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The great Serengeti migration: A quest for minerals Digestive system • Functions • Organs Organs of alimentary canal Figure 23.2 Small intestine Large intestine Accessory organs Salivary glands, liver, pancreas, gall bladder Figure 23.1 Digestive tracts of various vertebrates Digestive tracts of invertebrates and vertebrates Figure 4.1 The composition of the adult human body Nutrition • • • • Proteins Lipids Carbohydrates Vitamins and minerals Figure 4.2 Amino acid chemistry (Part 1) Figure 4.2 Amino acid chemistry (Part 2) Figure 4.3 Fatty acids and triacylglycerols (Part 1) Figure 4.3 Fatty acids and triacylglycerols (Part 2) Figure 4.4 Carbohydrate chemistry Figure 4.5 Vitamin structures Examples of feeding adaptations Food chains Feeding Figure 4.6 Some species feed by targeting and subduing individual food items (Part 1) Figure 4.7 Specialization of a vertebrate feeding apparatus Dentition Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 1) Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 2) Figure 4.10 The feeding apparatus of a baleen whale Figure 4.12 Reef-building corals of warm waters need light because they are symbiotic with algae (2) Figure 4.9 Short food chains deplete energy less than long food chains do Digestive systems of insects and crustaceans • Crustaceans’ digestive system is separate from the excretory system • Insects– the Malpighian tubules – excretory system is connected at the junction of the midgut and hindgut Figure 4.16 The digestive systems of two types of arthropods: insects and crustaceans Figure 23.1 Stomach (continued) • Contractions of the stomach churn chyme. – Mix chyme with gastric secretions. – Push food into intestine. Insert fig. 18.5 Small Intestine • Each villus is a fold in the mucosa. • Covered with columnar epithelial cells interspersed with goblet cells. • Epithelial cells at the tips of villi are exfoliated and replaced by mitosis in crypt of Lieberkuhn. • Lamina propria contain lymphocytes, capillaries, and central lacteal. Insert fig. 18.12 Histology of the Alimentary Canal Figure 23.6 Sensors of the GI tract– regulatory mechanisms • Mechanoreceptors and chemoreceptors involved • Located in the walls of the tract organs • Sensors respond to – Stretching – Osmolarity – pH – Presence of substrates and end-products Regulatory mechanisms (2) • Receptors initiate reflexes • Activate of inhibit glands that secrete digestive juices • Stimulate smooth muscle of GI tract – Move food along the tract – Mix lumen content Peristalsis and Segmentation Figure 23.3 Adaptation associated with animal’s diet • Microbe-assisted digestion –animals in hydrothermal vents-trophosomes • Dentition/mouth parts • Length of digestive tract – Herbivores – Carnivores – Omnivores – Sharks – Birds Microbe-dependent digestion • Digestion assisted by microbes Animals maintain symbiosis with three categories of microbes • Heterotrophic microbes – Organic compounds of external origin • Autotrophic microbes – Synthesize organic molecules from inorganic precursors • Chemosynthetic • Photosynthetic Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 1) Hydrothermal-vent worms • Symbiotic with chemoautotrophic bacteriatrophosomes • Worms have not mouth, gut, or anus • Food comes from sulfur-oxidizing chemoautotrophic bacteria • Organic molecules from bacteria meets nutritional needs • Vents- source of H2S Hydrothermal-vent worms • Symbiotic with chemoautotrophic bacteriatrophosomes • Worms have not mouth, gut, or anus • Food comes from sulfur-oxidizing chemoautotrophic bacteria • Organic molecules from bacteria meets nutritional needs • Vents- source of H2S Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 2) Comparison of the digestive tracts of carnivores and herbivores • Carnivores- foregut digestion • Herbivores – Hindgut – Foregut Figure 4.14 The digestive tract of ruminants (Part 1) Stomach of ruminants • Several chambers • Rumen – first chamber/fermentation occurs • Regurgitate fermenting materials from the rumen into mouth • Further grinding and reswallow • From rumen reticulum omasum abomasum (true stomach) Functions of microbes in ruminants • Synthesize B vitamins, essential amino acids • Fermentative breakdown of compounds that animals cannot digest– cellulose • Recycle waste nitrogen from animal metabolism • Make ammonia so other microbes can use it as nitrogen source Figure 4.14 The digestive tract of ruminants (Part 2) Figure 4.15 The digestive tracts of two hindgut fermenters Hind and midgut fermenters • Enlarged cecum/colon – Rabbits, horses, zebras, rhinos, apes, elephants • Break down of cellulose and carbohydrates • Forms short-chain fatty acid • B vitamins- not utilized, lost in feces • Coprophagy– rabbits eat special soft feces A comparison of the digestive tracts of a carnivore (coyote) and a herbivore (koala) Digestion and absorption • • • • Digestive enzymes in 3 spatial contexts Intraluminal enzymes Membrane-associated enzymes Intracellular enzymes Intracellular and extracellular digestion • Intraluminal and membrane-associated enzymes are responsible for extracellular digestion • Intracellular enzymes are responsible for intracellular digestion • Advantages and disadvantages of intraand extracellular digestions? Figure 4.17 The stomach of a clam (Part 2) Carbohydrate digestion Organ Substrate Enzyme End product(s) Oral cavity Starch Sal1vary amylase Maltose Stomach Amylase denatured Lumen of intestine Undigested polysaccharides Pancreatic amylase Maltose Brush border of small intestine Disaacharides: maltose Sucrose Lactose Maltase Sucrase Lactase Monosaccharides Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 2) Protein digestion Organ Substrate Enzyme End product(s) Stomach Polypeptides Pepsinogen +HCl = pepsin Smaller peptides Lumen of intestine Polypeptides Trypsinogen, chymotrypsinogen (inactive enzymes released from the pancreas, transported to duodenum via pancreatic duct. These enzymes are activated by enterokinase from small intestine to trypsin and chymotrypsin Smaller peptides Smaller polypeptides Aminopeptidase, carboxypeptidase Amino acids Dipeptides Dipeptidase Amino acids Brush border of small intestine Figure 4.18 The digestion of a short protein by three pancreatic peptidases Fat digestion Organ Substrate Enzyme Oral cavity No enzyme to digest fat Stomach No enzyme to digest fat Lumen of intestine Brush border of small intestine End product(s) Fat globules Bile salt from gallbladder Emulsified fat Fat globules lipase Glycerol, fatty acids Chemical Digestion: Fats Figure 23.35 Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 1) Chemical Digestion: Carbohydrates • Carbohydrates absorption: via cotransport with Na+, and facilitated diffusion – Enter the capillary bed in the villi – Transported to the liver via the hepatic portal vein Chemical Digestion: Proteins • Absorption: similar to carbohydrates • Enzymes used: pepsin in the stomach • Enzymes acting in the small intestine Chemical Digestion: Fats • Absorption: Diffusion into intestinal cells where they: – Combine with proteins and extrude chylomicrons – Enter lacteals and are transported to systemic circulation via lymph Coordination of digestion– neural and endocrine control • Controls of digestive activity • Extrinsic – Central nervous system and autonomic nervous system • Intrinsic – Hormone-producing cells in stomach and small intestine – Distributed via blood and interstitial fluid to target cells Endocrine control • • • • • Endocrine control Gastrin Secretin CCK GIP – – – – Where? When? Why? How? Figure 4.20 GI function after a meal is coordinated in part by hormones secreted by cells in the gut