skin profile (Anatomy)

 

                                                               SKIN ANATOMY (PROFILE)

 

Introduction:

• Skin is the largest organ of the human body. 
• Average adult’s skin = 8 pounds and covers 22 square feet.
• The skin has many important functions.
• We lose about 50 million skin cells a day

 

 

Divisions of the Skin:

1.       Epidermis

2.       Dermis

3.       Subcutaneous

 

 

Epidermis – cuticle or scarf skin:

Epidermis protects the delicate tissues of the body from injury .Epidermis is made of soft keratin, a protein. Soft keratin is found in the epidermis as flattened cells, or dry scales. Outermost layer of the skin; sheds daily with completely new cuticle layer by 28th day; tightly packed, scale like cells; turnover slows with age. Contains no blood vessels, but has many small nerve endings. Dispute over how many layers in epidermis, between 4 - 6. Bottoms layers are sometimes classified together, known as the basal layer. 

For our purposes, there are 4 main layers in epidermis. 

1. Stratum corneum: horny layer; tightly packed, scale-like cells, continuously shed & replaced.

2. Stratum lucidum: clear layer; small, transparent cells through which light can pass (only on hands and feet; not present where there are hair follicles); horny zone.

3. Stratum granulosum: granular layer; cells that look like distinct granuals; these cells are dying; horny zone.

4. Stratum spinosum: basal layer - prickle cell layer; as cells undergo mitosis below, they are pushed upward into this layer; begins basal layer.

5. Stratum mucosum: basal layer - also called stratum germinativum, but stratum germinativum refers to lowest row of cells to make up basal layer; basal zone (living stratum).

6. Stratum Germinativum: basal layer - composed of single layer of cells, lowest layer of cells to make up living stratum or basal layer; mitosis happens here and cells begin journey to surface, to replace older cells that are shed; approximately 28 days for journey; pigment granules produced here (melanocytes) to give skin color.

 

Epidermis includes the following layers:

Germinative layer (stratum basale or stratum germinativum):

 It consists of a single layer of columnar cells arranged like a palisade; between these cells there are slit-like spaces called intercellular bridges. Among the cells of germinative layer localize melanocytes, which produce melanin. Skin color straightly depends on the amount of melanin. This layer presents stem cells conerned to mitosis.

Prickle cell layer (stratum spinosum):

It Consists of 5 - 10 rows of cells , cuboid in deep parts of layer but become flatter gradually as they approach next layer, the granular layer The cells of the prickle-cell layer are marked by presence of specific tonofibrils in their cytoplasm. Special Langhan's cells are demonstrated in this layer, which carry immunological function.

Granular layer (stratum granulosum):

it Contains 1 / 2 / 4 rows of cells elongated parallel to epidermis It was considered previously that they were formed of a special substance called keratohyalin The presence of the keratohyalin granules is the first visible stage, of the beginning of the process of keratinization of the epidermal cells. Serve as water-proof layer.

The epidermal germinative, prickle-cell, and granular layers are sometimes embraced under the name of Malpighian layer.

Lucid layer (stratum lucidum):

It is Composed of elongated cells containing a special protein substance which refracts light strongly This substance resembles drops of oil and is called eleidin Besides its main component, eleidin, the stratum lucidum contains glycogen and fatty substances (lipoids, oleic acid)

Horny layer (stratum corneum):

 It is composed of fine, anuclear keratinized elongated cells They are firmly attached to one another and are filled with a horny substance (keratin) the chemical structure of which has still not been finally determined It is believed that this is an albuminoid substance poor in water and rich in sulphur and contains fats and polysaccharides. The outer part of stratum corneum is less compact and occasional lamina separate from the main bulk, i.e. the process of physiological desquamation occurs

Dermis Papillary layer:

It consists of thin bundles of astructural amorphous interstitial substance, collagen fibres & many fine elastic fibres Reticular layer - consists of collagen bundles are more compact and thick and intertwine into a thick network of loops The reticular and particularly the papillary layer of normal skin have a small number of various cell elements: fibroblasts, histiocytes, lymphocytes, mast, plasma cells & peculiar pigment cells Hairs, glands (epithelial appendages of the skin), muscles, vessels, nerves and nerve endings are located in the dermis

 

Dermis – derma or true skin:

Made of collagen and elastin (protein fibers); gives skin strength, form, flexibility. Blood vessels, fat cells, oil and sweat glands held together by collagen. Thickest layer of connective tissue; binds epidermis to subcutaneous tissue. Network of nerves, blood and lymph vessels provide nutrition to itself and epidermis. Vital functions of skin; composed of sweat and oil glands, blood & lymph vessels, nerve fibers, sensory receptors, hair follicles. Arrectorpili muscles (tiny muscles, generates heat when body is cold, contracts, causing hair to "stand up straight" on skin).Papillae (small, cone shaped projections of elastic tissue that point upward), contain nerve fiber endings for sense of touch. 

Dermis – 2 layers.

1. Papillary Layer: superficial layer. Lies directly beneath epidermis. Houses nerve endings (corpuscles) that provide body with sense of touch – pain, heat, cold, pressure, touch. Contains papillae, small, cone shaped projections of elastic tissue that point upwards .Papillae contain looped capillaries or nerve fiber endings.

2. Reticular Layer: deeper layer. Contains fat cells, blood .and lymph vessels, oil .and sweat glands, hair follicles, .arrectorpili muscles.

 

 

Subcutaneous Tissue- Fatty layer:

It attaches dermis to underlying structures. Also called adipose, or subcutis tissue. Composed of adipose and connective tissue. Serve as shock absorbers for vital organs, stores energy. Varies in thickness according to age, sex, general health of individual. Gives smoothness, contour to body, contains fats for use as energy, heat insulator. Circulation is maintained by network of arteries, and lymphatics (removes bacteria and foreign materials, produces antibodies to fight infection)

 

Functions of the Skin :

• Immunological function
• Secretory function
• Thermoregulation function
• Receptory function
• Excretory function
• Protective function

 

Cells of skin:

• Melanocytes
• Keratinocytes
• Langenhan cells
• Merkel’s cells