Gastro Flashcards
What are the 4 layers of the GIT?
Mucosa (innermost)
Submucosa
External muscle layers
Serosa (outermost)
What are the layers of the mucosa?
Epithelium
Lamina propria
Muscularis mucosae
What are the layers of the external muscle of the ileum
Circular muscle
Longitudinal muscle
What are the layers of the serosa?
Areolar connective tissue
Epithelium
What is the nervous supply to the ileum?
Myenteric plexus - Auerbach’s plexus
Submucosal plexus - Meissner’s plexus
What characteristics of the epithelium makes it good for its job?
Selectively permeable barrier - absorption
Facilitate transport and digestion of food
Promote absorption
Produce hormones
Produce mucus
What characteristics of the lamina propria makes it good for its job?
Lots of lymphoid nodules and macrophages
Produce antibodies mainly IgA which is resistant to proteases
What characteristics of the muscularis mucosae makes it good for its job?
Layers of smooth muscle orientated in different directions
Keeps epithelium in contact with gut contents
Helps keep crypt content dynamic - stasis quickly results in infection
Through what layers of the GIT would be classes as a peptic ulcer?
Ulceration breaching the muscularis mucosae
In which layer of the GIT is Meissner’s plexus found?
Submucosal layer
In which layer of the GIT is Auerbach’s plexus found?
muscularis propria
What does the submucosa contain?
Contains:
dense connective tissue, blood vessels, glands, lymphoid tissue
Submucosal plexus - Meissner’s
What innervation does the inner circular muscle of the ileum contain?
Myenteric plexus
What does the serosa layer contain?
Blood and lymph vessels and adipose tissue
Continuous with the mesenteries
What types of cells are found in the GIT?
Stratified squamous in oesephagus and distal anus
Simple columnar everywhere else
What is the cell shape of the enterocyte?
Simple columnar epithelium
What is the name for the folds of the small intestine?
Plicae circularis
Valvulae conniventes
What is the base called between two villi?
Crypts
What is the subunit of a villi that gives it the brush border appearance?
Microvilli
What happens to the number of goblet cells from Duodenum to the Colon?
Increasing in number
What forces the cell nucleus to be squished to the bottom of a mucosal epithelial cell?
Mucous
What is the function of the mucus in the GIT?
Protect the epithelium from:
Friction - acts as a lubricant
Chemical damage - acidic environment
Bacterial inflammation - forms physical barrier
What is the scientific name of the gastric mucous cells?
Foveolar cells
What do gastric mucous cells do and what is their location?
Bottom of the pits
Secrete mucous/ HCO3 that forms a barrier to stomach acid
What is the name for the temporary folds in the stomach?
Rugae
What cells are found in the crypts in the GIT?
Stem cells - the GIT epithelium is replaced in 2-4 days
Paneth cells - look after stem cells by guarding against infection
Enteroendocrine cells
What is the function of the paneth cells in the GIT?
Secrete antibacterial proteins that protect the stem cells
How much saliva is produced per day?
1.5L
How much gastric secretions are produced per day?
2L
How much pancreatic secretions are produced per day?
1.5L
How much bile is produced per day?
0.5L
How much secretions are produced by the SI per day?
1.5L
What are brunners glands?
Found in the duodenum - neutralise acid from the stomach by releasing a hypertonic solution. Protective layer of alkaline solution lining duodenum
Describe the structure of the abdominal wall
Skin Fascia/ fat - superficial and deep 3x anterolateral muscles - External oblique, Internal oblique, Transverse abdominis, Rectus abdominis Transversalis fascia Peritoneum
What direction does External oblique muscle run?
Back to front- hands in pockets direction
What direction does Internal oblique muscle run?
Inferior to superior from iliac crest to 8th and 12th ribs
What direction does transversus abdominis muscle run?
Transverse direction - across the body
What direction does Rectus abdominis muscle run?
Up and down direction
What makes up the rectus sheath?
Aponeurosis of the external oblique muscle - makes the anterior rectus sheath layer
Aponeurosis of the internal oblique muscle - makes up the anterior and posterior layers of rectus sheath
Aponeurosis of the transversus abdominis - contributing to posterior layer of rectus sheath
From what rib does rectus abdominis muscle originate from?
5th rib
What is the structure separating the two verticle layers of rectus abdominis in the middle of the body?
Linea alba
What is the structure that separate the horizontal layers of the rectus abdominis muscle?
Tendinous intersection
How many muscle bellies make up rectus abdominis?
10 muscle bellies. 5 on each side of the linea alba
What bone does rectus abdominis muscle insert onto?
Pubic crest
What bone does the oblique muscles of the abdomen insert onto?
Iliac crest - external oblique
And 5th to 12th Ribs - internal oblique
What ribs does external oblique originate from?
5th rib to the 12th rib
What ribs does internal oblique originate from?
5th rib to the 12th rib
What abdominal muscle have aponeurosis?
External, internal obliques and transverse abdominis
What is the arcuate line?
Lower limit of the posterior layer of rectus sheath
Roughly half way between umbilicus and pubic crest
What is the basic histology of the peritoneum?
Mesothelium lined cavity
Flattened simple squamous epithelium
Basement membrane
Dense irregular connective tissue
What is the name given to the viscera that are not enveloped by the peritoneum?
Retroperitoneal viscera
What 5 structures are retroperiteneal?
Pancreas
Kidneys
Duodenum
Abdominal aorta and vena cava
What is the embryological development pathway of the parietal peritoneum and what type of pain is felt on insult?
Somatic development - sensory pain
What is the embryological development pathway of the visceral peritoneum and what pain is felt on insult?
Splanchnic development - generalised pain - referred pain
What is a mesentry?
Double fold of peritoneum that attaches certain viscera to the posterior abdominal wall
What is contained in a mesentry?
Blood vessels
Lymph vessels
Nerves
Fat
What GI structures are intraperitoneal?
Jejunum Ileum Appendix Transverse colon Sigmoid colon Rectum
What 2 sphincters are found in the oesophagus?
Upper oesophageal sphincter - prevents air from entering GIT
Lower oesophageal sphincter - prevents reflux from stomach into oesphagus
What is chyme?
A fluid that passes out from the stomach that consists of gastric secretions and partially digested food
What is the function of the terminal ileum?
B12 absorption
What is the function of jejunum?
Nutrient absorption
What is the terminal ileum?
End of the ileum just before the start of the large bowel/ colon
What is the broad function of the large bowel?
Final water absorption
Temporary storage
Final electrolyte absorption - some bile salt absorption and production of short chain fatty acids
What is the broad function of the ileum?
Water/ electrolyte absorption
Bile recirculation
What is the broad nervous control of the GIT?
Parasympathetic NS
Vagus nerve
Pelvic splanchnic nerves (S2-S4)
Craniosacral outflow
What peptides are released by the PNS in the GIT?
Gastrin releasing peptide
Vasoactive-inhibitory peptide
What nerve roots give sympathetic control of the GIT?
T5-L2
What nerve roots make up the splanchnic nerves?
Greater - T5-T9
Lesser - T10-11
Least - T12
What is the function of Meissner’s plexus?
Secretions and blood flow
What is the function of Auerbach’s plexus?
Motility
What is the greater sac/omentum of the peritoneum?
The peritoneum connecting the stomach to the transverse colon that acts as an apron for the GIT
What is the ligament that connects the stomach to the transverse colon?
Gastro-colic ligament
What is the lesser omentum?
The peritoneum that connects the liver anteriorly and posteriorly to the stomach
What is the epiploic foramen?
The space between the stomach and the posterior peritoneum/ abdominal wall
What causes visceral pain?
Visceral stretching, inflammation, ischaemia
Describe visceral pain?
Diffuse/ poorly defined pain
Often midline
What is the sympathetic outflow to the GIT?
T5-L2 - preganglionic Pass through (paravertebral) sympathetic trunk without synapsing (preganglionic) Form (abdominopelvic) presynaptic splanchnic nerves (preganglionic) - greater, lesser, least
What do splanchnic nerves synapse with?
Prevertebral ganglia:
Coeliac, renal, superior mesenteric, inferior mesenteric plus others
What is a caecal volvulus?
Distended small bowel
What is the pathway of pain from the caecal volvulus to the pain perceived in its location?
General visceral afferents activated-> Afferent impulse goes back to superior mesenteric ganglia (prevetebral) -> continues back along least splanchnic nerve -> passes back through sympathetic chain (paravertebral) -> into dorsal horn of spine -> converge with somatic afferents at that spinal level -> brain interprets visceral afferent to be coming from the spinal level dermatomes -> peri-umbilical pain
What is a hernia?
Protrusion of part of the abdominal contents beyond the normal confines of the abdominal wall
What are signs and symptoms of a hernia?
Fullness or swelling
Gets larger when intra-abdominal pressure increases
Aches
What are signs and symptoms of an incarcerated hernia?
Pain
Cant be moved
Nausea and vomiting (and other signs of bowel obstruction)
Systemic problems if bowel has become ischaemic
What are the causes of hernia?
Congenitally related
Post surgery where wounds have not healed adequately (incisional hernia)
Normal point of weakness
Anything that increases abdominal pressure - Obesity, Weightlifting, Chronic constipation/ coughing
In basics what are the 3 parts of a hernia?
Sac
Contents of the sac
Coverings of the sac
What is included in the sac of a hernia?
Pouch of peritoneum
What is included in the contents of the sac?
Any structure found within the abdominal cavity
What is included in the coverings of the sac?
Layers of the abdominal wall through which the hernia has passed
Where are the anatomically normal areas of weakness in the abdominal wall?
Inguinal canal
Femoral canal
Umbilicus
Previous incisions
What is the inguinal canal?
Oblique passage through the lower part of the abdominal wall
In males - structure pass through from abdomen to the testis
In females - round ligament goes from uterus-labium majors
What is the processus vaginalis (becomes tunica vaginalis)?
Pouch of peritoneum
What is the Gubernaculum?
Condensed band of mesenchume that links inferior portion of testis to labioscrotal swelling
Why is a patent processus vaginalis a problem for hernias?
It is an open connection from the abdomen to the scrotum and this allows the abdominal contents to fall into the area
What makes up the posterior wall of the inguinal canal?
Transversus abdominis
What makes up the superior wall (roof) of the inguinal canal?
Internal oblique/ transversus abdominis - muscular arches
Aponeurosis
What makes up the anterior wall of the inguinal canal?
External oblique and the aponeurosis of the external oblique muscle
What makes up the floor of the inguinal canal?
Inguinal ligament + lacunar ligament (medially)
What two structures does the inguinal ligament join?
ASIS and pubic tubercle
What is the deep ring?
Hole in the transversalis fascia
What is the conjoint tendon?
Internal oblique and tranversus abdominus muscle aponeurosis that inserts into the crest of the pubis
What is the superficial ring?
A hole in the aponeurosis of the external oblique muscle
What is the difference between the direct and indirect inguinal hernia?
Indirect - through inguinal canal
Direct - through abdominal wall at Hesselbachs triangle - doesn’t go through the inguinal canal
What is the important landmark of the inferior epigastric vessels in the context of inguinal hernia?
A direct hernia will be medial to the inferior epigastric vessels and does not traverse the epigastric vessels.
Indirect will be lateral to the inferior epigastric vessels.
What are the landmarks of Hesselbachs triangle?
Medial border - Rectus abdominis muscle lateral wall
Superior border - Inferior epigastric vessels
Lower border - Inguinal ligament
What is the purpose of the deep inguinal ring?
It allows ductus deferens to pass through it with blood vessels
What does incarcerated refer to in hernias?
Stuck hernia that cant be reducible - strangulated
What is an omphalocele and why does it happen?
Failure of the midgut to return to the abdomen during development
Viscera persist outside the abdominal cavity within umbilical ring - abdominal cavity may not grow to correct side to accommodate viscera
Viscera are covered in peritoneum - gut has a chance to develop relatively normally - then feeding can commence
It is often associated with other genetic problems - mortality rate is high
What is gastroschisis and when do problems arise?
Defect in ventral abdominal wall
Abdominal viscera not covered in peritoneum - exposed amniotic fluid
Tend to get problems with gut development (intestinal atresia, short/ inflamed gut) - problems arise around feeding
What has a better survival omphalocele or gastroschisis?
Gastroschisis - because there is less of a genetic component to it which can be closed at birth
Describe a umbilical hernia?
Commonly found in infants
Hernia at the site of the umbilicus
Not usually painful
80-90% close by age 3
Describe a paraumbilical hernia?
Central midline hernia
Goes through linea alba in region of umbilicus
F>M
Obesity
Risk of strangulation as defect is often small
What are symptoms of a hernia?
Based around if the bowel loop gets trapped:
Pain, Vomiting, Sepsis
What is a problem with strangulated hernia?
Blood supply is disrupted - can lead to tissue necrosis
In what week of the embryonic period does the embryo fold?
4th week
Laterally and cephalocaudally
Describe in embryological terms what the gut tube is
Endoderm lined tube Runs the length of the body Blind pouches at the head and tail end Opening at the umbilicus Splanchnic mesoderm covering
Embryonically what is classed as the foregut, midgut and hindgut?
Foregut - oesophagus, stomach, pancreas, liver, gall-bladder, duodenum (proximal to entrance of bile duct)
Midgut - duodenum (distal to entrance of bile duct), jejunum, ileum, cecum, ascending colon, proximal 2/3 transverse colon
Hindgut - Distal 1/3 transverse colon, descending colon, sigmoid colon, rectum, upper anal canal, internal lining of bladder and urethra
What does the classification system of foregut, midgut and hindgut help us understand?
The blood supply to the gut - each embryonic segment receives blood supply from a distinct branch of the abdominal aorta.
Foregut - coeliac trunk
Midgut - Superior mesenteric artery
Hindgut - Inferior mesenteric artery
What is the caveat to the blood supply to the foregut, midgut and hindgut?
The structures that develop close to the junction between the foregut and midgut will have a mixed blood supply
What is the blood supply to the duodenum proximal entry of bile duct?
Gastroduodenal artery and superior pancreaticoduodenal artery (CT)
What is the blood supply to the duodenum distal to the entry of the bile duct?
inferior pancreaticoduodenal artery (SMA)
What is the difference in blood supply to the pancreas?
Head - superior pancreacticoduodenal artery (CT) AND inferior pancreacticoduodenal artery (SMA)
What two embryonic mesentries are attached to the gut tube?
Dorsal mesentery - the whole gut tube
Ventral mesentery - only foregut
Embryonically what do the dorsal and ventral mesentries in the foregut help to form?
Form a left and right sac
Left sac - greater sac
Right sac - lesser sac - comes to lie behind the stomach
Describe the greater and lesser omenta
Omenta are specialised regions of peritoneum
Greater omentum - formed from the dorsal mesentery and is the first structure seen when the abdominal cavity is opened anteriorly
Lesser omentum - formed from the ventral mesentery - lesser curve of the stomach - free edge conducts the portal triad
What is a secondarily retroperitoneal structure?
The structure began development invested by the peritoneum, had a mesentery but with successive growth and development the mesentery is lost through fusion at the posterior abdominal wall
How does the GI and resp tracts separate?
Had 2 buds - lung bud and liver bud
Separation occurs in 4th week to form a respiratory diverticulum and the oesophagus
What are the potential problems seen with abnormal positioning of the tracheosophageal septum?
- Proximal blind-end oesphagus with tracheosophageal fistula
- Blind ended oesophagus and trachea
- Distal blind ended oesophagus and tracheoesophageal fistula proximally
- Tracheosophageal fistula in both proximal and distal oesophagus
- Incomplete separation of both pathways
What mesentery in development derives the liver and biliary system?
Ventral mesentery
What mesentery in development derives the pancreas?
Components develop in both ventral and dorsal mesenteries
Uncinate process and inferior head = ventral
Superior head, neck, body and tail = dorsal
What is the falciform ligament?
AKA round ligament
Is the ligament that is vertical in its line along the liver
What is the primary intestinal loop?
The midgut elongates enormously
Runs out of space
Makes a loop that has the SMA as its axis - is connected to the yolk sac by the vitelline duct and has cranial and caudal limbs
During which week of gestation does the primary intestinal loop elongate?
6th week
Why do intestines loop out of the body during growth?
Liver grows rapidly and so there is less space to accommodate the small intestine
How does the midgut rotate and in which direction?
Rotation along the superior mesenteric artery
The cranial and caudal limbs rotate in an anticlockwise direction
From a cranial and caudal orientation it changes to a lateral orientation
What are the risks associated with midgut defects?
Volvulus - strangulation/ ischaemia
Volvulus= twisting on itself
Obstruction
What is a vitelline cyst?
Vitelline duct forms fibrous strands but leaves a fluid-filled cyst in the band
What is a vitelline fistula?
Gut is open to the outside. Therefore contents leak out
What is a Meckel’s diverticulum?
Ileal diverticulum +/- the vitelline duct may or may not be patent
What is a vitelline duct?
A tube that connects the yolk sac to the midgut lumen of the developing foetus. This is usually only present from the 4th week and obliterates in 9th week
What is the rule of 2’s in Meckel’s diverticulum?
2% of population 2:1 Males to females 2 feet from the ileocaecal valve Usually detected in under 2's 2inches long
What type of tissue is usually found in a Meckel’s diverticulum?
Ectopic gastric or pancreatic tissues
Why is recanalisation of the gut tube important for later life?
Primitive gut is a simple tube -> but cell growth becomes so rapid that the lumen is partially or completely obliterated (oesophagus, bile duct, small intestine)
Recanalisation occurs to restore the lumen
If recanalisation is wholly or partially unsuccessful, atresia or stenosis of the structure
Where is recanalisation least likely to occur successfully?
Duodenum - due to vascular accidents
What is a common abnormality of the stomach in infants?
Pyloric stenosis
What causes pyloric stenosis?
Hypertrophy of the circular muscle in the pyloric sphincter region
What is a symptom of pyloric stenosis?
Projectile vomiting in infants
What is the pectinate line?
Anal canal is divided by the pectinate line into histologically distinct superior and inferior parts
Indicates difference in arterial supply, venous and lymphatic drainage and innervation
What is the blood supply, innervation, histological features and lymphatic drainage of the anal canal above the pectinate line?
Blood supply - IMA
Innervation - S2,3,4 pelvic parasympthetics
Histological features - Columnar epithelium
Lymph drain= internal iliac nodes
What is the blood supply, innervation, histological features and lymphatic drainage of the anal canal below the pectinate line?
Blood supply - pudendal artery
Innervation - S2,3,4 pudendal nerve
Histological features - Stratified epithelium
Lymph drainage - superficial inguinal nodes
What is the difference in the sensory afferents of the areas above and below the pectinate line?
Above the pectinate line - sensation only to stretch
Below the pectinate line - temperature, touch and pain
What are the names of the areas of pain felt by the foregut, midgut and hind gut?
Foregut - epigastrium
Midgut - periumbilical
Hindgut - suprapubic
What structures in the GIT retain mesenteries?
Jejunum Ileum Appendix Transverse colon Sigmoid colon
What structures in the GIT are secondarily retroperitoneal?
Duodenum
Ascending colon
Descending colon
Rectum (no peritoneal covering in distal 1/3)
What structures of the GIT are in the cranial and caudal limbs of the primary bowel loops?
Cranial - distal duodenum, jejunum, proximal ileum
Caudal limb - distal ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
What parts of the GIT are more commonly found to have atresia?
Duodenum> Jejunum = Ileum > colon
What nerve innervates the midgut?
Parasympathetic - vagus
Sympathetic - superior mesenteric ganglion and plexus
What nerve innervates the hindgut?
PNS - pelvic - S2,3,4
SNS - Inferior mesenteric ganglion and plexus
What is the composition of saliva?
Mostly water
Hypotonic - depending on flow rate - not enough time to make ionic changes
Rich in potassium and bicarbonate (pH slightly acidic to 8)
Mucins help with lubrication
Amylase - secrete by salivary glands
Lingual lipase - secreted by lingual glands
Immune proteins - IgA, lysozyme, lactoferrin - sequesters iron because bacteria need iron to grow
What is xerostomia?
Dry mouth
What is the problem with dry mouth?
Decreased antibacterial properties therefore increased likelihood of getting dental carries, ulcers and bad breath
What are the salivary glands?
Parotid gland
Submandibular gland
Sublingual gland
What does the parotid gland lie on top of?
Masseter muscle
What is interesting about the parotid gland duct in its pathway?
Penetrates the buccinator muscle opposite the crown of the 2nd upper molar tooth
What is the difference in the innervation of the glands of the mouth?
Above oral fissure - greater petrosal nerve of facial nerve (CN VII)
Below oral fissure - chordates tympani of facial nerve (CN VII)
Parotid gland - innervated by CN IX - glossopharyngeal nerve
What is the big problem with mumps and the face?
Parotitis - very painful as there is a capsule therefore can’t swell appropriately.
Trigeminal nerve is sensory to parotid gland
What imaging method is used to check the parotid gland function?
Parotid sialography
What are the 3 phases of swallowing
Oral preparatory phase
Pharyngeal phase
Oesophageal phase
Of the oral preparatory phase of swallowing what are the 3 main features of it?
Voluntary
Pushes bolus back towards the pharynx
Once bolus touches pharyngeal wall the pharyngeal phase begins
Of the pharyngeal phase of swallowing what are the 6 main features of it?
Involuntary
Soft palate seals off nasopharynx
Pharyngeal constrictors push bolus downwards
Larynx elevates, closing epiglottis
Vocal cords adduct (protecting airway) and breathing temporarily ceases
Opening of the upper oesophageal sphincter
Of the oesophageal phase of swallowing what are the 3 main features of it?
Involuntary
Closure of the upper oesophageal sphincter
Peristaltic wave carries bolus downwards into oesphagus
What is the neural control of swallowing and the gag reflex?
Mechanoreceptors in pharyngeal wall -> Glossopharyngeal nerve (sensory CN IX) -> Medulla in brain stem -> Vagus nerve (motor to pharynx CN X) -> Pharyngeal constrictors
What could be the problem if swallowing solid foods is a problem?
Oesophageal stricture/ physical mass
What could be the problem is swallowing liquids is a problem?
Stroke - muscles of facial expression for example can prevent food staying in the mouth therefore liquid falls out of the mouth
What happens to the muscle type as you go from oesophagus to stomach?
Skeletal muscle transitions to smooth muscle
What factors help prevent gastro-oesophageal reflux?
- Functional sphincter formed from smooth muscle of distal oesophagus - LOS
- Diaphragm - contracting around the oesophagus prevents food entering the stomach on inhalation
- Intra-abdominal oesophagus gets compressed when intra-abdominal pressure rises
- Mucosal rosette at cardia of stomach
- Acute angle of entry of oesophagus
What cells aid in secretion of HCl in the stomach?
Enterochromaffin - like cells.
Release histamine
What is paracrine secretion?
Hormone has effects only in the vicinity of the gland secreting it
What do D- cells in the stomach do?
Acid stimulates somatostatin release to inhibit meal-stimulated gastrin secretion from the G-cell
Give an example of a neuroendocrine cell in the stomach?
Gastrin releasing peptide - released by neurones in the GIT
It is released from the post-ganglionic fibres of the vagus nerve - which causes release of gastrin from G cells.
Where are the majority of G- cells found in the stomach?
Antrum on the greater curvature
Where are the majority of the parietal cells found in the stomach?
Fundus/ body of the stomach on the greater curvature
What neurotransmitter is released from the vagus nerve in the stomach to cause release of gastrin?
ACh
What is cholecystokinin?
Hormone that translates directly into bile sac move
Causes release of bile into the CBD
What cell is responsible for releasing cholecystokinin?
I cells
Where are I cells found and why?
Duodenum and jejunum
Once food has been digested the cells are stimulated to cause immediate release of bile salts and pancreatic secretions
What prevents pancreatic and bile secretions being released into the duodenum?
Sphincter of Oddi
Through which structure does bile and pancreatic secretions leave from the major papilla?
Ampulla of Vater
What is the name of the two tubes that connect the ducts from the pancreas and bile duct to the duodenum?
Minor and major papilla
What are the two pancreatic ducts?
Main pancreatic duct
Accessory pancreatic duct
What are the two broad families of gastrointestinal hormones?
Secretin and Gastrin
What cells release secretin?
S cells
What is the location of the S cells?
Duodenum
What do S cells do?
Increase HCO3 secretion from the pancreas/ gallbladder
Decreases gastric acid secretion
What stimulates S cells to release secretin?
H+ concentration and fatty acids
What stimulates cells to release gastric inhibitory peptide?
Sugars
Amino acids
Fatty acids
What is the problem with GIP release?
Increases insulin which is a problem for diabetics
What is the function of GIP?
Decreases gastric acid secretion
Where in the GIT can GIP secreting cells be found?
Duodenum and jejunum
What are the 4 main basic functions of the stomach?
Receive food - short term storage
Disrupt food - vigorous contractions of the smooth muscle
Continue/ commence digestion - mainly proteins
Disinfect
Why can epigastric pain be confused for a heart attack?
The heart sits close to the cardia of the stomach which is the area with the LOS
If the patient has reflux then pain will be felt in this location and can be confused for a heart attack hence why history and type of pain is important to differentiate
What is the longer and short edges of the stomach called?
Greater and lesser curvature of the stomach
What is the folds in the stomach called?
Rugae
What is the location of the LOS called in the stomach?
Cardia
What is the highest point of the stomach called?
Fundus
What is the last part of the stomach called which has the sphincter?
Pylorus
What is the part of the stomach between the pylorus and the body of the stomach called?
Antrum
What is the largest part of the stomach in the middle of it called?
Body
What is the part of the lesser curvature of the stomach called where it curves sharply towards the pylorus?
Angularis
Which part of the stomach gets free gas and can be seen on x-ray?
Fundus
What is the basic histology of the epithelium from lower oesophagus to the stomach?
Abrupt transition of stratified squamous epithelium to columnar
Mucosa/submucosa has folds - rugae
What 4 basic cells are in the stomach epithelium?
Mucous cells
Parietal cells
Chief cells
G cells
Describe the contraction types between the upper and lower stomach?
Upper stomach - sustained contractions creating a basal tone
Lower stomach - Strong peristalsis mixes stomach contents. Coordinated movements with contractions every 20 seconds in a proximal to distal direction.
Why is the shape of stomach good for its function of moving food along?
Larger proximally getting smaller in the distal direction
Contents accelerates towards pylorus but only smaller particles of food is allowed to exit into the duodenum.
Lumps are left behind and so this helps separate out the food and concentrate digestion on the larger food particles.
How many times per minute is chyme ejected from the stomach?
3 times a minute
What is the blood supply to the stomach and what are the branches?
Coeliac trunk to the stomach generally
Lesser curvature proximal 1/2 = left gastric artery
Lesser curvature distal 1/2 = right gastric artery branch off the common hepatic artery
Greater curvature proximal 1/3 = short gastric artery from the splenic artery
Greater curvature middle 1/3 = left gastroepiploic artery from splenic artery
Greater curvature distal 1/3 = right gastroepiploic artery from gastroduodenal artery
What is important about the gastroduodenal artery and its location?
It sits behind the pylorus which is a location of potential gastric ulceration and hence it can cause a hole in this artery which could lead to internal bleeding quickly as the blood supply is directly off the coeliac trunk
What is the venous drainage to the stomach and what are the branches?
Lesser curvature posterior part = left gastric vein drains into splenic vein
Lesser curvature anterior part = right gastric vein drains into portal vein directly
Fundus = Short gastric vein -> splenic vein
Body = left gastro-omental vein
Antrum = Right gastro-omental vein
Pylorus = Pancreaticoduodenal vein -> SMA OR Pre-pyloric vein-> right gastric vein -> portal vein
With all of the drainage from the stomach where does the blood all end up in?
Hepatic portal vein
What feature of the stomach allows expansion to facilitate the consumed food?
Gastric mucosal folds - rugae
What cells release pepsinogen into the stomach?
Chief cells
What happens to pepsinogen in the stomach?
It interacts with the acidic environment and as it is a proenzyme prior to entry into the stomach it becomes an enzyme which is then able to break down proteins
What do D cells release?
Somatostatin
What is pernicious anaemia caused by?
Antibodies against the parietal cells causes them to be destroyed
The patient then produces less intrinsic factor and so then less B12 is absorbed further down the GIT
What cells make up a gastric gland?
Mucous neck cells
Parietal cells
Chief cells
Enteroendocrine cells
Where are chief cells mainly found in the stomach?
Body
What hormones are mainly released from the pylorus of the stomach?
Gastrin and somatostatin
What stimulates the release of HCl in the stomach?
Gastrin released from G cells into the blood supply
Histamine from ECL-cells
ACh from vagus nerve
What receptor does gastrin act on in the stomach?
CCK receptors as there is cross reactivity
What is the control mechanism for gastrin secretion?
- Peptides and amino acids stimulate the release of gastrin
- Vagal stimulation via ACh and Gastrin-releasing peptide (GRP)
- Somatostatin acts on S receptor on the G cell
What inhibits HCl production?
When food leaves stomach pH drops (food is a buffer)
Low pH activates D cells which release somatostatin
Somatostatin inhibits G cells and ECL cells
Stomach distension reduces which then reduces vagal activity
Where are D cells located?
Antrum of the stomach at the lesser curvature
How is HCO3- made in the stomach epithelium?
CO2 from the blood enters the cells and they then have carbonic anhydrase in them which then produces HCO3-
Why is carbonic anhydrase in the stomach important?
It converts CO2+ H2O into H+ and HCO3-
H+ is then used to make stomach acid
HCO3- is used later in the duodenum to neutralise this acid
What is the process of acid release into the lumen of the stomach?
H+ made using carbonic anhydrase is exchanged for K+ in the lumen using the H+/K+ ATPase anti-porter.
K+ enters the cell but is then goes down conc gradient through K channels into the stomach lumen
How does the chloride part of HCl in stomach acid end up in the lumen of the stomach?
Cl- is exchanged for HCO3- in the basolateral membrane of the stomach. Cl- enters the cells and HCO3- leaves the cells. Cl- then passes through the Cl- channel on the apical membrane into the lumen of the stomach
What are the 3 phases of digestion?
Cephalic phase
Gastric phase
Intestinal phase
What happens in the cephalic phase of digestion?
- Vagus nerve stimulates gastric secretion even before food is swallowed
- 30% of total HCl is released during this phase
- Direct stimulation of parietal cells via vagus nerve
- Stimulation of G cells vagus (GRP released)
What happens in the gastric phase of digestion?
- Food stretches the stomach and activates myenteric and vagovagal reflexes - stimulates parietal cells and G cells.
- Histamine and gastrin also stimulate acid and enzyme secretion
- 60% of total HCl is released during this phase
- Amino acids and small peptides stimulate G cells
- Food acts as buffer in stomach: removes inhibition on gastrin production
- Enteric NS and gastrin: cause strong smooth muscle contractions
what 4 actions does the vagus nerve have on the secretion of acid?
1 - acts on Chief cells to release Pepsinogen
2 - acts on G cells to release gastrin -> Parietal cells to release H+
3 - acts on parietal cells to release H+ directly
4 - acts on ECL-cells to release histamine -> Parietal cells to release H+
What happens in the intestinal phase of digestion?
- Intestinal gastrin briefly stimulates the stomach (chyme is acidic and hypotonic) but then secretin, GIP, CCK, and the enterogastric reflex inhibit gastric secretion and motility while the duodenum processes the chyme already in it. Sympathetic nerve fibres suppress gastric activity, while vagal stimulation of the stomach is now inhibited
- 10% of total HCl production during this phase
- Lipids activate enterogastric reflex which reduces vagal stimulation
- Chyme stimulates CCK and secretin (helps suppress secretion of acid)
What cells produce and release mucin?
Foveolar cells
What is the function of mucin in the stomach?
- Prevent self digestion by proteases
- Mucous adhere to the epithelium - prevents physical damage