CATDOLL : CATDOLL: How many layers does a cat's skin have? Introduction to the physiological structure of cat skin

How many layers does a cat's skin have? Skin disease is ultimately a disease whose symptoms appear on the skin, so before treating a cat's skin disease, we must first understand the cat's skin structure.

1. Epidermis

The epidermis forms the outermost layer of the skin, which serves to isolate the harsh external environment and protect the body from various chemical, physical and biological factors. Although the epidermis is very thin, it has a strong protective effect on the body with the help of hair, keratinocytes and glands. The epidermis is tightly combined with the dermis, exchanging cells and body fluids to obtain sufficient nutrition supply. The epidermis is composed of stratified squamous (flat) epithelium, which is only 0.2-0.5mm thick. The thickest epidermis is distributed on the nose and foot pads (1.5mm). The epidermis is composed of keratinocytes, pigment cells, Langer cells, etc. Keratinocytes account for 85% of epidermal cells, and the morphology of each layer in the epidermis is slightly different. In the basal layer, it appears as a tightly connected columnar epithelium, connected to the basement membrane area. As the cells divide, the daughter cells enter the spinous layer, and the morphology is polyhedral, and the granular layer is flat. The stratum corneum appears as a flat shape with the cell nucleus disappeared. Keratinocytes are not only an important component of the skin structure, but also an important member of the skin's immune system. Their ability to engulf and process antigens is even greater than that of Langer cells, specialized immune cells in the epidermis. Under the influence of interferon-γ, keratinocytes have a stimulating and buffering effect on T lymphocytes. After interacting with antigens, they produce interleukin-1, which further stimulates the production of a wider range of cytokines, stimulating and inhibiting immune responses. Interleukin-1 can also be released into the dermis to cause inflammatory responses.

2. Dermal-epidermal junction - basement membrane

The basement membrane is the foundation of the epidermis. The epidermis is firmly fixed to the dermis through it, maintaining normal function and proliferation of the epidermis, maintaining tissue structure, helping wound healing, and also serving as a barrier between the dermis and epidermis, maintaining the exchange of cells and body fluid elements between the epidermis and dermis.

The basement membrane consists of four parts:

(1) Tensile filament-hemidesmosome complex (attached to the basal layer cells);

(2) The main components of the transparent plate are collagen XVII (i.e., 180 kDa bullous pemphigoid antigen, BP180) and fixed fibers;

(3) The dense plate contains type IV collagen, laminin isoforms, entactin, and basement membrane proteoglycan;

(4) Under the basement membrane: The fixed fibers and acid-resistant filaments formed by the dense thin layer extend to the superficial layer of the dermis. In the very rare bullous pemphigoid, the main target of autoantibodies is collagen XVII (BP180).

3. Dermis

The main part of the skin, with a firm, flexible and elastic texture. The dermis provides physical, blood and neural support to the epidermis and is the body's complete connective tissue. The dermis is mainly composed of dermal fibers and soluble polymers, with cells dispersed in it. Most of the accessory structures in the skin are located in the dermis.

(1) Dermal fibers: collagen and elastin.

(2) Soluble polymers: proteoglycans and hyaluronan.

(3) Cells in the dermis: fibroblasts and dendritic cells.

(4) Accessory structures: follicular units, arrector pili muscles, blood vessels, lymphatic vessels, and nerves. Lesions in the dermis often occur in and around blood vessels. Other lesions of the dermis are very rare, for example, skin lesions caused by abnormal collagen structure - Ehrlich-Danlos disease (also known as systemic elastic fiber dysplasia syndrome) are hereditary collagen synthesis and distribution abnormalities, mainly manifested as excessive stretching of the skin.