Skin and Bone
Why do we consider skin and bone organs?
Because organs are things composed of two or more tissue types, and skin and bone are both
composed of more than two.
How is that defined and what are the specific components for each?
Skin: Epithelial, Connective, Neural, Muscle
Bone: Connective (majority), Neural, Muscle and Epithelial (as part of blood vessels)
What are the functions of each of these organs? How do some of the
tissues contribute to this?
Skin: Holds body together, provides cover/protection from dehydration and microorganisms,
insulates and regulates temp, sensory receptor
Bone: Inner support for the body, reserves minerals (Calcium and Phosphorus), attachment for
What are the characteristics of the epidermis: structural and functional?
(i.e. what is it made up of and how do these components serve the
functional aspects of the skin?)
It has numerous layers of cells (mostly epithelial). There are 45 named layer types of the
epidermis (2 of which are easily identifiable):
stratum corneum: outermost layer which consists of many rows (up to 25 layers of this) of dead
cells filled with keratin that easily brush off via friction. These cells have been dying as they’ve
moved up to the outer layer and they got filled up with keratin in the process.
stratum basale: the deepest layer (single layer) of cells which can divide and thus regenerate the
What are Langerhans cells, melanocytes, and basal cells and what are their
Langerhans (or Dendritic) cells: these cells detect any microorganism that penetrate the
epithelium and communicate with the immune system to help eliminate those.
Melanocytes: produce pigment that is dispersed in the skin layers, mostly melanin (brown) and
pheomelanin (yellow). They have projections that bring the granules with pigment molecules to the
upper surface of the epidermis. Melanin production is stimulated by sunlight. What are the dermal components and what functions does each serve?
The dermis primarily consists of connective tissue with all other cell/tissue types within it. It consists
of two main layers:
Papillary Layer: the upper 20% of the dermis, which is mainly loose areolar connective tissue (so
contains collagen and elastic fibers). It also has capillaries, loose nerve endings, Meissner and
other sensory structures
Reticular Layer: the deeper 80% of the dermis, which has dense bundles of fibers that give rise to
tension or cleavage lines (like creases on the inside of fingers). It also has hair follicles, sebaceous
glands, sweat glands, blood vessels, and nerve endings.
What are the dermal papillae and what is their significance?
They are ridges caused by the dermis that elevate the epidermis (right on the border between
them). These give rise to our friction ridge patterns (finger and footprints).
What types of sensory structures are found in the skin?
Various nerve endings and nerve tissues (corpuscles), which are involved in touch and vibration.
They are located right under the epidermis.
Hair shafts also contract when we get cold/frightened.
What kind of glandular tissue is found in the skin and what types of
secretions are produced?
Eccrine sweat gland: pretty deep in the dermis, and they have an exit route all the way out to the
pores. More salty (aqueous) solution (sweat).
Sebaceous (oil) gland: usually found around the hair shaft, and produce a mucusy secretion that
lubricates the hair and also the skin.
What are: hard or compact bone, spongy bone, the diaphysis, the
periosteum, the endosteum, the epiphyseal plate, Haversian canals,
Hard (compact/lamellar) bone: harder, denser bone type that is able to withstand pressure.
Spongey bone: airier, less dense, less compact bone type, which can contain red marrow.
Diaphysis: the shaft of the bone, which consists of hard bone
Periosteum: the outer layer (surface) of the bone
Endosteum: the inner layer (of the diaphysis) of regenerating bone
Epiphyseal plate: the area of cartilage that grows and allows the bone to increase in length as we
grow from babies to adults (it can give rise to new cells). Haversian canals:
What are the cellular components of bone? What are their functions?
There are three types of cells in bones:
Osteoblasts: give rise to bone tissue. They are metabolically active and produce bone matrix.
Osteocytes: These are metabolically active but no longer produce bone matrix. They are still
involved as maintaining the bone as a living tissue. They get trapped in the lacunae.
Osteoclasts: these are giant multinucleated cells that break down bone and are essential for bone
remodeling – in order for bone to be built, old bone needs to be broken down. (make the mess and
clean it up)
• Secrete lysosomal enzymes and acids (that solubilize calcium salts) to break down
• Phagocytize dead osteocytes and matrix: basically engulfs bone components that
have been broken down, which allows for b