Transcript Circulatory System

Circulatory System
Why the need?
Why do organisms need a circulatory system?
To exchange materials with their environment
– nutrients, wastes, O2, CO2, etc.,
• Organisms need a system that will do this.
• The more complex the organism, the more
complex this system must be.
• Unicellular organisms, and those that have
few layers of cells - rely on diffusion and
exocytosis.
Two Types of Circulatory Systems
1. Open Circulatory Systems
• Arthropods (insects, spiders lobsters etc.,)
– blood is pumped by the heart through simple
open ended tube – it flows through the body
cavity, bathing the internal organs.
2. Closed circulatory system
More efficient system
Found in higher invertebrates (ex earthworm) and all
invertebrates
Cardiovascular Systems of
Vertebrates
• Composed of a heart, arteries and veins.
• blood stays in the circulatory system
• chemicals are exchanged by diffusion at
capillaries.
Heart
• A specialized muscle that contracts regularly
and continuously, pumping blood to the body
• May be two, three or four chambered.
– Two - fish
– Three – frogs
– Four – humans
Heart
• Chambers are called atria (receive blood from
veins) and ventricles (send blood to the
arteries)
Arterial to Venule System
• Arteries carry blood away from the heart
– Aorta divides into arteries which divide to
form arterioles.
Arterial to Venule System
• Veins carry blood to the heart
– Venules become Veins, which become the
Vena cava
• The finest (smallest) divisions of the vascular
system are capillaries
• Where arterioles transition to venules.
The distinction between arteries and veins is by direction
of blood flow, not oxygen content.
• Veins carry blood toward the heart
• Arteries carry it away from the heart.
• Because of this, not all arteries carry
oxygenated blood.
• Two major arteries do not carry oxygenated
blood.
1. The pulmonary artery carries deoxygenated
blood from the heart to the lungs (to pick up
oxygen there)
2. The umbilical arteries which carry
deoxygenated blood away from the baby’s
body to the placenta (to pick up oxygen
there).
• Higher vertebrates have double circulation:
– Right side a pump for the pulmonary circuit (to
the lungs)
– Left side is pump for the systemic circuit (to the
body)
– Because the left side has to pump to a larger area
the muscles of the left ventricle are larger than
those of the right
Pulse
• Absent in veins
• Blood is moved by:
1. The contraction of the muscles surrounding the
veins
2. Gravity
3. The contracting heart pulls blood along the veins
towards it.
Blood is prevented from flowing back by valves.