Digest Excret And Circulation

8/8/2019 Digest Excret And Circulation

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The ability of an organismto to regulate its internal

environment so as to

maintain a stable condition

Homeostasis

Self regulation (Feedback)

by molecular, cellular, processes; tissues, organs. of gases (O2, CO2), nutrients, inorganic substances (salts),

metabolic wastes; etc.


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ImportanceImportance:: maintain optimum conditions for life-processes,

in spite of continual internal & external changes

AdvantageAdvantage:: A constant internal environment allows cells tobecome more specialized and efficient at a particular task.

CostCost:: Energetic; increased dependence on specializedsystems.


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Systems are needed to:

Ingest the food (feed),

break it down (digestion), and

make the products available toall the cells.

In metazoa, most cells do not comeinto contact with the food source.


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Feeding modes

Absorptive feeders(usually lack mouth parts; absorbs nutrients)

Substrate or

deposit feeders(mouth partsmanipulate substratecontaining food )

Fluid feeders(mouth partspenetrate (fluid)food source; suction)

Ingestive feeders

(mouth partsmanipulate solid food)

Filter feeders(mouth parts (mostly) not responsiblefor extracting food from medium)


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Digestion

Intra-cellular

The process of breaking down food into itsmolecular and chemical components so that thesenutrient molecules can cross plasma membranes

Extra-cellular


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Digestion: Intra-cellular(Protozoa, Porifera, Cnidaria)

Food is taken into cells by phagocytosis (endocytosis);digestive enzymes are secreted into the phagocytic vesicles;nutrients are released into the cytoplasm


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Digestion:Extra-cellular

In the lumen of the digestive system; uses mechanical,chemical (e.g. PH), enzymatic and possibly bacterialdigestion to release nutrient molecules, which aretransferred to the body fluid.

Advantage:Advantage:

ability to feed uponability to feed upon

food items largerfood items largerthan those that canthan those that canbe phagocytizedbe phagocytized


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The digestive tract- the tube within a tube design

Reception: Buccal cavity

& salivary glands

Conduction: Pharynx& Esophagus

Storage & earlydigestion: Crop

Grinding: Gizzard

Midgut: final digestion& nutrient absorption

Hindgut: waterabsorption & solidconcentration

Ectodermal originEndodermal origin

ForegutBuccal cavity ( )Pharynx ()Esophagus ()Crop () (?)

Gizzard/ Stomach ( \ )

Midgut & Cecum ( )

Hindgut ( )

Rectum


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Summary

the tube within a tube design

Sequential steps:

Movement of food

Secretion of gastric juices & enzymesDigestions: mechanical, chemical & enzymatic

Absorption of nutrients

Elimination of undigested food & wastes.

Advantage:

Enables sequential processing of food; no lossof undigested food while disposing of solid wastes.


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Waste products ofheterotrophic nutrition

1. CO2

2. Solid wastes

(indigestible material)

3. Metabolic wastes

(nitrogenous; from intra-cellular

breakdown of amino & nucleic acids)


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Excretory Systems

Functions:

1) Remove metabolic (nitrogenous) wastes.

2) Regulate solute concentrations byselective secretion or reabsorption.

3) Regulate water volume by excretion orretention of water.


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Nitrogenous wastes

products of cellular protein (& nucleic-acid) catabolism

Amino acid + O2 Ketoacid + Ammonia (NH3)

Metabolicpaths

Highly soluble & toxicQuick disposal


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Nitrogenous

wastes

1Common in aquatic invertebrates2 Uncommon (Terrestrial Platyhelminthes, Annelids & Molluscs)3 Most terrestrial invertebrates (arthropods)

Ammonia1

Urea2U

ric acid3

Diffusion (gills, ectoderm)

Excretion

ExcretionExcretion


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Which molecule to use?

Energy Toxicity/solubilityWater use

Ammonia1 low high highUrea2 medium medium medium

Uric acid3 High low low


Considerations:

Amount of energy needed to dispose of excess nitrogen

Amount of water needed to keep concentrations below toxic levels


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Diffusion of ammonia through the outerDiffusion of ammonia through the outerand/or respiratory membranes of aquaticand/or respiratory membranes of aquaticinvertebrates (e.g. crustaceans, cnidaria)invertebrates (e.g. crustaceans, cnidaria)


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The Excretory Process

Involves two steps:

1. Ultrafiltration: filtration of hemolymph or bloodacross a semi-permeable membrane, due to

differences in hydrostatic pressure (water andsolutes [ammonia/urea, salts, glucose] move from highto low pressure area). Forms filtrate ().

2. Active transport: The selective secretion andabsorption of solutes to/from the filtrate (mediatedby membrane-bound proteins). Forms urine.


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Excretory Systems


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ProtonephridiaPlatyhelminthes

Ultrafiltration: Flagella ofFlame Cells create lowpressure in the tubules;water and solutes followpressure gradient into thetubules.

Active secretion & re-absorption of physiologically

important molecules (e.g.glucose) take place beforeurine empties into theexternal environment via

theN

ephridiopores.


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Ultrafiltration across themembrane of the major bloodvessels; water and solutes moveinto coelomic fluid due to highblood pressure (noultrafiltration bymetanephridia)

Coelomic fluid entersthe the metanephridiatubules via a funnel shapedopening - Nephrostome.

Active transport of materialsto/from blood in capillarynetwork, or sinus, thatsurrounds the tubules. Urine

exists via the nephridopore.

MetanephridiaAnnelids, Molluscs


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(Meta)nephridia

Annelids, Molluscs


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Malpigian tubulesInsects, some spiders

Closed tubules that open to the gut

Salts are actively transported from thehemolymph into the tubules; Osmotic

gradient draws water and dissolvedwastes into the tubules

Rectal glands reabsorbwater, and nutrients

Uric acid is precipitated;crystals are excreted withfaeces


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Antennal (green) glands

Osmotic regulation incrustaceans;

(ammonia excretion bydiffusion through gills)

Ultrafiltration directlyinto end sac due to

hydrostatic pressure ofthe blood


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Heterotrophy

1. Feeding

2. Digestion


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Antennal (green) glands(in freshwater crustaceans; osmotic regulation;

ammonia excretion by diffusion through gills)

Nephridial canalSite of active secretion/absorption

Bladder

End sacSite of ultrafiltration due tohydrostatic pressure in hemocoel)


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Nitrogenous wastes

products of cellular protein (& nucleic-acid) catabolism

Amino acid + O2 Ketoacid + Ammonia (NH3)

Ammonia1 Urea2 Uric acid3



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Physiological Systems

The Digestive System

The Excretory System

The Respiratory System

The Circulatory System


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Respiration

Cellular respirationCellular respiration: the release of energy by theoxidation of food (in mitochondria), forming ATP & CO2as a byproduct

External respirationExternal respiration: the exchange of oxygen and

carbon-dioxide between an organism and its environment


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Gases enter and leave the body by diffusingacrossa moist respiratory surface.

Gas exchange

Diffusion rate depends on:

Diffusion coefficient Surface area Concentration gradient Distance

Diffusion: the random

spreading of molecules dueto their kinetic energy &momentum

D=(C1-C2) / x2


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O2 consumption and CO2 production ratesare proportional to the organisms volume.

Constraints leading to the evolution of

respiratory and circulatory systems

Larger animals have a smaller

surface-area to volume ratio, andlonger average distance betweencells and the respiratory surface

Respiration based ondiffusion across theepidermis sets an upperlimit to body (& cell) size


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Cutaneous respiration:Gas exchange across the outer membrane

Protozoa Flat worms

Nematoda

Restricted to aquaticor moist environments(drying would reduce thediffusion coefficient)

Distance betweenmetabolizing tissue andrespiratory surface


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For organisms to grow larger and still

depend on diffusion, would require:

1. Larger respiratory surface, with noincrease in volume.

2. Active maintenance of concentrationgradient:ventilation.

3. Shorter distances across which gases

have to travel by diffusion (O2 delivery,and CO2 removal, to/from cells).

Respiratory and Circulatory systems


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3. Shorter distances across which gases

have to diffuse (O2 delivery, and CO2removal, to/from cells).

Respiratory system

More efficient gas

exchange withexternal medium


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Respiratory systems

Trachea - insects, some spiders

Fine air-conducting tubules, enablinggas exchange at the cellular level.

Functions in exchange & delivery.

~0.1um


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Titanus giganteus

~15 cm~60cm

Mechanical limit to the size oftrachea restricts the max. sizeof insects (given atmosphericO2 concentrations)


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Ventilation

- Maintains a concentrationgradient across the respiratorysurface

- Common in active species

Respiratory systems

Poor flow of external mediumaround respiratory membrane: weak concentration gradient slow diffusion


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Respiratory systems

Hemocoel Book lungs

Pneumostome

Lungs - Spiders; Scorpions (book lungs)- Terrestrial Gastropods

- Highly branched membrane;spatially localized.

- Ancestral to trachae (less efficient)


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Respiratory systems

Trachea (& Lungs): internal

Gills: often external


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3. Shorter distances across which gaseshave to travel by diffusion (O2 delivery,and CO2 removal, to/from cells).

Circulatory system


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Circulatory systems

OpenArthropods, most Molluscs

ClosedAnnelids, Cephalopods

GastrovascularCnidaria; [flat worms]

Active transport of: - dissolved gases

- nutrients and waste products


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Circulatory systems

Gastrovascular (Cnidaria, [flat worms] )

Medium of transport: waterPropulsive mechanism: cilia/flagella; body movement


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Circulatory systems

Separation between external and internal medium

Circulatory system can be used to transport othermaterials; e.g. hormones, elements of the immune system

Open(Arthropods, most Molluscs)

Closed(Annelids, Cephalopods)


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Circulatory systems

Medium of transport: blood; separated from lymphPropulsive mechanism: muscular heart(s)/arteriesVessels: arteries; veins; capillaries

Closed

(Annelids, Cephalopods)


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Circulatory systems

Open(Arthropods, most Molluscs)

Medium of transport: hemolymph(no separation between blood and lymph)

Propulsive mechanism: muscular heart(s)/arteriesVessels: arteries; sinusesi.e. Tissues in direct contact with hemolymph


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Circulatory systems

embryology


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Advantages of the closed system:Advantages of the closed system:

Separation of oxygenated and de-oxygenated bloodincreases the gas-exchange efficiency; high metabolicrates and activity levels

Regulation of blood flow to to specifictissues/organs (e.g. Oxygenated blood can be directedquickly to muscles during rapid movement)


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The cephalopod heart

separation of oxygenatedand de-oxygenated blood


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Respiratory pigments -

increases the bloods carrying capacity of O2

Pigment Location Metal found in

Haemoglobin * Cells/

free

Iron Annelids, Arthropods,

Molluscs

Haemocyanin Free Copper Crustaceans, Cephalopods

Haemerythrin Cells Iron Polychaetes

Chlorocruorin Free Iron Polycaetes

Proteins with a metal ion, capable of binding oxygen reversibly

Can occur in blood cells, plasma, or within tissues

Found in ~1/3 of invertebrate phyla

No pattern in taxonomic distribution; independent evolution

* Most common


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Counter current exchangehigher gas-exchange efficiency in gills

There is only 1/20 the amount of oxygenpresent in water as in the same volume of air


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water

blood

blood

water


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Summary

Physiological constraint:O2 & nutrients delivery; CO2 & metabolic waste removal

Evolutionary solution:

Circulatory system - transport/deliveryRespiratory system gas exchange

Consequences:

The evolutionary increase in body sizeHigher metabolic rates (more active life style)

The evolution of exoskeleton

Radiation to drier terrestrial habitats


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Respiratory systems

Trachae - insects,some spiders

Fine air-conductingtubules, enabling gas

exchange at thecellular level.(Functions in exchange &

delivery).

~0.1um


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Diving beetles Aquatic larval stages


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Gases enter and leave the body by diffusing across a

moist respiratory surface, following a concentrationgradient and at a rate that is proportional to the areaof the respiratory surface.

The rate with which a given cell can exchange gases

depends on its distance from the respiratory surface. O2 consumption and CO2 production rates areproportional to the organisms volume.

Gas exchange


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Digest Excret And Circulation

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