These blood vessels also help remove cellular waste products that would otherwise kill the skin cells if they were allowed to accumulate. The pink tint to the skin of light-skinned individuals is due to the blood vessels found here.
In fact, when you blush, it is the dilation of these blood vessels that causes you to turn red. The reticular layer serves to strengthen the skin and also provides our skin with elasticity. Elasticity refers to how our skin is able to spring back into shape if deformed by something like a pinch. The reticular layer also contains hair follicles, sweat glands, and sebaceous glands. The sweat gland can either be apocrine, such as those found in the armpits and the groin area, or the eccrine glands, which are found all over the body.
The former help contribute to body odor along with the bacteria on our skin , and the latter help regulate our body temperature through the process of evaporation.
The sebaceous glands found in the dermis secrete a substance called sebum that helps to lubricate and protect our skin from drying out. Beneath the dermis is the deepest layer of our skin.
It is alternatively termed hypodermis, subcutis, or subcutaneous tissue. It contains many collagen cells as well as fat. Fat, in particular, helps insulate our body from the cold and act as a cushion for our internal structures such as muscles and organs when something hits us. Fat can also be called upon by the body in times of great need as an energy source.
Given the alternative names for this layer, it should come as no surprise that this is the layer where subcutaneous injections are given into via a hypodermic needle. Skin sensory receptors: Those nearest the surface of the skin include receptors that detect gentle pressure, temperature, and vibrations, as well as naked nerve endings dendrites that detect pain. Deeper in the dermis are naked dendrites that wind around the bases of hair follicles and detect motions of the hairs, as well as receptors such as Pacinian corpuscles that respond to strong pressure and vibrations.
Skin color is determined largely by the amount of melanin pigment produced by melanocytes in the skin. Skin color is largely determined by a pigment called melanin but other things are involved. Your skin is made up of three main layers, and the most superficial of these is called the epidermis.
The epidermis itself is made up of several different layers. Melanocyte: Cross-section of skin showing melanin in melanocytes. The deepest of the epidermal layers is called the stratum basale or stratum germinativum. In this layer lie important cells called melanocytes. Their name is derived from two parts: melano-, which means black or darkness, and -cyte, which means cell.
Melanocytes are irregularly shaped cells that produce and store a pigment called melanin. The most abundant type of melanin is called eumelanin. This pigment is stored in organelles called melanosomes. Eumelanin is responsible for the brown and black pigmentation of human skin or the lack thereof if little of it is produced. The production of melanin is called melanogenesis—genesis means formation or development.
Regardless of background, every person has largely the same number of melanocytes, but the genetics of each person is what determines how much melanin is produced and how it is distributed throughout the skin. For example, light skinned individuals may have darker places like nipples and moles. Conversely, dark skinned individuals have a lighter tone to the palms of their hands. Another critical factor, exposure to sunlight, triggers the production of melanin as well. This is what gives us a tan.
References: [1] [2] [3] Cells of the skin Cells of the epidermis [1] The epidermis is mainly composed of four different types of cells. Keratinocytes Definition : principal cells of the epidermis Location Throughout the whole epidermis Mitotically active in the basal layer basal cells Connected to the basement membrane via hemidesmosomes Function Primarily protect against environmental damage and form a barrier against pathogens Protect against ultraviolet UV radiation by storing melanin produced by melanocytes Produce proinflammatory mediators to activate the immune system when exposed to pathogens Aid in the process of wound healing Form tight junctions with nerve endings and hold lymphocytes and Langerhans cells in place.
Clinical significance Abnormal keratinocyte desquamation contributes to the development of acne. Sunburn : apoptosis of keratinocytes Blistering skin disorders e.
Dendritic processes transfer melanosomes to adjacent and distant keratinocytes. Langerhans cells Definition : : macrophages of the skin ; a type of dendritic cell Location : : stratum spinosum Characteristics Langerhans cells act as antigen-presenting cells APCs.
Characteristics Rich in keratin filaments, desmosomes , and small, dense blue granules Merkel cells are connected to enlarged axon terminals via synapse -like junctions. The Merkel cell-neurite complex is known as a Merkel disc receptor. Hair shaft Extends above the epidermis Connects to the hair root in the deep dermis Hair bulb Root of the hair follicle ; located deep in the dermal papilla Receives blood and nutrients from a capillary network of vessels to sustain hair growth Arrector pili muscle Description: obliquely directed smooth muscle fibers that attach to the dermal sheath surrounding hair follicles Function Contraction, which is responsible for piloerection goosebumps Conservation of body heat Innervated by the sympathetic autonomic nervous system Glands Sebaceous glands Sweat glands Eccrine sweat glands Apocrine sweat glands Description Exocrine holocrine branched glands Composed of a secretory unit called glomerulum or acrosyringium; surrounded by myoepithelial cells The combination of sebaceous gland , arrector pili muscle , and hair follicle is known as the pilosebaceous unit.
Exocrine glands with a spiral duct acrosyringium and secretory ducts that open into sweat pores Exocrine glands with a secretory unit glomerulum and excretory ducts that open into hair follicles Location and distribution Dermis Predominantly located on the face and scalp Absent on palms and soles Deep in the dermis and hypodermis Most areas of the body Absent in lips , ear canal, clitoris , labia minora , and glans penis Mostly axilla , perineum , areola of the nipple , and external ear Function Secretion of sebum An oily, waxy substance which is a lubricant and a waterproof layer for the skin and hair Has photoprotective, antimicrobial, and antioxidant properties Secretion of sweat thermoregulation Modified apocrine cells produce ear wax or breast milk.
References Fuchs E. Scratching the surface of skin development. Lookingbill and Marks' Principles of Dermatology. Saunders Elsevier ; Layers of the Skin. Updated: May 15, Accessed: May 15, At the bottom of the follicle is the papilla puh-PILL-uh , where the actual hair growth happens. The papilla contains an artery that nourishes the root of the hair.
As cells multiply and make keratin to harden the structure, they're pushed up the follicle and through the skin's surface as a shaft of hair. Hair grows by forming new cells at the base of the root. These cells multiply to form a rod of tissue in the skin. The rods of cells move upward through the skin as new cells form beneath them.
As they move up, they're cut off from their supply of nourishment and start to form a hard protein called keratin. This process is called keratinization ker-uh-tuh-nuh-ZAY-shun. As this happens, the hair cells die. The dead cells and keratin form the shaft of the hair. Hair grows all over the human body except the palms of the hands, soles of the feet, and lips.
Hair grows faster in summer than winter, and slower at night than during the day. Nails protect the sensitive tips of fingers and toes. We don't need our nails to survive, but they do support the tips of our fingers and toes, protect them from injury, and help us pick up small objects.
Without them, we'd have a hard time scratching an itch or untying a knot. Nails grow out of deep folds in the skin of the fingers and toes.
They contain Birbeck granules, tennis racket shaped cytoplasmic organelles. Merkel cells are oval-shaped modified epidermal cells found in stratum basale, directly above the basement membrane. These cells serve a sensory function as mechanoreceptors for light touch, and are most populous in fingertips, though also found in the palms, soles, oral, and genital mucosa.
They are bound to adjoining keratinocytes by desmosomes and contain intermediate keratin filaments and their membranes interact with free nerve endings in the skin. The dermis is connected to the epidermis at the level of the basement membrane and consists of two layers, of connective tissue, the papillary and reticular layers which merge together without clear demarcation.
The papillary layer is the upper layer, thinner, composed of loose connective tissue and contacts epidermis. The dermis houses the sweat glands, hair, hair follicles, muscles, sensory neurons, and blood vessels.
The hypodermis is deep to the dermis and is also called subcutaneous fascia. It is the deepest layer of skin and contains adipose lobules along with some skin appendages like the hair follicles, sensory neurons, and blood vessels. Excerpt Skin is the largest organ in the body and covers the body's entire external surface. Skin Thickness The thickness of each layer of the skin varies depending on body region and categorized based on the thickness of the epidermal and dermal layers.