Gastrointestinal Principles Flashcards
What are the four generalised components of the digestive tract wall?
Mucosa
Submucosa
Muscaularis Externa
Serosa
What is the alimentary canal?
The whole passage along which food passes through the body from mouth to anus during digestion
What are the four major functions of the alimentary canal?
Motility
Secretion
Digestion
Absorption
What happens to the lumen when circular muscle contracts?
It becomes narrower and longer
What happens to the intestine when longitudinal muscle contracts?
It becomes shorter and fatter
What happens when the muscularis mucosae contracts?
Change in absorptive and secretory area mucosa and mixing activity
What is the function of the Myenteric Plexus?
Regulates motility and sphincters
What is the function of the Submucous Plexus?
Modulates epithelia and blood vessels
What is glycogenesis?
Synthesis of glycogen from glucose
What is glycogenolysis?
Breakdown of glycogen to form glucose
What is gluconeogenesis?
De novo synthesis of glucose from metabolic precursors
What are the metabolic precursors for the synthesis of glucose?
Lactate
Amino Acids
Glycerol
What is the role of Glycogen Synthase?
Synthesis of glycogen from UDP-glucose by extending chains of glycogen
What are the three components of the small intestine?
Duodenum
Jejunum
Ileum
What are the three components of the large intestine?
Caecum
Appendix
Colon
What are the three additional features of the digestive system?
Liver and Gallbladder
Pancreas
Salivary Glands
Where is the myenteric plexus located?
Muscularis Externa
Where is the submucosal plexus located?
Submucosa
What is the name of gastrointestinal pacemaker cells?
Interstitial cells of cajal
What type of epithelium is in the oesophagus?
Stratified Squamous Epithelium
What type of epithelium is in the stomach?
Stratified Columnar Epithelium
What do chief cells in the stomach secrete?
Digestive enzymes
What do parietal cells in the stomach secrete?
Hydrochloric acid
What is the top portion of the stomach called?
Cardia
What is the middle main part of the stomach called?
Body/Fundus
What is the bottom portion of the stomach called?
Pylorus
How does the Muscularis Externa differ in the stomach?
It has an additional oblique muscle layer to aid with the churning of food
Where is the pyloric sphincter?
Between the stomach and the duodenum of the small intestine
What are enterocytes?
Cells of the digestive system. Tall columnar cells with a brush border and are the principle absorptive cells
What is the role of goblet cells?
Produce mucin to protect epithelium and lubricate passage of material
What are Paneth Cells?
Found at the base of the crypts of Lieberkuhn and have a defensive function
What is the role of neuroendocrine cells in the small intestine?
Produce hormones that contribute to the control of secretion and motility
What is the role of stem cells in the small intestine?
Found at the base of the crypts of Lieberkuhn to divide to replenish epithelium
What are Peyer’s Pathches?
Aggregation of lymphoid tissue
What is in the portal triad?
Hepatic Artery
Portal Vein
Bile Duct
What type of collagen is in reticular fibres?
Type III Collagen with some Type I Collagen
What are hepatic stellate cells?
Modified fibroblasts that deal with connective tissue and store vitamin A within fat droplets
What are kupffer cells?
Resident macrophages within the liver sinusoids that remove particular matter from the blood and help remove worn out blood cells
What is a mesentery?
A fold of the peritoneum which attaches the stomach, small intestine, pancreas, spleen, and other organs to the posterior wall of the abdomen
What is the omenta?
A fold of peritoneum connecting the stomach with other abdominal organs
What nerves form the parasympathetic innervation of the GI tract?
Vagal and Pelvic Nerves
Where do the vagal nerves originate to supply the GI tract?
Medulla Oblongata
Where do the pelvic nerves originate to supply the GI tract?
Sacral Spinal Cord
What does excitatory parasympathetic innervation of the GI tract cause?
Increased gastric, pancreatic and small intestinal secretion
Increased blood flow
Increased smooth muscle contraction
What does inhibitory parasympathetic innervation of the GI tract cause?
Relaxation of some sphincters
Receptive relaxation of the stomach
Where do the sympathetic nerves of the GI tract originate from?
Thoraco-lumbar region
What does excitatory sympathetic innervation of the GI tract cause?
Increased sphincter tone
What does inhibitory sympathetic innervation of the GI tract cause?
Decreased motility
Decreased secretion
Decreased blood flow
What is colonic mass movement?
A powerful sweeping movement that forces faeces into the rectum
What is the migrating motor complex?
A powerful sweeping contraction from the stomach to the terminal ileum
What are tonic contractions?
Sustained contractions that can occur at varying pressures at different points in the GI tract
What joint opens the mouth?
Temporomandibular joint
What are the three pairs of jaw closing muscles?
Masseter
Temporalis
Medial Pterygoid
What muscle is involved in jaw opening?
Lateral Pterygoid
What nerve innervates the muscles of the jaw?
Mandibular division of the trigeminal nerve - CN V3
What are the three main salivary glands called?
Parotid
Submandibular
Sublingual
What are the four extrinsic muscles of the tongue?
Palatoglossus
Styloglossus
Hyoglossus
Genioglossus
At what vertebral level does the pharynx become the oesophagus?
C6 vertebral level
What are the two neuroendocrine hormones that report fat status to the brain?
Leptin
Insulin
What is the major site of amino acid degredation?
Liver
What is the function of aminotransferases in transamination?
Move the amino group for alpha amino acids to alpha keto acids
What are the major carriers of nitrogen in the blood to the liver?
Alanine and Glutamine
What chemicals digest protein?
Pepsin and Hydrochloric Acid
What chemicals digest carbohydrates?
Salivary Amylase
What do mucous cells in the GI tract secrete?
Mucous and Bicarbonate
What do parietal cells in the GI tract secrete?
Hydrochloric acid
What do endochromaffin-like cells in the GI tract secrete?
Histamine
What do G cells in the GI tract secrete?
Gastrin
What do D cells in the GI tract secrete?
Somatostatin
What do chief cells in the GI tract secrete?
Pepsinogen
What is glycogenin?
An enzyme that acts as a glycogen primer by polymerises the first few molecules of glucose to form the glycogen primer for glycogen synthesis
What is transglycosylase?
A branching enzyme that introducglycosidic branches onto glycogened alpha 1-6
What is the role of brunners glands and where are they located?
They broduce and alkaline substance to neutralise the chyme and are found in the submucosa of the duodenum
What are the strips of smooth muscle in the large intestine called?
There are 3 Teniae Coli
What is billirubin?
A normal by-product of the breakdown of red blood cells
What are the four anatomical segments of the liver?
Right lobe
Left lobe
Caudate lobe
Quadrate lobe
What artery provides blood supply to the gallbladder?
Right hepatic artery
What are the three branches of the celiac trunk?
Splenic artery
Hepatic artery
Left gastric artery
What are the branches of the hepatic artery?
Gastroduodenal then Superior pancreatico-duodenal
What arteries supply the lesser curvature of the stomach?
Right and left gastric arteries
What arteries supply the greater curvature of the stomach?
Right and left gastro-omental arteries
What vein drains the organs of the foregut?
Splenic vein
What vein drains the organs of the hindgut?
Inferior mesenteric vein
What vein drains the organs of the midgut?
Superior mesenteric vein
What does the endoderm give rise to in GI embryology?
Epithelium of the mucosa
Associated ducts and glands
What does the visceral mesoderm give rise to in GI embryology?
Lamina propria Muscularis Mucosa Muscularis Externa Connective tissue of the submucosa External Connective tissue
What does the neural crest give rise to in GI embryology?
Enteric nervous system
Meissners plexus
Auerbachs plexus
What hormone triggers the Migrating Motor Complex?
Motilin
What hormones inhibit the Migrating Motor Complex?
Gastrin
Cholecystokinin
Where is gastrin released?
Released from G cells of gastric antrum and duodenum
What is the action of gastrin?
Stimulates proton secretion by gastric parietal cells
Stimulates growth of gastric mucosa
Where is secretin released?
Released from S cells of the duodenum in response to protons and fatty acids in the lumen
What is the action of secretin?
Promotes secretion of pancreatic and biliary bicarbonate
Where is Cholecystokinin released?
Released from I cells of the duodenum and jejunem in response to monoglycerides, free fatty acids, amino acids and small peptides in the lumen
What is the action of Cholecystokinin?
Inhibits gastric emptying
Causes secretion of pancreatic enzymes required for digestion
Stimulates relaxation of the sphincter of oddi and contraction of the gall bladder to eject bile into the duodenum
Potentiates the action of secretin
Where is Glucose dependent insulinotropic peptide released?
Released from K cells of the duodenum and jejunum in response to glucose, amino acids and fatty acids
What is the action of Glucose dependent insulinotropic peptide?
stimulates release of insulin from pancreatic β-cells (incretin action)
inhibits gastric emptying
Where is Glucagon like peptide 1 released?
from L cells of the distal ileum, released primarily in response to glucose and fats
What is the action of Glucagon like peptide 1?
stimulates insulin secretion (incretin action)
inhibits glucagon secretion from pancreatic α-cells
decreases gastric acid secretion and emptying and also appetite
Where is Motilin released?
from M cells of duodenum and jejunum, secreted during fasting state
What is the function of Motilin?
initiates the migrating motor complex
Where is Ghrelin released?
from Gr cells of the gastric antrum, small intestine and elsewhere (e.g. pancreas)
What is the function of Ghrelin
stimulates appetite
What receptor do peptide hormones bind to?
G-protein coupled receptors
What is the juice secreted from the small intestine called?
Succus Entericus
Where are the digestive enzymes of the pancreas released from?
Blind ended ACINAR CELLS
Why is there a high bicarbonate solution released from the pancreas into the duodenum?
To neutralise the acidic chyme
What mediates the cephalic phase of pancreatic secretion?
Vagus stimulation of mainly acinar cells
What mediates the gastric phase of pancreatic secretion?
gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells
What phase results in the majority of pancreatic secretion?
Intestinal phase
What are the two types of digestion in the small intestine?
Luminal digestion
Membrane digestion
What mediates luminal digestion?
Pancreatic enzymes
What mediates membrane digestion?
Enzymes situated at the brush border of epithelial cells
What is absorption?
the processes by which the absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes (absorptive cells of the intestinal epithelium)
What is the term that encompasses digestion and absorption?
Assimilastion
Give examples of polysaccharides…
Starch
Glycogen
Give examples of oligosaccharides…
Sucrose
Lactose
What are the limits of alpha amylase?
Cannot cleave terminal alpha 1,4 links, alpha 1,6 links or alpha 1,4 links next to branch points
What can alpha amylase break amylose into?
Maltotriose
Maltose
What can alpha amylase break amylopectin into?
Maltotriose
Maltose
Alpha limity dextrins
Why is there a rate limit on assimilation?
The rate of digestion is faster than the rate of absorption (except for lactose)
What is the name of the space between the endothelial cells and hepatocytes in the sinusoids of the liver?
Space of Disse
What type of collagen supports the parenchyma of the liver?
Type III collagen along with some type I collagen in the space of disse.
What are hepatic stellate cells?
They are modified fibroblasts involved in connective tissue. They store vitamin A fat droplets in the cytoplasm.
What can happen to hepatic stellate cells in some pathological conditions?
They can transform into myofibroblasts and create scar tissue.
What are Kupffer cells?
They are resident macrophages in the sinusoids. They remove particulate matter from the blood and remove worn out RBC.
What is bile?
Bile is an alkaline solution containing water, ions, phospholipids, bilirubin and bile salts.
What is bilirubin?
This is a pigment responsible for the breakdown of haemoglobin. It is excreted in the bile and results in the brown colour of faeces.
What are bile salts?
They are used for the emulsification of fats in the digestive tract.
What are bile canaliculi?
These are small channels that bile flows through that is formed by tight junctions of adjacent hepatocytes.
What enzyme activates the proenzyme trypsinogen from the exocrine pancreas?
Enteropeptidases
What is the role of vomiting?
It is a defence mechanism triggered by the emetic centre located in the brainstem
What different systems act on the vomiting centre?
Higher cortical centres Vestibular nuclei Chemoreceptor trigger zone Vagal afferents Enterochromaffin cells
What drugs act on the higher corticol centres?
Antihistamines
What drugs act on the vestibular nuceli?
Antimuscarinics
What drugs act on the chemoreceptor trigger zone?
Phenothiazines Domperidone Metoclopramide Dopamine receptor antagonists 5-HT3 Receptor andagonists
What drugs act on enterochromaffin cells?
Nablione
Metoclopramide
5-HT3 Receptor andagonists
Neurokinin-1 receptor antagonists
What are the main neurotransmitter systems involved in nausea and vomiting?
5-HT, dopamine and ACh
Examples of antihistamines…
Cyclizine
Promethazine
Diphenydramine
Examples of antimuscarinics…
Scopolamine (hyoscine)
Examples of 5-HT3 receptor antagonists…
Ondasetron
Granisetron
Palonosetron
Examples of dopamine receptor antagonists…
Chlorpromazine Droperidol Haloperidol Prochlorperazine Metoclopramide
Examples of neurokinin-1 receptor antagonists…
Fosaprepitant
Aprepitant
What is the action of antihistamines?
Antagonist at histamine H1 receptors in the brain
What is the action of antimuscarinics?
Antagonist at muscarinic acetylcholine M1 receptors in the brain
What is the action of 5-HT3 receptor antagonists?
Act primarily as antagonists at 5-HT3 receptors in the chemoreceptor trigger zone of the medulla in the hindbrain.
Also act on 5-HT3 receptors in the GI tract
What is the action of dopamine receptor antagonists?
Act primarily as antagonists at D2 receptors in the chemoreceptor trigger zone in the medulla.
Also act on D2 receptors in the GI tract
What is the action of neurokinin-1 receptor antagonists?
Act primarily as NK1 receptors in the GI tract and the chemoreceptor trigger zone of the medulla, blocking the effects of substance P which evokes vomiting
Examples of antidiarrhoeal drugs…
Loperamide, diphenoxylate
Examples of laxatives…
Ispaghula husk, senna, lactulose
What is the action of loperamide and diphenoxylate?
Opiates that bind to nano-opiate receptors.
What is the peritoneum?
A thin, transparent, semi-permeable serous membrane that lines the abdominal cavity.
What is an intraperitoneal organ?
An organ that is covered on both the anterior and posterior side by the visceral peritoneum
What is a retroperotineal organ?
An organ that is covered only on the anterior surface by the visceral perotineum
What is a mesentery?
A double layer of visceral perotineum that suspends the organ from the posterior abdominal wall
How do the greater and lesser peritoneal sacs communicate?
Through the omental foramen
What organs are retroperitoneal?
SAD PUCKER
S- Supraadrenal glands
A- Aorta
D- Duodenum
P- Pancreas U-Ureters C- Colon K- Kidneys E- (O)esophagus R- Rectum
Describe the greater omenta…
It consists of four layers pf visceral peritoneum. It descends from the greater curvature of the stomach and proximal part of the duodenum and doubles back up to attach to the anterior portion of the transverse colon.
What type of nerves supply the abdominal organs?
Sensory- Visceral Afferent
Motor- Autonimic Motor Nerves
The Enteric Nervous System
Derscribe the route of visceral afferent nerves from the abdomen…
They typically run alongside sympathetic fibres back to the spinal cord.
At which spinal cord level do foregut visceral afferents enter?
T6-T9
At which spinal cord level do midgut visceral afferents enter?
T8-T12
At which spinal cord level do hindgut visceral afferents enter?
T10-L2
At what level do the sympathetic fibres leave the spinal cord to reach abdominal organs?
T5-L2
Describe the route of sympathetic nerves to the abdominal organs…
- They leave the spinal cord between T5-L2
- They move into the sympathetic truck but don’t synapse
- The move out of the sympathetic trunk through abdominopelvic splanchnic nerves and synapse at the prevertebral ganglia
- They then move alongside the branches of the aorta and other nerves as part of a periatrerial plexus
- They then reach the smooth muscle and glands of the organs
Name the nerves that supply the abdominal body wall…
Thoracoabdominal nerves
Subcostal Nerve
Iliohypogastirc Nerve
Ilioinguninal Nerve
Name the three branches of the coeliac artery…
Common hepatic artery
Splenic artery
Left gastric artery
Name some branches of common hepatic artery…
Gastroduodenal artery
Superior pancreatic duodennal artery
What vessels are the main blood supply of the stomach?
Right and left gastric arteries- lesser curvature
Right and left gastro-omental arteries - greater curvature
What vessels supplies blood to the gall bladder?
Cystic artery
What muscles facilitate the closure of the jaw?
Masseter
Medial Pterygoid
Temporalis
What muscle facilitates the opening of the jaw?
Lateral Pterygoid
What cranial nerve supplies the muscles of mastication?
The mandibular division of the trigeminal nerve (CN V3)
What is the name of the upper dental arch?
Maxillary
What is the name of the lower dental arch?
Mandibular
What is the course of CN V3?
- Pons
- Foramen Ovale
- Muscles of mastication and general sensory area
What is the course of CN V2?
- Pons
- Foramen Rotunda
- Sensory Area
Which nerves supply sensation to the anterior 2/3rds of the tongue?
General sensory (touch) - CN V3 Special Sensory (taste) - CN VII
Which nerve supplies the posterior 1/3rd of the tongue?
General and special sensory - CN IX
What is the course of CN VII?
- Pontomedullary Junction
- Internal Acoustic Meatus
- Stylomastoid Foramen
- Sensory and Motor Area
What is the chorda tympani?
Branch of the facial nerve (CN VII) that connects to the lingual branch of CN V3
What are the exrinsic muscle of the tongue?
Palatoglossus
Hyoglossus
Styloglossus
Genioglossus
What nerve supplies the muscles of the tongue?
Hypoglossal (CN XII)
What nerves supplied the longitudinal muscles of the pharynx?
CN X and CN IX
What nerve supplies the circular muscles of the pharynx?
CN X
Where does the oesophagus begin?
The inferior edge of the cricopharyngeus muscle ( @ vertebral level C6)
Where are peptic ulcers most commonly located?
Duodenal bulb or the antrum of the stomach
What is the cause of peptic ulcers?
Acid pepsin results in mucosal damage and gastric ulcers
What are the two kinds if peptic ulcers?
Gastric and duodenal ulcers
What is the most common cause of peptic ulcers?
H. Pylori
What are some other causes of peptic ulcers?
Long term use of NSAIDs
How can we differentiate between gastric and duodenal ulcers?
Gastric - worsened by eating
Duodenal - improved by eating
What are the investigations for H. Pylori Infection?
Urea breath test or stool antigen test
Eating what food can lead to Bacillus Cereus?
Reheated rice
What is the role of chief cells?
Release pepsinogen which is changed to pepsin in the presence of HCL
ECL cells
Release histamine which is used to help with acid secretion
Parietal cells
Macin acid secreting cells, also secreted intrinsic factor which absorbs B12
What are the three phases of digestion?
- Cephalic phase
- Gastric Phase
- Intestinal Phase
What are the triggers of the cephalic phase?
Psychological triggers
What mediates the cephalic phase?
Vagus nerve and ACh mediates response
What is the role of ACh in the cephalic phase?
Stimulates acid and histamine release directly
What is the role of the Vagus Nerve in the cephalic phase?
Stimulates gastrin releasing peptide for gastrin secretion
What triggers the gastric phase?
Distention of the gastric wall
What mediates the gastric phase?
Distention detected by vagal afferent and increases vagal efferent activity for acid secretion.
Local plexuses activated
In which digestive phase is the highest amount of acid secreted?
Gastric phase
What triggers the intestinal phase?
Triggered when food enters the duodenum
What mediates the intestinal phase?
CCk released from I cells and GIP released fromK cells due to the presence of lipids and carbohydrates
What is the role of secretin and CCK in the intestinal phase?
Secretin and CCK stimulates pancreatic and biliary stimulation