1. Unit Four: The Circulation
Chapter 15: Vascular Distensibility and Functions of the Arterial and Venous Systems
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Vascular Distensibility
Units of Vascular Distensibility
Differences in Distensibility of Arteries and Veins
Veins are about 8X more distensible
Therefore, an increase in pressure causes about
8X as much increase in a vein than in an artery
c. Increase about 6X in the pulmonary circulation

3. Distensibility (cont.)
Vascular Compliance (Vascular Capacitance)
Compliance is equal to distensibility times
volume
Usually more important to know the total
quantity of blood

4. Volume-Pressure Curves
Fig “Volume-pressure curves” of the systemic arterial and venous systems, showing the
effects of stimulation or inhibition of the sympathetic nerves to the CV system

5. Delayed Compliance (Stress-Relaxation) of Vessels
Fig Effect of the intravascular pressure of injecting a volume of blood into a venous segment
and later removing the excess blood, demonstrating the principle of delayed compliance

6. Arterial Pressure Pulsations
Fig Pressure pulse contour in the ascending aorta

7. Arterial Pressure Pulsations (cont.)
Systolic Pressure- the pressure at the top of each
pulse
Diastolic Pressure- the pressure at the bottom of
each pulse
Pulse Pressure- the difference between the systolic
and diastolic pressures

8. Arterial Pressure Pulsations (cont.)
Pulse Pressure- depends on two major factors
Stroke volume output
Compliance (total distensibility)

9. Abnormal Pressure Pulse Contours
Fig. 15.4

10. Changes in Pressure Pulse Contours
Fig. 15.6

11. Veins and Their Functions
General Functions
By constricting and enlarging they can store
either large or small amounts of blood and make
it available to the rest of the circulation when
needed
Propel blood forward by the “venous pump”

12. Veins and Their Functions (cont.)
Venous Pressures
Central venous pressure (pressure of the right
atrum. Regulated by a balance between
The ability of the heart to pump blood to
the lungs, and
The tendency of blood to flow from the
peripheral veins into the right atrium

13. Veins and Their Functions (cont.)
Increase in venous return is influenced by
Increased blood volume
Increased large vessel tone resulting in
increased peripheral venous pressure
Dilation of the arterioles
Venous resistance and peripheral venous pressure

14. Fig. 15.9 Compression points that tend to collapse
the veins entering the thorax

15. Veins and Their Functions (cont.)
Effect of Gravitational Pressure on Venous Pressure
Fig Effect of gravitational pressure on the venous pressures throughout the body

16. Veins and Their Functions (cont.)
Venous Valves and the Venous Pump
Valves are arranged so that so that the direction
of blood flow can only be toward the heart
Every time someone contracts a muscle or tenses
a muscle, a certain amount of venous blood is
propelled toward the heart

17. Veins and Their Functions (cont.)
Blood Reservoir Function
Specific blood reservoirs
Spleen (red pulp)
Liver
Large abdominal veins
Venous plexus beneath the skin