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Integumentary System Essay Topics

Skin

The skin is the largest organ in the body and has a dual origin: (1) A superficial layer, the epidermis, develops from the surface ectoderm. (2) A deep layer, the dermis, develops from the underlying mesenchyme.

Epidermis

Initially, the embryo is covered by a single layer of ectodermal cells (Fig. 21.1A). In the beginning of the second month, this epithelium divides, and a layer of flattened cells, the periderm, or epitrichium, is laid down on the surface (Fig. 21.1B). With further proliferation of cells in the basal layer, a third, intermediate zone is formed (Fig. 21.1C). Finally, at the end of the fourth month, the epidermis acquires its definitive arrangement, and four layers can be distinguished (Fig. 21.1D):

Figure 21.1.Formation of the skin at various stages of development.

A. 5 weeks. B. 7 weeks. C. 4 months. D. Birth.

The basal layer, or germinative layer, is responsible for production of new cells. This layer later forms ridges and hollows, which are reflected on the surface of the skin in the fingerprint.

A thick spinous layer consists of large polyhedral cells containing fine tonofibrils.

The granular layer contains small keratohyalin granules in its cells.

The horny layer, forming the tough scale-like surface of the epidermis, is made up of closely packed dead cells containing keratin.

Cells of the periderm are usually cast off during the second part of intrauterine life and can be found in the amniotic fluid. During the first 3 months of development, the epidermis is invaded by cells arising from the neural crest. These cells synthesize melanin pigment in melanosomes. As melanosomes accumulate, they are transported down dendritic processes of melanocytes and are transferred intercellularly to keratinocytes of the skin and hair bulb. In this manner, pigmentation of the skin and hair is acquired.


Clinical Correlates

Pigmentary Disorders

A large number of pigmentary disorders occur, and these can be classified as diseases of melanocyte development, function, and survival. Examples of abnormalities of melanocyte function include piebaldism (patchy absence of hair pigment) and Waardenburg syndrome (WS), which feature patches of white skin and hair. There are several types of WS, but they share some common characteristics, including patches of white hair (usually a forelock), heterochromia irides (eyes of different colors), white patches of skin, and deafness.

The defects arise because of faulty migration or proliferation of neural crest cells (absence of melanocytes derived from these cells in the stria vascularis in the cochlea accounts for deafness in these diseases). Some types of WS result from mutations in PAX3, including WS1 and WS3.

Diseases of melanocyte function include the various forms of albinism characterized by globally reduced or absent pigmentation in the skin, hair, and eyes. These cases are classified as different types of oculocutaneous albinism (OCA). In most cases, abnormalities of melanin synthesis or processing produce the abnormalities.

Vitiligo results from a loss of melanocytes due to an autoimmune disorder. There is patchy loss of pigment from affected areas, including the skin and overlying hair and the oral mucosa. Vitiligo is also associated with other autoimmune diseases, particularly of the thyroid.

Fingerprints

The epidermal ridges that produce typical patterns on the surface of the fingertips, palms of the hand, and soles of the feet are genetically determined. They form the basis for many studies in medical genetics and criminal investigations (dermatoglyphics). In children with chromosomal abnormalities, the epidermal pattern on the hand and fingers is sometimes used as a diagnostic tool.


Dermis

Dermis is derived from mesenchyme that has three sources: (1) lateral plate mesoderm supplying cells for dermis in the limbs and body wall, (2) paraxial mesoderm supplying cells for dermis in the back, and (3) neural crest cells supplying cells for dermis in the face and neck. During the third and fourth months, this tissue, the corium (Fig. 21.1D), forms many irregular papillary structures, the dermal papillae, which project upward into the epidermis. Most of these papillae contain a small capillary or a sensory nerve end organ. The deeper layer of the dermis, the subcorium, contains large amounts of fatty tissue.

At birth, the skin is covered by a whitish paste, the vernix caseosa, formed by secretions from sebaceous glands and degenerated epidermal cells and hairs. It protects the skin against the macerating action of amniotic fluid.


Clinical Correlates

Keratinization of the Skin

Ichthyosis, excessive keratinization of the skin, is characteristic of a group of hereditary disorders that are usually inherited as an autosomal recessive trait but may also be X-linked. In severe cases, ichthyosis may result in a grotesque appearance, as in the case of a harlequin fetus (Fig. 21.2).

Figure 21.2.Ichthyosis in a harlequin fetus with massive thickening of the keratin layer, which cracks to form fissures between thickened plaques.


Hair

Hairs begin development as solid epidermal proliferations from the germinative layer that penetrates the underlying dermis (Fig. 21.3A). At their terminal ends, hair buds invaginate. The invaginations, the hair papillae, are rapidly filled with mesoderm in which vessels and nerve endings develop (Fig. 21.3B,C). Soon, cells in the center of the hair buds become spindle-shaped and keratinized, forming the hair shaft, while peripheral cells become cuboidal, giving rise to the epithelial hair sheath (Fig. 21.3B,C).

Figure 21.3.Development of a hair and a sebaceous gland.

A. 4 months. B. 6 months. C. Newborn.

The dermal root sheath is formed by the surrounding mesenchyme. A small smooth muscle, also derived from mesenchyme, is usually attached to the dermal root sheath. The muscle is the arrector pili muscle. Continuous proliferation of epithelial cells at the base of the shaft pushes the hair upward, and by the end of the third month, the first hairs appear on the surface in the region of the eyebrow and upper lip. The first hair that appears, lanugo hair, is shed at about the time of birth and is later replaced by coarser hairs arising from new hair follicles.

The epithelial wall of the hair follicle usually shows a small bud penetrating the surrounding mesoderm (Fig. 21.3C). Cells from these buds form the sebaceous glands. Cells from the central region of the gland degenerate, forming a fat-like substance (sebum) secreted into the hair follicle, and from there, it reaches the skin.


Clinical Correlates

Abnormalities of Hair Distribution

Hypertrichosis (excessive hairiness) is caused by an unusual abundance of hair follicles. It may be localized to certain areas of the body, especially the lower lumbar region covering a spina bifida occulta defect or may cover the entire body (Fig. 21.4).

Figure 21.4.Child with hypertrichosis.

Atrichia, the congenital absence of hair, is usually associated with abnormalities of other ectodermal derivatives, such as teeth and nails.


Sweat Glands

There are two types of sweat glands: eccrine and apocrine. Eccrine sweat glands form in the skin over most parts of the body beginning as buds from the germinative layer of the epidermis. These buds grow into the dermis, and their end coils to form the secretory parts of the glands. Smooth muscle cells associated with the glands also develop from the epidermal buds. These glands function by merocrine mechanisms (exocytosis) and are involved in temperature control.

Apocrine sweat glands develop anywhere there is body hair, including the face, axillae, and pubic region. They begin to develop during puberty and arise from the same epidermal buds that produce hair follicles. Hence, these sweat glands open onto hair follicles instead of skin. The sweat produced by these glands contains lipids, proteins, and pheromones, and odor originating from this sweat is due to bacteria that break down these products. It should be noted that these glands classified as apocrine because a portion of the secretory cells is shed and incorporated into the secretion.

Mammary Glands

Mammary glands are modified sweat glands and first appear as bilateral bands of thickened epidermis called the mammary lines or mammary ridges. In a 7-week embryo, these lines extend on each side of the body from the base of the forelimb to the region of the hindlimb (Fig. 21.5C). Although the major part of each mammary line disappears shortly after it forms, a small portion in the thoracic region persists and penetrates the underlying mesenchyme (see Fig. 21.5A).

Here it forms 16 to 24 sprouts, which in turn give rise to small, solid buds. By the end of prenatal life, the epithelial sprouts are canalized and form the lactiferous ducts. Initially, the lactiferous ducts open into a small epithelial pit (Fig. 21.5B). Shortly after birth, this pit is transformed into the nipple by proliferation of the underlying mesenchyme. At birth, lactiferous ducts have no alveoli and therefore no secretory apparatus. At puberty, however, increased concentrations of estrogen and progesterone stimulate branching from the ducts to form alveoli and secretory cells.

Figure 21.5.

A,B. Sections through the developing mammary gland at the third and eighth months, respectively. C. Positions of accessory nipples (blue line, mammary line).


Clinical Correlates

Mammary Gland Abnormalities

Polythelia is a condition in which accessory nipples have formed resulting from the persistence of fragments of the mammary line (Fig. 21.5C). Accessory nipples may develop anywhere along the original mammary line (Fig. 21.6) but usually appear in the axillary region.

Figure 21.6.Child with bilateral polythelia (supernumary nipples).

Polymastia occurs when a remnant of the mammary line develops into a complete breast.

Inverted nipple is a condition in which the lactiferous ducts open into the original epithelial pit that has failed to evert.


Summary

The skin and its associated structures, hair, nails, and glands, are derived from surface ectoderm. Melanocytes, which give the skin its color, are derived from neural crest cells, which migrate into the epidermis. The production of new cells occurs in the germinative layer. After moving to the surface, cells are sloughed off in the horny layer (Fig. 21.1). The dermis, the deep layer of the skin, is derived from lateral plate mesoderm and from dermatomes of the somites.

Hairs develop from downgrowth of epidermal cells into the underlying dermis. By about 20 weeks, the fetus is covered by downy hair, lanugo hair, which is shed at the time of birth. Sebaceous glands, sweat glands, and mammary glands all develop from epidermal proliferations. Supernumerary nipples (polythelia) and breasts (polymastia) are relatively common (Figs. 21.5 and 21.6).

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Integumentary System Essay

668 WordsApr 8th, 20123 Pages

THE INTEGUMENTARY SYSTEM
The integumentary system also known as skin; surrounds the entire human body therefore being the largest organ. The skin and its annexes like hair, sweat glands, sebaceous glands, nails, etc. The main functions of the integumentary system is to function as a protective barrier, that keeps our body free from intrusion of foreign materials, microorganisms and prevents dehydration as well as protecting from desiccation and there are other functions also helps in elimination of waste products and in the regulation of our body tempeture. There are many other functions of the integumentary system and each organ involved in this system has its own particular use
The main parts of the integumentary system are the skin…show more content…

The body temperature is also maintained within this layer by insulating the body to the temperature fluctuations.
The skin carries out the following main functions of the integumentary system. * Thermoregulation: The thermoregulation of the skin is carried out with the help of evaporation of the sweat and regulation of the blood flow to the dermis. * Sensations: The cutaneous sensations like touch, pressure, vibration, pain, cold, hot, etc, are felt by the skin. * Protection: The protective barrier of the skin helps prevent diseases, infections, dehydration, etc. * Production of Vitamin D: The sign present in the skin and UV rays, helps in the production of vitamin D, an important nutrient of the body. * Healing: When the epidermis breaks away due to a minor cut or burn, the cells on the lower layers of the skin migrate upwards as a sheet. When two ends of the sheet meet, the cells stop growing due to a process called 'contact inhibition'. Thus, the epidermis is sealed and the skin returns to normal.
Hair: composed of columns of dead, keratinized cells bound together by extracellular proteins. Hair has two main sections: The shaft- superficial portion that extends out of the skin and the root- portion that penetrates into the dermis. Surrounding the root of the hair is the hair follicle. At the base of the hair follicle is an onion-shaped structure called the bulb Papilla of the hair and the matrix within the bulb

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