Week 4 The digestive system I Flashcards
What is digestive physiology?
All tissues that contribute to physical and chemical breakdown of food.
What is included in an overview of digestive physiology?
Sensory system - neurosensory machinery
-locates food ( eyes,nostrils,antennae)
Physical structures- specialised structures
-mechanically disrupt food (tongue,teeth,madible)
Chemical processes
-break down food/digest it (enzymatic-outside animal)
Undigested food expelled by egestion
What is assimilation?
Sequential process of nutrient acquisition and absorption.
What cell types accomplish assimilation?
Absorptive - take up nutrients
Glands (endocrine and exocrine) - secrete chemicals e.g. mucus,acid,ions,enzymes
Muscles- control GIT shape and motility
Nerves- regulate GIT function
How do animals sense food?
Using chemical,thermal and electrical cues.
They link a receptor to a signalling pathway which determines the behavioural response that alters feeding.
What does an olfactory receptor detect?
Smell
What chemical signals are used by cestodes?
Cestodes (tapeworms), e.g. Hymenolepis diminuta
-diurnal migrations up/down GIT of host following nutrients (the chemicals) released from meal.
What chemical signals are used by Cnidarians?
Cnidarians, e.g. Hydra
-chemicals tells them prey is nearby (proline, reduced glutathione)
What chemical signals are used by Complex Animals?
Complex animals, (herbivorous insects) e.g. aphids
• use gustatory & olfactory receptors
(taste-gustatory / smell-olfactory)
• some chemicals stimulate feeding (phagostimulant)
• some chemicals deter feeding (phagodeterrent)
What chemical signals are used by vertebrates?
Vertebrates
-carrion eaters detect chemicals in rotting flesh
What chemical signals are used by sharks?
Sharks • gustatory signal • chemicals found in vertebrate blood • frenzied feeding behaviour – amplification cascade • sharks feed - more blood - ↑ gustatory signal - more sharks arrive to feed
How do Energetic Signals work?
Predator senses energy emitted/reflected from animal
• light, sound, heat, electricity
What are some examples of energetic signals?
Bird of prey (golden eagle)
• uses visual system to locate field mouse
Insects
• detect infrared light emission from warm bodies
Firefly, Photuris
• predatory species produce light pattern that mimics mating signal
Bat-eared fox, Otocyon megalotis
• Detects prey using audible sounds
Bats
• Detect ultrasonic signals
• Emit signals & detect return of signal
- echolocation
Snakes
• Detect thermal energy emitted from live prey
• Thermal detection on both sides of head
- When signals are equal? - middle route-
Which animals use echolocation to determine prey?
Bats and Dolphins
What are energetic signals?
- visual system
- infrared light emission
- light pattern
- audible sounds
- ultrasonic signals (echolocation)
- thermal energy
What does GIT stand for?
Gastrointestinal tract
How did the digestive system evolve?
• increasing anatomical and functional specialisation
2-way gut
1-way gut
What is a two-way gut?
Simple digestive sacs - food enters & leaves through a single opening
Give an example of a two-way gut.
Platyhelminths
• Simple sac (small flatworms)
• Complex sac with many side branches, diverticula (larger flatworms)
How does digestion in a two-way gut work?
Digestion – begins in lumen
Proteases secreted from sac wall – digest food > small particles
Cells lining sac phagoctose partially digested particles
NB. cells have subtly different functions > regional specialisation
What is a one-way gut?
Food ingested at one end, egested at other end
Specialised regions more developed
• vary widely among animals
• increase efficiency of digestion (important)
What are some specialised regions of GIT?
Specialised regions - aid digestion
-General plan of GIT is common in vertebrates
-Many animal taxa differ in terms of modified regions
• Oesophagus of birds includes crop
• Stomach of birds includes gizzard
• Modified digastric stomach in ruminants
• Ceca in birds and bony fish (commensal bacteria)
What are the regions of mammalian GIT?
• Mouth • Pharynx • Oesophagus • Stomach(s) • Small intestine (duodenum, jejunum & ileum) • Large intestine (cecum & colon) • Rectum • Anus
What is the upper region of a mammalian GIT and what does it do?
• Mouth
• Pharynx
• Oesophagus
- all of these are responsible for mechanical breakdown of food
What is the gastric region of a mammalian GIT?
-Stomach(s)
in most animals is acidic
What is the upper intestine of a mammalian GIT and what does it do?
-Small intestine (duodenum, jejunum & ileum)
Neutralises acidic solution
Carries out digestion
Carries out nutrient absorption
What is the lower intestine of a mammalian GIT and what does it do?
-Large intestine (cecum & colon)
Reabsorbs water & electrolytes
What does the rest of a mammalian GIT do?
-Rectum & Anus
Package & release of
indigestible material
What parts are not included in the mammalian GIT yet regulate digestion as well?
-Side chambers that branch out from main GIT
-Muscular valves (sphincters) that regulate passage through different
compartments e.g. cardiac and pyloric sphincters
How do different species differ in their GIT?
-Different species evolved different regions to manage different diets
-Most mammals are monogastric
-Ruminants are polygastric
e.g. cattle, sheep, deer
• rumen
• reticulum
• omasum
• abomasum
What does a polygastric GIT include?
- rumen
- reticulum
- omasum
- abomasum
What is the first pair of compartments of a polygastric GIT and what does it do?
rumen & reticulum - contain fermentative bacteria • digests cellulose • produces volatile fatty acids & gases (CO2 & methane)
What is the second division of compartments of a polygastric GIT and what does it do?
omasum & abomasum
-obomasum = glandular stomach
• secretes digestive enzymes
What developmental GIT variations exist within species?
Mammalian fetus & infant
• maternal blood borne nutrients (placenta)
• mammary gland secretions
• solid food
Insects e.g. larval lepidopterans (catapillars) & butterflies
• plant leafy material vs nectar
What other inter-species GIT variation exists?
-Sexual variation
Male & female mosquitos
• nectar vs blood
What are all inter-species GIT variations?
- monogastric vs polygastric variation
- developmental variation
- sexual variation
What is Ingestion?
primary route to gain chemicals from environment
How are nutrients obtained and what is done with them?
-MOST animals – absorb nutrients across epithelium of GIT
-Aquatic animals – obtain some essential ions across external epithelial
surface e.g. skin, gills
-Absorbed nutrients may be catabolised (to yield energy) OR
anabolised (used to create new molecules)
What are essential nutrients? Give examples
Nutrients that can only be obtained from the diet
• cannot be made de novo
– Vitamins (e.g. VitC humans)
– Minerals (e.g. Na, K, Ca)
– Amino acids (typically 8 essential AA)- isoleucine, leucine, lysine, methionine, phenylalanine,threonine, tryptophan & valine
– Essential fatty acids (omega-3 & omega-6)
What is protein quality?
Protein is the dietary source of AA
Protein quality – profile of AA in dietary protein
Is Plant protein higher quality dietary protein than animal protein? Explain your answer
No, that is false.
-Animal protein – higher-quality dietary protein
• AA profile more closely matched to the needs of animal
-Plant protein – often deficient in 1/more essential AA
• E.g. maize protein lacks lysine, wheat protein lacks tryptophan
• Significance = herbivore must eat range of plants to ensure it gets
ALL essential AA
What are non-essential nutrients?
Nutrients that animals can produce from other molecules
• can be made de novo
• metabolise essential nutrients using enzymes
What/Which are digestive enzymes and what is their function?
-most animals use same family of digestive enzymes
• convert complex macromolecules into form that is readily absorbed
by animal
– Lipases
– Proteases
– Amylases
– Nucleases
What are lipases/ what do they do?
Lipases
– Release FA from triglycerides & phospholipids
– E.g.Triglyceride lipase & phospholipase
What are proteases/ what do they do?
-Break down proteins into shorter polypeptides (e.g. trypsin)
Different types attack protein at different points
– E.g. Peptidases, aminopeptidases, carboxypeptidases, dipeptidases
What are amylases/ what do they do?
-Break down polysaccharides into oligosaccharides (e.g. dextrinase)
Disaccharidases break down specific disaccharides
– e.g. maltase hydrolyses maltose into glucose
What are Nucleases/ what do they do?
- Break down DNA into nucleotides
- Nucleotides broken down into nucleosides & nitrogenous bases
- no example
Is a oneway or twoway gut more efficient?
One-way gut, allows for better absorption of nutrients.
