Lec 23 - Integument

Cards (31)

  • The skin is organized into three distinct layers
    • epidermis (uppermost)
    • dermis
    • hypodermis
  • The dermis further divides into
    • papillary layer (LCT, has lymph vessels)
    • 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 stratified squamous keratinized 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 hair follicles - 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 present antigen 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