LECTURE 8: Nutrition Among Animals (2)

• Salivary amylase breaks down disaccharides, oligosaccharides, and starch in oral cavity.
• Salivary amylase secreted by salivary glands of some herbivorous mollusc, insects and primates.
• Segmentation is mixing movement.
• Peristalsis is forward propulsion.
• 2 types of involuntary movement in the digestive tract:

  • peristalsis
  • segmentation
• Esophagus is a muscular tube that propels food from mouth to stomach.
• Crop serves as temporary storage of ingested food.
• Stomach is for digestion, grinding and storage.
• Insects have stomach w/ tooth like debticles in their muscular proventiculus.
• Insect stomach have one to several chambers.
• Proventriculus of an insect is an organ fir grinding food.
• Herbivores stomach has presence of grinding and crushing devices in addition to microflora that aid in digestion of cellulose.
• Gizzard is found in terrestrial oligochaete worms and in birds.
• Ruminants have several stomach chamber to assist in digestion of cellulose from plants.
• Stomach chambers: rumen, reticulum, omasum, abomasum.
• Rennin is a milk curdling enzyme found in the stomach of ruminants.
• Carnivores have single chambered stomach.
• Carnivores have glands that produces proteolytic enzyme and strong acid for digestion of meat.
• Stomach of omnivores are single chambered.
• cardia - is attached to the esophagus; has cardiac sphincter.
• fundus - is the part protruding towards the diaphragm
• corpus - is the body of the stomach
• pylorus - is the distal end attached to the small intestine; has pyloric sphincter
• inside the stomach are gastric folds called - rugae
• food remains in the stomach for 2-4 hours, afterwhich it turns into chyme, a semi-fluid pulp that will move to the small intestine
• in humans, inner lining of the stomach (mucosa) is renewed every 3 to 5 days
• Hydrochloric acid

  cell responsible: parietal cells

  function: converts inactive pepsinogen to pepsin; maintains acidity of the stomach.
• Pepsin

  cell responsible: chief cells

  function: protein-digesting enzyme; converted from pepsinogen (inactive form or zymogen)
• Mucus

  cell responsible: mucus neck cells

  function: coats the wall of the stomach against HCl and pepsin action
• Intrinsic factor

  cell responsible: parietal cells

  function: binds to Vit. B12 and is essential for its absorption
• Gastrin

  cell responsible: G cells (enteroendocrine cell)

  function: stimulates HCl secretion of parietal cells
• Small Intestine is the site of final digestion and absorption
• In invertebrates the small intestine, structures to increase surface area are generally absent
• typhlosole is an inward infolding of the dorsal intestinal wall found

  in some invertebrates.
• typhlosole increase surface area because body

  space is lacking for coiled intestine
• lampreys and sharks have longitudinal or spiral folds in the small intestine to augment surface area.
• amphibians and reptiles developed elaborate folds as small intestine.
• birds and mammals have minute finger-like projections called villi (singular: villus) on the wall of the small intestine.
• microvilli - are found on the surface of each cell lining the mucosa of each villus; further augment surface area for digestion and absorption.
• Segments of small intestine among vertebrates

  a.duodenum - connected to the stomach.

  b. jejunum - middle segment and usually the longest

  c. ileum - distal segment connected to the cecum