Chapter 2: Nutrition in Animals

• Animal Nutrition: Includes nutrient requirements, mode of intake of food, and its utilization in the body.
• Digestion: The breakdown of complex components of food (like carbohydrates) into simpler, absorbable substances.
• Modes of Feeding: Varies across organisms:
  • Bees and hummingbirds: Sucking nectar.
  • Infants (humans/animals): Feeding on mother's milk.
  • Snakes (e.g., python): Swallowing prey whole.
  • Aquatic animals: Filtering tiny floating food particles.
  • Starfish: Pops out its stomach through its mouth to digest soft animals inside calcium carbonate shells.

A continuous canal beginning at the buccal cavity and ending at the anus, consisting of:

1. Buccal Cavity (Mouth)
2. Foodpipe / Oesophagus
3. Stomach
4. Small Intestine
5. Large Intestine (ending in the rectum)
6. Anus

The Digestive System is formed by the alimentary canal combined with associated secretory glands (salivary glands, liver, and pancreas).

• Ingestion: The process of taking food into the body.
• Teeth Types:
  • Incisors: Biting and cutting.
  • Canines: Piercing and tearing.
  • Premolars & Molars: Chewing and grinding.
• Milk Teeth: First set of teeth growing during infancy, falling off between 6 to 8 years. Replaced by Permanent Teeth.
• Saliva: Secreted by salivary glands; breaks down starch into sugars.
• Tongue: A muscular organ that mixes food with saliva, aids in swallowing, and contains taste buds to detect sweet, salty, sour, and bitter tastes.
• Tooth Decay: Caused by acids released by bacteria breaking down leftover sugars in the mouth.

• Passes swallowed food down to the stomach via wave-like muscular movements (peristalsis).
• A flap-like valve closes the windpipe during swallowing to prevent food from entering the respiratory tract.

• A thick-walled, J-shaped bag that is the widest part of the alimentary canal.
• Secretes:
  • Mucous: Protects the inner stomach lining.
  • Hydrochloric Acid (HCl): Kills harmful bacteria and creates an acidic medium for digestive juices.
  • Digestive Juices: Break down proteins into simpler substances.

• Highly coiled, about 7.5 meters long.
• Receives secretions from:
  • Liver: Largest gland; secretes bile juice (stored in the gall bladder) which digests fats.
  • Pancreas: Secretes pancreatic juice to break down carbohydrates, fats, and proteins.
• Absorption: Digested food passes into blood vessels in the intestinal wall.
• Villi: Finger-like outgrowths that vastly increase the surface area for absorption.
• Assimilation: Transport of absorbed substances to body organs to build complex proteins.

• About 1.5 meters long; wider and shorter than the small intestine.
• Absorbs water and salts from undigested food.
• Egestion: Removal of remaining semi-solid faecal waste through the anus.
• Diarrhoea: Excessive loss of water and salts; treated using Oral Rehydration Solution (ORS).

• Rumen: A specialized part of the stomach where grass-eaters quickly store swallowed grass.
• Cud: Partially digested food in the rumen.
• Rumination: The process where the cud returns to the mouth in small lumps for the animal to chew. These animals are called ruminants.
• Cellulose Digestion: Grass is rich in cellulose (a carbohydrate), digested by specialized bacteria in a large sac-like structure called the Caecum (located between the oesophagus and small intestine; absent in humans).

• Amoeba: A microscopic, single-celled organism found in pond water.
• Pseudopodia: "False feet" or finger-like projections used for movement and capturing food.
• Food Vacuole: Temporary cavity where food is trapped and digested using secreted digestive juices. Undigested residue is expelled outside by the vacuole.