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. Cuticle2. Upper epidermis3. Pallisade parenchyma4. Bundle sheath5. Xylem6. Phloem7. Lower epidermis9. Spongy parenchyma10. Guard cells11. Intercellular spaceThe cells between the upper andlower epidermis are calledmesophyll 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 systemAlimentary 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

Saliva Salivary amylase

Starch Maltose Slightly acidic or neutral; Mucus help form bolus

Stomach Gastric glands Gastric juice Pepsin Proteins Peptides and peptones

0.5% Hcl provides acidic medium for pepsin

Rennin Milk protein Clots milk

Duodenum Pancreas Pancreatic Juice

Trypsin Peptides and peptones

Amino acids Bile emulsifies fats and aids in their absorption into lacteals; Doudenum contents are slightly acidic.

Amylase Starch Maltose

Lipase Fats Fatty 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

Liver Bile No enzymes but has sodium salts and bile pigments

Fats Emulsified fats Sodium salts provide alkaline medium

Ileum Lining of the ileum

Succus Entericus

Erepsin Peptides Amino Acids Most absorption occurs in the ileum

Lipase Fats Fatty acids and Glycerol

Maltase Maltose Glucose

Sucrase Sucrose Glucose and Fructose

Lactase Lactose Glucose and Galactose