gastrointestinal Flashcards
- GI embryology
- gastroschisis
- omphalocele
- foregut-pharynx to duodenum
- midgut-duodenum to transverse colon
- hindgut-distal transverse colon to rectum
-developmental defects of anterior abdominal wall due to failure of:
1.rostral fold closure: sternal defects
2.lateral fold closure: omphalocele, gastroschisis
3.caudal fold closure: bladder exstrophy
-omphalocele–persistence of herniation of abdominal contents into umbilical cord, covered by peritoneum
-gastroschisis–extrusion of abdominal contents through abdominal folds; not covered by peritoneum
-duodenal atresia–failure to recanalize (trisomy 21)
-jejunal, ileal, colonic atresia–due to vascular accident (apple peel atresia)
-midgut development:
6th week–midgut herniates through umbilical ring
10th week–returns to abdominal cavity + rotates around SMA
-pathology–malrotation of midgut, omphalocele, intestinal atresia or stenosis, volvulus
tracheoesophageal anomalies
- esophageal atresia (EA) with distal tracheoesophageal fistula (TEF) is most common (85%)
- results in drooling, choking, vomiting with first feeding
- TEF allows air to enter stomach (visible on CXR)
- cyanosis is 2’ to laryngospasm (to avoid reflux-related aspiration)
- clinical test: failure to pass NG tube into stomach
- in H-type it is a fistula alone
- in pure atresia (isolated) EA the CXR shows gasless abdomen
congenital pyloric stenosis
- hypertrophy of the pylorus causes obstruction
- palpable “olive” mass in epigastric region and nonbilous projectile vomiting at ~2 wks of age.
- tx is surgical incision
- occurs in 1/600 live births, more often in first born males
pancreas & spleen embryology
pancreas–derived from foregut. ventral pancreatic buds contribute to the pancreatic head and main pancreatic duct. The uncinate process is formed by the ventral bud alone. The dorsal pancreatic bud becomes everything else (body, tail, isthmus, accessory pancreatic duct)
- annular pancreas–ventral pancreatic bud normally encircles 2nd part of duodenum; forms a ring of pancreatic tissue that may cause duodenal narrowing
- pancreas divisum–ventral and dorsal parts fail to fuse at 8 wks.
- spleen– arises in mesentery of stomach (hence is mesodermal) but is supplied by foregut (celiac artery)
retroperitoneal structures
- retroperitoneal structures include GI structures that lack a mesentery and non-GI structures
- injuries to retroperitoneal structures can cause blood or gas accumulation in retroperitoneal space
SAD PUCKER: Suprarenal (adrenal) gland Aorta & IVC Duodenum (2nd & 3rd parts) Pancreas (except tail) Ureters Colon (descending & ascending) Kidneys Esophagus (lower 2/3) Rectum (lower 2/3)
important GI ligaments: connects-->structures contained-->notes 1.facioform 2.hepatoduodenal 3.gastrohepatic 4.gastrocolic 5.gastrosplenic 6.splenorenal
- liver to anterior abdominal wall–>ligamentum teres hepatis (derivative of fetal umbilical vein)–>derivative of ventral mesentery
- liver to duodenum–>portal triad: hepatic artery, portal vein, common bile duct–>pringle maneuver–ligament may be compressed btw thumb and index finger placed in omental foramen to control bleeding. Connects greater and lesser sacs
- liver to lesser curvature of stomach–>gastric arteries–>separates greater and lesser sacs on the right. May be cut during surgery to access lesser sac
- greater curvature and transverse colon–>gastroepiploic arteries–>part of greater omentum
- greater curvature and spleen–>short gastric, left gastroepiploic vessels–>separates greater and lesser sacs on the left
- spleen to posterior abdominal wall–>splenic artery and vein, tail of pancreas
digestive tract anatomy
- layers of gut wall (inside to outside)–MMS):
1. mucosa–epithelium (absorption), lamina propria (support), muscularis mucosa (motility)
2. submucosa–includes Submucosal nerve plexus (Meissner’s)
3. Muscularis externa–includes myenteric nerve plexus (Auerbach’s)
4. Serosa (when intraperitoneal)/adventitia (when retroperitoneal) - ulcers can extend into submucosa, inner or outer muscular layer. Erosions are in the mucosa only
- frquencies of basal electric rhythm (slow waves):
1. stomach–3 waves/min
2. duodenum–12 waves/min
3. ilieum–8-9 waves/min
Digestive tract histology: organ based
- esophagus
- stomach
- duodenum
- jejunum
- ileum
- colon
- nonkeratinized stratified squamous epithelium
- gastric glands
- villi and microvilli inc absorptive surface. Brunner’s gladns (submucosa) and crypts of Lieberkuhn.
- Plicae circulares and crypts of Lieberkuhn
- Peyer’s patches (lamina propria, submucosa), plicae circulares (proximal ileum), and crypts of Lieberkuhn. largest number of goblet cells in the small intestine
- colon has crypts but no villi, numerous goblet cells
abdominal aorta and superior mesenteric artery syndrome
- arteries supplying GI structures branch anteriorly. Arteries supplying non-GI structures branch laterally
- superior mesenteric artery (SMA) syndrome occurs when the transverse portion (third segment) of the duodenum is entrapped between SMA and aorta, causing intestinal obstruction.
GI blood supply and innervation
- embryonic gut regions (3)
- artery
- parasympathetic innervation
- vertebral level
- structures supplied
Foregut
- artery–celiac
- parasympathetic innervation–vagus
- vertebral level–T12/L1
- structures supplied–>stomach to proximal duodenum; liver, gallbladder, pancreas, spleen (mesoderm)
Midgut
- artery–SMA
- parasympathetic innervation–vagus
- vertebral level–L1
- structures supplied–distal duodenum to proximal 2/3 of transverse colon
Hindgut
- artery–IMA
- parasympathetic innervation–pelvic
- vertebral level–L3
- structures supplied–distal 1/3 of transverse colon to upper portion of rectum; splenic flexure is a watershed region
celiac trunk
- branches of celiac trunk: common hepatic, splenic, left gastric. These constitute the main blood supply of the stomach
- short gastrics have poor anastomoses if splenic artery is blocked
- strong anastomoses exist btw: L & R gastroepiploics, L&R gastrics
collateral circulation
- if branches off the abd aorta are blocked, these arterial anastomosis (origin) compensate:
1. superior epigastric (internal thoracic/mammary) inferior epigastric (external iliac)
2. superior pancreaticoduodenal (celiac trunk) inferior pancreaticoduodenal (SMA)
3. middle colic (SMA) left colic (IMA)
4. superior rectal (IMA) middle and inferior rectal (internal iliac)
Portosystemic anastomases
- site of anastomosis (3)
- clinical sign
- portal systemic
what’s commonly seen with portal HTN?
What treatment relieves portal HTN and how?
Esophagus
- clinical sign
- esophageal varices - portal systemic
- L gastric esophageal
Umbilical
- clinical sign
- Caput medusae - portal systemic
- paraumbilical superificial and inferior epigastric below the umbilicus, superior epigastric & lateral thoracic above the umbilicus
Rectum
- clinical sign
- internal hemorrhoids - portal systemic
- superior rectal middle and inferior rectal
- varices of gut, butt, caput (medusae) are commonly seen with portal HTN
- tx c a transjugular intrahepatic portosystemic shunt (TIPS) btw portal vein & hepatic vein percutaneously relieves portal HTN by shunting blood to systemic circulation
Pectinate (dentate) line
- where is it form?
- above pectinate line
- below pectinate line
- formed where endoderm (hindgut) meets ectoderm
- above pectinate line
- internal hemorrhoids, adenocarcinoma. Arterial supply from superior rectal artery (branch of IMA). Venous drainage is to superior rectal vein–>inferior mesenteric vein–>portal system.
- internal hemorrhoids receive visceral innervation and are therefore not painful
- lymphatic drainage to deep nodes - below pectinate line
- external hemorrhoids, squamous cell carcinoma
- arterial supply frm inferior rectal artery (branch of internal pudendal artery).
- venous drainage to inferior rectal vein–>internal pudendal vein–>internal iliac vein–>IVC
- external hemorrhoids receive somatic innervation (inferior rectal branch of pudendal nerve) and are therefore painful
- lymphatic drainage to superficial inguinal nodes
liver anatomy
Zones I-III
- apical surface of hepatocytes faces bile canaliculi
- basolateral surface faces sinusoids
- Zone I: periportal zone affected 1st by viral hepatitis
- Zone II: intermediate zone
- Zone III: pericentral vein (centrilobular) zone:
1. affected 1st by ischemia
2. contains P-450 system
3. most sensitive to toxic injury
4. site of alcoholic hepatitis
Biliary structures
- gallstones that reach the common channel at ampulla of Vater can block both the bile and pancreatic ducts
- tumors that arise in the head of the pancreas (near the duodenum) can cause obstruction of the common bile duct
Femoral region
- organization
- femoral triangle
- femoral sheath
- organization
- lateral to medial: Nerve-Artery-Vein-Empty-space-Lymphatics
- you go from lateral to medial to find your NAVEL - femoral triangle
- contains femoral vein, artery, nerve
- venous near the penis - femoral sheath
- fascial tube 3-4cm below inguinal ligament
- contains femoral vein, artery, and canal (deep inguinal lymph nodes) but not femoral nerve
Hernias:
Diaphragmatic hernia
- a protrusion of peritoneum through an opening, usually a site of weakness
- abdominal structures enter the thorax; may occur in infants as a result of defective development of pleuroperitoneal membrane
- most commonly a hiatal hernia, in which stomach herniates upward through the esophageal hiatus of the diaphragm
- sliding hiatal hernia is most common. GE junction is displaced incr; “hourglass stomach.”
- paraesophageal hernia- GE junction is normal. Fundus protrudes into the thorax
Hernias:
Indirect inguinal hernia
- goes through the internal (deep) inguinal ring, external (superfiical) inguinal ring, and into the scrotum.
- enters internal inguinal ring lateral to inferior epigastric artery
- occurs in infants owing to failure of processus vaginalis to close (can form hydrocele). much more common in males
- an indirect inguinal hernia follows the path of descent of the testes. Covered by all 3 layers of spermatic fascia
Hernias:direct inguinal hernia
-protrudes through the inguinal (Hesselbach’s) triangle.
-bulges directly through abdominal wall medial to inferior epigastric artery
-goes through the external (superficial) inguinal ring only
-covered by external spermatic fascia
-usually in older men
**MDs don’t LIe:
medial to inferior epigastric artery=direct hernia
lateral to inferior epigastric artery=indirect hernia
Hernias: femoral hernia
Hesselbach’s
-protrudes below inguinal ligament through femoral canal below and lateral to pubic tubercle
-more common in XX
leading cause of bowel incarceration
-Hesselbach’s triangle:
1. inferior epigastric vessels
2. lateral border of rectus abdominis
3. inguinal ligament
GI hormone: gastric
- source
- action-
- regulation-
- notes-
GI hormone: gastric
- source- G cells (antrum of astomach)
- action-
- inc gastric H+ secretion
- inc growth of gastric mucosa
- inc gastric motility - regulation-
- inc by stomach distention/alkalinization, amino acids, peptides, vagal stimulation
- dec by stomach pH < 1.5 - notes-
- much inc in Zollinger-Ellison syndrome
- inc by hcronic PPI use
- phenylalanine and tryptophan are potent stimulators
GI hormone: cholecystokinin
- source-
- action-
- regulation-
- notes-
GI hormone:cholecystokinin
- source- I cells (duodenum, jejunum)
- action-
- inc pancreatic secretion
- inc gallbladder contraction
- decr gastric emptying
- inc sphincter of Oddi relaxation - regulation-incr by fatty acids, amino acids
- notes-CCK acts on neural muscarinic pathways to cause pancreatic secretion
GI hormone: secretin
- source
- action-
- regulation-
- notes-
GI hormone:secretin 1.source- S cells (duodenum) 2. action- -incr pancreatic HCO3- secretion -decr gastric acid secretion -incr bile secretion 3. regulation- incr by acid, fatty acids in lumen of duodenum 4. notes- --incr HCO3- neutralizes gastric acid in duodenum, allowing pancreatic enzymes to function
GI hormone:somatostatin
- source
- action-
- regulation-
- notes-
GI hormone:somatostatin
- source- D cells (pancreatic islets, GI mucosa)
- action-
- decr gastric acid and pepsinogen secretion
- decr pancreatic and small intestine fluid secretion
- decr gallbladder contraction
- decr insulin and glucagon release - regulation-
- incr by acid
- decr by vagal stimualtion - notes-
- inhibitory hormone
- antigrowth hormone effects (inhibits digestion and absorption of substances needed for growth)
GI hormone: glucose-dependent insulinotropic peptide
- source-
- action-
- regulation-
- notes-
GI hormone: glucose-dependent insulinotropic peptide
- source- K cells (duodenum, jejunum)
- action-
- exocrine: decr gasric H+ secretion
- endocrine: incr insulin release - regulation-
- incr by fatty acids, amino acids, oral glucose - notes-
- also known as gastric inhibitory peptide (GIP)
- an oral glucose load is used more rapidly than the equivalent given by IV due to GIP secretion
GI hormone: vasoactive intestinal polypeptide (VIP)
- source
- action-
- regulation-
- notes-
GI hormone:vasoactive intestinal polypeptide (VIP)
- source- parasympathetic ganglia in sphincters, gallbladder, small intestine
- action-
- incr intestinal water and electrolyte secretion
- incr relaxation of intestinal smooth muscle and sphincters - regulation-
- incr by distention and vagal stimulation
- decr by adrenergic input - notes-
- VIPoma- non alpha, non-beta islet cell pancreatic tumor that secretes VIP.
- copius Water Diarrhea Hypokalemia Achlorhydria (WDHA syndrome)
GI hormone: nitric oxide
- source
- action-
- regulation-
- notes-
GI hormone: nitric oxide
- source-
- action- incr smooth muscle relaxation, including lower esophageal sphincter
- regulation-
- notes-loss of NO secretion is implicated in incr lower esophageal tone of achalasia
GI hormone: motilin
- source
- action-
- regulation-
- notes-
GI hormone: motilin
- source- small intestin
- action- produces migrating motor complexes (MMCs)
- regulation- inc in fasting state
- notes- motilin receptor agonists (such as erythromycin) are used to stimulate intestinal peristalsis
GI secretory products: intrinsic factor
- source-
- action-
- regulation-
- notes-
GI secretory products: intrinsic factor
- source- parietal cells (stomach)
- action- vitamin B12 binding protein (required for B12 uptake in terminal ileum)
- regulation-
- notes- autoimmune destruction of parietal cells–>chronic gastritis and pernicious anemia
GI secretory products: gastric acid
- source-
- action-
- regulation-
- notes-
GI secretory products: gastric acid
- source-parietal cells (stomach)
- action-decr stomach pH
- regulation-incr by histamine, ACh, gastrin; decr by somatostatin, GIP, prostaglandin, secretin
- notes- Gastrinoma–gastrin-secreting tumor that causes continuouos high levels of acid secretion and ulcers
GI secretory products: pepsin
- source-
- action-
- regulation-
- notes-
GI secretory products: pepsin
- source- chief cells (stomach)
- action- protein digestion
- regulation- incr by vagal stimulation, local acid
- notes- inactive pepsinogen–>pepsin by H+
GI secretory products: HCO3-
- source-
- action-
- regulation-
- notes-
GI secretory products: HCO3-
- source- mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner’s glands (duodenum)
- action- neutralizes acid
- regulation- incr by pancreatic and biliary secretion with secretin
- notes- HCO3- is trapped in mucus that covers the gastric epithelium
Saliva
- secretion from parotid, submandibular, sublingual glands
- stimulated by sympathetic and parasympathetic activity
- amylase digests starch, HCO3- neutralizes bacterial acids, mucins lubricate food
- normally hypotonic because of absorption but more isotonic with higher flow rates (less time for absorption)