Inside-Out Anatomy: The Digestive System

What is the digestive system?

Digestive System: Facts, Function & Diseases
The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus. This section needs expansion with: Most of the time infections of the intestines end in diarrhoea or infectious disease , nausea, vomiting , and abdominal cramping. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. The heart is an extremely interesting and powerful pump. Saliva also contains a starch-digesting enzyme called amylase ptyalin , which initiates the process of enzymatic hydrolysis; it splits starch a polysaccharide containing many sugar molecules bound in a continuous chain into molecules of the double sugar maltose.

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What Are the Three Main Functions of the Digestive System?

Its capillaries nourish the epithelium and absorb digested nutrients. Its isolated lymphoid follicles which are a part of MALT ,. Large collections of lymphoid follicles occur in the pharynx tonsils and appendix. External to the lamina propria is the musularis mucosae , a layer of smooth muscle cells that produces local movements of mucosa.

The submucosa , just external to the mucosa, is areolar connective tissue containing a rich supply of blood and lymphatic vessels, lymphoid follicles, and nerve fibers which supply the surrounding tissues of the GI tract wall.

Its elastic fibers enable the stomach to regain its normal shape after temporarily storing a large meal. Th muscularis externa, also called the muscularis surrounds the submucosa. The muscularis is responsible for segmentation and peristalsis. It typically has an inner circular layer and an outer longitudal layer of smooth muscle cells. In several places along the tract, the circular layer thickens and forms sphincters that act as valves that control food passage from one organ to the next, they also prevent backflow.

In most alimentary canal organs, its made up of areolar connective tissue covered with mesothelium , a single layer of squamous epithelial cells. In the esophagus, which is located in the thoracic instead of the abdominopelvic cavity, the serosa is replaced by an adventitia , ordinary fibrous connective tissue that binds the esophagus to surrounding structures.

Retroperitoneal organs have both a serosa facing the peritoneal cavity and an adventia on the side abutting the dorsal body wall. Movements of the lower jaw in chewing are brought about by the muscles of mastication the masseter, the temporal, the medial and lateral pterygoids, and the buccinator.

The sensitivity of the periodontal membrane that surrounds and supports the teeth, rather than the power of the muscles of mastication, determines the force of the bite. Mastication is not essential for adequate digestion. Chewing does aid digestion, however, by reducing food to small particles and mixing it with the saliva secreted by the salivary glands. The saliva lubricates and moistens dry food, while chewing distributes the saliva throughout the food mass.

The movement of the tongue against the hard palate and the cheeks helps to form a rounded mass, or bolus , of food. The lips, two fleshy folds that surround the mouth, are composed externally of skin and internally of mucous membrane , or mucosa. The mucosa is rich in mucus-secreting glands, which together with saliva ensure adequate lubrication for the purposes of speech and mastication. The cheeks, the sides of the mouth, are continuous with the lips and have a similar structure.

A distinct fat pad is found in the subcutaneous tissue the tissue beneath the skin of the cheek; this pad is especially large in infants and is known as the sucking pad.

On the inner surface of each cheek, opposite the second upper molar tooth, is a slight elevation that marks the opening of the parotid duct, leading from the parotid salivary gland , which is located in front of the ear. Just behind this gland are four to five mucus-secreting glands, the ducts of which open opposite the last molar tooth. The roof of the mouth is concave and is formed by the hard and soft palate.

The hard palate is formed by the horizontal portions of the two palatine bones and the palatine portions of the maxillae, or upper jaws. The hard palate is covered by a thick, somewhat pale mucous membrane that is continuous with that of the gums and is bound to the upper jaw and palate bones by firm fibrous tissue. The soft palate is continuous with the hard palate in front. Posteriorly it is continuous with the mucous membrane covering the floor of the nasal cavity. The soft palate is composed of a strong, thin, fibrous sheet, the palatine aponeurosis, and the glossopalatine and pharyngopalatine muscles.

A small projection called the uvula hangs free from the posterior of the soft palate. The floor of the mouth can be seen only when the tongue is raised. In the midline is a prominent, elevated fold of mucous membrane frenulum linguae that binds each lip to the gums, and on each side of this is a slight fold called a sublingual papilla , from which the ducts of the submandibular salivary glands open.

Running outward and backward from each sublingual papilla is a ridge the plica sublingualis that marks the upper edge of the sublingual under the tongue salivary gland and onto which most of the ducts of that gland open.

The gums consist of mucous membranes connected by thick fibrous tissue to the membrane surrounding the bones of the jaw. The gum membrane rises to form a collar around the base of the crown exposed portion of each tooth. Rich in blood vessels, the gum tissues receive branches from the alveolar arteries; these vessels, called alveolar because of their relationship to the alveoli dentales, or tooth sockets, also supply the teeth and the spongy bone of the upper and lower jaws, in which the teeth are lodged.

We welcome suggested improvements to any of our articles. Thereby in a dry diet, more saliva mucus is secreted while in a moist diet, only an amount to assist with swallowing is secreted.

Saliva generally contains very low levels of amylase, the enzyme that hydrolyses starch to maltose. The contribution of digestive enzymes from saliva is minor but still noteworthy. Once food is chewed and mixed with saliva, it passes though the mouth, pharynx and then the oesophagus to the stomach.

Movement though the oesophagus involves muscle peristalsis, whichis the contraction and relaxation of muscles to move the food. The stomach is a muscular organ responsible for storage, initiating the breakdown of nutrients, and passing the digesta into the small intestine.

The stomach has four distinct areas which include the oesophageal, cardiac, fundic and pyloric regions Figure 2. The oesophageal region is located at the entrance of the stomach from the oesophagus. This region of the stomach does not secrete digestive enzymes but has significance in that this is where ulcer formation in pigs occurs. Irritation in this area due to fine particle size, stress or other environmental factors can contribute to ulcer formation in swine.

Once food passes though this region, it enters the cardiac region. In the cardiac portion of the stomach, mucus is secreted and mixed with the digested food. Food then passes into the fundic region which is the first major portion of the stomach that begins the digestive process. In this region, gastric glands secrete hydrochloric acid, resulting in a low pH of 1. This reduced pH kills bacteria ingested with the feed. Other secretions in this region are present in the form of digestive enzymes, specifically pepsinogen.

Pepsinogen is then broken down by the hydrochloric acid to form pepsin, which is involved with the breakdown of proteins. Finally the digesta moves to the bottom of the stomach, which is the pyloric region. This region is responsible for secreting mucus to line the digestive membranes to prevent damage from the low pH digesta as it passes to the small intestine. The phloric sphincter regulates the amount of chyme digesta that passes into the small intestine. This is an important function not to overload the small intestine with chyme so proper and efficient digestion and absorption of nutrients occurs.

In addition, once the chyme leaves the stomach, the material is quite fluid in consistency. The small intestine is the major site of nutrient absorption, and is divided into three sections.

The first section is the duodenum. The duodenum is approximately 12 inches long and is the portion of the small intestine that ducts from the pancreas and the liver gall bladder. The pancreas is involved with both exocrine and endocrine excretions.

Digestive System of the Dog