Circulatory Systems

Circulatory Systems

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A circulatory system consists of: A muscular pump – the heartA fluid – bloodA series of conduits – blood vessels

Together these are called the cardiovascular system

www.olympusmicro.com/galleries/abramowitz/images/

Capillary bed injected with

dye

Some animals do not need circulatory systems:Single-celled organisms exchange

nutrients, gases, wastes directly with their environment

Structures and flattened body shapes increase surface area to enhance exchange between cells and environment○ E.g. gastrovascular cavities – highly branched

cavity in flatworms and cnidarians bring environment inside animal

http://webpages.ursinus.edu/jsidie/pictures

Larger animals must use circulatory systems to deliver nutrients & O2 and remove wastes & CO2

Cells are supported by extracellular fluid for nutrient delivery and waste removal ○ Fluid in circulatory system (blood plasma)○ Fluid around cells (interstitial fluid)

www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages

Longitudinal sections of capillaries in

connective tissue supporting cardiac

muscle cells

Extracellular fluid in an open circulatory system:Combines with fluid

of circulatory system — hemolymph

Fluid leaves circulatory system and moves between cells then returns to be pumped again

Extracellular fluid in a closed circulatory system:Refers to fluid in the

circulatory system and outside it

Fluid in the circulatory system is blood plasma

Fluid around cells (outside circulatory system) is interstitial fluid

Advantages of closed circulatory systems:Faster transport through vesselsBlood can be directed to specific tissuesSpecialized carriers can travel in vessels and

transport hormones or nutrients to specific sites

Can support higher metabolism with better oxygen delivery

Exception are insects – they have very high metabolic demand but the have tracheal system that allows air to enter to deeper tissues

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Cephalopods have a closed circulatory system, unlike other molluscs.

Two circulatory circuits have evolved in vertebrates:Pulmonary circuit: blood is pumped from

heart to lungs and back again Systemic circuit: blood travels from heart to

rest of the body and back to heart

Closed vascular system contains:Arteries carry blood away from heart and

branch into arterioles that feed capillary beds

Capillaries are site of exchange between blood and tissue fluid

Venules drain capillary beds and form veins, which deliver blood back to heart

FishFish hearts have two chambers:

One atrium – receives blood from body

One ventricle – receives pumped blood from atrium and sends it to gills

Pay attention to # chambers and general blood flow in vertebrates

Crocodilian Heart – 4 chambers, 2 connected aortas

Right Atrium (deoxygenated)

Ventricle (partially separated)

Lungs Right aorta

Left Atrium (oxygenated)

Ventricle (partially separated)

Left Aorta

Arterioles and capillaries (becomes deoxygenated)

Lungfish – making transition to landLungfish have three-chambered hearts adapted to

breathe in air as well as water Lung formed from gut outpouching functions in

air Divided atrium separates blood into pulmonary

and systemic circuits 3 chambers Bloodstreams stay separate through single

ventricle

http://www.sheddaquarium.org/images/articles/Australian_Lungfish_Five.JPG

Amphibians

Reptiles (except crocs)• Behavior of reptiles - Activity comes in

bursts followed by periods of inactivity• When they aren’t breathing, it would

be a waste of energy to send blood to lungs

Reptiles - CrocsCrocodilians have true 4-

chambered heart (completely separated ventricle), 2 connected aortas

This allows greater control of shuttling blood away from pulmonary circuit when not breathing (submerged)

Birds and MammalsBirds and mammals

have four-chambered hearts and separate pulmonary and systemic circuits with the following advantages:Systemic circuit always

receives blood with higher O2 content

Gas exchange is maximized

Circuits can operate at different pressures

Valves prevent backflow of blood: Atrioventricular valves ○ lie between atria and

ventricles ○ prevent backflow when

ventricles contractPulmonary valve and

aortic valve (semilunar valves)○ lie between ventricles

and major arteries ○ prevent backflow when

ventricles relax

Heart FunctionCardiac cycle

Both sides of heart contract at same time○ first the two atria contract, then the two

ventriclesTwo phases:○Systole – when ventricles contract○Diastole – when ventricles relax

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Cardiac cycle 1. atria contract filling ventricles 2. Ventricle contract shutting AV valves

“lub” Systole

3. blood pumped out of ventricles into pulmonary artery and aorta

4. ventricles relax, aortic and pulmonary valves shut

“dup” Diastole

5. ventricles fill with blood as they relax, # 1 is happening

Pacemaker CellsResting membrane potential is less

negative than other cardiac cells○ Less stable

Action potentials are different from other cells○ Slower to rise○ Broader○ Slower to return to resting potential

How do pacemaker cells differ from rest of muscle?When Na+ and Ca2+ channels open, positive

charges flow into cell causing membrane potential to be less negative○ Causes action potential (cell “fires”) – membrane less negative○ Na+ channels in pacemaker cells are more open, resting potential is

LESS negative Pacemaker cells can fire more readily

When K+ channels open, positive charges flow out and membrane becomes more negative○ Cell membrane returns to more negative resting potential when

Na+, Ca2+, and K+ balance○ Pacemaker cells have unstable resting potential because of the specific

behavior of these cation channels This unstability causes SA node to fire stimulating rest of atria

Nervous system controls heart rate by influencing resting potential:Norepinephrine from sympathetic nerves

increases permeability of Na+/K+ and Ca2+ channels○ Resting potential rises more quickly and action

potentials are closer together

Acetylcholine from parasympathetic nerves increases permeability of K+ and decreases that of Ca2+ channels – opposite effect of norephinephrine○ Resting potentials rise more slowly and action

potentials are farther apart

Heart muscle contraction is coordinated:Action potential is

generated in the sinoatrial node (those pacemaker cells)

Action potential spreads through gap junctions in atria both atria contract together

But action potential does not spread to ventricles

Instead, action potential in atria stimulates atrioventricular nodeNode consists of non-

contracting cells that send action potentials to ventricles via bundle of His○Bundle divides into

right and left bundle branches that run to tips of ventricles

http://www.univie.ac.at/cga/courses/BE513/EKG/condHeart.gif

From apex, Purkinje fibers spread throughout ventricles

Contraction spreads rapidly and evenly throughout ventricles

Delay between atrial contraction and ventricles ensures proper blood flow

Electrocardiogram aka ECG or EKGuses electrodes to

record events in cardiac cycle

Large action potentials in heart cause electrical current to flow outward to all body parts

Electrodes register voltage difference at different times

Wave patterns EKG are labeled with letters corresponding to eventsP-wave: Atria

depolarization Q,R, and S waves:

Ventricular depolarization

T-wave: Relaxation and repolarization of ventricles

Blood pressure & flow through large arteries are highFlow through capillaries is lower Pressure is reduced in smaller vessels

because:○ Arterioles are highly branched larger total

cross-sectional area○ Capillaries contribute an enormous surface area

Atherosclerosis: “hardening of the arteries”Endothelial lining of arteries is damaged by

high blood pressure, smoking, diet, or microorganisms

Plaque forms at sites of damageDamaged cells attract migration of smooth

muscle cells

www.med.uottawa.ca/patho/cardio/ www.cardiocheck.co.uk/mediac/400_0/media/

Figure 50.15 Atherosclerotic Plaquewww.pathguy.com/lectures

Thrombus, or blood clot, removed from artery