Bates’ Visual Guide to Physical Examination

6.3 Anatomy and Review Video Transcript

Narrator: The skin is the heaviest single organ of the body. Its major function is to keep the body in homeostasis, despite daily assaults from the environment. The scan provides boundaries for body fluids while protecting underlying tissues from microorganisms, harmful substances and radiation. The skin also modulates body temperature and synthesizes vitamin D.

The most superficial layer, the epidermis, is thin and has no blood vessels. It is divided into two layers; and outer horny layer of dead keratinized to cells and in intercellular layer where both melanin and keratin are formed.

For its nutrition, the epidermis depends on the underlying dermis which is well supplied with blood. The dermis contains connective tissue, sebaceous glands, sweat glands and hair follicles. The dermis merges below with subcutaneous tissue, or adipose, also known as fat.

Sebaceous glands produce a fatty substance secreted through the hair follicles. These glands are present on all skin surfaces except the palms and soles.

Sweat glands are either eccrine or apocrine. The eccrine glands are widely distributed, open directly onto the skin surface and help control body temperature through sweat production. In contrast, the apocrine glands are found chiefly in the axillary and genital regions. They usually open into hair follicles and are stimulated by emotional stress.

The color of normal skin depends primarily on four pigments:

• Melanin, the brownish pigment of the skin, is genetically determined and is increased by sunlight.
• Carotene, a golden yellow pigment, is found in subcutaneous fat and heavily keratinized areas such as the palms and soles.
• Hemoglobin, present in the red blood cell, carries most of the oxygen of the blood.
• Oxyhemoglobin is a bright red pigment that predominates in the arteries and capillaries. Deoxyhemoglobin is a darker and somewhat bluer pigment occurring when oxyhemoglobin loses its oxygen to body tissues while passing through the capillary bed.

An increased concentration of deoxyhemoglobin in cutaneous blood vessels gives the skin a bluish cast known as cyanosis. Skin color is affected not only pigments but also by the scattering of light as it is reflected back through the turbid superficial layers of the skin or vessel walls.

Appendages of the skin include the hair and nails. Adults have two types of hair; vellus hair, which is short, fine, inconspicuous and relatively on pigmented and terminal hair, which is coarser, thicker, more conspicuous and usually pigmented. Scalp hair and eyebrows are examples of terminal hair.

Nails protect the distal ends of the fingers and toes. The firm rectangular and usually curving nail plate gets its pink color from the vascular nail bed to which the plate is firmly attached. Note the whitish mountain or lunula and the free edge of the nail plate. The proximal nail fold covers roughly 1/4 of the nail plate called the nail root. The cuticle extends from the proximal nail fold and functioning as a seal. It protects the space between the fold and the plate from external moisture. Lateral nail folds cover the sides of the nail plate. Note that the angle between the proximal nail fold and the nail plate is normally less than 180°.

In conditions of chronic hypoxia, however, you may detect clubbing in which case the nail plate may become more convex with the angle increasing to greater than 180°.