chapter 34

• Other multicellular animals digest their food extracellularly, within a digestive cavity and single celled organism and sponges digest their food intracellularly
• Cnidarians and flatworms have a gastrovascular cavity with only one opening, and no specialized regions
• Specialization occurs when the digestive tract has a separate mouth and anus

  
• Nematodes have the most primitive digestive tract, a tubular gut lined by an epithelial membrane

  
• More complex animals have a digestive tract specialized in different regions
• Digestive process


  1. Ingestion

  2. Physical fragmentation(mastication)

  3. Chemical digestion(stomach)

  4. Absorption(small intestines and large intestines)

  5. Excretion

  
• Vertebrate digestive systems consist of a tubular gastrointestinal tract and accessory organs

  
• Components of the vertebrate digestive system

  • Mouth and pharynx( entry of the food and mastication)
  • Esophagus( connect pharynx and stomach together)
  • Stomach( digestion)
  • Small intestine(absorption)
  • Large intestine(absorption water and minerals)
  • Cloaca or rectum(storages wast)
  • Anus

  
• Accessory organs of the vertebrate digestive system

  • Liver( produce bile)
  • Gallbladder( store and concentrate bile)
  • Pancreas( produces pancreatic juice and digestive enzyme and bicarbonate buffer)

  
• Birds lack teeth and break up food in a two-chambered stomach, with a gizzard that uses ingested pebbles to pulverize food
• Patterns of dentition depend on diet

  • Herbivores - large flat teeth for grinding
  • Carnivores - pointed teeth without flat grinding surfaces
  • Omnivores - carnivore-like teeth in front, herbivore-like teeth in back
• Functions of the mouth

  1. Mixing food with saliva

  2. Moistening and lubricating food

  3. Initiating breakdown of starch with salivary amylase (Tasting, smelling, and thinking about food stimulate increased salivation)
• The esophagus is a muscular tube that actively moves a bolus through peristalsis
• The stomach has a convoluted surface that allows expansion, and contains three layers of smooth muscle for mixing food with gastric juice(produced by the lining of stomach)
• Types of secretory cells in the stomach


  • Mucus-secreting cells
  • Parietal cells (secrete HCl)
  • Chief cells (secrete pepsinogen)
• Low pH in the stomach helps denature food proteins, activate pepsin, and keep it functioning

  
• The mixture of partially digested food and gastric juice is called chyme and chyme leaves the stomach and enters the small intestines it get absorbed of carbohydrates and lipid, protein.
• The small intestine is about 4.5 m long with a small diameter

  
• The small intestine consists of the duodenum, jejunum, and ileum

  
• The small intestine receives chyme from the stomach, digestive enzymes and bicarbonate( denatures the chyme ) from the pancreas, and bile from the liver and gallbladder- mixes in the duodenum

  
• The epithelial wall of the small intestine is covered with villi, which are covered by microvilli( create a brush border that absorbs) to greatly increase the surface area

  
• Functions of the pancreas

  • Secretes pancreatic fluid into the duodenum
  • Enzymes (trypsin, chymotrypsin, pancreatic amylase, lipase)
  • Bicarbonate to neutralize acidic chyme
• Functions of the liver-larges organ

  • Secretes bile
  • Chemically modifies substances absorbed from the digestive tract
  • Metabolizes ingested alcohol and other drugs
  • Removes toxins, pesticides, and carcinogens
  • Regulates levels of steroid hormones
  • Produces most proteins found in plasma

  
• Absorption

  1. Amino acids and monosaccharides transported through epithelial cells to blood then the blood carries this product to hepatic portal vein absorbed

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

  3. Almost all fluid reabsorbed if wont secret feces

  
• the small intestines empties directly into the large intestine which has two vestigial structures, cecum and appendix. No digestion occurs in the large intestine, which functions to reabsorb water, electrolytes, and vitamin K, and prepare waste for expulsion

  
• Many bacteria live and reproduce within the large intestine
• Gastrointestinal activities are coordinated by the nervous( stimulate salivary and excretion) and endocrine systems
• Proteins in the stomach stimulate the release of gastrin, which triggers the secretion of HCl and pepsinogen
• Enterogastrones( regulate the passage of ingested material) or duodenal hormones


  • Cholecystokinin (CCK)
  • Secretin
  • Gastric inhibitory peptide (GIP)
• Enterogastrones inhibit stomach contractions and prevent additional chyme from entering the duodenum
• CCK also stimulates gallbladder contraction and pancreatic enzyme secretion, while secretin stimulates pancreatic bicarbonate secretion
• One of the major physiological challenges facing multicellular animals is obtaining sufficient oxygen and disposing of excess carbon dioxide
• In vertebrates, gases diffuse(passive) into the aqueous layer covering the epithelial cells that line the respiratory organs

  
• Evolutionary changes have occurred to optimize the rate of gas diffusion, by increasing surface area, decreasing distance, and increasing pressure difference
• Gas exchange systems in different animals

  • Amphibians - respire across their skin
  • Echinoderms - have protruding papulae
  • Insects - have an extensive tracheal system
  • Fish - use gills
  • Mammals - have a large network of alveoli
• The gills of bony fishes are located between the oral (buccal or mouth) cavity and the opercular cavities, which function as pumps that alternately expand to move water over the gills. some bony fishes have immobile opercular swim with mouth open to constantly force water over gills (ram ventilation) and have flexible gills.
• Each gill arch has two rows of gill filaments, and each gill filament consists of thin membranous lamellae
• Gill function in bony fish

  Water moves into the mouth, over the gills, and out of the fish through the open operculum or gill cover
• Bony fish with immobile opercula


  • Swim constantly to force water over gills (ram ventilation)
• Bony fish with flexible gill covers


  • Can switch between ram ventilation and pumping action