CIRCULATION

Circulatory systems are the transportation

highways of the animal body.

There are Open and Closed Circulatory Systems

Open circulatory systemThe open circulatory system is common to molluscs and arthropods. Open circulatory systems (evolved in crustaceans, insects, molluscs and other invertebrates) pump blood into a haemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood.

Closed circulatory systemVertebrates, and a few invertebrates, have a

closed circulatory system. Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels, and does not normally fill body cavities.

A heart is a means to circulate blood through the body of an animal. Among the lower species such as insects, arachnids, and others, the heart may simply be an expanded area in a blood vessel and may occur a number of times.

The earthworm, for example, has 10 such "hearts." These areas contract rhythmically to force the blood through the aorta, or blood vessel.

Not until the evolution of the higher vertebrates does the heart achieve its ultimate form, that of a chambered organ with differentiated purposes.

Practical activities to come..

Earthworm dissection(Click here to see video)

Crayfish dissection(click to see video)

Human heart vs. Crayfish heartThe human heart has 4 separate chambers

The crustacean heart is a single-chambered sac made up of layers of muscular leaflets.

Crayfish heart and circulationThe heart is suspended in the pericardial cavity by

several suspensory ligaments under the dorsal carapace of the thorax.

The cardiac ganglion in the heart generates the heartbeat rhythm.

There are several arteries, but no vein. Haemolymph (blood) in the pericardial cavity flow

into the ventricle through valvular openings called Ostia.

The haemolymph is then pumped out through the arteries.

There are also valvular muscles between the ventricle and the arteries, the cardio-arterial valves.

The heart as a pumpIn order for the heart to work as a pump,

the intake valves (Ostia) must be closed and the outlet valves (cardio-arterial valves) opened during systole, and vice versa during diastole

The cardio-arterial valves and the Ostia in the crayfish heart seem to work like the air pump for an air bed is a good example for the use of the passive valves. In the air pump,  simple flaps work as the valves, and the pressure change in the pump makes them open and close.

Human Heart and circulationMammals have a four-chambered heart consisting of two atria and two

ventricles; the right and left sides are completely separate from each other so there is no mixing of oxygenated and deoxygenated blood.

Oxygenated blood from the pulmonary veins enters the heart through the left atrium, passes to the left ventricle, and leaves the heart through the aorta.

Deoxygenated blood from the vena cava enters the right atrium and is pumped through the right ventricle to the pulmonary artery, which conveys it to the lungs for oxygenation.

The tricuspid and bicuspid valves ensure that there is no backflow of blood.

The contractions of the heart are initiated and controlled by the sinoatrial node ; an average adult human heart contracts about 70 times per minute.

Circulation

Circulatory systems of an insect

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.

Structure of an artery.

ActivityDescribe the following terms: Molluscs Haemocoel Vertebrates Invertebrates Blood Species Arachnids Evolution Organ Chordates Amphioxus Ventricle Pericardial cavity Cardiac ganglion Ostia Cardio-arterial Valves 

 

References http://www2.gsu.edu/~bioasx/zindex.htm http://science.jrank.org/pages/15595/heart.html#ixzz0kTtppJws http://science.jrank.org/pages/3248/Heart.html#ixzz0kTuRF7G8 http://mackers.com/crayfish/info.htm#internal Images from Purves et al., Life: The Science of Biology, 4th

Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.

http://www2.gsu.edu/~bioasx/closeopen.html http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookcirc

SYS.html http://cas.bellarmine.edu/tietjen/images/Circulation.htm Songs: Black Eyed Peas - Don't Funk With My Heart.mp3

Billy Ray Cyrus - Achy Breaky Heart.mp3 School House Rocks - Do The Circulation.mp3 Black Eyed Peas - Pump It.mp3