Gastrointestinal System Flashcards
What is the composition of saliva? (5)
- Mostly water in a hypotonic solution
- Potassium and bicarbonate ions
- Mucins
- Digestive enzymes e.g. amylase, lingual lipase
- Immune proteins e.g. lysozyme, lactoferrin
List 4 functions of saliva (4)
- Lubrication and moistening of food to form a bolus
- Solvent for taste molecules
- Initiation of digestion of food
- Oral hygiene (neutralises acidity on teeth)
Describe the appearance of the mouth of a patient with xerostomia (3)
- Tongue appears red, swollen and sore
- Mouth and lips appear dry
- Poor oral hygiene
Where does the duct to the parotid salivary gland enter the oral cavity?
Opposite crown to the 2nd upper molar tooth
Describe the locations of the sublingual and submandibular salivary glands in relation to the floor of the mouth
- Sublingual gland sits above the floor of the mouth
- Submandibular gland sits below the floor of the mouth
Which nerve innervates the parotid gland?
Glossopharyngeal nerve (cranial nerve IX)
Which nerve innervates the sublingual gland?
Facial nerve (cranial nerve VII)
Which nerve innervates the submandibular gland?
Facial nerve (cranial nerve VII)
Which gland can be affected by the mumps virus?
Parotid gland
What is a sialography and what is it used for?
- Radiological investigation of salivary glands by means of injecting a contrast medium followed by X-ray
- Used to investigate blockages by stones, presence of tumours etc.
Describe the events that occur in the oral preparatory phase of swallowing (2)
- Voluntary manipulation of food into a bolus by the tongue (secretion of saliva helps to lubricate and moisten food)
- Tongue pushes bolus towards the pharynx and pharyngeal phase begins
Describe the precautions taken in the pharyngeal phase of swallowing to ensure the bolus is sent down the correct passage (5)
- Soft palate moves up to close off nasopharynx
- Tongue moves up to block entrance to oral cavity
- Pharyngeal sphincters constrict to push bolus down
- Larynx moves up and epiglottis moves down to close of the glottis and entrance to the airways
- Vocal chords close to close off airways
Describe the oesophageal phase of swallowing (2)
- Opening of the upper oesophageal sphincter to allow bolus to enter oesophagus
- Closure of sphincter and peristaltic waves allow bolus to be pushed down the oesophagus through contraction of the circular and longitudinal layers of the muscularis externa in the wall
Why can babies swallow and breathe at the same time?
Epiglottis extends up towards nasopharynx in babies allowing them to swallow and breathe whilst still protecting airways
Which 2 cranial nerves are involved in swallowing and the gag reflex? (2)
- Glossopharyngeal nerve (IX)
- Vagus nerve (X)
What is dysphagia?
A condition in which the patient has difficultly swallowing
Give 3 possible causes of dysphagia (3)
- Oesophageal tumour
- Stroke
- Bulbar palsy
Describe 3 ways in which gastro-oesophageal reflux is avoided (3)
- Functional sphincter formed from the smooth muscle of the distal oesophagus to prevent acid reflux from stomach
- Acute angle of entry of oesophagus into stomach makes reflux difficult and unlikely
- Resting tone of diaphragm keeps oesophagus closed
Describe the structure of the oesophagus (5)
- Upper oesophageal sphincter
- 1/3 skeletal muscle
- 1/3 skeletal and smooth muscle
- 1/3 smooth muscle
- Lower oesophageal sphincter
Describe the arterial blood supply to the stomach
- Lesser curvature - left gastric (celiac trunk) and right gastric (common hepatic)
- Greater curvature - left gastroepiploic (splenic) and right gastroepiploic (gastroduodenal)
Where is the arcuate line (Line of Douglas) positioned and what is its significance? (2)
- 1/3 of the way down between umbilicus and symphysis pubis
- Site of Caesarian section
Describe the composition of the abdominal wall from external to internal
Skin/subcutaneous tissue; superficial and deep fascia; external oblique; internal oblique; transversalis abdominus; transversalis fascia; peritoneumw
Describe the sheathing of the rectus abdominus muscle
- Above umbilicus: sheathed anteriorly and posteriorly
- Below umbilicus: sheathed anteriorly only
Describe the direction of the muscle fibres in the external oblique, internal oblique and transversalis abdominus muscles (3)
- External oblique: fibres run inferiomedially
- Internal oblique: fibres run superiomedially
- Transversalis abdominus: fibres run anterioposteriorly
What is the main cause of a diavarication of recti?
Laxity of the linea alba (NOT A HERNIA)
Describe how you could test the strength of the rectus abdominus muscle
Ask patient to lie flat and lift head off the floor, then lift feet off the floor
Where is the main site for an appendicectomy located?
- McBurney’s point
- 2/3 of the way between the umbilicus and the right ASIS
What is a gridiron incision?
- Made at McBurney’s point for an appendicectomy
- In the direction of the muscle fibres of the external oblique muscle (separate the muscle fibres and go in between them)
What is referred pain?
Pain perceived at a site distant from the site causing the pain
What is somatic referred pain?
Pain caused by a noxious stimulus to the proximal part of a somatic nerve which is perceived in the distal dermatome of the nerve
Name 4 causes of visceral pain in the abdomen (4)
- Ischaemia
- Abnormally strong muscle contractions
- Inflammation
- Stretch
Where is visceral pain normally distributed? (3)
- Epigastric region (foregut)
- Periumbilical region (midgut)
- Suprapubic region (hindgut)
What is a hernia?
Protrusion of part of the abdominal contents beyond the normal confines of the abdominal wall/its containing cavity
What does a hernia consist of? (3)
- The sac (peritoneum)
- Coverings of the sac (layers of abdominal wall)
- Contents of the sac (abdominal viscus)
What is the inguinal canal and what structures pass through it? (3)
- Oblique passage through the lower part of the abdominal wall
- Spermatic cord (M), round ligament of uterus (F) and ilioinguinal nerve pass through here, along with other structures
Where does the the round ligament of the uterus run in females?
From the uterine horns in the parametrium, it enters the pelvis via the deep inguinal ring, passes through the inguinal canal to the labia majora
Where does the inguinal ligament run in relation to the external oblique muscle?
Runs inferomedially from the ASIS to the pubic tubercle, forming the free edge of the external oblique muscle
What forms the superficial inguinal ring?
External oblique aponeurosis (thickened medially and laterally by crura)
What is the conjoint tendon?
Merged fibres of the internal oblique and transverse abdominus muscles at the pubic tubercle which reinforces the inguinal canal medially
What forms the deep inguinal ring?
Transversalis fascia at the midpoint of the inguinal ligament
What forms the floor of the inguinal canal?
Inguinal ligament (+ lacunar ligament medially)
What forms the anterior wall of the inguinal canal?
External oblique aponeurosis
What forms the posterior wall of the inguinal canal?
Transversalis fascia (+ conjoint tendon medially)
What forms the roof of the inguinal canal?
Internal oblique and transverse abdominus muscle fibre arches + associated aponeuroses
What is the most common type of abdominal hernia?
Indirect inguinal hernia (M>F 7:1), mainly right sided
Describe the difference in the location of the deep inguinal ring and the femoral artery
- Deep inguinal ring - midpoint of the inguinal ligament, between ASIS and pubic tubercle
- Femoral artery - mid inguinal point, between the ASIS and the symphysis pubis
Explain the significance of the inferior epigastric vessels as a landmark for inguinal hernias
- Indirect inguinal hernias form LATERAL to the inferior epigastric artery and vein
- Direct inguinal hernias form MEDIAL to the inferior epigastric artery and vein
Describe the path of an indirect inguinal hernia
- Enters inguinal canal through deep inguinal ring, lateral to the inferior epigastric vessels, and protrudes out of the superficial inguinal ring
- Can progress to the scrotum depending on where the processus vaginalis was obliterated
Describe the path of a direct inguinal hernia
Protrudes through HESSELBACH’S TRIANGLE, generally in the vicinity of the superficial inguinal ring, medial to the inferior epigastric vessels
What are the borders of Hesselbach’s Triangle? (3)
- Lateral: Rectus abdominus
- Superomedial: inferior epigastric artery and vein
- Inferomedial: inguinal ligament (+ lacunar ligament)
Why does a direct inguinal hernia not usually progress to the scrotum?
Does not pass through the inguinal canal
Why is a femoral hernia more common in females?
Angle of pelvis is wider than males (childbirth)
Explain why a femoral hernia is more common to strangulation than other hernias
Borders of the femoral canal are tight (not lax) so can cut off blood supply to the section of herniated bowel
Where does a femoral hernia pass?
Through the femoral ring and into the femoral canal, out through the saphenous opening (can get trapped beneath the inguinal ligament -> strangulated hernia)
What is the difference between omphalocele and gastroschisis?
- Both occur due to defects in the anterior abdominal wall resulting in abdominal contents herniating out of the body cavity
- Omphalocele is similar to an umbilical hernia and bowel is usually covered with umbilical cord/visceral peritoneum, whereas in gastroschisis the bowel is uncovered
Explain the difference between an infant and adult umbilical hernia
- Infant: contents herniates through weakness in scar of umbilicus
- Adult: contents herniates through weakness in the linea alba in the region of the umbilicus (para-umbilicus)
Where does an epigastric hernia occur?
Through the linea alba between the xiphoid process and the umbilicus (usually fat, but chronic straining forces can eventually pull peritoneum through)
What is meant by ‘reduction’ of a hernia?
Hernia can be pushed back into the containing body cavity
When does a hernia become incarcerated and what is a possible consequence of this? (2)
- Hernia becomes STUCK or is IRREDUCIBLE
- Can lead to STRAGULATION
What is strangulation and what are its consequences?
- Blood supply cut off to an incarcerated hernia leading to bowel ischaemia
- Can eventually lead to necrosis (infarction) of herniated bowel
What is the difference between a ‘sliding’ hiatus hernia and a ‘rolling’ hiatus hernia?
- Sliding: gastro-oesophageal junction may slide through diaphragm into the chest cavity
- Rolling: part of the fundus of the stomach may slide through diaphragm into the chest alongside the oesophagus
What is the main predisposition to diaphragmatic hernias?
Developmental defects in the diaphragm muscle which allow any viscus to herniate into the chest cavity
What is the blood supply to the fundus of the stomach?
Small gastric arteries which branch from the splenic artery
Which arteries supply the lesser curvature of the stomach?
- Right gastric (branch of common hepatic)
- Left gastric (branch of celiac trunk)
Which arteries supply the greater curvature of the stomach?
- Right gastroepiploic (branch of gastroduodenal)
- Left gastroepiploic (branch of the splenic)
What is the function of rugae?
Non-permanent folds in the mucosa/submucosa which allow distension of the stomach so it can hold large volumes of food
Describe the arrangement of the stomach glandular structures microscopically
- GASTRIC PITS
- Continuous with gastric glands and contain specialised cells for the function of the stomach
What is the function of the muscularis externa of the stomach?
- Provides smooth contractions which mix and grind the contents of the stomach
- Move contents of stomach along to the pyloric sphincter
Describe how the contractions of the upper stomach aid in the transport of contents along the stomach (2)
- Fundus produces sustained contractions
- Creates a basal tone so the general direction of flow continues down the tube
Describe the muscular contractions of the lower stomach and how this helps in the transport of chyme into the duodenum (2)
- Strong peristaltic waves (proximal to distal) in antrum and pylorus to accelerate contents towards pyloric sphincter in a coordinated movement
- Large lumps get left behind so only small particles and water can pass through to the duodenum
Explain how the shape of the stomach aids in its function (2)
- Larger (proximal) to smaller (distal) so allows acceleration of contents along the tube to the pyloric sphincter
- Large lumps are left behind and liquid chyme passes into duodenum ~3 times per min
Explain the mechanisms by which the stomach is able to store food and the importance of this (3)
- Receptive relaxation of the orad stomach as food enters fundus from oesophagus (stomach dilates to avoid rise in intragastric pressure)
- Gastric mucosal folds (rugae) allow stomach distension
- Maintenance of intragastric pressure prevents reflux of stomach contents during swallowing
Give 3 reasons why the stomach contents needs to be acidic (3)
- Allows unravelling/breakdown of proteins
- Activation of proteases e.g. Pepsinogen
- Disinfection (kills bacteria)
Which cells secrete acid (HCl) into the stomach?
Parietal cells in the gastric pits
Describe the mechanism by which parietal cells produce an acidic environment within the stomach (2)
- Hydrolysis of water in mitochondria produces H+ and OH-
- OH- combines with CO2 to produce HCO3- which is secreted into the blood (alkaline tide) leaving H+ in the stomach
Explain the role of the ‘alkaline tide’ (2)
- HCO3- produced in the stomach is secreted into blood
- Re-secreted into the duodenum from the liver and pancreas to neutralise the acidic chyme leaving the stomach
Name 3 substances that stimulate parietal cells to secrete acid
- Gastrin
- Acetylcholine
- Histamine
Where is histamine secreted from in the stomach and what is its main role? (2)
- Released from enterochromaffin-like cells (ECL, mast cells)
- Acts on H2 receptors on parietal cells to stimulate acid secretion
What is the role of chief cells?
Release of protease Pepsinogen into stomach which is cleaved by HCl into PEPSIN - digestion of proteins into amino acids
Describe the cell distribution through the stomach (3)
- Cardia: predominantly mucus-secreting cells
- Fundus/body: parietal cells, chief cells, mucous cells
- Pylorus: G cells, D cells
What is the role of G cells?
Release of gastrin hormone which stimulates acid secretion from parietal cells
What is the role of D cells and where are they located? (2)
- Release of somatostatin which inhibits acid secretion via negative feedback
- Pyloric region of stomach
Describe how gastrin acts in parietal cells to stimulate acid secretion
Released from G cells and acts on CCK receptors on parietal cells to stimulate release of H+ into stomach lumen
Describe 3 ways parietal cells can be stimulated to secrete H+ (3)
- Binding of Gastrin (from G cells) to CCK receptors
- Binding of Histamine (from enterochromaffin-like cells) to H2 receptors
- Binding of Ach (from parasympathetic nerves) to muscarinic (M1) receptors
What stimulates gastrin secretion? (2)
- Vagal stimulation (release of Ach and GRP)
- Presence of peptides/AA in stomach lumen
How does somatostatin inhibit acid secretion? (3)
- As stomach empties, pH drops which stimulates D cells in antrum to release somatostatin
- Binds to S receptors on G cells inhibiting gastrin secretion and enterochromaffin-like cells inhibiting histamine secretion
- Gastrin and histamine therefore cannot bind to parietal cells and stimulate H+ secretion
Which channel do proton pump inhibitors act on?
H+/K+ ATPase on parietal cells, inhabiting acid secretion into stomach lumen
Explain how HCl is formed in parietal cells (2)
- Hydrolysis of water forms H+ and OH- ions
- OH- + CO2 (catalysed by carbonic anhydride) makes HCO3- which is transported out of the cell into the blood in exchange for Cl- via an anion exchanger (alkaline tide)
- (H+ + Cl- -> HCl)
Explain what occurs during the cephalic phase of digestion (2)
- Sight/smell/taste/swallowing of food stimulates vagus nerve
- Parasympathetic stimulation triggers release of Acetylcholine and GRP which stimulates G cells
Describe how food acts as a buffer during the gastric phase of digestion
Balances pH by buffering acidic conditions of the stomach thereby removing inhibition of gastrin secretion
Describe the gastric phase of digestion (3)
- Food buffers acidity of stomach thereby disinhibiting gastrin hormone secretion
- Acids and proteases break down proteins into peptides/AA, the presence of which further stimulate gastrin secretion from G cells
- Distension of the stomach stimulates vagus nerve via stretch receptors so increases parasympathetic stimulation
Describe the intestinal phase of digestion (3)
- Chyme detected in the duodenum signals for decrease in rate of digestion by inhibition of G cells (as food leaves pH drops)
- Presence of lipids stimulates enterogastric reflex which reduces vagal stimulation to the stomach
- Release of hormones from intestines such as CCK and GIP act to reduce acid secretion
Name 2 defence mechanisms of the stomach to protect against its acidic conditions
- Thick layer of alkaline mucus produced by mucus secreting cells which traps H+ ions and protects mucosa
- HCO3- ions secreted from mucous cells reacts with H+ to neutralise acid
Which hormone stimulates the stomach defences?
Prostaglandins
Name 3 things which can disrupt the stomach’s defences and lead to gastritis/ulceration (3)
- Alcohol (excess ingestion)
- Helicobacter Pylori infection
- NSAIDS
Describe how NSAIDS may lead to gastritis
- Inhibition of cyclo-oxygenase enzyme which is required for the production of prostaglandins
- Prostaglandins are required for the defence of the stomach mucosa so lack of these can leave stomach vulnerable to damage from acid, leading to inflammation of the mucosa
Describe 3 ways in which prostaglandins affect the stomach (3)
- Inhibit acid secretion from parietal cells
- Stimulate mucus and HCO3- secretion from mucus cells
- Maintain mucosal blood flow to provide nutrients to mucosal cells
What property of gastric mucosal cells can help in preventing gastric ulceration?
High cell turnover rate so rate of renewal exceeds rate of damaged, thereby preventing ulceration
Describe how excess alcohol ingestion can lead to gastritis
Alcohol dissolves the mucus layer in the stomach leaving the mucosa vulnerable to the acidic conditions of the contents
Describe how Helicobacter Pylori can lead to ulceration of the stomach mucosa
Causes CHRONIC active inflammation of the stomach mucosa leading to gastritis and potentially ulceration
Name 2 drugs which can be used to reduce acid secretion in the stomach and state their action (2)
- Cimetidine (H2 channel antagonist)
- Omeprazole (H+/K+ ATPase antagonist)
