The Body's Coverings: An Overview

• بسم الله الرحمن الرحيم translates to "In the name of God, the Most Gracious, the Most Merciful."

Introduction to Anatomy

• Anatomy is the study of the structure of the human body.
• In Greek, anatomy means "to cut."
• In Latin, anatomy means "to dissect."

Levels of Studying Anatomy

• Macroscopic or gross anatomy involves studying structures visible to the naked eye
• Microscopic anatomy (histology) involves studying structures at the cellular level
• Radiological anatomy involves studying structures using imaging techniques.

Anatomical Position

• The standard reference position for accurate anatomical descriptions
• The whole body is standing erect
• The eyes are looking forward
• Upper limbs are positioned at the sides
• The palms of the hands are facing forward
• Thumbs pointing outwards
• The legs are close together
• Feet are pointing forward.

Other Body Positions

• Supine position is lying face up
• Prone position is lying face down
• Right lateral and left lateral positions are lying on the right or left side respectively.

Anatomical Terms of Position

• Superior indicates towards the head
• Inferior indicates towards the feet
• Anterior (ventral) indicates the front of the body
• Posterior (dorsal) indicates the back of the body
• Medial indicates toward the midline of the body
• Lateral indicates away from the midline of the body
• Proximal indicates closer to the trunk of the body
• Distal indicates further away from the trunk of the body
• Superficial indicates closer to the surface of the body
• Deep indicates further away from the surface of the body.

Anatomical Planes

• The median plane divides the body into right and left halves
• The paramedian plane is parallel to the median plane
• The frontal plane divides the body into anterior and posterior parts
• The transverse plane divides the body into upper and lower parts

Common Anatomical Terms of Movements

• Flexion decreases the angle between body parts.
• Extension increases the angle between body parts
• Abduction moves a limb away from the midline
• Adduction moves a limb toward the midline.
• Pronation rotates the forearm so the palm faces posteriorly or inferiorly
• Supination rotates the forearm so the palm faces anteriorly or superiorly.
• Inversion refers to the movement of the sole of the foot inwards
• Eversion refers to the movement of the sole of the foot outwards.

Coverings of the Body

• The coverings of the body include the skin and fascia.

The Skin

• The skin protects underlying tissues
• It defends the body against microorganisms
• The skin regulates body temperature
• It can form vitamin D
• The skin can absorb certain substances
• The skin has sensory nerve endings that provide information about the external environment.

Skin Structure

• The skin consists of a superficial layer (epidermis)
• The skin consists of a deep connective tissue layer (dermis)
• Deep to the dermis lies the superficial fascia or the hypodermis

Epidermis

• The epidermis is the most superficial layer of the skin
• It is formed of 4 to 5 layers (strata) of cells
• The superficial layer is formed of flat cells filled with keratin (keratinized stratified squamous epithelium)
• Keratin is a water-insoluble protein
• The epidermis is devoid of blood vessels
• The cells of the deep layer have the capacity for regeneration (by mitotic division)
• The epidermis is generally thin except in the palms of the hand and the soles of the feet to protect these parts from friction, tear, and rubbing.

Dermis

• The dermis lies deep to the epidermis
• It is formed of connective tissue containing blood vessels, lymph vessels, sensory nerve endings, smooth muscles, hair follicles, sweat glands, and sebaceous glands.

Appendages of the Skin

• The appendages of the skin are hairs, sweat glands, sebaceous glands, and nails.

Hairs

• Hairs cover most of the body surfaces except for the palms, soles, and red margin of the lip
• Hairs can be moved by a band of smooth muscle called arrector pili
• These muscles are supplied by sympathetic nerve fibers.

Sebaceous Glands

• Sebaceous glands lie within the dermis
• Their ducts open into the side of a hair
• Sebaceous glands secrete sebum to lubricate hair and skin
• There are no sebaceous glands on the palms or soles.

Sweat Glands

• Sweat glands are long tubular glands
• Sweat glands extend through the full thickness of the dermis
• Sweat glands are present all over the body except the red margins of the lips, the nail beds, the glans penis, and the clitoris.

Nails

• A nail is a flat horny plate on the dorsal surface of the distal phalanx of the fingers and toes
• Nails have a root, body, nail fold, and a bed.

Infections of Skin

• Pathogenic organisms, usually staphylococci, can enter the tissue through nail folds, hair follicles, and sebaceous glands
• If the infection happens between the nail and the nail fold, it is called paronychia.

The Fascia

• Fascia is the connective tissue that lies between the skin and the underlying muscles and bones, divided into superficial & deep layers.

Superficial Fascia

• Superficial fascia is found immediately under the skin uniting it to the underlying tissues
• It consists of a layer of loose connective tissue, which contains a variable amount of fat, blood vessels, and nerves of the skin
• It is extremely thin in the eyelids, external ear, penis, and scrotum.
• Superficial fascia keeps the body temperature
• It gives the body a rounded contour, especially in females
• Superficial fascia stores fat
• It contains blood vessels, lymphatics, and nerves of the skin
• It allows free mobility of the skin on the underlying structures.
• Superficial fascia contains muscles in the face (muscles of facial expressions) and in the neck (platysma).

Deep Fascia

• Deep fascia is a dense, inelastic fibrous membrane which separates the superficial fascia from the 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: it invests the muscles to separate the different muscle groups.
• In the distal joints, it is thickened for protection, forming retinaculae
• In the palm of the hand and sole of the foot, it forms aponeuroses
• Deep fascia serves as pulleys around which the tendons can move
• It surrounds blood vessels and nerves forming a sheath as a carotid sheath in the neck.

Explore the coverings of the human body. This includes the skin, hair, and nails. Understanding their structure and function is key to overall health.