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Circulation
By Nick Onuska
Evolutionary Development of
Circulation
In unicellular protists, nutrients and oxygen can
be obtained by basic diffusion in an aquatic
environment
 This is true because of the simple body structure
of the animals
 In larger animals, cells and tissues are simply
too far away from the surface or digestive cavity
to obtain oxygen in this way
 Instead, they obtain oxygen through an internal
fluid

– This is the circulatory system
Evolutionary Development of
Circulation

Two main types of circulation
– Open
– Closed

In an open system there is no
distinction between the blood
and the extracellular fluid
– This fluid is known as
hemolymph

In a closed system, the blood
is always enclosed with blood
vessels that transport it to a
pumping system.
– Ex. Heart
Purpose of Circulatory System

The circulator system serves several
purposes
– Transportation
– Regulation
– Protection
Transportation

Substances needed for cellular metabolism
are transported by the circulatory system
– This can be broken down into
 Respiratory: Red blood cells carry oxygen and CO2
 Nutritive: Nutrients from broken down food
 Excretory: Waste products being transferred top
kidneys
Regulation

The circulatory system helps to regulate
the body by transporting hormones and
regulating temperature
– Hormone Transport: Carries hormones from
endocrine glands
– Temperature Regulation: Maintains
temperature by using countercurrent heat
exchange
Protection

The circulatory system protects the body
from injury and toxins
– Blood Clotting: Prevents against blood loss
– Immune Defense: White blood cells provide
immunity against disease
Structure and Function of the
Circulatory system
Blood
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Blood is made up of a
fluid called plasma
and several different
types of cells that
exist in this fluid
 Metabolites, wastes,
and hormones
 Ions
 Proteins

Metabolites, wastes, and hormones

Plasma contains many dissolved
metabolites that are used by cells
– Ex. Glucose, Amino Acids, and vitamins
Hormones that regulate cell activity are
also dissolved in plasma
 In addition, wastes like CO2 are also
contained and transported in plasma

Ions
Similar to a sea,
plasma is a salt
solution
 It contains many
different ions

– Ex. Na+, Cl+,
bicarbonate ions

However, plasma has
a lower ion
concentration then
seawater
Proteins

Most proteins in plasma are produced by
the liver
– Albumin: Most of the plasma protein
– Alpha and Beta Globulins: Carry lipid and
steroid hormones
– Fibrinogen: essential for clotting

Plasma without Fibrinogen is known as
serum
Types of Blood Cells

Erythrocytes

Leukocytes

Platelets
Erythrocytes



Erythrocytes are also
known as red blood cells
In vertebrates,
Erythrocytes contain
hemoglobin, a substance
that transports oxygen
Erythrocytes also develop
from stem cells and are
constantly developed in
the bone marrow
Leukocytes
Leukocytes are also known as white blood cells.
Their primary job is to defend the body
 There are several kinds of Leukocytes each with
their own specialized functions
 Granular leukocytes

– Neutrophils
– Eosinophils
– Basophils

Non Granular leukocytes
– Monocytes
– Lymphocytes
Platelets
The primary goal of
Platelets is to help
blood to clot
 They come from
Megakaryocytes,
large cells in bone
marrow

– A piece of the
cytoplasm is pinched
off and becomes a
platelet
Platelets
When a blood vessel
breaks, platelets build
up at the site and
plug it up by sticking
to each other
 The protein fibrin
reinforces this plug
 Often red bloods are
caught in this plug
and create a blood
clot

Blood Vessels

Blood exits the heart
through vessels called
arteries.
– These eventually branch
out, reaching every organ
in the body

The smallest vessels are
known as arterioles
– Blood from these enters
the capillaries, a large
quantity of very narrow,
thin walled tubes
Blood Vessels

After leaving the capillaries, blood flows into the
vessels which will eventually lead back to vessels
called veins
– Veins carry blood back to the heart
The walls of capillaries are thin enough that
molecules and ions can diffuse out of them,
leave by filtration from pores on the cell, or
transport through the endothelial cells.
 This means that blood traveling in capillaries
exchanges nutrients with fluids and cells in the
body

Arteries
Arteries
Arteries work by transporting blood away
from the heart
 Arteries often have elastic fibers that allow
them to recoil along with the beating of
the heart
 Having so many arteries often presents a
risk with friction

– Smaller arteries have the highest resistance
Arteries

There are several ways Arteries can get around
this resistance
– Vasoconstriction: contracts smooth muscle, increase
resistance, decreases flow
– Vasodilatation: relaxes smooth muscle, decreases
resistance, increases blood flow

Some organs regulate blood flow by a ring of
muscle around the arteroids where they empty
into capillaries
– Known as precapillary sphincters
Exchange in Capillaries
Exchange in Capillaries

Capillaries are very small
– 1mm in long and 8 micrometers in diameter
– However, the is a very large amount of
Capillaries in the human body

This allows blood more time to exchange
molecules with extracellular fluid
Venules and Veins
Blood flows back to
the heart in Venules
and Veins
 The have the same
tissue layers as
arteries
 However, the pressure
in veins is much less,
so less smooth
muscle is needed

Venules and Veins

Sometimes the
pressure in veins is
not enough to return
the blood back to the
heart
– In that case, muscles
around the vein
contract around it.
 This is called venous
pump
Lymphatic System

The circulatory system is consider closed
– There are no open ended vessels

However, water and solutes enter the
walls of capillaries
– Interstital (tissue) fluid
Lymphatic System
This is caused by the pressure of blood
and helps to supply tissues with oxygen
and other molecules and nutrients
 Fluid return occurs due to osmosis
 If blood pressure is too high, interstital
fluid would start to build up

– However, excess fluid drains into the lymph
node
Lymphatic System

This fluid, now known
as lymph, travels
though vein like
structures and
eventually dumps into
veins on the side of
the neck.
Interdependence

The circulatory and respiratory systems
are very closely related
– The respiratory system draws oxygen into the
lungs
– The circulatory system exchanges carbon
dioxide for oxygen.
– The respiratory system expels the waste gas
during exhalation
– The circulatory system delivers oxygen to cells
throughout the body
REMEMBER!
Vertebrates have a closed circulatory
systems
 Blood is fluid plasma in which different
types of cells are suspended
 Blood leaves through arteries and travels
back though veins
 Diffusion occurs in capillaries

Diseases and Disorders
Anemia: Anemia occurs when there is a below
normal level of red blood cells. This can be
caused by a poor diet or excessive bleeding
 Hypertension: Elevated blood pressure caused
by a hardening of the arteries over time. Once
the arteries have hardened, they can no longer
regulate pressure
 Thrombosis: a clot in vessels that blocks the
path to the heart. Often caused by cholesterol
deposits and the narrowing of blood vessels
disrupts the secretion of prostacyclin and causes
clots
