Views:4 Author:Site Editor Publish Time: 2020-10-01 Origin:Site
Skin: An organ that is wrapped on the surface of the body and directly contacts the external environment. It has the functions of protecting, excreting, regulating body temperature and feeling external stimuli. It is the largest organ in the human body.
Skin: It is composed of epidermis, dermis, subcutaneous tissue and skin appendages;
1. Epidermis: It is composed of multiple layers of flat epithelium, from shallow to deep, in order of stratum corneum, transparent layer, granular layer, spinous layer and germinal layer. The stratum corneum is composed of multiple layers of keratinized epithelial cells (the nucleus and organelles are lost, and the cell membrane is thicker). It is inanimate, impermeable, and has the functions of preventing tissue fluid from outflow, anti-friction and anti-infection. The germinal layer cells continue to proliferate and gradually migrate outward to supplement the constantly shedding stratum corneum. The germinal layer contains a kind of melanocyte, which can produce melanin. The color of the skin is related to the amount of melanin.
2. Dermal layer: It is composed of dense connective tissue, from shallow to deep, the papillary layer and the reticular layer, with no obvious boundary between the two layers. The thickness of the dermis is about 0.07～0.12 mm; the dermis of the palms and soles is thicker, about 1.4 mm; the eyelids and tympanic membranes are thinner, about 0.05 mm. The papillary layer is connected to the germinal layer of the epidermis, which is rich in capillaries, lymphatic vessels, nerve endings and tactile corpuscles. The reticular layer is connected to the subcutaneous tissue, and it contains abundant collagen fibers, elastic fibers and reticular fibers. They are intertwined into a net to make the skin more elastic and tough. There are also abundant blood vessels, lymphatic vessels and nerve endings in the reticular layer.
3. Subcutaneous tissue: It is the loose connective tissue and fat tissue below the skin, which connects the skin and muscles, and is often called superficial fascia. The subcutaneous tissue is located between the skin and the deep tissues, giving the skin a certain degree of mobility. The thickness of the subcutaneous tissue varies greatly depending on the individual, age, gender, location, nutrition, disease, etc. Generally, the abdomen and buttocks are the thickest, and the adipose tissue is abundant. The eyelids, the back of the hands, the back of the feet and the penis are the thinnest, without fatty tissue.