Integumentary System PDF

Integumentary System • Skin • Associated glands: sebaceous glands, sweat glands • Hairs • Nails The skin It is the most extensive organ of the body. It covers the whole organism and continues with the mucous membranes of the digestive, respiratory and genitourinary tracts. It also covers the ext...

Integumentary System • Skin • Associated glands: sebaceous glands, sweat glands • Hairs • Nails The skin It is the most extensive organ of the body. It covers the whole organism and continues with the mucous membranes of the digestive, respiratory and genitourinary tracts. It also covers the external auditory canal and the outer surface of the eardrum and in the eyelid continues with the conjunctiva of the eye. It consists of two layers: - Epidermis - Dermis In the different regions of the body the skin presents different texture and thickness. In general, we speak of thick skin to refer to the skin of the palm of the hand and the sole of the foot, which has a very thick epidermis and does not contain hairs, but many sweat glands. The rest is considered thin skin, although it will have slight variations depending on the part of the body in which we are. Epidermis It is the outermost part and is composed of a flat stratified keratinized epithelium. This epithelium is formed by four types of cells: - Keratinocytes. The most abundant. - Melanocytes - Langerhans cells - Merkel cells Keratinocytes are continuously removed from the surface of the epidermis, so they must be continuously renewed. The keratinocytes of the deeper layers suffer mitosis and, as new cells are formed, the cells above are pushed to the surface. On that journey to the surface, these cells accumulate filaments of keratin in their cytoplasm. In the end these cells die and flake off. As a result of all this process, we can differentiate the five layers of the epidermis. Epidermis 1. Stratum basale (basal layer): it is the deepest layer; it rests on the basement membrane of the epithelium. Formed by a single layer of cylindrical or cubic cells that undergo mitosis frequently to renew the keratinocyte population. 2. Stratum spinosum: following the basal. It is the thickest layer of the epidermis, composed of several layers of polyhedral cells that can also undergo mitosis. They contain numerous filaments of keratin that penetrate cell extensions where the cell is attached to other cells by desmosomes. These prolongations are what give these cells a thorny appearance. 3. Stratum granulosum: consists of 3 to 5 layers of flat keratinocytes. Its cytoplasm contains large and irregular granules of keratohyalin. The keratin filaments pass through these granules. 4. Stratum lucidum: only appears on thick skin. It is a thin, homogeneous cell layer with weak staining. These cells do not have a nucleus or organelles but retain filaments and keratin granules. 5. Stratum corneum: the most superficial layer of the skin. Composed of numerous layers of flat keratinized cells. These cells do not have a nucleus or organelles (dead cells), and as they lose contact with each other, they become desquamated. Other cells of the epidermis • Langerhans cells: they are also called dendritic cells because they have long and numerous extensions. They are scattered throughout the epidermis, but their extensions are located mainly in the stratum spinosum. These cells participate in the immune response, acting as antigen-presenter cells. • Merkel cells: they are located mainly in the stratum basale. The sensory nerve endings cross the basement membrane to approach these Merkel cells and thus form complexes that act as mechanoreceptors. • Melanocytes: they are also located in the stratum basale. When stimulated by UV radiation, these cells secrete melanin, a dark pigment that gives color to the skin and protects from UV radiation. Dermis It is the region of the skin located after the epidermis. It supports the epidermis and connects the skin to the hypodermis. It is composed of two layers: - Papillary dermis: more superficial, forms ridges or dermal papillae that provide a greater contact surface with the epidermis to give it greater support. It is formed by loose connective tissue with abundant type I collagen, as well as reticular and elastic fibers. It also contains numerous capillaries that help regulate body temperature and nourish the epidermis. - Reticular dermis: continues with the papillary layer. It is formed by dense irregular connective tissue with abundant type I collagen and elastic fibers. Located in some dermal papillae are the Meissner corpuscles, which are mechanoreceptors encapsulated in the shape of a pear and that respond to small deformations of the epidermis. Other encapsulated mechanoreceptors also present in the papillary layer are the Krause terminal bulbs. Its function is not very clear. They can also appear in the reticular layer. In the reticular layer we can find other encapsulated mechanoreceptors such as Paccini's corpuscles, which respond to pressure and vibrations. Ruffini's corpuscles respond to tension forces and also appear in the reticular layer. Hypodermis It is not part of the skin, but it is what binds it to the body. It surrounds the entire organism and is attached to the dermis. It is formed by a loose connective tissue that contains a variable amount of fat. When there is a large amount of fat deposited in this layer, it is called an adipose panniculus. Functions • Protection: against physical abrasions, entry of microorganisms or toxic substances and against dehydration. • Corporal temperature regulation • Receiving stimuli from the environment: touch, temperature, pain. • Excretion: from the sebaceous and sweat glands. • Absorption of ultraviolet radiation protects against burns and also allows the synthesis of vitamin D. Glands of the skin • Sebaceous glands • Sweat glands • Odoriferous/apocrine glands Sebaceous glands They are distributed through the skin of the whole body except in the thick skin. They are especially abundant on the face and scalp. They secrete an oily substance known as sebum, which helps maintain skin texture and hair flexibility; also exhibits waterproof and antimicrobial properties. These glands are acinar and have a holocrine secretion, that is, their cells break and die to release the secretion product. They are polyhedral cells filled with lipid drops (secretion). The secretion is poured into the hair follicle that serves as an excretory duct. Only in very specific regions they are not associated with hair, such as the lips. Eccrine sweat glands They are found all over the skin and open to pores. They have a simple and coiled tubular shape. The secretory part is coiled and from there the duct will go through the dermis to communicate with the outside through the sweat pore. The epithelium is simple cuboidal in the secretory part and bistratified cuboidal in the conductive zone. They are merocrine glands, and their secretion product is sweat. The main function of this secretion is thermoregulation, although it also serves as an excretory mechanism. Sudoriferous glands They are apocrine glands. They have the same structure as sweat glands but are larger and pour their secretion to the hair follicles. They are only found in specific locations in the body, such as the armpit, areola of the nipple and perianal region. They release their secretion in an apocrine manner and this secretion is odorless, but when metabolized by skin bacteria, it has a characteristic odor. The science of skin - Emma Bryce - YouTube