This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Hyperemia signifies superabundance of blood in the blood vessels, but this term is restricted to such a condition existing in a definite organ or portion of an organ; hence hyperemia and dilatation of blood vessels are so intimately connected that the one cannot exist without the other.
It is also necessary that the capillaries as well as the arteries and veins should be injected, in order that the color of the region so affected should be increased, as the former constitute a dense network, which traverses the entire organ, while the latter only form single branches which occupy limited spaces. There are two forms of hyperemia, active and passive; in the active form there is an increased quantity of arterial blood passing into the part, while in the passive form a partial or complete stagnation of the blood through the vessels occurs.
The term Plethora, as distinguished from hyperemia, signifies a superabundance of blood in the entire circulatory system - an increased amount of blood in all the vessels of the body. Active hyperemia in the skin and mucous membranes is characterized by a diffuse bright-red coloration, the parts so affected having a higher temperature than those around them. The diffuse coloration is caused by the bright-red arterial blood which fills the capillaries; and the elevation of the temperature is due to the presence of the blood, which heats the skin or mucous membranes, and the more quickly the blood circulates the warmer the tissues become, until at length the highest degree of blood heat is accomplished.
Passive hyperemia denotes a condition of the tissues characterized by a diffuse venous, not arterial, coloration and a relatively low temperature. In passive hyperemia the capillaries are also dilated, but the blood-current through them is retarded ; hence the tissues so affected are of a venous color instead of the bright-red or arterial color of active hyperemia.
The term Anemia signifies a condition in which there is an abnormal diminution in the amount of blood, and is the opposite to that of Plethora, being characterized by a pale face, lips, gums and mucous membranes. But the normal amount of blood may be present, and yet the characteristic paleness denote an anemic condition, for the reason that the number of red blood corpuscles are decreased and replaced by white blood corpuscles, or by blood plasma.
Again, the paleness of an anemic condition may be due to a deficiency of the red coloring matter of the red blood corpuscles. A permanent contraction of the blood vessels may also cause a paleness of the face, lips, gums and mucous membranes.
The term Ischemia is also employed to denote local poverty of the blood, a deficiency of the coloring matter (hemoglobin).
The direct cause of hyperemia, and also of ischemia, is a change of calibre of the blood vessels, namely, dilatation and contraction. This dilatation and contraction of the blood vessels are due to the elastic and contractile elements of the sheaths and walls of the arteries and veins, and both the dilatation and contraction are regulated by the spinal cord, through the medium of the vaso-motor nerves. It is a common opinion that hyperemia cannot exist without the influence of the vaso-motor nerves.
Irritation indicates the condition of a tissue in which there exists an excess of vital action, on account of the disordered state of the nerves of the affected part or organ. It is commonly manifested by such symptoms as increased circulation, warmth and sensibility, and functional disturbance of a greater or less degree.
What inflammation is to the vascular system, irritation is to the nervous system, and the difference between these two conditions is defined by the explanation that the latter terminates when the former begins. Irritation is generally excited by the action of certain stimuli upon organic tissues, by which the sensibility of such tissues is perverted and the circulation deranged; such pathological conditions when they are not the precursor of inflammation, soon passing off, and the affected tissue regaining its normal state when the exciting cause ceases to operate. Irritation may be direct and indirect - direct when the irritation manifests itself at the point where the impression to which it owes its origin is received; indirect when the irritation, through sympathy and reflex action, is transmitted to more or less remote parts or organs. An example of direct irritation may be adduced by friction upon the skin or mucous membrane of the mouth sufficient to cause redness in the first tissue, and increased coloration in the second; or indirect irritation, in the 8 convulsions attending difficult dentition, the irritation being communicated to the brain by the fifth pair of nerves, and from thence to the nerves of the voluntary muscles, the seat of the spasmodic action. Dental caries also affords another example of indirect irritation, in the form of neuralgic pains of the temple, face, ear, eye, and of even more remote parts, such as the uterus.
The effect of irritation upon the vascular system is manifested by dilatation of the blood vessels; but the immediate effect, however, of a slight chemical or mechanical irritant is not at once apparent in the capillaries, but first causes contraction of the smaller arteries, and sometimes of the veins, such contraction being followed by a dilatation, the immediate cause of which is yet obscure. It is, however, supposed to be the result of relaxation or a temporary paralysis of the walls of the vessels, a condition following contraction, and which, as a consequence, causes a decrease of their resistance to the pressure of the blood within them. The irritation either perverts the function of the nerves of the vessels, or of the lining cell substance of the capillary walls; or the disturbance is due to reflex action.
Inflammation denotes an abnormal process or condition characterized by certain changes of texture, which, although uniform in type differ widely in appearance, and terminate in different results, according to the nature and permanency of the causes upon which such a condition depends, or which have given rise to it.
The symptoms of inflammation consist of the phenomena which accompany the textural changes characteristic of this condition, and its pathology the textural changes which occur during the continuance of this condition. The essential features of inflammation are an increased afflux of blood to the affected part, with a greatly increased tendency to cell proliferation and tissue formation.
The causes of inflammation determine in a great degree its treatment on account of the influence they exert upon its destructive tendency, and they may be classified as those arising- 1st, from mechanical violence; 2d, from irritating and destructive chemical action; 3d, from poisonous infection, and the effect of injurious micro-organisms - the latter being regarded as "immediate determining causes of the more destructive phases of the inflammatory process." When inflammation owes its origin to an evident injury, or the reverse, it is termed traumatic, or idiopathic, and when no apparent cause can be discovered it is termed spontaneous.
The causes of inflammation are divided into predisposing and exciting.
Among the more important predisposing causes are impoverished blood - defective in quality - such as may result from a want of proper food and of fresh air, the effects of such deprivations being manifested in the case of a neglected child where a hard swelling occurs in the cheek, which, after a few days, presents a gangrenous condition, constituting the disease known as cancrum oris or gangrcenopsis. On the other hand an habitual excess of food and drink is also a predisposing cause of inflammation, the blood, as a consequence, being impaired, and also the tissue which it supplies. Blood poisoning is also another predisposing cause, resulting, it may be, from the presence of certain diseases, such as syphilis, diabetes, mellitus, eczema, etc. A local hyperemia, constituting the first stage in the development of inflammation, may result from certain poisons in the blood, which cause it to stagnate in limited areas, through an inability to stimulate the heart and blood vessels. Syphilitic ulceration of the mucous membrane of the mouth is an example of such a predisposing cause. Weakened vitality of parts is also a predisposing cause of inflammation and may result from habitual ill feeding, protracted illness, overwork, long exposure to extreme cold. Parts such as the mucous membrane of the mouth, which have already been the seat of inflammation, are prone to such a condition subsequently, from slight provocation.
Defective or perverted nervous supply may also be regarded as a predisposing cause of inflammation. Certain forms of skin disease, and inflammatory conditions of the mucous membrane of the mouth, furnish examples; also, of the peridental membrane of the teeth, resulting in severe periodontitis and alveolar abscess.
The influence of climate is also regarded as a predisposing cause, for, in tropical regions, inflammation of certain organs, often terminating in abcesses, are very prevalent. The midsummer and fall months are considered to be more favorable for surgical operations, on account of the comparative absence of inflammatory complications at such times.
Age has also some influence as a predisposing cause of inflammation. In childhood acute hyperemia is induced by comparatively slight exciting causes, as then the process of nutrition is at its greatest period of activity, and any interruption of its process is followed by derangement of health.
The effects of the irritation of the first dentition may be adduced as an example. Old age induces weakness in the tissues and decrease of power of resistance to the exciting causes of inflammation.