the interstitial ﬂ
uid. Absorption from interstitial ﬂ uid to
plasma is favored by the protein concentration difference
between the plasma and the interstitial ﬂ
b. Filtration and absorption do not change the concentrations
of crystalloids in the plasma and interstitial ﬂ uid because
these substances move together with water.
c. There is normally a small excess of ﬁ ltration over absorption,
which returns ﬂ uids to the bloodstream via lymphatic vessels.
I. Veins serve as low-resistance conduits for venous return.
II. Veins are very compliant and contain most of the blood in the
a. Sympathetically mediated vasoconstriction reﬂ exly alters
venous diameters so as to maintain venous pressure and
b. The skeletal muscle pump and respiratory pump increase
venous pressure locally and enhance venous return. Venous
valves permit the pressure to produce ﬂ ow only toward the
The Lymphatic System
I. The lymphatic system provides a one-way route for movement
of interstitial ﬂ uid to the cardiovascular system.
II. Lymph returns the excess ﬂ uid ﬁ ltered from the blood vessel
capillaries, as well as the protein that leaks out of the blood
III. Lymph ﬂ ow is driven mainly by contraction of smooth muscle
in the lymphatic vessels, but also by the skeletal muscle pump
and the respiratory pump.
Additional Clinical Examples
I. Disease states that alter the Starling forces can result in edema
(e.g., heart failure, tissue injury, liver disease, kidney disease,
and protein malnutrition).
SECTION C KEY TERMS
atrial natriuretic peptide
capillary ﬁ ltration
diastolic pressure (DP)
ﬂ ow autoregulation
ﬂ ow-induced arterial
mean arterial pressure
net ﬁ ltration pressure
skeletal muscle pump
SECTION C CLINICAL TERMS
SECTION C REVIEW QUESTIONS
1. Draw the pressure changes along the systemic and pulmonary
vascular systems during the cardiac cycle.
2. What are the two main functions of the arteries?
3. What are normal values for systolic, diastolic, and mean arterial
pressures? How is mean arterial pressure estimated?
4. What are two major factors that determine pulse pressure?
5. What denotes systolic and diastolic pressure in the
measurement of arterial pressure with a sphygmomanometer?
6. What are the major sites of resistance in the systemic vascular
7. Name two functions of arterioles.
8. Write the formula relating ﬂ ow through an organ to mean
arterial pressure and to the resistance to ﬂ ow that organ offers.
9. List the chemical factors thought to mediate active hyperemia.
10. Name the mechanism other than chemical factors that
contributes to ﬂ ow autoregulation.
11. What is the only autonomic innervation of most arterioles?
What are the major adrenergic receptors inﬂ uenced by these
nerves? How can control of sympathetic nerves to arterioles
12. Name four hormones that cause vasodilation or vasoconstriction
of arterioles, and specify their effects.
13. Describe the role of endothelial paracrine agents in mediating
arteriolar vasoconstriction and vasodilation, and give three
14. Draw a ﬂ ow diagram summarizing the factors affecting
15. What are the relative velocities of ﬂ ow through the various
segments of the vascular system?
16. Contrast diffusion and bulk ﬂ ow. Which mechanism exchanges
nutrients, oxygen, and metabolic end products across the
17. What is the only solute that has signiﬁ cant concentration
differences across the capillary wall? How does this difference
inﬂ uence water concentration?
18. What four variables determine the net ﬁ ltration pressure across
the capillary wall? Give representative values for each of them
in the systemic capillaries.
19. How do changes in local arteriolar resistance inﬂ uence local
20. What is the relationship between cardiac output and venous
return in the steady state? What is the force driving venous
21. Contrast the compliances and blood volumes of the veins and
22. What three factors inﬂ uence venous pressure?
23. Approximately how much ﬂ uid do the lymphatics return to the
blood each day?
24. Describe the forces that cause lymph ﬂ ow.
systolic pressure (SP)