Digestive System PDF

Digestion – a physical as well as a chemical process of changing food from insoluble to soluble form. Food must be changed into a simple liquid form to facilitate its transport by the blood. FUNCTIONS – primarily for digestion The process of digestion includes several processes like: 1. Ingestion –...

Digestion – a physical as well as a chemical process of changing food from insoluble to soluble form. Food must be changed into a simple liquid form to facilitate its transport by the blood. FUNCTIONS – primarily for digestion The process of digestion includes several processes like: 1. Ingestion – taking in of food through the mouth. 2. Digestion – changing of food from solid to liquid state. 3. Absorption – passage of simple food from the digestive tract to the blood and lymph. 4. Circulation – transport of the absorbed food to the tissues of the body. 5. Assimilation – incorporation of absorbed simple food as part of the protoplasm. 6. Egestion – passing out of the undigested food or residue through the anus. Invertebrate Digestive System 1. Protozoa – provided with organelle, the food vacuole, which serves as an organ for digestion. Digestion is intercellular ( takes place within the cells ) 2. Porifera – with schizocoel and choanocytes - digestion is intracellular. 3. Coelenterata – with gastrovascular cavity, which serves as an incomplete digestive tube ( a type of digestive tube with only one opening which serves for both entrance and exit; with a mouth but no anus ). Digestion is both intracellular and extracellular ( type of digestion that takes place outside the cell, usually within the digestive cavity ). a. Intracellular – smaller food particles are absorbed into the vacuoles of the cell of the gastrodermis. b. Extracellular – the glandular cells of the gastrodermis secrete enzymes into the gastrovascular cavity where the digestion of the large particles takes place. Platyhelminthes – has an incomplete, branched digestive tube; an exception is the tapeworm which has no digestive tract. ▪ Tapeworm have no digestive tract and absorb food directly through their body walls ▪ The head of the tapeworm is called scolex – structure that contain suckers and hooks ▪ The scolex is used to attached their bodies into the intestinal wall of their host ▪ Diphylobothrium lutum (fish tapeworm) Hymenolopis Nana (dwarf tapeworm) ▪ Taenia Saginata (beef tapeworm) Taenia solium (pork tapeworm) ▪ Echinococcus granulosus (hydatid cyst disease) Echinococcus Multicularis (alveolar cyst disease) Nemathelminthes – has complete digestive tube ( type of digestive tube with a mouth for entrance and anus for exit. ▪ Nemathelminthes – roundworms like ascaris ▪ Annelida – a typical example of an invertebrate with a complete digestive tube. - digestion is extracellular. Parts of the digestive tube of the earthworm: 1. Mouth – the anterior opening which is provided with prostomium or lips used for grasping the food. 2. Buccal cavity- 3. Pharynx muscular structure which facilitates sucking in of food. 4. Crop – an expanded portion of the esophagus which serve for temporary storage of food. 5. Gizzard – very muscular structure which through its grinding motion with bits of sand present in it that act as an abrasive material ( aids in cutting the food into smaller bits ). 6. Intestine – place where digestion of food takes place; digestion is hastened by the secretion of enzymes secreted by the intestinal glands. Enzymes present: a. amylopsin – acts on carbohydrates b. pepsin – acts on protein c. lipase – acts on fats d. cellulase – acts of cellulose 7. Anus – the terminal opening of the digestive tube, an exit of digestive waste products Mollusca – with a complete digestive tube in some the mouth is provided with horny teeth that rasp off food particles. - digestion takes place in the stomach - absorption takes place in the intestine and residue exit through the anus. Echinodermata – with complete digestive tube ( incomplete in some )- the stomach is usually everted on the food, mucus is secreted, then the stomach with its contents is withdrawn into the body.- large bits are cast out through the mouth.- the intestines is mainly for excretion Arthropoda – with a complete digestive tube - mouth parts are modified appendages and are specialized for various purposes depending upon the feeding habits of the animal ( chewing, piercing, lapping, sucking) Enzymes present: a. amylopsin – acts on carbohydrates b. pepsin – acts on protein c. lipase – acts on fats d. cellulase – acts of cellulose