Integumentary System Histology

Sensory nerves that terminate with capsules (mechanosensory nerve organs). The capsules are modified Schwann cells.

Encapsulated Nerve Endings

_____ sweat gland secretion is viscous and contains lipids, ammonia, protein, carbohydrates and other organic compounds. Although the secretion is initially odorless and sterile, bacteria like to eat it, generating odorous and musky compounds in the process. In other mammals, these compounds are pheromones.

apocrine

______ glands are large and less dense sweat gland (8-43 per cm2) and occur only in the human axilla, areola, periumbilical, anal and pubic regions. Their coiled tubular acini are found in the deep dermis and hypodermis and derived from the epithelial down-growths that give rise to hair follicles.

apocrine

sweat glands are either categorized as _____ or _____

apocrine, eccrine

Skin can be classified as hairless (______) or hairy. Hairless skin tends to be ________. skin on the hands and soles of feet is hairless thin skin, with grooves and ridges called _________, which assist with grip.

glabrous, thicker, dermatoglyphs

pilosebaceous unit (4)

hair follicle, hair shaft, arrector pili muscle, sebaceous gland

_______ are responsible for the production and growth of hairs. They go through a growth phase and resting phase, which is reflected in their histological appearance.

hair follicles

contain myofilaments that contract to encourage movement of sweat from the secretory acini to the duct. They are found only in the basal aspect of the secretory portion and lie between the secretory cells. Their abundant actin causes them to strain eosinophilic (pink).

myoepithelial cells

_______: just deep to the epidermal-dermal junction, It is made of loose, areolar connective tissue. The fibrous matrix is anchored to the basal lamina of the epidermis by Type VII collagen fibrils. Each papilla contains fine, interwoven Type I and Type III collagen bundles and thread- like elastic fibers that decrease with age. Capillary loops supply blood and nutrients to (but do not enter) the epidermis, and body temperature can be regulated by regulating blood flow through these loops. Free nerve endings pass into the epidermis and some regions (especially thick hair-less skin) contain tactile (Meissner's) corpuscles. Also contain fibroblasts, adipocytes and transient connective tissue cells (macrophages, plasma cells, mast cells).

papillary layer

hair follicle + hair shaft +arrector pili muscle + sebaceous gland

pilosebaceous unit

Nails are plates of keratinized epithelial cells on the dorsal aspect of each distal phalanx. Average nail growth is 1-2mm per month. The nail _______ is made up of multiple, compacted layers of squamous keratinized epithelial cells that do not desquamate and contain hard keratin. The nail _____ is the underlying epithelial cells that correspond to the stratum basale and stratum spinosum of the epidermis. The nail plate tightly adheres to the nail bed until it becomes free, distal to the ___________. The nail ______ is the proximal part of the nail that is hidden in the nail _______, and it covers the nail ______. Stem cells of the nail matrix divide and migrate towards the root, then differentiate and produce hard keratin. Keratinization at the nail root cause the nail plate to move distally over the nail bed (causing nail growth). The edge of the skin fold (epidermis) that covers the nailroot is called the _________ (cuticle). The white crescent-shaped part at the proximal part of the nail is called the ________.

plate, bed, onychodermal band, root, groove, matrix, eponychium, lunula

____________: are slow-adapting mechanoreceptors,found deep between the papillary dermis and hypodermis. Their capsules are spindle-shaped, often oriented parallel to the stretchlines of skin, and are particularly sensitive to cutaneous stretch caused by limb and digit movement. A single myelinated axon enters the capsule, where it loses its myelin and branches like a tree. They also respond to sustained pressure and are considered important for the modulation of grip on an object, including the sense of finger control and position. Recent research suggests that they are relatively scarce in skin (0.3 corpuscles/mm2). They are also found in joint capsules, tendons and ligaments where they register joint deformation and provide proprioceptive feedback in response to internally generated stimuli.

Bulbous (Ruffini) Corpuscles

are a type of unencapsulated sensory nerve that detects light touch, pain and temperature. They are the "naked "terminal branches of afferent nerve fibers that end freely without structural specialization. As the branches terminate, their unmyelinated axons lose their Schwann cells and come in direct contact with the epithelial cells of the stratum granulosum. ***s form networks around hair follicles to sense movement.

FNE (free nerve endings)

detect deep pressure andvibration. They are ovoid, can be large (up to 1 mm) andare typically located in the deep dermis and hypodermis,especially in the palms and soles. Because of their deeplocation, they sense stimuli from a wide area, but with low specificity. The capsule is formed by Schwann cells arranged in concentric lamellae, resembling an onion under light microscopy.

Lamellar (Pacinian) Corpuscle

Hair follicles are divided into 4 parts: __________: extends from the epidermal surface opening of the follicle to the opening of the associated sebaceous gland. ____________: extends from the opening of the sebaceous gland to the arrector pili insertion. ____________: protrudes from the follicle near arrector pili insertion and contains epidermal stem cells ____________: extends from the follicular bulge to the proximal end of the hair (hair bulb)

Infundibulum, Isthmus, Follicular bulge, Inferior segment

The most the most common type of cell in the epidermis (85-90%). Highly specialized epithelial cells that originate in stratum basale, and are continually renewed as the apical layer is sloughed off.

Keritinocytes

Reticular layer: Dense connective tissue layer that is deep to and thicker than the papillary layer. Irregular bundles of collagen and coarse elastic fibers form a deformable 3D lattice. The primary orientation of these bundles may relate to the development of skin lines (Langer Lines) and reflect local mechanical forces on the dermis. Skin incisions parallel to these lines heal with the least scarring. Contains fibroblasts, lymphocytes, macrophages, and adipocytes. Encapsulated mechanoreceptors: ________ and ________ sense pressure and vibration and stretch (respectively). Some regions may contain smooth muscle

Lamellar (pacinian), bulbous (ruffini) corpuscles

Mechanoreceptors that respond to directional deformation of epidermis and the movement of hair, by releasing transmitter from dense-core granules. Plentiful in the basal layer of skin with acute sensory perception, like the fingertips and lips. Attached to surrounding keratinocytes by desmosomes and to adjacent basal keratinocytes via short, stiff processes. Closely associated with afferent myelinated nerve fibers with plate-like ending disc receptors. The neuron plus associated epidermal (***) cell is called _______.

Merkel cells, Merkel Corpuscle

_______: (or stratum germinativum) Deepest layer of epithelium consists of a single layer of low columnar to cuboidal cells resting on the basal lamina.

Stratum basale

hairs are made up of ______ and ______

follicles (deep, not visible above skin), shafts (visible above skin)

________ are small bundles of smooth muscle, connecting to the connective tissue sheath surrounding the hair follicle. Form oblique link between papillary layer of dermis and the hair follicle. When the muscle contracts, it causes the hair to become erect and dimples to form on the skin (goosebumps). The angle between the *** muscle and the hair follicle is occupied by a ____________.

arrector pili muscles, sebasceous gland

are secretory epithelial cells that produce a watery, electrolyte-rich (glycogen) secretion. They appear triangle-shaped (ish), and wedged between the dark cells, with their narrow end facing the lumen. They have basolateral infoldings.

clear cells

The secretory portion contains three types of cells:

clear cells, dark cells, myopeithelial cells

Stratum Corneum: Is the most superficial layer and final product of epidermal differentiation. It's thickness widely varies. The stratum corneum is made up of 15-50 layers of overlapping, non-nucleated, flat keratinized cells (squames). "Cornified" means "converted into horn" and is another way to say "keratinized." The keratinocytes in this layer are non-living packets of keratin filaments, and their plasma membranes contain structural proteins, forming a ___________. Lipids released from membrane coating granules (_____________) coat the envelope and are released into the extracellular space to form an _____________. The plasma membrane plus the lipid layer is called the _________________. _____________ is the sloughing off of the outermost cells of the stratum cornuem. This occurs at around the same rate as new cell formation (in the stratum basale).

cornified cell envelope, lamellar bodies, epidermal water barrier, compound cell envelope, desquamination

secretory epithelial cells that produce mucous. They are densely packed with glycoprotein-staining secretory granules. These triangle shaped cells line up with their bases facing the lumen and narrow portions facing (but not always reaching) the basal lamina (but does not always reach it).

dark cells

melanocytes are _________.

dendritic cells

the epidermal-dermal junction is characterized by interdigitation of ______ and _______. ______ are rounded projections of dermis that project upwards into the dermis, while the ______ extend from the epidermis down into the dermis. thick skin tends to have a more complex epidermal-dermal junction.

dermal ridges (papillae), epidermal ridges (rete ridges), papillae, rete ridges

paillary layers: It is made of loose, areolar connective tissue and is named for the papillae of the dermis (_______) that interdigitate with the epidermal (_____) ridges. The fibrous matrix of the papillary dermis is anchored to the basal lamina of the epidermis by Type VII collagen fibrils. Each papilla contains fine, interwoven Type I and Type III collagen bundles and thread- like elastic fibers that decrease with age. Capillary loops supply blood and nutrients to (but do not enter) the epidermis, and body temperature can be regulated by regulating blood flow through these loops. Free nerve endings pass into the epidermis and some regions (especially thick hair-less skin) contain _________. Also contain fibroblasts, adipocytes and transient connective tissue cells (macrophages, plasma cells, mast cells).

dermal ridges, rete, tactile (Meissner's) corpuscles

Appendages from the epidermis (e.g., sebaceous glands, sweat glands, hair follicles) extend into the _______.

dermis

dense irregular connective tissue and many elastic fibers

dermis

Each hair follicle has a bulbous terminal expansion (hair root) in the ________, surrounded by a connective tissue sheath. At the base of each hair root, blood is supplied by a ________, consisting of loose connective tissue and a rich capillary network that projects into the follicle. the _______ consists of the hair root plus its dermal papilla. The hair bulb actively produces hairs.

dermis, dermal papilla, hair bulb

The ducts of ____ sweat glands extend from the secretory acinus to the surface of the epidermis, opening at the sweat pore.

eccrine

avascular stratified keritinized squamous epithelium

epidermis

layer of skin that contains keritinocytes, melanocytes, lymphocytes, langerhans cells, merkel cells

epidermis

The Hair bulb consists of the hair root plus its dermal papilla. The hair bulb actively produces hairs (as follows). Epidermal stem cells adjacent to the follicular bulge migrate to the hair root. Once there, they rapidly divide and differentiate and are collectively referred to as ___________. The proliferation of these cells accounts for hair growth. The internal root sheath is made up of matrix cells and has three layers that cover the deep part of the hair: ______________: flattened, overlapping scale-like cells, closest to hair shaft _________: 1-2 layers of flattened cells, intermediate layer __________: single layer of cuboidal cells adjacent to external root sheath

hair matrix cells, Cuticle of internal root sheath, Huxley layer, Henle layer

The ________ is the long, filamentous structure that passes through the surface of the epidermis. It is formed by matric cells and has three regions: _______: outermost layer of hair. Cuboidal to columnar then keratinized shingles. Protects hair and determined its porosity. _______: middle layer, where hair proliferates. 80% of total mass of hair filled with hard keratin intermediate filaments, surrounded by amorphous space containing keratin-associated proteins. determines texture of hair. _______: When present (in thick hair), it is the innermost layer and contains soft keratin.

hair shaft, Cuticle, Cortex, Medulla

Deep to reticular layer is the __________ (superficial/subcutaneous fascia). Mostly adipose tissue, but also contains nerves, vessels and lymphatics. Serves as energy reserve, insulation and mediates mobility of the skin. The _______ muscles are smooth muscle cells (or bundles of cells) that connect the dermal sheaths of hair follicles to the papillary dermis. Contraction raises the hair and dimples the epidermis, causing "goose bumps." In the head and neck, a think thin layer of striated muscle forms the muscles of facial expression.

hypodermis, arrector pili

here is no difference in the number of melanocytes between individuals with different skin pigmentation. Individuals with darker skin tend to have larger, more dendritic melanocytes that contain many mature late-stage melanosomes and thus, keratinocytes containing more evenly distributed individual melanosomes. Individuals with paler skin tend to have melanosomes that are bound by secondary lysosomes into melanosome complexes.

just read.

The process of keratinocyte maturation (keratin fibril formation) is called __________. Keratinocytes begin their journey in the stratum basale, accumulating keratin filaments (intermediate filaments) as they are pushed upwards towards the epidermal surface. Keratinization begins in the stratum spinosum with the production of keratohyalin granules that bind to the intermediate filaments to assemble thick bundles called ________.

keratinization, tonofibrils

most epidermal cells are _____, but it also contains _____, _____, ____ and _____.

keritinocytes, melanocytes, lymphocytes, langerhans cells, merkel cells

dendritic, antigen presenting cells (APC's) in the stratum basale and stratum spinosum that send their processes between tight junctions in the stratum granulosum to test the microenvironment of outermost layers of skin (stratum corneum). They stimulate cell-mediated immunological responses.

langerhans cells

Melanocytes have clear cytoplasm and a large euchromatic nucleus and contain oval membrane-bound organelles (melanosomes) that synthesize store and transport melanin. The process is regulated by _________ and triggered by exposure ________. In short, ________ is transported into the melanosomes where it is oxidized by tyrosinase into __________ and converted to melanin.

melanin-stimulating hormone (MSH), UV light, tyrosine, DOPA (dihydroxyphenylanine)

Matrix cells in the cortex synthesize and accumulate keratohyalin granules and keratin granules as they are pushed towards epidermal surface. Hair color is determined by the activity of _________ in the hair bulb (deep between the papilla and the epithelial cells of the hair root). They in the hair produce and transfer *** to epithelial cells in similar manner as in the epidermis.

melanocytes (As people age, melanocytes in the matrix gradually lose the ability to produce tyrosinase, and thus, melanosomes. This leads to the loss of melanin transfer from melanocytes to the hair shaft, and an increase in grey hair)

apocrine sweat glands are discharged by exocytosis (______ secretion)

merocrine

The outer root sheath surrounds the inner root sheath and consists of a single layer of ___________ cells surrounding the hair bulb. It is a tubular evagination of the epidermis, that expands into multiple layers near the surface of the skin but does not contribute to hair formation. The follicular epithelium and connective tissue sheath are separated by a thick ____________ (basement membrane).

multipotent, glassy membrane

Dense connective tissue layer that is deep to and thicker than the papillary layer. Irregular bundles of collagen and coarse elastic fibers form a deformable 3D lattice. The primary orientation of these bundles may relate to the development of skin lines (Langer Lines) and reflect local mechanical forces on the dermis. Skin incisions parallel to these lines heal with the least scarring. Contains fibroblasts, lymphocytes, macrophages, and adipocytes. Encapsulated mechanoreceptors: Lamellar (Pacinian) and Bulbous (Ruffini) corpuscles sense pressure and vibration and stretch (respectively). Some regions may contain smooth muscle

reticular layer

holocrine glands that secrete an oily substance. They are present on most of the body (except on glabrous skin of palms, soles) and often closely associated with hair follicles. *** glands are most numerous on the face and scalp. *** glands are acinar glands with several acini that open into short duct. The duct typically ends in the upper third of a hair follicle, but in some regions, it opens directly onto epidermal surface.

sebaceous glands

contains cholesterol, triglycerides and cellular debris from the secretary unit, and acts to maintain the texture and flexibility of hair and maintain the water barrier of skin. It also has antimicrobial properties.

sebum

in the ________, the cytoplasm of immature keratinocytes contains many free ribosomes that will engage in keratin synthesis. As new cells are produced in the stratum basale, apical cells are pushed upwards towards the next layer.

stratum basale

Melanocytes are interspersed in this layer (__________) and vesicles containing melanin, called ___________, may accumulate on the "sunny side" (over the apical side of the nucleus) of the basal keratinocytes. Merkel cells (discussed later) may also be found here.

stratum basale, melanosomes

______: Is the most superficial layer and final product of epidermal differentiation. It's thickness widely varies. The *** is made up of 15-50 layers of overlapping, non-nucleated, flat keratinized cells (squames). "Cornified" means "converted into horn" and is another way to say "keratinized." The keratinocytes in this layer are non-living packets of keratin filaments, and their plasma membranes contain structural proteins, forming a cornified cell envelope. Lipids released from membrane coating granules (lamellar bodies) coat the envelope and are released into the extracellular space to form an epidermal water barrier. The plasma membrane plus the lipid layer is called the compound cell envelope. Desquamation is the sloughing off of the outermost cells of the stratum cornuem. This occurs at around the same rate as new cell formation (in the stratum basale).

stratum corneum

in the _______ the keratinocytes in this layer are terminally differentiated, non-living packets of keratin (squames). The plasma membrane is reinforced by structural proteins (involucrin and cystatin α) to form a cornified envelope. Lipids coat the membrane and occupy extracellular space, forming the compound cornified envelope). The squames contain mainly tonofibrils (tonofilaments bound by keratohyalin granules) and they become dense, ompacted and dehydrated as they're pushed superficially within the layer. Deeper cells are connected to the underlying keratinocyte layer by tight junctions and to each other by desmosomes, but as they migrate upwards, these connections are broken down by Kallikrein-related serine proteases (KLKs). When pH is neutral, (lymphoepithelial Kazal-type inhibitor (LEKTI) prevents KLKs from cleaving the desmosomes, but the pH of the epidermis decreases superficially. This causes LEKTI to release KLK and desmosome destruction as the cells reach more superficial layers. This tightly regulated process results in the sloughing off of the superficial-most keratinocytes (__________).

stratum corneum, desquamation

in the _______, the number of keratohyalin granules increases, and they become more noticeable in light microscopy. Keratohyalin granules contain trichohyalin and filaggrin (keratin filament aggregating protein), which combine with tonofibrils to initiate the conversion of granular cells into cornified cells.

stratum granulosum

___________: Most superficial layer of the epidermis below the lipid barrier (discussed later). Lots of changes are happening here, including the degeneration of nuclei and organelles, but the keratinocytes are not yet fully keratinized. This layer is characterized by the many intensely/dark staining ___________ present in 3- 5 layers of flattened cells. These granules contain the precursors of filaggrin (cystine and histadine-rich proteins), the protein responsible for aggregating the keratin filaments of the stratum corneum.

stratum granulosum, keratohyalin granules

in the ______, Remaining organelles are dissolved by lysosomes.

stratum lucidem

___________: A subdivision of the stratum corneum that is only present in palmar and plantar skin. It appears translucent or may be lightly strained. The cytoplasm is mostly made of dense keratin filaments embedded in electron-dense matrix, without apparent nuclei or organelles.

stratum lucidum

Keratins are produced most heavily in this layer. Keratin synthesis begins as the as free ribosomes of the keratinocytes produce keratohyalin granules. Keratohyalin (protein components: trichohyalin and filaggrin) binds to and assembles intermediate filaments into thick bundles called tonofibrils (which stain eosinophilic).

stratum spinosum

__________: (prickle cell layer). Contains several layers of closely packed keratinocytes, that are noticeably larger than in the basal layer. This layer is characterized by interconnected cytoplasmic processes (spines) of keratinocytes which contain intermediate filaments. During tissue prep, intracellular space develops as the cells shrink, making the spines more prominent and "spiny" under a light microscope. As the cells mature and move towards the surface, they enlarge and flatten into a plane parallel to surface. Melanocytes are also present in this layer.

stratum spinosum

total cellular turnover time of the skin is about 52-72 days. most of the action occurs in the _______.

stratum spinosum

a clear, odorless, hypotonic fluid that contains mainly sodium and chlorine ions (but also potassium, bicarbonate, calcium, urea, lactate, amino acids, immunoglobulins and other proteins). When first secreted, the fluid is similar to other initial fluids, but as it passes through the duct, it is modified by the basal cells to reabsorb some sodium, chloride and water.

sweat

_________ are small nerve ending organs (NEOs) in the papillary dermis of hairless skin (just below epidermis), particularly on the fingertips, toes and the lips. They are rapidly adapting and sensing fine touch, pressure, and low frequency vibration.

tactile (Meissner's) Corpuscles

Most of the hair on the human body is fine and ______. In contrast, the ______ hairs grown on the scalp are longer, thicker and darker. Increasing androgens at puberty triggers regional development of ________ hair.

vellus, terminal, terminal