A nail is a keratinized plate located on the dorsal aspect of the distal phalanges. A section through a nail plate is shown here. The nail itself (N) is difficult to stain. Under the free edge of the nail is a boundary layer, the hyponychium (Hypon), which is continuous with the stratum corneum of the adjacent epidermis. The proximal end of the nail is overlapped by skin; here, the junctional region is called the eponychium (Epon) and is also continuous with the stratum corneum of the adjacent epidermis. Under the nail is a layer of epithelium, the proximal portion of which is referred to as the nail matrix (NM). The cells of the nail matrix function in the growth of the nail.
Together, the epithelium under the nail and the underlying dermis (D) constitute the nail bed. The proximal portion of the nail, covered by the fold of the skin, is the root of the nail (NR).
The relationship of the nail to other structures in the fingertip is also shown in this figure. The bone (B) in the specimen represents a distal phalanx. Note that in this bone there is an epiphyseal growth plate (EP) at the proximal extremity of the bone but not at the distal extremity. Numerous Pacinian corpuscles (PC) are present in the connective tissue of the palmar side of the finger. Also seen to advantage in this section is the stratum lucidum (SL) in the epidermis of the thick skin of the fingertip.
PLATE 47 KEY B, bone C, cortex D, dermis DS, dermal sheath EP, epiphyseal plate Epon, eponychium HP, dermal papilla of hair follicle Hypon, hyponychium M, medulla N, nail or nail plate NM, nail matrix NR, nail root PC, Pacinian corpuscles RS, root sheath SL, stratum lucidum asterisks, cuticle of hair numbers: 1, external root sheath; 2, Henle’s layer; 3, Huxley’s layer; 4, cuticle of inner root sheath; 5, future cuticle of the hair
Digestive System I: Oral Cavity and Associated Structures
OVERVIEW OF THE DIGESTIVE SYSTEM / 526 ORAL CAVITY / 527 TONGUE / 529 TEETH AND SUPPORTING TISSUES / 534 Enamel / 536 Cementum / 539 Dentin / 539 Dental Pulp and Central Pulp Cavity (Pulp Chamber) / 543 Supporting Tissues of the Teeth / 544 SALIVARY GLANDS / 545 Secretory Gland Acini / 546 Salivary Ducts / 549 Major Salivary Glands / 550 Parotid Gland / 550 Submandibular Gland / 551 Sublingual Gland / 551 Saliva / 551 Folder 16.1 Clinical Correlation: The Genetic Basis of Taste / 533 Folder 16.2 Clinical Correlation: Classification of Permanent (Secondary) and Deciduous (Primary) Dentition / 534 Folder 16.3 Clinical Correlation: Dental Caries / 547 Folder 16.4 Clinical Correlation: Salivary Gland Tumors / 555
The digestive system consists of the alimentary canal and its principal associated organs, namely, the tongue, teeth, salivary glands, pancreas, liver, and gallbladder.
The lumen of the alimentary canal is physically and functionally external to the body.
As it passes through the alimentary canal, food is broken down physically and chemically so that the degraded products can be absorbed into the body. The various segments of the alimentary canal are morphologically specialized for specific aspects of digestion and absorption.