Lower GIT: Small Intestine, Large Intestine, and Anus
Accessory Organs: Liver and the Hepatic Portal System, Pancreas, and Gallbladder
Learning Objectives
Describe the overall function of the digestive system and differentiate the gastrointestinal tract/alimentary canal from the accessory digestive organs.
List and define the major processes occurring during digestive system activity.
Draw the major subdivisions of the anterior abdominal wall, and identify the organs located in each subdivision.
Describe the location and function of the peritoneum and peritoneal cavity.
Differentiate between intraperitoneal and secondarily retroperitoneal digestive organs. Name the mesenteries associated with the intraperitoneal digestive organs.
Describe the splanchnic circulation and indicate the importance of the hepatic portal system.
Describe the tissue composition and general function of each of the four layers of the alimentary canal.
Describe stimuli and controls of digestive activity via the enteric nervous system.
Activities of the Digestive System
Ingestion
Mechanical breakdown
Mixing and propulsion
Digestion (chemical)
Absorption
Elimination
Abdominopelvic Cavity
Contains regions of the anterior abdominopelvic cavity.
The Peritoneum
Associated with the liver and mesentery.
The Mesenteries
Hold organs in place, store fat, and provide a route for blood vessels and nerves to reach visceral organs.
Ventral mesenteries: falciform ligament and lesser omentum.
Dorsal mesenteries: greater omentum, mesentery, transverse mesocolon, and sigmoid mesocolon.
Intraperitoneal and Retroperitoneal Organs
Distinction between the two.
Retroperitoneal Organs
Organs located behind the peritoneum.
Histology of the Gastrointestinal Tract
Smooth muscle fibers (smooth muscle cells).
Alternate waves of contraction and relaxation.
The walls of the gastrointestinal tract have the same four tissue layers:
Mucosa
Submucosa
Muscularis externa
Serosa
Mucosa
The mucosa, or inner lining, is a mucous membrane composed of:
Epithelium
Lamina propria
Muscularis mucosae
Major functions:
Secrete mucus, digestive enzymes, and hormones
Absorb end products of digestion into the blood
Protect against infectious disease
Submucosa
A thin meshwork of collagenous fibers, nerves, and blood vessels.
Contains the submucosal plexus.
Muscularis Externa
A double layer of smooth muscle: an inner sheet of circular fibers, and an outer sheet of longitudinal fibers.
Responsible for peristalsis and segmentation.
Contains the myenteric plexus.
Serosa
A serous membrane composed of connective tissue and simple squamous epithelium.
Superficial layer of portions of the gastrointestinal tract that are suspended in the abdominopelvic cavity.
Secretes a serous fluid.
Histological changes reflect functions of various regions.
Splanchnic Circulation
Arterial and venous circulation.
Enteric Nervous System
All digestive tract regulatory mechanisms control luminal conditions.
The enteric nervous system, or gut brain, consists of 100 million neurons (more neurons than the spinal cord!).
It is a semiautonomous, in-house nerve supply.
The plexuses interconnect like chicken wire all along the GI tract and regulate digestive activity throughout its length.
Enteric Nervous System - Plexuses
Submucosal plexus regulates movements of the mucosa, vasoconstriction of blood vessels, and innervates secretory cells of mucosal glands.