The dermis contains two layers: The thin papillary layer is composed of loose connective tissue and connects to the epidermis with papillae. Papillae may nourish the epidermis or act as touch receptors. And the thick reticular layer is made of dense connective tissue with irregular bundles of collagen fibers dense irregular connective tissue. The reticular layer contains hair follicles, sweat glands, Pacinian corpuscles, which sense pressure, lymph vessels and smooth muscle. To read about the skin in more detail, check out this link.
Which connective tissue composes the dermis of the skin? Diagram of different layers of skin: Keratinocyte differentiation throughout the epidermis is in part mediated by a calcium gradient, increasing from the stratum basale until the outer stratum granulosum, where it reaches its maximum, and decreasing in the stratum corneum. Calcium concentration in the stratum corneum is very low in part because those relatively dry cells are not able to dissolve the ions.
This calcium gradient parallels keratinocyte differentiation and as such is considered a key regulator in the formation of the epidermal layers. Elevation of extracellular calcium concentrations induces an increase in intracellular free calcium concentrations.
Epidermal organogenesis , the formation of the epidermis, begins in the cells covering the embryo after neurulation , the formation of the central nervous system. In most vertebrates , this original one-layered structure quickly transforms into a two-layered tissue ; a temporary outer layer, the periderm , which is disposed once the inner basal layer or stratum germinativum has formed. This inner layer is a germinal epithelium that give rise to all epidermal cells.
It divides to form the outer spinous layer stratum spinosum. The cells of these two layers, together called the Malpighian layer s after Marcello Malpighi , divide to form the superficial granular layer Stratum granulosum of the epidermis. The cells in the stratum granulosum do not divide, but instead form skin cells called keratinocytes from the granules of keratin. These skin cells finally become the cornified layer stratum corneum , the outermost epidermal layer, where the cells become flattened sacks with their nuclei located at one end of the cell.
After birth these outermost cells are replaced by new cells from the stratum granulosum and throughout life they are shed at a rate of 0. Epidermal development is a product of several growth factors , two of which are: The epidermis serves as a barrier to protect the body against microbial pathogens, oxidant stress UV light and chemical compounds and provides mechanical resistance.
Most of that function is played by the stratum corneum. The ability of the skin to hold water is primarily due to the stratum corneum and is critical for maintaining healthy skin.
The amount and distribution of melanin pigment in the epidermis is the main reason for variation in skin color in Homo sapiens.
Melanin is found in the small melanosomes , particles formed in melanocytes from where they are transferred to the surrounding keratinocytes. The size, number, and arrangement of the melanosomes varies between racial groups, but while the number of melanocytes can vary between different body regions, their numbers remain the same in individual body regions in all human beings.
In white and Asian skin the melanosomes are packed in "aggregates", but in black skin they are larger and distributed more evenly. The number of melanosomes in the keratinocytes increases with UV radiation exposure, while their distribution remain largely unaffected. Laboratory culture of keratinocytes to form a 3D structure artificial skin recapitulating most of the properties of the epidermis is routinely used as a tool for drug development and testing.
From Wikipedia, the free encyclopedia. Redirected from Epidermis skin. This article is about human skin. For the outer layer of cells in plants, see Epidermis botany. For other uses, see Epidermis disambiguation. Microscopic image of the epidermis, which constitutes the outer layer of skin, shown here by the white bar. Microscopic image showing the layers of the epidermis. The stratum corneum appears more compact in this image than above because of different sample preparation.
For a comprehensive list, see List of cutaneous conditions. Epidermis and dermis of human skin. Cross-section of all skin layers. Illustration of epidermal layers. Optical coherence tomography of fingertip. Wheater's functional histology a text and colour atlas. Lookingbill and Marks' Principles of Dermatology 4th ed. Rook's Textbook of Dermatology 7th ed.
Histochemistry and Cell Biology. The Journal of Physiology. Clinical Dermatology 10th ed. Archived from the original PDF on Journal of Dermatological Science.
Figure 1. Layers of Skin. The skin is composed of two main layers: the epidermis, made of closely packed epithelial cells, and the dermis, made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures.
Choose from different sets of term:epidermis = the outermost layer of skin. flashcards on Quizlet. Log in Sign up term:epidermis = the outermost layer of skin.
Layer of epidermis that is the deepest, and is composed of columnar cells that are constantly undergoing mitosis Dermis The thicker layer of skin that has nerves and blood vessels, and is made of connective tissue. Anatomy and Physiology of the Integumentary System (Primary) Description. Term. Epidermis: Definition. this layer of skin contains mostly dead cells; composed of keratinized and nonkeratinized simple squamous epithelial tissue deepest layer of the epidermis composed of a single row of cuboidal or columnar keratinocytes; contains .
The epidermis is composed of 4 or 5 layers depending on the region of skin being considered. Those layers in descending order are:  cornified layer (stratum corneum). The epidermis is the outermost layer of our skin. Its main purpose is protection. The epidermis is made of four main layers, or strata: The stratum corneum is the thick, tough outer layer. It is made mostly of dead cells that slough off constantly. The stratum basale is comprised of new cells that are constantly dividing to replace the stratum corneum.