Transcript presentation

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
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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...