Hypodermis-epidermis

Suberin is tightly associated with the cell wall and cannot be removed in a pure form. The outer layer is usually removed physically and then treated with pectinase, cellulase and organic solvents to yield an enriched fraction. The crude suberin must then be subjected to chemical treatment in order to depolymerize it for chemical analysis (references in Kolattukudy, 1980). Crude suberin preparations have also been isolated from endodermis (Robards et al.y 1976) and hypodermis-epidermis (Clarkson et al.y 1978) but the amounts obtained from these sources are usually too small for meaningful analyses to be performed. 

Collagen fibers are long and thick in the middle dermis but become increasingly fine toward the outer epidermis as well as toward the inner hypodermis. Apart from this structural characteristic, which is common to all animals, the skin of each species has a different and unique morphology that significantly affects its properties (Calnan and Haines 1991). 

Microscopically, the skin is a multilayered organ composed of many histological layers. It is generally subdivided into three layers the epidermis, the dermis, and the hypodermis [1]. The uppermost nonviable layer of the epidermis, the stratum corneum, has been demonstrated to constitute the principal barrier to percutaneous penetration [2,3]. The excellent barrier properties of the stratum corneum can be ascribed to its unique structure and composition. The viable epidermis is situated beneath the stratum corneum and responsible for the generation of the stratum corneum. The dermis is directly adjacent to the epidermis and composed of a matrix of connective tissue, which renders the skin its elasticity and resistance to deformation. The blood vessels that are present in the dermis provide the skin with nutrients and oxygen [1]. The hypodermis or subcutaneous fat tissue is the lowermost layer of the skin. It supports the dermis and epidermis and provides thermal isolation and mechanical protection of the body. 

Structure of skin. Skin is composed of two layers, the epidermis and the dermis, separated by a basement membrane zone. Hypodermis, composed of adipose tissue, sweat glands, and pacinian corpuscles, is not part of the skin.45... 

Appendageal structures commonly found within the skin are the hairs, hair follicles, associated sebaceous glands, apocrine and eccrine sweat glands, and arrector pili muscles. Hairs are formed by epidermal invaginations. These keratinized structures traverse the dermis and may extend into the hypodermis. The free part of the hair above the surface of the skin is the hair shaft, and the part deep within the dermis is the hair root, which forms an expanded knob-like structure called the hair bulb. This is composed of a matrix of epithelial cells in different stages of differentiation. Hair is composed of three concentric epithelial cell layers the outermost thin cuticle, a densely packed keratinized cortex, and a central medulla of cuboidal cells. The hair follicle consists of four major components (1) internal root sheath (internal root sheath cuticle, granular layer, pale epithelial layer) (2) external root sheath (several layers similar to the epidermis) (3) dermal papilla (connective tissue) and (4) hair matrix (comparable to the stratum basale of the epidermis). 

The skin is the largest organ in the human body and has many physiological functions. The skin serves to regulate overall body homeostasis, protect the body from external pathogens and chemicals, as well as control water loss from the body. The skin has three main layers. The epidermis, which is the outermost layer, is the thinnest layer of the skin and provides the most significant barrier function [7]. Beneath the epidermis, the dermis provides mechanical support to the skin and the third layer, immediately under the dermis, is a layer of subcutaneous fat called the hypodermis. 

The dermis (corium) consists of connective vascularized tissue composed of collagen, elastic and reticular fibres anchoring sweat and sebaceous glands, and hair follicles. Capillaries pervading the dermis and hypodermis (subcutis, located beneath the dermis) allow systemic distribution of toxic compounds once they have passed the epidermis. Therefore, percutaneously incorporated poison may be directly transported by the circulation to any... 

Figure 1 Autoradiogram of skin treated by the passive application of H-estradiol, in dimethylsulfoxide, for 2 hours. The exposure time was 81 days. (A) A macroscopic view illustrating the regions of the epidermis, hair shafts, and sebaceous glands with the highest levels of radioactivity is shown. (The arrow points at a sebaceous gland.) Penetration gradients of radioactivity are apparent between the epidermis and dermis (B-C) and regions of hair shafts and the hypodermis (D-E). The scale bar is 25 pm. (Reprinted with permission from Ref. 11.)...

Figure 19 SEM and energy dispersive analysis micrographs (175x) showing mineral distribution, Ca, Si, and Al, localization in a frozen, planar transverse section 1 mm behind the tip in a second year needle of Pinus strobus (Eastern white pine) (a) secondary electron image, (b) calcium distribution, (c) Si distribution, and (d) Al distribution. Abbreviations endodermis (en), epidermis (ep), hypodermis (hy), mesophyll (me), transfusion tissue (tr), vascular tissue (vt), and xylem wall (xw) (courtesy of M. J. Hodson and A. G. Sangster, unpublished collection).

Outer Cortex (hypodermis), a zone of several layers of thick-walled lignified cells separating the epidermis from the inner cortex beneath. Its main function is to support the epidermis. 

Fig. 15.—Transverse section of stipe of Dryopteris Filix-mas showing- epidermis (e) hypodermis (/i) inner cortex (tc) concentric fibre vascular bundles, one of which is shown at (b) endodermis (en) pericambium xylem and phloem (p). (Photomicrograph.) X iO.4.

Fig. 59.—Part of a transverse section of Honduras sarsaparilla root showing epidermis (r), root hair (ha), hypodermis (A), cortex (c), rendodemis (en), peri-cambium (p), trachea of one of the numerous xylem patches (1), and pith (m). The phloem patches are the small oval cellular areas wedged in between the outer portions of adjacent xylem masses. (Photomicrograph.)...

Hypodermis, a layer of somewhat thick walled cells just beneath the epidermis. 

Pig. 61.—Photomicrograph of a transverse section of a California Privet root of primary growth showing epidermis (e) hypodermis (A) cortex (c) endodermis (en) pericambium (p) a xylem arm of the radial bundle (f) and pith (m). 

Epicarp, consisting of epidermis and hypodermis. The epider-. mis consists of a layer of thick-walled epidermal cells whose outer... 

For the purpose of topical formulation design and application, we can examine the structure and function of human skin categorised into four main layers 1—the innermost subcutaneous fat layer (hypodermis), 2—the overlying dermis, 3—the viable epidermis and 4—the outermost layer of the tissue (a non-viable epidermal layer) the stratum corneum (Figure 1). 

The skin has many important functions. Its three layers— the epidermis, dermis, and hypodermis (subcutaneous tissue)— provide a barrier, prevent dehydration, protect from external injury or microorganisms, maintain body temperature, and even express emotions through dilation or constriction of blood vessels. The dermal layer contains most of the structural components of skin, such as mast cells, fibroblasts, collagen, elastic fibers, sweat glands, sebaceous glands, pigment-producing melanin cells, and vasculature. 

Figure 7. (A) Skin of razorback suckers Xyrauchen texanus) not exposed to UV. Mucous cells (open arrows) line the very outer surface of the epidermis. A major portion of the epidermis is composed of large PAS-negative cells (filled arrows). Bar equals 50 /zm. (B) Skin of razorback sucker after 72 h of UV exposure. The epidermis is thickened to hyperplasia and hypertrophy of the large PAS-negative cells. There are many leucocytes infiltrating the basal portion of the epidermis (filled arrows), melanocyte accumulations below the dermis (open arrows) and inflammation in the hypodermis. The changes observed were reversible and non-lethal. Bar equals 50 /zm. [From Blazer et al. 15.]...

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