ANA 203 Histology SKIN Flashcards
The skin is composed of 2 parts
Epidermis: an epithelial layer of ectodermal origin
Dermis: a layer of mesodermal connective tissue.
Derivatives of the epidermis
Hairs
Nails
Sebaceous glands
Sweat glands
What is the subcutaneous tissue and its function?
Subcutaneous tissue is a loose connective tissue layer (aka hypodermis) underneath the dermis usually containing pads of adipocytes.
The subcutaneous tissue binds the skin loosely to the underlying tissues and corresponds to the superficial fascia of gross anatomy.
Cells of the skin
Stratified squamous epithelium (keratinocytes)
Pigment-producing melanocytes
Antigen-presenting Langerhans cells
Tactile epithelial cells called Merkel cells
Describe the basale layer
The basal layer (stratum basale) is a single layer of basophilic cuboidal or columnar cells on the basement membrane at the dermal-epidermal junction.
The stratum basale is characterized by intense mitotic activity and contains, along with the deepest part of the next layer, progenitor cells for all the epidermal layers.
Presence of basal stem cells for keratinocytes.
Keratinocytes are held together by desmosomes
How often is the human epidermis renewed and what is this dependent on?
The human epidermis is renewed every 15-30 days, depending on age, the region of the body, and other factors
How often is the human epidermis renewed and what is this dependent on?
The human epidermis is renewed about every 15-30 days, depending on age, the region of the body, and other factors
What are friction blisters?
are lymph-filled spaces created
between the epidermis and dermis of thick skin by excessive rubbing, as with ill-fitting shoes or hard use of the hands
What causes corns and calluses?
protective thickening and hardening of the outer cornified epidermal layers is due to prolonged friction over thick skin
What causes corns and calluses?
protective thickening and hardening of the outer cornified epidermal layers is due to prolonged friction over thick skin
Describe the stratum spinosum?
Thickest layer
It consists of polyhedral cells with a central nuclei and cytoplasm synthesizing keratin
What are tonofibrils?
Tonofibrils are cytoplasmic protein structures in epithelial tissues that converge at desmosomes and hemidesmosomes. They consist of fine fibrils in epithelial cells that are anchored to the cytoskeleton.
Describe stratum granulosum
The granular layer (stratum granulosum)
consists of three to five layers of flattened cells, now undergoing the terminal differentiation process of keratinization.
Their cytoplasm is filled with intensely basophilic masses called keratohyalin granules.
What are keratohyalin granules?
These are dense, non–membrane-bound masses of filaggrin and other proteins associated with the keratins of tonofibrils, linking them further into large cytoplasmic structures.
Describe the stratum lucidum
(only found in thick skin)
It consists of a thin, translucent layer of flattened eosinophilic keratinocytes held together by desmosomes.
Nuclei and organelles have been lost, and the cytoplasm consists almost exclusively of packed keratin filaments embedded in an electron-dense matrix.
