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Animal nutrition Biology 2: Form and Function Types of nutritional system • Heterotrophs must obtain energy sources externally – Fungi digest via external digestion using mycelial mat of hyphae – Animals tend towards internalized ingestion • Herbivory, Carnivory, Omnivory Animal nutritional systems • Invertebrate: – Porifera use spongocoel – Cnidaria, Platyhelminthes use gastrovascular cavity (GVC) or are parasitic – Nematoda and upwards use complete gastrointestinal tract (GI) Nutrition in Sponges • Flagella from Choanocytes waft current through pores of sponge wall into spongocoel and out via osculum • Membranous collar of choanocytes captures food particles (unicellular algae) • Particles brought into choanocyte by endophagocytosis, transferred to amoebocytes by exophagocytosis • Amoebocytes digest and transport food to rest of sponge Nutrition in GVC animals • One entry/exit to chamber • Convoluted edge/lobes to maximize surface area • Specialized cells in gastrodermis secrete digestive enzymes into sealed GVC • Cilia or movement of animal stirs mixture of food particles with enzymes • Digested products absorbed by gastrodermis through diffusion Animals with complete GIs • Tubular gut allows for specialization and storage • Digestive systems usually have 4 stages: – Ingestion – Digestion • Mechanical (grinding) • Chemical (hydrolysis) – Absorption – Egestion The vertebrate digestive system • Mouth and pharynx leading to esophagous • Some digestion in stomach, which can be multiple chambered (ruminants) • Digestion continues in small intestine, which is also where absorption occurs (some guts include a cecum) • Water and minerals absorbed by large intestine • Undigested remains move to rectum and egested through anus Human digestion 1 • Ingestion into buccal cavity • Mechanical digestion through mastication, lubricated with mucus • Chemical digestion intiated in salivary glands via salivary amylaze (acts on carbohydrates) • Food bolus swallowed and passed onto stomach via peristalsis • Epiglottis prevents bolus going into trachea 2/2 Incisors 1/1 Cuspids 2/2 Premolars 3/3 Molars =32 Human digestion 2 • Food bolus swallowed and passed onto stomach via peristalsis • Epiglottis prevents bolus going into trachea • Swallowing against back of throat stimulates neurons to cause swallowing response Chewing and swallowing QuickTime™ and a Cinepak decompressor are needed to see this picture. Human digestion 3 – Food passage into stomach controlled by cardiac sphincter – Stomach convoluted and lined with pits; in humans, can expand from 50 ml to 2–4 L – Secretory cells line pits of stomach • Parietal cells (HCl) • Chief cells (Pepsinogen) – Pepsinogen (a proenzyme) converts to Pepsin in the presence of HCl (mixing aided by churning of stomach). Mixture called Acid Chyme – Pepsin and acidic action of HCl hydrolyse peptide bonds Human digestion 4 – Acid chyme released into lower intestine via pyloric sphincter into lower (small) intestine • Duodenum, jejenum, ileum – Duodenum is a u-shape, into which flows pancreatic duct, from pancreas – Pancreas secretes further enzymes, including pancreatic amylaze, peptidases = pancreatic juice – Pancreatic juice combined with bicarbonates and bile from gallbladder that neutralizes acidic substrates Human digestion 5 – Small intestine is lined with villi (singular = villus), which are further lined by microvilli – Villi are finger-like projections that form a brush border – Each villus is supplied by capillaries (cardiovascular) and a lacteal (lymphatic) Human digestion 6 – Brush-border is the site of final digestion, and absorption of monomer products of digestion • Non-lipids -> capillaries -> hepatic portal vein • Lipids -> lacteal – Large intestine absorbs water and minerals, working in conjunction with E. coli Summary of digestive enzymes Where Salivary glands Stomach Pancreas Brush-border What Amylase Pepsin Lipase Trypsin Chymotrypsin Nucleotidase Peptidases Nucleases Lactase Maltase Sucrase Result Polysacchs. Proteins Lipids Proteins Proteins DNA/RNA Protein Dinucleotides Lactose Maltose Sucrose Summary of digestive hormones Hormone Gastrin Site Stomach Cholecystokinin Duodenum Gastrin inhibitory peptide Pyloric sphincter Secretin Duodenum Action Stimulates HCl/pepsinogen Stimulates secretion of pancreatic juice Slows flow of acid chyme from stomach Stimulates bicarbonates Variations on a theme...