reticular layer (DICT, gives skin its stretchiness and resistance to force)
The skin is the largest organ in the body - makes up 15 - 20% body mass
The epidermis is the epithelial layer and is avascular
The vast of the nervous tissue, vasculature, hair bulbs, ducts, and skin modifications are found in the dermis
The hypodermis is made up of Loose connective tissue, find a lot of adipose tissue, and glandular tissue
The epidermis is made up of stratifiedsquamouskeratinized epithelium
Functions of the skin
barrier
water homeostasis
temperature homeostasis
peripheral nervous system receptors
vitamin D production (endocrine)
excretion
immunologic functions
endocrine
The blood supply that feeds the skin is mostly coming in from the subcutaneous plexus which is in the hypodermis
Blood supply in the skin
subcutaneous plexus - in the hypodermis
cutaneous plexus - in the dermis
subpapillary plexus - in the papillary layer of the dermis which allows nutrient provision to the epidermis
Layers of the epidermis
stratum basale
stratum spinosum
stratum granulosum
stratum lucidum (only in thick skin)
stratum corneum
The stratum basale is the layer of the epidermis that contains mitotically active cells, pigmented melanocytes, and sensory cells. This layer is one cell thick
The stratum spinosum is a layer of the epidermis that contains many layers of keratinocytes and langerhans cells
The stratum granulosum is a layer of the epidermis that contains darkly stained keratohyalin granules (secretory granules) - usually 1-2 cell layers thick
The stratum lucidum is a layer of the epidermis that is only present in thick skin (palms and soles), it is a bluish layer, where apoptosis occurs, and lots of lipids are released for the function of water proofing the skin
The stratum corneum is the outermost layer of the epidermis where cells are dead and keratinized. They contain lipids between the keratinocytes
Thick skin does not contain hairfollicles - therefore ther are no sebaceous glands
Fingerprints are formed by epidermal ridges - formed by the interdigitation of the epidermis and dermis (interpapillary peg and dermal papilla)
Keratinocytes are linked together by a lot of intermediate filaments and desmosomes and anchored to the basement membrane by hemidesmosomes and integrins
The special cells of the epidermis are
langerhans cells (dendritic cells
merkel cells (mechanoreceptors)
melanocytes (pigmented cells)
The special cells of the epidermis are not intrinsically native to skin, they migrate in as the skin is developing (most from mesenchyme)
Langerhans cells (dendritic cells) are monocytes derived from lymphoid precursor cells - they are the macrophages of the skin and are located in the stratum spinosum
Merkel cells are mechanoreceptor cells that detect fine touch and are located in the stratum basale
Melanocytes are pigmented cells that produce melanin. They are located in the stratum basale but they contain projections that project up into the stratum spinosum
Skin pigmentation
tyrosine converted into dopa which is the precursor of melanin
melanin accumulates in pre-melanosomes after synthesis from dopa
melanosomes (secretory vesicles) migrate upward to the tip of the melanocyte processes that invaginate between keratinocytes
keratinocytes phagocytose the tips of the processes - called melanosomes
melanosomes release the melanin into the cytoplasm, which then accumulates at the UV side of the nucleus
Everyone has the same amount of melanocytes but different types of melanin and different people break down melanin more readily
Langerhans cells phagocytose and presentantigen on its surface then migrate out of the skin into the dermis and out into the lymphatic vessels, go to a lymph node and interacts with T-cells
Merkel cells are associated with the peripheral nervous system and connect with free nerve endings. They secrete granules that are going to interact like a synapse with the free nerve ending. They respond to mechanical movements, really fine touch and pressure. They are found in the stratum basale
Label the layers of the skin
A) epidermis
B) dermis
C) papillary layer
D) reticular layer
E) hypodermis
Label the layers of the epidermis
A) stratum basale
B) stratum spinosum
C) stratum granulosum
D) stratum lucidum
E) stratum corneum
The encircled cell is an example of a melanocyte - dark staining nucleus with clear halo cytoplasm