32 [16-1]:INTEGUMENT

The integument includes the dermis, epidermis, and epidermal appendages. The dermis is a deep layer of connective tissue which is derived from mesoderm. It gives both mechanical and nutritive support to the epidermis, which forms the surface layer of skin. The epidermis consists of a stratified squamous epithelium derived from the embryonic ectoderm. The epidermis in turn gives rise to special appendages such as hair, nails, and glands.

[16-2]:A. DERMIS

The dermis is a vascularized layer of connective tissue which supports the avascular epidermis.

Skin, Thick (H&E) [#47]- The dermis shows a strong eosinophilic staining reaction due to the presence of large amounts of collagen. Cells are relatively sparse in the dermis as indicated by the number of nuclei. Beneath the dermis is the hypodermis, which usually contains large amounts of fat tissue. The border between the dermis and hypodermis is often indistinct. The dermis is highly vascularized, and numerous capillaries are present in the region adjacent to the epidermis. Observe the dermal papilli which are finger-like projections of the dermis which interdigitate with the epidermal ridges. Examine those dermal papilli for the presence of Meissner's corpuscles which contain nerve endings sensitive to touch.

[16-3]:A. DERMIS

The dermis is a vascularized layer of connective tissue which supports the avascular epidermis.

Skin, Thick (H&E) [#47]- The dermis shows a strong eosinophilic staining reaction due to the presence of large amounts of collagen. Cells are relatively sparse in the dermis as indicated by the number of nuclei. Beneath the dermis is the hypodermis, which usually contains large amounts of fat tissue. The border between the dermis and hypodermis is often indistinct. The dermis is highly vascularized, and numerous capillaries are present in the region adjacent to the epidermis. Observe the dermal papilli which are finger-like projections of the dermis which interdigitate with the epidermal ridges. Examine those dermal papilli for the presence of Meissner's corpuscles which contain nerve endings sensitive to touch.

[16-4]:Pacinian Corpuscles (H&E) [#52]- Examine the hypodermis for Pacinian corpuscles which are touch receptors for deep pressure and vibration.

[16-5]:TEM #11-2 (Dermis-Mouse, X8,750)- As illustrated in this section, most of the dermis is composed of a cellular connective tissue. Large numbers of collagen fibrils can be seen in both longitudinal (5) and cross (6) section. Fibroblasts (1) may also be observed in the process of secreting tropocollagen (4), the precursor of the collagen fibrils.

[16-6]:B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-7]:B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-8]:B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-9]:B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-10]:

B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-11]:

B. EPIDERMIS The epidermis is the outer, avascular layer of the integument.

(Skin, Thick, H&E) [#47]- Examine the epidermis which is composed of stratified squamous epithelium. Its deepest cells form a single layer of low columnar cells, the stratum basale. The next few layers are called stratum spinosum or the prickle-cell layer, so-called because contact points between adjacent cells are drawn out to form spines or prickles. These projections mutually form intercellular bridges (desmosomes) between the two adjacent cells. In the next layer, the stratum granulosum, the cells become somewhat dehydrated and laden with keratohyalin granules that stain deeply with H&E. This is the most superficial layer which contains living cells. In the next layer, the stratum lucidum consists of the dead cells which are flattened into a translucent mass. The most superficial epidermal layer is the stratum corneum which consists of desquamating, flattened, cornified, dead cells that contain keratin.

[16-12]:Skin, Thin (H&E) [#48]- Relative to thick skin, in thin skin most layers are greatly attenuated. The stratum lucidum is entirely absent.

[16-13]:TEM #11-5 (Skin Human in the Stratum Basale, X17,300)- These cells lie on the basal lamina (2) which comprises the upper most layer of the basement membrane (6). The keratinocytes in this layer are actively dividing cells which contain keratin filaments (organized into tonofibrils) (4) and demosomes. These cells also contain a number of melanin granules which they have phagocytized from melanocytes.

[16-14]:TEM #11-6 (Skin-Human, X19,000)- This section shows a keratinocyte in the stratum spinosum of the epidermis. This keratinocyte is also referred to as prickle cell due to the large number of desmosomal junctions (4) which it forms with neighboring cells giving it a spiked appearance. Keratin filaments grouped as tonofibrils (3) may be seen coursing through the cytoplasm and abutting the desmosomal junctions. The dark staining bodies (2) in the cytoplasm are melanin granules.

[16-15]:TEM #11-1 (Epidermis-Mouse, X82,500 and Chorio-Allantoic Membrane, Chick Embryo, X100,000)- Examine the fine structure of the desmosomes in these high power micrographs. Note that keratin filaments insert into the cytoplasmic side of the junction.

[16-16]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-17]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-18]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-19]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-20]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-21]:

C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-22]:

C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-23]:C. EPIDERMAL APPENDAGES

In humans, the epidermal appendages include hairs and nails (both of which contain hard keratin) and various glands.

Scalp, Human (H&E) [#49]- and Scalp, Human, (Orcein-PIC) [#50]- Examine these photomicrographs for the structure of the hair. You will note that in many cases, the hair shaft has been lost from the section leaving only an empty follicle. In an intact hair shaft (which is often heavily pigmented) locate the medulla, cortex and cuticle. The boundaries between these structures may be rather indistinct depending upon the location of the section. Examine the hair follicle and note the darker staining (by orcein-PIC) internal root sheath surrounded by the lighter staining external root sheath. The external root sheath is in turn bounded by the glassy membrane. At the base of the hair follicle you may be able to locate a dermal (hair) papilla. Note the melanin granules located in the hair matrix immediately above the dermal papilla. Locate the arrector pili muscles which are a band of smooth muscles running from the lower part of the hair shaft to the epidermis. The sebaceous gland is often located between a hair follicle and the pili muscle. The cells of this gland are large, have distinct nuclei and borders, and have a foamy appearance due to the presence of large numbers of lipid vesicles.

[16-24]:TEM #11-3 (Hair Follicle in Cross-section, X30,000)- This section was taken from a deep region of the hair follicle in which the internal root was still present. Going from the center to the outside of the follicle, the various layers are- medulla (1), cortex (2), cuticles of both internal root sheath and the hair shaft (3), inner root sheath which is composed of Huxley's (inside) layer (4) and Henle's (outside) layer (5), external root sheath (6), glassy membrane (7), and the connective tissue of the dermis.

[16-25]:TEM #11-4 (Skin Mouse, X5,400)- This cross-section of a hair follicle (1) was taken from the dermal layer of the skin at the level of the sebaceous gland. Lipid droplets (3) which will eventually become a component of sebum, can be observed inside the sebaceous gland cells (nuclei shown at 2).

[16-26]:Finger (H&E) [#10]- Examine the tip of this section through a finger. The nail plate should be apparent as an eosinophilic structure which shows laminations. The nail plate lies on a continuation of the epidermis known as the nail bed. In the root section, the nail bed merges with the nail matrix which is responsible for the growth of the nail plate. Locate both the eponychium and hyponychium.

[16-27]:Finger (H&E) [#10]- Examine the tip of this section through a finger. The nail plate should be apparent as an eosinophilic structure which shows laminations. The nail plate lies on a continuation of the epidermis known as the nail bed. In the root section, the nail bed merges with the nail matrix which is responsible for the growth of the nail plate. Locate both the eponychium and hyponychium.

[16-28]:D. GLANDS

The glands of the integument include the sebaceous glands, merocrine (eccrine) sweat glands, the apocrine sweat glands, and the mammary glands. In this section, only the two sweat glands will be considered since the sebaceous glands were examined in conjunction with the hair. The mammary glands will be covered in the section on the female reproductive tract.

Skin, Thick (H&E) [#47]- or Skin, Thin (H&E)[#48]- Examine the dermal layer for presence of merocrine sweat glands. The secretory portion is distinguished from the duct portion in that it is more highly coiled and stains a lighter color. The secretory portion consists of simple epithelium resting on a basement membrane. Myoepithelial cells are also present, located between the secretory cells and the basal lamina. However, under the light microscope only the nuclei of these cells may be observed. The duct portion of the glands consists of 2 layers of cuboidal cells, however, the cell boundaries may be difficult to distinguish under the light microscope. Myoepithelial cells are absent from the duct portion of the gland.

[16-29]:D. GLANDS

The glands of the integument include the sebaceous glands, merocrine (eccrine) sweat glands, the apocrine sweat glands, and the mammary glands. In this section, only the two sweat glands will be considered since the sebaceous glands were examined in conjunction with the hair. The mammary glands will be covered in the section on the female reproductive tract.

Skin, Thick (H&E) [#47]- or Skin, Thin (H&E)[#48]- Examine the dermal layer for presence of merocrine sweat glands. The secretory portion is distinguished from the duct portion in that it is more highly coiled and stains a lighter color. The secretory portion consists of simple epithelium resting on a basement membrane. Myoepithelial cells are also present, located between the secretory cells and the basal lamina. However, under the light microscope only the nuclei of these cells may be observed. The duct portion of the glands consists of 2 layers of cuboidal cells, however, the cell boundaries may be difficult to distinguish under the light microscope. Myoepithelial cells are absent from the duct portion of the gland.

[16-30]:D. GLANDS

The glands of the integument include the sebaceous glands, merocrine (eccrine) sweat glands, the apocrine sweat glands, and the mammary glands. In this section, only the two sweat glands will be considered since the sebaceous glands were examined in conjunction with the hair. The mammary glands will be covered in the section on the female reproductive tract.

Skin, Thick (H&E) [#47]- or Skin, Thin (H&E)[#48]- Examine the dermal layer for presence of merocrine sweat glands. The secretory portion is distinguished from the duct portion in that it is more highly coiled and stains a lighter color. The secretory portion consists of simple epithelium resting on a basement membrane. Myoepithelial cells are also present, located between the secretory cells and the basal lamina. However, under the light microscope only the nuclei of these cells may be observed. The duct portion of the glands consists of 2 layers of cuboidal cells, however, the cell boundaries may be difficult to distinguish under the light microscope. Myoepithelial cells are absent from the duct portion of the gland.

[16-31]:Sweat Gland, Apocrine (H&E or Orcein-PIC) [#51]- Examine the apocrine sweat glands in this photomicrograph and compare them with the merocrine sweat glands of the previous image. Observe that the lumina of these glands are much larger than for merocrine or eccrine sweat glands.

[16-32]:HISTOLOGIC LOOK-ALIKES

Thin vs Thick Skin

Similarity- Both have a surface epidermis which consists of keratinizing stratified squamous epithelium.

Eccrine vs Apocrine Sweat Glands

Similarity- Both are simple coiled tubular glands associated with the skin.