Section II. PROPERTIES AND FUNCTIONS.
The actions of the capillary vessels are essential to the production of most operations required for the support of life. The opinions of physiologists are divided as to the existence of an active contractile power in these small blood-vessels; and when the great importance of the question is considered, we cannot be surprised at the number of writers who have engaged in the controversy. According to some authorities, the capillaries are merely passive tubes, which are not provided with irritability. Others contend that they have a contractile power, which enables them to carry on the circulation quite independently of the heart; but many excellent physiologists suppose that the capillary circulation is influenced by the action of the heart, but that the small vessels have an active force, which enables them to assist in propelling their contents, and which may be exercised independently of the heart. As it would be difficult to introduce within the limits of this work the numerous considerations that are connected with this most comprehensive subject, I shall confine myself to pointing out some facts which appear to prove the correctness of the last opinion.
It has been already shown that the propulsive power of the ventricle extends to the venous system; now it is evident that that power must have previously acted on the capillaries. I conceive the first part of the theory must be fulfilled, viz., that the capillary circulation is influenced by the action of the heart.
The second part of this opinion may be substantiated by observing certain phenomena which occur in the human body, and by the results of experiments performed on the living animals. It is well known that local action frequently takes place, by which blood, and other fluids, are determined towards individual parts of the body, without the heart's action or the general circulation being affected. Mental emotion is often the exciting cause of the great local accumulation. Thus, shame causes blushing; voluptuous ideas produce erection; and the sight of food excites, in a hungry person, a flow of saliva. At other times local action may be produced by mechanical irritation; for example, tickling causes erection of the nipple, a particle of iron renders the vessels of the conjunctiva turgid, etc. Against in local inflammation, the activity of the small arteries is increased, although the condition of the heart is not affected. It has, indeed, been implied, by an author of great excellence, that, in similar instances to those above mentioned, a prior action occurs in the heart, which is the occasion of the local distention. But, if this supposition were founded in truth, which there is great reason to think it is not, it would not explain the phenomena which are observed, much an increase in the power of the heart would certainly accelerate the general circulation; but we cannot conceive how it could influence the flow of blood in any particular set of vessels, unless those vessels had themselves a local source of action.
The important experiments which have been performed by Dr. W. Philip, Dr. Thompson and Dr. Hastings show, in a still more striking manner, the contractile power of the capillaries. Thus the circulation continues in them, after a ligature has been tightly bound around the leg of a frog — after the great vessels of the heart have been all tied — nay, more, after the heart has itself been removed, or has long ceased to act.
<Callout type="important" title="Key Observation">The capillaries can continue circulation independently of the heart.</Callout>
The arteries and the veins are connected with processes which effect the vital functions in the completion of which, these vessels have a direct share. For, in these vessels, the blood falls into a state of equilibrium after traversing the capillary tubes, and it is there that the change takes place by which it becomes unfit for the purpose of economy.
In the lungs, the chyle and the lymph are assimilated with the nutritive fluid.</Callout>
<Callout type="risk" title="Heart's Role">The heart's role in capillary circulation is complex; direct action may not always be necessary.</Callout>
Key Takeaways
- Capillaries can continue to circulate independently of the heart.
- Local actions, such as mental emotions or mechanical irritations, can affect blood flow in specific areas.
- The capillary system plays a crucial role in the overall circulation and function of the body.
Practical Tips
- Monitor local changes in blood flow when assessing injuries to ensure proper treatment.
- Understand that while the heart is vital, it may not always be directly responsible for localized blood movement.
- Recognize the importance of capillaries in the overall health and function of the body.
Warnings & Risks
Complexity of Circulation
The relationship between the heart and capillary circulation is complex, and direct action from the heart may not always be necessary.
Incorrectly attributing localized blood flow to the heart can lead to misdiagnosis or inappropriate treatment. Failing to understand the difference between local and general circulation can result in overlooking critical issues.
Modern Application
While this chapter provides valuable insights into capillary function, modern medical knowledge has expanded our understanding of circulatory systems. However, recognizing the independent action of capillaries remains crucial for effective triage and emergency response, especially in situations where the heart's direct influence may be compromised.
Frequently Asked Questions
Q: How do mental emotions affect blood flow according to this chapter?
According to the text, mental emotions such as shame can cause blushing by determining blood towards specific parts of the body without affecting the general circulation. This demonstrates that local actions can significantly impact blood flow.
Q: What experiments demonstrate the contractile power of capillaries?
The chapter mentions important experiments performed by Dr. W. Philip, Dr. Thompson, and Dr. Hastings showing that the circulation continues in capillaries even after a ligature has been tightly bound around the leg of a frog, or after the heart itself has been removed.
Q: What role do the lungs play in blood circulation according to this chapter?
The text states that in the lungs, the chyle and lymph are assimilated with the nutritive fluid. This indicates that the lungs play a significant role in the overall circulatory process by facilitating the exchange of substances between the blood and the body's tissues.