animal nutritions

• Nutrient


  Any substance consumed by an animal that is needed for survival, growth, development, tissue repair, or reproduction
• Purposes of ingested organic macromolecules

  • To provide energy
  • To make new molecules (biosynthesis)
• All animals require the same fundamental organic macromolecules
• How animals eat


  1. Ingestion

  2. Digestion (chemical and mechanical)

  3. Absorption

  4. Elimination
• Types of digestive systems

  • Single-celled organisms and sponges digest their food intracellularly
  • Other multicellular animals digest their food extracellularly within a digestive cavity

  
• Digestive systems with a gastrovascular cavity


  • Cnidarians and flatworms

  
• Alimentary canal (digestive tract)

  Tube from mouth to anus

  
• Alimentary canal process


  1. Ingestion (food into mouth)

  2. Digestion (mechanical and chemical)

  3. Absorption (nutrients and water)

  4. Elimination (feces)

  
• Mouth


  • Saliva begins initial processing of food
  • Moisten and lubricate food to facilitate swallowing
  • Dissolve food particles to facilitate taste
  • Kill ingested bacteria
  • Initiate digestion of polysaccharides with amylase
• Pharynx and esophagus


  • Pathway to stomach only
  • Do not contribute to digestion or absorption
  • Swallowing begins in esophagus as voluntary action
  • Action continues by involuntary peristalsis

  
• Crop


  • Storage organ
  • Dilation of lower esophagus
  • Little or no digestion
  • Birds that eat primarily grains and seeds have larger crops than birds that eat insects and worms
• Birds' digestive system


  • Mouth has no teeth and cannot grind food
  • Proventriculus secretes acid and enzymes
  • Gizzard contains tiny pebbles that help pulverize food
  • Intestine digests and absorbs food
  • Esophagus moves food to the crop by peristalsis
  • Crop stores and softens food
  • Cloaca receives undigested material for excretion

  
• Vertebrate digestive tract layers

  • Mucosa (innermost epithelium lining the lumen)
  • Submucosa (connective tissue)
  • Muscularis (circular and longitudinal smooth muscle layers)
  • Serosa (outermost epithelium covering external surface)

  
• Stomach


  • Saclike portion of tract
  • Convoluted surface allows expansion
  • Contains 3rd layer of smooth muscles for mixing food with gastric juice
  • 3 kinds of secretory cells: mucus-secreting, parietal (secrete HCl and intrinsic factor), and chief (secrete pepsinogen)
• Herbivore stomachs


  • Herbivores must digest cellulose but lack cellulase
  • Rely on microbes to digest cellulose into monosaccharides
  • Simple stomach uses cecum at connection between small and large intestine
  • Complex stomach has several chambers (e.g. ruminant)
• Small intestine


  • Nearly all digestion of food, and absorption of food and water
  • Hydrolytic enzymes found on luminal surface or secreted by pancreas into lumen
  • Specialized for increased surface area (600x via folding, villi, microvilli)
  • Products of digestion absorbed across epithelial cells and enter blood (or lymph vessels)
  • Vitamins, mineral and water also absorbed

  
• Accessory organs associated with small intestine

  • Pancreas
  • Liver
  • Gallbladder
• Absorption in small intestine

  1. Protein, amino acids and carbohydrates transported through epithelial cells to blood

  2. Fatty acids and monoglycerides diffuse into epithelial cells, reassembled into triglycerides and chylomicrons, enter lymphatic system then circulatory system

  3. Almost all fluid reabsorbed
• Large intestine (colon)


  • Much shorter than small intestine, but has larger diameter
  • Small intestine empties directly into the large intestine at a junction where cecum and appendix remain
  • No digestion occurs
  • Function to reabsorb water, remaining electrolytes, and vitamin K
  • Prepare waste for expulsion

  
• Regulation of digestion


  • Nervous system affects control of muscular and glandular activity
  • Hormones secreted mainly by cells in stomach and small intestine, target cells in pancreas and gallbladder
• Proteins in stomach


  Stimulate the release of gastrin, which triggers the secretion of HCl and pepsinogen from the gastric glands
• Enterogastrones or duodenal hormones

  Inhibit stomach contractions and prevent additional chyme from entering duodenum
• Enterogastrone hormones


  • Cholecystokinin (CCK)
  • Secretin
  • Gastric inhibitory peptide (GIP)
• Enterogastrone hormones


  All inhibit gastric motility and secretions

  CCK also stimulates gallbladder contraction and pancreatic enzyme secretion

  Secretin also stimulates the secretion of pancreatic bicarbonate