modifications of the skin (epidermis) and consist essentially of the same structure as it. Hair consists of the root, the part implanted in the skin; the shaft, the portion extending from the surface; and the point. The root of the hair presents at its deep extremity a bulb-like enlargement, the hair-bulb, which is lodged in a follicular involution of the epidermis called the hair follicle. The hair follicle commences in the surface of the skin with a funnel-shaped opening, and passes inward in an oblique direction, to become dilated at its deep extremity or fundus, where it corresponds with the bulbous shape of the hair which it contains. Each hair follicle has at its base a small, conical, vascular eminence or papilla, the hair papilla, similar to the papillae found upon the surface of the skin. The latter are highly vascular and probably supplied with nerve fibrils. Each hair follicle has an opening into it near its free extremity, the openings or orifices of the ducts of one or more sebaceous glands. Connected with the hair follicles are minute bundles of involuntary muscle fibers called arrectores pilorum. They originate from the superficial surface of the true skin, or corium, and are inserted into the outer surface of the hair follicle, below the orifice of the duct of the sebaceous gland. They are located on the side toward which the hair slopes, and when they contract elevate the hair. The Sebaceous Glands. — These are simple and compound racemose glands which open into the hair follicle, and sometimes the skin surface, by means of a duct. These glands are lodged in the surface of the true skin or corium. They are very plentiful, and are found in all parts of the body, especially in the skin of the face and scalp; also numerous around the openings of the mouth, anus, nose, and external ear, but are not found in the skin covering the palms of the hands and the soles of the feet. Their structure consists of a delicate transparent membrane, enclosing epithelial cells. Sebum is the oily fluid secreted by the sebaceous glands. It contains, by analysis, water, epithelium, proteins, fats, cholesterin, and inorganic salts. The pouring-out of sebum by the glands is not a true secretion, but occurs as a result of multiplication and breaking down of the gland epithelium. Sebum when first secreted is oily and semiliquid, but soon becomes hard and acquires a cheese-like consistency. It lubricates the hair and skin and prevents dryness and roughness. Vemix caseosa is the whitish, oily substance seen covering the body of the newborn child. It is supposed to keep the skin in a normal condition by protecting it from the effects of the long-continued action of the amniotic fluid in which the fetus is suspended during intra-uterine development. The Sweat Glands. — The sweat glands are the glands which when active promote perspiration and aid in heat dissipation, at the same time eliminating waste products as the result of body metabolism, brought to them by the blood. They are situated in the lower part of the corium, derma, or true skin, and sometimes in the subcutaneous tissue. The glands are tubular, and the lower or inner extremity is coiled upon itself a number of times, forming a rounded mass. Extending from this coil to the epidermis is the duct which follows a straight course in this situation, and after a few spiral turns, opens onto the surface of the skin. The glands consist of epithelial cells which rest upon a very thin basement membrane. These glands are very numerous; it has been estimated that they average from 2,000,000 to 2,500,000. They are more abundant in some localities than others. Each sweat gland is richly supplied with bloodvessels and nerves (vasomotor and secretor). Perspiration. — Perspiration or sweat is the fluid secreted by the sweat glands of the skin. It is a clear, colorless liquid of a specific gravity varying from 1.003 to 1.006; slightly acid in reaction and salty to the taste. Except when collected from the soles of the feet and palms of the hands, it is mixed with epithelial cells and sebum — secreted by the sebaceous glands. The amount of sweat secreted in twenty-four hours has been estimated at 700 to 1000 grams; however, this is uncertain, owing to the difficulty of collection, and the influence temperature, diet, drink, season of the year, etc., exert upon its secretion. The secretion of sweat, though essentially an excretion, is chiefly concerned in the regulation of the body temperature in maintaining heat dissipation, rather than the elimination of waste materials by means of the sweat glands brought to them by the blood and lymph vessels. The Part Played hy the Nerve System on the Produc- tion of Sweat. — The secretion of sweat is practically the result of the activity of the epithelial cells of the sweat glands and is regulated by the nerve system. The fluid contained in the sweat is derived from the materials in the lymph channels, furnished by the blood. To produce sweat there must be a glandular activity, and a regulation of the blood-supply. The former is brought about by a set of nerves called the secretor, which stimulate the cells to activity; the latter is regulated by nerves called the vasomotor, that regulate the blood-pressure of the capillaries and increase or decrease the blood-supply to the glands. Other influences increase the production of sweat, by their related nerve centres sending out impulses in two ways: first, by nerve impulses from the central dominating centre, supposed to be located in the medulla, being stimulated by mental emotions, as shock, shame, etc., venosity of the blood, hot drinks, violent muscular exercise, etc.; second, by reflex impulses being conveyed to the centres in the spinal cord by the sensor nerves in the skin, as a result of hot applications, high external temperature, etc. The nerve centres which regulate the secretion of sweat are located in the spinal cord and reach the glands of the skin by means of the sympathetic nerves with which the spinal nerves communicate. The dominating centre which is influenced to activity by emotional states, etc., is situated in the medulla oblongata and sends its impulses down the spinal cord and out through the spinal nerves and the sympathetic system to the cells of the glands. Sweat may be produced by a general relaxation of the bloodvessels which supply the sweat glands, resulting from a stimulation of the vasomotor nerves. But it must be remembered that a normal production of sweat is based on the activity of both the nerves influencing the blood supply to the glands, and the nerves which stimulate the cells of the sweat glands to secrete.
Key Takeaways
- Hair consists of a root implanted in the skin, a shaft extending from the surface, and a point.
- Sebaceous glands secrete an oily fluid called sebum that lubricates hair and skin.
- Sweat glands produce perspiration to regulate body temperature.
Practical Tips
- Understand the role of sebaceous glands in maintaining skin health by keeping it hydrated and protected from external elements.
- Recognize how sweat glands help in thermoregulation, which is crucial for survival in extreme temperatures.
- Be aware that emotional states can trigger sweating, a useful physiological response to stress or danger.
Warnings & Risks
- Overproduction of sebum can lead to skin issues like acne and should be managed with proper hygiene.
- Excessive sweating can result in dehydration if not properly managed, especially in hot environments.
- Injury to hair follicles can disrupt the normal function of sweat glands, affecting thermoregulation.
Modern Application
While the chapter provides foundational knowledge on skin anatomy and physiology, modern readers should be aware that advancements in medical science have improved our understanding and treatment methods. However, this historical text remains valuable for its detailed description of basic physiological processes, which are still relevant to survival scenarios where immediate medical care may not be available.
Frequently Asked Questions
Q: What is the function of sebaceous glands?
Sebaceous glands secrete an oily fluid called sebum that lubricates hair and skin, preventing dryness and roughness.
Q: How do sweat glands contribute to thermoregulation?
Sweat glands produce perspiration which helps in heat dissipation by evaporating from the skin surface, thus regulating body temperature.
Q: What triggers the production of sweat according to this chapter?
The secretion of sweat is regulated by nerve impulses from the central dominating centre (in the medulla) and reflex impulses from sensor nerves in the skin due to external stimuli like hot applications or high temperatures.