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1. Circulation
Dr. Abdirahman MBBS, MD.
GSU

2. Blood Circulation Dynamics
• Blood vessels
• Biophysics of blood flow
• Blood pressure
• Lymphatic circulation anatomy and
interstitial fluid uptake

3. Function of the Circulation
• To serve the needs of the body tissues
• To transport nutrients to the body
tissues
• To transport waste products away
• To transport hormones from one part of
the body to another
• To maintain an appropriate
environment for survival and optimal
function of the cells.

4. Blood Vessels
• Arteries and arterioles
• Capillaries
• Veins and venules

5. Arteries
• Their function is to transport blood
under high pressure to the tissues.
• Arteries have strong walls, and blood
flows at a high velocity.

6. Arterioles
• Arterioles are the last small branches
of the arterial system
• They act as control conduits through
which blood is released into the
capillaries.
• Arterioles have strong muscular walls
that can close or dilate them.
– Thus, capable of altering blood flow in
each tissue in response to its needs.

7. Capillaries
• Their function is to exchange;
– Fluid, nutrients, electrolytes, hormones,
and other substances between the blood
and the interstitial fluid.
• To serve this role;
– The capillary walls are thin
– They have numerous minute pores
permeable to water and other small
molecular substances.

8. Capillaries

9. Venules
• Collect blood from the capillaries.
• Gradually coalesce into progressively
larger veins.

10. Veins
• They transport blood from the venules
back to the heart.
• They serve as a major reservoir of extra
blood.
• Because the pressure in the venous
system is very low, the venous walls
are thin.
• The Veins Are Much More Distensible
Than the Arteries.

11. Blood Flow
• Blood flow means the quantity of blood
that passes a given point in the
circulation in a given period of time.
• Ordinarily, expressed in ml/min or
L/min.
• Blood flow in the total circulation of an
adult person at rest is about 5000
ml/min.
– This is called the cardiac output.

12. Laminar Flow
• When blood flows at a steady rate
through a long, smooth blood vessel, it
flows in streamlines, with each layer of
blood remaining the same distance
from the vessel wall.
• This type of flow is called laminar flow
or streamline flow.
• It is the opposite of turbulent flow.

13. Blood Flow

14. Turbulent Flow
• Turbulent flow means blood is flowing
in all directions in the vessel and
continually mixing within the vessel.
• Causes of Turbulent flow include:
– Rate of blood flow becomes too great
– Blood passes by an obstruction in a vessel
– Blood makes a sharp turn
– Blood passes over a rough surface

15. Blood Flow

16. Blood Pressure
• Blood pressure means the force exerted
by the blood against any unit area of the
vessel wall.
• Blood pressure almost always is
measured in millimeters of mercury (mm
Hg).
• Occasionally, pressure is measured in
centimeters of water (cm H2O).
• 1 mm Hg pressure equals 1.36 cm H2O
pressure

17. Blood Pressure
• Systolic pressure: Maximum pressure
exerted on the walls of arteries when
the left ventricles pushes blood
through the aortic valve into the aorta
during contraction.
• Diastolic pressure: the lower pressure
present at all times within the arteries
when the ventricles are at rest.

18. Lymphatic System
• Accessory route through which fluid
can flow from the interstitial spaces
into the blood.
• Can carry proteins and large particulate
matter away from the tissue spaces.
• It works in close cooperation with the
immune system.

19. Formation of Lymph
• Lymph is derived from interstitial fluid
that flows into the lymphatics.
• Most of the fluid filtering from the
arteries 90% is reabsorbed back into
the venous ends of the blood
capillaries.
• Lymph is made up of the remaining
10% of the returning interstitial fluid.

20. Lymphatic System

21. Formation of Lymph
• Lymph is a clear, watery fluid
containing electrolytes and proteins.
• Lymph collects the protein molecules
created within the cells as it leaves.

22. Formation of Lymph
• Lymph also removes dead cells, debris,
and pathogens (including cancer cells)
that were still left in the intercellular
spaces.
• The lymph enters very small capillaries
within the tissues and then flows into
progressively larger vessels and ducts.

23. Lymph Channels of the Body
• Almost all tissues of the body have
special lymph channels that drain
excess fluid directly from the interstitial
spaces.
• All the lymph vessels from the lower
part of the body empty into the thoracic
duct.
– Which in turn empties into the blood
venous system.

24. Lymph Channels of the Body
• Lymph from the left side of the head,
the left arm, and parts of the chest
region also enters the thoracic duct
before it empties into the veins.

25. Lymph Channels of the Body
• Lymph from the right side of the neck
and head, the right arm, and parts of
the right thorax enters the right lymph
duct
– Which empties into the blood venous
system at the juncture of the right
subclavian vein and internal jugular vein.

26. Lymphatic System

27. Rate of Lymph Flow
• About 100 ml/hr of lymph flows through
the thoracic duct of a resting human.
• Approximately another 20 milliliters
flows into the circulation each hour
through other channels.
• Thus, a total lymph flow of about 120
ml/hr or 2 to 3 liters is estimated per
day.

28. Lymphatic Circulation
• Work closely with blood circulation.
• Thus often referred to as the secondary
circulatory system.
• Lymphatic system depends on the
pumping motion of muscles to move the
fluid upward.
• Lymph flows in only one direction.
• From its point of origin, lymph can move
only upward until it returns to the
circulatory system at the base of the neck.

29. Lymphatic Circulation
• Once lymph enters a lymphatic
capillary, it must continue this upward
flow.
• Lymph is filtered by lymph nodes,
which are located along lymphatic
vessels.
• The lymphatic vessels are not readily
visible, since lymph is a clear fluid.