Digestive System of Cockroach

The digestive system of the cockroach is made up of three parts working together: the mouthparts (described under external morphology), a long alimentary canal, and a pair of salivary glands.

The alimentary canal is a long tube, about 6–7 cm, running from the mouth to the anus, and its diameter is not uniform along its length. Based on its embryonic origin and function, it is divided into three main regions: the fore-gut (stomodaeum), the mid-gut (mesenteron) and the hind-gut (proctodaeum).

Mouth. The mouth, or pre-oral chamber, is the narrow space enclosed by the mouthparts. The hypopharynx sits at its centre, and the salivary duct opens at the hypopharynx's base so that saliva is mixed with food right at the point of entry. The mouth leads directly into the fore-gut.

Fore-gut (stomodaeum). This region consists of the pharynx, oesophagus, crop and gizzard, in that order.

• The pharynx is a very short, narrow, muscular tube lined with taste-sensing sensillae, leading into the oesophagus.
• The oesophagus is a somewhat longer, narrow tube that carries food onward and opens into the crop.
• The crop is a large, pear-shaped sac that temporarily stores swallowed food before releasing it in a controlled way into the gizzard.
• The gizzard (proventriculus) is a small, rounded, muscular organ. Internally it bears a ring of six hard chitinous teeth along with backward-pointing bristles: the teeth grind and crush the food into fine particles, while the bristles act as a filter that only allows sufficiently crushed food through. The fore-gut ends at the gizzard.

Mid-gut (mesenteron). This region consists of the stomach (ventriculus) and the hepatic caecae. The stomach is a short, narrow, straight tube lined with glandular epithelium that secretes digestive enzymes, so most chemical digestion and nutrient absorption happens here. The hepatic caecae are a set of thin-walled, transparent, short, blind-ending (closed) tubules that also secrete digestive enzymes into the mid-gut, helping break down food further.

Hind-gut (proctodaeum). This region consists of the ileum, colon and rectum. The ileum is the short, narrow first part of the hind-gut; the Malpighian tubules (the excretory tubules) open into its front end, close to where the mid-gut meets the hind-gut, and a sphincter guards its posterior end. The ileum passes nitrogenous wastes and any undigested food onward to the colon. The colon is longer and wider, and besides moving waste toward the rectum it also reabsorbs water from the waste as the body needs it. Finally, the rectum is an oval or spindle-shaped terminal chamber whose internal wall carries six rectal pads specialised for further water absorption, conserving water before the waste is expelled. The rectum opens to the outside through the anus, located on the ventral side of the tenth abdominal segment; the anus is the last opening of the digestive system and releases the undigested food as waste. …