Skin is the largest organ of our body. It wraps the adult body in about 20 sq. ft., that weights 6 or 7 pounds. Skin has 650 sweat glands and 20 blood vessels.
Layers of skin:
1. Epidermis
2. Dermis
3. Hypodermis
1. Epidermis: Outermost layer of skin. It produces water proof barrier and creates skin tone. Function of epidermis is protection, absorption of nutrients and homeostasis. It contains different types of cells.
i. Keratinolytes: It is a major cells of epidermis which produces keratin. Keratin is fibrous protein that aids in protection. The most common cells are squamous cells, scaly cells and basal cells.
ii. Melanocyte: It produces melanin which gives skin a color. Accumulation of melanin are packed in metanosomes. These granules form a pigment shield against UV radiation.
iii. Langerhan’s cells: Epidemis contains Langerhan’s cell produced in bone marrow.
iv. Markel cell: It is found in hairless area. Eg: finger tips, lips located in the deepest layer of the epidermis. Markel cells contact nerve endings in the dermis below and function as a type of touch receptor.
Epidermis has 5 layers:
a. Stratum corneum/ Horny layer
b. Stratum lucidem
c. Stratum granulosum
d. Stratum spinosum
e. Stratum basale/ germinativum
a. Stratum corneum or Horny layer:
Stratum corneum is also called horny layer because its cells are toughed like animal’s horn. It is outermost layer of epidermis with an average 20 sub layers of flattened dead cells depending on where the body skin is. These dead cells are shed regularly in a process known as desquamation. This shedding process turnover every 28-30 days in young while same process takes 45-50 days in elders.
b. Stratum lucidem:
It is a clear layer not seen in all the skin regions. It is present only where skin is hairless and extra thick like palms of hand and soles of feet.
c. Stratum granulosum:
It is called stratum granulosum because when this section of skin is stained with dyes and look at them under microscope, this layer has a granular appearance.
d. Stratum spinosum:
It is composed of newly formed epidermal cells called keratinocytes, they are joined each other by spiny outgrowths. These give individual cells appearance of pricky goose berries. Hence they are called prickle cells. These interconnecting outgrowths are called desmosomes.
e. Stratum basale or germanativum:
The bottomed layer cells in this layer are column shaped. In this layer, cells constantly undergoing mitosis (cell division) and push already formed cells into higher layer. These cells move into higher layers, they fall and eventually die.
2. Dermis:
It is a middle layer of skin. It contains or composed of connective tissues, hair follicle, sweat gland, sebaceous gland, blood vessels, lymph vessels, sensory receptor, nerve fibers and muscle fibers. Blood vessels in dermis provide nourishment and waste removal from its own cell as well as stratum basale of epidermis.
Dermis contain 2 layers:
i. Papillary dermis
ii. Reticular layer
iii. Papillary dermis
i. Papillary dermis:
It is more superficial of two and lies beneath epidermis junction. It is thin, made of loose connective tissues which includes: Capilaries, Elastic fibres, Reticular fibres, Collagen.
It is named for its finger like projection called papillae that extend towards epidermis. In palms, finger, soles and toes, the influence of the papillae projecting into epidermis forms contours in the skin’s surface. The epidermal ridges occur in pattern (finger print) that are genetically determined and are therefore unique to the individual, making it possible to use finger prints or foot prints as a means of identification.
ii. Reticular layer:
It is a deeper layer which contain fat cells, blood and lymph vessels, oil and sweat gland, hair follicles, arrector pilli muscles. Its purpose is to attach the skin underlying bone and muscles as well as supplying it with blood vessel and nerves. The main cells type found in reticular layer are fibroblast, macrophages and adipocytes.
iii. Hypodermis:
The bottom, innermost layer of the skin, largely made up of fat cells that insulate the body and made skin appear pump and full. It also contains sebaceous gland, sweat gland, hair follicles and other structure.
Function of skin:
1. Temperature regulation:
Our normal body temperature is 98.4-degree F. No matter how cold and hot air is, the skin helps to keep the body temperature constant. When the cells of body break down the food, heat is produced and when blood carries heat to the skin, where the evaporation of the sweat cools the body.
2. Protection:
Skin protects against UV rays through the production of melanin. It protects the body from bacteria, chemical substance which are allergic. It protects intestinal tissues from injuries.
3. Secretion:
Sebaceous glands secretes sebum into hair follicle. Sebum is an oil that keeps skin moist and soft and acts as barrier against foreign substances.
4. Excretion
5. Synthesis of Vitamin D and melanin
6. Absorption of drugs
7. Sensation
Skin is a receptor i.e. a sensory organ. Therefore, it is used as feeling and stimulation like pain, touch, heat and cold.
Article By: Nisha Joshi (Nepal)
Article By: Nisha Joshi (Nepal)