Digestive Systems Functions of digestive system: Break down food into organic molecules Physically (teeth, gizzard) Chemically (by hydrolysis in stomach, intestines) polysaccharides HO H H2O fats proteins H HO Absorb subunits of organic molecules Monosaccharides, amino acids, fatty acids
Digestive Systems Types of digestive systems: None (intracellular digestion) Phylum Porifera (sponges)
Digestive Systems Types of digestive systems: Open ‘sac’ (gastrovascular cavity) Phylum Cnidaria (jellyfish, sea anemone, Hydra) Enzymes secreted from cells lining cavity Two-way system (food and waste enter and leave mouth) No specialization
Digestive Systems Types of digestive systems: One-way digestive systems Phylum Annelida (earthworm) Phylum Arthropoda (grasshopper, crayfish) Phylum Chordata (frog) one-way system (food enters mouth, leaves anus) Specialization of digestive tasks Tube-within-tube body plan
Digestive Systems Specialization in vertebrate digestive systems: Gastrointestinal tract Mouth and structures to grind or break apart food Mammals: teeth Sharp, pointed canines to tear flesh Large, flat teeth to grind plants Birds: gizzard (swallow grit) Saliva released in mouth -- moisten food and releases salivary amylase Food swallowed and passes through pharynx to esophagus
Digestive Systems Specialization in vertebrate digestive systems: Gastrointestinal tract Esophagus Muscular tube that connects pharynx to stomach Successive waves of contractions (peristalsis)
Digestive Systems Specialization in vertebrate digestive systems: Gastrointestinal tract Stomach Saclike portion of digestive tract Inner surface convoluted (able to expand > 50x empty size) Gastric glands release HCl (stomach pH=2) Helps break down proteins Kills most bacteria Gastric glands also release pepsinogen (activated into protein-digesting enzyme called pepsin) Partially digested food and gastric ‘juice’ passes into small intestine
Digestive Systems Specialization in vertebrate digestive systems: Gastrointestinal tract Small Intestine Tube for chemical digestion and absorption of organic molecules Small intestine receives: Chyme from stomach Digestive enzymes and bicarbonate from pancreas Bile from liver Inner surface of small intestine lined with fingerlike villi (and microvilli on cells) Increases surface area for digestion (by enzymes in microvilli) and absorption (by epithelial cells)
Digestive Systems Specialization in vertebrate digestive systems: Gastrointestinal tract Large Intestine (colon) Large diameter but short length Some absorption of ions and vitamins, but main function is to concentrate digestive wastes (absorb water) Many bacteria live within large intestine -- bacteria fermentation produces ‘gas’ Feces produced in large intestine passed to rectum and exit body through anus
Digestive Systems Specialization in vertebrate digestive systems: Accessory organs Pancreas Liver Gall bladder