Write their structure and function of gizzard of cockroach
Answers
The digestive system of cockroach consists of alimentary canal and digestive glands. One of the peculiarity of the digestive system is that the system although mainly involved in the process of digestion, it also takes part in excretion being associated with Malpighian tubules which open into the alimentary canal at the junction of midgut and hind gut.
Alimentary canal: It is complete, coiled and like a long tube of varying diameter. It is divisible into three main parts i.e. (i) Foregut or stomodeum (ii) Midgut or Mesenteron and (iii) Hindgut or Proctodeum (Fig.).
The foregut is ectodermal in origin and is lined internally with cuticle. It includes preoral cavity, a pseudocoel bounded by mouth parts lying in front of mouth. Hypopharynx, a tongue like projection hangs in it at tip of pre-oral cavoty. The mouth is a slit like aperture. The preoral cavity has the openings of the common salivary duct at the base of hypopharynx.
Posteriorly pre oral cavity (mouth cavity) communicates with the short, tubular pharynx by a small opening. The pharynx crosses the head region and after entering the thorax it joins the oesophagus, a short, narrow and tubular structure. The oesophagus dilates to form the sac-like crop which occupies whole of thorax and a few abdominal segments. The crop serves as reservoir of food. At its porterior extremity the crop narrow down and opens into a small, conical and thick walled sac, the gizzard which is broad anteriorly and narrow posteriorly.
The anterior part of gizzard (also called armarium) has six longitudinal folds bearing six chitinous teeth and in the posterior part, six cushion like pads (also called pulville) with chitinous hair are present. When the muscular wall of gizzards contracts the teeth work against each other and grind the food , while the hairs act as sieve or strainer stomodael valve present also in the posterior partnership the of gizzard prevents regurgination of food.
Function:
Hepatic caeca produces digestive enzymes. With the help of these digestive enzymes the digestion of food takes place in the mesentron. After the digestion the nutrient such as carbohydrates, fats and proteins are absorbed by the midgut, especially in the more anterior parts including the caeca. All the nutrients are absorbed. Remaining nutrients and water are absorbed in the hindgut especially in the rectum.
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