GI Flashcards
What is the fluid balance of hype GI tract?
In 1kg food 1.5 L saliva 2.5 L stomach secretions 9 L small intestine and pancreatic secretions Total 14L
Out
- 5L absorbed in small intestine
- 35L absorbed in large intestine
- 15L faeces
What must the GI tract convert food too?
Sterile
Neutral
Isotonic
Small particles
What does the lower oesophageal sphincter comprise of?
Acute angle of entry of oesophagus
Oesophagus passes through oesophageal hietus and right crux of diaphragm
High pressure in abdomen collapses oesophagus
Circular muscle of oesophagus
Folds of oesophageal mucus membrane
What are the functions of saliva?
Lubricate food Begin digestion of carbs Moisten mucus membranes Clean teeth Reduce breakdown of teeth Immune response
Why is saliva necessary in the mouth?
Non keratanized epithelium so vulnerable to dehydration
Mucus membrane exposed to external environment so vulnerable to infection
Teeth would decay rapidly without protection and maintainance
What are the constituents of saliva that aid its function?
Salivary amylase Calcium Iodine Lysozyme Bicarbonate ions Mucin Hypotonic
What types of saliva are there?
Mucous - rich in mucin
Serous - rich in enzymes
Which salivary glands produce which types of saliva? What volume of saliva does each contribute?
Parotid - serous - 25%
Sublingual - mucus - 5%
Submandibular - both - 70%
What distinguishes the submandibular gland Histologically?
The presence of demilunes - serous glands that move back out of the acini during preparation.
What do the acinar cells secrete when making saliva?
An isotonic solution with normal cations, high iodine and consequently low chlorine ions.
How are acinar secretions modified by ductal cells?
Absorption of Na+ with less K+ excretion thus hypotonic
Exchange of Cl- for HCO3- thus alkali
How is a sodium gradient set up in saliva ductal cells?
Na+/K+ ATPase on basal membrane extrudes Na+ setting up a gradient in the cell drawing ductal Na+ in
Some K+ released into duct
Remainder of K+ excreted in cotransport with Cl- into the blood
How is HCO3- created within the ductal salivary cells?
Inward diffusion of CO2
Combination with H2O creating HCO3- and H+
H+ extruded into blood in exchange for Na+ down its gradient
How does resting saliva differ from stimulated saliva?
More hypotonic (less Na+, marginally higher K+) due to longer spent in duct Less HCO3- and less enzymes as less stimulation for their release
How is saliva secretion controlled?
Stimulation (taste, smell, reflex) trigger increased parasympathetic stimulation to the glands - this causes increased secretion. Reduced sympathetic stimulation causes vasodilation resulting in increased blood flow
Stimulation of the sympathetic NS also increases gland activity but reduces blood flow, as a result secreation decrease
Which cranial nerves supply which salivary glands?
Parotid - CN IX - glossopharangeal
Sl and SM - CN facial via the chorda tympani
What is the term for:
Difficulty in swallowing
Painful swallowing
Dysphagia
Odynophagia
What can cause dysphagia?
Neurological causes - cve, myesthenia gravis, parkinsons, MS
Oesophageal causes - tumour, stricture, right atrial hypertrophy, enlarged aorta, achalaesia (lack of peristalsis due to enteric NS destruction).
How does lateral folding of the embryo contribute to the formation the GI tract?
Somatic mesoderm that surrounds the amniotic cavity pinches the yoke sac creating a tube suspended by splanchnic mesoderm lined with ectoderm.
What does craniocaudal folding cause in the GI tract?
Cuts the connection between the GI tract and the yoke sac down to one tube - the vitelline duct
What occurs at either end of the primitive gut tube?
Direct connections between endoderm and ectoderm - the stomatodeum and proctodeum
What does endoderm form in the GI tract?
The epithelium
What forms the GI tract muscles? What else does this layer form?
The splanchnic mesoderm.
Also forms the visceral peritoneum
What are the divisions of the gut?
Foregut - oesophagus to major duodenal papilla
Midgut - major duodenal papilla to 2/3rds along transverse colon
Hindgut - last 1/3rd of transverse colon to rectal canal (pectinate line)
How is the gut tube suspended in its cavity?
What splits this cavity?
The dorsal mesentery
The diaphragm
Which section of the gut also has a ventral mesentery?
What does this do to the cavity?
Forgut - stomach to major duodenal papilla.
Divides the intraembryonic coelom into a right and left sac.
How do the mesenteries change around the stomach?
The stomach twists clockwise carrying the mesenteries with it. The stomach also tilts as the greater curvature (was posterior now right side) grows faster than the lesser. This causes the dorsal mesentery to become horizontal on its attachment to the bottom edge of the stomach.
What develops in the dorsal and ventral mesogastrium?
Dorsal - spleen
Ventral - liver
What does the ventral mesogastrium form in the adult?
The lesser omentum connecting the lesser curvature to the liver
The surroundings of the liver
The falciform ligament connecting the liver to the anterior abdominal wall
What does the dorsal mesogastrium form in the adult?
The splenorenal ligament anchoring the spleen to the posterior abdo wall
The greater omentum from the greater curvature of the stomach draping down then back up attaching to the transverse colon
What attaches the transverse colon to the posterior abdominal wall?
What does this form?
The mesocolon
This forms the lesser sac in conjunction with the greater and lesser omentum
What is the communication between the greater and lesser sac called?
The epiploic foramen of Winslow (omental foramen)
What is the function of the lesser sac?
Gives the stomach room to expand
What abdominal organs are retroperitoneal?
Kidneys Aorta Pancreas Most of the duodenum Acending and descending colon
What occurs with the mesentery of secondary retroperitoneal organs?
Fuses with the posterior abdominal wall becoming fusion fascia
What are the anterior abdominal wall muscles and where do the hey attach attach from superficial to deep
External oblique - runs inferiomedially from lower ribs to central aponeurosis
Internal oblique - runs superiomedially from iliac spine to central aponeurosis
Transverse abdominus - runs around the trunk from the transverse processes of the vertebra to the central aponeurosis
What two layers sit behind the 3 layers of anterior abdominal muscles?
The transversalis fascia
The parietal peritoneum
What muscles are found within the central aponeurosis? What lines border them?
The rectus abdominus
Laterally bound by Lina semilunaris
Centrally divided by Lina alba
Divided horizontally by tendinous intersections
What is the difference between superior and inferior to the arcuate line of Douglass?
Superior to it the tendons forming the aponeurosis pass either side of rectus abdominus
Below it all fibres of the aponeurosis pass in front of rectus abdominus leaving just the transversalis fascia behind.
Where is the arcuate line of Douglass?
1/3rd of the distance from the umbilicus to the pubis symphysis
Describe with an example, referred pain on a somatic nerve
Stimulation of a proximal part of the nerve causing pain to be perceived at the distal part of the nerve - e.g shingles
What fibres do visceral sensory fibres follow back to the spine?
What does this cause?
Afferent sympathetics
Perception of sensation of the dermatome at the level that the sympathetic fibres left the cord.
What stimulates visceral sensation?
Ischemia
Inflammation
Stretching
Strong muscle contraction
Roughly where do the 3 gut regions refer pain?
Foregut - epigastric
Midgut - umbilical
Hindgut - suprapubic
Where does pain from Appendix Liver Spleen Retroperitoneal Renal colic Gall bladder Diaphragm Refer?
Appendix - umbilicus
Liver - right hypochonrium
Spleen - left hypochonrium
Retroperitoneal - central back to umbilical
Renal colic - flank to groin
Gall bladder - right hypochondriac to epigastric to right scapula tip
Diaphragm - left shoulder
What is a connection between the umbilicus and bladder called? How does it present?
Patent urachus
Failure of closure of alantosis
Urine from umbilicus either at birth, or in later life when obstruction (e.g. Enlarged prostate) causes raised pressure.
Can cause an umbilical cyst
What is a patent vitelline duct? How does it present? He can it be differentiated from a Urachal problem?
Failure of the vitelline duct to close
Connection between bowel and umbilicus
Causes an umbilical cyst
Differentiate from Urachal cyst by injecting die and seeing if it goes to bowel or bladder.
What is the rule applied to merkals diverticulum?
2% of population
2” long
2’ from the cecum within the ilium
2 types of tissue (gastric and intestinal)
Differentiate the types of congenital GI content herniation
Exampholos (omphalocele) - herniation of abdo contents including peritoneum - high rates of mortality due to concurrent abnormalities
Gastroschisis - abdominal contents without peritoneum off midline. No usual concurrent abnormalities so low mortality
What is divarication of recti?
Midline bulge due to weakness in Lina alba. Evident when sitting up.
What is the commonest abdominal hernia?
Inguinal hernia
Which sex gets more femoral hernias?
Women
What are the two sorts of inguinal hernia? Differentiate them.
Direct - bowel passes medial to the inferior epigastric vessels through a weakness in hesselbachs triangle. It passes out of the superficial inguinal ring external to the spermatic cord.
Indirect - bowel passes through the internal inguinal ring lateral to the inferior epigastric vessels, through the inguinal canal and out through the external inguinal ring within the spermatic cord. As a result can enter the scrotum.
What triangle do direct inguinal hernias pass through?
Hesselbachs triangle
Where do femoral hernias pass?
Inferior to the inguinal ligament through the femoral canal
Why are femoral hernias more serious than inguinal hernias?
They are more likely to strangulate
What is a spigelian hernia?
A hernia medial to the Lina semilunaris at or below the arcuate line of Douglas.
Rare!
What is the term for a partial hernia? What are the risks associated with this?
A richters hernia
Can strangulate without obstructing the bowel so harder to detect
What is a common complication of any operation to the abdo?
Incisional hernia
What are the main complications of a hernia?
Incarceration (not reducible)
Strangulation (painful, red, hard, non reducible mass - causes ischemic bowel)
What size of hernia is more likely to strangulate?
Small - they have a smaller opening!
What are the functions of the stomach? How does it meet them?
Store food between meals - expandable
Sterilise food - acidic
Digest food - secretes enzymes, mechanical churning, acidic
What enzyme does the stomach secrete? What cell type secretes it?
Pepsinogen from chief cells, cleaved to pepsin
Why does pepsin have an action large than just the individual breakdown of proteins in the stomach?
Proteins tend to be structural - holding other substances together, thus breaking down proteins causes the food to disintegrate increasing surface area
Where is acid secreted into the stomach (region, cell and region of cell) ?
From parietal cells located in gastric pits. Components are secreted into cannuliculi
How is acid secreted in gastric cells?
Mitochondria split h2o to h+ and oh-
oh- combined with co2 to hco3-
hco3- secreted into blood in exchange for Cl-
H+ pumped into canaliculus in exchange for K+ using ATP.
Cl- also secreted
What does the production of h+ in parietal cells of the stomach do to the blood?
Alkali tide
How is acid secretion controlled in the stomach? What triggers/inhibits each modality?
A combination of the vagus nerve releasing ach, mast cells releasing histamine and g cells releasing gastrin.
All three methods stimulate parietal cells.
Vagus activity is triggered stomach distension, anticipation etc.
Gastrin activity is triggered by sensing polypeptides in the lumen and inhibited by sensing of low pH and by somatostatin release.
Histamine is stimulated ach and gastin, thus serves to amplify the effects of there other two.
What are the phases of control during stomach acid secreation?
Cephalic - feel, smell, taste all trigger CNx stimulation releasing acid
Gastric - stomach distension triggers CNx stimulation, peptides in lumen trigger gastrin secretion, food buffers stomach raising pH triggering gastrin secretion
Intestinal phase - stomach empties - pH drops reducing gastrin secretion, chyme enters duodenum, initially increases acid secretion then triggering somatostatin release inhibiting gastrin. Decreased stomach stretch lowers CNx activity.
Which stomach cells secrete mucus?
Neck cells
Why does mucus stay in position around the stomach?
Sticky so hard to displace
Thixotrophic (if disturbed becomes more runny so fills any gaps)
How does gastric mucus protect against acid?
Contains HCO3- and basic groups which buffer the acid
Constantly replaced so as it becomes saturated new is produced below.
Unstirred thus h+ has to diffuse right through to reach stomach wall
What controls gastric mucus secretion?
Prostaglandins
These increase in response to the same stimuli as acid secretion so attack is matched with defence.
What drugs increase stomach defence?
H2 receptor antagonists - eg ranitidine - inhibit the actions of histamine preventing amplification of CNx and gastrin
Proton pump inhibitors - inhibit the H+/K+ synporter a in the caniculus.
H-pylori elimination therapy
Drugs that harm stomach defences
NSAIDs - inhibit COX reducing prostaglandins decreasing mucus production
Aspirin - as per NSAIDs non-ionised in stomach so absorbed into lining then ionises causing damage
Alcohol - irritates stomach causing gastritis
How does the stomach expand?
What is the advantage of this method?
Actively relaxes under vagus nerve control
No pressure increase therefore decreased reflux
How do stomach contractions move food?
Pacemaker in cardia fires 3/minute initiates wave of contraction
Slows as stomach widens then accelerates as it narrows towards the pyloric antrum
Small particles are pushed ahead of the wave but larger ones are overtaken sorting food ready to be squirted into the duodenum
When the wave reaches the pylorus it causes contraction closing the sphincter.
What slows emptying of the stomach?
Lipids in duodenum
Low pH in duodenum
Hypertonicity in duodenum.
What is the timeframe for physiological herniation?
Week 6 to week 10
Why does the midgut herniate?
The entire GI tract expands out of proportion to the rest of the body, the midgut most of all
How can the midgut be subdivided?
On which subdivision is the cecum located?
The vitelline duct divides the midgut into a cranial and caudal limb
The cecum is on the caudal limb
What rotations does the midgut undergo? On what axis?
On the axis of the SMA
3 x 90 degree anticlockwise rotations, 1 on herniation, 2 on return
The rotation brings the caudal limb in front of the cranial (colon in front of duodenum
How does the midgut return to the abdominal cavity?
The jejunum first moving to the left side then successive return of the rest to the right side. The cecum returns to the right upper quadrant the decends.
What are the devisions of the peritoneum? What is the mobility of each?
Superior, descending, inferior, ascending.
First 3cm of superior is intraperiotoneal
. Rest of duodenum is retroperitoneal
What problems can arise from physiological herniation?
All malrotations increase risk of volvulus
Only one 90 degree turn - the colon returns first and all sits on the left with the small intestine on the right
The first turn is clockwise - the duodenum and SMA sit anterior to the transverse colon - risk of compression
Sub hepatic cecum - failure of cecum to decend - appendix then also in this region!
What effect does cell proliferation have in the GI tract?
Blocks the lumen of the oesophagus, bile duct and proximal small intestine.
What is recanalisation?
What happens if it fails?
The reopening of the areas of the GI tract that became obstructed.
Atresia (obstruction) or stenosis (narrowing) of the tract
What is the main cause of atresia in the jejunum, ilium and large bowel?
Vascular accident causing necrosis - can cause unjointed sections, holed sections or sections joined by a fibrous band.
How does the hindgut contribute to the urinary system?
Forms the epithelium. Of. The. Bladder
What forms the end. Of the hindgut?
The cloacal membrane with the proctodeum
What separates the hindgut from the alantosis?
The urorectal septum
What is the innervation to the proctodeum?
Somatic sensation
What divides the region derived from the proctodeum and that derived from the hindgut in the adult?
The pectinate line
What pathologies can effect the anal canal/rectum?
Imperforate anus - failure of the cloacal membrane to rupture
Hind gut fistula - failure of the urorectal septum to fully separate the hindgut from the alantosis (bladder)
What sort of bacteria causes stomach ulcers, what is its specifics?
Helicobacter pylori
Gram -ve flagellated, helical aerobe.
Produces urease breaking down urea to co2 and ammonia to produce alkali environment in stomach
How do h pylori protect themselves from stomach acid?
Produce ammonia from urea making CO2 using urease
Live under the stomach mucus layer
How is h pylori transmitted?
Who is most at risk?
Oral oral and faeco oral routes
Percentage increases with age - thought to be due to more chance of transmission when the older generation were children rather than more risk as elderly. Cohort effect!
More effected in developing countries.
What does h pylori cause?
Peptic ulcers (implicated in 95%)
Gastritis (implicated in 80%)
Small implication in GI cancer
What are the two sorts of GI ulcer?
Peptic ulcer - ulcer in the stomach or duodenum
Duodenal ulcer - ulcer of the duodenum only
What is the effect of an antral h pylori infection?
Increased acid secretion due to increased parietal cells and gastrin
Metaplasia of duodenum to stomach like columnar cells
H pylori colonise proximal duodenum
Formation of duodenal ulcers