Integumentary Accessory Structures: Nails

Within the integumentary system, four main accessory structures aid in thermoregulation, sense of touch, protection, and much more. These four main accessory structures are:

  1. Hair Follicles
  2. Nails
  3. Sebaceous Glands
  4. Sweat Glands

The nails can be found on the tips of your toes and fingers. The main function of these structures is to protect these areas from damage and the surrounding environment. They also function as a tool and aid in gripping things for picking them up, climbing, and most other things you do with your fingers.

The structure of your nail has two major parts, the area that is below the skin and the area above (visible). On the most distal portion of the finger, you have the free edge. This is the white area of the nail that is usually cut. This is the weakest part of the nail and can be broken or damaged very easily. Where the free edge meets the finger you have the hyponychium. The hyponychium is an area of skin that connects to the bottom of the free edge. The purpose of this structure is to prevent harmful things from entering the nail bed (germs, debris, etc.)

The major part of the external surface of your nail is called the nail body. It is sometimes referred to as corpus unguis and the nail plate. The nail body is the part of the nail that ranges from the free edge to the skin where your nail begins. This nail body is made of a specific type of keratin that makes it translucent as well as layers of dead cells that makes it strong and flexible.

Below the nail body is the nail bed. The nail bed functions to support the nail body during growth. The nail bed is made of tissues such as the hyponychium and the onychondermal. The onychondermal is the strongest attachment point between your nail and the underlying tissue. Both the onychondermal and hyponychium function for attachment and protection against pathogens and the surrounding environment.

The area that is at the base of the nail body is called the lunula. This structure is usually lighter and more white in color. It is also described as a half-crescent moon. The function of the lunula is to provide a defining change in structure between the nail edge and the root. Having a lunula usually means that your root matrix is working properly and well.

At the lateral edges of the nail body, where the nail meets your skin, the lateral nail fold begins. The lateral nail fold functions to aid in the protection of the finger on the lateral edges as well as aid in guiding the proper growth of the nail.

The area where the lunula meets the proximal nail fold is called the eponychium. This structure functions similarly to the hyponychium. It seals the passageway that would be present into the proximal nail fold and into the nail plate. This functions to prevent diseases, pathogens, and other harmful debris from entering parts of the nail that can become infected.

The proximal nail fold works in combination with the eponychium to prevent debris from entering the nail plate. It also functions similar to the lateral nail folds to guide and support nail growth. Finally, the nail fold protects the nail root and matrix that is present below this area.

The nail root is located within the epidermis several millimeters below the surface. The nail root place at which most of the nail is produced and where growth begins.

Dermis

Layers Of The Dermis

The dermis layer is located inferior to the epidermis layer in the cutaneous layer. This layer is made of connective tissue and can be divided into two layers:

  1. Papillary Layer
  2. Reticular Layer

The papillary layer of the dermis is the most superficial layer of the two. It is inferior to the epidermis and superior to the Reticular layer. Within the papillary layer there are:

  • Dermal Papillae
  • Axons of Neurons
  • Loose Connective Tissue
  • Capillaries

This layer’s main function is to provide attachment to the epidermis layer but, it also provides nutrients through capillaries and sense through neurons.

The reticular layer of the dermis is inferior to the papillary layer and superficial to the subcutaneous layer. This layer consists of:

  • Sebaceous Glands
  • Hair Follicles
  • Networks of Dense Irregular Connective Tissue
  • Sweat Glands

The dermis layer functions to provide structure and integrity to the dermis layer. The networks of dense irregular tissue results in strong and elastic tissue within the skin. It also houses and supports accessory structures such as hair follicles and vital glands.

Organization Of The Dermis

Within the dermis, two major fibers contribute to the structure and organization of your skin. Collagen fibers are responsible for providing tensile strength to the skin or the resistance of something to break under tension. Elastic fibers are responsible for providing elasticity to the skin. Not only does it allow the skin to be elastic, but it also allows your skin to return to its original shape. Bother of these fibers can be seen in use when you stretch the skin on any part of your body.

So, if there are fibers responsible for keeping your skin strong and not distorted, why do we get wrinkles? Wrinkles can be attributed to three major factors:

  1. Age
  2. UV light
  3. Hormones

As a person gets older, their body begins to slow down and produce less of the essential materials needed for good health. One of the things the body reduces in producing as you get older is natural oils that keep your skin moisturized and elastic. Thus, with a decreased amount of oil that helps keep elastic fibers and collagen fibers healthy, your skin will become weaker and form wrinkles.

UV light is directly responsible for the majority of the damage that is caused to the dermis layer. UV light will penetrate the skin and damage collagen fibers. As a result of damaged collagen fibers, elastic fibers will have an increased chance of being produced abnormally. This creates wrinkles in the skin.

Hormones, believe it or not, play a role in the development of wrinkles and the overall health of your skin. One of the major hormones that have been linked to wrinkles being formed is estrogen. A decrease in estrogen can trigger an increased deterioration of elastic fibers in the dermis.

Stretch Marks

Stretch marks can be caused by large amounts of growth in a short period or over-stretching of the skin. This can be done during a growth spirt of puberty, pregnancy, and obesity. When this overstretching happens, the reticular fibers that are holding the layers of skin together break. These fibers do not recoil and do not return to normal after this. Instead, these broken fibers create wrinkles, creases, and stretch marks.

Tension Lines

Tensions lines, also known as cleavage lines, are patterns of collagen fibers that are made within the dermis. Since collagen fibers and elastic fibers usually organize themselves in a parallel pattern, the body has a grid of tension lines that is used heavily in the medical field. These patterns are formed from the mechanical stress of the body. Areas that need more structural support will have tension lines pulling on them in a certain direction.

These tension lines are used heavily in the medical field to avoid the formation of scars. Cutting perpendicular to these tension lines increases the risk of scarring on the body. Thus, surgeons will cut parallel to these lines to make the recovery of the patient as easy as possible. The reason for this is that cutting a tension line perpendicular causes more stress and damage to the fibers than if you cut parallel.

Blood Supply To The Skin

Within the skin, there are two major networks of arteries, veins, and smaller blood vessels. These networks form a plexus or a network of interconnecting blood vessels:

  1. Cutaneous Plexus
  2. Subpapillary Plexus

The cutaneous plexus is composed of arteries and veins. This network supplies the hypodermis, hair follicles, fatty tissue, glands, and deep areas of the dermis. This network is about 1.5 mm from the surface of your skin.

The subpapillary plexus is made of smaller blood vessels. It is located below the dermal papillae and superficial areas of the dermis. Within each dermal papilla, there is a capillary loop that helps supply blood to those areas of the skin.

Both the cutaneous plexus and the subpapillary plexus are direct contributors to thermoregulation or the ability to control the temperature of your body using the cardiovascular system. When the surrounding environment is hot and the body temperature is too high, the vessels will dilate to allow more blood flow to the surface. This helps dissipate some of the heat that is trapped in the body. When it is too cold, the vessels will constrict and focus blood on vital parts of the body such as the heart, lungs, and internal organs.

Nerve Supply To The Skin

The integumentary system is a vital part of sensing the surrounding area. The nerves that are embedded inside our skin can tell us if it is hot, cold, windy, rainy, if you are in pain, and so much more. Most of these senses are sent back to the central nervous system where the body will decide on how to maintain homeostasis.

As well as sensing the surrounding area, the nervous system is responsible for adjusting secretion rates and controlling the flow of blood.

H.A. 101: Membranes

Membranes are a vital component in protecting the body from its surrounding environment. In the human body, membranes are composed of Epithelial and Connective tissue. Each one of these membranes will consist of a sheet of epithelial cells and an underlying connective tissue layer. Membranes can be divided into four main categories:

  1. Mucous Membranes
  2. Serous Membranes
  3. Cutaneous Membranes
  4. Synovial Membranes
Mucous Membranes

Mucous membranes can be found in the digestive, urinary, respiratory, and reproductive tracts due to their ability to secrete a barrier of protection. This barrier of protection is responsible for resisting pathogen entry into the body and deeper tissues. The layer of secretion is created by mucous glands and it also helps maintain the moisture of epithelial cell surfaces.

In mucous membranes, the tissue that connects the epithelium to the underlying tissue is called the lamina propria. This is an areolar tissue that allows the epithelium to move free when compared to the deeper tissue.

Serous Membranes

Serous membranes are located in the lining of body cavities. Within these membranes, there are two major layers, the visceral and parietal layers. The visceral layer is responsible for covering the organ of the cavity. The parietal layer can be found lining the walls of the cavity the organ is located in. It is also important to know that within serous membranes there is a fluid called transudate. This serous fluid is responsible for reducing friction between layers. There are three types of serous membranes:

  1. Pleura
  2. Peritoneum
  3. Pericardium

Pleura serous membranes are responsible for lining the lungs. The parietal layer of this membrane is attached to the chest wall while the visceral layer is attached to the lungs. The fluid between these two layers is called the pleural fluid.

Peritoneum serous membranes can be found lining the peritoneal cavity (abdominal cavity). In this membrane, the visceral layer attaches itself to the organs of the peritoneal cavity such as the intestines, and helps hold it in place. This membrane helps reduce friction and maintain the organization of the organs during bodily processes and mechanical movements.

The pericardium serous membranes are found lining the heart. The main function of this membrane is to hold the heart in place and help it function properly.

Cutaneous Membranes

The cutaneous membrane is one of the largest membranes in your body and the most recognizable. This layer of epithelial cells and connective tissue in your skin consists of keratinized stratified squamous epithelium. The keratinization of the epithelium results in a waterproof and thick characteristic. The deeper cells are connected to areolar tissue and dense irregular tissue that helps maintain and secure the epithelial cells.

Synovial Membranes

Synovial membranes can be found lining the joint cavities of bones. These membranes are different from the other ones because it has no basal lamina or reticular lamina, the cells are created from fibroblasts and macrophages, and there are gaps between the cells.

Within this membrane, there is a fluid produced called synovial fluid. This functions to reduce friction between the joints to reduce damage to the bones and cartilage.