Page 5 - Human anatomy COMPLETELY DONE1

INTEGUMENTARY SYSTEM

Overview
The skin is the largest organ of the human body. The total area of the skin in an average

adult is about 2 square meters and accounts for about 20% of the body weight.
Layers of the Skin (Figure 1)
The human skin consists essentially of three superimposed layers. From the outside to
the inside, these are called:
-The epidermis, the outermost layer of skin, provides a waterproof barrier and
creates our skin tone.
-The dermis, beneath the epidermis, contains tough connective tissue, hair
follicles, and sweat glands.
-The hypodermis is the deeper subcutaneous tissue and is made of fat and
connective tissue.
THE EPIDERMIS
Between 0.03 mm and 2 mm thick. In the basal layer, basal cells are constantly
renewed. After several weeks, these cells penetrate the layers to get to the surface, the
horny layer. By this, the epidermis is renewed once a month. Within the epidermis we
can also find cells responsible for tanning of the skin (melanocytes), which is a
protective reaction to sunlight (UV radiation).
Sebum is an oily substance secreted onto hair.
THE DERMIS
The dermis is an elastic and resistant skin layer with a thickness of between 0.5
mm and 1.5 mm. It has small blood vessels (capillaries) and lymph channels passing
through it. Additionally, sweat and sebaceous glands (oil glands) are found in the
dermis, particularly in the roots of hairs rising from the skin (hair follicles).
THE HYPODERMIS
The hypodermis consists mainly of fatty tissue. Depending on the thickness of
the fat layer, it is between 0.5 mm and 30 mm thick. First and foremost, it functions as
a connecting layer between the upper skin and the dermis (together called cutis) and the
underlying muscle tissue, as well as energy storage and isolation.

Layers of the Skin
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