Digestive System

Digestion The process of breakdown of complex food molecules into simple molecules. Process involves Ingestion (Intake of Food) Digestion( breakdown of food) Absorption ( Movement of digested food into the blood stream) Assimilation (The process by which cell use the food for cellular build up and processes) Egestion ( removal of waste as solid form)

Classification of organisms on the basis of nutrition Nutrition: The process of intake of food and its conversion into living protoplasm in cells. Autotrophs- Organisms which can prepare their food Heterotrophs- Organism which cannot prepare their own food due to lack of chlorophyll.

Holophytic Nutrition: the mode of nutrition in which living organisms use inorganic material to prepare their own food Holozoic Nutrition: The mode of nutrition in which living organisms ingest food from outside and digest it in their body to obtain energy.

Classification of Heterotrophs Herbivores Carnivores Omnivores Parasites Scavengers Saprophytes Sanguivores.

Nutrition in Plants Plants are autotrophs and therefore prepare their own food by the process of photosynthesis. Photosynthesis: The process by which green plants prepare their own food in the presence of sunlight utilizing chlorophyll, CO2, water and minerals.

Structure of Leaf- 1. Cuticle 2. Upper epidermis 3. Pallisade parenchyma 4. Bundle sheath 5. Xylem 6. Phloem 7. Lower epidermis 9. Spongy parenchyma 10. Guard cells 11. Intercellular space The cells between the upper and lower epidermis are called mesophyll cells.

Process of Photosynthesis Photosynthesis is a two phase process: Light Reaction -Light dependent reaction takes place in the thylakoids in grana. During this phase- a) Light is absorbed by photosensitive pigment chlorophyll present in the thylakoids. b) Photolysis of water takes place. This forms H+ ions. c) The energy currencies ATPs are generated. d) Reducing agent NADPH are formed.

Dark Reaction -Light independent reaction takes place in the stroma or the matrix of the chloroplast. During this reaction – a) CO2 is reduced into carbohydrates

Digestion in unicellular organisms Intracellular digestion by intracellular enzymes.

Nutrition in Amoeba In amoeba, The food is engulfed by the process of phagocytosis, and then digested intracellularly by enzymes. Waste is expelled out by the Contractile Vacuole

Contractile Vacuole in amoeba

Digestion in Human beings. Digestive system Alimentary Canal Associated Glands

Structure of the alimentary canal Mouth- Oral cavity or Buccal cavity. Lined by squamous epithelial tissue. Contains tongue, teeth, salivary glands. Tongue – muscular organ used for taste, mixing food and cleaning the oral cavity. Teeth- set of teeth is called Dentition. Human dentition is Heterodont (4 kinds of teeth), Thecodont (Tooth in sockets in gums), Diphydont (Formed twice) Teeth help in mastication of food.

Structure of the alimentary canal Oesophagus Muscular tube connecting oral cavity to the stomach Conveys masticated food (bolus) by waves of relaxation and contraction – This is called Peristalsis.

Structure of the alimentary canal Stomach Main organ of digestion Highly muscular Food is further churned and broken into simpler molecules by the action of enzymes. Inner lining of stomach is called Mucosa. Stomach contains gastric cells that secrete HCL and gastric juice. Entry of food guarded by Cardiac Sphincter and Exit of food regulated by Pyloric sphincter.

Structure of the alimentary canal Small Intestine Divided into three parts : Duodenum, Jejunum and ileum Longest part of the alimentary canal. Site for digestion and absorption of digested food (maximum) Inner lining folded into finger like projections called villi. Receives digestive juices from liver, gall bladder and pancreas.

Structure of the alimentary canal Large intestine Divided into : Caecum, colon rectum and anus. Most of the water is absorbed from the waste. Stores solid waste (faeces) in the rectum temporarily. Exhibit muscular contractions and relaxation called bowel movements – helping in defecation. The exit is guarded by the anal sphincter

Structure of Associated Glands Salivary glands- present in the oral cavity. Three pairs called parotid, sub maxillary and sub-lingual Secretes saliva containing enzyme – salivary amylase and a bactericidal enzyme called lysozyme.

Structure of Associated Glands Liver The largest gland of the body Exocrine in nature Synthesizes and Secreted Bile. Regulates blood sugar by storing excess glucose as glycogen Stores iron Converts excess amino acids into urea Manufactures fibrinogen and heparin( natural anti- coagulant) Detoxifies body metabolites. Stores Vitamin a and D

Structure of Associated Glands Pancreas Lobed mixed gland Secretes pancreatic juice Also secretes hormones Drains its secretions through the common bile duct.

Structure of Associated Glands Gall Bladder Small gland which store bile temporarily

Process of digestion of food Region of Alimentary Canal Digestive glands Digestive Juice Enzyme in the juice Class of food acted upon Substance produced Notes Mouth Salivary Glands SalivaSalivary amylase StarchMaltoseSlightly acidic or neutral; Mucus help form bolus Stomach Gastric glandsGastric juicePepsinProteinsPeptides and peptones 0.5% Hcl provides acidic medium for pepsin RenninMilk proteinClots milk Duodenum PancreasPancreatic Juice TrypsinPeptides and peptones Amino acidsBile emulsifies fats and aids in their absorption into lacteals; Doudenum contents are slightly acidic. AmylaseStarchMaltose LipaseFatsFatty Acids and Glycerol

Process of digestion of food Region of Alimentary Canal Digestive glands Digestive Juice Enzyme in the juice Class of food acted upon Substance produced Notes LiverBileNo enzymes but has sodium salts and bile pigments FatsEmulsified fatsSodium salts provide alkaline medium Ileum Lining of the ileum Succus Entericus ErepsinPeptidesAmino AcidsMost absorption occurs in the ileum LipaseFatsFatty acids and Glycerol MaltaseMaltoseGlucose SucraseSucroseGlucose and Fructose LactaseLactoseGlucose and Galactose