HOMEOSTASIS AND EXCRETION
Homeostasis is the maintenance of a constant internal environment.
Our outer environment/surroundings are constantly changing.
→ Temperature and humidity,
But, your body keeps the environment in the body constant at all times.
Homeostasis helps your cells work as efficiently as possible. It controls body
temperature and glucose content.
THE CONTROL OF BODY TEMPERATURE
MAMMALS AND BIRDS ARE HOMEOTHERMIC:
Homeothermic refers to the ability to control own body temperature despite the
temperature of the environment.
Advantages
• Temperature (37˚C) is kept at optimum for enzymes to work efficiently.
• Metabolism keeps going/working even when it is cold.
• Homeothermic animals can be active regardless of whether it is cold of night
time.
Disadvantages
• Homeothermic animals require more energy to maintain heat and must eat
more to be able to respire at a sufficient rate to accomplish this.
Another term for animals who can do this is “endothermic”.
Animals that are not homeothermic/endothermic are poikilothermic/ectothermic,
SKIN
Human skin is made up of two layers (epidermis + dermis).
Epidermis:
These are cells that protect the deeper layers.
Made in the Malpighian layer and divide via the process of mitosis.
,The new cells that are made, in the Malpighian layer move up but die on the way and
are filled with a protein called keratin which.
The cornified layer is the top layer of the skin that is made up of these dead cells. It
protects everything underneath it as it is hard and waterproof.
Melanin is a dark brown pigment that is in the epidermis to absorb harmful UV rays.
Hair follicle: folds in the epidermis where hair grows. A component of hair is keratin.
What is keratin? ____________________
Sebaceous gland is an opening on the side of the follicle that makes an oily liquid
called sebum that keeps the skin and hair soft.
Dermis:
Dermis = connective tissue – elastic and collagen fibres.
As you get older, the fibres get less elastic and wrinkles are formed.
Sweat glands: secrete sweat (water salt and urea), travels through ducts to the skin
surface where it functions to help regulate temperature.
Blood vessels and nerve endings in the dermis are sensitive to changes in the
environment such as temperature.
The adipose layer is a layer of fat under the dermis that helps insulate the body.
HYPOTHALAMUS
➔ Part of the brain that coordinates temperature control
How? → it senses the temperature if the blood running through it. If the blood id too
hot or too cold then the hypothalamus sends out impulses to the parts of the body that
function to regulate temperature.
When the body is too cold, nerve impulses from the hypothalamus cause:
1. Muscle work
Shivering: rapid contraction and relaxation of muscles to produce heat which warms
the blood which is distributed throughout the body.
2. Metabolism may increase
Increased metabolic reactions such as respiration release heat.
3. Hair stands up
In hairy animals, this reaction traps warm air in the layer above the skin, thus acting
as an insulator.
, 4. Blood system conserves heat.
Vasoconstriction: constriction of blood capillaries near the surface of the skin so that
blood flows mainly in the deeper layers instead of the surface where it could lose heat.
When he body is too hot, nerve impulses from the hypothalamus cause:
1. Hair lies flat.
2. Blood system loses heat
Vasodilation: widening of the capillaries near the surface of the skin (dilation) so that
more blood will flow near the surface and heat can be lost from the blood to the air.
3. Sweat
Sweat is secreted and lies on the surface of the skin, when it evaporates, it takes the
heat from the skin with it and the body cools down.
NEGATIVE FEEDBACK
QUESTIONS!!!
11.1. Outline two advantages and one disadvantage of maintaining a constant
body temperature.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
11.2. Give two functions of the fat layer beneath the skin.
___________________________________________________________________
___________________________________________________________________
11.3. Explain how sweating helps to cool down the body.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
11.4. Explain what vasodilation is and how it helps to cool the body.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Homeostasis is the maintenance of a constant internal environment.
Our outer environment/surroundings are constantly changing.
→ Temperature and humidity,
But, your body keeps the environment in the body constant at all times.
Homeostasis helps your cells work as efficiently as possible. It controls body
temperature and glucose content.
THE CONTROL OF BODY TEMPERATURE
MAMMALS AND BIRDS ARE HOMEOTHERMIC:
Homeothermic refers to the ability to control own body temperature despite the
temperature of the environment.
Advantages
• Temperature (37˚C) is kept at optimum for enzymes to work efficiently.
• Metabolism keeps going/working even when it is cold.
• Homeothermic animals can be active regardless of whether it is cold of night
time.
Disadvantages
• Homeothermic animals require more energy to maintain heat and must eat
more to be able to respire at a sufficient rate to accomplish this.
Another term for animals who can do this is “endothermic”.
Animals that are not homeothermic/endothermic are poikilothermic/ectothermic,
SKIN
Human skin is made up of two layers (epidermis + dermis).
Epidermis:
These are cells that protect the deeper layers.
Made in the Malpighian layer and divide via the process of mitosis.
,The new cells that are made, in the Malpighian layer move up but die on the way and
are filled with a protein called keratin which.
The cornified layer is the top layer of the skin that is made up of these dead cells. It
protects everything underneath it as it is hard and waterproof.
Melanin is a dark brown pigment that is in the epidermis to absorb harmful UV rays.
Hair follicle: folds in the epidermis where hair grows. A component of hair is keratin.
What is keratin? ____________________
Sebaceous gland is an opening on the side of the follicle that makes an oily liquid
called sebum that keeps the skin and hair soft.
Dermis:
Dermis = connective tissue – elastic and collagen fibres.
As you get older, the fibres get less elastic and wrinkles are formed.
Sweat glands: secrete sweat (water salt and urea), travels through ducts to the skin
surface where it functions to help regulate temperature.
Blood vessels and nerve endings in the dermis are sensitive to changes in the
environment such as temperature.
The adipose layer is a layer of fat under the dermis that helps insulate the body.
HYPOTHALAMUS
➔ Part of the brain that coordinates temperature control
How? → it senses the temperature if the blood running through it. If the blood id too
hot or too cold then the hypothalamus sends out impulses to the parts of the body that
function to regulate temperature.
When the body is too cold, nerve impulses from the hypothalamus cause:
1. Muscle work
Shivering: rapid contraction and relaxation of muscles to produce heat which warms
the blood which is distributed throughout the body.
2. Metabolism may increase
Increased metabolic reactions such as respiration release heat.
3. Hair stands up
In hairy animals, this reaction traps warm air in the layer above the skin, thus acting
as an insulator.
, 4. Blood system conserves heat.
Vasoconstriction: constriction of blood capillaries near the surface of the skin so that
blood flows mainly in the deeper layers instead of the surface where it could lose heat.
When he body is too hot, nerve impulses from the hypothalamus cause:
1. Hair lies flat.
2. Blood system loses heat
Vasodilation: widening of the capillaries near the surface of the skin (dilation) so that
more blood will flow near the surface and heat can be lost from the blood to the air.
3. Sweat
Sweat is secreted and lies on the surface of the skin, when it evaporates, it takes the
heat from the skin with it and the body cools down.
NEGATIVE FEEDBACK
QUESTIONS!!!
11.1. Outline two advantages and one disadvantage of maintaining a constant
body temperature.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
11.2. Give two functions of the fat layer beneath the skin.
___________________________________________________________________
___________________________________________________________________
11.3. Explain how sweating helps to cool down the body.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
11.4. Explain what vasodilation is and how it helps to cool the body.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
