INTEGUMENTARY SYSTEM (1).pdf
- 1. INTEGUMENTARY SYSTEM By Dr. S Divya Assistant Professor Dept. of Pharmacy Practice 1
- 2. INTRODUCTION The integumentary (in-inward; tegere-to cover) system is composed of the: o skin, o hair, o oil and sweat glands, o nails, and o sensory receptors The integumentary system contributes to homeostasis by protecting the body and helping regulate body temperature The integumentary system helps maintain a constant body temperature, protects the body, and provides sensory information about the surrounding environment. 2
- 3. SKIN Of all the body’s organs, none is more easily inspected or more exposed to infection, disease, and injury than the skin. Although its location makes it vulnerable to damage from trauma, sunlight, microbes, and pollutants in the environment, the skin’s protective features ward off such damage. Because of its visibility, skin reflects our emotions (frowning, blushing) and some aspects of normal physiology (such as sweating). Changes in skin color may also indicate homeostatic imbalances in the body. o For example, the bluish skin color associated with hypoxia (oxygen deficiency at the tissue level) is one sign of heart failure as well as other disorders. Dermatology (dermato- skin; logy-study of) is the medical specialty that deals with the diagnosis and treatment of integumentary system disorders 3
- 4. STRUCTURE OF SKIN The skin (also known as the cutaneous membrane or integument) is the largest organ in the body and covers the external surface of the body. In adults, the skin covers an area of about 2 square meters (22 square feet) and weighs 4.5–5 kg (10–11 lb), about 16% of total body weight. It ranges in thickness from 0.5 mm (0.02 in.) on the eyelids to 4.0 mm (0.16 in.) on the heels. However, over most of the body it is 1–2 mm (0.04–0.08 in.) thick. It includes glands, hair and nails. There are two main layers of skin: Epidermis (superficial, thinner portion, which is composed of epithelial tissue) Dermis (deeper, thicker connective tissue portion) 4
- 5. Between the skin and underlying structures is the subcutaneous layer (also called hypodermis) composed of areolar tissue and adipose (fat) tissue. The subcutaneous layer serves as a storage depot for fat and contains large blood vessels that supply the skin. This region also contains nerve endings called pacinian (lamellated) corpuscles that are sensitive to pressure 5 Sectional view of skin
- 6. EPIDERMIS The epidermis is composed of keratinized stratified squamous epithelium. It contains four principal types of cells: ▪ Keratinocytes ▪ Melanocytes ▪ Langerhans cells ▪ Merkel cells 6
- 7. I. Keratinocytes: About 90% of epidermal cells are keratinocytes (keratino- horn like; cytes- cells), which are arranged in four or five layers and produce the protein keratin. Keratin is a tough, fibrous protein that helps protect the skin and underlying tissues from heat, microbes, and chemicals. Keratinocytes also produce lamellar granules, which release a water-repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials. II. Melanocytes About 8% of the epidermal cells are melanocytes (melano- black), which develop from the ectoderm of a developing embryo and produce the pigment melanin. Their long, slender projections extend between the keratinocytes and transfer melanin granules to them. 7
- 8. Melanin is a yellow-red or brown-black pigment that contributes to skin color and absorbs damaging ultraviolet (UV) light. Once inside keratinocytes, the melanin granules cluster to form a protective veil over the nucleus, on the side toward the skin surface. In this way, they shield the nuclear DNA from damage by UV light. Although their melanin granules effectively protect keratinocytes, melanocytes themselves are particularly susceptible to damage by UV light. III. Langerhans cells Langerhans cells arise from red bone marrow and migrate to the epidermis, where they constitute a small fraction of the epidermal cells. They participate in immune responses mounted against microbes that invade the skin, and are easily damaged by UV light. Their role in the immune response is to help other cells of the immune system recognize an invading microbe and destroy it. 8
- 9. IV. Merkel cells Merkel cells are the least numerous of the epidermal cells. They are located in the deepest layer of the epidermis, where they contact the flattened process of a sensory neuron (nerve cell), a structure called a Merkel (tactile) disc. Merkel cells and their associated Merkel discs detect touch sensations Layers of Epidermis In most regions of the body the epidermis has four strata or layers: o stratum basale o stratum spinosum o stratum granulosum, o stratum corneum (thin skin) 9
- 10. Where exposure to friction is greatest, such as in the fingertips, palms, and soles, the epidermis has five layers: o stratum basale o stratum spinosum o stratum granulosum o stratum lucidum o stratum corneum (thick skin) 10
- 11. 11 Layers and cell types in epidermis
- 12. Stratum basale: Deepest layer, composed of a single row of cuboidal or columnar keratinocytes that contain scattered tonofilaments (intermediate filaments). Stem cells undergo cell division to produce new keratinocytes. Melanocytes and Merkel cells associated with Merkel discs are scattered among the keratinocytes The stratum basale is also known as the stratum germinativum to indicate its role in forming new cells. Stratum spinosum: (spinos- thorn like) Eight to ten rows of many-sided keratinocytes with bundles of tonofilaments. This arrangement provides both strength and flexibility to the skin. It includes arm like processes of melanocytes and Langerhans cells. 12
- 13. Stratum granulosum: Stratum granulosum (granulos- little grains) contains three to five rows of flattened keratinocytes, in which organelles are beginning to apoptosis (programmed cell death) A distinctive feature of cells in this layer is the presence of darkly staining granules of a protein called keratohyalin, which converts tonofilaments into keratin, The keratinocytes also contain lamellar granules, which release a lipid-rich, water-repellent secretion. The lipid rich secretion acts as a water-repellent sealant, retarding loss and entry of water and entry of foreign materials. Stratum lucidum The stratum lucidum (lucid- clear) is present only in the thick skin of areas such as the fingertips, palms, and soles. It consists of three to five layers of flattened clear, dead keratinocytes that contain large amounts of keratin and thickened plasma membranes. 13
- 14. Stratum Corneum : The stratum corneum (corne- horn or horny) consists on average of 25 to 30 layers of flattened dead keratinocytes. These cells are continuously shed and replaced by cells from the deeper strata. The interior of the cells contains mostly keratin. Between the cells are lipids from lamellar granules that help make this layer an effective water- repellent barrier. Its multiple layers of dead cells also help to protect deeper layers from injury and microbial invasion. *Keratinization Newly formed cells in the stratum basale are slowly pushed to the surface. As the cells move from one epidermal layer to the next, they accumulate more and more keratin, a process called keratinization. Then they undergo apoptosis. Eventually the keratinized cells slough off and are replaced by underlying cells that in turn become keratinized. The whole process takes about four weeks in an average epidermis of 0.1 mm (0.004 in.) thickness 14
- 15. DERMIS The second, deeper part of the skin, the dermis, is composed of a strong connective tissue containing collagen and elastic fibers. This woven network of fibers has great tensile strength (resists pulling or stretching forces). The dermis also has the ability to stretch and recoil easily. The few cells present in the dermis include predominantly fibroblasts, with some macrophages, and a few adipocytes near its boundary with the subcutaneous layer. Blood vessels, nerves, glands, and hair follicles (epithelial invaginations of the epidermis) are embedded in the dermal layer. The dermis is essential to the survival of the epidermis, and these adjacent layers form many important structural and functional relations. Based on its tissue structure, the dermis can be divided into a superficial papillary region and a deeper reticular region 15
- 16. ➢ Papillary region The superficial portion of the dermis and makes up about one-fifth of the thickness of the dermis. It consists of areolar connective tissue with thin collagen and fine elastic fibers. Its surface area is greatly increased by dermal papillae, small, fingerlike structures that project into the undersurface of the epidermis. Some dermal papillae also contain tactile receptors called Meissner corpuscles or corpuscles of touch, nerve endings that are sensitive to touch, and free nerve endings, dendrites that lack any apparent structural specialization. 16
- 17. ➢ Reticular region The reticular region, which is attached to the subcutaneous layer, consists of dense irregular connective tissue containing fibroblasts, bundles of collagen, and some coarse elastic fibers. The collagen fibers in the reticular region interlace in a netlike manner. A few adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands occupy the spaces between fibers. The combination of collagen and elastic fibers in the reticular region provides the skin with strength, extensibility (ability to stretch), and elasticity (ability to return to original shape after stretching) 17
- 18. ACCESSORY STRUCTURES OF SKIN Accessory structures of the skin are: hair, skin glands, and nails, which develop from the embryonic epidermis. HAIR: ❑ Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the fingers, the soles, and plantar surfaces of the feet. ❑ In adults, hair usually is most heavily distributed across the scalp, in the eyebrows, in the axillae (armpits), and around the external genitalia. ❑ Hair on the head guards the scalp from injury and the sun’s rays. It also decreases heat loss from the scalp. ❑ Eyebrows and eyelashes protect the eyes from foreign particles, as does hair in the nostrils and in the external ear canal. ❑ Touch receptors (hair root plexuses) associated with hair follicles are activated whenever a hair is moved even slightly. Thus, hairs also function in sensing light touch. ❑ Hairs are growths of epidermis composed of dead, keratinized epidermal cells. 18
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- 20. SKIN GLANDS: The glands are epithelial cells that secrete a substance. Several kinds of exocrine glands are associated with the skin: sebaceous (oil) glands, sudoriferous (sweat) glands, and ceruminous glands. Mammary glands, which are specialized sudoriferous glands that secrete milk. Sebaceous glands (sebace- greasy) or oil glands are simple, branched acinar glands. Sebaceous glands secrete an oily substance called sebum, a mixture of triglycerides, cholesterol, proteins, and inorganic salts. Sebum coats the surface of hairs and helps keep them from drying and becoming brittle. These glands are present in some locations, such as the lips, glans penis, labia minora, and tarsal glands of the eyelids, skin of the breasts, face, neck, and superior chest 20
- 21. Sudoriferous glands: There are three to four million sweat glands, or sudoriferous glands ( sudor- sweat; ferous -bearing). The cells of these glands release sweat, or perspiration, into hair follicles or onto the skin surface through pores. Sweat glands are divided into two main types, eccrine and apocrine, based on their structure, location, and type of secretion. Eccrine sweat glands (eccrine-secreting outwardly), also known as merocrine sweat glands, are simple, coiled tubular glands that are much more common than apocrine sweat glands. These are especially present in the skin of the forehead, palms, and soles Apocrine sweat glands (apo- separated from) are also simple, coiled tubular glands. They are found mainly in the skin of the axilla (armpit), groin, areolae (pigmented areas around the nipples) of the breasts, and bearded regions of the face in adult males 21
- 22. Ceruminous Glands are modified sweat glands in the external ear, called ceruminous glands (cer- wax), produce a waxy lubricating, yellow colored secretion called cerumen Cerumen, together with hairs in the external auditory canal, provides a sticky barrier that impedes the entrance of foreign bodies and insects. NAILS: Nails are plates of tightly packed, hard, dead, keratinized epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of the digits. Each nail consists of a nail body, a free edge, and a nail root. Functionally, nails help us grasp and manipulate small objects in various ways, provide protection against trauma to the ends of the digits, and allow us to scratch various parts of the body. 22
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- 24. FUNCTIONS OF SKIN The numerous functions of the integumentary system (mainly the skin) include thermoregulation, storage of blood, protection, cutaneous sensations, excretion and absorption, and synthesis of vitamin D. Thermoregulation Thermoregulation is the homeostatic regulation of body temperature. The skin contributes to thermoregulation in two ways: o by liberating sweat at its surface and o by adjusting the flow of blood in the dermis. In response to high environmental temperature or heat produced by exercise, sweat production from eccrine sweat glands increases; the evaporation of sweat from the skin surface helps lower body temperature. 24
- 25. In addition, blood vessels in the dermis of the skin dilate (become wider); consequently, more blood flows through the dermis, which increases the amount of heat loss from the body. In response to low environmental temperature, production of sweat from eccrine sweat glands is decreased, which helps conserve heat. Also, the blood vessels in the dermis of the skin constrict (become narrow), which decreases blood flow through the skin and reduces heat loss from the body. Blood Reservoir The dermis houses an extensive network of blood vessels that carry 8–10% of the total blood flow in a resting adult. For this reason, the skin acts as a blood reservoir. 25
- 26. Protection The skin provides protection to the body in various ways: Keratin protects underlying tissues from microbes, abrasion, heat, and chemicals and the tightly interlocked keratinocytes resist invasion by microbes. Lipids released by lamellar granules inhibit evaporation of water from the skin surface, thus guarding against dehydration; they also retard entry of water across the skin surface during showers and swims. The oily sebum from the sebaceous glands keeps skin and hairs from drying out and contains bactericidal chemicals that kill surface bacteria. The acidic pH of perspiration retards the growth of some microbes. The pigment melanin helps shield against the damaging effects of ultraviolet light. 26
- 27. Epidermal Langerhans cells alert the immune system to the presence of potentially harmful microbial invaders by recognizing and processing them. Macrophages in the dermis phagocytize bacteria and viruses. Cutaneous Sensations Cutaneous sensations are sensations that arise in the skin, including tactile sensations—touch, pressure, vibration, and tickling; as well as thermal sensations such as warmth and coolness. Another cutaneous sensation, pain, usually is an indication of impending or actual tissue damage. There is a wide variety of nerve endings and receptors distributed throughout the skin, including the tactile discs of the epidermis, the corpuscles of touch in the dermis, and hair root plexuses around each hair follicle 27
- 28. Excretion and Absorption The skin normally has a small role in excretion, the elimination of substances from the body, and absorption, the passage of materials from the external environment into body cells Despite the almost waterproof nature of the stratum corneum, about 400 mL of water evaporates through it daily. Besides removing water and heat from the body, sweat also is the vehicle for excretion of small amounts of salts, carbon dioxide, and two organic molecules that result from the breakdown of proteins—ammonia and urea. The absorption of water-soluble substances through the skin is negligible, but certain lipid-soluble materials do penetrate the skin. These include fat-soluble vitamins (A, D, E, and K), certain drugs, and the gases oxygen and carbon dioxide. 28
- 29. Synthesis of Vitamin D Synthesis of vitamin D requires activation of a precursor molecule in the skin by ultraviolet (UV) rays in sunlight. Enzymes in the liver and kidneys then modify the activated molecule, finally producing calcitriol, the most active form of vitamin D. Calcitriol is a hormone that aids in the absorption of calcium in foods from the gastrointestinal tract into the blood. Only a small amount of exposure to UV light (about 10 to 15 minutes at least twice a week) is required for vitamin D synthesis. 29
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