Skin and Body Membranes

The Human Skin

CXC Biology

Objectives

• to relate the structure of the skin to its role in temperature regulation

The Structure of the Human Skin

• The skin is the largest organ of the body. it has three layers: the epidermis, the dermis and the subcutaneous (fat) layer.

The Epidermis

The epidermis is the outermost layer of the skin. It is very thin and lacks blood vessels and so is dependent on the dermis (the layer below) for nutrients and waste removal.

(In the image the dermis is the darker pink area with a thin layer of dead cells on top of it.)

The Dermis

The dermis is the middle layer of the skin. This is the thickest layer of the skin. It is made up of fibrous and flexible tissue that give the skin its flexibility and strength.

The Subcutaneous Layer

The subcutaneous layer of the skin is the innermost layer of the skin. It is composed of fatty and connective tissue. It is also called the hypodermis or fat layer. This layer also contains large blood vessels and nerves. That fat in this layer is important energy storage that also functions in insulating the body.

Multiple Choice

How many layers are present in the human skin?

• 1

• 2

• 3

• 3

Multiple Choice

This layer of skin is the thickest layer.

• The epidermis

• The dermis

• The subcutaneous layer

The Skin and Temperature Regulation

Why is temperature regulation important?

(Video)

Temperature Regulation

• Body temperature regulation is important in all living organisms as they have enzymes that requires specific temperature ranges within which they work.

• In humans, normal body temperature is about 37 degrees Celsius

• Some organisms are able to maintain their body temperatures within a narrow range.

• Organisms that are able to regulate their body temperatures are called homeotherms (eg. mammals and birds).

Temperature Regulation: Homeotherms

• Most of the heat is generated during metabolic reactions that is transported in the circulating blood.

• The layer of fat in the innermost layer of the skin acts a s insulation (heat retention).

Temperature Regulation: Homeostasis

• The role of the skin in regulating body temperature is very important.

• The hypothalamus (part of the brain) detects changes inn body temperature below or above 37 degrees Celsius and stimulates nerves in the skin which generate an appropriate response

• The intricate in which the body controls its temperature is one type of homeostasis.

• Homeostasis is the maintenance of a constant internal environment that will sustain life

How the Skin Loses Heat

The skin lose heat by different methods.

-Most of the heat lost from the body is by conduction (the body loses heat through physical contact)

-convection (the transfer of heat through fluids-liquids, gases) eg. cooling down in front of a fan

-radiation is the loss of heat from the skin to the atmosphere

-evaporation of water from the skin such as during sweating

Multiple Choice

What is the main source of heat in the human body?

• the sun

• warm clothing

• metabolic reactions

• the subcutaneous layer

Multiple Choice

Which of the following is not a way the skin loses heat?

• conduction

• convection

• goosebumps

• sweating

Multiple Select

Check all that apply. These animals are able to control their internal body temperatures.

• birds

• homeotherms

• mammals

• frogs

Multiple Choice

This part of the brain detects and controls processes to help regulate body temperature in humans.

• the cerebrum

• the medulla

• hypothalamus

• the brain stem