SPMD 201 Digestive System

SPMD 201 Digestive System Anatomy - ANSWER-The digestive system consists of the digestive tract, a tube extending from the mouth to the anus, and its associated accessory organs—primarily glands located outside the digestive tract that secrete fluids into it. The digestive tract is also called the alimentary tract, or alimentary canal. Technically, the term gastro-intestinal tract refers only to the stomach and intestines, but it is often used as a synonym for digestive tract. Histology - ANSWER-The digestive tube consists of four major tunics, or layers: an internal mucosa and an external serosa, with a submucosa and a muscularis in between. These four tunics are present in all areas of the digestive tract, from the esophagus to the anus. Three major types of glands are associated with the intestinal tract: (1) unicellular mucous glands in the mucosa, (2) multicellular glands in the mucosa and submucosa, and (3) multicellular glands (accessory glands) outside the digestive tract. Mucosa and Submucosa - ANSWER--The innermost tunic, the mucosa (mū-kō′să), or mucous membrane, consists of three layers: (1) the inner mucous epithelium, which is moist stratified squamous epithelium in the mouth, oropharynx, esophagus, and anal canal and simple columnar epithelium in the remainder of the digestive tract; (2) a loose connective tissue called the lamina propria (lam′i-nă prō′prē-ă); and (3) a thin outer layer of smooth muscle, the muscularis mucosae. -The epithelium extends deep into the lamina propria in many places to form intestinal glands and crypts. Two types of specialized cells in the mucosa are mechanoreceptors involved in peristaltic reflexes and chemoreceptors that detect the chemical composition of food. -Beneath the mucosa lies the submucosa, a thick connective tissue layer containing nerves, blood vessels, lymphatic vessels, and small glands. A network of nerve cells in the submucosa forms the submucosal plexus (plek′sŭs), or Meissner plexus, consisting of axons, many scattered neuron cell bodies, and neuroglial cells. Muscularis & Serosa - ANSWER--The next tunic is the muscularis, which consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Two exceptions are the upper esophagus, where the muscles are striated, and the stomach, which has three layers of smooth muscle. Another nerve plexus, the myenteric (mī-en-ter′ik) plexus, or Auerbach plexus, also consists of axons, many scattered neuron cell bodies, and neuroglial cells and is between these two muscle layers (figure 24.4). The myenteric plexus, which is much more extensive than the submucosal plexus, controls the motility of the intestinal tract -When the outer layer of the digestive tract is derived from adjacent connective tissue, the tunic is called the adventitia and consists of a connective tissue covering that blends with the surrounding connective tissue