Page 38 - 84 human physiolofy part-1

Chapter 3

reticular layer is composed of irregularly arranged fibers and resists stretching.

The hypodermis is not part of the skin, and lies below the Clinical Application:
dermis. Its purpose is to attach the skin to underlying bone and The patch drug delivery system. The
muscle as well as supplying it with blood vessels and nerves. It transdermal patch is an increasingly
consists of loose connective tissue and elastin. The main cell popular drug delivery system. These
types are fibroblasts, macrophages and adipocytes (the patches are designed so that the drug
hypodermis contains 50% of body fat). Fat serves as padding molecules diffuse through the
and insulation for the body. epidermis to the blood vessels in the
dermis layer. A typical patch works
well for small lipid-soluble molecules
Functions (for example, estrogen, nitroglycerin,
and nicotine) that can make their way
1. Protection: Skin gives an anatomical barrier between between epidermal cells.
the internal and external environment in bodily defense;
Langerhans cells in the skin are part of the immune system
2. Sensation: Skin contains a variety of nerve endings that
react to heat, cold, touch, pressure, vibration, and tissue
injury; see somatosensory system and touch.
3. Heat regulation: The skin contains a blood supply far
greater than its requirements which allows precise control of
energy loss by radiation, convection and conduction. Dilated
blood vessels increase perfusion and heat loss while
constricted vessels greatly reduce cutaneous blood flow and
conserve heat. Erector pili muscles are significant in
animals.
4. Control of evaporation: The skin provides a relatively
dry and impermeable barrier to fluid loss. Loss of this
function contributes to the massive fluid loss in burns.
5. Excretion: The concentration of urea is 1/130th that of
urine. Excretion by sweating is at most a secondary function
to temperature regulation.

In medicine, the branch concerned with the skin is called dermatology.

Tumors:

• Benign tumors of the skin: Squamous cell papilloma
• Skin cancer
• Acne
• Keratosis pilaris
• Fungal infections such as athlete's foot
• microbial infections
• calcinosis cutis
• ulcer

38 | Human Physiology