INTRODUCTION:
The body is covered with skin, nails, and hair. Together with glands found in the skin, they make up the integumentary system. It gets its name from the Latin word integumentum meaning "covering".
The skin is an organ, just like the heart and lungs. It is the largest organ in the body. The skin has two layers. The outer layer (epidermis) helps prevent harmful substances from entering the body. The inner layer (dermis) contains glands that secrete important substances, nerves that carry electrical impulses, and blood vessels that help keep the body at the right temperature.
The epidermis is the outer layer of the skin. The dermis is under the epidermis. Subcutaneous tissue is under the dermis. |
Epidermis:
The epidermis is an organ made of tissue called epithelium. The cells are called epithelial cells. The epidermis is a protective covering over the entire body and lines body cavities and covers organs.
The epidermis protects us from the sun's rays by producing melanin. Melanin is produced by cells in the epidermis called melanocytes. Darker skin has more melanocytes than lighter skin. Skin with more melanin has better protection from the sun.
Skin also protects by keeping infectious materials from entering the body and it waterproofs the body and prevents fluid loss.
Dermis:
The dermis is made of connective tissue. A major component of connective tissue is collagen, which makes the skin flexible and strong.
The dermis contains blood vessels and nerves, they give us sensations such as touch, pain, temperature, and pressure. Also in the dermis are glands and hair follicles. These parts are discussed below under the heading Accessory Structures.
Subcutaneous Tissue:
Subcutaneous tissue is deep to the dermis and is composed of mostly adipose tissue. its cells are called adipocytes. Besides storing fat, this layer loosely connects the skin to the underlying muscles and protects us from injury. It is also known as superficial fascia. Fascia is a connective tissue that holds parts together.
Accessory Structures:
Glands
There are glands in the dermis that secrete substances necessary for skin function. Sebaceous glands secrete oil called sebum. It keeps the skin and the hair soft and pliable (flexible). sweat glands help regulate temperature by secreting sweat onto the surface of the skin. When the sweat evaporates, the skin cools. Specialized glands in the ear named ceruminous glands secrete cerumen a waxy substance that helps prevents bacterial infection.
Hair Follicles
There are also hair follicles in the dermis. They grow the hairs that cover our skin in certain places. When hair is lost on top of the head, the person is said to be bald. The medical word for bald. The medical word for bald is alopecia. The opposite, the presence of excessive body and facial hair, especially in women, is called hirsutism.
Nails
Nails are protective coverings on the ends of fingers and toes. Nails are epithelial cells that have been hardened. At the base of each nail is the white, half-moon shaped lunula. other anatomical structures are the nail bed and the cuticle or eponychium.
