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

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• 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

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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...