Animal Nutrition System

• Animal Nutrition is about energy and materials for growth and repair
• Nutrients


  • simple inorganic compounds
  • more complex organic compounds
  • can be synthesized within the organism
  • must be taken in from the environment
• Nutrients


  • proteins
  • carbohydrates
  • fats
  • vitamins
  • minerals
  • water
  • fiber (indigestible materials)
• Carbohydrates


  Supply energy for body functions
• Fats


  Supply energy; storage form of fuel in the body
• Proteins


  Growth and repair of body tissue; can supply energy
• Water


  Solvent in which chemical reactions take place; transport of materials
• Minerals


  Body building; regulation of metabolism
• Vitamins


  Coenzymes in metabolic reactions
• Energy content of some common food

  • Apple (70 kcal)
  • Banana (85 kcal)
  • White bread (70 kcal)
  • Egg (80 kcal)
  • Milk (150 kcal)
  • Potato (105 kcal)
  • Cheese (35 kcal)
• Calorie


  Amount of heat needed to raise the temperature of 1 g of water by 1°C
• Energy content of a food

  The amount of energy given off by the complete breakdown of that sample
• Single-celled organisms digest their food intracellularly
• Other animals digest their food extracellularly, within a digestive cavity
• In coelenterates and flatworms, the gastrovascular cavity has only one opening that serves as both mouth and anus
• The most primitive digestive tract is seen in nematodes; a tubular gut lined by an epithelial membrane
• Earthworms have a digestive tract specialized in different regions for the ingestion, storage, fragmentation, digestion, and absorption of food
• All higher animal groups, including all vertebrates, show similar specializations in their digestive system
• Parts of the vertebrate gastrointestinal tract

  • Mouth and pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Accessory digestive organs


  • Liver
  • Gallbladder
  • Pancreas
• The teeth


  • Chewing (mastication) breaks up food into small particles and mixes it with fluid secretions
  • Carnivorous mammals have pointed teeth that lack flat grinding surfaces, adapted for cutting and shearing
  • Grass-eating herbivores have large, flat teeth with complex ridges well-suited to grinding
• Human teeth


  • Four front teeth in the upper and lower jaws are sharp incisors for biting
  • On each side of the incisors are sharp, pointed "canine" teeth for tearing food
  • Behind the canines are two premolars and three molars, all with flattened, ridged surfaces for grinding and crushing food
• The mouth


  • The tongue mixes food with saliva, which moistens and lubricates the food, and initiates the breakdown of polysaccharides
  • When food is ready to be swallowed, the tongue moves it to the back of the mouth
• The esophagus and stomach

  • The esophagus is a muscular tube that delivers food to the stomach, where some preliminary digestion occurs
  • The stomach contains an extra layer of smooth muscle for churning food and mixing it with gastric juice, an acidic secretion
  • Digestion of proteins (partially), no significant digestion of carbohydrates or fats
• The small intestine


  • The first 25 cm is the duodenum, which receives acidic chyme from the stomach, digestive enzymes and bicarbonate from the pancreas, and bile from the liver and gallbladder
  • The pancreatic juice enzymes digest larger food molecules into smaller fragments, primarily in the duodenum and jejunum
  • The epithelial wall of the small intestine is covered with tiny, fingerlike projections called villi, each with a brush border of microvilli that complete the digestive process
• The brush border enzymes hydrolyze the disaccharides
• The products of digestion are then transported across the membrane and into the blood capillaries within the villi
• Digestion in the small intestine


  1. Digestive enzymes and bicarbonate from the pancreas, and bile from the liver and gallbladder are released

  2. Pancreatic juice enzymes digest larger food molecules into smaller fragments

  3. This occurs primarily in the duodenum and jejunum
• Small intestine


  • Epithelial wall is covered with tiny, fingerlike projections called villi
  • Each epithelial cell lining the villi has many foldings of the plasma membrane that form cytoplasmic extensions called microvilli (brush border)
• Digestion in the small intestine

  1. Brush border enzymes hydrolyze the disaccharides (e.g. lactose intolerance)

  2. Brush border enzymes complete the digestive process started by pancreatic enzymes
• Absorption in the small intestine

  1. Amino acids and monosaccharides are transported across the brush border into the epithelial cells

  2. Fats (triglycerides) are hydrolyzed into fatty acids and monoglycerides, which are absorbed into the epithelial cells and reassembled into triglycerides

  3. Triglycerides then combine with proteins to form chylomicrons, which are absorbed into lymphatic capillaries instead of the hepatic portal circulation
• Approximately 9 L/day of fluid enters the small intestine, with about 8.5 L absorbed and only 350 mL entering the large intestine. Only about 50 gr of solid and 100 mL of liquid leave the body.
• Digestion in the large intestine

  1. No digestion, about 4% of fluid absorption

  2. Na, Vit.K, and some products of bacterial metabolism are absorbed

  3. Primary function is to concentrate waste material (bacterial fragments and cellulose)
• Ruminants (e.g. cows)


  • Have stomachs with multiple chambers where bacteria aid in the digestion of cellulose
• Other herbivores (e.g. rabbits, horses)

  • Digest cellulose (with the aid of bacteria) in a blind pouch called the cecum located at the beginning of the large intestine
• Digestion in ruminants


  1. The rumen is a fermentation vat where bacteria and protozoa convert cellulose and other molecules into simpler compounds

  2. The cud is then swallowed and enters the reticulum, from which it passes to the omasum and then the abomasum, where it is finally mixed with gastric juice
• This process leads to a far more efficient digestion of cellulose in ruminants than in mammals that lack a rumen, such as horses.
• Pancreas


  • Secretes pancreatic fluid into the duodenum, containing enzymes like trypsin, chymotrypsin, pancreatic amylase, and lipase, as well as bicarbonate to neutralize HCl
  • Also secretes hormones like insulin and glucagon into the blood to control nutrient levels
• Liver and gallbladder


  • The liver's main exocrine secretion is bile, a fluid mixture of bile pigments and bile salts that is delivered into the duodenum during digestion
  • Bile salts disperse large drops of fat into smaller droplets, increasing the surface area for lipase to act
• Regulation of digestion


  1. The nervous system stimulates salivary and gastric secretions in response to the sight and smell of food

  2. Food in the stomach stimulates the secretion of gastrin, which then stimulates the secretion of HCl and pepsinogen

  3. HCl lowers the pH of the gastric juice, which inhibits further secretion of gastrin (negative feedback)

  4. The passage of chyme from the stomach into the duodenum inhibits the contractions of the stomach, mediated by a neural reflex and the hormone enterogastrone

  5. The duodenum secretes the hormones cholecystokinin (CCK) and secretin, which stimulate the gallbladder to release bile and the pancreas to release bicarbonate, respectively