Physiology Topics
The skin has two layers: epidermis and dermis. Under the skin is a subcutaneous layer made up mostly of adipose tissue.
The epidermis is the surface layer, made of tightly packed epithelial cells. Below the epidermis is the dermis, made up mostly of connective tissue. Accessory organs, like hair follicles, sweat glands and sebaceous glands are epithelial structures that originate in the epidermis and extend into the dermis. Since the epidermis does not have vasculature, it must remain relatively thin in order to receive an appropriate supply of nutrients from blood vessels in the dermis.
The epidermis is made up of multiple layers of keratinocytes, which originate in the basal layer and migrate towards the surface of the skin. Keratinocytes produce keratin, and by the time they reach the surface they are dead cells without nuclei, full of keratin.
Other cell types found in the epidermis are Merkel cells, melanocytes and langerhans cells. Merkel cells are attached to tactile discs in the basal layer, which interfaces with the dermis, and produce touch sensations. Melanocytes produce melanin keratinocytes for uptake by keratinocytes. One melanocyte has many projections to interact with several keratinocytes at the same time. Langerhans cells provide biological protection, and also have projections to interact with several keratinocytes at the same time.
UV radiation increases melanin generation. Racial differences in skin coloration depend on differences in production and chiral properties of melanin, not in the number of melanocytes. Other pigments that cont5ribute to skin coloration are hemoglobin and carotene. Bilirubin is not a normal skin colorant, but may give the skin a yellowish hue as a result of liver disease or underdeveloped enzymatic systems (newborns).
The dermis contains fibroblasts, immune cells and some adipocytes (not as much as the subcutaneous layer) and blood vessels. The interface between the dermis and the epidermis is called the papillary layer because of its finger-like structures. As the epidermis conforms to the uneven surface of the dermis, the ridges formed give rise to fingerprints and similar patterns in the soles.
Continue to "Skin Appendages" or take a quiz: [Q1] [Q2].
Need more practice? Answer the review questions below.
1- Describe the epidermis.
2- List the cell types in the epidermis and their function.
3- Explain how melanin production can be changed in a person or from one person to another.
4- List the skin pigments, and why isn't billirubin a skin pigment.
5- Describe the dermis.
6- What is the papillary layer?
7- Explain why we have fingerprints.