A continuous tube that extends through the thoracic and abdominal cavities from the esophagus to the anus
Organs of the digestive canal
Esophagus
Stomach
Small intestine
Large intestine
Anal canal
Accessory digestive organs
Mouth
Teeth
Tongue
Salivary glands
Pharynx
Liver
Gallbladder
Pancreas
Digestive canal
Length is about 5-7 meters in a living person
Length is about 7-9 meters in a cadaver
Functions of the digestive system
1. Ingestion
2. Secretion
3. Mixing and propulsion
4. Digestion
5. Absorption
6. Defecation
Ingestion
Taking food and liquids into the mouth (eating)
Secretion
Cells within the walls of the digestive canal and accessory digestive organs secrete water, acid, buffers, and enzymes into the lumen of the digestive canal
Motility
The capability of the digestive canal to mix and move material along its length
Mechanical digestion
The teeth cut and grind food before it is swallowed, and smooth muscles of the stomach and small intestine churn the food
Chemicaldigestion
Large carbohydrate, lipid, protein, and nucleic acid molecules in food are split into smaller molecules by hydrolysis catalyzed by digestive enzymes
Absorption
The movement of the products of digestion from the lumen of the digestive canal into blood plasma or lymph plasma
Defecation
Wastes, indigestible substances, bacteria, cells, and unabsorbed digested materials leave the body through the anus
The wall of the digestive canal has four layers: mucosa, submucosa, muscular layer, and serosa/adventitia
Mucosa
The inner lining of the digestive canal, composed of epithelium, lamina propria, and muscularis mucosae
Submucosa
Areolar connective tissue that binds the mucosa to the muscularis, containing blood/lymphatic vessels and the submucosal neural plexus
Muscular layer
Contains an inner circular muscle layer and an outer longitudinal muscle layer, responsible for involuntary contractions that break down food and propel it along the canal
Serosa
The superficial layer of the digestive canal suspended in the abdominal cavity, composed of areolar connective tissue and simple squamous epithelium
Enteric nervous system (ENS)
The intrinsic set of nerves that regulate the digestive canal, consisting of the myenteric and submucosal neural plexuses
Myenteric neural plexus
Located between the longitudinal and circular smooth muscle layers, controls digestive canal motility
Contains motor, sensory, and interneurons
Submucosal neural plexus
Located within the submucosa, controls secretions of the digestive canal organs
Contains motor, sensory, and interneurons
Muscular layer of the mouth, pharynx, and superior and middle parts of the esophagus
Contains skeletal muscle that produces voluntary swallowing
Skeletal muscle also forms the external anal sphincter, which permits voluntary control of defecation
Muscular layer of the rest of the digestive canal
Consists of smooth muscle that is generally found in two sheets: an inner sheet of circular fibers and an outer sheet of longitudinal fibers
Involuntary contractions of the smooth muscle help break down food, mix it with digestive secretions, and propel it along the digestive canal
Serosa
A superficial layer on portions of the digestive canal that are suspended in the abdominal cavity
Serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium)
Also called the visceral peritoneum
The esophagus lacks a serosa; instead, only a single layer of areolar connective tissue called the adventitia forms the superficial layer of this organ
Enteric nervous system
Consists of neurons arranged into the myenteric and submucosal neural plexuses
Myentericneural plexus
One of the neural plexuses of the enteric nervous system
Submucosal neural plexus
One of the neural plexuses of the enteric nervous system
The entericnervoussystem is regulated by the autonomic nervous system
Digestivecanalreflexpathway
Involves sensory receptors, sensory neurons, and neurons in the enteric, autonomic, and central nervous systems that regulate digestive canal secretion and motility
Peritoneum
The largest serous membrane of the body, consisting of a layer of simple squamous epithelium (mesothelium) with an underlying supporting layer of areolar connective tissue
Parietal peritoneum
Lines the wall of the abdominal cavity
Visceral peritoneum
Covers some of the organs in the abdominal cavity and is their serosa
Peritoneal cavity
The slim space containing lubricating serous fluid that is between the parietal and visceral portions of the peritoneum
Ascites
Condition where the peritoneal cavity becomes distended by the accumulation of several liters of fluid
Retroperitoneal
Organs that lie on the posterior abdominal wall and are covered by peritoneum only on their anterior surfaces, not in the peritoneal cavity
Major peritoneal folds
Greater omentum
Falciform ligament
Lesser omentum
Mesentery
Mesocolon
Greater omentum
The longest peritoneal fold, drapes over the transverse colon and coils of the small intestine “fatty apron”
A double sheet that folds back on itself, giving it a total of four layers
Contains a considerable amount of adipose tissue
Falciform ligament
Attaches the liver to the anterior abdominal wall and diaphragm
Lesser omentum
Arises as an anterior fold in the serosa of the stomach and duodenum, and connects the stomach and duodenum to the liver
Mesentery
A fan-shaped fold of the peritoneum that binds the jejunum and ileum of the small intestine to the posterior abdominal wall