SkinSkin

Human Anatomy and PhysiologyHuman Anatomy and Physiology

SkinSkin

The skin is considered the The skin is considered the largest organ of the body largest organ of the body

Functions in Functions in thermoregulation, thermoregulation, protection, metabolic protection, metabolic functions and sensation. functions and sensation.

Two main regions, the Two main regions, the epidermis, and the dermisepidermis, and the dermis

The dermis is attached to The dermis is attached to an underlying hypodermis, an underlying hypodermis, also called subcutaneous also called subcutaneous connective tissue, which connective tissue, which stores adipose tissue.stores adipose tissue.

EpidermisEpidermis The epidermis is the most The epidermis is the most

superficial layer of the skin superficial layer of the skin The first barrier of protection from The first barrier of protection from

the invasion of foreign substancesthe invasion of foreign substances The epidermis is subdivided into The epidermis is subdivided into

five layers or strata, five layers or strata, the stratum basale the stratum basale (b(bGG), ), the stratum the stratum spinosumspinosum((SSSS), the ), the stratum stratum granulosumgranulosum((SGRSGR), ), the stratum the stratum lucidumlucidum(not seen in this (not seen in this photomicrograph) and the stratum photomicrograph) and the stratum corneum(corneum(SCSC) in which a ) in which a keratinocyte gradually migates to keratinocyte gradually migates to the surface and is sloughed off in a the surface and is sloughed off in a process called desquamation. process called desquamation.

Stratum GerminatumStratum Germinatum

The stratum basale (bThe stratum basale (bGG) ) provides the germinal cells provides the germinal cells necessary for the regeneration necessary for the regeneration of the layers of the epidermis. of the layers of the epidermis. These germinal cells are These germinal cells are separated from the dermis by a separated from the dermis by a thin layer of basement thin layer of basement membrane. After a mitotic membrane. After a mitotic division a newly formed cell will division a newly formed cell will undergo a progressive undergo a progressive maturation called keratinization maturation called keratinization as its migrates to the surface. as its migrates to the surface.

Stratum Spinosum (Stratum Spinosum (SSSS) )

The cells that divide in The cells that divide in the stratum basale the stratum basale soon begin to soon begin to accumulate many accumulate many desmosomes on their desmosomes on their outer surfaceouter surface

Stratum spinosum Stratum spinosum ((SSSS) )

KeratinizationKeratinization

The progressive maturation of a The progressive maturation of a keratinocyte is charcterized by keratinocyte is charcterized by the accumulation of keratin, the accumulation of keratin, called keratinization. The cells called keratinization. The cells of the stratum basale (of the stratum basale (SBSB) ) accumlate dense basophilic accumlate dense basophilic keratohyalin granules (seen on keratohyalin granules (seen on the close-up view). These the close-up view). These granules contain lipids, which granules contain lipids, which along with the desmosomal along with the desmosomal connections, help to form a connections, help to form a waterproof barrier that functions waterproof barrier that functions to prevent fluid loss from the to prevent fluid loss from the body. body.

Stratum LucidumStratum Lucidum

Epidermis varies in Epidermis varies in thickness throughout the thickness throughout the body depending mainly on body depending mainly on frictional forces and is frictional forces and is thickest on the palms of thickest on the palms of the hands and soles of the the hands and soles of the feet. The stratum lucidum feet. The stratum lucidum is normally only well seen is normally only well seen in thick epidermis and in thick epidermis and represents a transition represents a transition from the stratum basale to from the stratum basale to the stratum corneum. the stratum corneum.

Stratum CorneumStratum Corneum A cell matures and accumulates A cell matures and accumulates

keratin keratin The dead and dying cells filled The dead and dying cells filled

with mature keratin form the with mature keratin form the stratum corneum (stratum corneum (SCSC). The ). The deeper cells of the stratum deeper cells of the stratum corneum retain their corneum retain their desmosomal junctions, but as desmosomal junctions, but as they are pushed to the surface they are pushed to the surface by newly forming cells of the by newly forming cells of the stratum basale (Bstratum basale (BGG), the dead ), the dead cells gradually break apart and cells gradually break apart and are lost, a process called are lost, a process called desquamation. desquamation.

DermisDermis The dermis (The dermis (DD) assumes the ) assumes the

important functions of important functions of thermoregulation and supports the thermoregulation and supports the vascular network to supply the vascular network to supply the avascular epidermis with nutrients.avascular epidermis with nutrients.

Two zones, a papillary dermis and a Two zones, a papillary dermis and a reticular layer. reticular layer.

The dermis contains mostly The dermis contains mostly fibroblasts which secrete collagen, fibroblasts which secrete collagen, elastin and ground substance that elastin and ground substance that give the support and elasticity of the give the support and elasticity of the skin.skin.

Also present are immune cells that Also present are immune cells that are involved in defense against are involved in defense against foreign invaders passing through foreign invaders passing through the epidermisthe epidermis

Papillary DermisPapillary Dermis The papillary dermis (The papillary dermis (PDPD) contains ) contains

vascular networks that have two vascular networks that have two important functions. important functions.

– support the avascular epidermis with support the avascular epidermis with vital nutrients vital nutrients

– secondly to provide a network for secondly to provide a network for thermoregulation. The vasculature is thermoregulation. The vasculature is organized so that by increasing or organized so that by increasing or decreasing blood flow, heat can either be decreasing blood flow, heat can either be conserved or dissipated. conserved or dissipated.

The vasculature interdigitates in areas The vasculature interdigitates in areas called dermal papillae (called dermal papillae (DPDP). The ). The papillary dermis also contains the free papillary dermis also contains the free sensory nerve endings and structures sensory nerve endings and structures called called

Meissner’s corpuscles( the free sensory Meissner’s corpuscles( the free sensory nerve endings in) highly sensitive areas. nerve endings in) highly sensitive areas.

Reticular LayerReticular Layer

The reticular layer of the The reticular layer of the dermis (dermis (RDRD) consists of ) consists of dense connective tissuedense connective tissue

The reticular layer houses The reticular layer houses important epithelial derived important epithelial derived structures such as glands structures such as glands and hair follicles. Pacinian and hair follicles. Pacinian corpuscles are also found corpuscles are also found here. They are deep here. They are deep pressure receptors derived pressure receptors derived from nervous tissue. from nervous tissue.

Serous MembraneSerous Membrane

Serous membrane Serous membrane contains epithelial tissue.contains epithelial tissue.

Found in body cavities not Found in body cavities not open to exterior.open to exterior.

Two layersTwo layers– Visceral Visceral – ParietalParietal

Named for locationNamed for location– Thoracic: plueraThoracic: pluera– Abdominal: peritoneumAbdominal: peritoneum– Cardiac: pericardiumCardiac: pericardium

Serous membrane Serous membrane

Serous membraneSerous membrane Visceral pleuraVisceral pleura Parietal pleuraParietal pleura Visceral peritoneumVisceral peritoneum Parietal peritoneumParietal peritoneum Visceral pericardiumVisceral pericardium Parietal pericardiumParietal pericardium

Mucous membrane Mucous membrane

Epithelium resting on loose Epithelium resting on loose C.T. (lamina propria)C.T. (lamina propria)

Lines cavities that are Lines cavities that are open to exterioropen to exterior

Respiratory ciliated Respiratory ciliated columnarcolumnar

Digestive simple columnarDigestive simple columnar ReproductiveReproductive Urinary no mucus Urinary no mucus

Synovial membraneSynovial membrane

Connective tissueConnective tissue Line fibrous capsule Line fibrous capsule

around jointaround joint Line bursaeLine bursae Line tendon sheathLine tendon sheath