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Animal Physiology
Or how things happen
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Class schedule ZOOL2402DATE WEEK LAB LECTURES05/03/2012 1 a) Lab test ZOOL 2401 How to eat green stuff
b) Gut Histology and gut length12/03/2012 2
a) Length:Weight, Proportions and energyMetabolic rate and size
b) Lung volume, gill area How to get oxygen
19/03/2012 3 a) Heart rate, BP and exercise. BMI How to move
b) Metabolic rate and heat. How to be cool.25/03/2012 4 a) Data Interpretation Getting rid of stuff
b) Urinalysis
02/04/2012 5 a) Endocrine structures Sugar sex and nerves
b) NIL Easter
09/04/2012 6 a) NIL Easter Seeing it
b) Lab test
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What is Physiology?
Physiology is the analysis of function inliving organisms
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How to eat Green stuff
Or The problems of Herbivory
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For the organism the balance of energy isimportant. It must minimize energy expenditurewhile maximizing energy generation.
Ultimately energy generation occurs throughbreakdown of glucose in respiration but prior tothis process the glucose molecules must begenerated to enter into the Krebs cycle or
glycolysis. Thus the function of digestion is to produce
simple molecules which can be broken down toyield energy.
This process however REQUIRES energy, so forthe organism, the energy gain must exceed theenergy lost through instigating the breakdownprocess
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This is the basis of energetics-the study of energybalance in an organism.
Basic energetics equation:
E(In) = E(Out) +E(P). Where E(P)=Energy retainedfor production or growth.
The equation can be expanded to:
R=F+U+M+P
Where :
R = Ingested energy
F and U = Energy losses in faeces and excretoryproducts respectively
M = Energy lost in metabolism.
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M can be further subdivided into:
1) Energy for bodily functions
2) Energy used for movement
3) Energy used for digestion absorption and processingof food.
P can be further subdivided into:
1) Energy used in production of gametes.2) Energy used for somatic growth
The partitioning of energy into the various
components can be determined experimentallyand constitutes determination of the energy budget
for the organism
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Digestive difficulties with Plant
material
Plant cells characteristically have cell walls. These are composed of a variety of substances
celluloses ,hemicelluloses, lignin etc.
These structural polysaccharides are large
molecules composed of sugar units joined byglycosidic links.
Number one problem is that most macro-organisms (herbivores) lack the appropriate
enzymes to break the bonds in themacromolecule and thus the cell contents arelargely resistant to digestion.
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Plant Structural Compounds
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Plant structural Carbohydrates
Main compound in plant cell walls is Cellulose.
Insoluble
Most abundant organic chemical on Earth
Linear
Consists of glucopyranose units linked by 1-4 glycosidic linkages.
Each molecule has about 3000units Cellulose molecules are aligned in parallel fashion to form microfibrils
which are several m in diameter and between 10-20 nm in length. Highlyordered arrangement of molecules is maintained by hydrogen bondingbetween the chains.
This ordered arrangement gives the molecule its property of insolubility
and its great strength. Microrganisms secrete cellulases which can break the linkages but the
released glucose is fermented in the gut of herbivorous mammals to giveshort chain fatty acids such as butyric acid which can be absorbed by theanimal in the intestine
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Hemicelluloses
Three types.
Xylans,mannans and glucomannans
Many have same 1-4 glycosidic backbone ascellulose but have side chains which prevents
close packing.
This allows some solubility
Xylans found in seed coats
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Possible solutionsPlant material decomposes once it dies.
Decomposition is carried out by micro-
organisms which DO possess cellulose
digesting enzymes: cellulases.
These micro-organisms are mainly fungi and
bacteria.
Possible Solution 1. Allow material to die and
decomposition to begin and then consume
decomposing material and decomposers.
This solution is seen in detritivores. Very common
in fishes.
Possible Solution 2. Incorporate decomposers within thedigestive system to allow breakdown process to occur within digestive
System. Symbiosis. This occurs in most terrestrial herbivores but has
evolved in a number of different ways
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Possible solution 2:Variants
1)Many chambered stomach-Ruminants and ruminant-like animals.
2)Digestive chamber (caecum) and enlarged gut eg Perissodactlys, Fishes.
3) Digestive chamber (caecum) and refection eg Lagomorphs and rodents.
Detail
The following are organisms which possess a multichambered stomach which
houses microorganisms:Ruminants; cows, sheep, deer, goats etc.
Ruminant like organisms; camels, llamas, hippopotamuses
pigs, sloths, some marsupials, langur monkey
Importance of Ruminants
1) Main herbivores in a number of ecosystems eg antelope in the Africansavannah.
2)Major domestic animals in agricultural setting eg cows, sheep, goats.Source of wool milk ,meat.
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Ruminant digestion
Digestive tract greatly enlarged. Microbial digestion slow process .Fermentation. Needs ability to store large amounts of food. Feedingcontinuous. Typical capacity of cow 91 litres.
Requires large amounts of saliva. Saliva high in bicarbonate contentnecessary to neutralise acidic pHs generated in the stomach by microbialdigestion. Main digestion products organic acids lowers pH.
Structure of the rumen 4 chambers: rumen ,reticulum and omasum linedwith keratinised squamous epithelium. None of them produces digestiveenzymes. Abomasum normal mammalian stomach.
house the microbial flora.
Microbial flora consists of a wide variety of microorganisms thusequipping the animal with the ability to break down a range of structuralcompounds. Not Lignin.
Chief fermentation end product: organic acids : acetic, proprionic, butyricetc.
Little glucose from digestion of cellulose as this is used by microorganisms
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Certain microorganisms responsible for splitting proteins into amino
acids. Mainly theses are taken up by the microorganismsthemselves. BUT microorganisms are ultimately digested as asource of protein by the ruminant.
Ruminant microorganisms are able to utilize urea and ammonia tosynthesise protein thus increasing protein content using wasteproducts.
Urea produced in the liver is returned to the rumen in the salivaand in the blood by diffusion from the blood. Some is converted toammonia.
Both components are used in protein synthesis by themicroorganisms.
Microorganisms are also responsible for the synthesis of B vitamins(particularly B12) and vitamin C.
Microorganisms synthesise all essential amino acids. Ruminants
able to survive irrespective of protein quality Both these abilities allow ruminants to survive on poor quality plant
material or during times of drought.
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Summary of processes in ruminant
stomach
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Description of digestive process
1. Food passes into rumen/reticulum where it is churnedto a fine consistency. Food is fermented here.
2. Food returned to mouth via contractions of rumen .
3. Chewed again
4. Compression in omasum. Removal of water (up to70%).
5. Digestion with enzymes and gastric juice inabomasum
6. Food may be returned to mouth for further chewingprior to passing directly to the intestine whereabsorption occurs.
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Energy Budget
Energy Budget :
Percentage of original intake
Free fatty acids 20
Digested by normal processes 25
Bacteria digested by normal processes 15Subtotal of utilizable energy 60
Faeces 25
Gas and Heat 15Subtotal of energy lost 40
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Fermentation products major source of
energy.
Approximately 70% of energy needs of a cow
met from organic acids.
Large quantity of energy lost as methane
gas(>10% of daily digested food energy)
eg Cow fed 5kg hay produces 191litres of
methane
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Caecum
Can be defined as a blind ending diverticulum in the digestive tractwhere microbial digestion/fermentation takes place. Usually foundat the junction of the small and large intestines
Found in a number of groups: perissodactyls (horses, zebras,rhinoceroses), elephants and hyraxes, lagomorphs and rodents and
dugongs are the mammal groups. Also Green turtles, Iguanas, and some birds eg willow ptarmigan
feeds on leaves and twigs. Derives 30% of energy fromfermentation.
Green turtles feed on sea grasses. 90% of cellulose digested byfermentation.
Common iguana -fermentation in hind gut. Captive rearedindividuals need to acquire correct flora from feeding on the faecesof wild individuals
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Advantages of ruminants
Location of fermentation chamber at anterior of gutallows digested products to pass through smallintestine and be subjected to further digestion.
Regurgitation is possible. Finer breakdown of plantmaterial. Compare cow and horse faeces.
Recycling of urea allows nitrogen that would be lost tobe utilised. Allows ruminants to survive on low-gradefood Also seen in macropode marsupials eg kangeroos.
Saftey. Anmal is able to continue processing food whichis stored in the digestive tract in safety. Less exposureto predators
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Sloth Stomach (Bradypus)
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Caecum plus refection
With a caecum alone much of the material which is digested by themicroorganisms is lost as it is poorly absorbed or is not subject to furtherdigestion.
Solution pass material through the digestive system twice. This is effectedby lagomorphs and rodents and is known as corophagy or refection.
If prevented from this rats develop vitamin deficiency and a 15-25%growth rate deficiency.
Similarly in rabbits-poor protein utilization and nitrogen retention.
In rabbits reingested faeces not masticated but pass to fundus of stomachand are stored there covered by a membrane . Fermentation maycontinue.
Rodents possibly masticate reingested faeces.
Other mammals which practice corophagy: prosimians, shrews, somemarsupials.
Shrews are insectivorous and use the process to assist in breakdown ofchitin which is a nitrogen containing polysaccharide
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Rabbit Stomach
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Herbivory in Fishes. Many fishes eat plant material.
There are a number of strategies employed:
Detritivory. This is particularly common in freshwater fishes
which rely on bacteria in the environment to digest the
structural carbohydrates. Many such fishes have pyloric caeca
which are a site of absorption in detritivorous fishes
Long intestine. Generally fishes which digest plant material
have a much longer intestine relative to body length than
fishes which feed on animal material. Many of these fishes
lack a stomach, e.g. Scaridae, (parrot fishes), Cyprinidae(carps).
Ratio of intestine length to body length:
Carnivores:033-075. Herbivores:2-20. Detritivores > 5.
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Pyloric Caeca in Teleost fishes
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Gizzard-like stomach. Some fishes employ a grinding
mechanism to mechanically rupture the cell walls of plant
material e.g. Mugilidae (grey mullets) which have a muscular
gizzard like stomach Caecum The family Kyphosidae which is found in Australia
have a caecum like structure with microflora: ciliates and
bacteria, which is used for fermentation and produces short-
chain fatty acids as a digestion product. Teeth Many fishes have grinding molariform teeth in the
mouth but the most common mechanism is the presence of
pharyngeal teeth. These are located in the pharynx
(surprisingly!) and give a very efficient grinding mechanism to
rupture the cell walls of plant material. Seen in Cyprinidae and
Cichlidae. This process is known as Trituration
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Pharyngeal Teeth of Teleost fish
Low pH in stomach Plant cells walls can also
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Low pH in stomach. Plant cells walls can also
be ruptured by exposing them to low pH
(approximately 1 or 1.5). This is seen in a
variety of plant eating fishes e.g. Cichlidae.This process is known as Lysis.
Most herbivorous fishes use a combination of
strategies
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Humans
Humans are defined as omnivores they however havethe ability to digest plant material.
This takes place in the caecum by means offermentation.
The constraints in terms of energy yield are the sameas for other animals with a caecum.
Dietary fibre is the edible parts of plants which areresistant to digestion and absorption in the humanintestine with complete or partial fermentation in thelarge intestine.
Physiological benefits: 1) laxation, 2) attenuation of blood glucose and/or cholesterol.
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Fibre in the human diet 1
1) Significantly lower incidence of constipation,diverticulosis and digestive cancer associated withhigh fibre diets. Mechanism. Bulk due to fibre improves the
musculature of the intestinal wall and lessens thetime that potential carcinogens are held in theintestine
Butyric acid derived from fermentation ofcellulose is toxic to tumor cells, inducingapoptosis.
Short chain fatty acids promote the growth ofbifidobacteria which prevent the establishment ofnondesirable intestinal flora
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Fibre in the human diet 2
2) glucans are another type of structural polysaccharide which aresoluble due to the presence of a 1-4 glycosidic backbone alongwith 1-3 side chains which confer solubility. Oat porridge.
Beneficial as they lower the level of blood cholesterol and reducethe incidence of heart disease. Mechanism. Viscous nature impedes the resorption of cholesterol and bile
acids in the intestine thereby placing a drain on the bodys cholesterolsynthesis.
In general structural carbohydrates help
decrease the glycaemic index of food thus slowing
down the uptake of glucose. This has particular benefits
for controlling blood glucose levels.Gums (soluble structural carbohydrates)probably bind to bile acids resulting
in more of them being passed out in the faeces and thus placing a drain on
the synthesis and metabolism of cholesterol
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Bile acids and Cholesterol
Absorption of lipids occurs in the small intestine. The process is aided by bile salts.
Examples of bile salts are sodium glycholate and taurocholate. These are derived from cholesterol in the liver
Bile salts are produced by the liver and pass along the bileduct where they are retained at the sphincter of Oddi. Thebile is also concentrated at this point by active transport ofNa+ ions
Release is stimulated by a variety of factors: presence of fattyacids in the intestine and the gastric hormone CCK
Bile salts combine with digested food products to form watersoluble micelles which enter the epithelial cells.
.
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Recycling of bile salts
The micelles which enter the epithelial cells areresynthesised into triacylglcerols at the ER and thesebecome part of droplets called chylomicrons.
The chylomicrons enter the lacteals and eventually the
veins. Most are stored as adipose tissue with only smallamounts being oxidized for energy at this time
Bile salts are resorbed from the intestine and returnedto the liver.
This occurs by means of the Enterohepatic circulation.
Any process that slows resorbtion of bile salts isthought to be beneficial in lowering the levels ofcholesterol
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Invertebrate digestion of plant
structural compounds
Plant material is digested by a number ofinvertebrates.
Obvious examples are : snails and silverfish.
Termites live exclusively on wood and rely onTrichomonas in the hind gut to provide cellulases.
Trichomonas is a flagellate which exists only inthe anaerobic conditions of the hind gut. If the
symbiont is removed the termite is unable tosurvive .Nitrogen fixing bacteria are also presentin the hind gut of termites
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Plant defences and their physiological
effects
Many plants have chemical defence mechanisms
to prevent them from being eaten by herbivores.
Some examples follow:
Alkaloids-affect CNS, opium, morphine, nicotine
Glycosides. Breakdown leads to toxic compounds
eg cyanide from cassava.
Enzyme inhibitors e.g. trypsin inhibitors in soyabeans. Low protein utilization of nuts, beans.
Heat sensitive.
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Plant defences and their physiological
effects
Cruciferae eg cabbage. Compounds which
suppress thyroid function. May lead to goitre if
excess in diet in combination with poor nutrition.
Compounds affecting reproduction. Mimics ofjuvenile hormone in insects-certain trees.
Oestrogen mimics particularly abundant in plants
of the pea family during arid years thus reducingreproductive success of herbivores. Also soya.