Laboratory Exercise: Integumentary System

Learning objectives

1. Know the layers of the skin.2. Understand how the components of the skin serve its various functions.

This laboratory exercise serves both as an introduction to the skin, the largest organ of the body, and as a review of the major tissues. As you study the slides of the skin, identify examples of epithelium, connective tissue, muscle and nerve.

The majority of skin (integument) is thin skin, most of which is hairy. Thick skin is restricted to the ventral surface of the hands and feet. All skin is made up of three layers:

Epidermis- stratified squamous keratinizing epitheliumDermis - a superficial papilllary layer of loose connective tissue, underlain by a reticular layer of dense fibrous irregularly arranged connective tissueHypodermis - deepest layer of skin, also called subcutaneous tissue, loose connective tissue, containing adipose tissue

Basic Review:

Specimen: Brown Skin (HUMAN)

Epidermis: The stratified squamous keratinizing epithelium of the epidermis is made up primarily of keratinocytes. The form and function of these cells changes as they pass from basal to superficial locations. This layer is particularly conspicuous in thick skin. Identify:

Stratum basale (germinativum). Cells of all the layers are generated from the keratinocytes in this layer. Therefore, you may see mitotic figures. The keratinocytes in this and the overlying layers contain melanin granules that have been transferred to them by melanocytes. Cells within the stratum basale with unstained cytoplasm are likely to be melanocytes. Special staining methods are required to identify melanocytes definitively.

Stratum spinosum. This is several cell layers in thickness. The cells are attached to each other by intercellular bridges (desmosomes). Because the cells are artifactually pulled apart, the attachment sites give the cells a spiny appearance.

The cells of the stratum granulosum are recognized by their basophilic keratohyalin granules. This epidermal layer marks the boundary between the non-keratinized and keratinized layers of the epidermis. The stratum lucidum is not clearly identifiable in this slide.

The superficial keratinized layer is the stratum corneum. In some areas it is partially disrupted by sectioning; this is a common artifact that may fortuitously show the lamellar nature of this layer.

Dermis: Papillary layer: loose connective tissue underlying the basal layer of the epidermis, and containing blood vessels, nerves and lymphatic vessels. Dermal papillae may contain sensory nerve endings, the Meissner's corpuscles. Reticular layer: dense, irregularly arranged connective tissue.

Eccrine sweat glands are present in high concentration in the dermis and subcutaneous tissue. They are coiled tubular glands surrounded by connective tissue. The coiled portion of each gland contains a secretory segment and part of the duct system.

The secretory tubules have a larger diameter and an acidophilic margin, which corresponds to the layer of myoepithelium. The duct tubules are smaller, darker, and formed by a double layer of cuboidal epithelial cells, which may not be obvious in every sectioned duct. A straight portion of the duct passes through the superficial dermis to the basal aspect of the epidermis where it again assumes a coiled pathway. Note the terminal corkscrew-like path of the duct in the stratum corneum.

Pacinian corpuscles, another type of nerve ending, are found in the dermis or subcutaneous tissue. They are made up of an axon surrounded by numerous concentric cellular lamellae. These are also found in other regions of the body. They respond to vibration and deep pressure.

Subcutaneous tissue (hypodermis): This is loose connective tissue containing abundant adipose tissue. It is a good region to examine glands, ducts, blood vessels and nerves.

Specimen: Human Scalp

Hair follicles, sectioned longitudinally, are well demonstrated in this slide. The thin epidermis, characteristic of hairy regions, has a lacy or frayed stratum corneum whose appearance is an artifact of sectioning. In life, this layer of the epidermis would be more compact and only the most superficial keratinized cells would be desquamating.

The deepest part of the hair follicle is expanded into a bulb and is invaginated by connective tissue, the dermal papilla. The follicle cells adjacent to the papilla are the germinative cells, and it is by their division and differentiation that a hair shaft and a multi-layered inner root sheath are formed. Melanocytes are adjacent to the dermal papilla and contribute melanin granules to the developing hair. The cytoplasm of melanocytes is unstained. The fully formed hair is usually lost from the section.

Sebaceous glands are associated with the hair follicle and their secretions empty into the hair follicle, between the hair shaft and the follicle wall. Arrector pili muscle is a band of smooth muscle that inserts on the hair follicle, deep to the sebaceous glands. Superficially it inserts at the base of the epidermis. Some eccrine sweat glands are dispersed between the hair follicles.

Review of Specimen:

Epidermis (LPO) Epidermis (LPO)

Dermis (HPO) Dermis (HPO)

Hypodermis (LPO) Hypodermis (HPO)

Questions:

1. Which of the following is composed of loose connective tissue?a. Epidermisb. Reticular layer of dermisc. Hypodermisd. Both a and be. Both b and c

2. Where is thick skin found?a. Over the kneeb. Sole of the feetc. Breastd. Lipse. All of the above

3. Which layer of the epidermis has cells which have keratohyaline granules?a. Stratum basaleb. Stratum spinosumc. Stratum granulosumd. Stratum lucidume. Stratum corneum

4. Which cell is a macrophage found in the skin?a. Kupffer cellsb. Histiocytec. Dust celld. Langerhans celle. Microglia

5. A new miracle skin cream recently hit the beauty counters which is suppose to stimulate collagen production. Which cell is it supposedly stimulating?

a. Langerhans cellb. Keratinocytec. Melanocyted. Merkel celle. Fibroblast

6. What is the half moon shaped white area on a nail called?a. Lunula b. Eponychium c. Matrix d. Nail bed e. Root

7. What is the growing part of the nail?a. Lunula b. Eponychium c. Matrix d. Nail bed e. Root

8. What type of glands are the ceruminous glands?a. Sebaceous glandsb. Eccrine sweat glandc. Endocrine glandd. Apocrine sweat glande. Oil gland

9. Which of the following is the most abundant sensory receptor of the skin?a. Free nerve endingsb. Ruffini's corpusclesc. Pacinian corpusclesd. Krause's end bulbse. Meissner's corpuscle

10. Where can hair be found?a. Palms of hand b. Soles of feet c. Urogenital openings d. Lips e. Eyelid

III. Review Questions:

1. What are the five layers of the epidermis? Stratum2. What is the name and function of the two layers of the dermis? 3. During the healing process of the skin, what type of tissue is an open wound filled with? 4. What type of gland produces a non-viscus, watery solution which helps regulate body temperature? 5. In what layer does the body store fatty tissue? 6. In what areas of the body would you find an extra layer of skin, known as the strantum lucidum? 7. Name one function the Integumentary system does to release heat. 8. What Abnormal skin coloration deals with pale skin, whit hair, and pink color of the iris in the eye? 9. Name three functions of the skin.