Animal nutrition Biology 2: Form and Function. Types of nutritional system Heterotrophs must obtain...
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Transcript of Animal nutrition Biology 2: Form and Function. Types of nutritional system Heterotrophs must obtain...
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
• 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
Human digestion 1
2/2 Incisors1/1 Cuspids2/2 Premolars3/3 Molars
=32
• 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
Human digestion 2
Chewing and swallowing
QuickTime™ and aCinepak decompressor
are needed to see this picture.
– 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 3
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 enzymesWhere
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 hormonesHormone
Gastrin
Cholecystokinin
Gastrin inhibitory peptide
Secretin
Site
Stomach
Duodenum
Pyloric sphincter
Duodenum
Action
Stimulates HCl/pepsinogen
Stimulates secretion of pancreatic juice
Slows flow of acid chyme from stomach
Stimulates bicarbonates
Variations on a theme...