Layers of the skin; cutaneous senses

Layers of the skin; cutaneous senses

The skin is the soft outer covering of our body, its three layers are the epidermis, the dermis and the hypodermis.

Biology

Keywords

skin, first line of defense, epidermis, dermis, hypodermis, cutaneous sense, stratified epithelium, Keratinized epithelium, sensory organ, integument, sweat gland, sebaceous gland, hair bulb, keratinous layer, hair, stimulus, signal, nervous system, central nervous system, perception, receptor, pain, heat, human, biology

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Scenes

Anatomy of the skin

  • epidermis - Its two main layers are the outer keratinous layer and the living epidermis. The bottom layer of the living epidermis consists of stem cells which divide continuously and create new epithelial cells. Older epithelial cells are pushed towards the surface by the new ones; meanwhile they undergo apoptosis (programmed cell death) and keratin accumulates within them. The dead epithelial cells filled with keratin form the keratinous layer, which has a protective function. Its thickness varies depending on the location in the body. The epidermis does not contain blood vessels; it receives nutrients from the blood vessels of the dermis indirectly, through diffusion. It does not contain nerve endings, except free nerve endings that detect pain.
  • dermis - It consists mainly of loose connective tissue and contains receptors and blood vessels too. These blood vessels also provide nutrients for the epidermis indirectly, through diffusion. Ridges increase the surface area between the dermis and the epidermis, thereby strengthening the junction between these two layers and increasing the exchange of nutrients between them.
  • hypodermis - It consists mainly of fatty tissue (adipose tissue), which plays an important role in protecting the body against mechanical effects, in thermal insulation, as well as in storing nutrients and fat-soluble vitamins (A,D,E and K).
  • receptors - Its different types detect different stimuli (heat, cold, pain, pressure, vibration).
  • capillaries - There are capillaries in the dermis and the hypodermis, but not in the epidermis. The epidermis receives nutrients through diffusion. Capillaries in the dermis play an important role in thermoregulation.
  • nerve - The skin is rich in nerve endings, which play important roles in the senses of touch, temperature and pain.
  • sweat gland - It plays an important role in thermoregulation. These glands help to remove a large amount of water from the body. Since the specific heat capacity of water is high, perspiration (that is, the removal of warm water) reduces the temperature of the body. This effect is further strengthened by the cooling effect of evaporation.
  • sebaceous gland - It is connected to the hair follicle. Its oily secretion provides protection for the skin. Sebaceous glands may get clogged and inflamed, which causes pimples on the skin.
  • arrector pili muscle - Hair erector muscle: its contraction causes the hair to ‘stand on end’. In animals with fur, this results in the thickening of the fur, which, in turn, results in better insulation and makes the animal appear larger and more intimidating for rivals. Body hair in humans has become vestigial over the course of evolution, but the arrector pili muscle reflex has not disappeared.
  • hair bulb - The division of its cells causes the hair to grow.
  • hair - It serves the thermal insulation and protection of the body. Body hair in humans has become vestigial over the course of evolution.

The skin covering the outer surface of the human body is our heaviest organ. It accounts for about 15-20% of the total body mass. The skin has a layered structure, it consists of the epidermis, dermis and hypodermis.

The topmost layer is the epidermis which consists mainly of epithelial cells and is 10-30 cells thick. Keratin accumulates in the cells located in the outermost layer of epidermis, making the skin waterproof and protecting the cells below. As these cells die, they fall off, get into the air and account for almost 50% of the dust in homes. Besides epithelial cells, epidermis also contains melanocytes, i.e. pigment-producing cells, responsible for absorbing harmful UV radiation.

Lying underneath the epidermis is the dermis, the second layer of the skin. The dermis is usually 15-40 times thicker than epidermis. It contains connective tissue which makes it elastic, protecting the skin from tearing and enabling it to spring back into shape when stretched. This layer also contains neurons, muscle cells, receptors, sweat glands, sebaceous glands and hair follicles.

Underneath the dermis is the hypodermis, a layer made up of connective tissue. It stores fat and helps maintain the body’s temperature.

The lower layers of the epidermis, the dermis, and rarely, the hypodermis contain a variety of receptors which respond to the mechanical, thermal and chemical stimuli coming from the outside world. Receptors are not evenly distributed in the body. The skin of fingertips, for example, contains a large number of receptors for fine touch. The sole, however, has a high density of receptors detecting stronger pressure. The impulses formed in the receptors of the skin are transmitted to the brain stem or to the spinal cord via sensory nerves. The information is processed in the sensory cortex of the cerebrum.

Detection of pain

  • free nerve ending detecting pain - It is also present in the epidermis. It detects harmful stimuli that cause pain. It is sensitive, among other things, to potassium ions released by damaged cells, or proinflammatory substances, such as histamine.

Pain is triggered by mechanical, thermal and chemical stimuli that present a danger to the body. Pain is never a pleasant feeling, yet it is beneficial. It warns you of danger and encourages you to avoid it. Pain is detected in the skin by free nerve endings.

Detection of pressure, touch

  • Pacinian corpuscle (vibration) - Vibration or a change in pressure creates a nerve impulse in it, which is then transmitted to the central nervous system.
  • tactile corpuscle (pressure change) - Vibration or a change in pressure creates a nerve impulse in it, which is then transmitted to the central nervous system.

Our skin contains a variety of receptors which respond to the mechanical stimuli coming from the outside world. These receptors include the tactile corpuscles that comprise a free nerve ending and a capsule. They are sensitive to light touch and are concentrated mostly at the fingertips.

The Pacinian corpuscles (or Lamellar corpuscles) are mechanoreceptors located deeper in the skin, and having a structure that resembles that of a slice of onion. These are sensitive to rapid pressure changes and vibration.

Detection of heat

  • warm receptor - The detected heat creates a nerve impulse in these receptors, which is transmitted to the central nervous system.
  • perspiration - The liquid secreted by sweat glands onto the surface of the skin evaporates, which reduces the temperature of the body.
  • vasodilation - Increased blood flow aids heat release. This is why our skin becomes red when it is hot.

The detection of heat and thus the consequent cooling of the body are essential to maintain a constant body temperature. Warm receptors in the dermis are responsible for detecting heat. When the stimuli detected by the receptors are transmitted to the central nervous system, the blood vessels of the skin dilate and the sweat glands become more active. The evaporation of perspiration on the skin further cools the body.

Detection of cold

  • cold receptor - The sense of cold is not formed by the lack of activity of thermoreceptors, but by the nerve impulse created in the cold receptors. The nerve impulse is then transferred to the central nervous system.
  • contraction of the arrector pili muscle - It causes the layer of hair to become thicker, which aids thermal insulation.

The detection of cold also serves to maintain a constant body temperature. Cold receptors in the dermis are responsible for the sensation of cold. Upon the detection of cold, the arrector pili muscles contract and the hair of the skin, which is normally flattened against the body, stands on end, resulting in better thermal insulation.

Animation

  • epidermis - Its two main layers are the outer keratinous layer and the living epidermis. The bottom layer of the living epidermis consists of stem cells which divide continuously and create new epithelial cells. Older epithelial cells are pushed towards the surface by the new ones; meanwhile they undergo apoptosis (programmed cell death) and keratin accumulates within them. The dead epithelial cells filled with keratin form the keratinous layer, which has a protective function. Its thickness varies depending on the location in the body. The epidermis does not contain blood vessels; it receives nutrients from the blood vessels of the dermis indirectly, through diffusion. It does not contain nerve endings, except free nerve endings that detect pain.
  • dermis - It consists mainly of loose connective tissue and contains receptors and blood vessels too. These blood vessels also provide nutrients for the epidermis indirectly, through diffusion. Ridges increase the surface area between the dermis and the epidermis, thereby strengthening the junction between these two layers and increasing the exchange of nutrients between them.
  • hypodermis - It consists mainly of fatty tissue (adipose tissue), which plays an important role in protecting the body against mechanical effects, in thermal insulation, as well as in storing nutrients and fat-soluble vitamins (A,D,E and K).
  • nerve - The skin is rich in nerve endings, which play important roles in the senses of touch, temperature and pain.
  • sweat gland - It plays an important role in thermoregulation. These glands help to remove a large amount of water from the body. Since the specific heat capacity of water is high, perspiration (that is, the removal of warm water) reduces the temperature of the body. This effect is further strengthened by the cooling effect of evaporation.
  • free nerve ending detecting pain - It is also present in the epidermis. It detects harmful stimuli that cause pain. It is sensitive, among other things, to potassium ions released by damaged cells, or proinflammatory substances, such as histamine.
  • Pacinian corpuscle (vibration) - Vibration or a change in pressure creates a nerve impulse in it, which is then transmitted to the central nervous system.
  • tactile corpuscle (pressure change) - Vibration or a change in pressure creates a nerve impulse in it, which is then transmitted to the central nervous system.
  • warm receptor - The detected heat creates a nerve impulse in these receptors, which is transmitted to the central nervous system.
  • cold receptor - The sense of cold is not formed by the lack of activity of thermoreceptors, but by the nerve impulse created in the cold receptors. The nerve impulse is then transferred to the central nervous system.
  • contraction of the arrector pili muscle - It causes the layer of hair to become thicker, which aids thermal insulation.

Narration

The skin covering the outer surface of the human body is our heaviest organ. It accounts for about 15-20% of the total body mass. The skin has a layered structure, it consists of the epidermis, dermis and hypodermis.

The lower layer of epidermis, the dermis, and rarely, the hypodermis contain a variety of receptors which respond to the mechanical, thermal and chemical stimuli coming from the outside world. Receptors are not evenly distributed in the body. The skin of fingertips, for example, contains a large number of receptors for fine touch. The sole, however, has a high density of receptors detecting stronger pressure. The impulses formed in the receptors of the skin are transmitted to the brain stem or to the spinal cord via sensory nerves. The information is processed in the sensory cortex of the cerebrum.

Pain is triggered by mechanical, thermal and chemical stimuli that present a danger to the body. Pain is never a pleasant feeling, yet it is beneficial. It warns you of danger and encourages you to avoid it. Pain is detected in the skin by free nerve endings.

Our skin contains a variety of receptors which respond to the mechanical stimuli coming from the outside world. These receptors include the tactile corpuscles that comprise a free nerve ending and a capsule. They are sensitive to light touch and are concentrated mostly at the fingertips.

The Pacinian corpuscles (or Lamellar corpuscles) are mechanoreceptors located deeper in the skin, and having a structure that resembles of a slice of onion. These are sensitive to rapid pressure changes and vibration.

The detection of heat and thus the consequent cooling of the body are essential to maintain a constant body temperature. Warm receptors in the dermis are responsible for detecting heat. When the stimuli detected by the receptors are transmitted to the central nervous system, the blood vessels of the skin dilate and the sweat glands become more active. The evaporation of perspiration on the skin further cools the body.

The detection of cold also serves to maintain a constant body temperature. Cold receptors in the dermis are responsible for the sensation of cold. Upon the detection of cold, the arrector pili muscles contract and the hair of the skin, which is normally flattened against the body, stands on end, resulting in better insulation.

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