Transcript The mammalian circulatory system is a vast network of blood

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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 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 heart, together
The circulatory system
with the blood vessels and the
is linked with exchange blood that they contain forms
surfaces
THE CIRCULATORY SYSTEM
The Human Circulatory System is a Double Circulation
The human heart,
except during fetal
life, is completely
divided into right
and left sides
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)
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
CAPILLARIES
IN LUNGS
RA
RV
The LEFT SIDE
of the heart
receives
OXYGENATED
BLOOD
from the lungs
and then delivers
it to the body
tissues
LA
LV
CAPILLARIES
AROUND
BODY TISSUES
LORD
The RIGHT SIDE
of the heart
receives
DEOXYGENATED
BLOOD
from the body
tissues and then
delivers it to the
lungs
Left side of the heart receives
Oxygenated blood and delivers
it to the body tissues
Right side of the heart receives
Deoxygenated blood and
delivers it to the lungs
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
CAPILLARIES
IN LUNGS
RA
This circuit in which
blood flows from the
heart TO the body
systems and back
to the heart is called
THE
SYSTEMIC
CIRCULATION
RV
The heart pumps
deoxygenated blood
TO the lungs
and receives
oxygenated blood
FROM the lungs
LA
LV
This circuit in which
blood flows from the
heart TO the lungs
and back to the
heart is called
THE
PULMONARY
CIRCULATION
CAPILLARIES
AROUND
BODY TISSUES
The human circulation is a double circulation as there are two distinct
circuits along which blood flows
Naming The Blood Vessels
The CAROTID
ARTERY delivers
oxygenated blood
to the neck,
head and brain
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
The VENAE CAVAE deliver
deoxygenated blood
to the RIGHT ATRIUM
HEPATIC
of the heart
VEIN
The liver receives blood HEPATIC
from BOTH the hepatic PORTAL
artery AND the
VEIN
HEPATIC PORTAL
VEIN
RENAL
VEIN
lungs
head
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
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
liver
gut
kidneys
other body
organs
The HEPATIC ARTERY
delivers oxygenated blood to
the liver
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
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
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
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
Endothelial cells
whilst the nucleus
of the other cell is
The two epithelial cells
located in a different
are separated from
plane and hence
one another by very
not visible within
narrow gaps or
this thin section
capillary pores
LUMEN
through which most
small molecules
cross the wall by
Capillary pore
diffusion
Some larger molecules
pass through the
endothelial cells by
pinocytosis
The wall of the
capillary rests upon
a basement membrane
Capillary Cross Section
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
Arteriole end
of capillary
CAPILLARY
TISSUE FLUID
BODY
CELLS
Venule end
of capillary
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
Arteriole end
Venule end
of capillary
of capillary
Hydrostatic
pressure
(kPa)
4.3
CAPILLARY
1.8
BODY
CELLS
1.6
TISSUE FLUID
1.8
small artery
small vein
lymphatic
cells
arteriole
capillaries
venule
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
Acknowledgements
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