Question

Describe the organs of the alimentary canal:

-Note any specializations in the layers that make up the walls of these organs.

-Note the epithelial tissue that lines the lumen

- Describe / list the sub-regions of these organs where appropriate (e.g. in the small and large intestine)

Answer 1

Alimentary canal also called the gastrointestinal tract  begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body. Throughout its length, the alimentary tract is composed of the same four tissue layers,  these layers are the mucosa, submucosa, muscularis, and serosa,

The mouth which is uppermost opening of the alimentary canal.Saliva is produced here.

Pharynx which is the common passageway for food and air, during the swallowing of food, the epiglotis, which is flap like structure closes the windpipe which prevents food entering the respiratory tract

Osephagus is the muscular tubular structure which helps in the movement of bolus from the phrynx to the stomach in prsence of peristalic movements, th eepithelial cells present here secretes mucus which helps ineasy movement of bolus.

Stomach is an elastic pouch made up of muscular walls situated right below the diaphragm, the stomach can be divided into five parts, cardiac stomach, fundus stomach, the body, the antrum stomach and the pyloric stomach. in the stomach food is broken down chemically, by gastric juice, and mechanically, by contraction of the three layers of smooth muscle in the muscular externa layer. The broken up food at the end of this process is called chyme. Gastric juice is secreted by gastric mucosal glands, and contains hydrochloric acid, mucus, and proteolytic enzymes pepsin (which breaks down proteins), and lipase (which breaks down fats).

Small intestine is divided into three parts, a) The duodenum is the first of the three parts of the small intestine that receives partially digested food from the stomach and begins with the absorption of nutrients, Histologically , it consists of the typical three layers common to all hollow organs of the gastrointestinal tract, but it has Brunner's glands, which is the characteristic feature of the duodenum.The Brunner glands, empty into the intestinal glands, secrete an alkaline fluid composed of mucin, which exerts a physiologic anti-acid function by coating the duodenal epithelium, therefore protecting it from the acid chyme of the stomach. b) The jejnum,The central of the three divisions of the small intestine that lies between the duodenum and the ileum, the inner surface of the jejunum, its mucous membrane, is covered in projections called villi, which increase the surface area of tissue available to absorb nutrients from the gut contents. The epithelial cells which line these villi possess even larger numbers of microvilli. c) The Ileum, the last, and usually the longest, division of the small intestine; the part between the jejunum and large intestine, The function of the ileum is mainly to absorb vitamin B12, bile salts, and any products of digestion that were not absorbed by the jejunum.

Large intestine has four parts: cecum, colon, rectum, and anal canal. Partly digested food moves through the cecum into the colon, where water and some nutrients and electrolytes are removed. The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anal canal and rectum orifice. The large intestine completes absorption, and retrieves water and sodium from the luminal contents which become fecal residue. It secretes large amounts of mucus, and some hormones, but no digestive enzymes.