fuels used
0.4% body mass
8% BMR
glucose
58
how are fuels stored
amino acids/triglycerids/glucose to liver then converted
fat - adipose tissue
glucose - muscle
59
what fuels does muscle store
protein and glycogen
60
what fuels does adipose tissue store
triglycerides from glycerol and fatty acids
61
how much are excess glycogen stores and how long would they last
up to 15kg and up to 12 hours
62
how much are excess lipid stores and how long would they last
just 350g but last up to 3 months
63
how much are excess protein stores and how long would they last
only used in times of prolonged starvation about 6kg and last up to 10 days
64
what is glycogen
principle dietary polysaccharidealpha 1,4 glycosidic + 1,6 glycosidic links
65
what is starch
majority alpha 1,4 glycosidic, fewer 1,6 than glycogen
66
what is cellulose
only beta 1,4 glycosidic linkages
67
name 3 important fatty acids we absorb
palmitic acidstearic acidoleic acid
68
what are the 3 monosaccharides
glucosefructosegalactose
69
how many essential amino acids are there
8
70
what is vitamin A used for
cellular growth
vision
skin/mucous membranes
71
name 4 sources of vitamin A
liver
dairy
oily fish
fruit and veg
72
what occurs in vitamin A deficiency
night blindness
growth retardation
increase infection risk
73
what is vitamin C used for
collagen synthesis
| antioxidant
74
name 2 sources of vitamin C
citrus fruit
| green vegetables
75
what occurs in vitamin C deficiency
scurvy
bleeding gums
aching bones
76
what is vitamin B12 used for
DNA synthesis
| brain development
77
name a source of vitamin B12
meat
78
what occurs in vitamin B12 deficiency
anaemia
79
what is vitamin D used for
calcium absorption in gutreabsorption in kidneys
80
name 2 sources of vitamin D
liverfish
81
what occurs in vitamin D deficiency
frequent bone fractures
muscle weakness
bone pain
82
what is vitamin E used for
antioxidant protects cell walls
83
name a source of vitamin E
nuts
84
what occurs in vitamin E deficiency
muscle weaknessretina degeneration
85
what is vitamin K used for
blood clotting
86
name a source of vitamin K
green vegetables
87
what occurs in vitamin K deficiency
bleeding gumseasy bruising
88
what are the functions of the stomach (6)
1. store/mix food
2. kill microbes
3. secrete intrinsic factor
4. secrete/activate proteases
5. lubrication
6. mucosal protection
89
what are the 6 key cell types of the gastric mucosa
1. mucous cell
2. parietal cell
3. chief cell
4. enterochromaffin-like cell ECL
5. G cell
6. D cell
90
what do parietal cells secrete and why
1. HCl = activation of pepsinogen, host defence
| 2. intrinsic factor = absorption of B12 in terminal ileum
91
what do chief cells secrete and why
pepsinogen = converted to pepsin by gastric acid
92
what do G cells secrete and why
gastrin = upregulates acid secretion as binds to parietal + ECL cells
93
what do D cells secrete and why
somatostatin = inhibits gastrin secretion
94
what do ECL cells secrete and why
histamine = upregulates acid secretion from parietal cells
95
describe the lining of the stomach
= epithelial layer invaginates into mucosa to form many tubular glands
96
describe the lining of the upper portions of the body of the stomach
thinner wallparietal cells = HCl chief cells = pepsinogem
97
describe the lining of the lower portion of the stomach
antrum has thicker smooth muscle layer
| glands secrete little acid but contain G cells = gastrin
98
describe gastric acid secretion
1. H+ from bicarbonate reaction in parietal cell = transported into lumen by H+/K+ATPase
2. Cl- enter parietal cell by exchange of HCO3- from bicarbonate reaction into capillary
3. Cl- leave parietal cell via channels
4. combine in stomach to form HCl
99
turning on acid secretion: when is the cephalic phase
during a meal
100
turning on acid secretion: what occurs in the cephalic phase
= stimulated by parasympathetic NS = sight/smell/taste/chewing- ACh released = trigger gastrin from G cells + histamine from ECL cells- increase HCl production
101
what is the effect of histamine and gastrin release
increase number of H+/K+ATPase pumps on plasma membrane of parietal cells = more HCl
102
turning on acid secretion: when is the gastric phase
once food has reached the stomach
103
turning on acid secretion: what occurs in the gastric phase
= initiated by gastric distension + presence of peptides/aa from protein digestion - gastrin and histamine released = parietal cell increase HCl- net increase in acid production
104
how does protein in the stomach turn on gastric acid secretion
= direct stimulus to G cells = positive feedback loop= acts as buffer to reduce H+ ions so pH rises = decrease somatostatin = more parietal cell activity
105
turning off gastric acid secretion: what occurs in the gastric phase
low luminal pH =
1. directly inhibits gastrin = indirectly inhibit histamine
2. stimulates somatostatin = inhibit parietal cell
106
turning off gastric acid secretion: what initiates the intestinal phase
duodenal distension
low pH
hypertonic solutions presence of aa/FA
107
what occurs in the intestinal phase
= release of enteragastrones
1. secretin
2. cholycystokinin
3. trigger neural pathways to reduce ACh
108
what is secretin
produced by S cellsact on G cells to inhibit gastrin secretion + promotes somatostatin
109
what is CCK
produced by I cells
act on parietal cells and pancreas to inhibit HCl secretion
promotes flow of digestive enzymes from pancreas/bile to gallbladder
110
describe protease secretion
1. pepsinogen secreted alongside HCl
2. pepsinogen activated in lumen of stomach
3. HCl cleaves pepsinogen to pepsin
4. pepsin can cleave more pepsinogen in positive feedback loop
111
what irreversibly inactivates pepsinogen
HCO3- released in duodenum
112
what is the volume of the stomach when eating
1.5L = little increase in luminal pressure bc receptive relaxation
113
what is responsible for receptive relaxation
smooth muscle in body and fundus
114
what is receptive relaxation mediated by
parasympathetic NS acting on enteric nerve plexuses with coordination from afferent from stomach (vagus) and swallowing centre of brain
115
what occurs in receptive relaxation
nitric oxide/seratonin released by enteric nerves = relaxationACh activates parietal/chief cells = initiates receptive relation
116
where do peristaltic waves begin
body of the stomach
117
describe peristalsis in the stomach (4)
1. more powerful contractions in gastric antrum
2. pyloric sphincter closes as peristaltic wave reaches
3. little chime enters duodenum
4. most rebound back to antrum for mixing again
118
what determines the frequency of peristalsis in the stomach
pacemaker cells in longitudinal smooth muscle impulse to trigger contractions = 3 times per minute
119
what do the interstitial cells of Cajal do
pacemaker cells of peristalsis
120
describe the action of pacemaker cells
undergo slow depolarisation/repolarisation cycles
waves of depolarisation transmitted through gap junctions to adjacent smooth muscle cells = do not cause significant contraction in empty stomach
121
how is the strength of peristaltic contractions varied
excitatory neurotransmitters and hormones further depolarise membranes
action potentials when threshold reached = threshold can be altered by enteric NS
122
what increases the strength of gastric contractions
gastrin
| gastric distension
123
what decreases the strength of gastric contractions
duodenal distension
increase in duodenal fat/osmolarity
decrease in duodenal pH
increase sympathetic/decrease parasympathetic stimulation
124
what is dumping syndrome
overfilling of duodenum by hypertonic solution
125
what natural mechanisms delay gastric emptying
plasma enterogastronesneural receptors
126
what is gastric reflux
lower oesophageal sphincter opens/doesnt close enough = acid moves up oesophagus
127
what is gastroparesis
delayed gastric emptying
128
name the 4 protective mechanisms of gastric mucosa
1. alkaline mucus on luminal surface
2. tight junctions between epithelial cells
3. replacement of damaged cells as stem cells at base of pits
4. feedback loops for gastric acid regulation
129
what is GORD and what are the symptoms
gastro-oesophageal reflux disease - heartburn- regurgitation- acid reflux- dysphagia = swallowing problems
130
where does the majority of water reabsorption occur
80% in small intestine
131
what is chyme
= gastric juices/partially digested food
mostly water
Na+ = most abundant solute
132
describe water transport in small intestine
epithelial membranes v permeable to water = net diffusion
133
describe ion transport in small intestine
Na+ most of AT solutes = from lumen in cell membranes of jejunum/ileum membrane transport = variably coupled with glucose/amino acids/others
134
describe water transport in the colon
contents = iso-osmotic so Na+ actively pumped out of lumen = water follows
135
describe potassium reabsorption in the colon
by passive diffusion due to potential difference between lumen/capillaries
136
describe chloride reabsorption in the colon
actively reabsorbed in exchange for bicarbonate = intestinal contents more alkaline
137
which vitamins are at soluble
KADE
138
where are fat soluble vitamins absorbed
in micelles
139
which vitamins are water soluble
B + C
140
where are water soluble vitamins absorbed
jejunum except B12
141
name 2 important dietary disaccharides
lactosesucrose
142
where is starch first digested
in the mouth by ptyalin (alpha amylase) with optimal pH 6.7
143
where does the majority of starch digestion occur
95% in small intestine by pancreatic alpha amylase= produce maltose + mixture of others
144
describe the digestion of starch in the small intestine
maltose = broken down into monosaccharides by oligosaccharide enzymes from luminal membrane of epithelial cells
145
name 4 oligosaccharidases
maltase
lactase
sucrase
alpha-limit dextrinase
146
what are alpha-limit dextrins
branched polymers of glucose consisting of around 8 units
147
describe the absorption of hexoses/pentoses
rapidly absorbed across intestinal mucosa then enter the capillaries then to hepatic portal vein
148
what is galactose
a D-isomer of glucose
149
how is glucose/galactose absorbed
secondary active transport with Na+ through a sodium-glucose cotransporter = SGLT1 = requires high Na+ conc at mucosal surface
150
how is fructose absorbed
facilitated diffusion via glucose transporter GLUT5 then exits via GLUT2
151
how does glucose/galactose enter interstitial fluid
exit cell via GLUT2 receptors on basolateral membrane
152
which amino acid optical isomers are found in proteins we utilise
L forms
153
how are amino acid zwitterions formed
HN2 is a stronger base than COOH acid
| NH2 picks up H+ from COOH to form zwitterion with +ve NH3 and -ve COO-
154
what is pepsinogen 1
fragment only found in HCl secreting region of stomach
155
what is pepsinogen 2
fragment found in pyloric region of stomach
156
what is the optimum pH for pepsins
1.6-3.2
157
describe the digestion of proteins in the duodenum
small peptides further fragmented by pancreatic enzymes = endopeptidases/exopeptidases
158
name 3 endopeptidases
trypsin
chymotrypsin
elastase
159
name 2 exopeptidases
carboxyl dipeptidase
| amino peptidases of brush border= further digestion of peptide fragments to free amino acids
160
where does final digestion of peptides occur
intestinal lumenbrush borderwithin cell
161
how are free amino acids absorbed
via Na+ cotransporter on apical membrane then facilitated diffusion on basolateral membrane to portal blood
162
how are di/tripeptides absorbed
H+ dependent cotransporters on apical membrane hydrolysed within cell to aa leave via facilitated diffusion to portal blood
163
where does digestion of lipids occur
limited in mouth stomach by lingual/gastric lipases but mainly in small intestine
164
what is lipase
digestive enzyme made in pancreas splits triglycerides to monoglyceride and 2 FA
165
what is emulsification
lipid droplets converted into very small droplets
166
what does emulsification require
1. mechanical disruption = motility of GI tract
| 2. emulsifying agent = phospholipids from food/bile salts
167
what are bile salts formed from
cholesterol in the liver
168
describe the action of bile salts on lipids
non-polar parts associated = polar portions exposed to prevent aggregation of lipid droplets
HOWEVER lipase cannot access
169
what is the action of colipase
binds to lipase and lipid droplet to hold them together
170
what are micelles
lipid droplets converted into smaller = micelles
consist of bile salt
vitamins KADE
cholesterol
FA
monoglycerides and phospholipids clustered together= continuously breaking down/reforming
171
describe absorption of lipids
1. pancreatic lipase breakdown TG
2. bile salts emulsify FA into micelles
3. micelles taken up by mucosal membrane
4. inside cell = re-esterified to form original lipids = maintain diffusion gradient
5. lipids are packaged with cholesterol to form chylomicron
6. chylomicron too large to enter circulation = lymphatic system via lacteals
172
what are chylomicrons made up of
phospholipids
triglycerides
cholesterol
fat soluble vitamins
173
what happens to chylomicrons after entering lymphatics
1. lipase converts triglycerides in chylomicrons to glycerol + FA
2. FA enter myocite/adipocyte and are oxidised as fuel/reesterified for storage
174
what is malnutrition
deficiencies, excesses, imbalances of persons intake of energy/nutrients
175
what is 'MUST'
malnutrition universal screening tool
176
what are the steps of MUST
1. measure height/weight/BMI
2. note percentage unplanned weight loss
3. establish acute disease effect/score
4. add scores from 1,2,3 = overall risk
5. use management guidelines to develop care plan
177
what epithelium are the lips
stratified squamos non-keratinising
178
describe histology of lip skin
sub-mucosa = collagen/elastin
deeper layers = glands/striated
skeletal muscle
small blood vessels at sub-mucosa = moist
179
describe the histology of the inner lips
small clumps salivary tissue
| sebaceous glands = fordyce's spots open to surface
180
what type of epithelium is the tongue
```
ventral/lower surface = SSNKE
dorsal/upper = SSKE
skeletal muscles insert to lower jaw + fibrous connective tissue underlying mucosa
mixed sero-mucous salivary glands
lymph nodules
```
181
describe the histology of serous glands of the tongue
more pink staining
smallcluster of grapes
nucleus on base
182
describe the histology of mucous glands of the tongue
small
| michael palin = mucous pale
183
name 3 types of taste buds
filiform papillae
fungiform papillae
circumvallate papillae
184
describe filiform papillae
most common
tall
pointed at whole anterior 2/3
185
describe fungiform papillae
mushroom-like
pale staining
spindle shaped
nerves
186
describe circumvallate papillae
v shaped row
| at margin of anterior 2/3 and post 1/3
187
what 2 cell types are found in parotid glands
secretory cells = pyramidal, spherical nucleus, rich rER cytoplasm, prominent pink staining granulesstriated ducts = invaginations
