Objectives
- Identify different types of skin.
- Identify different layers of the epidermis.
- Identify the structures found in the dermis.
Skin Overview
Skin is also referred to as the integumentary system. The skin covers the entire outer surface of the body and constitutes 15-20% of the body’s mass. Skin can be characterized as thick or thin. Functions include acting as a physical/chemical/biologic barrier; provides immunologic information; maintains homeostasis through regulation of temperature and water loss; conveys sensory information; endocrine function by secreting hormones, cytokines, and growth factors; and functions in excretion of glandular products. Skin can be described as thick or thin.
Layers and derivatives of skin:
- Epidermis– derived from ectoderm, composed of keratinized stratified squamous epithelium; 5 layers in thick skin basal to apical:
- Stratum basale (mitotically active) > Stratum spinosum > Stratum granulosum > stratum lucidum (thick skin only) > Stratum corneum (keratinized layer)
- Dermis– derived from mesoderm
- Consists of a thin papillary layer, just deep to the epidermis, made of loose connective tissue
- Deep to the papillary layer is the reticular layer consisting of dense irregular connective tissue
- Hypodermis– derived from mesoderm, deep to the dermis and contains variable amounts of adipose tissue arranged in lobules that are separated by CT; described as subcutaneous fascia in gross anatomy
- Hair follicles and Hair
- Sweat glands– eccrine sweat glands produce sweat and are found throughout the body while apocrine sweat glands produce sweat with high concentrations of carbohydrates, lipid, and proteins and are found in the axilla, areola and nipple of the breast, around the anus and external genitalia.
- Sebaceous glands produce sebum
- Nails
- Mammary glands (breast tissue; discussed in a separate topic)
Cells of the epidermis:
- Keratinocytes– make up the majority of cells, function to separate the human or animal from its external environment and produce keratins for tonofilaments (intermediate filaments), found throughout the layers of the epidermis in different shapes and loose their nucleus as they approach the most apical layer.
- Melanocytes– make up about 5% of the epidermis, pigment- producing, derived from neural crest cells found in the stratum basale and extend processes into stratum spinosum.
- Macrophage Langerhan cells– antigen-presenting cells of the immune system that make up 2-3% of the epidermis and migrate from the epidermis to lymph nodes. Not easily identifiable in routine H&E stains.
- Tactile epithelial (Merkel) cells– mechanoreceoptor cells with sensory nerve endings that make up <1% of the epidermis. Found in the stratum basale with a lobed nucleus and more dense cytoplasm than melanocytes and macrophage (Langerhan) cells.
Encapsulated nerve endings in skin are found in the dermis:
- Lamellar (Pacinian) corpuscles– detect pressure and vibration, found in the reticular dermis
- Tactile (Meissner’s) corpuscles– detect light touch, found in the dermal papillae
- Bulbous (Ruffini’s) corpuscles– detect stretch and torque, found in the reticular dermis
- Bulboid corpuscle (Krause’s end bulb)– detects cold
Skin Slides
Don’t forget to zoom into each annotation box to review all of the structures closely. Large annotation boxes may have smaller arrows not noticed until you zoom in further.
This is a specimen of thick skin which is typically found on the soles of feet and palms of the hands. You should note that there are no hair follicles, which is typical of thick skin. In this specimen, you will examine the epidermis and dermis. You will observe that the epidermal-dermal junction is an irregular border with projections of the dermis into the epidermis called dermal papillae. These are part of the more superficial papillary layer of the dermis consisting of loose connective tissue. As you move deeper into the reticular dermal layer, you will see an increase in collagen and dense irregular connective tissue. In the epidermis, you will identify the layers including (deep > superficial): stratum basale > stratum spinosum > stratum granulosum > stratum lucidum (thick skin only) > and stratum corneum (look for lack of nuclei). You will mainly see keratinocytes but may come across the other cells types in the more basal layers. In the dermis, you will find eccrine sweat glands, tactile (Meissner’s) corpuscles and lamellar (Pacinian) corpuscles. You will also see vessels and adipocytes throughout the dermis and come across eccrine sweat glands. These glands have 3 cell types: clear cells, dark cells, and myoepithelial cells in a pseudostratified epithelium while the ducts that travel toward the epithelium have a stratified cuboidal epithelium.
This specimen is an example of thin skin. Which layer of the epidermis is not included here? You will notice the stratum corneum is much thinner compared to the thick skin of the previous slide. The separation of this layer in the slide is due to tissue processing artifact. You will observe the presence of melanin on some of the cells in the stratum basale which is secreted from melanocytes. There are some hair follicles which are associated with arrector pili muscles and sebaceous glands. We will examine the hair follicle more closely in the scalp slide below.
This specimen is taken from the axilla region. Like other parts of the body, there are a few hair follicles and eccrine sweat glands. You can also find apocrine sweat glands which are limited to the axilla and few other regions of the body listed above. Apocrine glands tend to have a wider lumen than the eccrine glands and consists of only 1 cell type arranged in a simple epithelium structure. Use this slide to review the layers of the epidermis and identify hair follicles and glandular tissue.
Using the specimen of the scalp, we can closely observe the structure of the hair follicle. The roots are found deep in the hypodermis. Throughout the section, you can see different angles of the hair shafts due to how the tissue was sectioned. When viewing the hair follicles, look for the sebaceous glands and their ducts emptying into the hair follicles. You will see hair bulbs and the layers of the follicle including the inner and outer root sheaths and connective tissue glassy membrane. The inner root sheath is made up of 2 layers: Huxley layer (inner flat cells) and Henle layer (outer cuboidal cells). The Huxley layer is difficult to appreciate as the nuclei are difficult to see. You will also see examples of the hair shafts consisting of the medulla (very center), cortex, and cuticle (very outer region of the hair shaft). Hair shafts are often missing in preparations but here there are examples where the hair shaft is present and some where it is not. You should also be able to find the arrector pili muscles. Take a close look and decide if these are skeletal or smooth muscle.
More Practice
Use this specimen to determine whether you are looking at thick or thin skin. Identify the different layers of the epidermis and the structures found in the dermis.
Use this specimen to practice identifying structures within the hair follicle and those associated with the hair follicle. You can also review layers of the epidermis and other structures of the dermis.
More Practice Answers
Slide Michigan 03 Skin
- A) Thick skin; B) black- s. corneum; white- s. lucidum; yellow- s. granulosum; green- s. spinosum; blue- s. basale
- A) white arrows- dermal papillae; B) red arrow- tactile (Meissner’s) corpuscle (capsulated nerve)
- A) eccrine sweat glands; B) myoepithelial cells
- Lamellar (Pacinian) corpuscle (encapsulated nerve)
Slide Michigan 107 Scalp
- A) epidermis between 2 black arrows; B) blue- dermis; C) yellow- hypodermis
- A) black- papillary layer; B) blue- reticular layer
- A) black- sebaceous gland; B) blue- eccrine sweat gland
- black- arrector pili muscle, smooth muscle
- A) boxed area: distal part of hair follicle; B) green- Hair shaft (medulla in center); C) yellow- Huxley layer of inner root sheath; D) white- Henle layer of inner root sheath; E) blue- outer root sheath (multi cell layer)
- Medulla of Hair shaft
