BIO 004 · Human Anatomy
The Alimentary Canal
Block 4 · Module 2: The Digestive System, the Alimentary Canal
A reference for the alimentary canal video and lab. This page covers the wall of the digestive tube, the peritoneum, and the regions of the canal from the mouth to the anus, with the named features of the stomach and the intestines. The focus is on the structures and the job each one does.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level depth for this course.
- Distinguish the alimentary canal from the accessory organs and name the four layers of its wall.
- Trace the pathway of food from the mouth to the anus.
- Identify the named features of the stomach, small intestine, and large intestine.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The alimentary canal
Add a labeled overview of the digestive tube from the mouth to the anus.
The wall of the tube
Add a labeled cross-section showing the mucosa, submucosa, muscularis, and serosa.
The stomach
Add a labeled view of the stomach with the cardia, fundus, body, and pyloric part.
The Alimentary Canal, an Overview
The digestive system has two groups of organs. The alimentary canal is the continuous tube that food travels through; the accessory organs sit alongside it and empty their secretions in. This page covers the canal.
- Digestive systemthe organs that take in food and eliminate waste; the alimentary canal plus the accessory organs
- Alimentary canalthe gastrointestinal tract; a continuous muscular tube from the mouth to the anus
- Organs of the canalthe mouth, most of the pharynx, the esophagus, the stomach, the small intestine, and the large intestine
- Accessory organsthe teeth, tongue, salivary glands, liver, gallbladder, and pancreas; covered on their own sheet
- Lumenthe open interior space of the tube, continuous with the outside world at the mouth and anus
- Lengthabout 16 to 23 feet in a living person, longer once muscle tone is lost
The Wall of the Alimentary Canal
From the lower esophagus to the anal canal, the wall of the tube is built from the same four layers, deep to superficial. Compare them.
| Layer | What it contains |
|---|---|
| Mucosa | the inner lining; an epithelium in contact with food, the lamina propria of areolar connective tissue beneath it, and a thin muscularis mucosae |
| Submucosa | areolar connective tissue with blood and lymphatic vessels, and the submucosal nerve plexus |
| Muscularis | usually an inner circular and an outer longitudinal layer of smooth muscle, with the myenteric nerve plexus between them |
| Serosa | the outermost layer; a serous membrane, also called the visceral peritoneum, replaced by a fibrous adventitia on the esophagus |
Two nerve networks in the wall make up the enteric nervous system, the nerve supply of the gut.
- Submucosal plexusthe nerve network in the submucosa that controls the secretions of the gut
- Myenteric plexusthe nerve network between the muscle layers that controls the movement of the gut
The Peritoneum
The peritoneum is the large serous membrane of the abdomen. Its folds anchor the digestive organs and carry their vessels and nerves.
- Parietal peritoneumthe layer that lines the wall of the abdominal cavity
- Visceral peritoneumthe layer that covers the organs; it is the serosa of those organs
- Peritoneal cavitythe slim, fluid-filled space between the parietal and visceral layers
- Retroperitoneal organsorgans behind the peritoneum, not within its cavity; the kidneys, pancreas, duodenum, and parts of the colon
Five large folds of peritoneum weave among the organs. Compare what each one connects.
| Fold | What it connects |
|---|---|
| Greater omentum | the largest fold; a fatty apron hanging from the stomach over the intestines |
| Lesser omentum | connects the stomach and duodenum to the liver, and carries vessels to the liver |
| Falciform ligament | attaches the liver to the anterior abdominal wall and the diaphragm |
| Mesentery | a fan-shaped fold binding the jejunum and ileum to the posterior abdominal wall |
| Mesocolon | binds the transverse and sigmoid colon to the posterior abdominal wall |
The Mouth, Pharynx, and Esophagus
Food enters at the mouth, is swallowed through the pharynx, and travels the esophagus to the stomach.
- Oral cavitythe mouth; bounded by the cheeks, the lips, the palate, and the tongue
- Hard palatethe bony anterior roof of the mouth, formed by the maxillae and palatine bones
- Soft palatethe muscular posterior roof of the mouth
- Uvulathe finger-like projection of the soft palate that closes off the nasopharynx during swallowing
- Faucesthe opening from the mouth into the oropharynx
- Palatine and lingual tonsilslymphatic tissue between the palatal arches and at the base of the tongue
- Pharynxthe funnel-shaped passage with three regions: the nasopharynx, oropharynx, and laryngopharynx
- Esophagusthe collapsible muscular tube, about 10 inches long, that carries food from the laryngopharynx to the stomach
- Esophageal hiatusthe opening in the diaphragm that the esophagus passes through
- Upper and lower esophageal sphinctersthe rings of muscle that guard the top and bottom of the esophagus; the lower is also called the cardiac sphincter
The Stomach
The stomach is a J-shaped widening of the tube below the diaphragm. It is a mixing chamber and a holding reservoir.
- Cardiathe region that surrounds the opening from the esophagus
- Fundusthe rounded portion that bulges above and to the left of the cardia
- Bodythe large central portion of the stomach
- Pyloric partthe region that connects the body to the duodenum; it has the pyloric antrum, pyloric canal, and pylorus
- Pyloric sphincterthe ring of smooth muscle between the pylorus and the duodenum
- Lesser curvaturethe concave superior border of the stomach
- Greater curvaturethe convex inferior border of the stomach
- Rugaethe folds of the inner stomach lining that flatten as the stomach fills
- Gastric pits and glandsthe pits in the stomach lining that lead to the gastric glands, the secreting glands of the stomach
- Muscularis of the stomachthree layers of smooth muscle, an inner oblique, a middle circular, and an outer longitudinal; one more than the rest of the tube
The Small Intestine
The small intestine is the long, coiled region where most absorption happens. Its lining is folded again and again to expand the surface area.
- Duodenumthe first and shortest region, about 12 inches, curving from the pyloric sphincter; mostly retroperitoneal
- Jejunumthe middle region, about 3 feet long
- Ileumthe longest region, about 6 feet, joining the large intestine at the ileocecal sphincter
- Ileocecal sphincterthe valve of smooth muscle where the ileum meets the large intestine
- Circular foldsthe plicae circulares; permanent ridges of the mucosa and submucosa that increase surface area
- Villifinger-like projections of the mucosa that give the lining a velvety look and greatly increase surface area
- Lactealthe lymphatic capillary inside each villus that absorbs dietary fats
- Microvillithe microscopic projections of the absorptive cells that form the brush border
The Large Intestine
The large intestine is the wider, final region of the canal. It absorbs water and forms and stores the feces.
- Cecumthe pouch at the start of the large intestine, just below the ileocecal valve
- Vermiform appendixthe narrow, worm-like tube of lymphatic tissue attached to the cecum
- Colonthe long portion with four parts: the ascending, transverse, descending, and sigmoid colon
- Rectumthe straight portion, about 6 inches, anterior to the sacrum and coccyx
- Anal canalthe last 2 to 3 cm of the tract, ending at the anus
- Internal and external anal sphinctersthe involuntary smooth muscle and voluntary skeletal muscle that guard the anus
- Teniae colithree thickened bands of longitudinal muscle running the length of the colon
- Haustrathe pouches that give the colon its puckered appearance, formed by the teniae coli
- Omental appendicessmall fat-filled pouches of peritoneum attached to the teniae coli
The Pathway of Food
Food moves through the alimentary canal in one direction, through each region in turn.
- Mouthfood is taken in, chewed, and mixed with saliva
- Pharynxthe swallowed food passes through the oropharynx and laryngopharynx
- Esophagusmuscular contractions carry the food down to the stomach
- Stomachfood is churned and held as it becomes a liquid
- Small intestinethe duodenum, jejunum, and ileum, where most absorption occurs
- Large intestinethe cecum, colon, rectum, and anal canal, where water is absorbed and feces form
- Anusthe feces are eliminated
Common Disorders of the Alimentary Canal
Compare the common disorders of the canal by the structure each one affects.
| Disorder | What it is |
|---|---|
| Gastroesophageal reflux disease (GERD) | stomach contents flow back up through a weak lower esophageal sphincter and irritate the esophagus |
| Hiatal hernia | part of the stomach pushes up through the esophageal hiatus of the diaphragm |
| Peptic ulcer | an eroded sore in the wall of the stomach or duodenum |
| Appendicitis | inflammation of the vermiform appendix; rupture can spread infection to the peritoneum |
| Diverticulosis | small pouches that bulge outward through weak spots in the colon wall |
| Inflammatory bowel disease | chronic inflammation of the intestinal wall, as in Crohn disease and ulcerative colitis |
| Hemorrhoids | swollen, dilated veins in the wall of the anal canal and rectum |
| Colorectal cancer | a malignant tumor of the colon or rectum |
See also: The Accessory Digestive Organs for the liver, gallbladder, and pancreas, and Histology: The Four Tissue Types.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the four layers of the gut wall from the lumen outward, and state the tissue that dominates each.
- Compare the stomach, small intestine, and large intestine by one structural feature each that suits its job.
- Trace a bite of food through every named segment of the alimentary canal in order, mouth to anus.
- Where are the major sphincters of the alimentary canal, and what does each one separate?
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.