Review of GI Anatomy I Flashcards
The elimination of insoluble substances and other materials occurs in the
Large intestine
After the oral cavity, the digestive system consists of which 4 layers?
- ) Mucosa
- ) Submucosa
- ) Muscularis Externa
- ) Serosa/adventitia
Epithelium of the mucosal layer lines the lumen of the digestive tract and originates from ENDODERM for
Forgut, midgut, and hindgut derivatives (pharynx to large intestine)
The things that are derived from ectoderm are derivatives of the
Stomodeum and proctodeum (mouth and lower anal canal)
Forms from invagination of the developing gut epithelium and intramural-extramural glands extend through the gut layers with ducts that carry secretions to the luminal surface
Glandular Epithelium
Surrounds the endoderm and forms connective tissue, muscle, and serosa of the digestive viscera
Mesoderm
Neural crest cells migrate into the gut to form the
Enteric ganglia
By week 4, the primordial gut is made up of endoderm-lined
Foregut, midgut, and hindgut
Forms epithelium of the pharynx, esophagus, stomach, proximal duodenum and liver, gall bladder, pancreas with associated duct systems
Foregut endoderm
Forms epithelium of the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal ⅔ transverse colon
Midgut endoderm
The midgut is initially connected to the yolk sac via the
Vitteline Duct
Forms epithelium of the distal ⅓ transverse colon, descending colon, sigmoid colon, rectum, proximal part of anal canal
Hindgut endoderm
The ectoderm-endoderm membranes of the stomodeum and foregut form the
Oropharyngeal/buccopharyngeal membrane
A birth defect in which the gut structures remain herniated at the umbilicus because of failure of intestines to return back to abdominal cavity during development
Omphalocele
In omphalocele, are the intestines in contact with the amniotic fluid?
No
Early in development, the embryonic body cavity (intraembryonic coelom) is lined with
Mesoderm
Divides into visceral and parietal mesoderm with an intervening body cavity
Lateral Plate mesoderm
Thus, the body cavity in the abdominopelvic region is the
Peritoneal cavity
Organs that protrude into the peritoneal cavity only slightly are
-Example: kidneys
Retroperitoneal
Others such as the stomach and spleen protrude completely and are
Intraperitoneal
Intraperitoneal organs are connected to the posterior abdominal wall by a
Mesentery
Between the thoracic diaphragm superiorly, pelvic diaphragm inferiorly, abdominal wall anterolaterally, vertebral column-muscles posteriorly
Abdominopelvic cavity
A serosa/serous membrane that covers intraperitoneal organs and peritoneal walls
Peritoneum
Consists of mesothelium (simple squamous epithelium) with a thin layer of supportive loose connective tissue
Serosa
Continuity between parietal and visceral peritoneum occurs in
Mesentery
Double-layered peritoneal membranes that form from continuity between parietal and visceral peritonea passing between the posterior body wall and the viscera
Mesenteries
The hepatoduodenual ligament is a double layer of peritoneum at the free edge of the lesser omentum that connects duodenum to liver. It conducts the
Portal triad (hepatic portal vein, proper hepatic artery, common bile duct)
The parietal peritoneum is supplied by the same neurovasculature as the overlying body wall and is thus sensitive to
Pressure, pain, heat, cold, and laceration
Somatic pain from the parietal peritoneum is generally
Well localized
Patients experience more pain with large incisions of the well-innervated parietal peritoneum. Small laparoscopic incisions reduce pain and potential for contamination and
Peritonitis
Insensitive to touch, heat, cold, and laceration
Visceral peritoneum
Poorly localized visceral pain from the visceral peritoneum is activated by stretching and chemical irritation and is referred to
Dermatomes
Where is pain from the foregut, midgut, and hindgut typically located?
- ) Foregut = epigastric
- ) Midgut = umbilical
- ) Hindgut = hypogastric
Include stomach, liver, gall bladder, spleen, tail of pancreas, beginning of duodenum, jejunum, ileum, cecum, appendix, transverse colon, sigmoid colon
Intraperitoneal organs
Include most of duodenum, ascending colon, descending colon, most of pancreas, upper rectum
Secondarily retroperitoneal organs
Include kidney, adrenal gland, ureter, aorta, IVC, lower rectum, anal canal
Primary retroperitoneal organs
Inflamed peritoneum (from surgery or infection) can lead to surfaces that are sticky with
Fibrin
During healing, fibrous scar tissue can form abnormal attachments between visceral and parietal serosal layers, known as
Adhesions
This tethering may cause chronic pain or emergency complications such as
Intestinal obstruction
The arterial supply to the structures of the oral cavity, pharynx, and upper esophagus are from
Branches of external carotid and subclavian arteries, and the thoracic aorta
Venous drainage from the structures of the oral cavity, pharynx, and upper esophagus is from tributaries to the
Subclavian vein, azygous vein, SVC, and IVC
Branches of the abdominal aorta include the
Celiac trunk, SMA, and IMA
Supplies derivatives of the foregut in the abdominopelvic cavity
Celiac trunk
Supplies the midgut
Superior Mesenteric Artery (SMA)
Supplies derivatives of the hindgut and abdominopelvic cavity
Inferior Mesenteric Artery (IMA)
Anastomoses between these branches occur through the
Marginal Artery
May help demonstrate obstruction of branches, which can result in ischemia and necrosis (tissue death)
An arteriogram
The necrotic segment may become non-functional. This will result in colicky pain as well as
Abdominal distinction, vomiting, fever, and dehydration
Much of the gut drains into the hepatic portal vein via the
Splenic vein, SMV, and IMV
The hepatic portal vein is flanked by capillary beds, with one capillary bed in the gut and the other in the
Liver (as sinusoids)
Anterior to the IVC and posterior to the neck of the pancreas
Hepatic portal vein
The hepatic protal vein is formed by the union of the
SMV and splenic vein
Drains into splenic vein (60%) or juncture of splenic vein with SMV (40%)
IMV
Blood entering the hepatic portal veins contains products of RBC breakdown from the spleen and absorbed nutrients from
Intestines
Portal-systemic anastomoses, in which the portal venous system communicates with the systemic venous system, can be seen in the submucosa of the
Inferior esophagus, peri-umbilical region, and inferior anal canal
Portal circulation through the liver can be impeded because of cirrhotic liver disease that causes
Portal hypertension
The collateral circulation seen in portal hypertension is possible because the hepatic portal vein and its tributaries lack
Valves
However, the excess blood volume in the collateral venous routes may lead to potentially fatal
Hemorrhage
Presynaptic sympathetic fibers in the greater, lesser, least, lumbar splanchnic nerves synapse on postsynaptic sympathetic prevertebral ganglia associated with branches of the
Abdominal Aorta
Postsynaptic sympathetic axons and presynaptic parasympathetic axons make up the
Periarterial plexuses
Periarterial plexuses that travel along branches of the celiac trunk, SMA, IMA to provide autonomic innervation to smooth muscles and glands of the
Foregut (celiac), midgut (SMA)., and hindgut (IMA)
The submucosal plexus of Meisser and myenteric plexus of Auerbach are located within the gut wall layers and receive stimulatory input from preganglionic parasympathetic axons to
Promote Digestion
The submucosal plexus of Meisser and myenteric plexus of Auerbach are located within the gut wall layers and receive inhibitory input from postganglionic sympathetic axons to
Slow Digestion
Thus, although the intrinsic, enteric nervous system can function independently, it is induced by the parasympathetic preganglionic fibers of the vagus and pelvic splanchnic nerves to increase
Smooth muscle peristalsis and glandular secretion for digestion
Thus, although the intrinsic, enteric nervous system can function independently, it is inhibited by sympathetic postganglionic fibers whose cell bodies are located
Prevertebral ganglia
Act in the digestive system to stimulate smooth muscle peristalsis and glandular secretion
Parasympathetics
Act in the digestive system to inhibit digestion and induce vasoconstriction
Sympathetics
Poorly localized pain
Visceral pain
Visceral pain from foregut derivatives, for example, refers to the epigastric dermatomes because pain afferents accompany the sympathetic greater splanchnic nerve to reach
T5-T9 segments
The MOUTH is the opening to the digestive tract and includes the
Lips, cheeks, teeth, gums/gingivae, tongue, and palate
The dorsum (top surface) of the TONGUE has a
Sulcus terminalis and lingual papillae
Separates the anterior body of the tongue from the posterior root
Sulcus terminalis
Made up of filiform, fungiform, and circumvallate types, some of which have taste buds
Lingual papillae
Sensation from the anterior 2/3 of the tongue is conveyed via
- ) CNVII for taste
2. ) CNV3 for general
All sensation from the posterior 2/3 of the tongue is conveyed via
CNIX (w/ some taste from CNX also)
Can be seen on the posterior tongue
Lingual tonsils
Almost all tongue muscles are innervated by the
Hypoglossal nerve (CNXII)
In adult humans, what is the make up of permanent teeth?
16 mandibular and 16 maxillary
Twenty (20) deciduous teeth precede permanent teeth and are also called
Milk or baby teeth
The hardest substance in the body (contains ~95% hydroxyapatite)
Enamel
Tooth enamel forms by secretions from ectoderm-derived
Ameloblasts
Deep to enamel, dentin forms from
Neural crest-derived odontoblasts
Surrounds the soft mesenchyme-like tooth pulp that contains vessels and nerves
Dentin
Surrounds the outer surface of the tooth root
Cementum
Passes masticated food in the form of a bolus from the mouth and pharynx through the ESOPHAGUS to the stomach
Peristalsis
The portion of the diaphragm that surrounds the esophagus forms the
Lower/inferior esophageal sphincter
The collapsed lumen of the empty esophagus also prevents food or stomach juices from
Regurgitating
Most of the esophagus is covered by an outer adventitial layer of connective tissue except for visceral peritoneum covering the
Abdominal esophagus
The squamocolumnar juncture where the esophageal mucosa changes to gastric mucosa
Z-line
Immediately superior to the Z-line
Lower esophageal sphincter
If gastric acid reflux from the stomach to the esophagus occurs, abnormal metaplasia (change in epithelial type) may occur in the esophagus and result in
Chronic inflammation (reflux esophagitis), ulceration, or difficulty swallowing (dysphagia)
Weakening of the diaphragmatic musculature that forms the lower/inferior esophageal sphincter may be seen in middle age (incidence increases with age) and can lead to widening of the esophageal hiatus and even
Hiatal hernia
In a hiatal hernia, a portion of the stomach moves through the esophageal hiatus into the
Posterior mediastinum of the thoracic cavity
Over 95% of hiatal hernias are
Type 1 (sliding type) hernias
The abdominal part of esophagus and the cardiac-fundus parts of the stomach slide through hiatus into thorax in a
Sliding type hernia
Because of its course through the neck, thorax, and abdomen, multiple arteries supply the esophagus, including branches of the
External Carotid, subclavian, and thoracic-abdominal aorta
Can occur as a result of portal hypertension
Submucosal esophageal varices
Causes a reversal of blood flow in the valveless esophageal veins so that there is increased blood volume in the dilating submucosal esophageal veins and tributaries to the systemic venous circulation
Portal hypertension due to liver cirrhosis
For larger meals, gastric rugae (mucosal-submucosal folds) distend and can expand to hold
2-3L of food
The microscopic glands within the stomach mucosa are tubular in shape with branching at the deeper/lower ends. The branched ends are
Gastric glands
