Skin Layers and Functions

Introduction to Anatomy

• Prepared by Dr. Sayed Mostafa and modified by Dr. Eid Nassar Ali. Anatomy is derived from Greek and Latin terms meaning "to cut" and "to dissect," respectively.

Levels of Studying Anatomy

• Macroscopic/Gross Anatomy
• Microscopic Anatomy
• Histology
• Radiological Anatomy

Anatomical Position

• Serves as a standard reference for accurate descriptions of body parts and regions.
• Characteristics include standing erect, eyes looking forward, upper limbs at the sides, palms facing forward, thumbs pointing outwards, legs close together, and feet looking forward.

Other Body Positions

• Supine Position
• Prone Position
• Right Lateral Position
• Left Lateral Position

Anatomical Terms of Position

• Directional terms indicate where body parts are located in reference to the body in the anatomical position.

Anatomical Planes

• Median Plane: Divides the body into right and left halves.
• Paramedian Plane: Parallel to the median plane.
• Frontal (Coronal) Plane: Divides the body into anterior and posterior parts.
• Transverse Plane: Divides the body into upper and lower parts.

Common Anatomical Terms of Movements

• Flexion
• Extension
• Abduction
• Adduction
• Pronation
• Supination

More Common Anatomical Terms of Movements

• Rotation
• Inversion
• Eversion
• Dorsiflexion
• Plantar flexion

Coverings of the Body

• Includes: The skin and the fascia.

The Skin

• Protects underlying tissues
• Defends the body against microorganisms
• Regulates body temperature
• Forms vitamin D
• Absorbs certain substances
• Sensory nerve endings provide information about the external environment (heat, cold, pain, pressure).

Structure of the Skin

• Superficial layer (Epidermis)
• Deep Connective Layer (Dermis)
• Superficial fascia or Hypodermis.

Epidermis

• Most Superficial Layer
• Formed of Strata of cells.
• Superficial layer is formed of flat cells filled with keratin (Keratinized stratified squamous epithelium).
• Keratin is a water-insoluble protein.
• Devoid of blood vessels.
• Deep layer cells have the capacity for regeneration (by mitotic division).

Thickness of the Epidermis

• Generally thin, except in the palms of the hand and soles of the feet.
• This is to protect these parts and withstand friction, tear, and rubbing in these regions.

Dermis

• Lies deep to the epidermis
• Made of connective tissue containing blood vessels, lymph vessels, sensory nerve endings, smooth muscles, hair follicles, sweat & sebaceous glands.

Appendages of the Skin

• Hairs
• Sweat glands
• Sebaceous glands
• Nails

Hairs

• Cover most of the body surfaces, except palms, soles, and the red margin of the lip.
• Can be moved by a band of smooth muscle called arrector pili, supplied by sympathetic nerve fibers.

Sebaceous Glands

• Lie within the dermis.
• Ducts open into the side of a hair.
• Secretes sebum to lubricate hair and skin.
• Absent on the palms or soles.

Sweat Glands

• Long tubular glands.
• Extend through the full thickness of the dermis.
• Present all over the body, except the red margins of the lips, nail beds, glans penis, and clitoris.

Nails

• Flat, hard plate over the dorsal surface of the distal phalanx of fingers/toes
• Root, Body, Nail fold and a Nail Bed.

Clinical Applications (Skin Infections)

• Pathogenic organisms (usually staphylococci) can enter the tissue through:
  • Nail folds
  • Hair follicles
  • Sebaceous glands
• If the infection happens between the nail and the nail fold, it is called Paronychia.

The Fascia

• Connective tissue between the skin and underlying muscles and bones.
• Divided into superficial and deep layers.

Superficial Fascia

• Found immediately under the skin, uniting it to the underlying tissues.
• Consists of loose connective tissue with variable amounts of fat, blood vessels, and nerves.
• Extremely thin in the eyelids, external ear, penis, and scrotum.

Function of Superficial Fascia

• Keeps body temperature
• Gives body a rounded contour, especially in females.
• Stores fat
• Contains blood vessels, lymphatics, and nerves of the skin.
• Allows free mobility of the skin on the underlying structures.

Muscles in the Superficial Fascia

• In the face: muscles of facial expressions
• In the neck: platysma.

Deep Fascia

• Dense, inelastic fibrous membrane separating the superficial fascia from deeper structures.
• Covers most of the body, but is absent in certain regions like the face, scalp, and anterior abdominal wall.

Functions of Deep Fascia

• Invests muscles to separate different muscle groups.
• Thickened for protection in distal joints, forming retinaculae in the palm of the hand and sole of the foot form aponeuroses.
• Serves as pulleys around which tendons can move.
• Surrounds blood vessels and nerves, forming the carotid sheath in the neck.

Explore the layers of the skin: hypodermis, dermis, and epidermis. Understand their relative positions and the unique adaptations of skin, especially on the soles of the feet, to withstand tearing and rubbing forces.