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Renin Angiotensin Mechanism.

Integumentary System: Skin

 Integumentary System: Skin.

Introduction:

  • Integument means “Covering”, this system is made of structures which provide covering to the body.

  • Skin along with subcutaneous tissue and accessory structures like hair, sweat glands etc. forms integument of the human body.

Skin:

  • It is the largest organ of the body.

  • It constitutes around 7% of the total body weight.

  • Skin is made up of two layers;

    • Epidermis.

    • Dermis.

Epidermis of Skin:

  • The epidermis is made of stratified squamous keratinizing epithelial tissue.

  • It is thickest on the palms and soles.

  • It is avascular in nature i.e. there is no blood supply.

  • Cells are very closely packed.

  • It contains four types of cells as 

    • Keratinocytes.

    • Melanocytes.

    • Langerhans Cells.

    • Merkel Cells.

  • The epidermis of skin is made up of Four or Five layers as;

    • Stratum corneum.

    • Stratum lucidum.

    • Stratum granulosum.

    • Stratum spinosum.

    • Stratum basale.

Cells of the Epidermis of Skin:

  1. Keratinocytes:

  • Most abundant.

  • Contain keratin protein.

  • Synthesize a defensive substance called “Defensine”. 

  1. Melanocytes:

  • They are in less numbers as compared to Keratinocytes.

  • They have large processes that connect to many keratinocytes.

  • They synthesize a chemical “Melanin”  and inject it into attached keratinocytes.

  • Melanin is a coloring pigment of reddish brown or yellowish red in color responsible for skin color.

  • Melanin protects the cells from harmful UV radiations.

  1. Langerhans Cells:

  • These large cells are basically “Macrophages” formed in bone marrow and migrated towards the skin.

  • They perform the function of defense.

  1. Merkel Cells:

  • These cells are found in the last layer of epidermis called Stratum basale.

  • These cells are along with sensory nerves from Merkel discs.

  • They perform functions of sense.

Layers of Epidermis of Skin:

  • Layers of epidermis are called “Strata”.

  • The thin skin contains Four layers;

    • Stratum corneum.

    • Stratum granulosum.

    • Stratum spinosum.

    • Stratum basale.

  • While thick skin contains Five layers;

    • Stratum corneum.

    • Stratum lucidum.

    • Stratum granulosum.

    • Stratum spinosum.

    • Stratum basale.

  1. Stratum corneum:

  • The outermost layer.

  • Contains many layers of dead squamous keratinized epithelium cells.

  • The cells that compose a large proportion are called “Corneocytes”.

  • As cells contain keratin this layer provides waterproof property to the skin.

  • It has a defensive function as bacteria and most of the harmful chemicals  cannot enter the unbroken layer.

  1. Stratum lucidum:

  • Only present in the thick areas of the skin like palms and soles. 

  • It is made up of 4-5 layers of dead cells.

  • It appears translucent under a microscope.

  1. Stratum granulosum:

  • It is present between Stratum lucidum and Stratum spinosum.

  • The cells appearing in this layer triggers Apoptosis (Programmed Cell Death).

  • They appear granular and start producing lamellar bodies that impart hydrophobicity to the skin.

  • Cells contain a protein called “Keratothylline” that produces keratin from intermediate keratin filaments.

  1. Stratum spinosum:

  • It is made up of 8-10 layers of the cells.

  • When observed under the microscope, cells show the presence of thorns like spines and hence the name is given “Spinosum”.

  • It mainly contains keratinocytes and a few melanocytes, merkel cells and Langerhans cells.

  1. Stratum basale:

  • The deepest and last layer of epidermis.

  • Also called Stratum germinativum.

  • Made up of a single row of cuboidal or columnar keratinocytes (Some cells are stem cells).

  • Melanocytes, Merkel cells along with discs are scattered in the layer.

  • The cells are anchored to the basement membrane present between epidermis and dermis with help of hemidesmosomes.

  • The cells show continuous cell divisions.

Dermis:

  • It is a deeper layer of the skin and is present below the epidermis.

  • Basically it is irregular strong connective tissue.

  • It is vascular and has nerve supply.

  • It shows the presence of collagen and elastin fibers.

  • The cell component of dermis contains fibroblasts, mast cells, eosinophils etc.

  • The matrix component is made up of Hyluronic acid and proteoglycans.

  • Dermis is divided into two layers;

    • Papillary Region.

    • Reticular Region.

  1. Papillary Region:

  • It is a small layer and consists of one-fifth of the total layer’s thickness.

  • Its surface area that protrudes in epidermis is finger shaped and called “Dermal papillae” hence the name “Papillary region”.

  • Dermal papillae increases the surface area significantly.

  • This layer consists of small collagen fibers and fine elastin fibers.

  • It also shows the presence of blood vessels, touch receptors and free nerve endings.

  1. Reticular Region:

  • It has a net like structure and hence the name is given Reticular Region. 

  • It contains thicker collagen fibers arranged in a net like formation, stronger elastin fibers and several fibroblasts along with many wandering cells like macrophages, mast cells, eosinophils etc.

  • Adipocytes are also present in this region.

  • Blood vessels, nerves, hair follicles, sebaceous (oil) glands, and sudoriferous (sweat) glands are found in the spaces between fibers.

  • A smooth muscle called as “Arrector pili” is present alongside the hair follicle.

Commonly Asked Questions.

  1. With help of a well labelled diagram explain the structure of skin.

  2. Draw a well labelled diagram of LS of skin.

  3. Write in short about various layers of the epidermis of skin.

  4. Name different cells found in epidermis of the skin.
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