Study

1. Systemic circulation
By: Riham El Fawal

2. Objectives
At the end of the lecture, you will be able to:
• Enumerate different types of blood circulations
• Define systemic circulation
• Enlist the factor affecting blood flow & systemic circulation
• Differentiate between central venous pressure & peripheral venous
pressure.

3. CIRCULATION:
IS MOVEMENT OF BLOOD IN THE BODY.
it is divided into the
-systemic circulation and
-pulmonary circulation.
SYSTEMIC CIRCULATION:
The general circulation, carrying oxygenated blood from the left ventricle to the
body tissue and returning venous blood to the right atrium is called systemic
circulation.
It supplies all the tissues of the body except lungs. Its is also called as greater
circulation or peripheral circulation.

5. SYSTEMIC CIRCULATION
• The systemic circulation provides the functional blood supply to
all body tissue. It carries oxygen and nutrients to the cells and
picks up carbon dioxide and waste products.
• Systemic circulation carries oxygenated blood from the left
ventricle, through the arteries, to the capillaries in the tissues of
the body.
From the tissue capillaries, the deoxygenated blood returns
through a system of veins to the right atrium of the heart.

6. Various physical characteristics of systemic circulation:
These either directly or indirectly affects the systemic circulation and are interrelated to
each other.
1.Cross sectional area of the vessels.
2. Pressure in various portions.
3. Resistance provided by various structures.
4. Venous return
5. Blood flow
6. Vascular distensiblity.
7. Vascular compliance.

7. I. Cross sectional area:
It is the diameter of the vessel. The velocity of blood flow in each segment of the circulation
is inversely proportional to its cross-sectional area.
Total crossectional area (cm2) Average velocity of blood flow
Aorta 4.5 40 cm/sec
Small arteries 72 (16times that of aorta) 1.4 cm/sec
Arterioles 400 0.5 mm/sec
Capillaries 4500 (1000 times that of aorta 0.3 mm/sec
Small veins 80 1-2 cm/sec
Inferior vena cava and superior vena
cava
18 7-10 cm/sec

8. II. Pressure in various portions:
Pressure means the force exerted by the blood against any unit area of the
vessel walls. It is divided as:
-arterial pressure
-venous pressure
Pressure in major vessels are as follows
Left ventricle 120 mmHg
Aorta and its larger branches 120 mmHg
Arterioles 60 mmHg
Metarterioles 40 mmHg
Capillaries 25 mmHg
Venules and larger veins 10 mmHg
Vena cava(superior and inferior) 2 mmHg

9. Venous pressure:
is pressure exerted by the contained blood in the veins. It of 2 types:
1. Central venous pressure
(CVP)
2. Peripheral venous pressure (PVP)
Blood from all systemic veins
flow into right atrium, therefore
right atrium pressure is called
central venous pressure.
Normally it is 1-6 mmHg.
It is the pressure in peripheral veins.
Large veins offer considerable resistance to
blood flow because they remain compressed
at many points by the surrounding tissues.
e.g abdominal veins by diff. organs and intra-
abdominal pressure, arm veins by first rib and
neck vein by atmospheric pressure.
It is about 10 mmHg.

10. III. VENOUS RETURN:
The quality of blood flowing from veins into the right atrium per minute
Factors affecting venous return
 Venous pressure
 Position of the body: From lying to standing – increase of
the blood in veins – dilation of veins in the lower part of the
body – decrease of venous return
 Action of “muscular pump”
 Respiration movement.
 Gravity

11. IV. RESISTANCE OF VARIOUS STRUCTURES:
Arterioles, metarterioles and pre- capillary sphincters provide
internal resistance to circulation where as skin and skeletal muscle
provides peripheral resistance.

12. V. BLOOD FLOW:
Blood flow means simply the quantity of blood that passes a given point in the circulation in
a given period.
Factors determining blood flow are:
• Pressure gradient i.e.: p1- p2
Where p1 is pressure at proximal end of vessel & p2 pressure at distal end of
vessel. Pressure gradient is directly proportional to blood flow.
• Viscosity of blood: volume of blood flow is inversely proportional to
viscosity of blood.
• Diameter of blood vessels: volume of blood flow is directly proportional to
the diameter of vessel.
• Resistance to blood flow: Resistance= pressure gradient/volume of blood
flow

13. Relationship among pressure, flow and resistance:
• According to OHM’S law:
F=ΔP/R
Where F= blood flow
ΔP= pressure gradient
R= vascular resistance

14. VI. VASCULAR DISTENSIBILITY:
• When the pressure in blood vessels is increased, this dilates the blood
vessels and therefore decreases their resistance.
• The result is increased blood flow not only because of increased pressure but
also because of decreased resistance.
• The most distensible by far of all the vessels are the veins. Even slight
increases in venous pressure cause the veins to store 0.5 to 1.0 liter of extra
blood.
• Therefore, the veins provide a reservoir function for storing large quantities
of extra blood that can be called into use whenever required elsewhere in
the circulation.

15. VII. VASCULAR COMPLAINCE
• It is Important to know the total quantity of blood that can be stored in a
given portion of the circulation for each millimeter of mercury pressure rise
than to know the distensibilities of the individual vessels.
• This value is called the compliance or capacitance of the respective vascular
bed; that is,