biology 201 dr. edwin demont st. francis xavier university circulation
TRANSCRIPT
Biology 201Dr. Edwin DeMont
St. Francis Xavier University
Circulation
St. Francis Xavier University
Circulation
The evolution of multicellularity required the development of fluid transport systems.
Why?
St. Francis Xavier University
Circulation
An internal transport system is useful because it reduces the distances over which substances must
diffuse—substances can be brought close to a target point via the blood and then diffuse outward from
that point
St. Francis Xavier University
Circulatory Systems
Internal transport systems of invertebrates range from simple fluid filled cavities to open systems and
some even have closed systems, analogous to vertebrate systems.
Open circulatory system: the heart pumps fluid out into the body cavity or at least to parts of the body
cavity, and bathes the cells, tissues and organs.
Closed circulatory system: fluid circulates in the confines of tubular vessels.
St. Francis Xavier University
Transport Systems
St. Francis Xavier University
Transport Systems
St. Francis Xavier University
Circulatory Systems
Fluid: Hemolymph High volume and slow circulation
Cells: Hemocytes
St. Francis Xavier University
Circulatory Systems
Blood is always in arteries, arterioles, capillaries, venules, veins, or within
the chambers of the heart.
St. Francis Xavier University
Fluid flow
Heart generates high pressure.
Blood moves at high velocity.
Total cross-sectional area of capillaries is large and velocity of flow is very
small.
Diffusion occurs here so need low velocity.
Best to move blood over large distances in
large vessels.
St. Francis Xavier University
Vertebrates
The disadvantage of this system is the low
pressure flow through the gills supports only a
low metabolic rate.
Energy is lost as the blood flows
through the capillaries – why?
St. Francis Xavier University
Vertebrates
A double circuit occurs when blood from the lungs is sent directly to the heart, and blood from the tissues
also goes to the heart—these systems are the
pulmonary and systemic circulations, respectively
St. Francis Xavier University
Blood vessels
Arteries are characterized as elastic vessels that carry blood away from the heart (high pressure).
Veins are larger, less elastic vessels that carry blood to the heart (low pressure).
Capillaries are one cell layer
thick – to allow diffusion.
St. Francis Xavier University
Blood
Blood contains a fluid matrix called plasma and cellular elements called formed elements.
Plasma is primarily composed of water, and also contains proteins, ions, hormones, nutrients, and
wastes.
St. Francis Xavier University
Blood: Formed elements
Erythrocytes (red blood cells) contain hemoglobin, which binds to oxygen for transport from lungs to other tissues.
Leukocytes (white blood cells). These cells function in immunity.
Thrombocytes (platelets). They function in clotting of the blood in response to injury.
St. Francis Xavier University
Red Blood Cells
Each cell has about 280 million molecules of hemoglobin.
The biconcave shape of RBCs is adaptive, as it gives 30% more surface area than a sphere.
RBCs are slightly larger than capillaries and have to squeeze through the
tiny capillaries.
This is adaptive. Why?