Pharmacognosy I (PG202) BARKS Lecture 5 PDF

Pharmacognosy I ( PG202) BARKS Lecture 5 Prof. Dr. Magda Tohamy Professor and Head of Pharmacognosy Department 1 ◼ It is the portion of the trunk, Barks stem, branches or roots of trees...

Pharmacognosy I ( PG202) BARKS Lecture 5 Prof. Dr. Magda Tohamy Professor and Head of Pharmacognosy Department 1 ◼ It is the portion of the trunk, Barks stem, branches or roots of trees and shrubs exterior to the cambium. ◼ It includes all tissues outside to the cambium which is the place where the separation take place readily because cell are young, very soft and easily ruptured. ◼ Cambium ( thin layer between the xylem and phloem of meristematic undifferentiated cells) which actively grow and differentiate in other cells ❑Morphological characters of the bark: Shape: a) Flat: e.g.. Quillaia & Cinchona. very thick bark and dried under pressure b) Curved: concave e.g.. Wild Cherry. c) Re-curved: e.g.. Pomegranate root bark. d) Channeled: deeply concave e.g.. Cassia e) Single quill: e.g.. Cascara f) Double quill: both edges are separately enrolled. e.g.. Frangula g) Compound quill: single or double quills are packed one inside the other. e.g.. Cinnamon Collection is usually done in spring or early summer or after a rainy season when the bark is most easily collected. The collected bark is dried in sun or using artificial heat. The inner surface of bark (phloem side) lose more water and shrink more than the outer surface (cork side), therefore, the peeled bark get curved after drying Secretory structures In addition to glandular hairs and nectar discs, plant can secrete volatile oil, resin, etc. through internal structures. These structures could be: 1. Secretory cell, e.g., Oil cell in cinnamon and cassia. 2.Secretory Cavities or Sacs (Internal Glands) a) Schizogenous, e.g., orange b) Lysigenous c) Schizolysigenous, e.g., clove 3.Secretory duct Outer surface: It’s slightly lighter in color than the inner one. Usually exhibits important features: 1. It may bear certain epiphytes such as: a) Lichens [grayish thalloid structure] as in Cinchona. b) Liverwort [foliaceous, consists of very small stems to which small leaves are attached in one plane] as in Cascara. c) Mosses [stem bearing spirally arranged leaves each possesses a midrib and lamina of one cell thick]. 2. Lenticles: placed transversely, the shape and abundance of which may help in distinguishing the bark. Lenticels, are breathing Outer Surface: (Cont.) 3. Cracks and fissures: arise owing to continued increase in growth and to the lack of elasticity. 4. Wrinkles and furrows: The greater shrinkage of the softer tissues result in formation of wrinkles because the shrinkage of the barks during drying occur chiefly transversely. 5. Smooth: when the cork is evenly developed. 6. It may be rugged and scaly due to exfoliation of the outer tissues. Young herbaceous stem respirate through stomata Old woody stem respirate through lenticels (openings in cork layers) Inner surface: It’s usually darker in color and is described as: ◼ Smooth: as quillaia ◼ Finely striated: as cinnamon ◼ Coarsely striated: as cascara. ◼ Corrugated ‫مموج‬: when showing transverse parallel wrinkles e.g.. cascara Fracture: It’s the behavior of the bark when broken transversely, it gives an idea about the nature of the tissue present. may be: Fibrous, Horney, Granular, Brittle, Flexible Keep in mind 1. The cambium is originated in the parenchyma of the phloem ; in the conducting parenchyma and in the pericycle, appearing when becoming continuous, as stellate or wavy ring. 2. The cambium gives to the inner side more xylary tissue than it gives phloem tissue to the outside, thus pushing the primary phloem outwards and in many cases, the primary xylem inwards, thus in later stage the 11 cambium becoming circular in form. Keep in mind 3. Opposite each protoxylem group, the cambium usually produces parenchyma only forming the primary medullary ray. 4. The primary phloem is crushed and becomes hardly distinguished or even totally absorbed or occasionally transformed into sclerenchyma. 5. At the same time a phellogen is developed in the pericyclic region giving cork to the outside and large amount of phelloderm to the inside. As a result of this, the endodermis, primary cortex and epidermis may be thrown off and are absent in old root or trunk. 6.The primary meduallary rays usually become narrower except in certain herbaceous plants where the primary rays remain very wide, dividing the secondary xylem to separate distinct wedges. 12 Keep in mind II- The Old plant of the dicotyledons is histologically characterized by the following features: As a result of secondary thickenning of the primary root. 1 Cork 4 Secondary phloem 2 Secondary cortex 5 cambium 3 Primary phloem 7 Primary xylem 6 Secondary xylem 13  ❑So, Microscopical characters of the bark: Barks may consists of some or all the following tissues starting outside to inwards: 1-Rhytidoma 2- Periderm (cork, phellogen and secondary cortex). 3- Primary cortex. 4- Pericycle. 5- Primary phloem 6- Secondary phloem Decortication is done for the following reasons: 1- They contain low percentage or no active constituent. 2- They contain undesirable amounts of tannins, of coloring matters or of other undesirable constituents. ❑ Rhytidoma : - It’s not frequently present in commercial barks, being removed during the preparation. - It’s formed of dead usually collapsed tissues including the epidermis , some cortical parenchyma &even other deeper tissues. It may be consists of alternate layers of dead cork &other collapsed dead tissues as in Quillaia ❑ Cork: - It’s protective tegamentary tissue of secondary origin (c.f. epidermis) developed from a secondary meristimatic layer, the phellogen or cork cambium , by repeated division. - It’s formed of radially arranged rows of suberized sometimes lignified dead cells appearing polygonal in surface view.  Medullary rays: The phloem medullary rays are formed of rectangular and radially elongated cells.. The cells are parenchymatous may be lignified and pitted as in quillaia. They contain starch granules and occasionally calcium oxalate e.g. Canella.  Queshrel Querfa Cinnamon bark Origin: It is the dried bark of the shoots of coppiced trees of Cinnamomum zeylanicum family Lauraceae deprived of most of its cortex and known as Ceylon cinnamon indigenous to and cultivated in Ceylon.  Macroscopical characters : Occurs in long slender flexible sticks about 1 metre in length and 6 mm in width each consists of about 40 channelled pieces or single quills forming a long stick of compound double quills.. The outer surface : Yellowish – brown smooth with paler longitudinal lines (bundles of pericycle fibres) and occasional small scars or holes indicating the insertion of leaves or branches. ◼..The inner surface : Is darker than the outer and finely longitudinally striated the fracture is short and splintery. The bark has aromatic fragrant odour and sweet aromatic taste.  Microscopical characters :.. Cork and cortex are absent. 1-The pericycle 2-Primary phloem 3-Secondary phloem: it shows. Medullary rays.Phloem fibres. Phloem parenchyma. Idioblasts. Secretion Cell  Powder:..It is light brown or yellowish brown with aromatic odour and sweet taste it is Characterised by : 1. Numerous unequally thickened isodiametric sclerides which occur singly or in small groups 2. Abundant fibres which usually occur singly or associated with the sclereids of the pericycle. 3. Others occur associated with the oil cells and the parenchyma of the phloem. 4. Abaundnt starch granules 5. Thin walled parenchyma and medullary rays of phloem containing small acicular crystals of calcium oxalate. 6. Very few cork cells 7. Fragments of parenchyma accompanied by oil cells.  Constituents: 1- Volatile oil composed of cinnamic aldehyde, eugenol and other terpens 2-Tannins and mucilage. Uses : 1-Carminative 2-Flavouring agent 3-Aromatic antiseptic and mild astringent THANK YOU For any questions feel free to contact me by mail [email protected] Dr. Magda Tohamy Ibrahim Professor of Pharmacognosy 26