GI/Liver: GI Flashcards
1
Q
What is the function of the gut?
A
To take relatively large solids and digest them into smaller molecules which can be absorbed, while still providing a barrier to toxins/bacteria etc.
2
Q
Roughly how much fluid does the gut process per day?
A
9L
3
Q
Where does the largest volume of fluid processed in the gut come from, ingestion or secretions?
A
Secretions.
4
Q
Name 6 sources of fluid entering the gut.
A
- Ingested fluids.
- Saliva
- Gastric secretions
- Pancreatic juices
- Bile
- Intestinal secretions
5
Q
Where is more fluid reabsorbed, in the small intestine or the colon?
A
Small intestine (7.5L/day)
6
Q
What are the three segments of the small intestine?
A
Duodenum
Jejunum
Ileum
7
Q
Where is B12 absorbed?
A
In the terminal ileum.
8
Q
Describe the 2 stage transcellular process by which water is absorbed in the gut.
A
1st stage: Co-transporter protein allows Na & glucose from intestinal lumen into epithelial cell along concentration gradient (passive transport).
2nd stage: Na/K ATPase moves K+ into cell from blood and Na+ out of cell into blood against concentration gradient (active transport).
Water moves with the Na+ due to osmosis, through the epithelial cell along the concentration gradient and into the blood.
9
Q
What ion channel allows chloride ions from the cell into the crypt?
A
CFTR
10
Q
What activates CFTR channels to open, causing chloride ions to move into the crypt?
A
cyclic AMP
11
Q
What does accumulation of negatively-charged chloride anions in the crypt cause to then also move into the crypt via tight junctions?
A
Na+ moves into crypt to balance charge = NaCl.
NaCl creates osmotic gradient, drawing water into crypt.
12
Q
A patient is admitted with severe cholera. Which transport mechanism is MOST directly affected by the cholera toxin?
A
CFTR chloride channel (because cholera toxin creates excess cAMP).
13
Q
What is the main function of amylase?
A
Break down starch (polysaccharide) into disaccharides.
14
Q
What are the three key disaccharides and their enzymes?
A
Maltose (maltase)
Sucrose (sucrase)
Lactose (lactase)
15
Q
What two monosaccharides does maltase break down maltose into?
A
2x glucose.
16
Q
What two monosaccharides does sucrase break down sucrose into?
A
1 glucose and 1 fructose.
17
Q
What two monosaccharides does lactase break down lactose into?
A
1 glucose and 1 galactose.
18
Q
Which monosaccharide can be absorbed by facilitated transport?
A
Fructose.
19
Q
Which two monosaccharides are absorbed by Na-dependent secondary active transport?
A
Glucose and galactose.
20
Q
What enzyme in the stomach breaks down proteins into polypeptides?
A
Pepsin.
21
Q
What organ produces important enzymes to break down proteins into amino acids?
A
Pancreas
22
Q
What is necessary for enzymes to break down fats and why?
A
Bile; it’s an emulsifier which means it has an affinity for both fat and water, allowing the two to mix and enzymes to access the fats.
23
Q
Describe the journey of bile acids.
A
Produced by liver, stored in the gallbladder, released into small intestines by bile ducts. In the ileum, after performing function, majority are reabsorbed and taken back to the liver to be recycled (remainder excreted).
24
Q
How many times a day are bile acids recycled?
A
5-6 times a day.
25
Name four organs which produce digestive enzymes.
Salivary glands.
Stomach.
Pancreas.
Intestines.
26
What cells in the stomach produce hydrochloric acid?
Parietal cells.
27
What cells in the stomach produce pepsinogen?
Chief cells
28
Which cells in the stomach stimulate gastric acid secretion? What do they produce to do this?
G cells, they produce gastrin.
29
Which type of fibre promotes movement of food through the digestive system and increases bulk, helping with constipation?
Insoluble fibre.
30
Which type of fibre dissolves in water to form a gel-like material?
Soluble fibre.
31
The minor salivary glands produce roughly 20% of saliva. Where are the minor salivary glands?
Submucosa of oral mucosa e.g. lips, cheeks, palate, tongue.
32
What types of cells produce saliva?
Serous and mucous acini cells.
33
What is the difference between the contents of saliva produced by serous and mucous acini?
Serous = water and amylase.
Mucous = water and glycoproteins.
34
What are the functions of salivary ducts?
Conduit for saliva.
Electrolyte composition of saliva is modified in the ducts.
35
Is the final saliva (after passing through ducts) isotonic or hypotonic?
Hypotonic.
36
Which salivary gland has only serous acini?
Parotid gland.
37
Which salivary gland has a mix of serous and mucous acini?
Submandibular glands.
38
Which salivary gland has mainly mucous acini?
Sublingual glands.
39
Are the minor salivary glands mainly mucous or serous?
Mucous.
40
Which salivary glands are continuously active?
Submandibular, sublingual, and minor glands.
Parotid gland only produces saliva when stimulated.
41
What is xerostomia?
A dry mouth
42
Why does mumps cause pain over parotid gland?
Viral infection causing swelling of glands, but parotid gland is surrounded by a tough capsule which restricts swelling.
43
Where are the majority of salivary gland cancers?
Parotid gland
44
Are salivary gland tumours generally malignant or benign?
Benign (but more likely malignant if in minor glands or sublingual).
45
Why is the mylohyoid muscle important in swallowing?
It elevates the hyoid bone and the tongue.
46
What are the four extrinsic muscles of the tongue? What cranial nerves innervate them?
Hyoglossus, genioglossus, styloglossus (Hypoglossal/CNXII)
Palatoglossus (Trigeminal/CNV).
47
What are the four muscles of mastication? What cranial nerve innervates them?
Masseter
Temporalis
Lateral and medial pterygoid.
(Trigeminal/CNV)
48
Do the suprahyoid or infrahyoid muscles elevate the pharynx?
Suprahyoid.
(Infrahyoid lowers pharynx).
49
Why is the cricopharyngeus muscle important?
It forms the upper oesophageal sphincter.
50
Which stages of swallowing are voluntary?
Oral preparatory and oral propulsion.
51
When does swallowing become involuntary?
At the pharyngeal phase, when the bolus reaches the palatoglossal arch.
52
Which part of the brain coordinates swallowing?
The medulla oblongata.
53
What muscles elevate the soft palate to seal the nasopharynx during swallowing?
Tensor palatini and levator palatini.
54
In what stage of swallowing does swallowing apnoea occur?
Pharyngeal stage.
55
When swallowing, do the hyoid and larynx elevate or lower? Which muscles perform this action?
Elevate. Suprahyoid muscles.
56
How is the bolus transported down the pharynx during swallowing?
By peristaltic contraction of constrictor muscles.
57
What two muscles cause relaxation and opening of the upper oesophageal sphincter?
Thyrohyoid (contracts)
Cricopharyngeus (relaxes)
58
What state are the upper and lower oesophageal sphincters in when not swallowing? Why?
Both are constricted and closed; upper prevents air entering oesophagus, lower prevents stomach contents entering oesophagus.
59
Why do stomach contents enter the oesophagus if the lower oesophageal sphincter is dysfunctional?
Because pressure in the stomach is higher than atmospheric pressure, so rise up against gravity into the oesophagus.
60
What happens during the oesophageal stage of swallowing?
Upper oesophageal sphincter contracts.
Peristaltic contraction of oesophagus.
Lower oesophageal sphincter relaxes; bolus enters stomach and swallowing is complete.
61
Which 5 cranial nerves are involved in swallowing?
Trigeminal (V), facial (VII), glossopharyngeal (IX), vagus (X), hypoglossal (XII).
62
Which cervical nerves are involved with swallowing?
C1-C3 (ansa cervicalis)
63
At what vertebral level does the abdominal aorta bifurcate into the right and left common iliac arteries?
L4/5
64
What are the three unpaired branches which leave the anterior aspect of the abdominal aorta to supply the gut?
At what vertebral levels do they leave the aorta and which part of the gut do they supply?
Coeliac trunk, T12, foregut.
Superior mesenteric, L1, midgut.
Inferior mesenteric, L3, hindgut.
"Cards Try 12
Some Love 1
I Love 3"
65
What are the three branches of the coeliac trunk?
Left gastric artery
Splenic artery
Common hepatic artery
66
What artery supplies the distal oesophagus?
Left gastric artery.
67
Where are the two anastomoses in the major branches of the coeliac trunk?
Right and left gastro-omental arteries (inferior aspect of stomach).
Right and left gastric arteries (medial aspect of the stomach).
68
What are the main branches of the superior mesenteric artery?
Jejunal and ileal
Ileocolic
Right colic
Middle colic
69
What are the main branches of the inferior mesenteric artery?
Left colic
Sigmoid
Superior rectal
70
Where is the marginal artery?
At the anastomosis between the left branch of the middle colic artery and the ascending branch of left colic artery.
71
What arteries enter the liver? Where do they branch from?
Right and left hepatic arteries.
(Abdominal aorta -> coeliac trunk -> common hepatic artery -> hepatic artery proper -> right and left hepatic arteries)
72
What is the difference between systemic veins and portal veins?
Systemic veins carry venous blood directly to the IVC (without passing through the liver).
Portal veins carry nutrient rich blood from the gut to the liver.
73
Is the hepatic vein systemic or portal? Why?
Systemic, because it carries blood from the liver to the IVC.
74
Name the three main portal veins which converge to form the hepatic portal vein.
Splenic, inferior mesenteric, and superior mesenteric.
75
Which structures are supplied by the splenic artery?
Spleen, pancreas, and stomach.
76
Which artery supplies the caecum and appendix?
Ileocolic.
77
Which structures are supplied by branches from both the coeliac trunk AND the superior mesenteric artery?
Duodenum, pancreas.
78
The right gastro-omental artery arises from which vessel?
Gastro-duodenal artery.
79
The inferior mesenteric vein typically unites with which other vein?
Splenic vein.
80
What do parietal cells do?
Secrete H+ and Cl- to make HCl.
Secrete intrinsic factor.
81
Roughly how much hydrochloric acid is secreted per day?
Approx 2L
82
Why is gastric acid secretion an active process?
Because H+/K+ ATP proton pump moves hydrogen ions out of cell, and potassium ions in, against concentration gradient.
83
What allow K+ and Cl- to move freely out of the cell, balancing electrical charge in gastric lumen?
Ion channels.
84
What occurs in the cephalic phase of gastric acid secretion?
1. Parasympathetic nervous system is stimulated by sight/smell/taste of food.
2. Acetylcholine is released from parasympathetic nerves.
3. ACh stimulates enteroendocrine cells to release gastrin and histamine.
4. ACh, gastrin, and histamine all act on parietal cells to trigger HCl production.
85
What happens in the gastric phase of gastric acid secretion?
1. Gastric distension, presence of peptides and amino acids triggers gastrin production.
3. Gastrin triggers release of histamine.
4. Histamine and gastrin both act on parietal cells to trigger HCl production.
86
What paracrine factor is produced by D cells, and what does effect does it have?
Somatostatin, inhibits parietal cell activity.
87
What is the effect of low luminal pH on gastric acid secretion and through what processes?
Reduces gastric acid secretion.
Low pH directly inhibits gastrin secretion.
Indirectly inhibits histamine release (via gastrin).
Stimulates somatostatin release; inhibiting parietal cell activity.
88
What is chyme and what is its pH usually?
Chyme is the pulpy acidic fluid which moves from stomach to duodenum, made of gastric juices and partially digested food.
pH 2
89
What happens in the intestinal phase of gastric acid secretion?
Reduction of gastric acid secretion:
1. Chyme moves into duodenum = distension, low pH, hypertonic contents, presence of amino & fatty acids.
2. This all triggers release of enterogastrones by duodenum: Secretin inhibits gastrin release, promotes somatostatin release. Cholecystokinin triggers bile release and promotes somatostatin.
3. Neural pathways reduce ACh release.
90
List 4 defence mechanisms of the gastric mucosa.
1. Alkaline mucus layer over epithelium.
2. Tight junctions between epithelial cells.
3. Rapid replacement of damaged/dead cells.
4. Feedback loops to regulate gastric acid production.
91
What is the effect of proton pump inhibitors (PPIs) e.g. omeprazole?
Inhibits the H+/K+ ATP proton pump, preventing hydrogen ions from entering stomach lumen, stopping HCl production.
92
What is the effect of ranitidine?
H2 receptor antagonist; prevents histamine from acting on parietal cells therefore reduces gastric acid secretion.
93
Which neurotransmitter up-regulates the secretion of gastric acid by parietal cells?.
Acetycholine.
94
Which hormone increases gastric acid secretion by parietal cells?
Gastrin (histamine is a paracrine factor not a hormone).
95
Name the 4 duodenal factors that trigger the release of enterogastrones, due to chyme passing into the duodenum.
1. Duodenal distension.
2. Low luminal pH.
3. Hypertonic luminal contents.
4. Presence of amino and fatty acids.
96
Which cells secrete pepsin?
NONE! Or they would digest themselves!
Chief cells secrete pepsinogen, the precursor to pepsin.
97
What cleaves pepsinogen to create pepsin?
HCl and pepsin (positive feedback loop).
98
What is the function of pepsin?
Digest proteins into peptides.
99
When is conversion of pepsinogen to pepsin most efficient?
At pH of <2
100
What happens to pepsin in the small intestine?
It is irreversibly inactivated by HCO3-
101
What percentage of protein digestion normally takes place in the stomach?
20%
102
What is the volume of an empty stomach?
About 50ml
103
How much volume can the stomach accommodate? How can it do this with little increase in luminal pressure?
About 1.5-2L
Smooth muscle of stomach and fundus undergoes receptive relaxation to accommodate the increase in volume.
104
What nerve coordinates receptive relaxation in the stomach?
Vagus nerve (CN X)
105
How does the stomach churn food to help in digestion?
Peristaltic waves through the stomach's 3 layers of muscle.
Contractions get stronger as they approach the pyloric sphincter.
Pyloric sphincter closes and the contents are forced backwards.
106
Which cells in the stomach act as pacemakers, regulating the rhythm of gastric peristalsis?
Interstitial cells of Cajal, inside the muscularis propria.
107
What increases peristaltic contractions in the stomach?
Gastrin secretion.
Gastric distension.
108
Name 5 factors that decrease the strength of peristaltic contractions in the stomach.
1. Increase in duodenal luminal fat.
2. Increase in duodenal osmolarity.
3. Decrease in duodenal pH.
4. Increase in sympathetic stimulation.
5. Decrease in parasympathetic stimulation.
109
Why is it important to regulate peristaltic contractions in the stomach?
To prevent too much chyme entering duodenum at once as the stomach has a much larger capacity than the duodenum.
110
Is glucose absorbed in the colon, small intestine, or both?
Only in the small intestine. There are no Na/Glucose co-transporters in the colon.
111
Which two structures cause a depression in the oesophagus which can be seen on a barium swallow?
Arch of aorta and left main bronchus.
112
A 28-year-old man loses the enterocytes on the tips of his duodenal and jejunal villi due to gastroenteritis. What will he be unable to digest and why?
Lactose; lactase enzyme is found in the tips of the villi.
113
What effect does too much thyroxine have on metabolic rate?
Increases metabolic rate.
114
What is ghrelin and what is its function?
A peptide hormone released mainly by the stomach when empty to stimulate appetite.
115
What is leptin and what is its function?
A peptide hormone released by white adipose tissue. Leptin regulates the hunger response by suppressing the hunger response when your body doesn't need energy.
116
What happens to leptin in obesity?
In obesity, more white adipose tissue, therefore produce more leptin, but develop leptin resistance so no longer can suppress hunger response.
117
Name the 8 hormones that regulate fuel metabolism.
"CAT SINGG"
Cortisol
Adrenaline
Thyroxine
Somatostatin
Insulin
Noradrenaline
Growth Hormone (somatotropin)
Glucagon
118
Which part of the developing gut has both dorsal and ventral mesenteries?
The foregut.
119
How does the pancreas develop embryologically?
In two separate buds (dorsal and ventral) off the duodenum, which then eventually fuse together.
120
What happens to the orientation of the stomach during embryological development?
It rotates 90 degrees.
121
Why do the intestines herniate and rotate into the umbilical cord during embryological development?
Developing length of intestine too long to fit into abdominal cavity, returns into abdominal cavity after coiling of the small intestine.
122
Why does the most distal anal canal have different epithelium to the proximal anal canal (hint: embryology!)?
Different embryological origins.
Distal anal canal; ectoderm on outside of cloaca.
Proximal anal canal; endoderm on inside of cloaca.
Cloaca divided by urorectal septum, then ectoderm of cloaca invaginates into anal pit and cloacal membrane breaks down.
123
What does the growth of the liver divide the ventral mesentery into during embryological development?
Lesser omentum and falciform ligament.
124
Where is the lesser sac?
Posterior to the stomach.
125
What are the 3 key functions of the colon?
1. absorption of water and electrolytes.
2. excretion of waste
3. production of vitamins/regulation of immune system, microbiome.
126
What is a redundant colon?
Anatomical variation, longer part of colon e.g. redundant transverse colon. Can sometimes cause issues such as constipation or volvulus.
127
Which histological section of the colon contains the interstitial cells of Cajal?
In the muscularis propria, in the inner circular muscle.
128
Is the internal anal sphincter under voluntary or involuntary control?
Involuntary.
129
What causes the anorectal angle, helping to preserve continence?
The puborectalis muscle sling.
130
What happens in the nervous system when stool enters the rectum?
Stretch receptors relay information to the CNS, which sends motor signals to rectum and internal anal sphincter, which releases a small amount of stool into the anal canal.
131
What motor nerve keeps the external anal sphincter contracted until it is appropriate to defecate?
The pudendal nerve.
132
What are the 4 phases of defecation?
1. Basal
2. Pre-expulsive
3. Expulsive
4. Termination
