The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology. The skin is composed of surface epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology, exocrine components, connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology, muscles, and nerves. The primary role of the skin is to serve as a protective barrier between the internal body and the external environment; it also protects the body from excessive fluid loss.
Last updated: 9 May, 2022
Micrograph of melanocytes in the epidermis
Image: “Micrograph of melanocytes in the epidermis” by Setijanti, H.B., et al AL Amyloidosis. License: CC BY 4.0Section of skin showing large numbers of dendritic (Langerhans) cells in the epidermis:
Mycobacterium ulcerans
Mycobacterium ulcerans
A slow-growing Mycobacterium that infects the skin and subcutaneous tissues, giving rise to indolent buruli ulcer.
Mycobacterium infection,
S100
S100
A family of highly acidic calcium-binding proteins found in large concentration in the brain and believed to be glial in origin. They are also found in other organs in the body. They have in common the ef-hand motif (ef hand motifs) found on a number of calcium binding proteins. The name of this family derives from the property of being soluble in a 100% saturated ammonium sulfate solution.
Acoustic Neuroma immunoperoxidase stain
Mechanoreceptors:
The Ruffini and Pacinian corpuscles are located in the
deep dermis
Deep Dermis
Erysipelas, the Meissner corpuscles extend into the dermal
papillae
Papillae
Lips and Tongue: Anatomy, and the Merkel cell disks connect to the epidermis.
There are 5 layers of epidermis:
Beginning from the cells located in the stratum basale, they differentiate and proliferate toward the skin surface and integrate themselves into the other layers, the last layer being the stratum corneum, which is composed of dead keratinized cells.
The dermis is made up of 2 layers:
The papillary layer is made up of
collagen
Collagen
A polypeptide substance comprising about one third of the total protein in mammalian organisms. It is the main constituent of skin; connective tissue; and the organic substance of bones (bone and bones) and teeth (tooth).
Connective Tissue: Histology and elastin fibers and contains phagocytes,
fibroblasts
Fibroblasts
Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules.
Sarcoidosis, and
adipocytes
Adipocytes
Cells in the body that store fats, usually in the form of triglycerides. White adipocytes are the predominant type and found mostly in the abdominal cavity and subcutaneous tissue. Brown adipocytes are thermogenic cells that can be found in newborns of some species and hibernating mammals.
Adipose Tissue: Histology. The reticular layer gives the skin its
elasticity
Elasticity
Resistance and recovery from distortion of shape.
Skeletal Muscle Contraction and helps to toughen the skin.
Sweat glands
Sweat glands
Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct.
Soft Tissue Abscess and hair follicles are found at this layer. This layer is also well vascularized.
Each layer of the skin has a unique function.
Epidermis and dermis:
Hypodermis:
Structure of the follicular unit:
The hair bulb is located in the
deep dermis
Deep Dermis
Erysipelas/hypodermis, and the hair shaft extends through the dermis before exiting the epidermis. The arrector
pili
Pili
Filamentous or elongated proteinaceous structures which extend from the cell surface in gram-negative bacteria that contain certain types of conjugative plasmid. These pili are the organs associated with genetic transfer and have essential roles in conjugation. Normally, only one or a few pili occur on a given donor cell. This preferred use of ‘pili’ refers to the sexual appendage, to be distinguished from bacterial fimbriae, also known as common pili, which are usually concerned with adhesion.
Salmonella muscle is located in the dermis and is responsible for piloerection.
Cross section of a
hair follicle
Hair follicle
A tube-like invagination of the epidermis from which the hair shaft develops and into which sebaceous glands open. The hair follicle is lined by a cellular inner and outer root sheath of epidermal origin and is invested with a fibrous sheath derived from the dermis. Follicles of very long hairs extend into the subcutaneous layer of tissue under the skin.
Cowden Syndrome:
The hair is composed of keratinized cells that emerge and migrate upward inside the
hair follicle
Hair follicle
A tube-like invagination of the epidermis from which the hair shaft develops and into which sebaceous glands open. The hair follicle is lined by a cellular inner and outer root sheath of epidermal origin and is invested with a fibrous sheath derived from the dermis. Follicles of very long hairs extend into the subcutaneous layer of tissue under the skin.
Cowden Syndrome. When the hair shaft emerges from the skin surface, it does so at a slightly slanted angle. For every
hair follicle
Hair follicle
A tube-like invagination of the epidermis from which the hair shaft develops and into which sebaceous glands open. The hair follicle is lined by a cellular inner and outer root sheath of epidermal origin and is invested with a fibrous sheath derived from the dermis. Follicles of very long hairs extend into the subcutaneous layer of tissue under the skin.
Cowden Syndrome, there is an adjacent
sebaceous gland
Sebaceous Gland
Small, sacculated organs found within the dermis. Each gland has a single duct that emerges from a cluster of oval alveoli. Each alveolus consists of a transparent basement membrane enclosing epithelial cells. The ducts from most sebaceous glands open into a hair follicle, but some open on the general surface of the skin. Sebaceous glands secrete sebum.
Hordeolum (Stye).
Structure of the nail:
The whitish crescent-shaped end of the nail (toward the body) is referred to as the lunula (“small moon”). Between the lunula and skin, there is a protective layer, called the cuticle, that keeps pathogens from entering beneath the skin. Behind the cuticle (toward the body), is the nail root, which forms keratinized cells that push the nail forward.
Fingernails grow faster than toenails. The typical growth rate of a fingernail is 1
mm
MM
Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies.
Multiple Myeloma per week; a toenail grows 0.5
mm
MM
Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies.
Multiple Myeloma per week.