feeding and digestion Flashcards
Heterotrophy
The ingestion of food in order to satisfy energy requirements
Strategies for the ingestion of small particles
- pseudopodial/ciliated oral groove (protozoa)
- ciliate (bivalve molluscs)
- tentacular (cnidarians, annelids, bryozoa)
- mucoid (tunicates)
- setous (crustaceans, baleen whales, flamingos etc)
- deposit (annelids)
Setae
- extensions of exoskeleton, endoskeleton or dermally derived extensions involved in feeding
- crustaceans, baleen whales, flamingos etc
Strategies for the ingestion of large particles
- scraping/boring (gastropods)
- seizure of prey (carnivores)
- traps (spider webs, pits etc)
- fluid feeding
- direct absorption
Fluid feeding
- sucking without penetration (honeybees, hummingbirds, butterflies etc)
- sucking with penetration (leeches, ticks, aphids etc)
Direct absorption
- across body surface (endoparasites, aquatic invertebrates)
- from symbiotic partners (corals, ruminants)
Phagocytosis
- simplest form of heterotrophy, size restricted organisms
- protozoa, sponges
- create pseudopodia that surround food particle and engulf it
- create phagosome, food vacuole
- lysosome (digestive vacuole containing enzymes) fuse with phagosome
- digestion occurs inside phagolysosome, waste excreted via anal pore
- some protozoa have oral groove lined with cilia that beat, creating a current into their cytopharynx where phagosomes are formed
Ciliate feeding
- common in marine vertebrates and marine invertebrate larvae (suspension feeders)
- cilia in larvae for feeding and swimming, channels water down to mouth
- bivalves have a pair of gills covered in cilia
Ciliate feeding in bivalves
- mussels, oysters, clams etc
- pair of gills in mantle cavity covered in cilia
- 3 types of cilia, lateral, frontal and laterofrontal
- all beat, creating inhalant and exhalant current (unidirectional flow of water)
- particles trapped on cilia on inhalant current
- particles passed down gill to food grove at bottom
- trapped by a string of mucous that passes directly down into the stomach through a winding motion
Feeding through mucous nets
- tunicates (Cordate, non-vertebrate with a notochord), majority benthic
- large central atria (pharynx) lined with endostyle layer with stigmata (holes)
- inhalant current, water through incurrent siphon, though stigmata into pharynx
- particles trapped by iodine rich (homologous to vertebrate thyroid gland) mucous net
- very fine net, capable of trapping bacteria
- net periodically passed down into stomach, particles digested in stomach and intestine
- water flows out on exhalant through excurrent siphon
- anus next to excurrent siphon, faeces also carried out by exhalant current
Setae in crustaceans
- bristles, extension of exoskeleton, can’t use cilia for feeding because of exoskeleton
- larger than cilia but very efficient
- trap particles suspended in the water column and pass to the mouth
- krill, very fine setae project from walking legs at front, in winter they use them to brush algae off underside of ice (also shrink as there is little food)
- copepods have maxillipeds, feeding appendages with setae that beat
- copepods and krill are important zooplankton (2nd trophic level in marine food chain)
Setae, gill rakers
- setae derived from endoskeleton in filter feeding fish
- on first gill arches anterior to gill filaments
- swim with mouth open
- water passes along the side of gill rakers, catches suspended particles
- particles removed and periodically swallowed and digested
Baleen whales (Mysticeti), setae
- dermally derived baleen plates primarily composed of keratin
- many rows of frayed fibres along sides of top jaw
- whale opens mouth, water comes in through front
- whale closes mouth and reduces volume, forcing water laterally through baleen plates
- small fish and krill trapped by plates, tongue used to wipe plates clean, swallowed and digested
Deposit feeding
- ingestion of organic matter from the soil or sea floor
- gain nutrition from microorganisms stuck to particles or lumps of organic matter
- cheap feeding strategy, not much movement required
- subsurface or surface feeders
- non-selective or selective feeders
Deposit feeders, lugworm
-Arenicola marina
- marine annelid found on sandy beaches
- eats microbes that grow on sand particles
- selective subsurface feeder, uses proboscis to select particles of a specific size, smaller particles increase surface area microbes can grow on, only live on beaches with fine sand
- adult can grow up to 1ft, can burrow 20cm
- Sand cast on surface = faeces at top of tail shaft, dimple next to faeces = top of feeding funnel
- peristaltic contractions along body draws in water down tail shaft, along gills and out feeding funnel
- liquefies sand at feeding shaft, making it continuously fall down towards mouth
- well at top of feeding funnel creates turbulence in water flowing over it, organic matter suspended in water collects in funnel, provides carbon for the microbes it feeds on
- constantly feeding, limited by bacterial productivity
- bioturbation, turns over sediment
- lives in anoxic sediment (black sand), aerates surrounding sediment through irrigation
- critical to the ecology of sandy beaches
bioturbation
- turning over/reworking of the top 5-10cm sediment
- from feeding, burrow construction and maintenance, respiration, burrowing etc
- increases organic matter (nitrogen), facilitates species interaction (increases diversity), increases water content (easier to burrow), alterations in sediment biogeochemistry (O2 delivered alters chemical reactions) etc
rasping radula
- molluscs
- toothed tongue that scrapes/rasps surface of food
- radula along with cellulases critical to mollusc success
- teeth sit on cartilagenous rod
- tongue highly muscularised, protractor and retractor muscles
- new teeth continually synthesised at back and slowly passed to front at front teeth worn down
- limpet teeth though to be hardest know biological material (rasp rock)
examples of modified radula
- modified into harpoon or drill, specialised for carnivory
- oyster drills, drills into oyster, secretes digestive enzymes and eats oyster
- cone snail, harpoon with neurotoxin venom, predate on fish
carnivory in arthropods, crustacea
- modified chelate legs (pincers)
- chelae consist of last segment of leg (dorsal dactylus) with second last segment extending under (ventral propus)
- handedness, one crushing pincer (larger), one cutting pincer (smaller)
- location of crushing pincer depends on prey mollusc shell spiral direction, specialised to make it easier to break
- consume molluscs etc
carnivory in arthropods, chelicerata
- chelate pedipalps
- often used for mating in male spiders
traps
- capture passing prey
- Turbellaria, slime containing neurotoxins (flatworm)
- chelicerata, silk
- pits, Myrmeleiontidae
traps, pits
- Myrmeleiontidae (antlions)
- create pit in sand
- sit and wait for prey in burrow at bottom of pit
- steeply sloped pit (critical angle of repose), any disturbance of sand by prey will cause sediment to destabilise and sides to collapse, causing prey to fall into pit
vertebrates
- evolutionary adaptations of vertebrate digestive systems correlate with diet
- craniodental modifications (skull and jaw)
- stomach and intestinal adaptations
- mutualistic adaptations
hagfish
- deepsea marine scavengers, feeding opportunities rare so conserve energy and eat almost anything
- acute chemosensory organs
- agnathe (jawless), 2 plates in mouth with sharp tooth-like structures
- plates come forward when mouth opens, interdigitates when mouth closes (cutting motion)
- tentacles surround mouth for detection of prey
- can uptake dissolved organic matter directly across integument
- when it finds intact prey it embeds teeth in animal, knots tail and passes know forward to head to use as a lever to rip flesh (expensive strategy, only uses to make first incision in carcass)
Chondrichthyes/elasmobranchs, filter feeding
- diverse strategies, filter feeding to carnivory
- filter feeding using gill rakers
Chondrichthyes/elasmobranchs, carnivory
- cranial kinesis, motility within the head skeleton enables the consumption of large prey items
- hyostylic jaw suspension allows the jaw to be placed into multiple positions and
protrusion of the upper jaw - palatoquadrate = upper jaw
- mandible = lower jaw
- teeth on palatoquadrate large, serrated and recurved
- teeth sunk into prey by protruding upper jaw
- lateral undulations of body moves head and rips flesh
- very sensitive chemoreceptors and electroreceptors (ampullae
of Lorenzini), detect very weak electrical signals from prey
actinopterygii, teleosts
- evolution of specialisation of the jaw directly related to diet
- protrusible pharyngeal jaws important in this group, second set of jaws further back that can move forward
- diversity of feeding mechanisms from simple prey grabbing to specialised suction devices e.g. John Dory (evolved 3 or 4 times in different teleost clades)
feeding via symbiosis
- autotrophic: chemosynthetic e.g. Riftia (hydrothermal vents, thioautotrophic bacteria, feeds on sulphides), phototrophs e.g. coral and zooxanthellae
- heterotrophic e.g. ruminants
photoautotrophic symbionts
- very common to marine invertebrates
- coral (Cnidaria) and zooxanthellae (dinoflgellate, Symbiodinium microadriaticum, various different strains)
- live in a nutrient poor environment so coral relies on nutrition from symbiont
- can lose symbiont temporarily (coral bleaching, alga provides pigment), coral ingests or expels them in stressful conditions
- coral recycles CO2 back to zooanthellae
- different combinations of strains in different coral and different strains in different parts of coral
- anemones and zoochorellae (green alga, Zoochorella parasitica), more separate than corals
heterotrophic symbionts
- vertebrates cannot digest cellulose, so many rely on fermentation by microbes (protists, fungi and bacteria)
- 3 main groups
- foregut (fermentation chamber part of stomach), ruminants including cattle, sheep, giraffes, non-ruminants including kangaroos, sloths etc
- mid gut (fermentation chamber part of small intestine), very rare, found in herbiverous and omniverous fish like tilapia, carp etc
- hind gut (fermentation chamber part of large intestine), rabbits, horses, elephants, ostriches etc
herbivore foregut fermenters
- multi-chambered stomach
- rumen (anoxic), reticulum and omasum for storage and microbial processing (non-acidic)
- abomasum for digestion (acidic)
- very slow fermentation but effective, allows for digestion of moderately fibrous food
- less craniodental specialisations as chewing is less important
foregut fermenters, rumen
- anoxic and non-acidic fluid environment
- protists, bacteria and fungi break down cellulose into short chain fatty acids (SCFAs), acetic, propionic, butyeric
- vitamin B and essential amino acids also synthesised
- urea from blood transferred into rumen, symbionts convert urea into ammonium to use as a nitrogen source for protein synthesis
- SCFAs and amino acids absorbed, some ruminants digested to be able to absorb vitamin B
hindgut fermenters
- simple stomach and intestine, enlarged caecum or colon
- microbial breakdown of cellulose to form SCFAs
- relatively fast fermentation process, allows for ingestion of very fibrous food
- thought to be ancestral condition other forms of fermentation evolved from
- problem with fermentation occurring after small intestine, vitamin B and essential amino acids not absorbed/digested, nitrogen recycling cannot occur
- 2 strategies, coprophagy e.g. rabbits, chewing e.g. horses
coprophagy and chewing
- allows more absorption of vitamins/ amino acids
- coprophagy, rabbits have 2 types of faeces
- know when material is emptied from the caecum, eaten directly from anus, can access B vitamins as it passes through the small intestine
- horses reliant on eating and chewing a lot to obtain nutrients
nutrition
diet must supply
- chemical energy (ATP) and organic carbon and nitrogen for biosynthesis of complex molecules
- compounds that cannot be synthesised, essential nutrients including amino acids, fatty acids, vitamins and minerals
amino acids
- 20-200 amino acids required for the synthesis of all proteins in animals
- animals cannot create 8-10 essential amino acids
- animal products are ‘complete’, contain all essential amino acids
- plant products are ‘incomplete’, a variety of plants need to be eaten to obtain all essential amino acids
fatty acids
- essential fatty acids must be obtained from diet
- mammals cannot create double bonds at omega-3 and -6 positions, must be obtained from diet by consuming alpha-linoleic acid and linileic acid
- cholesterol important in maintaining fluidity of membranes and synthesising hormones
- fatty acid deficiencies very rare
- carbohydrates can also be converted into fats
vitamins
- must be obtained through the diet
- organic molecules required in small amounts
- diverse functions, cofactors for enzymes etc
- 2 groups
- fat soluble: A (retinal), D (absorbing calcium), E (antioxidant *OH), K (blood clotting)
- water soluble: B, C (antioxidant *OH)
minerals
- must be obtained through diet
- inorganic molecules required in small amounts (<1mg to ~2500mg)
- diverse functions, cofactors for enzymes, metalloproteins etc
- Ca and P for bone building and maintenance
- Ca for nerve function
- Fe for haemoglobin and cytochromes
- other include selenium, zinc, copper etc
- can become toxic in large amounts but unusual
digestion
= the breakdown of food molecules by enzymes into smaller molecules to facilitate distribution
2 types:
- extracellular = digestion occurs outside cells within ‘digestive cavity’ (evolved after intracellular)
- intracellular = digestion occurs within cells lining ‘digestive cavity’
absorption
= the transfer of nutrients from outside
of the animal across the gut wall and into the blood or haemolymph
Digestion, phylum Cnidaria
- intracellular and extracellular digestion
- evolution of digestive (gastrovascular) cavity, significant evolutionary step
- indigestible material rejected through mouth
- nutrients pass around animal via diffusion
Cnidaria, gastrodermis
lines gastrovascular cavity, has flagella to mix food
4 cell types
- enzymatic gland cells, secrete protolytic enzymes for extracellular digestion
- nutritive muscular cells, ingest food via pseudopodia for intracellular digestion
- mucous gland cells, concentrated around mouth, lubricant for prey entering and waste exiting
- nerve cells, make up nerve net, fewer in number
digestion in free living Platyhelminthes
- no through gut
- food enters mouth and muscular protrusible pharynx into gastrovascular cavity
- some are simple and unbranched, others divided into lobes to increase surface area
- enzymes released by cells, extracellular digestion
- nutrients pass around animal through diffusion
- majority carnivores, feed on dead or injured organisms
digestion in parasitic Platyhelminthes
- variable
- e.g. Tapeworm, (Taenia)
- no sensory organs, gut or mouth
- specialised hooks/suckers to attach to wall of small intestine
- already digested materials from small intestine absorbed across body
- protective cuticle highly resistant to digestive enzymes
evolution of through-gut and extracellular digestion
- as volume increases a greater SA for absorption and digestion is needed
- majority of animals have a through-gut,
staring with a mouth and terminating at the anus - allows for specialization of
the gut into various structures, stomach, intestine etc - efficient digestion and
absorption.
food processing
- ingestion, insoluble food in via mouth, chewing/mastication starts the digestion process
- digestion, mechanical and chemical (enzymes) breakdown
- absorption and assimilation, soluble product taken across gut wall and assimilated
- egestion, undigested material ejected as faeces
Phylum Annelida
e.g. Earthworms
- consume decaying organic matter (or microbes on OM?)
- specialised compartments along alimentary canal
- mouth
- pharynx (muscular, generates sucking motion for ingestion)
- oseophagus (peristaltic contractions)
- crop, main storage organ
- gizzard, secondary structure involved in mechanical breakdown of food, often contains swallowed stones
- intestine, symplified tube (no large and small) with typhlosole, indentation along dorsal side to increase surface area
- pygmidium, anus
Phylum Arthropoda, exoskeleton
- exoskeleton lining/cuticle also runs into and lines the the foregut and hingut
- doesn’t line midgut as this is where absorption takes place
Phylum Arthropoda, insects
- crop and gizzard/proventriculus for storage
- ceca (midgut), principle site of digestion and symbionts if present
- malpighian tubules in hindgut for osmoregulation
- rectum and anus
Phylum Arthropoda, crustaceans
Foregut:
- anterior/cardiac stomach, cuticle of exoskeleton serrated (gastric mill) for mechanical digestion
- posterior/pyloric stomach, some enzymatic action (enzymes move up from midgut), fine cuticular bristles (setae) strain particles on way to midgut
Midgut:
- hepatopancreas, large surface area for digestion, storage of certain lipids and toxin sequestration
- ceca (symbionts if present)
Hindgut/anus
components of vertebrate digestive system
- 4 parts (foregut divided into headgut and foregut)
- headgut, mouth, tongue and pharynx, capture/engulfment and preparation of food for digestion (mastication)
- foregut, oesophagus and stomach (or crop and gizzard), move food from headgut to stomach and start of mechanical digestion
- midgut, small intestine, main site of chemical digestion and absorption
- hindgut, large intestine, absorption of water and minerals, storage of waste prior to defecation
Myxini, Hagfish
- unique adaptations, lacks specialisation
- propels food along alimentary canal using ciliary action (unusual, usually peristaltic contractions)
- food enclosed within a mucoid bag which is secreted by the gut wall, permeable to enzymes (in) and digestive products (out)
- indigestible material secreted in the membrane
- unique to hagfish, functional significance unknown
- similar structure in blood sucking insects so could be an adaption to eating food with a high bacterial load (hagfish often eat carcasses)
Actinopterygii
- diversity of alimentary canal related to diet
- mouth with teeth and specialised jaws for prey capture etc
- many fish also have pharyngeal teeth/jaws for mastication
- oseophagus
- stomach, specialised
- pyloric sphincter to regulate food movement
- pyloric cacae at start of midgut, finger like extensions to increase surface area
- intestine (no large and small)
- diffuse pancreas, not obvious structure, found along length of intestine and around cacae
- anus
Actinoperygii, stomach specialisation
- some fish have no stomach, deposit feeders that are constantly eating so do not need a food storage organ (also no acid phase of digestion)
- some fish have a straight stomach
- some fish have a U or Y shaped stomach, more storage space for intermittent feeders
e.g. mackerel, starve for 4-5 months so food needs to be stored and needs to be able to eat large amounts of food at once when food is available
Actinopterygii, stomach specialisations
- carnivores e.g. rainbow trout have less specialisations and a relatively short intestine (meat easy to digest)
- omnivores specialising in animal sources e.g. Catfish, larger stomach, slightly longer intestine
- omnivores specialising in plant sources e.g. carp have a longer intestine (slows down digestion, plants harder to digest)
- Milkfish, microphagous planktivore (plants and animals) has a well defined gizzard and very long intestine
Class Aves
- specialisation of the oesophagus, crop for storage, feeding young (regurgitation, ‘crop milk’, nutritious fluid secretions e.g. in pigeons, important when food is scarce)
- stomach subdivided into proventriculus (chemical digestion) and gizzard (mechanical digestion)
- small intestine for chemical digestion and absorption
- ceca if present
- large intestine
- cloaca, waste storage and water absorption, formation of uric acid
Aves, seasonal variation in the alimentary canal
- related to changes in diet, alimentary canal can lengthen up to 20% or shorten
- longer intestines for plant material, requires longer time to digest, more time for enzyme and symbiont action
- smaller intestines for animal material, required less time to digest
Hoatzin bird
- foregut fermenter (unusual) in large crop
- had to displace flight muscles to make way for crop so very poor fliers
- primary predator defence is smell from foregut fermentation
mammalian alimentary canal
- mouth, teeth (mastication), salivary glands (lubrication, chemical digestion from amylase, antimicrobial)
- oesophagus (peristaltic contractions)
- sphincter prevents acid burning oesophagus (risk of oesophageal cancer)
- stomach, pepsin enzymes (chemical breakdown, requires pH 2), storage, mucous lining protects stomach lining from acid, churning (muscle contraction) for mechanical breakdown, water and ethanol absorbed
- emptying of stomach into duodenum (start of small intestine) highly regulated by sphincter
- secretions from gallbladder neutralises stomach acid
- chemical breakdown and absorption (some mechanical) in small intestine, enzymes secreted from pancreas and walls of small intestine
- large intestine (ascending, transverse and descending colon) reabsorbs water secreted from blood to assist with enzyme action
