What is the Integumentary System? 

The integumentary system encompasses a set of organs developing the external most layer of the body, where the skin and the appendages are found to function as a physical barrier for preventing the entry of pathogenic microbes and hazardous substances from the external environment. The structures associated with the integumentary system include scales, hair, nails, hooves, and feathers.

Structure

The integumentary system possesses numerous functions involving the maintenance of water balance in the body. It also guards the deeper tissues and mediates the excretion of wastes. The body temperature is detected and controlled by the action of the integumentary system. The sensory receptors are found to be connected to the body at this location. These receptors mediate the detection of different senses including temperature, pressure, sensation, and pain. The main structures found in the integumentary system include the skin and the hypodermis, where the skin includes layers such as the epidermis and dermis. 

The skin and hypodermis constitute the main regions of the integumentary system. The skin is considered as one of the largest organs found in the body and it constitutes 12-15 percent of the complete bodyweight. The skin includes two layers: epidermis and dermis. The epidermis is the external layer and it serves as a primary barrier to the external environment. The basement membrane is identified to separate the dermis and epidermis of the skin. The melanocytes present in the epidermis provide pigmentation to the skin. The deepest regions of the epidermis possess nerve endings. The dermis possesses two regions including the reticular layer and the papillary layer. It also has structures including the hair roots, connective tissues, glands, vessels, and follicles. A transitional substance composed of very loose connective and adipose tissue is located between the deep body musculature and the integument. The collagen bundles function in anchoring the hypodermis and the dermis.

Epidermis

The epidermis is very strong and is considered the superficial layer of the skin. The stratified squamous epithelial cells make the human epidermis and consist of layers including the stratum basale, stratum granulosum, stratum corneum, and stratum spinosum. The regions such as the soles and palms have thicker skin and they possess an additional layer of skin called the stratum lucidum.

The covering that forms the external layer of the epidermis is called the stratum carenum and is composed of dead keratinized cells. The multicellular epidermal glands are integrated into the dermis and are enclosed by blood capillaries mediating the supply of nutrients. The stiffening of the epidermal tissues to form fingernails is aided by the protein keratin.  The important function of the integumentary system involves homeostasis, protection, and the intake of nutrients. The four types of cells performing these functions include Langerhans cells, Merkel cells, melanocytes, and keratinocytes. The keratinocytes are the major cell types of the epidermal layer. They are associated with the production of keratin for meditating the protection of the skin. They form the water barrier of the body.

Dermis

The dermis is the connective tissue underlying epidermis. It provides support to the epidermis and is found to possess dense irregular connective tissue along with the areolar connective tissues including collagen.The layers of the dermis include the papillary dermis and the reticular layer. The papillary layer possesses finger-like projections and is highly vascularized. The reticular layer is the deepest and it has dense irregular connective tissue. These layers are functional in providing elasticity to the integument and permit stretching and resist sagging, wrinkling, and distortions.The blood vessels and nerves terminate at the dermal layer, which also has a deposit of numerous chromatophores. The bases of structures such as the glands, feathers, and hair are detected in the dermal layer. 

The dermis also contains sweat glands, hair follicles, sebaceous glands. The hair follicle provides the essential hormones that are required for the growth of hair. Thus, the hair follicle serves as a harbor of the hair shaft.The sweat gland produces sweat and helps maintain the body temperature.

Hypodermis of the Integumentary System

The hypodermis or the subcutaneous layers found below the skin. It invaginates into the dermal layer through elastin and collagen fibers. The adipocytes are the main cells associated with the formation of the hypodermis. These cells are concerned with the deposition of fat molecules. These cells are distinguished together in lobules isolated by the presence of connective tissue. The hypodermis function as the energy reserve and the fat found in the adipocytes can be returned to the circulating blood through the venous route. This process takes place during the lack of sufficient energy for processing. The hypodermal layer also functions as a thermoregulatory by installing the heat. 

Functions of the Integumentary System

• The integumentary system stabilizes the equilibrium of the body and functions in an interconnected manner to sustain the internal environment needed for the normal functioning of the body.
• It protects the internal organs and tissues and avoids the invasion of pathogenic microbes.
• It guards the body against undergoing dehydration and resists abrupt changes caused by temperature variation. It aids in the secretion of waste through the process of perspiration.
• Its functions as a sensory organ for sensing pain, pressure, touch, and cold and guards the body against sunburn through the secretion of melanin. It produces vitamin D during exposure to ultraviolet (UV) radiation. The system deposits substances including vitamin D, glucose, fat, and water.
• The body form is sustained by the integumentary system. The stratum germinativum of the skin generates new cells and thus mediates the repair of minor injuries.
• The body is found to be guarded against UV rays by the action of the integumentary system. 

Diseases detected in the Integumentary System

The integumentary system may be influenced by a range of diseases and it includes yeast infection, rash, athlete's foot, skin cancer, sunburn, albinism, herpes, acne, impetigo, cancer, rubella, psoriasis, rabies, eczema, atopic dermatitis, and rosacea. 

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for      

• Bachelors in Biochemistry and Molecular biology        
• Bachelors of Molecular and cellular biology       
• Masters in. Biological science
• Masters in Biomolecular chemistry
• Masters in Biotechnology

Related Concepts 

Skin infections, organ systems