Primary Functions
Transport oxygen and nutrients to
actively metabolizing tissues.
Remove carbon dioxide and other waste
products from tissues.
Transport signaling molecules and
immune cells throughout the body.
Diffusion
Unicellular organisms and some small
metazoans lack cardiovascular systems.
Rely on diffusion to transport molecules.
Slow across long distances.
Bulk Flow
Limitation on the rate of diffusion so
larger animals move fluids through their
body by a process called bulk flow
Occurs within a series of chambers &
tubes.
Faster across long distances than diffusion
Circulation Time
Mammal Body Mass
(kg)
Circulation
Time (sec)
Elephant 4000 140
Horse 700 90
Human 70 50-60
Rat 0.2 12
Shrew 0.003 4
Exercising Human = 12 seconds
Exercising Shrew = 1 second
Circulatory Systems
3 Main Components:
1. 1≤ pumps apply force to drive fluid flow.
2. A system of tubes, channels, or spaces through which the fluid can flow.
3. A fluid that circulates through the system.
Substantial diversity among animals
Pumping Structures
Chambered hearts:
◦ Chamber(s) that circulatory fluid first
enters is/are called atrium/atria
◦ Function as both reservoirs and pumps.
◦ Fluid flows from an atrium into a
muscular chamber called a ventricle.
◦ Functions as primary pump.
Open Circulatory Systems
Circulatory fluids flow through open
spaces called sinuses.
Sinuses allow circulatory fluids to make
direct contact with tissues.
Circulatory fluids therefore mix with
extracellular fluids.
Closed Circulatory Systems
Circulatory fluids flow through enclosed
blood vessels.
Blood vessels have specialized lining that
separates circulatory fluids from tissues.
Complete separation of circulatory fluid
and extracellular fluid.
Circulatory Fluids
Interstitial Fluid
◦ Extracellular fluid directly bathes tissues
Blood
◦ Closed circulatory systems.
Hemolymph
◦ Open circulatory systems
Sponges, Cnidarians and Flatworms
All lack a true circulatory system.
All have mechanisms for propelling fluid
around their bodies.
The bulk flow of fluids is part of a
combined respiratory, digestive, and
circulatory system.
Sponges, Cnidarians and Flatworms
The bulk flow of fluids is part of a combined
respiratory, digestive, and circulatory system.
Annelids
Most have closed
circulatory systems
◦ Polychaetes = tube worms
Some have open circulatory
systems
◦ Oligochaetes = earth worms
Series of small blood vessels
connect large dorsal and ventral
blood vessels
Mollusks
Most have open circulatory systems
◦ All have hearts or contractile organs
◦ Some have blood vessels
Mollusks: Squid & Octopuses
Have 3 muscular chambered hearts:
The systemic heart pumps oxygenated blood to the body.
Deoxygenated blood flows into the two branchial hearts that pump blood through the gills.
From the gills the oxygenated blood flows back into the systemic heart.
Vertebrates
All have closed circulatory systems.
◦ Blood remains within blood vessels
throughout all points of circulation.
Advantages:
◦ Ability to generate high pressure and flow
◦ Ability to control and direct blood flow to
specific tissues
Blood
Circulatory fluid in closed systems.
Plays many roles:
◦ Provide constant internal environment
◦ Transports – nutrients, oxygen, wastes
products, immune cells, and signaling
molecules around the body.
Composition of Vertebrate Blood
Blood Plasma:
◦ mostly water (93% by volume)
◦ contains dissolved proteins, glucose, clotting factors, dissolved ions, hormones and CO2
White Blood Cells = Leukocytes
◦ Immune System Cells
Red Blood Cells (RBCs) = erythrocytes
◦ Main Function = transport of oxygen
Red Blood Cells
Mammalian RBCs lack nuclei, mitochondria,
and other organelles including ribosomes.
Most mammalian RBCs are shaped like
biconcave disks.
Contain oxygen high concentration of binding
protein hemoglobin (Hb).
Red Blood Cells
Hb: increases the maximum amount of
oxygen that blood can carry by 50x
When you increase Hb you increase you
oxygen storage capacity of blood and
your ability to deliver oxygen to tissues.
Red Blood Cells
Hematocrit (HCT) = % blood that is made up of erythorcytes (RBCs)
Varies substantially among vertebrates (20-65%)
Acclimation of humans to high altitude causes an increase in HCT.
Circulatory Plan of Vertebrates
Arteries: carry blood away from heart
Arterioles: arteries branch into arterioles
Capillary Beds: dense networks of thin walled capillaries
Venules: capillaries coalesce into venules
Veins: venules coalesce into veins, which return blood to the heart
Blood Vessels - Wall Structure
Blood vessels are hollow and tubular
◦ Lumen = hollow area
Composed of up to 3 Layers:
◦ Tunica Intima
◦ Tunica Media
◦ Tunica Externa
Blood Vessels - Wall Structure
Tunica Intima – inner-most layer
◦ Inner lining called the vascular endothelium
Tunica Media – middle layer
◦ Composed of smooth muscle and elastin
◦ Vasodilatation and vasoconstriction
Tunica Externa – outer-most layer
◦ Composed of collagen fibers
◦ Support and reinforce blood vessel
Blood Vessels - Wall Thickness
Arteries: large diameter & thick-walled
◦ Aorta - highly elastic with a thick tunica
externa.
◦ Arteries farther from heart have a thicker
tunica media and are highly muscular.
Blood Vessels - Wall Thickness
Arterioles: thinner walls and lack
extensive tunica externa.
◦ Larger arterioles - extensive tunica media
◦ Smaller arterioles = single layer of smooth
muscle around the endothelium
allows for vasoconstriction and vasodilatation
Blood Vessels - Wall Thickness
Capillaries: lack tunica media and
externa.
Very small diameter
Extremely thin walled:
◦ composed of a single sheet of epithelial cells.
◦ Allows substances to pass between the blood
and tissues.
Capillaries
Substances can move across walls by:
◦ Diffusion – lipid-soluble substances
◦ Vesicle transport – proteins
◦ Paracellular pathway – small molecules like
water and ions can pass through pores
between cells of the capillary walls.
Capillaries – Tunica Intima
Continuous capillaries:
◦ seal between cells not usually complete allowing
fluids and small molecules to pass.
Fenestrated capillaries:
◦ Cells of vascular endothelium have many pores.
Passage of small molecules and fluids is easy.
Sinusoidal capillaries:
◦ Most porous of all capillaries.
◦ Allows proteins to move across capillary wall.
Blood Vessels - Wall Thickness
Capillaries empty into venules, which lead
to veins that return blood to the heart.
Vein usually has a thinner wall and larger
lumen than a similarly sized artery.
Thin tunica media, thick tunica externa.