1. © SSER Ltd.

2. The Mammalian Circulatory System
The mammalian circulatory system is a vast network of blood-filled
vessels that delivers blood to every cell of the organism
The circulatory system is a mass flow system, moving blood
on mass from one part of an organism to another
The circulatory system is essential for ensuring that materials are transported between the various exchange surfaces of the organism
The heart, together
with the blood vessels and the
blood that they contain forms
THE CIRCULATORY SYSTEM
The capillaries of the blood system are the sites for
exchange of materials between the blood and the tissues
The capillary networks surrounding the alveoli of
the lungs are the sites at which gas exchange takes place
The capillary networks within the villi of the small intestine
receive and transport the digested food materials needed
by the cells of the organism
The circulatory system
is linked with exchange
surfaces

3. The Human Circulatory System is a Double Circulation
The human heart,
except during fetal
life, is completely
divided into right
and left sides
The LEFT SIDE
of the heart
receives
OXYGENATED
BLOOD
from the lungs
and then delivers
it to the body
tissues
The heart has four
chambers with an
upper and a lower
chamber on each
side
The upper chambers
are the right and
left atria
(RA and LA), and
the lower chambers
are the ventricles
(RV and LV)
The RIGHT SIDE
of the heart
receives
DEOXYGENATED
BLOOD
from the body
tissues and then
delivers it to the
lungs
Blood always enters
the heart along
veins, which deliver
blood to the atria
Blood is pumped
away from the
heart along arteries,
which originate in
the ventricles
LORD

4. LORD Left side of the heart receives Oxygenated blood and delivers
it to the body tissues
LORD
Right side of the heart receives
Deoxygenated blood and
delivers it to the lungs

5. The Human Circulatory System is a Double Circulation
The heart pumps
oxygenated blood
TO the body tissues
and receives
deoxygenated blood
FROM the body
tissues
The heart pumps
deoxygenated blood
TO the lungs
and receives
oxygenated blood
FROM the lungs
This circuit in which
blood flows from the
heart TO the body
systems and back
to the heart is called
THE
SYSTEMIC
CIRCULATION
This circuit in which
blood flows from the
heart TO the lungs
and back to the
heart is called
THE
PULMONARY
CIRCULATION
The human circulation is a double circulation as there are two distinct
circuits along which blood flows

6. Naming The Blood Vessels
The CAROTID
ARTERY delivers
oxygenated blood
to the neck,
head and brain
THE PULMONARY VEIN
delivers oxygenated blood
from the lungs to the LEFT
ATRIUM of the heart
The oxygenated blood enters
the LEFT VENTRICLE,
which pumps the blood
along the AORTA towards
the body organs
Deoxygenated blood
enters the right
ventricle from where
it is pumped to the
lungs along the
PULMONARY ARTERY
Veins carry deoxygenated blood
away from the body organs. The
veins join to form two large veins
called the VENAE CAVAE
Smaller arteries branch
from the AORTA in order
to deliver this oxygenated
blood into the various organs
The CORONARY ARTERIES
deliver oxygenated blood to
the heart muscle
The VENAE CAVAE deliver
deoxygenated blood
to the RIGHT ATRIUM
of the heart
HEPATIC
VEIN
RENAL
The HEPATIC ARTERY
delivers oxygenated blood to
the liver
HEPATIC
PORTAL
VEIN
The liver receives blood
from BOTH the hepatic
artery AND the
HEPATIC PORTAL
VEIN
The RENAL ARTERIES
deliver oxygenated blood
to the kidneys
The hepatic portal vein carries blood, rich in the products of digestion, from the gut to the liver

7. Capillaries and Metabolic Exchange
The walls of the capillaries are only one cell
thick and composed of flattened or squamous
epithelium called the endothelium
The endothelium rests on a basement membrane
Capillaries are referred to as the exchange vessels,
since all the exchange of materials between the blood
and living cells takes place through their walls
The lumen of the capillary is just large enough for
red cells to move along in single file
Capillaries are so extensive that they permeate
between and around all body cells
The human body contains about 40,000 kilometres
of capillaries which is enough to circumscribe the
earth at the equator
At the capillaries, metabolites such as oxygen and nutrients diffuse from the blood into the respiring
tissues. Metabolites such as carbon dioxide and other waste materials diffuse from the tissues into the blood
As blood in the capillaries is always moving, then steep concentration gradients for oxygen, carbon dioxide and nutrients will persist across the capillary walls

8. Capillaries and Metabolic Exchange
Most materials enter and leave the blood by diffusion
According to Fick’s Law...
Rate of diffusion =
surface area x difference in concentration
thickness of exchange surface
The efficient rates of diffusion between the blood and
body cells occur as a result of:
the large surface area presented by the capillaries
the large differences in concentration of metabolites
between the blood and the cells
the thinness of the capillary walls

9. Capillaries and Metabolic Exchange
This cross-section of a capillary shows two endothelial cells forming
the wall around the lumen
The nucleus of one of
the endothelial cells
(coloured red) is visible
whilst the nucleus
of the other cell is
located in a different
plane and hence
not visible within
this thin section
Capillary Cross Section
Endothelial cells
The two epithelial cells
are separated from
one another by very
narrow gaps or
capillary pores
through which most
small molecules
cross the wall by
diffusion
LUMEN
Capillary pore
Some larger molecules
pass through the
endothelial cells by
pinocytosis
The wall of the
capillary rests upon
a basement membrane

10. Capillaries and Tissue Fluid Formation
The cells of the body are bathed in a fluid called tissue fluid
Tissue fluid is essential for the efficient exchange of materials
between the blood and the cells
Tissue fluid is formed at the arteriole end of the capillaries
CAPILLARY
TISSUE FLUID
Arteriole end
of capillary
Venule end
BODY
CELLS

11. Summary of Tissue Fluid Formation
At the arteriole end of the capillary, the outward hydrostatic pressure is
GREATER than the inward osmotic pull
Water, ions and small molecules are filtered out of the blood into the
spaces between the cells - this is tissue fluid
The loss of fluid from the blood leads to a fall in hydrostatic pressure as
the blood approaches the venule end of the capillary
At the venule end of the capillary, the inward osmotic pull now exceeds
the outward hydrostatic pressure and some of the water re-enters the
capillary by osmosis
Tissue fluid is drained away from the cells by the lymphatic system and returned
to the circulation near the heart
CAPILLARY
TISSUE FLUID
Arteriole end
of capillary
Venule end
BODY
CELLS
Hydrostatic
pressure (kPa)
1.6
1.8
4.3

12. lymphatic cells tissue fluid
small artery
lymphatic
small vein
cells
arteriole
venule
capillaries
tissue fluid
Tissue fluid is:
constantly being formed at the arteriole end of capillary beds
essential for the efficient exchange of materials between the blood and the cells
is constantly being drained away from the cells by lymph vessels

13. Acknowledgements
Copyright © 2003 SSER Ltd. and its licensors. All rights reserved. All graphics are for viewing purposes only.