Download Circulatory Systems 1 - Learning on the Loop

Animal Circulatory Systems
Chapter 44: pp. 944-1003
• Types of circulatory systems:
gastrovascular, open, closed.
• Vascular system: arteries, veins, capillaries.
• Capillary - tissue fluid exchange.
Absence of a Circulatory System
• Very small animals may not need a circulatory
system.
• Small size may permit nutrients and other
substances to reach all the body parts by simple
diffusion
figure 49-01.jpg
Larger Animals Without a Separate Circulatory System
Cnidarian Gastrovascular Systems
Some larger animals such as
sea anemones, jellyfish, and
flatworms lack a true
circulatory system.
The gastrovascular cavity
extends to most areas of the
body in these animals and
serves as a circulatory
system as well as a
digestive cavity.
Flatworm Gastrovascular System
Circulatory Systems
For larger or more active animals, some form of
more efficient circulatory system is necessary for
internal transport.
• Two types of circulatory system are found:
Open Circulatory Systems
Closed Circulatory Systems
Open Circulatory System
• Hemolymph leaves the
heart in short, branched
arteries that open up into
large spaces called sinuses.
• Hemolymph percolates
around organs, directly
bathing the cells.
• Hemolymph then returns to
the heart directly or through
short veins.
Open Circulatory System
• Advantage - Exchange of materials is direct
between the hemolymph and tissues. There
is no diffusion barrier.
• Disadvantage - Little fine control over
distribution of the hemolymph to body
regions. No mechanism for reducing flow to
a specific part of an organ.
Open Circulatory System
• Open circulatory systems tend to be found in more
inactive animals.
• Most molluscs have an open system, but the
highly active cephalopods (squid and octopus)
have evolved a closed system.
• Insects have circumvented limitation of their open
system by their tracheal system for oxygen supply.
Closed Circulatory System
• The blood is contained
within a completely closed
system of vessels.
• Vessels form a closed
loop, usually with some
sort of pumping organ like
a heart or contractile
vessels.
• Vessels branch into
smaller and smaller tubes
that penetrate among the
cells of tissues.
Closed Circulatory System
Advantages:
• Fine-scale control over the distribution of blood
to different body regions is possible.
• Muscular walls of vessels can constrict and dilate
to vary the amount of flow through specific
vessels.
• Blood pressures are fairly high and the circulation
can be vigorous.
Extensive
capillary beds:
Earthworm Circulation
Body wall
Gut wall
Excretory tubules
Coelomic Cavities - Circulatory Function
• Coelomic cavities are filled with fluid that can
transport materials around the body.
• Nematode worms have an extensive body cavity,
the pseudocoel, but lack a separate circulatory
system.
Ascaris
Cross-Section
Pseudocoel
(fluid-filled space)
The Vertebrate Vascular System: Arteries,
Veins, and Capillaries
Arteries and arterioles
have a layer of smooth
muscle tissue which
allows them to contract
(vasoconstrict) and
expand (vasodilate),
altering their diameter
and thus blood flow.
Walls of arteries and
arterioles have many
elastic fibers enabling
them to withstand high
pressures.
Artery and Vein
Artery
Vein
Note the much
thinner walls in
veins.
Blood Pressure
and
Flow Velocity
Capillaries
• Capillaries are very small,
about the diameter of a red
blood cell (8µm or less).
• Capillary walls are a single
layer of very thin endothelial
cells, attached at their edges
and surrounded by a basement
membrane (extracellular
matrix).
Endothelial cells
Filtration; fluid and
small, lipid-insoluble
molecules (water,
amino acids,
NaCl, glucose,
urea)
Diffusion;
lipid-soluble
molecules
(O2, CO2,
lipids)
Vesicles; large,
lipid-insoluble
(proteins)
Blood cells,
most
proteins.
Capillary - Tissue Fluid Exchange
Blood hydrostatic pressure exceeds the opposing
negative colloidal osmotic potential of the blood plasma.
Water, containing small dissolved molecules, is forced out of
the capillary through small pores in the capillary wall by the
excess hydrostatic pressure.
Capillary Fluid Exchanges
Blood pressure
(hydrostatic)
32 mm Hg
Plasma colloidal
osmotic potential
-22 mm Hg
Net pressure
10 mm Hg
Capillary Fluid Exchanges
Frictional
Blood pressure
(hydrostatic)
resistance
32 mm Hg
Blood pressure
(hydrostatic)
15 mm Hg
Plasma colloidal
osmotic potential
Plasma colloidal
osmotic potential
-22 mm Hg
-22 mm Hg
Net pressure
10 mm Hg
Net pressure
-7 mm Hg
Less water re-enters the capillary than
originally left at the arterial end.
The Lymphatic System
The lymphatic system,
returns excess tissue
fluid to the blood.
Capillary - Tissue Fluid Exchange
• The bulk flow of fluid out of the capillary
exchanges material much faster than would be
possible by simple diffusion alone.
• Nutrients and O2 are released to the tissues
rapidly.
• Wastes from cell metabolism are more rapidly
cleared away by the circulatory system.
Control of Capillary Circulation
• Arteries and arterioles that feed blood to the
capillaries contain a circular layer of smooth
muscle in their walls.
• Contraction of these smooth muscles
(vasoconstriction) is important in controlling the
blood flow through capillary beds.
• Relaxation of smooth muscles results in
vasodilation, an expansion of the vessel diameter
that increases blood flow.
figure 49-18.jpg
Circulatory Patterns in
Vertebrates
The circulatory pattern has been
modified during evolution of the major
groups of vertebrates.
(and capillaries)
Cardiac cycle
Blood flow in veins
One-way flow of blood (toward heart) is
determined by valves.
Human
blood
components