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Summary Junqueira's Basic Histology Chapter 18 Skin
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Comprehensive chapter summary of Junqueira's Basic Histolgy.
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Junqueira’s Basic Histology Text and Atlas, 16th EditionMescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
Chapter 18 Skin ▪ Human epidermis is renewed every 15-30 days.
• Largest single organ of the body, accounting for 15%-20% of total body weight and ▪ Keratinocytes of the stratum basale have cytoskeletal keratins, about 10
presenting 1.5-2 m2 of surface in adults. nm in diameters.
• Also known as the integument or cutaneous layer and composed of the epithelial layer of o Stratum spinosum
ectodermal origin, the epidermis, and a layer of mesodermal connective tissue, the dermis. ▪ Normally the thickest layer, especially in the epidermal ridges.
Beneath the dermis lies the subcutaneous tissue or hypodermis, a loose connective tissue ▪ Consist of polyhedral cells with cytoplasm actively synthesizing
layer. keratins.
• Specific functions of the skin include: ▪ Basal layer of the stratum spinosum may still divide, and this combined
o Protective zone with the stratum basale is called the stratum germinativum.
▪ Physical barrier against thermal and mechanical insults. ▪ Keratin filaments here are arranged in bundles called tonofibrils, which
▪ With resident lymphocytes and antigen-presenting cells (APCs). converge and terminates at the desmosomes.
▪ Melanin protects cell nuclei from UV radiation. ▪ Cells extend slightly at site of desmosomes, leading to the spinous
▪ Permeability barrier against excessive water loss. appearance of the cell surfaces.
o Sensory ▪ Thick skin has thicker stratum spinosum with more abundant tonofibrils
▪ Sensory receptors constantly monitor the environment. and desmosomes.
o Thermoregulatory o Stratum granulosum
▪ Constant body temperature is easily maintained due to its insulating ▪ Three to five layers of flattened cells undergoing terminal differentiation
components (adipose tissue and hair) and mechanisms for accelerating process of keratinization.
heat loss (sweat production and dense superficial microvasculature). ▪ Cytoplasm is filled with keratohyaline granules—dense, non-membrane
o Metabolic bound masses of filaggrin associated with the keratins of tonofibrils.
▪ Synthesize vitamin D3. ▪ Golgi-derived lamellar granules are present in this layer, which contain
▪ Subcutaneous layer stores significant amount of energy in the form of lipids and glycolipids. Lamellar granules are extruded into the
fat. intercellular spaces, creating a lipid-rich, impermeable layer around the
▪ Removal of excess electrolytes through sweat. cells attributing permeability barrier to water loss.
o Sexual signaling o Stratum lucidum
▪ Visual indicators of health involved in attraction between sexes. ▪ Found only in thick skin.
• Dermatoglyphs, AKA fingerprints and footprints are unique patterns of well-formed ridges ▪ Consists of a thin, translucent layer of flattened keratinocytes.
and grooves in thick skin of the palm and soles. These dermatoglyphs appear as combinations ▪ Nuclei and organelles have been lost, and the cytoplasm is composed
of loops, arches, and whorls. almost exclusively of keratin filament embedded in an electron-dense
• Skin is capable of self-renewal throughout life. matrix.
Epidermis o Stratum corneum
• Stratified squamous keratinized epithelium composed of keratinocytes. Melanocytes, ▪ 15 to 20 layers of squamous, keratinized cells filled with birefringent
Langerhans cells, and Merkel cells are also present in the epidermis. filamentous keratins.
▪ As cells differentiate, keratin tonofibrils become heavily massed with
• Forms the major distinction between thick skin of the palms and soles, and thin skin found
elsewhere in the body. filaggrin and other proteins in keratohyaline granules. By the end of
keratinization, cells contain only amorphous fibrillar proteins with
• Thin skin varies from 75 to 150 µm while thick skin varies from 400 to 1400 µm.
plasma membranes surrounded by the lipid-rich layer.
• Epidermis is avascular and gets its nourishment from the dermis via diffusion. ▪ Fully keratinized or cornified cells are called squames, are continuously
• Epidermis consists of four layers of keratinocytes (five layers in thick skin). shed at the epidermal surface as the desmosomes and lipid-rich cell
o Stratum basale envelopes break down.
▪ Single layer of cuboidal or columnar cells on the basement membrane at Melanocytes
the dermal-epidermal junction.
• Factors affecting skin color includes melanin and carotene content of keratinocytes and the
▪ Hemidesmosomes attaches the cells to basal lamina while desmosomes
number of blood vessels in the dermis.
bind cells in their lateral and upper surfaces.
• Eumelanins are the brown or black pigments produced by melanocytes.
▪ Characterized by intense mitotic activity and along with the deepest layer
of stratum spinosum, contains the progenitor cells for all the epidermal • Specialized epidermal cells at the basal layer and in hair follicles, derived from neural crest
layers. A niche of stem cells is also present in the follicle sheaths that are and migrate in the embryonic stratum basale.
continuous with the epidermis.
1 | Skin
, Junqueira’s Basic Histology Text and Atlas, 16th Edition
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
• Pale-staining, rounded cell bodies lacking attachments to the neighboring keratinocytes with • Dermal regions have rich network of blood and lymphatic vessels, forming two major
several irregular cytoplasmic extensions that penetrates the epidermis. plexuses:
• Melanin synthesis and accumulation: o Subpapillary plexus
o Tyrosinase converts tyrosine into 3,4-dihydoxyphenylalanine (DOPA) and further ▪ Between the papillary and reticular dermal layer, from which capillary
transformed and polymerized into the different forms of melanin. branches extended into the dermal papillae.
o Melanin pigments linked to structural proteins accumulates in vesicles and form o Deep plexus
mature granules called melanosomes. ▪ Lies near the interface of the dermis and the subcutaneous layer.
o Melanosomes are transported via kinesis to the tips of the cytoplasmic extensions. • Dermal vasculature has thermoregulatory function, which involves numerous arteriovenous
Neighboring keratinocytes phagocytose the tips, take in the melanosomes, and anastomoses or shunts, which decrease blood flow in the papillary layer during cold
transport them by dynein toward their nuclei. conditions and increase this flow during hot conditions.
o Melanosomes accumulate in the keratinocytes as a supranuclear cap that absorbs • Lymphatic vessels begin in the dermal papillae and converge to form two plexuses located
and scatter sunlight. with the blood vessels.
• One melanocyte plus the keratinocytes that receives melanosomes make up an epidermal- • Sensory afferent nerve fibers are present in the papillary dermis and around hair follicles.
melanin unit. • Autonomic effector nerves to dermal sweat glands and smooth muscle fibers are
• Tanning after exposure to solar radiation of 290-320 nm process: postganglionic fibers of sympathetic ganglia. No parasympathetic innervation is present.
o Physicochemical reaction darkens existing melanin. Subcutaneous Tissue
o Paracrine factors produced by melanocytes exposed to increase UV radiation • Loose CT that binds the skin to the subjacent organs.
accelerate melanin synthesis and accumulation. • Also called the hypodermis or superficial fascia.
• Extensive vasculature promotes rapid uptake of drugs.
Sensory Receptors
Langerhans Cells • Skin functions as an extensive receiver for various stimuli.
• APCs derived from monocytes, most clearly seen in the stratum spinosum. • Rich in both simple nerve endings with no Schwann cell and more complex structures with
• Bind, process, and present antigens to T lymphocytes. sensory fibers enclosed by glia and delicate CT capsules.
• Comprise a major component of the skin’s adaptive immunity. • Unencapsulated receptors include:
Merkel Cells or Epithelial Tactile Cells o Merkel cells
• Low-threshold mechanoreceptors for sensing gentle touch abundant in highly sensitive skin ▪ Associated with a disc or expanded axonal ending.
such as fingertips and bases of some hair. ▪ Tonic receptors for sustained light touch and for sensing texture.
• Present in both thick and thin skin. o Free nerve endings
• Resemble the surrounding keratinocytes but contain few, if any, melanosomes. ▪ Present in the papillary dermis and extend into lower dermal layers.
• Characterized by small Golgi-derived dense-core granules concentrated in the basolateral ▪ Thermoreception, pain (nociception), and itching (pruritus), but also
surface where the cells have synaptic contact with expanded discs of unmyelinated afferent function as important tactile receptors.
fibers penetrating the basal lamina. o Root hair plexuses
Dermis ▪ Web of sensory fibers surrounding the bases of hair follicles.
• Layer of CT that supports the epidermis and binds it to the subcutaneous tissue. ▪ Detect movements of hairs.
• Dermal surface has dermal papillae which interdigitate with the epidermal ridges. • Encapsulated receptors include:
• A basement membrane always occurs between the stratum basale and the dermis, and follows o Meissner corpuscles
the contour of the interdigitations. ▪ Elliptical structures, consisting of sensory axons winding around
• Dermis contains two sublayers: flattened Schwann cells arranged perpendicular to the epidermis in the
o Papillary layer dermal papillae.
▪ Includes the dermal papillae and consists of loose CT with types I and ▪ Generate impulses light touch against skin when their shape temporarily
III collagen fibers. deforms.
▪ Thin layer. o Pacinian corpuscles
o Reticular layer ▪ Large oval structures found deep in the reticular dermis and hypodermis.
▪ Much thicker layer. ▪ Their outer capsule is composed of 15-20 thin, concentric lamellae of
▪ Dense irregular CT mainly bundles of type I collagen fibers with a flattened Schwann cells surrounding a highly branched, unmyelinated
network of elastic fibers. axon.
▪ Dermatan sulfate is present between the collagen and elastic fibers. ▪ For sensing coarse touch, pressure (sustained touch), and vibrations.
2 | Skin
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