Digestive System of Cockroach

It consists of a long alimentary canal and a pair of salivary glands.

Alimentary canal:It is a long and somewhat coiled tube of varying diameter and divisible into three regions : foregut,midgut and hindgut. Foregut and hindgut are ectodermal and lined with a thin cuticle secreted by ectoderm.The midgut is endodermal devoid of cuticular lining and capable of absorbing digested food.

A. Foregut or stomodaeum:It includes mouth cavity, pharynx, oesophagus,crop and gizzard.

1. Mouth cavity and mouth:Mouth cavity Or preoral chamber is a small, ill-defined space outside mouth, surrounded by mouth parts. Hypopharynx divides preoral cavity into a posterior part, called salivarium, into which common salivary duct opens, and an anterior part or cibarium, which leads towards mouth as a narrow food passage.Food is crushed and acted upon by the salivary secretion or saliva in mouth cavity.True mouth is a small opening at the base of preoral cavity and leads into pharynx.

2. Pharynx. It is short and tubular and its cuticular lining is more folded posteriorly.

3. Oesophagus. From pharynx arises a long,straight narrow and laterally compressed tube, the oesophagus. It passes through the nerve collar,

Scanned with runs through the neck and enters thorax to merge with crop.

4. Crop. It is a large, thin-walled,

pear-shaped sac, which extends well up to the third or fourth abdominal segmnent. It is the largest part of foregut. Its internal epithelial and cuticular lining is very much folded.  Crop serves as a reservoir for storing food.

5. Gizzard. Crop leads behind into a small, cone-shaped, muscular and thick-walled chamber, the gizzard or proventriculus, which marks the

end of foregut. It consists of two parts, an anterior armarium and a posterior stomodaeal valve.

(a) Armarium. The armarium possesses internally six longitudinal folds that greatly reduce its lumen. Longitudinal folds alternate with six longitudinal grooves which also bear small secondary folds. Cuticular lining of each longitudinal fold forms, (i) in the anterior part, a thick plate produced centrally into strong, sharp teeth or denticles, (ii) in the posterior part, a thin plate. Behind cach longitudinal fold the cuticular lining of the gizzard forms a soft cushion-like lobe, the pad or pulvillus, with long,backwardly directed hairs which act as strainers and allow only finer food particles to pass into midgut.

(b) Stomodaeal valve. Behind pulvillus, the posterior end of gizzard extends into the lumen  of midgut as a spout-like narrow tube, the stomodaeal valve, The latter folds back on itself and is thus double-walled. Stomodaeal valve

prevents regurgitation of food from midgut into gizzard.

B. Midgut or mesenteron:Midgut is the short and narrow tube-like middle part of alimentary canal also known as ventriculus or mesenteron. It is internally lined by glandular epithelium and forms the true stomach serving mainly for digestion and absorption.

1. Hepatic caeca. Opening into the anterior end of midgut are 7 or 8 short, narrow, blindly ending hollow tubes, called enteric or hepatic

caeca. They secrete digestive enzymes.

2. Malpighian tubules. From the junction of midgut and hindgut arise 100 to 150 very narrow, thread-like, yellow-coloured blind tubules projecting freely into haemocoel. These are called Malpighian tubules and are excretory in function.

C. Hind gut or proctodaeum Ihe posterior 1/3 part of alimentary canal forms the hindgut. It is divided into three regions :ileum, colon and rectum.

1. Ileum. Ileumn is a narrow and short tube.

2. Colon. Colon is longer and wider and with an irregular shape.

3. Rectum. Rectum is an oval or spindle shaped sac with external ridges alternating with internal longitudinal thickenings called  rectal papillae, These are 6 in number and also known as rectal glands, Rectum opens to outside by anus, Lining of hindgut is also cuticular.

Salivary Apparatus

Lying in thorax, on either dorso-lateral side of oesophagus, is a pair of bipartite, diffuse and whitish salivary glands. Each gland consists of several secreting lobules or acini in grape-likeclusters and connected together by fine tubules.

Acini contain two types of cells, described by Day as zymogenic cells and ductule-containing cells. Both types of cells secrete saliva, that consists of an enzyme zymase and mucoid substance. Ductules from ductule-containing cells open into an intercalary duct, that leaves acinus to join similar ducts of other acini, to form a larger duct.

 Associated with each gland is an

elongated, sac-like, thin-walled reservoir or receptacle for the storage of saliva.Ducts from the two salivary glands unite to form a single common glandular duct, Similarly,ducts from two reservoirs unite with each other forming a common reservoir duct, Both common ducts then join to form a common efferentsalivary duct that opens at the base of hypopharynx in the salivarium of preoral cavity