Embryo/Anatomy/Physiology Flashcards
What structures are derived from the foregut, midgut and hindgut?
Foregut- pharynx to duodenum
Midgut- duodenum to proximal 2/3 of transverse colon
Hindgut- distal 1/3 of transverse colon to anal canal above pectinate line
Defects of anterior abdominal wall
Rostral fold closure failure- sternal defects
Lateral fold closure failure- omphalocele, gastroschisis
Caudal fold closure failure- bladder exstrophy
Gastroschisis
extrusion of abdominal contents through abdominal folds; NOT covered by peritoneum
Omphalocele
persistant herniation of abdominal contents into umbilical cord, sealed by peritoneum
Duodenal atresia
congenital failure of duodenum to canalize; associated with Down syndrome
Clinical features:
- polyhydramnios
- distention of stomach and blind loop of duodenum -> ‘double bubble’ sign on imaging
- bilious vomiting
Midgut developement
6th wk: midgut herniates through umbilical ring
10th wk: returns to abdominal cavity and rotates 270deg (90deg counterclockwise) around SMA
Most common tracheoesophageal anomaly
Esophageal atresia with distal tracheoesophageal fistula (TEF)
Symptoms: drooling, choking and vomiting with feeding, polyhydramnios, cyanosis secondary to laryngospasm
TEF allows air to enter stomach (air bubble on CXR)
Diagnosis: failure to pass NG tube into stomach
Congenital pyloric stenosis
Hypertrophy of pyloris -> obstruction; more common in males
Clinical features: typically presents ~2weeks
- nonbilious vomiting at 2-6weeks old
- visible peristalsis
- palpable olive mass in epigastric region
- hypokalemic hypochloremic metabolic alkalosis (secondary to vomiting of gastric acid and volume contraction)
Treatment: pyloromyotomy
What is derived from the ventral and dorsal pancreatic buds?
Ventral pancreatic buds: uncinate process and main pancreatic duct
Dorsal pancreatic bud: body, tail, isthmus, accessory pancreatic duct
Both: pancreatic head
Annular pancreas
ventral pancreatic bud encircles 2nd part of duodenum, may cause duodenal narrowing
Pancreas divisum
ventral and dorsal parts fail to fuse at 8 wk
usually asymptomatic, may cause chronic abdominal pain and/or pancreatitis
What is the embryological derivation of the spleen?
Mesoderm: arises in mesentery of stomach
Supplied by foregut- celiac artery
Retroperitoneal structures
Suprarenal (adrenal) glands Aorta and IVC Duodenum (2nd -4th parts) Pancreas (except tail) ureters colon (descending and ascending) Kidneys Esophagus (thoracic portion, lower 2/3) Rectum (upper 2/3)
Falciform ligament
Connects: liver to anterior abdominal wall
Structures contained: ligamentum teres hepatis (derived from fetal umbilical vein)
Notes: Derivative of ventral mesentery
Heaptoduodenal ligament
Connects: liver to duodenum
Structures contained: portal triad: proper hepatic artery, portal vein, common bile duct
Notes: Pringle maneuver- compress ligament to control bleeding; borders omental foramen which connects greater and lesser omental sacs (part of lesser omentum)
Gastrohepatic ligament
Connects: liver to lesser curvature of stomach
Structures contained: gastric arteries
Notes: separates greater and lesser sacs on right; may be cut during surgery to access lesser sac (part of lesser omentum)
Gastrocolic ligament
Connects: greater curvature and transverse colon
Structures contained: gastroepiploic arteries
Notes: Part of greater omentum
Gastrosplenic ligament
Connects: greater curvature of stomach and spleen
Structures contained: short gastrics, left gastroepiploic vessels
Notes: separates greater and lesser omental sacs on left
Splenorenal ligament
Connects: spleen to posterior abdominal wall
Structures contained: splenic artery and vein, tail of pancreas
Layers of gut wall (inside to outside)
Mucosa- epithelium, lamina propria, muscularis mucosa
Submucosa- includes Submucosal (Meissner) nerve plexus -> controls GI secretions
Muscularis externa - Myenteric (Auerbach) nerve plexus: controls motility
Serosa (intraperitoneal), adventitia (retroperiotoneal)
Ulcers vs erosions
ulcers extend into submucosa, inner or outer musxular layer
erosions - mucosa only
Digestive tract histology- esophagus and stomach
esophagus- non-keratinized stratified squamous epithelium
Stomach- nonciliated columnar epithelium with goblet cells
Digestive tract histology- duodenum, jejunum, ileum
duodenum: villi and microvilli, Brunner glands (secrete bicarb, in submucosa), crypts of Lieberkuhn (secretion, basal cells)
jejunum: plicae circulares (folds with villi) and cypts of Lieberkuhn
ileum: Peyer patches (lymphoid aggregates in lamina propria, submucosa, plicae circulares in proximal ileum, crypts of Lieberkuhn, Largest # of goblet cells in small intestine
Digestive tract histology- colon
crypts of Lieberkuhn, abundant goblet cells, NO villi
Blood supply, parasympathetic innervation and vertebral level for Foregut
Blood supply: Celiac artery
Parasympathetic innervation: Vagus nerve (CNX)
Vertebral level: T12/L1
Structures supplied: Pharynx (vagus nerve only, blood from thyroid arteries) and lower esophagus (celiac artery only) to proximal duodenum; liver, gallbladder, pancreas, spleen (mesoderm)
Blood supply, parasympathetic innervation and vertebral level for Midgut
Blood supply: SMA
Parasympathetic innervation: Vagus (CN X)
Vertebral level: L1
Structures supplied: Distal duodenum to proximal 2/3 of transverse colon
Blood supply, parasympathetic innervation and vertebral level for Hindgut
Blood supply: IMA
Parasympathetic innervation: Pelvic nerve
Vertebral level: L3
Structures supplied: Distal 1/3 of transverse colon to upper rectum
Splenic flexure
watershed region btwn SMA and IMA -> highly susceptible to ischemic damage
SMA syndrome
transverse portion (3rd part) of duodenum is entrapped btwn SMA and aorta -> intestinal obstruction
What is the blood supply of the lesser and greater curvature of the stomach?
lesser curvature- L and R gastric arteries
greater curvature - L and R gastroepiploic arteries
What are the branches of the celiac trunk?
common hepatic artery
splenic artery
L. gastric artery
What are the branches of the common hepatic artery?
gastroduodenal artery
Hepatic artery proper
R. gastric artery
What are branches of the splenic artery?
L. gastroepiploic artery
Short gastric arteries (poor anastomoses if splenic artery blocked, unlike gastroepiploic)
What are the portosystemic anastomoses and what the clinical signs?
- esophagus: left gastric and esophageal vein anastomosis -> can cause esophageal varices w portal HTN
- Umbilicus: Anastomosis btwn paraumbilical vein and small epigastric veins of anterior abdominal wall -> causes caput medusae with portal HTN
- Rectum: anastomosis btwn superior rectal vein with middle and inferior rectal veins -> causes anorectal varices
What procedure is done to relieve portal HTN?
Transjugular intrahepatic portosystemic shunt (TIPS) between portal vein and hepatic vein relieves portal HTN by shunting blood to systemic circulation and bypassing liver
Pectinate (detate) line
Endoderm (hindgut) meets ectoderm
Above pectinate line
- arterial supply: superior rectal artery (branch of IMA)
- venous drainage: superior rectal v -> IMV -> portal system
- lymphatic drainage - internal iliac LNs
- internal hemorrhoids (visceral innervation –> NOT painful)
Below pectinate line
- arterial supply: inferior rectal artery (branch of internal pudendal artery)
- venous drainage: inferior rectal v -> internal pudendal v -> internal iliac v -> common iliac -> IVC
- lymphatic drainage: superficial inguinal nodes
- external hemorrhoids (somatic innervation from inferior rectal branch of pudendal –> PAINFUL)
- anal fissures
- squamous cell carcinoma
Direction of blood flow through liver
Nutrient rich, low O2 blood enters via branch of portal vein and O2 rich blood enters via branch of hepatic artery into portal triad (zone I) and pass through basolateral surface of hepatocytes
Portal vein -> sinusoids (zone II) -> central vein (zone III) -> hepatic vein -> IVC
Direction of bile flow through liver
bile flows in opposite direction of blood, from zone III (centrilobular) to zone I (periportal) via bile canaliculi into hepatic bile ducts -> common hepatic bile duct -> common bile duct
-bile canaliculi face apical surface of hepatocytes
What is located in the femoral sheath?
3-4cm below inguinal ligament
Contains femoral vein, artery and canal (deep inguinal LNs)
Does NOT contain femoral nerve
What are the layers of the spermatocord? What are the layers derived from?
Outermost layer: External spermatic fascia, derived from external oblique aponeurosis
Middle layer: Cremasteric muscle and fascia, derived from internal oblique muscle
Inner layer: internal spermatic fascia, derived from transversalis fascia
What are the sites of protrusion of indirect and direct hernias?
indirect hernia- protrudes into internal inguinal ring
direct hernia protrudes into abdominal wall, usually medially to internal inguinal ring
Diaphragmatic hernia
abdominal structures enter thorax
- may occur due to congenital defect of pleuroperitoneal membrane or trauma
- commonly left sided due to protection of right hemi-daphragm by liver
Hiatal hernia
Most common diaphragmatic hernia
stomach herniates upward through esophageal hiatus of diaphragm
-most common subtype: sliding hiatal hernia - gastroesophageal jxn is displaced upward, “hour glass stomach” on imaging
Paraesophageal hernia
Fundus of stomach protrudes into thorax, gastroesophageal junction normal
Indirect inguinal hernia
Enters through internal (deep) inguinal ring lateral to inferior epigastric artery, then goes through external (superficial) inguinal ring and into scrotum
Occurs in infants from failure of processus vaginalis to close, covered by all 3 layers of spermatic fascia
Direct inguinal hernia
Protrudes through inguinal (Hesselbach) triangle -> bulges through abdominal wall medial to inferior epigastric artery
Goes through external superficial inguinal ring only
Covered by external spermatic fascia
Usually older men
Femoral hernia
Protrudes below inguinal ligament through femoral canal (below and lateral to pubic tubercle)
- common in females
- leading cause of bowel incarceration
What are the boarders of the inguinal (Hesselbach) triangle?
inferior epigastric vessels laterally
Lateral border of rectus abdominis medially
inguinal ligament inferiorly
Gastrin
Source: Antrum of stomach, duodenum (G cells)
Action: Increases gastric H+ secretion, growth of gastric mucosa and gastric motility
Regulation:
(+) stomach distention/alkalinization, amino acids, peptides, vagal stimulation
(-) low pH
Somatostatin
Source: Pancreatic islets and GI mucosa (D cells)
Action: Decreases gastric acid and pepsinogen secretion, decreases pancreatic and small intestine fluid secretion, decreases gallbladder contraction, inhibits release of hormones like insulin, GH and glucagon
Regulation: (+) low pH, (-) vagal stimulation
Notes: Octreotide is analog used to treat acromegaly, insulinoma, carcinoid syndrome and variceal bleeding
Cholecystokinin (CCK)
Source: Duodenum, jejunum (I cells)
Action:
Increases pancreatic secretion, gallbladder contraction and relaxes sphincter of Oddi. Decreases gastric emptying
Regulation: (+) fatty acids and amino acids
Notes: Acts on neural muscarinic pathways to cause pancreatic secretion
Secretin
Source: Duodenum (S cells)
Action: Increases pancreatic bicarb secretion and bile secretion. Decreases gastric acid secretion. –> increases pH
Regulation: (+) acid, fatty acids in duodenum
Notes: bicarb neutralizes gastric acid in duodenum to allow pancreatic enzyme fxn
Glucose-dependent insulinotropic peptide (GIP)
Source: Duodenum, jejunum (K cells)
Action: Exocrine: decreases gastric acid secretion. Endocrine: increases insulin release
Regulation: (+) fatty acids, amino acids, oral glucose
Notes: aka gastric inhibitory peptide. Oral glucose -> higher insulin compared to IV due to GIP secretion
Motilin
Source: Small intestine
Action: Produces migrating motor complexes (MMCs)
Regulation: (+) fasting state
Notes: motilin receptor agonists (erythromycin) stimulate intestinal peristalsis
Vasoactive intestinal polypeptide (VIP)
Source: Parasympathetic ganglia in sphincters, gallbladder, small intestine
Action: Increases: intestinal water and electrolyte secretion, relaxation of intestinal smooth muscle sphincters
Regulation: (+) distention, vagal stimulation
(-) adrenergic input
Notes: VIPoma- non-alpha or -beta islet cell pancreatic tumor secretes VIP - copious water diarrhea, hypokalemia and achlorhydria (WDHA syndrome)
Nitric oxide
Action: Relaxes smooth muscle of lower esophageal sphincter (LES)
Notes: Loss of NO secretion implicated in higher LES tone of achalasia
Intrinsic factor
Source: Parietal cells (stomach)
Action: Binds Vitamin B12, required for uptake in terminal ileum
Notes: Autoimmune destruction of parietal cells -> chronic gastritis and pernicious anemia
Gastric acid
Source: Parietal cells (stomach)
Action: lowers stomach pH
Regulation:
(+) Histamine, ACh, gastrin
(-) somatostatin, GIP, prostaglandin, secretin
Notes: Gastrinoma: gastrin secreting tumor causes high levels of acid and ulcers refractory to PPIs
Pepsin
Source: Chief cells (stomach)
Action: protein digestion
Regulation: (+) vagal stimulation, local acid
Notes: Pepsinogen -> pepsin in presence of H+
HCO3-
Source: Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum)
Action: neutralize acid
Regulation: (+) pancreatic and biliary secretion with secretin
Notes: bicarb is trapped in mucus covering gastric epithelium