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| Digestive System of cockroach |
By:
Snigdha |
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It includes the mouth parts, a long alimentary canal and a pair of salivary glands. The principal parts of the alimentary canal are the foregut, the midgut and the hindgut. The foregut and hind gut are ectodermal, lined with cuticle as in the prawn ; but the midgut is endodermal, without a cuticular lining.(1) Foregut—It includes the mouth cavity, pharynx, oesophagus, crop and gizzard.The ill-defined mouth cavity (or pre-oral chamber) is bounded by the labrum in front and labium behind, and contains the mandibles, the first maxillae and the hypopharynx. The true mouth, lying at the base of the mouth cavity, leads into a tubular pharynx from which arises a slender oesophagus.. The latter runs through the nerve collar and traverses the neck into the thorax, where it dilates into a large thin-walled, pear-shaped sac, the crop extending well into the abdomen. The crop serves as a reservoir for storing food. Its outer surface is covered by a network of tracheae. Posteriorly, the crop leads into a small, thickwalled, muscular and cone-shaped chamber, the proventriculus or gizzard, whose chitinous inner lining is raised in to six powerful teeth, which form an efficient grinding apparatus. Behind the teeth is a ring-shaped cushion covered with bristles, which form a strainer and allow only small particles of food to pass further along the alimentary canal. The gizzard marks the end of the foregut and projects backwards into the cavity of the midgut in the form of spout-like. narrow tube, called the stomodael valve which prevents the food from being regurgitated.
(2) Midgut—It is a short, narrow tube internally lined by glandular epithelium. It is the stomach or ventriculus of the cockroach, and serves as the main organ of digestion and absorption. Opening into the anterior end of the midgut are 7 or 8 blindly ending, short, finger-like, hollow tubes, called the hepatic or enteric caeca.
(3) Hindgut—The midgut is followed by a long convoluted and ectoderm-lined hindgut or proctodaeum. It anterior end gives off sixty to seventy very narrow, threac, like, blind and yellow Malpighian tubules, named after the great Italian anatomist, Malpighi. Their function is excretor
The hindgut is differentiated into (a) an anterior short;. narrow ileum or small intestine, (b) a middle, long coiled and wider colart or large intestine, and (c) a terminal, short and dilated. sac-like rectum. which opens at the anus
to the exterior. The rectum is thick walled and its inner lining is thrown into six prominent longitudinal folds or rectal papillae.Lying in the thorax on either side of
the crop is a pair of diffuse, whitish salivary glands. Between each pair lies a thin-wailed bladder, called the salivary receptacle or reservoir, in which the secretions of the glands are kept in reserve. The ducts of the two glands of one side unite into one duct, which runs forward to join its fellow of the opposite side to form a common salivary duct. Similarly, the ducts of the two receptacles unite into a common receptacular due. The two common ducts then join to form a common efferent salivary duct, which opens on the door of the mouth cavies at the base of the hypopharynx.
The cockroach is omnivorous feeding on any kind of organic matter, animal or plant, including bits of paper. oils, leather, cloth, hair, bodies of its fellows and even its own cast cuticle. The food is searched by the sweeping antennae, tasted by the maxillary and labial palps, seized with the help of forelegs, labrum and labium, chewed by mandibles and maxillae and pushed by them with the help of labium into the mouth cavity and hence into the pharvnx.The salivary secretion is poured into the mouth cavity, where it mixes with the food during mastication. The digestive enzymes of saliva digest the starchy matter contained in the food. The chewed food moistened with saliva is stored in the crop, thoroughly ground up in the gizzard by the cuticular teeth, and strained into the midgut. The enzymatic secretions of the hepatic caeca and midgut digest the proteins and fats of the food. The digested food is absorbed in the midgut and the caeca and stored in the diffuse fat bodies. In the rectum, excess of water is extracted and the faccal matter or undigested food is egested through the anus.
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