GI system Flashcards
What is the masseter muscle and what is it supplied by?
Muscles that power the teeth in mastication. Supplied by a branch of the trigeminal nerve
Where does the oropharynx lie
Between nasopharyns and laryngopharynx
uvula to hyoid bone
What are the functions of saliva?
Lubrication of food
Initiation of carbohydrate digestion
Protection of oral environment
What are the components of saliva?
Water, electrolytes, alkali, bacteriostats, enzymes, mucus
How does the concentration of electrolytes and HCO3- in saliva compare to plasma?
Higher K+, I-, Ca2+ and HCO3-
Lower Na+ and Cl-
Which salivary glands secrete a mixture of serous and mucous saliva?
Submaxillary
Parotid are just serous
What effect does a high flow rate have on serous saliva composition?
Decreases time available for ductal modification so saliva is less hypotonic but it also increases HCO3- secretion so saliva is more alkaline
How does Na-K-ATPase control saliva composition?
NKA decreased internal sodium conc so sodium passively diffuses into duct cell from lumen. NKA also increases internal potassium conc. so there’s increased action of K+Cl- symporter so there’s decreased Cl- conc internally. This increases action of Cl-/HCO3- antiporter, bringing Cl- into the cell and bicarbonate out into lumen
What parasympathetic nerves are the parotid glands innervated by?
Otic ganglion glossopharyngeal nerve (9th cranial)
What parasympathetic nerves are the submandibular and sublingual salivary glands innervated by?
Facial nerve (7th cranial) Submandibular ganglion
Which muscarinic receptors are found in salivary glands?
M1
What sympathetic nerve supplied salivary glands?
Superior cervical ganglion
What movements are triggered in the pharyngeal phase of swallowing?
Inhibition of breathing
closure of glottis
Opening of upper oesophageal sphincter
Raising of larynx
What normally helps prevent reflux of stomach contents?
Lower oesophageal sphincter
angle of His
Crus of diaphragm
What does craniocaudal folding of embryo achieve in terms of gut development?
Creates cranial and caudal pockets from the yolk sac
What embryonic layers do the linings of the primitive gut derive from?
Internal linings derive from endoderm
External linings derive from splanchnic mesoderm. Develop into musculature and visceral peritoneum
What structures are part of the foregut?
Oesophagus
Stomach
Gall bladder, liver, pancreas
Duodenum proximal to ampulla of vater
What main artery supplies the foregut?
Coeliac trunk
Describe the blood supply to the pancreas head
From coeliac trunk via superior pancreaticoduodenal artery and from superior mesenteric artery via inferior pancreaticoduodenal artery
What structures are part of the midgut?
Duodenum distal to ampulla of Vater Jejunum Ileum Caecum Ascending colon Proximal 2/3rds of transverse colon
What structures are contained within the hindgut?
Distal third of the transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra
What does the diaphragm do to the intraembryonic coelom?
Divides it into thoracic and abdominal cavities
What is the purpose of the mesentery that suspends the primitive gut from the abdominal wall?
Allows conduit for nerve and blood supply
Allows mobility when needed
How is the mesentery suspending primitive gut formed?
By condensation of double layer of splanchnic mesoderm
Where along the primitive gut tube is there ventral mesentery?
Only along the foregut
What are the origins of the greater and lesser omentum?
Greater omentum comes from dorsal mesentery
Lesser omentum comes from ventral omentum
What’s the significance of the free edge of the ventral mesentery?
Conducts portal triad in life and gives access to the lesser sac
Where does the greater sac originate from?
The left hand side division formed by dorsal and ventral mesenteries
What directions does the stomach rotate in?
Longitudinal 90degrees around it’s axis
Anteroposteriorly
What does rotation of the stomach achieve?
Pulls dorsal mesentery laterall, creating the lesser sac behind the stomach
Puts vagus nerves anterior and posterior to the stomach
Forms the greater omentum
Shifts the cardia and pylorus from the midline
Pulls developing liver to the right
How is development of GI and respiratory tract related?
Foregut extends from lung bud to liver bud. In week 4 respiratory diverticulum forms on ventral wall of foregut and develops, forming a tracheoesophageal septum, until respiratory primordium is a separate tube to the oesophagus.
What can happen if the tracheoesophageal septum is abnormally positioned?
Can get abnormal communications and fistulae or blind ending oesphagus
Which foregut glands develop in the ventral mesentery?
Liver, biliary system and uncinate process and inferior head of pancreas
Describe the process of intestinal looping
Midgut intestinal loop has cranial and caudal limbs that use the sma as their axis and connect to the yolk sac via the vitelline duct. In order to make space for the rapidly developing intestines and liver, the intestinal loop herniates out into the umbilical cord and then undergoes looping. In turns 180 degrees anticlockwise around its axis, bringing caudal limb superiorly and then returns to the abdominal cavity, there it completes a further 90 degree turn
Where’s the junction in an adult between cranial and caudal limb of embryonic midgut?
Within the ileum
What is meant by incomplete rotation of the intestinal loop?
If intestine only makes one 90 degree turn then there’s a left sided colon
What happens if there’s reversed rotation of intestinal loop?
May be one 90 degree turn clockwise then duodenum and cranial limb end up passing anteriorly to transverse colon. Can be prone to obstruction of the transverse colon
What are some examples of major midgut defects?
Sub-hepatic caecum if caecum doesn’t descend
Volvulus of colon to obstruct the duodenum
Compression of transverse colon by superior mesenteric artery
What can occur if the vitelline duct persists?
Vitelline cyst where cyst is joined either side by fibrous strands to umbilicus and intestine
Vitelline fistula where there’s direct communication between intestine and umbilicus
Meckel’s Diverticulum - diverticulum of ileum, connected to umbilicus via fibrous strand
What is meckel’s diverticulum?
Rule of 2’s - occurs in 2% of the population, 2 feet from ileocaecal valve, 2 inches in length with 2:1 ratio occurence in men:women
Can contain ectopic gastric or pancreatic tissue so is prone to inflammation. Similar presentation to appendicitis
Why might atresia/stenosis occur in GI tract?
In duodenum, oesophagus and bile duct, lumen gets obstructed by proliferating cells followed by recanalisation. If recanalisation fails either completely or partially, there’s atresia or stenosis
What causes pyloric stenosis?
Hypertrophy of circular muscle at pyloric sphincter. Presents in infants with projectile vomiting
What is gastroschisis?
Anterior abdominal wall fails to close completely in embryonic folding so normally folded intestines lie outside of body cavity. May be necrosis
What is omphalocoele/ examphalos?
Where intestinal loop fails to return to abdominal cavity after physiological herniation. Gut is outside of body, improperly folded, covered by amnion.
High likelihood of other developmental defects.
How is the anal canal formed?
Urogenital septum (mesoderm) descends to separate cloaca into anorectal canal and urogenital sinus. Sinus and canal are separated by perineal body exteriorly
What are the differences in nerve and blood supply between 2 parts of anal canal?
Below pectinate line - supplid by pudendal artery and nerve (s2-4) and drained by superficial inguinal nodes. Lined by stratified squamous epithelium. Sensitive to temperature, pain and touch.
Below pectinate line - supplied by IMA and pelvic nerves (s2-4) and drained by internal iliac nodes. Lined with columnar epithelium and sensitive to stretch only
What is the difference between an anorectal agenesis and an imperforate anus?
Imperforate anus is where anal membrane fails to rupture so there’s no communication of anal canal to outside. Anorectal agenesis is when there’s failure to form an anorectal canal
What is a hindgut fistulae?
Where hindgut makes inappropriate communications, eg rectum with bladder
What’s the difference between an indirect and a direct inguinal hernia?
Indirect hernias pass lateral to inferior epigastric vessels and occur through the deep inguinal ring whereas direct hernias pass medial to the inferior epigastric vessels and pass through a weakened area of tranversalis fascia called hesselbach’s triangle.
Indirect are normally of embryonic origin
What are the borders of hesselbach’s triangle?
Lateral - inferior epigastric artery
Medial - Lower lateral border of rectus abdominis
Inferior - medial inguinal ligament
Where is the inguinal canal?
Oblique passage between deep and superficial inguinal rings, between layers of anterior abdominal ,muscles. Runs parallel and superior to the medial inguinal ligament
What are the contents of the inguinal canal?
Ilioinguinal nerve
Spermatic cord or round ligament of uterus
How can an inguinal hernia be tested for?
By palpating either hesselbach’s triangle or the superificial inguinal ring and asking patient to cough. If a sudden impulse is felt then there is a hernia
Where do epigastric hernias occur?
In the midling between xiphoid process of sternum and the umbilicus through the linea alba. Commonly occurs in pregnancy or obesity
What is a Richter’s Hernia?
Where only part of the intestine protrudes through the defect, with the rest of the lumen remaining in the peritoneal cavity. At high risk of strangulation and perforation
What are spigelian hernias?
Hernia along semilunar lines of abdomen. Common in over 40s and the obese
Where do femoral hernias occur?
Into femoral canal through the femoral ring, bound laterally by femoral vein and medially by the lacunar ligament. Often presents as tender mass within femoral canal, inferolateral to pubic tubercle.
What are some complications of femoral hernias?
They compress the contents of the femoral canal and so they distend its walls. Also at high risk of strangulation due to the rigib borders of the femoral canal.
Can pass through saphenous opening into subcutaneous tissue of thigh where it can grow as it’s no longer contained by walls of canal
What is a divarication of recti?
Weakness in linea alba so rectus abdominis stretches apart. Often only cosmetic and most common in pregnancy and neonates
Why do umbilical hernia occur?
Most common in neonates. After ligation of umbilical cord, there’s weakness in abdominal wall as there is incomplete closure of umbilical ring so can be protrusion through umbilical ring.
Can be acquired, commonly in women or the obese.
Both often occur after increased intraabdominal pressure
What are the borders of the anterolateral abdominal wall?
Superiorly - cartilages of ribs 7-10 and xiphoid process of the sternum
Inferiorly - Inguinal ligament and superior margins of anterolateral aspects of pelvic girdle (iliac crests, pubic symphysis, pubic crests)
From anterior to posterior, what are the different layers of the anterolateral abdominal wall?
Skin Fatty layer of superficial subcutaneous tissue Deep membranous layer of subcutaneous tissue Superficial investing fascia External oblique muscle Intermediate Investing fascia Internal oblique muscle Deep investing fascia Transversus abdominis muscle transversalis fascia Extraperitoneal fat Parietal peritoneum
Roughly at which spinal level is the umbilicus?
L3
Where is heartburn most commonly felt?
In epigastric fossa which is a slight depression, just inferior to xiphoid process of the sternum
What is the linea alba?
An aponeurosis of abdominal muscles, that separates right and left rectus abdominis
What is the difference between the pubic crest and the pubic symphysis?
Crest is the upper margin of the pubic bones and the symphysis is a cartilaginous joint that unites these bones
What landmark marks the division between the thigh and abdominal wall?
The inguinal groove - skin crease just inferior to inguinal ligament
What is the arcuate line?
Where the posterior layer of the rectus sheath ends. It lies a third of the way down from umbilicus to pubic symphysis.
What nerve supplies the obliques and transversus abdominis?
Thoracoabdominal subcostal nerve, T6-T11
What is the rectus sheath?
A strong aponeurosis, made up of continuations of anterior and medial aponeuroses of the 3 flat muscles (obliques and transversus abdominis) which extend from mid-clavicular line to midline.
The sheath encloses rectus abdominis apart from below the arcuate line, where there’s no posterior covering
What are the layers, superficial to deep, surrounding rectus abdominis, above the arcuate line?
Skin Subcutaneous tissue External oblique fascia Internal oblique fascia Rectus abdominis Internal oblique fascia Transversus abdominis fascia Transversalis fascia Parietal peritoneum
What are the layers, superficial to deep, surrounding rectus abdominis, below the arcuate line?
Skin Subcutaneous tissue External oblique fascia Internal oblique fascia Transversus abdominis fascia Rectus abdominis Transversalis fascia Parietal peritoneum
What is the clinical significance of the arcuate line?
Used as marker in C-sections so incisions are made below this point to minimise structures cut through
Where is the pyramidalis muscle?
Enclosed in the rectus sheath, anterior to the inferior rectus abdominis. It’s attached to the anterior pubis and anterior pubic ligament and acts to tense the linea alba
What kind of an incision is one made along the linea alba?
Midine incision. Good for exploratory operations
Where do we cut in a transverse incision?
Along aponeurosis of external oblique muscle
Where do we cut in an appendicectomy?
At Mcburney’s point which is two thirds of the way from umbilicus to ASIS
What kind of incision is used in an appendicectomy?
Gridiron - Put scissors in and open and close to separate out muscle fibres, layer by layer
What is a pfannenstiel incision?
AKA suprapubic incision. Made at pubic hairline, transcects linea alba and rectus sheath. Used in OB-GYN operations, expecially c-sections
What’s the difference between a patent urachus and a patent vitelline duct?
Urachus connects bladder to umbilicus so can present either at birth or later in life due to outflow obstruction i.e. from prostatic hypertrphy.
Vitelline duct connects gut to umbilicus. Can cause various different problems such as vitelline cyst, meckel’s diverticulum or vitelline fistula (faecal matter comes out of umbilicus)
What is somatic referred pain?
Pain caused by noxious stimulus to the proximal part of a somatic nerve, that’s perceived in the distal dermatome of that nerve.
E.g. in shingles
What is visceral referred pain?
Visceral afferent pain fibres follow same route as sympathetic fibres back to spinal segment that gives rise to preganglionic sympathetic fibres. CNS then peceives the visceral pain as coming from the same somatic portion that’s supplied by that spinal cord segment
What stimuli can cause visceral referred pain?
Stretch, ischaemia, inflammation, Abnormally strong muscle contraction
Where is pain felt in renal or ureteric colic?
Right lower quadrant/right flank pain
What is felt in referred diaphragmatic irritation and what can cause it?
Blood pools in peritoneum so patient feels faint and lies down. Blood pools around diaphragm and this irritates the left diaphragm especially (no liver in the way) so there’s pain referred along the phrenic nerve (C3-C5) so is felt in left shoulder
What drains peritoneal fluid?
Lymphatics, especially of inferior diaphragm
Where are the openings of the peritoneum?
Completely closed in men.
In women there’s a communication via uterine tubes and vagina to the outside world
What is the peritoneum?
2 Continuous layers of mesothelium (simple squamous) membrane
What separates parietal peritoneum from the anterior abdominal wall?
Extrapertioneal connective tissue which is fatty and particularly dense posterior to linea alba and on inferior diaphragm
What is the embryological origin of peritoneum?
parietal from somatic mesoderm and visceral from splanchnic mesoderm
What is a mesentery?
A double layer of peritoneum that’s formed by invagination of peritoneum by an organ
What is the function of mesentery?
Connects organs to posterior abdominal wall
Provides pathways for nerves, blood and lymph vessels between abdominal wall and viscera (organs)
What is the greater omentum?
Four-layered, fatty, prominent peritoneal fold that goes from greater curvature of stomach and proximal duodenum, hangs down then loops back up to attach to anterior transverse colon
What is the function of the greater omentum?
Acts as the abdominal constable by migrating to infected viscera to wall off infection.
Also acts to cushion and insulate viscera
What is the lesser omentum?
A smaller, double-layered peritoneal fold that connects lesser curvature of stomach and poximal duodenum to the liver, via membranous hepatogastric ligament and the hepatoduodenal ligament which provides the thickened free edge. Lesser omentum also connects the stomach to the portal triad
What are peritoneal ligaments?
Double folds of peritoneum that connect organs either to another organ or to the abdominal wall
How does the liver connect to the abdominal wall?
Via the falciform ligament
What peritoneal ligament conducts the portal triad and what is the portal triad made up of?
Hepatoduodenal ligament
made up of hepatic artery, portal vein and bile duct
How does the stomach connect to the transverse colon?
By gastrocolic ligament/ greater omentum
Why do organs have bare areas?
To allow passage of neurovascular structures
What organs are retroperitoneal?
Suprarenal glands Aorta/IVC Duodenum (except cap) Pancreas Ureters Colon (ascending and descending) Kidneys Esophagus Rectum
What is the greater sac made up of?
Supracolic and infracolic compartments
What is the lesser sac?
An extensive sac like quality that lies posterior to the stomach, lesser omentum and adjacent structures. It’s limited superiorly by the diaphragm and coronary ligament of the liver and its inferior recess lies between superior layers of greater omentum but mostly gets sealed off in childhood.
It acts to allow free movement of the stomach on the structures posterior and inferior to it
What is the epiploic foramen?
AKA omental foramen. It’s how the greater and lesser sacs communicate. It’s situated posterior to the free edge of the lesser omentum and posterior to the gallbladder.
What are the 9 surface regions of the abdominal wall and what planes define them?
Between the two midclavicular lines are the epigastric, umbilical and hypogastric regions. These are separated by the subcoastal and transtubercular lines respectively.
To the right of this are the right hypochondriac, lumbar and iliac regions, separated by the same horizontal planes.
On the left are the left hypochondriac, lumbar and iliac regions
What are the supracolic and infracolic compartments?
Separated by the transverse mesocolon.
Supracolic contains the stomach liver and spleen and infracolic contains the small intestine and the ascending and descending colon.
The infracolic compartment lies posterior to the greater omentum and can be further divided into right and left infracolic compartments by the root of the mesentery of the small intestine.
How do the supracolic and infracolic compartments communicate?
Through the right and left paracolic gutters which are grooves between the posterolateral abdominal wall and the lateral aspects of the ascending and descending colon
What is the significance of the subphrenic spaces?
Common sites of fluid collection. The right space, especially after right-sided abdominal inflammation and the left, especially after a splenectomy
Where is the right subphrenic space?
Lies between the diaphragm and the anterior, superior and right lateral surfaces of the right lobe of the liver.
It’s bounded on the left by the falciform ligament and from behind by the superior coronary ligament.
Where is the left subphrenic space?
Lies between the diaphragm and the anterior and superior surfaces of the left lobe of the liver, the anterosuperior aspect of the stomach and the diaphragmatic surface of the spleen. It’s bounded on the right by the falciform ligament and from behind by the anterior left triangular ligament
What peritoneal pouches are there in females?
Vesicouterine pouch between superior bladder, cervix and fundus of uterus
Rectouterine puch of Douglas between fundus of uterus, Vaginal fornix and rectum
What peritoneal pouches are there in men?
Rectovesicle pouch between bladder and rectum
What is The Mesentery?
Broad, fan shaped fold that connects the jejunum and ileum to the posterior abdominal wall to allow them to move more freely within the abdominal cavity.
Where is the root of the mesentery of the small intestine?
Acts as division of right and left infracolic compartments.Runs obliquely from duodenojejunal flexure on the left of L2 vertebra to the ileocaecal junction on the right.
What does the root of the mesentery cross, left to right?
Second and third parts of the duodenum Abdominal aorta IVC Right ureter Right psoas major muscle Right gonadal artery
What is the sigmoid mesocolon?
Peritoneal fold attaching the sigmoid colon to the pelvic wall. Inbetween the folds of peritoneum are sigmoid and superior rectal vessels
What are the functions of the stomach?
Storage
Disinfection
Breakdown of food
What types of cells are found in gastric glands?
Parietal cells - release HCl
Chief cells - Release Proteolytic enzymes
G cells - Release gastrin
What is the alkaline tide?
Refers to the one mole of HCO3- that’s released into the blood for every one mole of H+ that’s released into stomach contents, by parietal cells.
How is gastric acid secretion controlled?
Stimulated by:
Gastrin which is stimulated by ACh and presence of peptides but is inhibited via negative feedback by acid
ACh which is stimulated by distension and post-ganglionic parasympathetic neurones.
Histamine which is released from mast cells and stimulated by ACh and gastrin
What are the 3 phases of gastric secretion?
Cephalic phase - ACh release in response to swallowing, smell and sight of food.
Gastric phase - Distension as food reaches stomach stimulates ACh. Also, food buffers acid so pH rises and gastrin is disinhibited.
Intestinal phase - When enough chyme is released into intestines, intestines release hormones - cholecystekinin and Gastric Inhibitory Peptide which act to antagonise gastrin. Also, there’s no more buffering of acid in stomach so gastrin is inhibited again
What drugs can be used to reduce gastric acid secretion?
Proton pump inhibitors which stop H+ being secreted into lumen
H2 histamine receptor blockers so there’s no amplification of signal from ACh and gastrin
What is the purpose of the mucus secreted by neck cells in the stomach?
The mucus is sticky and basic and forms an unstirred layer next to surface epithelial cells. Surface cells secrete HCO3- which stay in the mucus. H+ ions can slowly diffuse through to rect with this HCO3- and basic groups in the mucus. The pH of the unstirred layer is >6
This all acts to protect the mucosa of the stomach from the very low pH of the gastric contents (<2)
How can the stomach’s defences be breached?
Alcohol can dissolve mucus, exposing mucosa to damage.
If an H. Pylori infection takes hold, bacteria can inhibit mucus and HCO3- production, which damages the defenses.
NSAIDs inhibit prostaglandin production which normally act to stimulate mucus and HCO3- production.
Aspirin is also deionised by the stomach acid so it can easily pass through the mucus, into surface cells where it reionises.
Describe the process of receptive relaxation
On swallowing, there’s a vagal reflex for the stomach walls to relax. This allows accommodation of food but doesn’t act to increase the pressure so risk of reflux is reduced.
What effect do peristaltic contractions have on the stomach?
Stimulated 3 times a minute by pacemaker in cardia region. Causes contraction of smooth muscle from cardia to pylorus that accelerates as it goes. This forces contents towards the pyloric region for emptying, however, larger chunks are left behind in the fundus for further breakdown.
This combines with the funnel shape of the stomach to mix up and propel the contents of the stomach towards the pylorus for emptying into duodenum.
How is rate of gastric emptying controlled?
By pacemaker in cardia
By rate of acceleration
By release of hormones from intestine in response to fat content, pH and Hypertonicity.
What mechanisms are there to prevent gastro-oesophageal reflex?
Right crus of diaphragm acts as sling around lower oesophagus
Lower oesophageal sphincter is normally closed, only opens transiently in swallowing
Gravity
Secondary peristalsis
Oesophagus enters stomach within abdominal cavity which has higher pressure than thoracic cavity
Oesophagus enters stomach at acute angle
What is a hiatus hernia?
When part of stomach herniates up through opening of diaphragm that oesophagus runs through
What drugs are used to treat GORD?
Simple antacids
raft antacids
PPIs
H2 antagonists
What are the main features of peptic ulcers?
Recurrent, burning epigastric pain that’s worse at night
Anorexia and weight loss in gastric ulcers
May be nausea and vomiting
How are H pylori associated Peptic ulcers treated?
With triple therapy
PPI
Antibiotic
H2 antagonist
What are the main characteristics of Helicobacter pylori?
Gram negative, aerobic, urease producing, helical bacteria
What’s the advantage of H. pylori being a urease producer?
Urease produces ammonia which helps to neutralise the acidic environment around the bacteria, aiding survival
How does H pylori cause gastritis?
Colonises gastric epithelium and releases enzymes and induces apoptosis, damaging the epithelia.
It also stimulates an imflammatory response that causes further inflammation and damage
How is H pylori diagnosed?
IgG antibody serum test
13C-urea breath test
Endoscopy and gastric sample which is then cultured
At what vertebral level is the lower oesophageal sphincter?
T11
What is the z line of the oesophagus?
Point at which epithelia changes from oesophageal (stratified squamous) to gastric
What is the gastric canal?
A temporary groove formed in swallowing along the lesser curvature to allow the passage of saliva, small amounts of masticated food and other fluids to drain into the pylorus, when the stomach’s almost empty
What are the 3 most histologically distinct areas of the stomach?
Cardia - neck cells that secrete mucus
Fundus and body - neck cells, parietal cells that secrete acid and chief cells that secrete pepsiogen
Pyloris - neck cells and G cells that secrete gastrin
How many layers of smooth muscle are there in the stomach?
3 - longitudinal, circular and oblique
Describe the stomach’s blood supply
Derives from the coeliac trunk which gives off the left gastric and the common hepatic, which gives off the right gastric artery. These supply the lesser curvature.
Coeliac trunk also gives off the splenic and common hepatic which give off left and right gastroomental arteries respectively. These supply the greater curvature
The splenic artery also gives off the posterior and short gastric arteries which supply the fundus and body
Describe the venous drainage of the stomach.
Mirrors the arterial supply.
left and right gastric vein drain directly into hepatic portal vein. Short gastric and left gastroomental drain into splenic vein and right gastroomental drains into superior mesenteric vein.
Superior mesenteric and splenic then drain into the hepatic portal vein
What are the differences between the main components of bile?
Bile acid dependent component is secreted by hepatocytes into canaliculi. Contains bile acids and bile pigments, with little enzymes but does contain cholesterol.
Bile acid independent component is secreted by duct cells into bile ducts. Contains high levels of HCO3- and enzymes
Why is the gall bladder needed to store bile?
As, with enterohepatic circulation, bile acids return after they’re needed and need to be stored somewhere before they’re needed at the next meal
What stimulates gall bladder secretion?
Cholecystokinin (CKK) released by duodenum in response to high fat content/hypertonicity. Travels in blood to gall bladder where it stimulates gall bladder muscle to contract so bile is ejected into the cystic duct, where it mixes with enzymes from the pancreas and alkali from the pancreas and liver
How is bile modified in the gall bladder?
Epithelium of gall bladder removes Na+ from bile and so Cl- and water follow so bile becomes more concentrated but osmolarity stays the same. There’s therefore a higher concentration of other components, particularly bile acids, increasing the chance of precipitation formation and so the risk of gall stones forming
How are bile acids used in fat digestion?
In the stomach, as acid breaks down contents, fat forms large globules with a decreased surface area for enzyme action.
Bile acids allow fats to form micelles, with fat soluble vitamines, phospholipids and cholesterol on the inside and polar bile acids on the outside.
Micelles transport fats into unstirred layer of stomach, where fatty acids are released into epithelium where they are added to glycerol to make TAGs. These are then released as chylomicrons which facilitate transport of fat in the lyphatics system from gut to the rest of the body
What does the exocrine pancreas secrete?
Duct cells secrete an alkaline juice and acinar cells secrete enzymes such as proteases, amylases and lipases
What is exocrine pancreas secretion stimulated by?
Duct cells are stimulated by secretin which is released from jejunum in response to low pH and is amplified by CCK
Acinar secretion is stimulated by CCK
What is the process behind enzyme activation from the pancreas?
Synthesised on ribosomes and then packaged into condensing vacuoles by the golgi complex (inactive form) this makes zymogen granules which are released by exocytosis into the intestine, where the enzymes are activated by enzymatic cleavage
Describe enter-hepatic circulation
Bile acids are secreted into canaliculi and then as bile into the duodenum where they travel to the terminal ileum. Once there, they’re taken up by ileal epithelial cells and transported in portal system back to the liver where they’re actively absorbed by hepatocytes
What is the anatomical location of the liver?
Occupies most of the right hypochondrium and epigastrium and extends into left hypochondrium. Lies deep to 7th-11th ribs on the right and crosses the midline towards the left nipple. Its position changes slightly with respiration and when upright
What does the inferior border of the liver mark?
It follows the right costal margin.
Separates the concave inferoposterior visceral surface from the convex anterosuperior diaphragmatic surface
What is the subhepatic space?
Part of the supracolic compartment, directly below the liver
What are the right and left subphrenic spaces separated by?
Falciform ligament
What lies within the falciform ligament?
Remnant of the umbilical vein - ligamentum teres
What is the bare area marked by?
Peritoneal reflection into coronary ligament layers which then meet to form the right triangular ligament, then diverge left to form the left triangular ligament.
Anterior layer is continuous with right layer of falciform ligament and posterior layer is continuous with right layer of lesser omentum
Where is the visceral surface of the liver not convered with peritoneum?
Bare area
Fossa of the gallbladder
porta hepatis
What is the porta hepatis?
Transverse fissure for hepatic portal vein, hepatic artery and lymphatics
What are the different lobes of the liver?
2 anatomical - right and left, separated by falciform ligament.
2 accessory - right lobe separated by left and right sagittal fissures which form a space that’s separated by porta hepatis into caudate lobe (posterior and superior) and quadrate lobe (anterior and inferior)
What do the left and right sagittal fissures transport?
Left - ligamentum teres anteriorly and ligamentum venosum posteriorly
Right - Fossa of gallbladder anteriorly and IVC posteriorly
Describe where bile is carried from hepatocytes to the duodenum
Hepatocytes Canaliculi Interlobular biliary ducts Large collecting bile ducts Right and left hepatic ducts Common hepatic duct \+ cystic duct Bile Duct \+pancreatic duct Ampulla of Vater
What is the arterial supply to the gall bladder and biliary tree?
Coeliac trunk - common hepatic artery - right hepatic artery (supplies middle bile duct) - Cystic artery (supplies proximal bile duct)
Where does the cystic artery arise?
In cystohepatic triangle of Calot
Between common hepatic duct, cystic duct and visceral surface of the liver
What is the venous drainage of the gall bladder?
For neck of gall bladder and the cystic duct, drain via cystic veins which can drain into liver directly or into hepatic portal vein.
For body and fundus, drain directly into visceral surface of the liver into sinusoids
What is the anatomical location of the pancreas?
Retroperitoneal.
Crosses transversely L1 and L2 vertebrae at the level of the transpyloric plane. Lies posterior to the stomach, between the spleen and the duodenum.
What are the locations of the 4 different parts of the pancreas?
Tail lies anterior to the left kidney. It’s mobile and passes alongside the splenic vessels.
Body lies to the left of the superior mesenteric vessels. Its posterior is in contact with the aorta, superior mesenteric artery, left adrenal gland and kidney and the left renal vessels
Neck - overlies the superior mesenteric vessels which forma groove in the neck’s posterior surface.
Head - Has curve of duodenum wrapped around it. Lies to the right of the superior mesenteric vessels. The bile duct lies in a groove on the head’s posterosuperior surface`
Describe the passage of the main pancreatic duct
Runs the length of the pancreas from tail to head and starts to run inferiorly when it’s close to the bile duct. When the two meet, they form the dilated ampulla of Vater which opens into duodenum and the major duodenal papilla. Flow from ampulla into duodenum is controlled by the sphincter of Oddi.
What is the arterial supply to the pancreas?
Gastroduodenal artery gives off the anterior and posterior superiorpancreaticoduodenal arteries and the superior mesenteric artery gives off the anterior and posterior inferior pancreaticoduodenal arteries.These all form arcades that supply the pancreas along with pancreatic branches of the splenic artery
What is the venous drainage of the pancreas?
Head has corresponding superior and inferior pancreaticoduodenal veins. Mostly corresponding veins that drain into the splenic and superior mesenteric veins into hepatic portal system
Where is the spleen located?
In superolateral part of the left hypochondrium, resting on the left colic flexure
What are the functions of the spleen?
Lymphocyte proliferation
Antibody formation
Blood store
Destroys expended red blood cells and broken down platelets.
What are the anatomical relations of the spleen?
Anteriorly - Stomach, attached through gastrosplenic ligament
Superiorly and posteriorly - diaphragm
Inferiorly - Left colic flexure
Medially - Left kidney, attached by splenorenal ligament
Describe the arterial supply to the spleen.
Splenic artery is largest branch of celiac trunk. Passes posterior to omental bursa and anterior to the left kidney, along the superior border of the pancreas. Within the splenorenal ligament, it divides into branches which enter the splenic hilum and each supplies a different vascular segment
How does the location of a gall stone obstruction relate to its symptoms?
In gall bladder - asymptomatic
In cystic duct - cholecystitis with bile accumulation in gall bladder causing severe collicy pain
In Common bile duct - biliary obstruction and jaundice as hepatic outflow is affected
Terminal duct/ampulla - pancreatitis
How does saliva act as an innate barrier against infection?
Contain lysozymes and lactoperoxidases that break down peptidoglycan cell wall in gram +ve and -ve bacteria respectively. Also contains IgA and some neutrophils and complement molecules.
How do the secretions of the small intestine act as an innate barrier against infection?
Contain bile which is a detergent and proteolytic enzymes. Also anaerobic with very little nutrients and sheds epithelial cells of intestine - difficult for bacteria to adhere
What can cause achlorrhydria?
Pernicious anaemia
H2 antagonists
PPIs
What innate cellular barriers are there in the GI tract?
Neutrophils Eosinophils (esp. parasitic) Mast cells Macrophages Natural killer cells Portal system
What can cause inflammation of peyer’s patches?
Typhoid fever. Can be fatal if they rupture.
Inflammation can cause mesenteric adenitis which is often mistaken for appendicitis
What effect does alcohol abuse have on the liver?
Decreases fat metabolism so fat deposits in liver. Liver becomes large and greasy.
Alcohol is toxic so cells have granular cytoplasm
Cytotoxicity stimulates aggregation of neutrophils, macrophages and lymphocytes. Inflammatory response - Hepatitis
Cells try and regenerate but have lost their architecture so form nodules, separated by fibrous septa - cirrhosis
What are the different types of gall stone?
Mixed. Made of cholesterol and calcium and bile pigment. Medium sized and most common.
Cholesterol only. Very large and more pale.
Pigment stones. Very small and dark, made of calcium bilirubinate. Easily dislodge and cause obstruction
What are some complications of gallstones?
Mucocele Empyema Obstructive jaundice Ascending cholangitis Gallstone ileus Acute pancreatitis Gall bladder perforation
What is charcot’s triad of ascending cholangitis?
Right upper quadrant pain
Fever
Jaundice
What are the main causes of pancreatitis?
Gallstones Ethanol Trauma Steroids Mumps Autoimmune Scorpion bite Hyperlipidaemia ERCP/ Iatrogenis Drugs
What’s the difference in presentations between acute and chronic pancreatitis?
Acute is rapid onset with severe pain, vomiting, shock, dehydration and constipation. With haemorrhage and necrosis.
Chronic involves fibrosis and calcification due to progressive parenchymal destruction. Causes pain, diabetes mellitus, jaundice, weight loss
How can Colitis of Undetermined Type and aetiology be further differentiated?
If diagnosis made in acute phase, do serolgy testing for Anti Neutrophil Cytoplasmic Antibodies which are increased in ulcerative colitis of for Anti Saccharomyces Cervisiae Antibodies which are increased in Chron’s disease..
Sometimes diagnosis may only be possible with colectomy specimen
How does the distribution of inflammation in Crohn’s and Ulcerative colitis differ?
In UC, inflammation is superficial - confined to mucosa with inflammatory infiltrate into lamina propria. Inflammation starts at rectum and extends proximally through colon, to variable amount but always continuously
In Crohn’s inflammation is transmural and granulomatous and can occur anywhere in the GI tract from the mouth to the anus and can be discontinuous
What type of T helper cell is involved in UC and Crohns?
In UC it’s TH2 that release IL-5 and TGF
In Crohn’s it’s TH1 that release interferon gamma and IL-2
What are the names of the different types of ulcerative colitis?
Proctitis - only rectum affected
Left sided colitis - only part of colon affected
Pancolitis - entire colon affected
Backwash ileitis - terminal ileum affected due to backwash from incompetent ileocaecal valve
How is ulcerative colitis treated?
Mainly with corticosteroids.
Suppository/topical in proctitis. Topical enema in left-sided colitis and oral or anti-TNF antibodies in pancolitis
How can ulcerative colitis be treated surgically?
With colectomy or end ileostomy with rectal preservation. Only done in acute disease with patients with complications or corticosteroid dependence
How can crohn’s disease be treated pharmacologically?
Anti-TNF antibodies used to induce and maintain remission and in perianal disease.
To induce remission, also use glucocorticosteroids and enteral nutrition.
To maintain remission, also use methotraxate or azathioprine.
For perianal disease, can also use azathioprine or ciprofloxacin and metronadizole.
How can Chron’s disease be treated surgically?
With colectomy or ileorectal anastamosis. Used if other therapies have failed or if complications occur
How is the surface area of the small intestine increased?
Very long. Mucosa is also divided into villi with many enterocytes dividing in their crypts. Enterocytes gradually move up towards tips, acquiring ability to absorb as they go. THese enterocytes have microvilli on their luminal surface - further increases surface area
What functions are shared by all segments of the small intestine?
Secretion of proteases, carbohydrases and homones such as gastrin, secretin and cholecystokinin
Where in the small intestine is iron absorbed and what is the process?
Iron is solubilised into it’s ferrous form (Fe2+) by gastric acid and stomach secretes gastroferrin which maintains it in its ferrous form. Then enters duodenum where transferrin is secreted which binds to iron and the whole complex is taken up by duodenum. Iron is then liberated, enters blood stream where it binds to transferrin once more
What’s absorbed in the jejunum?
Amino acids, carbohydrates and small enough particles such as vitamins and minerals, fatty acids, electrolytes and water
What is absorbed in the ileum?
Bile, B12 and any substances not absorbed in jejunum
What does the large intestine absorb?
Water for compaction of faeces, any other absorbable nutrients not absorbed by small intestine, vitamins created by colonic bacteria (K, B12, riboflavin, thiamine)
What are the most common forms of carbohydrates in diet?
Amyloses which are straight chains with alpha 1-4 bonds and amylopectins which are branched with alpha 1-6 bonds
How are carbohydrates enzymatically digested?
Alpha amylases in saliva and pancreatic juices act at alpha 1-4 bonds to break down amyloses into glucose and maltose and to break down amylopectins into alpha-limit dextrins
Brush border enzymes then continue digestion
Isomaltase acts at alpha 1-6 bonds
Maltase breaks down maltose into glucose
Sucrase breaks down sucrose into glucose and fructose
Lactase breaks down lactose into glucose and galactose
How are monosaccharides absorbed?
Glucose (and galactose) enter via cotransport with sodium by SGLT1 contransporter and then removed basolaterally by GLUT2 channel
Lactose and fructose are absorbed by facilitated diffusion that’s not sodium linked
How are proteins broken down?
In stomach by pepsin into oligopeptides, cleaves bonds next to aromatic amino acids.
Then in duodenum by peptidases.
Trypsin cleaves near basic side chains
Chymotrypsin cleaves near aromatic side chains
Carboxypeptidase cleaves c-terminal amino acids with basic side chains
Describe motility of small intestine
Occurs through segmenting. Each segment has its own pacemaker. Contractions occur down the small intestine with decreasing frequency so an intestinal gradient forms and the net movement is towards the colon.
When it’s nearly empty, i.e. at night, there is peristaltic movement to remove dead cells
Describe motility of the colon
Colon divided into haustra. Each of these contract to shuttle contents down towards sigmoid colon. Once or twice a day, often associated with meal times due to gastrocolic reflex or at certain time due to habit, there’s propulsive, peristaltic movement from transverse colon to descending colon, forcing contents into rectum.
How is defecation controlled?
Pressure receptors initiate urge to defecate and rectal muscle contracts to move contents down towards the anus.
Internal anal sphincter us under parasympathetic control to relax and external anal sphincter is under voluntary control.
When both are relaxed, intraabdominal pressure in increased by abdominal muscles and there’s expulsion of faeces.
Voluntary control can be overridden by sacral reflexes if pressure is too high
Which segments of the intestines are mobile?
Jejunum, ileum, transverse colon and caecum
What are appendices epiploicae?
Fatty tags attached to the outer surface of the larger intestine
How is longitudinal muscle organised in the large intestine?
In 3 bands called teniae coli.
Describe the position of the duodenum
Starts at the pylorus and curves around the head of the pancreas to end and the duodenojejunal flexure on the left, roughly at the level of L2, 2cm left of the midline
What are the vertebral levels of the different parts of the duodenum?
Begins at L1 (anterolateral) at superior segment then descending portion extends down right hand side from L1-L3
Then turns into inferior segment which crosses over L3 and then Ascending segment rises from L3 to L2
What parts of the duodenum are mobile?
Ampulla/cap which is first 2 cm of superior duodenum. Is intraperitoneal
What are some possible complications of an ulcer is the duodenal cap?
If it erodes posteriorly, can perforate gastroduodenal artery so haemorrhage. If it perforates through duodenal wall, can cause peritonitis.
Inflamed duodenum can adhere to nearby structures ie pancreas, gallbladder and liver
Where on the duodenum does the hepatoduodenal ligament attach?
Superior part of the proximal superior segment of duodenum
Where in the duodenum does the ampulla of vater enter?
Posteromedial wall of the descending duodenum
What structures pass by inferior duodenum, posteriorly and anteriorly?
Anteriorly, it’s crossed by superior mesenteric vessels and root of the mesentery for the jejunum and ileum.
Posteriorly, it crosses the Right psoas major muscle, IVC, aorta and right testicular/ovarian vessels
What is the duodenojejunal flexure supported by?
Suspensory muscle of the duodenum- ligament of treitz which contracts to widen the flexure to allow movement of contents
Where does the root of The Mesentery run from and to?
From deuodenojejunal flexure to the ileocolic junction and right sacroiliac joint
Describe the blood supply to the jejunum and ileum.
From superior mesenteric artery via the jejunal and ileal arteries ~ 18 branches that unite to form arcades and these then give rise to straight vasa rectae
Where do the teniae coli start and finish?
Start at appendix and finish at rectosignoid junction
What are omental appendices?
Small, fatty omentum-like projections from outer wall of large intestine.
What are the 3 different bands of teniae coli?
Free
Omental
Mesocolic
Where is the caecum?
Lies in the iliac fossa, inferior to the ileocaecal junction. It’s very mobile but has no mesentery. Attached to the lateral abdominal wall by caecal folds of peritoneum to prevent displacement.
Normally within 2.5 cm of the inguinal ligament.
Describe the blood supply of the caecum and appendix
Both midgut so via superior mesenteric artery.
Caecum via the ileocolic artery and the appendix via the appendicular artery. Both are drained by ileocolic vein the the superior mesenteric vein
Where is the right colic flexure?
Deep to 9th and 10th ribs (on right), overlapped by inferior part of the liver.
Where is the left colic flexure?
Anterior to the inferior part of the left kidney, attached to the diaphragm via the phroicocolic ligament. More superior, less mobile and more acute angle than the right colic flexure
On average, at which vertebral level does the transverse mesocolon hang down to?
L3 - umbilicus
Where does the sigmoid colon run?
From left iliac fossa to S3 vertebra
Where does the root of sigmoid mesocolon run?
Superiomedially along external iliac vessels to the bifurcation of the common iliac vessels then inferomedially to anterior aspect of sacrum
What is the blood supply to the colon?
SMA gives off (clockwise) Ileocolic artery, supplying ascending colon, ileum and caecum
Right colic artery, supplying ascending colon
Middle colic artery supplying proximal 2/3 of transverse colon
IMA give off (clockwise) left colic artery supplying distal 1/3 of transverse colon and the descending colon
Sigmoid artery supplying descending colon and sigmoid colon
What parts of the rectum are covered in peritoneum?
Anterior of first 2/3 and lateral surfaces of first 1/3
Distal 1/3 is subperitoneal
What is the blood supply to the rectum?
Proximal rectum is supplied by IMA, via the superior rectal artery and drained by superior rectal vein - IMV - splenic vein - portal vein.
Distal rectum is supplied by common iliac artery - internal iliac arteries to Middle rectal artery and to the inferior pudendal artery - Inferior rectal arteries.
Drained by middle and inferior rectal veins to the IVC
What do the anal columns indicate?
Superior end of anal columns indicates anorectal junction where rectal ampulla crosses the pelvic diaphragm.
Inferior ends are joined by anal valves, forming anal sinuses. The line formed by the valves in the pectinate line, indicating differences in vasculature, innervation and lymphatic drainage above and below this line
What are the boundaries of the anal canal?
Begins when rectal ampulla narrows at the level of the sling formed by puborectalis muscle and ends at the anus.
descends posteroinferiorly between perineal body and anococcygeal ligament
What are the differences in blood and verve supply below and above the pectinate line?
Above, blood supply is IMA via the superior rectal artery and nerve supply is visceral, from s2-s4. Only sensitive to stretch.
Below, blood supply is IMA, via inferior rectal artery and nerve supply is somativ via the pudendal nerve.
What are the main gram negative and gram positive cocci bacteria? (In GI tract)
Positive - Staphylococci, streptococci and anterococci
Negative - Neisseria - Meningitidis and Gonorrhoeae
What are some common gram positive bacilli?
Clostridia Mycobacterium (tuberculosis) Corynebacterium Lactobacillus Bacillus
What are some common gram negative, enteric bacilli?
Bacteroides E. coli Pseudomonas Klebsiella Proteus Salmonella Shigella Vibrio cholera Campylobacter Helicobacter pylori
What are some common gram negative, non-enteric bacilli?
Haemophillus influenza
Brucella
Bordetella pertussis
What bacteria is parotitis normally caused by?
Staphylococcus aureus
What infection can steptococci cause in the neck?
Ludwig’s angina/ cellulitis with bilateral swelling around neck and lower jaw
What are the most common throat commensals and what pathogens can also occur in the throat?
Most common - Streptococcus viridans Staphylocci Neisseria meningitidis Less common - Strep pyogenes Candida albicans Haemophilus influenza Strep pneumoniae Lactobacillus Corynebacterium diptheriae
What is tonsillitis most commonly caused by?
Virus eg epstein barr, rhinovirus or adenovirus
How does oral thrush present?
Shiny tongue with frothy appearance to the mouth and angular chelitis
What is the normal function of lactobacillus in the vagina?
To convert glycogen to lactic acid to lower pH and prevent other bacteria from thriving
What are the 2 different types of oesophageal cancer and where do they occur?
Squamous cell carcinoma. Can be anywhere in oesophagus
Adenocarcinoma - only is distal 1/3 of oesophagus
What are the 2 different microscopic appearances of gastric cancers?
Can be intestinal with gland formation, derived from mucus-secreting cells. These have a well demarcated ‘pushing’ border.
Can be Diffuse with chains of non-cohesive singular cells with a poorly demarcated invasive border. These show signet ring signs due to vacuoles compressing nuclei
How can stromal cancers of the stomach be detected?
By testing for C-kit/CD117 which are expressed by tumour cells derived from intersitital cells of Cajal. CD117 only expressed in stromal gastric cancers and chronic myeloid leukaemia
What are the main types of gastric cancer?
Stromal
Lymphoma
Adenocarcinoma
What are the main classes of polyps in adenomas?
Can be pedunculated with a stalk or sessile, without a stalk.
Also be classed as tubular, which are mostly pedunculated or villous, which are mostly sessile
What are the main types of colonic cancer?
Adenocarcinoma which are mostly rectosigmoid
Carcinoid which are rare but can be distinctive carcinoid syndrome due to increased levels of 5-HT when metabolised by the liver
What mutations are involved in the adenomacarcinoma sequence?
K-ras/N-ras
P53/17p
18q (deleted in colorectal carcinoma)
Braf
How is the adenomacarcinoma sequence demonstrated?
Similar geographical and anatomical distributions of adenomas and carcinomas. Many carcinomas exhibit adenoma characteristics and most adenomas have a degree of dysplasia
What is cholangiocarcinoma?
Adenocarcinoma of the bile duct
When would an AXR be carried out?
In acute abdominal pain and suspected obstruction, renal colic or acute IBD exacerbation
What’s the difference in appearance of large and small bowel on an AXR?
Small bowel is central with valvulae conniventes that extend across whole lumen.
Large bowel is peripheral with haustra and lines that only extend part way across the lumen
What is lead pipe colon?
Sign of chronic ulcerative colitis. Colon is featureless with loss of haustra.
What is ultrasound used to investigate?
Appendicitis, acute cholecystitis and abdominal aortic aneurysms
What is the ‘rule of threes’ in reference to bowel obstruction?
If gas on AXR is >3cm, small bowel obstruction
If gas is >6cm, large bowel obstruction.
If caecum is >9cm, caecum is dilated but the ileocaecal valve is still competent
