Secretory canals

The antigenic component of poison ivy, poison oak and poison sumac, called urushiol, is found within secretory canals located in the plant s leaves, roots and phloem, which is just below the bark [30]. The active ingredient in poison ivy mostly comprises penta-dec(en)yl catechols [18], and for poison oak it is mostly comprises heptadec(en)yl catechols. In the case of T. radicansy exposure may occur to the tiny brown rootlets that attach the vine to the tree or post on which it climbs, but usually it occurs when the leaf surface is broken so that the sap containing the... 

Eccrine (merocrine) sweat glands are simple tubular glands that open directly onto the skin surface (Figure 35.1). In humans, they are found over the entire body surface except for the lips, external ear canal, clitoris, and labia minora. Myoepithelial cells located in the secretory portion of these glands are specialized smooth muscle cells, which, upon contraction, aid in moving the secretions toward the duct. The eccrine sweat gland duct is comprised of two layers of cuboidal epithelium... 

Answer C. This question helps review ANS drug actions on the eye. The pupil is controlled reciprocally by the SANS (iris dilator, alpha) and the PANS (iris sphincter, muscarinic) thus, alpha agonists cause mydriasis, and AChE inhibitors cause miosis (answers D and E are opposites ). Ciliary muscle contraction is controlled by the PANS, so choli-nomimetics lower IOP by putting tension on the trabecular network to facilitate outflow of aqueous humor through the canal of Schlemm—beta blockers decrease the secretory activity of ciliary epithelial cells (answers A and B are opposites ). Topical use of nonse-lective beta blockers can indeed worsen asthma ... 

H. perforatum ssp. veronense shows typical longitudinal dark canals on the petals, in addition to the usual dark secretory glands. Translucent glands are particularly abundant on the leaves of H. perforatum, which assume a perforated-like appearance when observed in transverse light. 

Terpenoids can be found in various plant organs. Concentrations of terpenoids in plant tissues are controlled by the availability of substrate and the activity and type of biosynthesis enzymes. Emission rates of volatile terpenoids from plant leaves are controlled by their synthesis rates and compound-specific physicochemical characteristics, mainly their solubility, volatility and diffusivity. These are affected by physicochemical constraints caused by temperature, stomatal conductance and leaf structure. Storage of terpenoids could be isolated from other plant tissues with specialized structures such as secretory cavities, resin canals (Fig. 94.1), latex canals (lactifers), and glandular trichomes. 

Fig. 94.1 Examples of terpenoid storage structures embedded in plant tissues, (a) Cross-section of (Pinus halepensis) needle showing four resin canals (R) in the needle mesophyll layer (micrograph provided by Dr. Minna Kivimaenpaa). (b) Secretory cavities of red grapefruit Citrus paradisii) peel for storage of monoterpenes, mostly limonene...

Essential oils are secondary metabolites produced in the plants as volatile aromatic principles. They are colorless and rarely colored and soluble in organic solvents. It is fotmd in all part of the plants and is stored in epidermal cells, trichomes, secretory cells, canals, and cavities. They are extracted by the use of liquid carbon dioxide or microwaves, expression and mainly steam or hydrodistillation process. Due to their biological, nutritive, and pharmaceutical properties, they are more attractive alternatives to synthetic chemical products to protect the equilibrium. 

The bulk of all spices and herbs is cellulose, which contributes nothing to the aroma and flavor of the material. The aromatic profile is largely determined by the essential oil content, quantitatively as a measure of aromatic strength, and qualitatively as a determinant of aromatic character. In most instances, the volatile oil preexists in the plant and is usually contained in special secretory tissues the nature of which is often associated with particular plant families (e.g., Zingiberaceae-oil cells, Umbel-liferae-vittae or oil canals, Labiatae-secretory hairs). For this reason one cannot over generalize on distillation techniques as optimum conditions will vary between different spices. Generally, younger plants produce more oil than older ones but the quality of such oils may lack the fuller aromatic attributes normally associated with... 

---