Digestive System and Nervous System of Invertebrate.pptx

This ppt explains about general digestive system and nervous system of invertebrates by taking model organism as cockroach

1. Digestive System and Nervous System of Invertebrate

2. Introduction to Cockroach Cockroach (P. americana ) belongs to the class Insecta of Phylum Arthropoda. It is a common nocturnal omnivorous household animal which acts as a scavenger. It prefers dark warm corners of kitchens, underground drains and places where food and humid atmosphere are available .

3. Feeding and Digestion in Cockroach Cockroaches have adopted themselves to all types and sizes of diet. To handle the various types of food all the appendages of cockroach act synchro­nously . Extracellular digestion is the characteristic like other developed animals. Digestion starts from the buccal cavity containing the mouth parts. The food is then subjected to a variety of biochemical reaction within a specialized digestive system.

4. Digestive System of Cockroach The digestive system, which is responsible for digestion and absorption of food materials, includes digestive canal or tract (also called alimentary canal) and diges­tive glands . The tract is about 6.7 cm in length. It is divisible into three distinct regions: ( i ) Fore Gut (ii) Mid Gut (iii) Hind Gut

5. Fore Gut It is also known as stomodaeum. It is lined internally by cuticle and includes the mouth, pharynx, oesophagus , crop and gizzard. The mouth denotes the beginning of the alimentary canal. This aperture leads to a small chamber called the buccal cavity between the mandibles and maxillae on either side. The labrum serves as upper lip and labium acts as lower lip.

6. A short tongue or hypo-pharynx is present on the floor of the buccal cavity. The buccal cavity opens into a short pharynx which is a small tube. The salivary duct opens within the pharynx near the base of hypo-pharynx. The pharynx leads into the next part of the fore gut, which is called the oesophagus

7. The oesophagus extends up to the prothorax and is followed by the crop . The dilated sac-like crop constitutes the largest part of the fore gut. The wall of the crop is composed of epithelial layer, circular and longitudinal muscle layers. The crop extends within the abdominal cavity and acts as a temporary reservoir of food, where ingested food may be retained for two months.

8. The crop leads into a short thick-walled gizzard , which forms the last part of the fore gut. It is divided into an anterior and a posterior part. The wall of the gizzard is highly muscular and its anterior part contains in its inner wall six chitinous teeth extending towards the cavity of the gizzard. The posterior part of the gizzard possesses two circular hairy cushions . The teeth are used for crushing the food and the hairy cushions work as sieve to permit only the finer particles of food to go inside the mid gut.

9. Mid Gut This undivided part of ali­mentary canal is also known as mesenteron . It is a slender tube having an internal lining of columnar epithelium. Near the junc­tion of the fore and mid gut, there are eight hollow slender tubes called hepatic caeca or digestive diverticula . All the caeca opens within the mid gut and are believed to pro­duce digestive juices. In the inner wall, the epithelial cells throw fine filaments within the lumen of mid gut. The junction of the mid and hind gut is marked externally by the presence of numerous yellowish threads called Malpighian tubules which are excretory organs and range between 100-150

10. Hind Gut It is divisible into follow­ing parts —ileum, colon, rectum and anus. The ileum is the first part of the hind gut and has small narrow lumen having epithelial lining. The ileum leads to colon , which is broad and slightly coiled. The inner lining of colon is thrown into irregular folds and is formed by slender epithelial cells having a chitinous covering. The colon con­tinues into a small sac-like rectum . The inner wall of the rectum is raised in the form of papillae . Special kinds of glands called rectal glands are present in the rectal wall for absorbing water. Thus the rectum not only stores the residual parts of the food but also helps in osmoregulation. The rectum opens to the exterior through an opening called the anus . The anus is provided with a sphincter muscle.

11. Digestion Procedure in Cockroach Within the buccal cavity, the food comes in contact with saliva and passes through the oesophagus into the crop. Both peristalsis and antiperistalsis take place in the crop. The passage of food from the crop to the gizzard depends upon the ingested fluid . From the crop, the food passes to the gizzard, where the cuticular teeth crushes the food and the hairy cushion permits only finer particles to enter the mid gut.

12. The lining of mid gut and hepatic caeca act both as secretory and absorptive areas. Following enzymes are present in the secretion of these regions—amylase, maltase, invertase , lac­tase, β-glucosidase, protease and lipase. The cellulase obtained in the mid gut is synthesised by the micro-organisms residing there. Most of the digested foods are absorbed only in the mid gut. Glucose is absorbed by the caeca . After the absorption of digested food, the rest passes within the hind gut, where water and salts are absorbed. Residual matter is temporarily stored in the rectum and are periodically rejected through the anusFood requires nearly 33 hours to travel the entire length of the alimentary canal.

13. Nervous System of Cockroach  The cockroach nervous system consists of CNS, PNS and sympathetic nervous system where CNS stands for the central nervous system and PNS stands for the peripheral nervous system. The cockroach nervous system is a series of fused segment ganglia that is connected to the ventral side with longitudinal connectors . The nervous system of cockroaches spreads throughout the body. Three ganglia in the thorax and six ganglia in the abdominal segments. In the head, a bit of the nervous system is present where the remaining part is located on the ventral side or belly side of the body.

14. Central nervous system The central nervous system consists of the supra- oesophageal ganglion or brain, sub- oesophageal ganglion, circum oesophageal commissure and the nerve cord . The supra- oesophageal ganglion or is a bilobed structure situated in the head in front of oesophagus . It is formed by the fusion of three pairs of ganglia. It represents the brain and is concerned chiefly with sensory function . From the supra- oesophageal ganglia arise two circumoesophageal connectives which encircle round the oesophagus and meet below it with the sub- oesophageal ganglion . The sub- oesophageal ganglion is also situated in the head and formed by the fusion of 3 pairs of ganglia. The sub- oesophageal ganglion is the principal motor centre and controls the movements of muscles, mouth parts, wings and legs.

15. Thus , the supra- oesophageal ganglion, circumoesophageal connectives and sub- oesophageal ganglion together constitute the nerve ring round the oesophagus in the head capsule. From the sub- oesophageal ganglion arises a double nerve cord which travels through the thorax and abdomen below the alimentary canal on the ventral side up to the posterior end of the body. The nerve cord has three large ganglia in the thorax , one each for pro-, meso - and metathoracic segments, therefore, they are called prothoracic, mesothoracic and metathoracic ganglia. Further the nerve cord has six ganglia in the abdomen which lie in the 1st, 2nd, 3rd, 4th, 5th and 7th segments.

16. Each ganglion of the nerve cord is formed by the fusion of two ganglia except the ganglion in the 7th segment. The ganglion in the 7th abdominal segment is the largest of all the abdominal ganglia and probably formed by the fusion of 3 pairs of ganglia. Commissure –  these are transverse fibers that unite the pair of ganglia of the system.

17. Peripheral nervous system The nerves originating from the nerve ring and ventral nerve cord to innervate different parts of the body constitute the peripheral nervous system. Three pairs of nerves originate from the supra- oesophageal ganglion— optic, antennary and labrofrontal nerves . The first two innervate the eyes and antennae but the third one divides into labral nerve supplying to the labrum and the frontal nerve which runs forwards to join the sympathetic nervous system . Similarly, three pairs of nerves originate from the sub- oesophageal ganglion— mandibular, maxillary and labial to innervate the mandibles, maxillae and labium respectively.

18. Several pairs of nerves arise from each thoracic ganglion to supply the different parts of their own segment. A pair of nerves, however, from metathoracic ganglion innervates the 1st abdominal segment. The nerves originating from first five abdominal ganglia innervate the 2nd, 3rd, 4th, 5th and 6th abdominal segments. From the last abdominal ganglion three pairs of nerves are given off to supply the 7th, 8th, and 9th segments. It also gives a branch to innervate the cercus and other associated structures.

19. Sympathetic nervous system The autonomic nervous system or sympathetic nervous system or visceral nervous system consists of the same ganglia and their connectives . It includes the frontal, esophageal, occipital (hypo cerebral), visceral or ingluvial and pre-ventricular ganglia. The nerves from these ganglia are connected with the supra- oesophageal ganglion. The frontal ganglion is a small ganglion situated on the oesophagus in front of the supra- oesophageal ganglion .  A pair of frontal connectives from the frontal ganglion is connected with the supra- oesophageal ganglion A median recurrent nerve passes backward from it and connects the occipital or hypo cerebral ganglion behind the supra- oesophageal ganglion. Oesophageal ganglion located on the dorsal side of the esophagus and a huge visceral ganglion on the dorsal surface crop are present . Pre-ventricular ganglion is situated on the gizzard

20. Male reproductive system A well-developed reproductive system is present. The male reproductive system consists of a pair of testes, vas deferens, utricular gland, ejaculatory duct, and phallic gland .  Testis:  A pair of trilobed testis present in the male reproductive system which is inside of the fourth to sixth abdominal segment. One in each . Vas-deferens :  vas deferens arise from each testis and pass down to connect seminal vesicles. This opens into the ejaculatory duct . Seminal vesicles:  A seminal vesicle is formed when the vas-deferens dilates; it contains many white sacs, which are used for storing sperms. Sperms are then glued together to form spermatophores .

21. Ejaculatory duct:  Ejaculatory ducts arise from the two seminal vesicles; during copulation or meeting, spermatophores move down these ducts and open to the outside through the genital pore situated ventral to the anus . Phallic gland: It is a club shaped gland present below ejaculatory duct and it secretes the outer layer of spermatophore Mushroom gland/ Utricular gland:   The seminal vesicles bear a number of finger-like projections forming characteristic mushroom-shaped glands in the 6th to 7th abdominal segments, which nourish the sperms with their secretions.

22. Genital pouch:  Genital pouch is located at the end of the abdomen. It contains the genital pore, dorsal anus, and gonapophysis . External genitalia:  The external genitalia is represented by an asymmetrical chitinous structure called the male gonapophysis or phallomere (right, left and ventral), which surrounds the male gonophore (genital pore).

23. Female reproductive system The female reproductive system consists of the following parts: a pair of ovaries, oviduct, genital chamber, vagina, and colleterial glands, spermatheca , and external genitalia . Ovaries –  In females, the female reproductive system consists of a pair of ovaries that are located between the 2nd and 6th abdominal segments. Each ovary contains a row of ova in various stages of development within a group of ovarian tubules. Oviduct and vagina –  An oviduct leads from the ovary to the genital cavity. The right and left oviducts form a single median oviduct, also called the vagina, which is connected to the genital chamber .

24. Spermatheca –  A pair of spermatheca located in the sixth segment opens into the genital chamber, and it stores sperm. The left spermatheca is larger and functional, and the right spermatheca is smaller and non-functional. Genital pouch or chamber –  A genital pouch is a boat-shaped structure surrounded by three pairs of chitinous plates supporting copulation and the deposition of the egg. It is formed by the 7th, 8th, and 9th abdominal segments. It has two chambers. Genital atrium smaller chamber opening for the collateral gland, spermatheca , and opening of the common oviduct. Vestibulum is known as the large posterior part.

25. Collateral gland –  these glands are present on either side of a genital chamber into which they open. They help in the formation of egg cases or ootheca . The ootheca is a dark reddish to the blackish brown capsule which is of 8mm size. They are dropped to a suitable surface which is usually in a crevice nine to ten ootheca are present each containing 14-16 eggs.