Integumentary system

Introduction of Integumentary system followed by layers of skin and other accessory organs

1. INTEGUMENTARY SYSTEM Presented by:- HIMIKA RATHI

2. INTRODUCTION The integumentary system is composed of the skin, hair, oil and sweat glands, nails, and sensory receptors . The integumentary system helps maintain a constant body temperature, protects the body, and provides sensory information about the surrounding environment.

3. STRUCTURE OF SKIN The skin (also known as the cutaneous membrane or integument) covers the external surface of the body and is the largest organ of the body in both surface area and weight. Structurally, the skin consists of two main parts. The superficial, thinner portion which is composed of epithelial tissue, is the epidermis . The deeper, thicker connective tissue portion is the dermis .

4. EPIDERMIS The epidermis is composed of keratinized stratified squamous epithelium. It contains four principal types of cells: keratinocytes, melanocytes, Langerhans cells, and Merkel cells About 90% of epidermal cells are keratinocytes, 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.

5. EPIDERMIS About 8% of the epidermal cells are melanocytes, which produces the pigment melanin. Their long, slender projections extend between the keratinocytes and transfer melanin granules to them. Melanin is a yellow-red or brown-black pigment that contributes to skin color and absorbs damaging ultraviolet (UV) light.

6. EPIDERMIS 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.

7. EPIDERMIS 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.

8. EPIDERMIS In most regions of the body the epidermis has four strata or layers — S tratum basale S tratum spinosum S tratum granulosum and a thin stratum corneum

9. Stratum basale The deepest layer of the epidermis is the stratum basale, composed of a single row of cuboidal or columnar keratinocytes. Stratum spinosum Superficial to the stratum basale is the stratum spinosum, arranged in 8 to 10 layers of many-sided keratinocytes fitting closely together . Stratum Granulosum At about the middle of the epidermis, the stratum granulosum consists of three to five layers of flattened keratinocytes.

10. Stratum Lucidum The stratum lucidum is present only in the thick skin of areas such as the fingertips, palms, and soles . Stratum Corneum The stratum corneum consists on average of 25 to 30 layers of flattened dead keratinocytes.

11. Dermis The second, deeper part of the skin, the dermis, is composed of a strong connective tissue containing collagen and elastic fibers . The dermis also has the ability to stretch and recoil easily. Leather , which we use for belts, shoes, baseball gloves, and basketballs, is the dried and treated dermis of other animals. Based on its tissue structure, the dermis can be divided into a superficial papillary region and a deeper reticular region.

12. The papillary region makes up about one-fifth of the thickness of the total layer. It consists of areolar connective tissue containing thin collagen and fine elastic fibers . 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 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).

13. Accessory structures of the skin Accessory structures of the skin—hair, skin glands, and nails—develop from the embryonic epidermis. They have a host of important functions. For example, hair and nails protect the body, and sweat glands help regulate body temperature .

14. 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. Although the protection it offers is limited, 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.

15. Anatomy of a Hair The shaft is the superficial portion of the hair, which projects above the surface of the skin. The root is the portion of the hair deep to the shaft that penetrates into the dermis, and sometimes into the subcutaneous layer. The shaft and root of the hair both consist of three concentric layers of cells: medulla, cortex, and cuticle of the hair . C uticle of the hair, the outermost layer, consists of a single layer of thin, flat cells that are the most heavily keratinized

16. Anatomy of a Hair Surrounding the root of the hair is the hair follicle, which is made up of an external root sheath and an internal root sheath, together referred to as an epithelial root sheath . The dense dermis surrounding the hair follicle is called the dermal root sheath . The base of each hair follicle and its surrounding dermal root sheath is an onion-shaped structure, the bulb.

17. 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 . The nail body (plate) is the visible portion of the nail . The free edge is the part of the nail body that may extend past the distal end of the digit. The free edge is white because there are no underlying capillaries.

18. Nails The nail root is the portion of the nail that is buried in a fold of skin. The whitish, crescent-shaped area of the proximal end of the nail body is called the lunula . The proximal portion of the epithelium deep to the nail root is the nail matrix , where cells divide by mitosis to produce growth .

19. Skin Glands Two types of Skin Glands are present: Sebaceous (Oil) Glands Sudoriferous (Sweat) Glands

20. Sebaceous (Oil) Glands Sebaceous glands or oil glands are simple, branched acinar glands . T hey are connected to hair follicles. The secreting portion of a sebaceous gland lies in the dermis and usually opens into the neck of a hair follicle. 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. Sebum also prevents excessive evaporation of water from the skin, keeps the skin soft.

21. Sudoriferous Glands There are three to four million sweat glands, or sudoriferous glands. 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 , also known as merocrine sweat glands, are simple, coiled tubular glands that are much more common than apocrine sweat glands

22. Sudoriferous Glands They are distributed throughout the skin of most regions of the body, especially in the skin of the forehead, palms, and soles. Eccrine sweat glands are not present, however, in the margins of the lips, nail beds of the fingers and toes,and eardrums. The secretory portion of eccrine sweat glands is located mostly in the deep dermis (sometimes in the upper subcutaneous layer)

23. Sudoriferous Glands The sweat produced by eccrine sweat glands (about 600 mL per day) consists of water, ions (mostly Na and Cl ), urea, uric acid, ammonia, amino acids, glucose, and lactic acid. The main function of eccrine sweat glands is to help regulate body temperature through evaporation.

24. Sudoriferous Glands Apocrine sweat glands are also simple, coiled tubular glands. Eccrine sweat glands start to function soon after birth, but apocrine sweat glands do not begin to function until puberty . Apocrine sweat contains the same components as eccrine sweat plus lipids and proteins.

25. Ceruminous Glands Modified sweat glands in the external ear, called ceruminous glands, produce a waxy lubricating secretion. The combined secretion of the ceruminous and sebaceous glands is a yellowish material called cerumen , or earwax. Cerumen also waterproofs the canal and prevents bacteria and fungi from entering cells.

26. Function of Skin Thermoregulation Blood reservoir Protection Cutaneous sensations Excretion Synthesis of vitamin D

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