UBSDM 2015 Histology
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| Elastic Artery | In elastic arteries the media is filled with wavy acidophilic bands called elastic laminae. The elastic laminae are composed of a protein (elastin) which behaves like a rubber band. It can be stretched and it can shrink (return to original size).
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| Muscular Artery | The tunica media consists of a thick layer of smooth muscle and is filled with as many as 40 tightly packed layers of smooth muscle cells that encircle the vessel wall.
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| Arteriole | The arteriole is a miniature muscular artery. It has a tunica intima, tunica media and tunica adventitia but contains only 1-7 layers of smooth muscle cells occupy the tunica media.
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| Venules | The smallest veins are called venules. Venules accompany arterioles and have 1-3 layers of smooth muscle cells in the tunica media.
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| Small and Medium Sized Veins | The small/medium veins are larger than venules. They accompany muscular arteries. The tunica media is as thin as or thinner than the adventitia, the muscle layer of the tunica media is not very compact
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| Large Vein | The large veins have a tunica intima, tunica media, and tunica adventitia. The key to recognizing them lies in the significant amounts of muscle that is bundled and arranged along the long axis of the tunica adventitia.
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| Precapillary Sphincter | Arteriole with complete smooth muscle layer that can occlude the lumen preventing blood flow to a capillary bed
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| Arterial Portal System | Artery Leads to a capillary bed and the capillary bed leads to an artery. Found in the Kidney
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| Venous Portal System | A Vein that is connected to a capillary bed that is connected to another vein. Found in the Liver and the Pituitary.
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| Capillaries | Single Layer of endothelial cells. Lumen Diameter of 5-7 um, not much bigger than an RBC.
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| Pericyte | Capillary associated cell that is enclosed in the basal lamina. It is important as the precursor to new blood vessels
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| Continuous Capillary | One or two endothelial cells form a ring that encloses or encircles the lumen. Adherent junctions join the ends of cells to allow material to move through cytoplasm to tissues.
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| Tight Junctions | Used in tissues with blood barriers to prevent material from moving between cells. Tight Junctions force material transfer through cell cytoplasm.
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| Fenestrated Capillary | Pores/Fenestrations are 60-90nm in diameter interrupt the continuous lumen. Allows for rapid and freer transfer of material to tissues 2 types: 1. has diaphragm 2. no diaphragm.
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| Sinusoidal Capillary (Discontinuous) | Larger than normal capillaries. Large gaps are in the vessel walls that allow for large molecules to pass directly into liver tissues. Most permeable vessel.
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| Post-Capillary Venule | Drains Capillary Beds. Resemble capillaries but are larger. White Blood Cells Leave circulation and enter tissues here.
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| Functions of Integument | Protective Barrier, Receptor via nerves, Heat Regulation, Mechanism of Secretion(Sweat), Vitamin D Synthesis (through UV)
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| Epidermis | Keritinized stratified squamous Epithelium
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| Dermis | Layer of Connective tissue Beneath Epidermis. Two Layers. Ridges, Dermal Papillae, formed at the junction create fingerprints
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| Thick Skin | Palmar and Plantar Surfaces. Numerous Sweat glands. No Hair. All Layers are thick
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| Thin Skin | Hair Follicles are present. Covers entirety of body except palms and bottom of feet.
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| Stratum Basale | Single Layer of basophilic columnar/cuboidal cells that sits on the basal lamina of dermal-epidermal junction. Connected to other cells through desmosomes. Stem Cells of Skin. Renewed 15-30 days.
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| Stratum Spinosum | Polygonal Cuboidal/ Slightly Flattened. Full of intermediate filaments attaching at desmosomes. Spiny look is artifact from shrinking during fixation
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| Stratum Granulosum | Thin Layer (3-5) of cells containing 2 types of granules. Keratohyalin: Basophilic, Rich in protein. Lamellar Granules: Secretory, EM-Flattened appearance. Exocyoses and creates a H2O-proof layer of lipids
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| Stratum Lucidum | Thin, Eosinophilic (white layer) No Organelles, mostly made of keratohyalin granules and dense filaments
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| Stratum Corneum | 15–20 layers of keratinized, flattened, denucleated cells whose "cytoplasmic sacs" are filled with keratin filaments embedded in an amorphous matrix
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| Melanocytes | Function: production of pigment of skin (melanin) Embryologic origin: neural crest cells.
Location: beneath and in-between cells of stratum basale,
Shape: round cell bodies with long irregular dendritic projections
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| Vitiligo | a genetically controlled degeneration and death of melanocytes leading to areas of depigmentation
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| Synthesis of Melanin | tyrosinase is made by ribosomes and is moved through rough ER to the Golgi and then into vesicles termed melanosomes. Tyrosinase activity in melanosome causes conversion of tyrosine to DOPA which in turn is converted to dopaquinone and then to melanin
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| Freckle | A large number of melanocytes in epidermis or dermis;
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| Langerhan's Cell | Dendritic Cell located in the stratum spinosum derived from CD34 cells in the bone marrow. Antigen presenting cell.
Involved in allergic dermatitis
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| How to ID Langerhan's Cell | — has clear cytoplasm in H & F stained sections (like melanocytes)
— nucleus is indented in many places (seen at EM level)
— rel. numerous, comprise ±5% of cells in epithelium
— Birbeck granules, appear as "long rods" at EM level
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| Merkel Cell | — present in basal layer
— dense core granules (EM level),
— Merkel cell-neurite complex, composed of these cells plus closely associated nerve endings of sensory nerves. Function: sensory receptors (mechanoreceptors)
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| Papillary Layer | • loose connective tissue immediately under the epidermis and its basal lamina
• co collagen fibers are more delicate than those in the reticular layer
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| Reticular Layer | • Located below the papillary layer
• junction between these two layers is indistinct
• dense irregular CT, mainly type I collagen
• more fibers, larger bundles and fewer cells than papillary layer
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| Nerves of the Dermis | • free nerve endings (many more in epidermis)
• encapsulated nerve endings: Meissner's and Pacinian corpuscles (the latter have onion-like appearance)
• an array of unmyelinated nerves are found around the entire length of a hair follicle
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| Leather | - the resultant product of denaturization of dermis by the tanning process.
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| Eccrine Sweat Glands (Merocrine) | - distributed over entire body surface except a few locations such as lips and external genitalia
- especially numerous in skin devoid of hair
- simple coiled tubular gland
- secretory portion of gland located deep in dermis or upper hypodermis
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| Dark Cells | • line most of luminal surface
• shape of inverted pyramid with broad base at luminal end
• basal surface does not touch basal lamima
• contain secretory granules probably composed of glycoprotein
(often listen to EMO)
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| Light (Clear) Cells | • pyramidal shape with base in contact with basal lamina
• EM reveals numerous surface folds and microvilli
• basal surface has numerous invaginations -- a structure characteristic of transepithelial fluid and salt transport
• produce watery secretion
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| Myoepithelial Cells | • surround the secretory portion of the gland, are enveloped by the basal lamina of the secretory cells
• propel the secretion out of the gland by contraction
• contain numerous contractile filaments
• innervated by cholinergic fibers
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| Eccrine Gland Duct | • consists of stratified cuboidal epithelium (only 2–3 cells thick)
• pass through the dermis and epidermis in a gentle spiral
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| Apocrine Sweat Gland | - limited distribution: present in axilla and circumanal region
- ducts open into hair follicles
- acini surrounded by myoepithelial cells under adrenergic control
- onset of secretory activity in puberty
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| Structure of Apocrine Gland | - similar to eccrine glands
- are larger 3–5 mm vs. 0.5 mm diameter
- produce a viscous secretion that is initially odorless and which acquires a distinctive odor as a result of bacterial decomposition
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| Sebaceous Glands | - develop as an outgrowth of the external root sheath of the hair follicle, usually several acini open into a duct
- in certain areas (glans penis, clitoris, lips, breast areolae) ducts open directly onto the epidermal surface
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| Structure of Sebaceous Gland | - acini with basal layer of flat undifferentiated cells
- cells proliferate, differentiate, become swollen with produced lipid, the nuclei shrink and the engorged cells rupture releasing sebum
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| Sebum | - Produced by the Sebaceous gland.
- Made of Waxes, cholesterol and triglycerides
- Functions as hair moisturizer
- Increased production at puberty
-Too much = zits
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| External Root Sheath | - the outermost layer of the hair follicle
- is a downgrowth of epidermis
- at its deepest point it forms the bulb-like expansion
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| Internal Root Sheath | -is a multilayered cellular covering that surrounds the deep part of the hair
- internal root sheath undergoes keratinization, becomes keratin and is dissolved at the level of the sebaceous gland
- Makes a space around the hair making it a free shaft
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| Glassy Membrane | Separates Hair Follicle from the Dermis
non-cellular hyaline thick basal lamina
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| Dermal Sheath | Forms Dense Connective tissue sheath. Attachment site for arrector pili muscle.
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| Pilosebaceous Unit | Hair follicle + Sebaceous Gland + Arrector Pili Muscle
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