A&P Essay Ch 5

Describe the major differences between thin skin and thick skin.

Thick skin is found on palms, palmar surfaces of digits, and soles, while thin skin is found in all other areas. Thick skin is 4-5× thicker than thin skin. The stratum lucidum is present exclusively in thick skin. Also, the stratum spinosum and stratum corneum are thicker in thick skin. Thick skin exhibits epidermal ridges, more sweat glands and a higher density of sensory receptors. Thin skin has hair follicles and sebaceous glands, while thick skin does not.

Describe how fingerprints are formed and what they are used for.

epidermal ridges develop during the third or fourth fetal month as the epidermis conforms to the contours of the underlying dermal papillae of the papillary region. The ridges increase the surface area of the epidermis and thus increase the grip of the hand or foot by increasing friction. Because the ducts of sweat glands open on the tops of the epidermal ridges as sweat pores, the sweat and ridges form fingerprints upon touching a smooth object. The epidermal ridge pattern is genetically determined and is unique for each individual allowing these patterns to be used to identify individuals.

Describe the structure and function of arrector pili.

Arrector pili are smooth muscles that extend from the superficial dermis of the skin to the dermal root sheath around the side of the hair follicle. In its normal position, hair emerges at an angle to the surface of the skin. Under physiological or emotional stress, such as cold or fright, autonomic nerve endings stimulate the arrector pili muscle to contract, which pulls the hair shafts perpendicular to the skin surface. This action causes "goose bumps" because the skin around the shaft forms slight elevations.

Briefly describe the steps in deep wound healing.

In deep wound healing, a blood clot forms during the inflammatory response and loosely unites the wound edges. Then in the migratory phase the clot becomes a scab and epithelial cells migrate beneath the scab to bridge the wound. Fibroblasts migrate along fibrin threads and begin synthesizing scar tissue and damaged blood vessels begin to regrow. During this phase, the tissue filling the wound is called granulation tissue. The proliferative phase is characterized by extensive growth of epithelial cells beneath the scab, deposition by fibroblasts of collagen fibers in random patterns, and continued growth of blood vessels. During the maturation phase, the scab sloughs off once the epidermis has been restored to normal thickness. Collagen fibers become more organized, fibroblasts decrease in number and blood vessels are restored to normal.

Briefly describe the steps in epidermal wound healing.

In response to an epidermal injury, basal cells of the epidermis surrounding the wound break contact with the basement membrane. The cells then enlarge and migrate across the wound. The cells appear to migrate as a sheet. When epidermal cells encounter each other they stop migrating due to contact inhibition. Migration of the epidermal cells stops completely when each is finally in contact with other epidermal cells on all sides. Epidermal growth factor is also secreted to stimulate the basal stem cells to divide and replace the ones that have moved into the wound. Epidermal cell division eventually regenerates the strata of the epidermis.

John has just been brought into the emergency room following a fiery explosion at a chemical plant. He is diagnosed with third degree burns over the anterior surfaces of his arms and trunk. What specific structural damage has occurred to his skin? What risks to John's life have resulted from this damage?

John has lost approximately 27% of his skin's surface area (according to the Rule of Nines), which leads to severe systemic effects. The epidermis, dermis, subcutaneous layer and associated structures have been destroyed. Sensory function is lost. Loss of epidermis (and so, lost keratin and Langerhans cells) makes John susceptible to microbial invasion. Loss of keratinized structures and lamellar granules allows for extreme loss of water, plasma, and plasma proteins, which causes shock; leading to dehydration, reduced blood volume and circulation, decreased urine output and diminished immune responses.

Describe the structural characteristics of the epidermis that contribute to its ability to protect the surface of an animal.

Multiple layers of cells in stratified squamous epithelium help resist friction. Keratin of intermediate filaments provides strength to tissue by binding cells tightly together and to underlying tissue, thus creating a barrier to microbes. Lamellar granules of keratinocytes produce a lipid rich, water repellent (sealant) to protect from dehydration and entry of foreign materials. Melanin, produced by melanocytes, protects underlying tissue from UV light. Sebum secreted onto the surface helps protect from dehydration and microbial invasion. Intraepidermal macrophages (Langerhans cells) participate in immune response to microbial invasion.

Describe the structure and function of the different types of exocrine glands found in the skin

Sebaceous glands are oil glands. They are connected to hair follicles (with few exceptions). The secreting portion lies in the dermis and opens into the neck of a hair follicle. They are absent in the palms and soles. The secretory product of sebaceous gland is known as sebum. Sebum prevents the hair from drying and becoming brittle. Sudoriferous glands are sweat glands. They release sweat into hair follicles or onto the skin surface through pores. There are two types of sweat glands: Eccrine and Apocrine. Eccrine sweat glands are distributed throughout the skin including the palm and the soles. The sweat produced by these glands contains water, ions, urea, uric acid, ammonia, amino acids, glucose and lactic acid. The main function of eccrine glands is to regulate body temperature. Apocrine sweat glands are predominantly found in the skin of the axilla, groin, areolae and the bearded region of the face.

List and briefly describe the major functions of the skin.

The functions of the skin include: 1) Thermoregulation: The skin thermoregulates in response to increased temperature by secreting sweat onto its surface and then increasing blood flow to the surface leading to cooling of the blood. In response to low temperatures, production of sweat is decreased and blood flow is diverted from surface to conserve heat. 2) The skin contains 8-10% of the blood and thus serves as a blood reservoir. 3) The skin covers the body and provides protection using keratin, lipids, secretions like oil and sweat, and immunological defenses. 4) The skin can detect and respond to cutaneous sensations. 5) The skin helps in excretion and absorption. 6) The skin also can synthesize vitamin D.