What Is the Integumentary System?

The epidermal system covers the surface of the organism and is tightly arranged for protection. The boundary between the organism and the external environment, and protect the organism from foreign objects. In the case of single-celled organisms, the outer skin is the cell membrane and secretions that adhere to the outer membrane. However, bacteria have cell walls to maintain the shape of cells and provide protection. Multicellular invertebrates, the epidermis is mostly a single layer of epithelial cells and secretions that adhere to the outer membrane. Vertebrate epidermal systems include skin and skin derivatives. The epidermal system is the animal's largest organ system. In addition to its protective functions, it also has functions such as sensation, regulation, secretion, excretion, breathing, and exercise. The vertebrate epidermal system includes skin and skin derivatives. The skin is composed of epidermis and dermis. Taking mammals as an example, the epidermis originates from the ectoderm and is located on the superficial layer of the skin. It is a stratified flat epithelium. The dermis originates from the mesoderm and is located below the epidermis. It consists of dense connective tissue and can be divided into the papillary layer and the reticular layer. Under the dermis is subcutaneous tissue, consisting of loose connective tissue and adipose tissue.

Epidermal system

(Animal epidermis)

Both the epidermis and dermis have skin derivatives. Epidermal derivatives include glands and epidermal exoskeleton. Glands are mucous glands, sebaceous glands, sweat glands, breast glands, scent glands, etc .; epidermal exoskeleton has keratinous scales,

The skin of Wenchang fish has epidermal and dermal differentiation. The epidermis consists of a single layer of columnar epithelium with sensory cells and single-cell glands inside. At larvae, cilia appear outside the epidermis. After adulthood, the epidermis is keratinized, forming a thin layer of cuticle with holes, and the cilia disappear. The dermis is inconspicuous. It is only a thin layer of irregular, gelatinous connective tissue with few fibers and cells.

The outermost layer of the ascidian wall is a thick and rough capsular, brown, composed of a translucent matrix secreted by ectoderm cells, scattered with scattered cells.

The skin of the eel is smooth and scale-free. The epidermis is composed of stratified epithelium, which contains single-cell glands that secrete mucus to make the body sticky. It has keratinous teeth on the mouth funnel and lingual end, which are derivatives of the epidermis. The dermis is connective tissue, which contains collagen fibers and elastic fibers, and contains star-shaped pigment cells. The pigment can be moved to change the body color.

Taking trout as an example, the skin is divided into a thin epidermis and a thicker dermis. The epidermis is composed of stratified flat cells, some of which contain keratin, and there are mucus glands in the epidermis. The mucus secreted by some fish has a strong adsorption force, which can cause sediment in muddy water. The dermis contains connective tissue fibers, nerves, pigment cells, and scales. The scales are hard-bone thin plates that overlap each other, which are hidden under the skin. The exposed parts have pigment cells that can control body color. The hard bone in the scales is constantly absorbed by osteoclasts, forming a ring pattern, which can be used to determine the age of the fish