Integumentary system is the largest organ system of our body and consists of skin, hair, nails, oil and sweat glands as well as nerves. All these organs collectively play a variety of roles in maintaining the normal body functions. Skin, the largest organ of our body, plays a protective role, and prevents the entry of foreign bodies like dust particles, bacteria, viruses and other pathogens. It is the site for synthesis of vitamin D in our body. Sensory receptors for touch, pain, pressure and heat are present in skin. These sensory structures are involved in the detection of stimuli and communicating the changes in stimuli to the effector organs of the body. Hair and the associated glands are involved regulating the body temperature (thermoregulation), and in maintaining the water balance of our body. The sweat glands are involved in excretion of electrolytes as well as inhibiting the colonization and growth of harmful bacteria on the skin surface. Nails confer protection to the fingertips and also aid in gripping objects with more precision. Thus, the integumentary system is essential for protection of the internal tissues and maintaining the internal integrity and equilibrium of the body.
The structures comprising the integumentary system and their corresponding functions have been detailed below.
Diagram of Integumentary System Organ ~ Skin
Parts of the Integumentary System
The skin is the most important organ of the body, as it protects the delicate organs of the body. The skin is divided into three separate layers as follows:
- Epidermis: This is the outermost layer of the skin that contains four separate layers of epithelial tissue. The outer most layer is the stratum corneum that is about 2 to 30 cells thick. These are keratinized and dead cells that make the skin waterproof! The second and third layer consists of the stratum granulosum and stratum lucidum, which contain cells that are not keratinised as yet. As these skin grows, the cells are pushed outward and come towards the surface. The last and the deepest layer of the epidermis is the stratum germinativum. These cells are active mitotically and have the ability to reproduce, as these cells are living, thus, making them the manufacturing center for growing skin.
- Dermis: The dermis lies immediately after the epidermis. The dermis consists of its own blood supply and thus contains many complex structures. The sweat glands are present in this layer that collect waters and waste products from the blood stream. This waste is excreted from the pores in the epidermis along with the water in form of sweat. The hair roots are also present in this layer that help in the growth of hair. When the hair reaches outside the epidermis, the cells are dead. The connective tissue made of collagen fibers are also found in the dermis that help give the skin elasticity and strength.
- Subcutaneous Layer: The last layer of the skin containing the adipose tissues, cushions the delicate organs beneath the skin. The body temperature is also maintained within this layer by insulating the body to the temperature fluctuations.
Functions of the Skin
- Thermoregulation: The thermoregulation of the skin is carried out with the help of evaporation of the sweat and regulation of the blood flow to the dermis.
- Sensations: The cutaneous sensations like touch, pressure, vibration, pain, cold, hot, etc, are felt by the skin.
- Protection: The protective barrier of the skin helps prevent diseases, infections, dehydration, etc.
- Production of Vitamin D: The precursor present in the skin and UV rays, helps in the production of vitamin D, an important nutrient of the body.
- Healing: When the epidermis breaks away due to a minor cut or burn, the cells on the lower layers of the skin migrate upwards as a sheet. When two ends of the sheet meet, the cells stop growing due to a process called 'contact inhibition'. Thus, the epidermis is sealed and the skin returns to normal.
Hair, feathers, scales, etc. are all derived from the skin. In case of humans, the hair extends to the surface from the hair roots or hair bulbs present in the dermis. The functions of the hair include protection and sensation to touch. Hair is made up of dead, keratinized cells that are bound together with the extracellular proteins. Each hair is divided into hair shaft that is the superficial layer and the root that is in the dermis. Hair follicle is the structure that surrounds the hair root. The oil glands present around the hair follicles help keep the hair and the surrounding skin moist. It also acts as a protective organ involved in temperature regulation.
Arrector Pili Muscles
These are smooth muscle cells that extend from the hair follicle till the papillary layer of the dermis. These arrector pili muscles cause the hair to become erect and give the feeling of 'goose bumps'. Hair can trap more warm air when they are erect. Hence, during extreme cold environment, these muscles contract leading to erect hair. Under conditions of high temperature, the arrector pili muscles relax so that the hair lie flat on the skin and thus aid in the escape of heat.
Nails, claws and horns are structures that are derived from the skin. The nail is a highly keratinized structure of modified epidermal cells. The nail bed gives rise to nails, that is thickened to form a lunula. The moon shaped structure that you observe at the base of your nails is called the lunula. The function of nails is to help in grasping and holding things. The nails act as counter force and help increase the sensitivity of the fingertip. They also protect the fingertips and underlying tissues from damage.
Sebaceous Glands and Nerves
Sebaceous glands secrete the oil coating for the hair shaft. When these sebaceous glands become clogged with dirt and microorganisms, they become infected and cause pimples or acne. The complex network of the nerves present all over the skin helps send and receive important impulses to and from the brain, thus playing a vital role in sense of touch.
Sweat glands have an opening through the skin pores, and they help in excretion of water and electrolytes. Eccrine sweat glands are found all over the body whereas apocrine sweat glands are present in armpits and groin. Eccrine glands are involved in the cooling mechanism of thermoregulation whereas, apocrine glands are involved in the secretion of chemicals and pheromones.
The integumentary system interacts with the various other human body systems and is involved in the physiological processes responsible for maintaining the internal equilibrium of the body.