GI Flashcards
What is the general blood supply to the midgut?
Superior mesenteric artery
What is the general blood supply to the hindgut?
Inferior mesenteric artery
What are the derivatives of the foregut?
Oesophagus to duodenum (proximal to bile duct), includes liver, gallbladder, pancreas
What are the derivatives of the midgut?
Duodenum (distal to bile duct) to proximal 2/3rd of transverse colon
What are the derivatives of the hindgut?
Distal 1/3rd of transverse colon to anal canal
Bladder and urethra
What are the 3 pairs of salivary glands? What do they secrete?
Parotid - serous secretions
Sub-maxillary - both
Sub-lingual - mucus secretions
Which salivary gland produces the most secretions?
Sub-maxillary - 75%
What ducal modifications occur to saliva?
Decrease Na
Increase K
Increase bicarbonate
Describe secretion of serous saliva
Acinar cells secrete isotonic fluid with enzymes (determines volume)
Duct cells modify saliva (determines composition)
How does ductal modification of saliva change when it is stimulated to when it is at rest
At rest: low volume, hypotonic, neutral/acidic, few enzymes
Stimulated: high volume, less hypotonic, alkaline, lots of enzymes
What is the afferent pathway for salivary secretion?
Afferent information from mouth/tongue, nose stimulate facial and glossopharyngeal nerves
What is the efferent stimulation for salivary secretion?
Facial nerve - submandibular ganglion - sub-maxillary and sub-mandibular glands
Glossopharyngeal nerve - otic ganglion - parotid gland
How does increased parasympathetic activity change salivary secretions?
Promotes primary secretions and bicarbonate secretion
How does increased sympathetic activity change salivary secretions?
Reduced blood flow so causes dry mouth
What are the layers of the oesophagus?
Mucosa (non-keratinised stratified squamous epithelia, laminar propria, muscularis mucosa)
Sub mucosa - contains glands
Muscularis externa (circular and longitudinal)
What are the phases of swallowing?
- Mastication produces bolus
- Voluntary phase
- Pharyngeal phase
- Oesophageal phase
What occurs during voluntary phase of mastication?
Bolus moved to pharynx by tongue
What occurs during pharyngeal phase of mastication?
Pressure receptors in palate and anterior pharynx send afferent information to swallowing centre in brain causing:
- Inhibition of respiration (soft palate blocks nasal cavity)
- Raises larynx
- Closes glottis by epiglottis
- Open upper oesophageal sphincter
What occurs during oesophageal phase of mastication?
Rapid peristaltic wave down oesophagus
Opening of lower oesophageal sphincter
Give a primary and secondary cause of dysphasia
Primary - Achalasia
Secondary - obstruction/compression
What are the anatomical mechanisms that prevent gastro-oesophageal reflux?
- Lower oesophageal sphincter - physiological
- Angle of His - angle at which oesophagus enters stomach
- Right crus of diaphragm - increased abdominal pressure tightens right crus around oesophagus
What the general blood supply to the foregut?
Celiac trunk
What does the greater omentum connect? And from what is it derived embryonically?
Connects greater curve of stomach to transverse colon
Derived from dorsal mesentary
What does the lesser omentum connect? And from what is it derived embryonically?
Connects lesser curve of stomach to liver
Derived from ventral mesentary
What attaches liver to anterior abdominal wall?
Falciform ligament
Describe the rotation of the midgut
270 degrees in counter-clockwise fashion
What are the consequences of malrotation with regards to the midgut?
Causes hypermobile gut - more likely to cause volvulus (bowel obstruction caused by bowel abnormally twisting on itself)
Incomplete rotation - left sided colon
Reversed rotation - duodenum passes anterior to transverse colon
Describe the consequence of the cloaca splitting in two with regards to anal canal
Superior part (above pectinate line) derived from hindgut Inferior part (below pectinate line) derived from ectoderm Consequences for innervation, blood supply, epithelia, lymphatic drainage
Describe the difference in blood supply, innervation, lymphatic drainage and epithelial lining above and below the pectinate line
Above pectinate line (hindgut derivative):
Blood supply: inferior mesenteric artery
Innnervation: S2-S4 pelvic, parasympathetic
Epithelia: Simple columnar
Lymphatic drainage: internal iliac nodes
Below pectinate line (derived from ectoderm):
Blood supply: pudendal artery
Innervation: S2-S4 pudendal nerve, somatic
Epithelia: stratified squamous, non-keratinised
Lymphatic drainage: superficial inguinal nodes
What is a Meckel’s diverticulum?
Results due to persistent of vitelline duct 'Cul-de-sac' in ileum Rule of 2's: 2% of population affected 2 feet from ileocaecal valve 2 inches long Usually detected in under 2's 2:1 male:female
What are the different abnormalities that can arise from a persistent vitelline duct?
Meckel’s diverticulum
Vitelline cyst
Vitelline fistula
What are the abnormalities that can arise from defects in abdominal wall?
Gastroschisis - failure of abdominal wall to close during lateral folding of embryo, results in gut tubes outside body cavity
Omphalocoele - persistence of physiological herniation into umbilical cord, results in epithelial layer covering defect
What is the arcuate line?
Point at which transversalis fascia and posterior part of internal oblique fascia does not cover rectus abdominus posteriorly
Occurs 1/3rd distance between umbilicus and pubic crest
Explain the difference between somatic referred pain and visceral referred pain
Somatic referred pain - pain felt in proximal part of somatic nerve felt at distal dermatome
Visceral referred pain - visceral afferent pain fibres follow somatic fibres back to same spinal cord segment, CNS perceives visceral pain as coming from somatic portion of the body
What is the difference of the peritoneal cavity in males and females?
Completely closed in males
Communicates with fallopian tubes in females
What is the ligamentum teres and where is it located?
Remnant of umbilical vein
Located in free edge of falciform ligament
Define a hernia
Protrusion of an organ or the fascia of a organ through the wall of the cavity that normally contains it
What are the contents of the inguinal canal in males and females?
Males: spermatic cord, ilioinguinal nerve
Females: round ligament of uterus, ilioinguinal nerve
What is the difference between direct and indirect hernia?
Direct - protrudes through weakened area on transversalis fascia (Hasselbach’s triangle), travels through only part of the inguinal canal
Indirect - protrudes through deep inguinal ring and travels through inguinal canal and out through superficial inguinal ring
Name the cells of the gastric pits and what they secrete
Chief cells - Enzymes
Parietal cells - Acid and intrinsic factor
Neck cells - Mucus
Endocrine cells (G-cells) - Gastrin
What causes secretion of gastrin?
Increased pH
Peptides
ACh
What receptors do histamine and acetyl choline work on in the stomach to secrete acid?
Histamine - H2
ACh - M3
What are the phases of control for acid secretion?
Cephalic - autonomic stimulation due to sight, smell, taste, thought
Gastric - food buffers acid (disinhibits gastrin), release of peptides (gastrin release), distension of stomach (ACh release). Gastrin and ACh cause histamine release
Intestinal (stomach emptying) - chyme stimulates hormone release (antagonises gastrin), decreased pH (inhibits gastrin)
Describe stomach defenses
Mucus ‘unstirred’ layer
Bicarbonate released in to unstirred layer - reacts with acid of stomach
Mucus and alkali secretion stimulated by prostaglandins
What are the branches of the coeliac trunk?
Splenic artery
Common hepatic artery
Left gastric artery
What is the blood supply to the lesser curve of the stomach?
Left and right gastric arteries
What is the blood supply to the greater curve of the stomach?
Left and right gastroepiploic arteries
What is the epiploic foramen?
Entrance to the lesser sac
What are the properties of chyme leaving the stomach? And how is it corrected?
Acidic - Bicarbonate secretion from pancreas, liver and duodenal mucosa
Hypertonic - osmotic movement of water into lumen from duodenum
Partially digested - digestion completed by enzymes from pancreas and duodenal mucosa
What is the most likely location of a gallstone causing biliary colic?
Hartmann’s pouch
Causes of pancreatitis
G - gallstones
E - ethanol
T - trauma
S - steroids M - mumps A - autoimmune S - scorpion bite H - hyperlipidaemia E - ERCP/iatrogenic D - drugs
Where is CCK realeased from and what are it’s actions?
APUD cells
Causes contraction of gallbladder, release of enzymes from pancreas, potentiates secretin’s action
What is bile composed of?
Bile acids and pigments - bile acid dependent
Alkaline juice from intrahepatic duct cells - bile acid independent
What are the two bile acids?
Cholic acid
Chendocholic acid
Which veins are implicated in oesophageal varicies
Left gastric vein to oesophageal vein
Which veins are implicated in a caput medusa
Para umbilical vein to epigastric vein
Para umbilical vein only opens in portal hypertension
Which veins are implicated in hemorrhoids
Superior rectal veins to middle and inferior rectal veins
What stimulates alkaline juice secretion from the pancreas and what causes its release
Secretin released in response to low PH from the jejenum
Describe the breakdown of alcohol
Ethanol > Acetaldehyde (via alcohol dehydrogenase) > acetate (via acetaldehyde dehydrogenase)
Describe how contents are moved along within the small intestines
Segmentation causes gentle agitation
Intestinal pacemakers at intervals, frequency highest at stomach end - intestinal gradient
Causes intermittent contraction of smooth muscle
Describe how contents are moved along within the large intestines
Haustral shuttling - contraction of muscle in haustra shuffles contents back and forth
Mass movement - infrequently there is a peristaltic wave from transverse through to descending colon - often triggered by eating, gastro-colic reflex
