Gastrointestinal: Anatomy/Physiology

Terms in this set (188)

What are the retroperitoneal structures of the abdomen?
1. Duodenum (2nd, 3rd, and 4th parts)
2. Descending colon
3. Ascending colon
4. Kidney and ureters
5. Pancreas (except tail)
6. Aorta
7. IVC
8. Rectum
9. Adrenal glands
What are the six important GI ligaments?
1. Falciform
2. Hepatoduodenal
3. Gastrohepatic
4. Gastrocolic
5. Gastrosplenic
6. Splenorenal
What does the falciform ligament connect?
Liver to anterior abdominal wall
Which structure does the falciform ligament contain?
Ligamentum teres
What embryologic structure is the falciform derived from?
Fetal umbilical vein
What structures does the hepatoduodenal ligament connect?
Liver to duodenum
Greater sac to lesser sac
What structures are contained inside the hepatoduodenal ligament?
Portal triad (hepatic artery, portal vein, and common bile duct)
What is a clinical application of the hepatoduodenal ligament?
Can be compressed between thumb and index finger placed in omental foramen (epiploic foramen of Winslow) to control bleeding
What does the gastrohepatic ligament connect?
Liver to lesser curvature of stomach
What structures are contained within the gastrohepatic ligament?
Gastric arteries
What clinical importance does the gastrohepatic artery have?
May be cut during surgery to access the lesser sac
What does the gastrosplenic ligament connect?
Greater curvature of stomach to spleen
What structures are contained within the gastrosplenic ligament?
Short gastrics
Which structures does the gastrosplenic ligament separate?
Left greater and lesser sacs
What structures does the gastrocolic ligament connect?
Greater curvature of the stomach to the transverse colon
What structures are contained within the gastrocolic ligament?
Gastroepiploic arteries
What structure is the gastrocolic ligament a part of?
Greater omentum
What does the splenorenal ligament connect?
Spleen to posterior abdominal wall
What structures are contained within the splenorenal ligament
Splenic artery and vein
What are the layers of the gut wall, from inside to outside?
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa/adventitia
What are the structures contained within the mucosa and their respective functions?
1. Epithelium (absorption)
2. Lamina propria (support)
3. Muscularis mucosa (motility)
What is the structure contained within the submucosa?
Submucosal plexus (Meissner's plexus)
What is the structure contained within the muscularis externa?
Myenteric plexus (Auerbach's plexus)
What is are the frequencies of the basal electric rhythm (slow wave) in the stomach, duodenum, and ileum, respectively?
3, 12, and 8 waves per minute
What are the two muscular layers of muscularis externa?
1. Inner circular layer
2. Outer longitudinal layer
What is the histological pattern of the esophagus?
Nonkeratinized stratified squamous epithelium
What is the histological pattern of the stomach?
Gastric glands
What is the histological pattern of the duodenum?
1. Villi and microvilli
2. Brunner's glands
3. Crypts of Lieberkuhn
In which layer are Brunner's glands found?
Submucosa
What is the function of villi and microvilli?
To increase the absorptive surface area
What is the histological pattern of the jejunum?
1. Large number of goblet cells
2. Plica circulares
3. Crypts of Lieberkuhn
What is the histological pattern of the ileum?
1. Peyer's patches
2. Plica circulares
3. Crypts of Lieberkuhn
What is the histological pattern of the colon?
1. Crypts
2. No villi
In which layers of the ileum are Peyer's patches found?
1. Lamina propria
2. Submucosa
In which segment of the ileum are plicae circulares found?
Proximal ileum
What kind of muscle is present in the upper 1/3 of the esophagus?
Striated muscle
What kind of muscle is present in the middle 1/3 of the esophagus?
Striated and smooth muscle
What kind of muscle is present in the lower 1/3 of the esophagus?
Smooth muscle
What are the major branches of the abdominal aorta, from top to bottom, including their vertebral levels?
1. Celiac trunk (T12)
2. Superior mesenteric artery (L1)
3. Left and right renal arteries (L1)
4. Testicular and ovarian arteries (L2)
5. Inferior mesenteric artery (L3)
6. Bifurcation (L4)
7. Right common iliac and left common iliac arteries
8. Internal and external iliac arteries
Which major artery supplies the structures of the foregut?
Celiac
Which nerve supplies the structures of the foregut?
Vagus
Which structures are supplied by the celiac artery?
1. Stomach to proximal duodenum
2. Liver
3. Gallbladder
4. Pancrease
5. Spleen
Which structure is supplied by an artery of the foregut, but is not a derivative of endoderm?
Spleen (mesoderm)
Which major artery supplies the structures of the midgut?
Superior mesenteric artery
Which nerve supplies the structures of the midgut?
Vagus
Which structures are supplied by the superior mesenteric artery?
Distal duodenum to proximal 2/3 of transverse colon
Which major artery supplies the structures of the hindgut?
Inferior mesenteric artery
Which nerve supplies the structures of the hindgut?
Pelvic
Which structures are supplied by the inferior mesenteric artery?
Distal 1/3 of transverse colon to upper portion of the rectum
What is the major watershed area of the intestines?
Splenic flexure (SMA to IMA)
What is the blood supply of the left lesser curvature of the stomach?
Left gastric from the celiac trunk
What is the blood supply of the right lesser curvature of the stomach?
Right gastric from common hepatic from celiac trunk
What is the blood supply of the left greater curvature of the stomach?
Left gastroepiploic from left splenic from celiac trunk
What is the blood supply of the right greater curvature of the sthomach?
Right gastroepiploic from right gastric from common hepatic from celiac trunk
What is the blood supply of the first 3 portions of the duodenum?
Superior pancreaticoduodenal from right gastroepiploic from common hepatic from celiac trunk
Which blood vessels near the stomach have poor anastomoses if the splenic artery is blocked?
Short gastrics
Which two sets of arteries constitute the major anastomoses of the stomach?
1. Left and right gastroepiploics
2. Left and right gastrics
If the aorta is blocked, what are the four arterial anastomoses that compensate?
1. Internal thoracic/mammary to superior epigastric to inferior epigastric
2. Superior pancreaticoduodenal to inferior pancreaticoduodenal
3. Middle colic to left colic
4. Superior rectal to middle rectal
What is the origin of the internal thoracic artery?
Subclavian
What is the origin of the superior epigastric artery?
Internal thoracic
What is the origin of the inferior epigastric artery?
External iliac
What is the origin of the superior pancreaticoduodenal artery?
Celiac trunk
What is the origin of the inferior pancreaticoduodenal artery?
Superior mesenteric artery
What is the origin of the middle colic artery?
Superior mesenteric artery
What is the origin of the left colic artery?
Inferior mesenteric artery
What is the origin of the superior rectal artery?
Inferior mesenteric artery
What is the origin of the middle rectal artery?
Internal iliac
Which varices typically present with portal hypertension?
1. Esophageal
2. Caput medusae
3. Internal hemorrhoids
Which anastomoses are responsible for esophageal varices?
Left gastric to esophageal arteries
Which anastomoses are responsible for umbilical varices?
Paraumbilical to superficial and inferior epigastric
Which anastomoses are responsible for internal hemorrhoids?
Superior rectal and middle and inferior rectal
What is the surgical treatment for portal hypertension?
TIPS procedure (transjugular intrahepatic portosystemic shunt)
What is the TIPS procedure?
A shunt is created between the portal vein and hepatic vein, relieving portal hypertension by shunting blood to the systemic circulation
What is the pectinate line?
Formed where the hindgut meets the ectoderm
What rectal pathologies occur above the pectinate line?
1. Internal hemorrhoids
2. Adenocarcinoma (endodermal)
What is the arterial supply of the rectum above the pectinate line?
Superior rectal artery
What is the venous drainage of the rectum above the pectinate line?
Superior rectal vein -> Inferior mesenteric vein -> portal system
What rectal pathologies occur below the pectinate line?
1. External hemorrhoids
2. Squamous cell carcinoma (ectodermal)
What is the arterial supply of the rectum below the pectinate line?
Inferior rectal artery from the internal pudendal artery
What is the venous drainage of the rectum below the pectinate line?
Inferior rectal vein -> internal pudendal vein -> inferior vena cava
Which kind of hemorrhoids are painful?
External
Why are internal hemorrhoids not painful?
Internal hemorrhoids receive visceral innervation
Why are external hemorrhoids painful?
External hemorrhoids receive somatic innervation
What is the innervation of external hemorrhoids?
Inferior rectal nerve by pudendal nerve
What is the structure of the biliary tree?
The left and right hepatic ducts join with the cystic duct to form the common bile duct, which joins with the pancreatic duct at the ampulla of Vater; the duct empties into the lumen of the duodenum at the sphincter of Oddi
What is a common complication of tumors of the head of the pancreas?
They can cause obstruction of the common bile duct
What are the boundaries of the femoral triangle?
The femoral triangle is formed by the adductor longus muscle, the sartorius muscle, and the inguinal ligament
What is the organization of the structures contained within the femoral triangle, from lateral to medial?
1. Nerve
2. Artery
3. Vein
4. Empty space
5. Lymphatics
**NAVEL**
**Venous near the Penous**
What structures are contained within the femoral sheath?
1. Femoral artery
2. Femoral vein
3. Deep inguinal lympth nodes (femoral canal)
What is the structure of the inguinal canal, from exterior to interior?
1. Inguinal ligament
2. Internal oblique
3. Transversus abdominis
4. Transversalis fascia
5. Parietal peritoneum
6. Abdominal wall
What are the layers of the spermatic cord?
1. External spermatic fascia
2. Cremasteric muscle and fascia
3. Internal spermatic fascia
What structures does the spermatic cord pass through?
1. Internal inguinal ring
2. External inguinal ring
On which side of the spermatic cord do the inferior epigastric arteries lie?
Medially
What is a hernia?
A protrusion of peritoneum through an opening, usually at a site of anatomical weakness
What is the pathophysiology of a diaphragmatic hernia in infants?
Abdominal structures may enter the thorax as a result of defective development of the pleuroperitoneal membrane
What is the most common variety of diaphragmatic hernia?
Sliding hiatal, where the stomach herniates upward through the esophageal hiatus of the diaphragm
What is seen on x-ray with a sliding hiatal hernia?
An "hourglass stomach" due to displacement of the GE junction
What is seen on x-ray with a paraesophageal hernia?
The GE junction is normal; the cardia of the stomach moves into the thorax
What is the pathway of an indirect hernia?
Goes through the INternal (deep) inguinal ring, external (superficial) inguinal ring, and INto the scrotum
Using anatomical landmarks, where is an indirect hernia located?
Lateral to inferior epigastric artery
What is the pathophysiology of an indirect hernia?
Failure of the processus vaginalis to close
What complication may accompany an indirect inguinal hernia?
Hydrocele
Which gender is more at risk for developing an indirect hernia?
Males
How many layers of spermatic fascia cover an indirect inguinal hernia?
All three
What is the pathway of a direct inguinal hernia?
Protrudes through Hesselbach's triangle, bulging directly through the abdominal wall medial to the inferior epigastric artery, passing through the external (superficial) inguinal ring only
How many layers of spermatic fascia cover a direct hernia?
Only one (external spermatic fascia)
What are the relationships of the direct and indirect hernias to the inferior epigastric arteries?
Medial to artery = Direct
Lateral to artery = Indirect
**MDs don't LIe**
Which population is most at risk for a direct inguinal hernia?
Older males
What is the pathway of a femoral hernia?
Protrudes below the inguinal ligament through the femoral canal below and lateral to the pubic tubercle
Which population is most at risk for a femoral hernia?
Women
What is the leading cause of bowel incarceration?
Femoral hernia
What are the boundaries of Hesselbach's triangle?
Medial: lateral border of rectus abdominus
Lateral: inguinal ligament
Superior: inferior epigastric artery
What are the GI hormones?
1. Gastrin
2. Cholecystokinin
3. Secretin
4. Somatostatin
5. Gastric inhibitory peptide
6. Vasoactive intestinal peptide
7. Nitric oxide
8. Motilin
What is the source, action, and regulation of gastrin?
Source: G cells in the antrum of the stomach
Action: Increases gastric acid secretion, stimulates growth of gastric mucosa, and increases gastric motility
Regulation: Increased by stomach distention, alkalinization, amino acids, peptides, and vagal stimulation; decreased by stomach pH lower than 1.5
When is very increased gastrin seen?
Zollinger-Ellison syndrome
Which two amino acids are the two most potent stimulators of gastrin release?
1. Tryptophan
2. Phenylalanine
What is the source, action, and regulation of CCK?
Source: I cells in the duodenum and jejunum
Action: Increases pancreatic secretion, stimulates gallbladder contraction, and decreases gastric emptying by contracting the sphincter of Oddi
Regulation: Increased by fatty acids and amino acids
By which pathways does CCK cause increased pancreatic secretion?
Neural muscarinic pathways
What is the source, action, and regulation of secretin?
Source: S cells in the duodenum
Action: Increased pancreatic HCO3 secretion, decreased gastric acid secretion, and increased bile secretion
Regulation: Increased by acid and fatty acids in the lumen of duodenum
What is the purpose of the HCO3 released by secretin?
To neutralize the gastric acid in the duodenum, allowing pancreatic enzymes to function
What is the source, action, and regulation of somatostatin?
Source: D cells of the pancreatic islets and GI mucosa
Action: Decreases gastric acid and pepsinogen secretion, decreases pancreatic and small intestinal fluid secretion, decreases gallbladder contraction, and decreases insulin and glucagon release
Regulation: increased by acid, decreased by vagal stimulation
What is the source, action, and regulation of GIP?
Source: K cells of the duodenum and jejunum
Action: Endocrine -> decreased gastric H+ secretion; Exocrine -> increased insulin release
Regulation: Increased by fatty acids, amino acids, and oral glucose
Why is an oral glucose load more stimulatory of insulin release than an IV load?
GIP
What is the source, action, and regulation of VIP?
Source: Parasympathetic ganglia in sphincters, gallbladder, and small intestine
Action: Increases water and electrolyte secretion, increases relaxation of intestinal smooth muscle and sphincters
Regulation: Increased by distention and vagal stimulation, decreased by adrenergic input
What are the findings in a VIPoma?
1. Copious diarrhea
Where is a VIPoma found?
In the non-alpha, non-beta cells of the pancreas
What is the action of nitric oxide?
Increases smooth muscle relaxation, including the lower esophageal sphincter
What disease process is the loss of NO secretion implicated in?
Achalasia
What is the source, action, and regulation of motilin?
Source: Small intestine
Action: produces migrating motor complexes (MMCs)
Regulation: Increased in the fasting state
What is the pharmacological use for motilin receptor agonists?
Stimulate peristalsis
What are the GI secretory products?
1. Intrinsic factor
2. Gastric acid
3. Pepsin
4. HCO3
What is the source, action, and regulation of intrinsic factor?
Source: Parietal cells of the stomach
Action: B12 binding protein (required for B12 uptake in the terminal ileum)
Regulation: N/A
What is diseases are caused by autoimmune destruction of parietal cells?
1. Chronic gastritis
2. Pernicious anemia
What is the source, action, and regulation of gastric acid?
Source: parietal cells of the stomach
Action: decrease stomach pH
Regulation: increased by histamine, ACh, and gastrin; decreased by somatostatin, GIP, prostaglandin, and secretin
What is a gastrinoma?
A gastrin secreting tumor that causes continuous levels of acid secretion and ulcers
What is the source, action, and regulation of pepsin?
Source: chief cells of stomach
Action: protein digestion
Regulation: Increased by vagal stimulation and local acid
How is inactive pepsinogen activated?
By the low pH of the stomach
What is the source, action, and regulation of HCO3 in the intestine?
Source: mucosal cells in the stomach, duodenum, salivary glands, and pancreas; Brunner's glands in the duodenum
Action: neutralizes stomach acid
Regulation: increased secretion with secretin
What gastric structure does HCO3 help form?
The mucus that covers the gastric epithelium
What glands provide salivation?
1. Parotid
2. Submandibular
3. Sublingual
What are the two types of salivary secretion?
1. Serous
2. Mucinous
Which salivary gland provides the majority of the serous salivation?
Parotid
**Serous on the Sides**
Which salivary gland provides the majority of the mucinous salivation?
Sublingual
**Mucinous in the Middle**
What are the five functions of saliva?
1. Contains alpha-amylase, which begins starch digestin
2. Contains bicarbonate, which neutralizes oral bacterial acids to help maintain dental health
3. Mucins lubricate food
4. Antibacterial secretory products
5. Growth factors promote epithelial renewal
How is salivary secretion regulated?
Both sympathetic stimulation from the superior cervical ganglion and parasympathetic stimulation from the facial and glossopharyngeal nerves
How does flow rate affect the contents of saliva?
Low flow rate = more reabsorption of Na and Cl = hypotonic saliva
High flow rate = less reabsorption of Na and Cl = isotonic saliva
Which nerve passes through the parotid gland, and what is its clinical significance?
CN VII can be damaged during surgery
What is the most important mechanism to decrease acid secretion in the stomach, and why?
Blocking histamine impairs both the direct H2 pathway and the stimulation of H2 cells by gastrin
What kind of receptor does acetylcholine bind to in the stomach?
M3 (Gq)
What kind of receptor does gastrin bind to in the stomach?
CCKb (Gq)
What kind of receptor does histamine bind to in the stomach?
H2 (Gs)
What kind of receptor does misoprostol bind to in the stomach?
Gi
What kind of receptor does somatostatin bind to in the stomach?
Gi
What is the mechanism of acid production in the stomach?
The H+/K+ ATPase extrudes H+ into the lumen of the stomach in exchange for potassium
What is the source of the H+ excreted by the H+/K+ pump?
Carbonic anhydrase cleaves CO2 into H+ and HCO3
What is the fate of the HCO3- created in the synthesis of H+ for the stomach?
It is secreted into the bloodstream, causing the "alkaline tide" after eating
What is unique about the action of atropine on the regulation of acid production in the stomach?
Atropine blocks vagal stimulation of parietal cells, but does not affect stimulation of G cells, as gastric releasing peptide is used instead of acetylcholine at this location
What is the function of Brunner's glands?
Secretion of alkaline mucus to neutralize acid contents entering the duodenum from the stomach
Where are Brunner's glands locate?
In the submucosa of the duodenum (the only GI submucosal glands)
In which disease state is hypertrophy of Brunner's glands seen?
Peptic ulcer disease
What are the major pancreatic enzymes?
1. Alpha-amylase
2. Lipase
3. Phospholipase A
4. Colipase
5. Trypsin
6. Chymotrypsin
7. Elastase
8. Carboxypeptidases
9. Trypinogen
What is the function of alpha-amylase?
Starch digestion
Which pancreatic hormones are secreted in active form?
1. Amylase
2. Lipase
3. Phospholipase
4. Colipase
Which pancreatic hormones are secreted in zymogen form?
1. Trypsin
2. Chymotrypsin
3. Elastase
4. Carboxypeptidase
How are the zymogenic forms of pancreatic enzymes activated?
Trypsinogen is activated to trypsin by enterokinase/enteropeptidase, an enzyme secreted from the mucosa of the duodenum; trypsin then activates other proenzymes and more trypsinogen
What is the function of lipase, phospholipase A, and colipase?
Fat digestion
What is the function of the peptidases?
Protein digestion
What is the sequence of carbohydrate digestion?
1. Salivary amylase starts digestion by hydrolyzing alpha-1,4-linkages to yield dissacharides (maltose and alpha-limit dextrans)
2. Pancreatic amylase occurs at highest concentration in the duodenal lumen, hydrolyzing starch to oligosaccharides and disaccharides
3. Oligosaccharide hydrolases at the brush border of the intestine produce monosaccharides from oligo and disaccharides
What is the rate-limiting step of carbohydrate digestion?
Hydrolysis by oligosaccharide hydrolases
What is the process of carbohydrate absorption, including the molecules and transporters involved?
1. Glucose and galactose are taken up by SGLT1 (Na+ independent transport)
2. Fructose is taken up by facilitated diffusion by GLUT-5
How are monosaccharides transported into the blood (transporter)?
Through GLUT-2
Where is iron absorbed in the intestines?
Duodenum
Where is folate absorbed in the intestines?
Jejunum
Where is B12 absorbed in the intestines?
Ileum
What are Peyer's patches?
Lymphoid tissue found in the lamina propria and submucosa of theh small intestine containing specialized M cells that take up antigen
What kind of immunoglobulin is produced by activated B cells of Peyer's patches?
IgA
**Secretory IgA, the Intragut Antibody**
What does IgA have to receive to be secreted into the lumen of the intestines?
Protective secretory component
What is bile composed of?
1. Bile salts
2. Phospholipids
3. Cholesterol
4. Bilirubin
5. Water
6. Ions
What are the bile acids conjugated to in the formation of bile salts?
1. Glycine
2. Taurine
What is the function of bile?
Bile is necessary to:
1. Digest triglycerides
2. Form micelles
What is the function of a micelle?
To help solubilize lipids and non-polar nutrients so they can be absorbed into the enterocytes of the small intestine
What is the only way cholesterol can be excreted from the body?
Bile
What is bilirubin?
A product of heme metabolism
How is heme from RBCs disposed of, from bloodstream to bile?
1. Macrophages ingest senescent RBCs and digest the heme into unconjugated bilirubin
2. Unconjugated bilirubin is carried on albumin to the liver, where it is conjugated by glucuronyl transferase
3. Conjugated bilirubin is excreted into the bile
What is the fate of bilirubin in bile?
1. In the large intestine bacteria digest bilirubin to urobilinogen
2. 80% of urobilinogen is secreted in the feces as stercobilin
3. 20% of urobilinogen is reabsorbed by the gut, with 90% returning to the liver and 10% secreted in the urine by the kidneys as urobilin
What is jaundice?
Buildup of bilirubin in tissues, causing yellow skin and sclera
What is direct bilirubin?
Bilirubin that has been conjugated with glucuronic acid to make it water soluble
What is indirect bilirubin?
Insoluble, unconjugated form of bilirubin
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