Final answer:
Fissures in the skin are deep linear cracks that reach into the dermis, contrasting with other skin lesions such as thinning or shallow erosions. The skin consists of the epidermis and the dermis, with the epidermis being the outer protective layer and the dermis providing structural support, containing various skin appendages and sensory receptors.
Step-by-step explanation:
Fissures in the context of skin pathology are defined as linear cracks in the epidermis that extend into the dermis. Unlike erosions, which are shallow and may not reach the dermis, or thinning that reduces the prominence of skin markings, fissures represent a split in the skin that can penetrate deeper than the superficial layers. The skin, including the epidermis and the dermis, has different thicknesses across various parts of the body, with the thinnest portion being on the eyelids and the thickest on the palms and soles of the feet.
The epidermis is the outer layer of skin that provides a barrier to the environment. Below it lies the dermis, which is a thicker layer containing blood vessels, sweat glands, and hair follicles, and it contributes significantly to the skin's strength and elasticity. As the body ages, changes in the skin include thinning of the epidermis, and a decrease in the regenerative capacity of the dermis, leading to slower wound healing and other age-related skin alterations.