Section III. PROPERTIES AND FUNCTIONS.
The resistance of the arteries after death is great, as demonstrated by Dr. Gordon's experiment where a portion of the common carotid artery from a man who died twelve hours ago did not yield to a weight of 30 lbs. avoirdupois. The strength in the transverse direction cannot be ascertained with precision but must be considerable.
<Callout type="important" title="Critical Observation">The internal coat, although thin, is that which opposes more than either of the others, to the bursting or preternatural dilatation of the arterial tube.</Callout>
The arteries are capable of being extended, especially in the direction of their length. If an artery be tied in two places and divided between the ligatures, the portion next the heart is sensibly elongated at each systole of the ventricle.
<Callout type="risk" title="Potential Danger">After yielding extensively without rupturing, it begins to tear, the internal coats giving way first, and subsequently the internal membrane, having been greatly elongated, is lacerated.</Callout>
The most important physical property of the arteries is their elasticity. Numerous instances might be adduced to illustrate the effects produced by this power, but I shall confine myself to some of the most remarkable.
<Callout type="tip" title="Practical Tip">After an artery has been extended either lengthwise or transversely, it suddenly retracts on itself when the extending force is removed and thus returns to its original state.</Callout>
The elastic property affects the arteries both longitudinally and transversely. In the former direction, its influence appears to be confined to restoring the vessels to their original state after they have been elongated in various motions of the body.
<Callout type="important" title="Critical Function">It is more difficult to determine the effects of elasticity in the transverse or circular direction, but I believe that its principal use is to keep the arteries patent and thus assist in the circulation by facilitating the flow of blood within those tubes.</Callout>
This power assists in the circulation, but its importance has been exaggerated by many physiologists who have attributed to this faculty effects which undoubtedly depend upon the action of the fibrous coat. The elastic property affects the arteries both longitudinally and transversely.
<Callout type="risk" title="Potential Risk">The coconsideration of the vital properties of the arterial system, embraces a most extensive field of inquiry, and only that has been a very prolific source of discussion among physiologists.</Callout>
The principal subject of this controversy relates to the existence or non-existence of an active power of contraction in the arteries. This property, which is variously denominated by the terms of irritability, timicity, contractility, and vital force of the arteries, has been denied by some unassumers and admitted by others.
<Callout type="important" title="Critical Experiment">The following are the principal objections that have been urged by Haller, Bichat, and other physiologists against the contractility of the arteries: it is stated that these vessels exhibit no marks of contraction when they are irritated either on their external or internal surface, by mechanical or chemical agents.</Callout>
<Callout type="tip" title="Practical Tip">The direct experiments of Verschuer, Hunter, Dr. W. Philip, Dr. Thompson, and Dr. Haslam have most satisfactorily controverted these objections, demonstrating that the arteries possess a proportional contractile power which may be excited by various stimuli.</Callout>
A careful consideration of the experiments and opinions of the physiologists who have investigated this subject, joined to the observations and experiments which I have myself had an opportunity of making, have convinced me that the arteries exert an active contractile power, which assists very essentially in the circulation of the blood.
<Callout type="important" title="Critical Observation">This force, which has a great resemblance to muscular contractility, appears to have the same relation to the arterial system as the power of the heart; being, under ordinary circumstances, independent of the nervous power but yet susceptible of being influenced by agents applied to the brain or spinal cord.</Callout>
The arteries are generally supposed to possess no sensibility in their healthy state, as they may be irritated in living animals by the scalpel, by the application of acids, &c., without producing any symptoms of pain. I believe, however, that the common opinion as to the insensibility of the blood- vessels is altogether unfounded.
<Callout type="risk" title="Potential Risk">This mistake has arisen in the present and in many other instances from the erroneous idea that parts which cause no pain on being irritated by mechanical or chemical agents are insensible.</Callout>
The importance of this property in a pathological point of view is illustrated by the important experiments that have been lately performed by Mr. Morgan and Ur. Addison, concerning the influence of poisons on the animal economy.
<Callout type="tip" title="Practical Tip">These gentlemen appear to have determined the long-disputed question as to the modus operandi of these deleterious agents, by ascertaining that the noxious effects of poisonous substances introduced into the current of the circulation do not result from their direct application to the brain itself but from the impression made upon the sensitive structure of the blood-vessels acting upon the heart through the medium of the nervous system.</Callout>
The use of the arteries is to convey the blood which they receive from the ventricles to all parts of the body. We learn from the preceding observations that these vessels are not passive tubes but that they are endowed with an active power of contraction and are at the same time highly elastic.
<Callout type="important" title="Critical Function">The arteries are constantly filled, their capacity varying according to the quantity of fluid they contain; this power of adaptation probably depends upon the tonic contraction of the fibrous coat, a property which is analogous with the tonicity of the muscles.</Callout>
Key Takeaways
- Arteries possess significant strength and elasticity.
- They are capable of contraction, which assists in circulation.
- Understanding arterial properties is crucial for managing blood flow during emergencies.
Practical Tips
- Recognize the importance of arterial elasticity in maintaining proper blood pressure and flow.
- Be aware that arteries can contract significantly under certain conditions, aiding in emergency situations like stopping bleeding.
- Understand that the tonicity of the fibrous coat plays a critical role in adapting to changes in fluid volume.
Warnings & Risks
- Do not assume all parts of the body are insensitive to mechanical or chemical irritation; some areas may have heightened sensitivity.
- Be cautious when applying pressure to arteries, as excessive force can cause damage or tearing.
- Understand that arterial properties can change under pathological conditions, which could affect your assessment and response.
Modern Application
While the specific techniques for managing arterial issues might differ from those described in this historical text, understanding the fundamental principles of arterial behavior remains crucial. Modern medical practices have advanced significantly, but recognizing these basic physiological functions is essential for effective emergency response and preparedness.
Frequently Asked Questions
Q: What experiments demonstrated that arteries possess a contractile power?
The direct experiments of Verschuer, Hunter, Dr. W. Philip, Dr. Thompson, and Dr. Haslam have most satisfactorily controverted the objections against the contractility of the arteries, demonstrating their proportional contractile power which can be excited by various stimuli.
Q: How does arterial elasticity affect blood flow?
Arterial elasticity assists in circulation by facilitating the flow of blood within those tubes and keeping the arteries patent. It helps restore vessels to their original state after they have been elongated during body motions.
Q: What is the significance of the contractility of the arteries?
The contractility of the arteries assists in circulation by aiding in the flow of blood within those tubes and helping to keep them patent. It also plays a role in adapting to changes in fluid volume.