The Skin

Identify the role of the skin

-an organ to separate the body from the external environment

• The skin is an organ to separate the body from the external environment. The epidermis forms an effective barrier to separate the rest of the body from the external environment.

• The stratum corneum, which forms part of the epidermis, consists of the dead skin cells that have died from lack of food and oxygen. These dead cells are firmly attached to one another and are keratinised.

• They protect the living cells beneath them and help reduce water loss. The dead cells flake away and form most of the dust that collects in our houses.

House dust and a dust mite

It has been calculated that the average person sheds about half a kilogram of skin a year,

an organ assisting in body temperature control

• The skin is an organ assisting body temperature control. Sweat glands, found in the dermis, produce a liquid that is released through the pores in the epidermis.

A sweat gland.

• When this liquid is released on the surface of the body it evaporates and this in turn cools the body surface. When the body becomes hot, the rate at which these glands produce sweat or perspiration increases.

Sweat Glands

Evaporative Cooling

• As well as this, when the body becomes hot, the blood vessels dilate, which allows loss of heat through the epidermis. These processes help to maintain the body temperature at 37oC

Dilated Blood Vessels

an organ to protect against entry by disease causing organisms

• The skin protects our body against disease in a number of ways:

• The shedding of the top layer of skin (the stratum corneum) helps prevent the entry of disease causing organisms.

• The film on the surface of our skin, that contains a mixture of sweat, sebum and microflora, is acidic. The acidity comes from the fatty acids that are present in the sebum and from the acids present in sweat.

Cultured Skin Microflora

• The acidity is increased by the presence of Staphylococcus epidermis, bacterial microflora that break down the fatty acids in the sebum. Many other bacteria cannot survive in such an acidic environment.

• The high concentration of salt in sweat creates an environment that is inhospitable to many bacteria.

• The presence of skin microflora holds in check the small number of pathogenic organisms that are on our skin surfaces.

• Different parts of the body have different populations of microflora, in balance with the small number of pathogens. This balance can be disturbed by variations in the diet, the use of antibiotics, the use of personal hygiene products and by physical injury.

Define the term ‘microflora’ and discuss the role of the microflora

on skin in different parts of the body

• Microflora are microorganisms, including bacteria, fungi, algae, protozoa and viruses, that live in harmless association with our skin. They are able to survive the acidic nature of our skin and sometimes actually help us against the entry of pathogens.

Microorganisms that cause disease are referred to as pathogens. The presence of the microflora limits the resources available for pathogenic bacteria that may be able to survive the acidic, salty environment.

• The microflora also increase the acidic nature of the skin therefore making it even more inhospitable to many pathogens.

• The number and type of microflora found on the skin varies in different parts of the body and between different individuals. The population of microflora of an individual is established soon after birth.

• Some of the microflora that are harmless on the surface of the skin can become quite dangerous if the skin surface is broken and they are able to enter the bloodstream. Staphylococcus aureus can cause serious disease if it gains entry to the bloodstream during medical procedures. Its presence is a serious problem for hospitals and surgeries.

• One species of microflora, Corynebacterium acnes, live in the hair follicles, usually without harm to a person. However, when the dead skin from the epidermis occasionally blocks a sebaceous gland of a hair follicle, the bacteria may infect surrounding tissue resulting in inflammation and causing a pimple.

Discuss the term pH in terms of its ability to

describe the acidity of a substance.

• The pH scale can be used very effectively to describe the degree of acidity of a substance. The pH scale commonly has the range of 0-14, where a pH of 7 is regarded as neutral. Substances with a pH below 7 are regarded as acidic and substances with a pH above 7 are regarded as alkaline. Indicators such as litmus paper, universal indicator paper or universal indicator solution, methyl orange or phenolphthalein can be used to determine the pH of a substance. Alternatively pH meters or probes can be used to determine the pH electronically

Explain the relationship between the natural pH of the skin and the action of

-microflora-natural oil produced by

glands in the skin.-perspiration

• pH and the skin: 

• The natural oil in the skin is produced by sebaceous glands and is slightly acidic.

• The sweat or perspiration on our skin is produced by the sweat glands and is also slightly acidic.

• Most bacteria can survive in a narrow pH range. The bacterial microflora on our skin are able to survive acidic conditions with a pH range 4-6. Other harmful bacteria cannot usually survive this environment and so our acidic skin protects us from harmful bacteria or pathogens.

• Some of our microflora are able to breakdown the fatty acid molecules (from the natural oils) in our skin and thereby increase its acidity.