5.8: Alternate Text Descriptions

Figure 5.1.1: Layers of Skin

This image is a cross-sectional diagram of the skin showing the three major layers: the epidermis, dermis, and hypodermis, along with associated structures.

Figure 5.1.2: Histology Slides of Skin

This image contains two side-by-side histology images, labeled (a) and (b). Both images show a tissue surface layer above underlying connective tissue. The purpose of the figure is to compare the thickness and contour of the upper tissue layer in the two samples.

In image (a), the upper tissue layer is thicker and darker than in the second image. It forms a continuous surface with several downward projections extending into the lighter tissue below. Beneath this upper layer is a broader region of lighter, fibrous-looking connective tissue.

In image (b), the upper tissue layer is thinner and less prominent. The boundary between the surface layer and the underlying connective tissue appears flatter and more irregular. The connective tissue below remains visible and occupies most of the image.

Figure 5.1.3: Histology of thick skin

This image illustrates histological microscopy image stained pink and purple, showing a cross‑section of skin and underlying tissue. At the top is the epidermis, appearing as a thin, dark pink, continuous layer. Beneath it lies the dermis, which is much thicker and lighter in color, containing irregular connective tissue with visible collagen fibers and small blood vessel spaces. The lower portion of the image shows a dense, darker pink band of skeletal muscle fibers arranged in parallel lines. In the bottom left corner, there is a smaller inset image that shows the same tissue section at a lower magnification, highlighting the relationship between the skin layers and the underlying muscle.

Figure 5.1.4: Layers of the Epidermis

This image is a microscopic diagram of thick skin showing the layers of the epidermis and selected cell types and structures.

Epidermis (from superficial to deep):

• Stratum corneum: The outermost layer, composed of dead cells filled with keratin that form a protective barrier.
• Stratum lucidum: A thin, translucent layer found only in thick skin.
• Stratum granulosum: Contains cells with lamellar granules, which contribute to the skin's waterproof barrier.
• Stratum spinosum: Contains numerous keratinocytes, the cells responsible for producing keratin.
• Stratum basale: The deepest layer of the epidermis. This layer contains melanocytes, which produce melanin pigment, and Merkel cells, which are associated with touch sensation. A sensory neuron extends upward from the dermis and makes contact with a Merkel cell.

Dermis:

• Located beneath the epidermis and shown as the pink connective tissue layer at the bottom of the figure.
• The cell bodies of the sensory neurons are not shown, but sensory nerve fibers extend from the dermis to the Merkel cells in the stratum basale.

The diagram emphasizes that the melanocyte and Merkel cell are located within the stratum basale of the epidermis, while the sensory neuron extends upward from the dermis to contact the Merkel cell.

Figure 5.1.5: Cells of the Epidermis

This image shows a high-magnification electron micrograph of the epidermis and underlying dermis, with labeled layers of the skin and associated structures.

The image is organized as a vertical cross-section of skin. The epidermis is located at the top, and the dermis is located below. The labels in the image include epidermis, dermis, stratum corneum, stratum granulosum, stratum spinosum, stratum basale (germinativum), capillary, and remnants of a cross-sectioned shed hair and its follicle.

In the epidermis, the outermost labeled layer is the stratum corneum. It is composed of flattened, tightly packed cells arranged in layers and appears as a dense surface layer. Its function is to provide a protective barrier, prevent water loss, and protect against environmental damage.

Below the stratum corneum is the stratum granulosum. This layer contains cells with visible internal structures associated with keratin production. Its function is to support keratin formation and waterproofing, and its cells begin to transition into the flattened protective cells of the outer layer.

Below the stratum granulosum is the stratum spinosum. This is a thicker layer composed of multiple rows of cells. The cells are more irregular in shape and closely connected. Its function is to provide strength and flexibility to the epidermis, and its cells are actively involved in producing structural proteins.

The deepest labeled epidermal layer is the stratum basale (germinativum). It is composed of a single layer of cells attached to the underlying tissue. Its function is cell division and regeneration of the epidermis. New cells are produced here and move upward as they mature.

In the dermis, the labeled structures include a capillary and remnants of a cross-sectioned shed hair and its follicle. The dermis is located beneath the epidermis and contains connective tissue with embedded structures. Its functions are to provide nutritional support to the epidermis through blood supply, contain structures that support skin function such as hair follicles, and contribute to strength, elasticity, and repair.

The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent water loss from the body, making the skin relatively waterproof. As new keratinocytes are produced atop the stratum basale, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum.

Figure 5.1.6: Layers of the Dermis

This image shows a histological section of human skin, focusing on the dermis, which is divided into two layers:

Papillary Layer

• Located just beneath the epidermis.
• Composed of loose connective tissue with fine collagen fibers and capillaries.
• Supports the epidermis and aids in nutrient exchange and sensory function.

Reticular Layer

• Found below the papillary layer.
• Made of dense connective tissue with thicker collagen fibers.
• Provides structural strength and elasticity.
• Contains sweat glands, hair follicles, and other deep dermal structures.

Figure 5.1.7: Skin Pigmentation

This image shows a side-by-side cellular comparison of dark and light skin, divided into two labeled sections:

• Left: "Dark"
• Right: "Light"

Skin Layers (Top to Bottom):

• Surface – Outermost skin layer
• Upper Keratinocytes – Contain melanin
• Melanosomes – Pigment organelles within keratinocytes
• Basal Keratinocytes – Base layer skin cells
• Melanocytes – Pigment-producing cells

Key Differences:

• Dark Skin has more melanin in keratinocytes and melanosomes. Melanocytes are more active.
• Light Skin has less melanin and fewer melanosomes. Melanocytes produce less pigment.

Figure 5.1.8: Moles

This image contains five close‑up photographs of skin lesions displayed together for comparison. Each photo shows a small area of human skin with a distinct raised or pigmented spot.

• The top row shows three lesions that are generally flat to slightly raised and dark brown in color. Their shapes vary from round to slightly irregular, and their borders range from smooth to uneven. The surrounding skin appears normal in texture and color.
• The bottom left image shows a larger, dark lesion that is clearly raised above the skin surface. It appears dome‑shaped with a rough, uneven texture and a shiny surface.
• The bottom right image shows a raised lesion that is lighter in color, pink to flesh‑toned, with a smooth, glossy appearance. Fine hairs are visible growing from the surrounding skin.

Figure 5.2.1: Hair Follicle

This image shows a cross-sectional diagram of a hair follicle embedded in the skin, including the structure of the hair and associated glands and tissues.

The diagram is organized as a vertical section of skin with the skin surface at the top and deeper layers extending downward. A hair follicle runs from the surface into the deeper tissue. The labels in the image include the hair shaft, cuticle, cortex, medulla, hair follicle, inner root sheath, outer root sheath, hair bulb, hair matrix, hair papilla, sebaceous gland, and arrector pili muscle.

At the top of the image, the hair shaft projects outward from the skin surface. An inset identifies three internal layers of the hair shaft. The labels for these layers are cuticle, cortex, and medulla. The cuticle is the outermost layer, the cortex is the middle layer, and the medulla is the innermost region. The hair shaft provides protection and insulation, and this layered structure contributes to the strength and flexibility of the hair.

Below the skin surface, the hair extends downward into the hair follicle, which is a tubular structure that surrounds and supports the hair root. The follicle anchors the hair in the skin and supports its growth.

Surrounding the hair within the follicle are two labeled sheath layers: the inner root sheath and the outer root sheath. These sheaths stabilize the growing hair and guide its upward movement toward the surface.

At the base of the follicle is an enlarged region labeled the hair bulb. Within the bulb is the hair matrix, which is composed of actively dividing cells. The hair matrix produces new cells that form the hair, and it is the primary site of hair growth.

Also at the base of the bulb is the hair papilla, which contains small blood vessels. The hair papilla supplies nutrients and oxygen to the growing hair cells and helps regulate hair growth activity.

Attached to the side of the hair follicle is the sebaceous gland. A short duct connects this gland to the follicle. The sebaceous gland produces sebum, an oily substance that lubricates and protects the hair and surrounding skin.

A band of muscle labeled the arrector pili muscle attaches to the hair follicle and extends toward the surrounding tissue. When this muscle contracts, it pulls the hair upright. This action contributes to goosebumps and helps move sebum along the hair shaft.

Figure 5.2.2: Histological Image of Skin

This image is a color‑stained histological image of skin viewed under a microscope. The image is predominantly pink and purple, indicating a standard tissue stain used to highlight cells and connective tissue. At the center of the image is a hair follicle, visible as an elongated, tube‑like structure running diagonally through the dermis. The follicle is surrounded by layers of cells that are darker purple, indicating densely packed epithelial tissue involved in hair growth. Around the hair follicle are sebaceous glands, which appear as clusters of pale, rounded cells attached to the follicle. These glands produce oil that lubricates the hair and skin. The surrounding area contains connective tissue with wavy collagen fibers, providing structural support. Toward the edges of the image, lighter circular spaces indicate adipose (fat) tissue, typical of the deeper dermal or subcutaneous layers. Overall, the image demonstrates the organization of skin structures beneath the surface, highlighting the relationship between the hair follicle, glands, connective tissue, and fat.

Figure 5.2.3: Structure of a Fingernail

This image is a structure of a fingernail, shown in external and cross-sectional views. The left panel shows the nail from the surface. The nail plate covers most of the top of the fingertip. The free edge is the white distal portion that extends beyond the fingertip. The lateral nail folds are the skin ridges along the sides of the nail plate. At the base of the nail is the proximal nail fold, which overlaps and protects the emerging nail. Just beneath it is the eponychium, or cuticle, a thin band of epidermal tissue that extends onto the nail plate and forms a protective seal. The lunula is the pale, crescent-shaped region near the base of the nail. The nail plate protects the fingertip, while the lateral and proximal nail folds guide and stabilize nail growth. The eponychium helps prevent the entry of microorganisms, and the lunula marks the visible portion of the active nail-growth region.

The right panel shows a cross section of the nail and fingertip. The nail body is the visible portion of the nail plate extending across the top of the fingertip. Beneath the proximal nail fold is the nail root, the embedded portion where nail growth begins. The proximal nail fold covers the root, and the eponychium extends onto the surface of the nail to form a seal at the base. The lunula appears near the base of the nail body and corresponds to the visible portion of the nail matrix. At the distal end of the finger, the hyponychium lies beneath the free edge of the nail and forms a protective barrier. Beneath the nail are the epidermis and dermis, which support and nourish the overlying structures. Deep to these tissues is the phalanx, the bone of the fingertip, which provides structural support. The nail root produces the nail, the nail body protects the fingertip and assists with fine manipulation, the hyponychium seals the area beneath the nail, and the phalanx forms the rigid framework of the finger.

Figure 5.2.4: Human Skin

This image is a cross-sectional anatomical diagram of human skin, showing multiple layers and internal structures.

Labeled Components:

• Skin Surface – Outermost visible layer
• Pores – Openings for sweat and oil release
• Eccrine Sweat Gland – Deep coiled gland that regulates body temperature

Additional Visible Structures (Unlabeled):

• Hair Follicles – Tubes housing hair roots
• Blood Vessels – Arteries and veins supplying nutrients
• Nerves – Sensory pathways for touch, temperature, and pain
• Other Glands – Likely sebaceous glands secreting oil near hair follicles

Figure 5.3.1: Meissner corpuscle

Microscopic image of skin tissue showing a thick, dark-stained epidermis overlying a lighter pink dermis. The epidermis has a wavy appearance with downward projections extending into the connective tissue below. Within a dermal papilla near the junction of the epidermis and dermis, a large black arrow points to an oval, lightly stained structure composed of layered cells. This structure is a Meissner corpuscle, a touch receptor located in the papillary layer of the dermis. The surrounding dermis consists of fibrous connective tissue with scattered cell nuclei. The image highlights the location of a Meissner corpuscle just beneath the epidermis.

Figure 5.3.2: Thermoregulation

This image is divided into three labeled panels that explain Thermoregulation, or how the body conserves or releases heat.

• Left panel (a): A person is outdoors in a cold, snowy environment while engaging in a winter sport. This panel represents cold conditions where the body works to conserve heat.
• Middle panel (b): This figure explains how blood flow near the skin surface affects body temperature regulation. The left side of the diagram shows a condition in which heat is retained by the body. In this condition, blood circulation avoids the surface of the skin to retain heat. The deeper position of blood flow reduces heat transfer at the skin surface. The right side of the diagram shows a condition in which heat is lost through radiation and convection. In this condition, blood circulates to the surface of the skin to dispel heat. Arrows rising above the skin surface indicate heat loss to the surrounding environment.
• Right panel (c): A person is exercising outdoors in a warm, green environment. This panel represents warm conditions where the body needs to release excess heat. Above the skin in the diagram are arrows rising upward, representing heat leaving the body through radiation and convection. In this case, blood vessels near the skin surface widen, allowing more blood to flow close to the skin to release heat. Labels indicate heat loss at the skin surface and increased circulation to help cool the body.

Figure 5.4.3: Melanoma

This image contains two side-by-side close-up images of pigmented skin lesions. In the left image, the lesion is dark brown with an irregular, uneven outline and multiple rounded projections extending from the main area. The pigmentation varies across the lesion, with darker and lighter brown regions. In the right image, the lesion is darker overall and appears nearly black. It also has an irregular outline with asymmetry and an uneven border. The surrounding skin in both images is lighter in color, which makes the lesions stand out clearly.

Doctors often give their patients the following ABCDE mnemonic to help with the diagnosis of early-stage melanoma. If you observe a mole on your body displaying these signs, consult a doctor.

• Asymmetry – the two sides are not symmetrical
• Borders – the edges are irregular in shape
• Color – the color is varied shades of brown or black
• Diameter – it is larger than 6 mm (0.24 in)
• Evolving – its shape has changed

Some specialists cite the following additional signs for the most serious form, nodular melanoma:

• Elevated – it is raised on the skin surface
• Firm – it feels hard to the touch
• Growing – it is getting larger

Figure 5.4.4: Eczema

This image contains two side-by-side clinical images for comparison. The left image shows both forearms with a widespread pink to red rash. The affected skin appears diffuse and patchy, extending over a broad area rather than appearing as isolated spots. The right image shows part of a leg with multiple small, separate raised red bumps clustered in several groups. These lesions are more discrete and localized than the rash in the left image. Some appear darker or more inflamed than others.

Figure 5.4.5: Acne

This image is a three‑panel medical diagram illustrating changes within the skin around a hair follicle as inflammation increases.

• Left panel: The skin is shown in cross‑section with labeled layers. The epidermis forms the outer surface. A hair follicle extends downward into the skin and is labeled as plugged. At the base of the follicle, there is an accumulation of shed keratin and sebum, shown as material filling the follicle opening. The surrounding tissue appears relatively normal, with no visible inflammation.
• Middle panel: This panel shows mild inflammation. The sebaceous gland, which produces oil, is labeled next to the hair follicle. The follicle remains blocked, and bacteria are shown proliferating within the plugged area. The surrounding skin appears slightly irritated, indicating an early inflammatory response.
• Right panel:This panel illustrates marked inflammation. The area around the hair follicle is enlarged and filled with inflammatory material. The surrounding tissue is shown as more intensely affected, indicating a stronger immune response. The follicle remains blocked, and the inflammation extends into the nearby skin layers

Figure 5.4.6: Calculating the Size of a Burn

This image is a medical reference diagram used to illustrate the rule of nines, a method for estimating the percentage of total body surface area associated with different regions of the body. Two full‑body outlines are shown side by side: a front view on the left and a back view on the right. Each major body region is labeled with a percentage:

• The head and neck together account for 9 percent of total body surface area.
• Each upper limb (arm) accounts for 9 percent, shown on both the front and back views.
• The trunk (chest, abdomen, and back combined) accounts for 36 percent, covering the largest central portion of the body.
• The genital area accounts for 1 percent, indicated at the lower central region of the body.
• Each lower limb (leg) accounts for 18 percent, shown extending from the hips to the feet on both views.