Unit 4: Lecture 2 Part 2 (Intro to the GI Tract)

GI Tract

What is a continuous, muscular tube extending from the oral cavity to the anus, measuring approximately 30 feet in length in adults? It functions in ingestion, digestion, absorption, and waste elimination.

Oral cavity, pharynx, esophagus, stomach, small intestine and large intestine

What are the primary organs of the GI tract?

Oral cavity

What is the initial site for ingestion and mechanical digestion?

Pharynx

What is the conduit for food and air, divided into nasopharynx, oropharynx, and laryngopharynx?

Esophagus

What is the muscular tube delivering food from the pharynx to the stomach?

Stomach

What is the mechanical and chemical digester, responsible for food storage and turning bolus of food into chyme?

Small intestine

What includes duodenum, jejunum, ileum; major site of digestion and nutrient absorption?

Large intestine

What includes cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal; involved in water absorption and feces formation?

True

(T/F) Motility disorders (e.g., achalasia, intestinal pseudo-obstruction) can impair the function of these hollow organs, leading to significant gastrointestinal symptoms.

Accessory digestive organs

What organs aid digestion by secreting enzymes, bile, or other digestive fluids?

Salivary glands, teeth and tongue, liver, gallbladder, and pancreas

What are the accessory digestive organs?

Salivary glands

What accessory digestive organ includes Parotid, submandibular, and sublingual glands - secrete saliva for food

breakdown and lubrication?

Teeth and tongue

What accessory digestive organs aid in mechanical digestion and food propulsion?

Liver

What produces bile for emulsifying fats?

Gallbladder

What stores and concentrates bile?

Pancreas

What secretes digestive enzymes and bicarbonate into the duodenum?

True

(T/F) Disorders of accessory organs, such as gallstones or pancreatitis, may present with referred pain, nausea, and systemic inflammation.

Ingestion, transportation, digestion, absorption, and excretion

What are the 5 primary functions of the GI tract?

Digestion

What is the mechanical and chemical process of breaking down food into smaller

molecules suitable for absorption into the bloodstream or lymphatics?

Absorption

What is the movement of digested nutrients across the mucosal lining into blood vessels (capillaries) and lymphatic vessels (lacteals) in the walls of the gastrointestinal tract?

Bolus

What is the soft mass of chewed food formed in the oral cavity, mixed with saliva for easier

swallowing?

Chyme

What is the semiliquid paste resulting from the mechanical and chemical breakdown of the bolus in the stomach, prior to entering the duodenum?

True

(T/F) Conditions like malabsorption syndromes or GI motility disorders impair specific functions (e.g., absorption or transportation), leading to systemic consequences such as nutrient deficiencies, bloating, or altered bowel habits.

Mucosa (mucous membrane), submucosa, muscularis externa, serous or adventitia

What are the 4 layers of the GI tract?

Mucosa (mucous membrane)

What layer of the GI tract is the primary site of nutrient absorption and is involved in

immune defense? Its disruption in diseases such as inflammatory bowel disease (IBD) leads to bleeding, ulceration, and malabsorption.

Mucosa (mucous membrane)

Which layer of the GI tract is described:

• Epithelium: forms the innermost lining of the GI tract and varies by location (e.g., stratified squamous in esophagus, simple columnar in intestines).

• Lamina propria: loose connective tissue layer containing GALT (gut-associated lymphoid tissue).

• Muscularis mucosae: thin layer of smooth muscle promoting localized movement of the

mucosa.

Submucosa

Which layer of the GI tract is described:

• Contains mucus glands, blood vessels, and the submucosal (Meissner's) nerve plexus.

• Supports the mucosa and regulates secretions and local blood flow.

Submucosa

Vascular components of the _________ are critical in conditions like GI bleeding and varices.

Inner circular layer and outer longitudinal layer

What are the two muscle layers of the muscularis externa?

Myenteric nerve plexus

What lies between the two muscular layers of the muscularis externa and is responsive for coordinates motility (peristalsis)?

Myenteric plexus

Dysfunction in the _____ _____ contributes to motility disorders like achalasia and Hirschsprung disease.

Serosa

What fourth layer of the GI tracts is present when the GI segment is intraperitoneal; composed of a thin layer of connective tissue and mesothelium?

Adventitia

What fourth layer of the GI tracts is found in retroperitoneal or extraperitoneal GI organs; composed of connective tissue that blends with surrounding structures?

True

(T/F) The type of outer layer affects surgical approach and pathology spread, especially in GI perforation or malignancy.

GI motility

What is the mixing and movement of ingested materials throughout the gastrointestinal tract. It is essential for the mechanical breakdown of food, propulsion, and optimizing contact with digestive enzymes and absorptive surfaces?

Peristalsis

What is the coordinated, rhythmic contractions of the smooth muscle layers (primarily the muscularis externa) that move ingested material distally along the GI tract?

Peristalsis

What involves:

• Circular muscle contraction behind the bolus

• Longitudinal muscle contraction ahead of the bolus to shorten the path

Propels food through the esophagus, stomach, and intestines and assists in movement from one region to the next, such as from the stomach to the duodenum

What are the functions of peristalsis?

Simple columnar epithelium

What type of epithelium is found in the mucosa of most of the GI tract?

Esophagus and anus

Where in the GI tract is the mucosa made up of stratified squamous epithelium rather than simple columnar epithelium?

Peristalsis

Impaired ______ is a hallmark of conditions like achalasia, intestinal pseudo-obstruction, or post-operative ileus, and often presents with dysphagia, bloating, and constipation.

Mixing

What is localized, non-propulsive contractions primarily in the small intestine that mix food with digestive enzymes and secretions that involves rhythmic contractions of circular smooth muscle, without net forward movement?

Enhances digestion by increasing contact between enzymes and food and improves absorption by maintaining solute gradients and exposing the mucosa

What are the functions of mixing?

Normal mixing patterns

In diseases such as celiac disease or Crohn's disease, inflammation may alter

____ ____ ____, contributing to malabsorption.

False

(T/F) Mixing moves food forward in the GI tract.

Muscularis mucosae

What is the thin layer of smooth muscle promoting localized movement of the mucosa?

Stomach

What is the only part of the GI tract that has 3 layers of muscle?

Lamina propria

What is loose connective tissue layer of the mucosa containing GALT (gut-associated lymphoid

tissue)?

Alimentary system

What encompasses the entire digestive system, comprising the alimentary canal (also known as the gastrointestinal or GI tract) and the accessory digestive organs, such as the liver, pancreas, gallbladder, and salivary glands? In contrast, the alimentary canal refers specifically to the continuous muscular tube from mouth to anus.

Alimentary canal and accessory organs

What are the two parts of the alimentary system?

Alimentary canal (GI tract proper)

What part of the alimentary system is the direct pathway for ingested food?

Accessory organs

What part of the alimentary system supports digestion via enzymatic or hormonal contributions?

Oral cavity, esophagus, stomach, small intestine, large intestine, rectum and anal canal.

What are the structures within the alimentary canal?

Foregut, midgut, and hindgut

What are the three major regions of the GI tract?

Distal esophagus, stomach, first half of duodenum, liver, gallbladder, pancreas, and spleen (not a GI organ)

What makes up the foregut?

Celiac trunk

What is the blood supply of the foregut?

Foregut

Pain from ______ structures typically refers to the epigastric region. Conditions like peptic ulcer disease and biliary colic classically present with symptoms in this area.

Distal half of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal two-thirds of transverse colon

What makes up the midgut?

Superior mesenteric artery

What is the blood supply to the midgut?

Midgut

_______ pain usually localizes to the umbilical region, especially in early appendicitis. This is due to visceral afferents entering the spinal cord around T10.

Distal one-third of the transverse colon, descending colon, sigmoid colon, rectum (proximal portion)

What makes up the hindgut?

Inferior mesenteric artery

What is the blood supply of the hindgut?

Hindgut

Pain from _____ structures is typically referred to the suprapubic (hypogastric) region. Disorders like diverticulitis and rectal cancers often present with pain or altered bowel habits corresponding to this distribution.

Carotid cartilage (C6)

Where does the esophagus start?

Cardiac orifice of the stomach (T11)

Where does the esophagus end?

Cervical, thoracic, and abdominal parts

What are the three regions of the esophagus?

Skeletal muscle

What kind of muscle is found in the proximal third of the esophagus?

Mixed skeletal and smooth muscle

What kind of muscle is found in the middle third of the esophagus?

Smooth muscle

What kind of muscle is found in the distal third of the esophagus?

Upper esophageal sphincter

What sphincter of the esophagus is composed primarily of the cricopharyngeus muscle and closes during inhalation to prevent air from entering the esophagus?

Lower esophageal sphincter

What sphincter of the esophagus is a physiological sphincter (not a distinct anatomical ring) — consists of a thickened region of circular smooth muscle in the distal esophagus, pevents gastric reflux into the esophagus, and relaxes during swallowing to allow passage of the bolus?

Lower esophageal sphincter

Incompetence of what structure can result in gastroesophageal reflux disease (GERD), which may lead to Barrett esophagus, a premalignant condition?

Non-keratinized stratified squamous epithelium for protection from mechanical

abrasion.

What is the esophagus lined with?

(T/F) Outer surface of the esophagus is composed of adventitia, not serosa, because it is extraperitoneal.

Submucosa

What layer within the esophagus contains esophageal glands that secrete mucus for lubrication?

True

(T/F) In Barrett esophagus, chronic acid exposure leads to metaplastic change from squamous to columnar epithelium with goblet cells—a known risk for esophageal adenocarcinoma.

Inferior thyroid artery

What is the blood supply to the upper esophagus?

Thoracic aorta

What is the blood supply to the middle esophagus?

Left gastric artery

What is the blood supply to the lower esophagus?

False

(T/F) The lower esophageal sphincter is an anatomical sphincter.

Esophageal hiatus (T10)

Where does the esophagus transverse the diaphragm?

Voluntary, pharyngeal (involuntary), and esophageal (involuntary) phases

What are the three phases of swallowing?

Voluntary phase

In what phase of swallowing is bolus is compressed by the tongue against the hard palate and pushed into the oropharynx?

Pharyngeal phase (involuntary)

In what phase of swallowing does bolus trigger reflex contraction; soft palate and uvula elevate to close off the nasopharynx; larynx elevates, and the epiglottis closes over the airway?

Esophageal phase (involuntary)

In what phase of swallowing does the upper esophageal sphincter close after passage; peristaltic waves propel bolus toward the stomach; LES relaxes to allow bolus entry into stomach?

Hiatal hernia

What occurs when part of the stomach herniates through the esophageal hiatus of the diaphragm and enters the thoracic cavity?

Widened esophageal hiatus, increased intra-abdominal pressure, obesity, pregnancy, heavy lifting, and chronic coughing or straining

What are common causes of hiatal hernia?

T10

At what level do hiatal hernias typically occur?

Sliding hiatal hernias

What is the most common type of hiatal hernia?

Sliding hiatal hernia

What occurs when gastroesophageal junction and a portion of the stomach slide upward into the thorax? Often associated with gastroesophageal reflux disease (GERD).

Paraesophageal (rolling) hiatal hernia

What occurs when the gastroesophageal junction remains in place, but a portion of the stomach herniates alongside the esophagus? Higher risk of strangulation or obstruction.

True

(T/F) Sliding hernias are often asymptomatic or present with GERD symptoms. In contrast, paraesophageal hernias can be more dangerous, requiring surgical evaluation due to risks of volvulus (obstruction caused by twisting) and ischemia.

Barium swallow radiography, endoscopy, and esophageal manometry

What are the 3 ways to diagnose hiatal hernia?

Barium swallow radiography

What diagnosis technique for hiatal hernia is used to visualize the stomach's position?

Esophageal manometry

What diagnosis technique for hiatal hernia is used to measure sphincter function and motility?

Endoscopy

What diagnosis technique for hiatal hernia is used to assess for esophagitis, Barrett esophagus, or other mucosal changes?

Heartburn, regurgitation, chest pain, dysphagia (difficulty swallowing), and in severe cases, dyspnea or GI bleeding

What are the symptoms of hiatal hernia?

Weight loss, head-of-bed elevation, diet changes

What lifestyle modifications can be made to treat hiatal hernias?

Proton pump inhibitors for GERD

What pharmacological therapy can be use to treat hiatal hernias?

True

(T/F) With hiatal hernias, surgical repair can be used for large or symptomatic hernias, especially paraesophageal types.