AP Biology

Circulatory Systems

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Exchange of materialsAnimal cells exchange material across their cell membrane

fuels for energy nutrients oxygen waste (urea, CO2)

If you are a 1-cell organism that’s easy!If you are many-celled that’s harder

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Overcoming limitations of diffusion

O2CHO

CHO

aa

aa

CH

CO2

NH3aa

O2

CH

aa

CO2CO2

CO2

CO2CO2

CO2 CO2

CO2

CO2

CO2

NH3

NH3 NH3

NH3

NH3

NH3

NH3NH3

O2

aa

CH

aa

CHO

O2

Diffusion is not adequate for moving material across more than 1-cell barrier

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In circulation…What needs to be transported

nutrients & fuelsfrom digestive system

respiratory gasesO2 & CO2 from & to gas exchange systems: lungs, gills

intracellular wastewaste products from cells

water, salts, nitrogenous wastes (urea)protective agents

immune defenseswhite blood cells & antibodies

blood clotting agentsregulatory molecules

hormones

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Circulatory systemsAll animals have:

circulatory fluid = “blood”tubes = blood vesselsmuscular pump = heart

open closed

hemolymph blood

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Open circulatory systemTaxonomy

invertebratesinsects, arthropods, mollusks

Structureno separation between blood & interstitial fluid

hemolymph

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Closed circulatory systemTaxonomy

invertebratesearthworms, squid, octopuses

vertebratesStructure

blood confined to vessels & separate from interstitial fluid

1 or more heartslarge vessels to smaller vesselsmaterial diffuses between vessels & interstitial fluid

closed system = higher pressures

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Vertebrate circulatory systemAdaptations in closed system

number of heart chambers differs

4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood; maintains high pressure

What’s the adaptive value of a 4 chamber heart?

2 3 4

low pressure to body

low O2 to body

high pressure & high O2 to body

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Evolution of vertebrate circulatory system

fish amphibian reptiles birds & mammals

A A

VV V VV

A AAAA

V

2 chamber 3 chamber 3 chamber 4 chamber

Birds AND

mammals!

Wassssup?!

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Evolution of 4-chambered heart

convergent evolution

Selective forces↑ body size

protection from predationbigger body = bigger stomach for herbivores

endothermycan colonize more habitats

flightdecrease predation & increase prey capture

Effect of higher metabolic rategreater need for energy, fuels, O2, waste removal

endothermic animals need 10x energyneed to deliver 10x fuel & O2 to cells

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Vertebrate cardiovascular systemChambered heart

atrium = receive bloodventricle = pump blood out

Blood vesselsarteries = carry blood away from heart

arteriolesveins = return blood to heart

venulescapillaries = point of exchange, thin wall

capillary beds = networks of capillaries

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Blood vesselsarteries

arterioles

capillaries

venules

veins

artery

arteriolesvenules

veins

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Arteries: Built for high pressure pumpArteries

thicker walls provide strength for high pressure pumping of blood

narrower diameterelasticity

elastic recoil helps maintain blood pressure even when heart relaxes

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Veins: Built for low pressure flowVeins

thinner-walled wider diameter

blood travels back to heart at low velocity & pressurelower pressure

distant from heartblood must flow by skeletal muscle contractions when we move

squeeze blood through veins

valvesin larger veins one-way valvesallow blood to flow only toward heart

Open valve

Blood flowstoward heart

Closed valve

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Capillaries: Built for exchangeCapillaries

very thin walls lack 2 outer wall layers only endothelium

enhances exchange across capillary

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Controlling blood flow to tissuesBlood flow in capillaries controlled by pre-capillary sphincters

supply varies as blood is neededafter a meal, blood supply to digestive tract increasesduring strenuous exercise, blood is diverted from digestive tract to skeletal muscles

capillaries in brain, heart, kidneys & liver usually filled to capacity

sphincters open sphincters closed

Why?

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Exchange across capillary walls

Arteriole

Bloodflow

Venule

Lymphaticcapillary

Interstitialfluid

Fluid & solutes flows out of capillaries to tissues due to blood pressure

“bulk flow”

Interstitial fluid flows back into capillaries due to osmosis

plasma proteins ↑ osmotic pressure in capillary

BP > OP BP < OP

15% fluid returns via lymph

85% fluid returns to capillaries

What about

edema?

Capillary

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Lymphatic systemParallel circulatory system

transports white blood cellsdefending against infection

collects interstitial fluid & returns to blood

maintains volume & protein concentration of blooddrains into circulatory system near junction of vena cava & right atrium

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Lymph System

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Mammalian circulation

What do blue vs. red areas represent?What do blue vs. red areas represent?

pulmonary

systemic

systemic

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Mammalian heart

Coronary arteries

to neck & head & arms

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Coronary arteries

bypass surgery

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AV

SL

AV

Heart valves4 valves in the heart

flaps of connective tissueprevent backflow

Atrioventricular (AV) valvebetween atrium & ventriclekeeps blood from flowing back into atria when ventricles contract

“lub”Semilunar valves

between ventricle & arteriesprevent backflow from arteries into ventricles while they are relaxing

“dub”

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AV

SL

AV

Lub-dub, lub-dubHeart sounds

closing of valves“Lub”

recoil of blood against closed AV valves

“Dub”recoil of blood against semilunar valves

Heart murmurdefect in valves causes hissing sound when stream of blood squirts backward through valve

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Cardiac cycle

systolic________diastolic

pump (peak pressure)_________________fill (minimum pressure)

1 complete sequence of pumpingheart contracts & pumpsheart relaxes & chambers fill contraction phase

systoleventricles pumps blood out

relaxation phasediastoleatria refill with blood

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Measurement of blood pressure

High Blood Pressure (hypertension)if top number (systolic pumping) > 150if bottom number (diastolic filling) > 90

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Bloody well ask some questions, already!