1. Chapter 6 Integumentary System

2. 6.1 Introduction When 2 or more types of tissues are grouped together and preforming specialized functions they constitute an organ The skin is the largest organ in the body by weight The integumentary system is made up of the skin and it’s various accessory structures, which include: Hair Fingernails Sensory receptors glands

3. 6.2 Skin and it’s tissues Skin is vital to maintaining homeostasis. it helps regulate body temperature Prevents water loss from deeper tissues Houses sensory receptors Synthesizes various biochemical Excretes small amounts of wastes

4. Skin plays a role in production of vitamin D. This is necessary for normal bone and tooth development Vitamin D can be obtained by the diet OR Form from a substance that is synthesized by cells in the digestive system when it reaches the skin by the blood and is exposed to ultraviolet light from the sun it is converted to vitamin D.

5. The skin has 2 distinct layers: Outer layer, made of stratified squamous epithelium – epidermis Inner layer – dermis Thicker Includes connective tissues and epithelia tissue Smooth muscle Nervous tissue Blood The basement membrane anchors the epidermis to the dermis.

6. Subcutaneous Layer (hypodermis) Not a true layer of skin Made mostly of adipose tissue Binds skin to the underlying organs No sharp boundary defines it from the dermis. Contains major blood vessels that supply the skin and underlying adipose tissue.

7. Epidermis Lacks blood vessels Deepest layer is called stratum basale and is nourished by dermal blood vessels The newest layers divide at the bottom and as they are pushed away from nourishment they die Keratinization- is the process where the older cells harden Cytoplasm fills with strands of keratin protein Results of keratinization is many tightly packed layers of dead cells that make up the stratum corneum (outermost epidermis)

8. Epidermis has 4 layers (usually), but there are 5 in total 1. stratum basale 2.Stratum spinosum 3.Stratum granulosum 4.Stratum corneum 5. stratum corneum – found only on palms and soles Healthy skin produces cells at about the same rate that we loose dead cells. Where skin is rubbed the body produces more skin cells resulting in calluses on palms and soles, and corns on toes.

9. Epidermis has several important functions: Shields the moist underlying tissue Prevents water loss Mechanical injury Effects harmful chemicals (prevents) Keeps out disease causing microorganisms Melanin – a dark pigment that provides skin color produced in special cells called melanocytes Absorb ultraviolet radiation, preventing it from causing mutations to DNA in the cells.

10. Skin Color Due largely to melanin All people have about the same number of melanocytes in their skin Differences in skin color come largely from the amount of melanin produced Skin color is mostly genetically determined ** there are hundreds of genes that control skin and hair color**

11. Environmental and physiological factors also influence skin color Sunlight and ultraviolet light and X rays stimulate the additional production of pigment Blood also gives the skin a pinkish color (in light skinned people) When blood oxygen concentrations is low, hemoglobin (a dark red) is produced and makes skin appear bluish A diet high in yellow vegetables may turn skins orange- yellow, these foods are high in the pigment beta- carotene Newborns can have jaundice, which makes their skin a yellow color and is the build up of bilirubin

12. Dermis Fingerprints are formed from the uneven boundary between the epidermis and the dermis Ridges of the epidermis project inward into the dermis making dermal papillae. These are found all over the body but are very abundant on hands and feet. Genes determine fingerprints.

13. The dermis binds the epidermis to underlying tissue Dermal blood vessels supply nutrients to all the skin cell; which help regulate body temperature. Nerve cell processes are scattered throughout the dermis. Motor cell processes carry impulses out from the brain or spinal cord to dermal muscles and glands. Contains specialized accessory structures: Hair follicles Sebaceous glands Sweat glands

14. 6.3 Accessory Structures of the Skin

15. Nails Nails are protective coverings on the ends of fingers and toes Each nail has a nail plate that overlies a nail bed The most active part of the nail bed is the lunula The white moon shaped region of the nail

17. As the cells become keratinized some of the scales become part of the nail. The keratin of nails is harder than that produced by the epidermal stratum corneum. The nail plate extends beyond the nail bed and with normal use, wears away.

18. Hair Follicles Hair is present everywhere except: Palms Soles Lips Nipples Parts of the external reproductive organs Hair develops from a hair follicle which is a group of epidermal cells at the base of a tube-like depression.

19. The follicle extends from the surface to the dermis and contains the hair root. Hair is composed of dead epidermal cells that have keratinized and are pushed upwards.

21. Genes determine hair color, by telling melanocytes how much pigment to produce. Dark hair has a pigment called eumelanin (brownish- black) Blonde and red hair have pheomelanin (reddish- yellow) The lack of pigmentation in the skin and hair is called albinism.

22. A bundle of smooth muscle cells attaches to each hair follicle. This is positioned so that the hair will stand on end when the muscle is contracted. If a person is upset or cold nerve impulses may stimulate the muscles to contract, causing goose bumps.

23. Sebaceous Glands A type of holocrine gland usually associated with hair follicles Sebum (oily mixture of fatty material and cellular debris) helps keep the hair and skin soft, pliable and waterproof Acne is the skin condition that results in the sebaceous glands becoming swollen and clogged which produces blackheads and pimples.

24. Sweat Glands Sweat glands are also known as sudoriferous glands are exocrine glands. Each gland is made of a ting tube that originates as a ball shaped coil in the deeper dermis or superficial subcutaneous layer. The coiled portion of the gland is closed at its deep end and is lined with sweat- secreting epithelial cells.

25. The most common type of sweat gland are the eccrine glands. These glands response to elevated heat by physical exercise or environmental heat. These are common on the forehead, neck and back. They also produce moisture that appears on palms and soles when someone is emotionally stressed.

26. The other type of sweat glands, apocrine glands, become active at puberty. They secret the same way as the eccrine glands. Apocrine glands become active when a person is emotionally upset, frightened, in pain or during sexual arousal. In adults they are found in the axillary regions and groin. The scent of the sweat that is secreted by these glands develops as they are metabolized by skin bacteria.

27. Sweat is mostly water but it also contains small amounts of salt and wastes (urea and uric acid) The average square inch of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes and more than a thousand nerve endings!

29. 6.4 Regulation of Body Temperature The human body needs to remain at 37 0 C (98.6 0 F) in order to carry out metabolic functions at the correct rate. The skin plays a key role in the maintenance of this stable environment.

30. How it works… When the body temperature rises above a set point the nervous system tells the skin and other organs to release heat. Ex.) During physical exercise the active muscles will release heat which is carried away by the blood. The blood goes to the brain and past the hypothalamus which acts as the thermostat for the body The hypothalamus then singles muscles in the walls of the dermal blood vessels to relax. These vessels dilate (vasodilation) more blood enters them and some of the heat in the blood escapes to the outside.

31. 6.5 Healing of Wounds A wound and the area surrounding it usually become red and painfully swollen. This is the result of inflammation and is normal response to injury or stress. Blood vessels in the area will dilate and become permeable allowing fluids to leak into the damaged tissue. The skin may become reddened, warm, swollen and painful to the touch.

32. These dilated blood vessels are providing the tissues with more nutrients and oxygen to aid in the healing process.

33. Injury beyond the epidermis Injury in the dermis or subcutaneous layer where blood vessels break and the released blood forms a clot generally take longer to heal than those in just the epidermis.

34. The blood clot and dried tissue fluid form a scab. This will cover and protect the underlying tissues. Fibroblasts will migrate to the area and begin secreting collagenous fibers that bind the edges of the wound. Suturing (or putting a band-aide) on the wound will speed the process

35. As the wound continues to heal phagocytic cells will remove the dead cells and other debris. Eventually the scab will fall off after damaged tissues are replaced. If the wound is deep, a scar may form. A scar is a extensive production of collagenous fibers that form above the normal surface of the epidermis

37. Large wounds In large open wounds healing is accompanied by formation of granulations (small rounded masses) This consists of new blood vessel branches and a cluster of collagen- secreting fibroblasts that the vessel nourishes. Eventually the granulations will disappear and leave a scar of collagen fibers.

38. Burns