Homeostasis - Breaking Out In A Sweat

Question 1

What is homeostasis?

Answer 1

The maintenance of a constant internal environment

Question 2

Why would metabolic rate decrease if the body temperature became too high?

Answer 2

• Enzymes would become denatured due to them vibrating too
• This breaks the hydrogen bonds that hold together the 3D shape
• Loss of 3D shape means active site has changed shape so no longer works as a catalyst

Question 3

Give an example of negative feedback in the body

Answer 3

The controlling of body temperature

Question 4

How is temperature controlled in mammals?

Answer 4

• Thermoreceptors in the skin detect a change in temperature
• The receptors send impulses along sensory neurons to the hypothalamus (brain)
• The hypothalamus then sends impulses along motor neurons to effectors

-The effectors restore body temperature to normal
eg hair errector muscles contract when body temperature is too low

Question 5

What is the process called of maintaining body temperature?

Answer 5

Thermoregulation

Question 6

What feedback mechanism is stimulated when the body increases in temperature?

Answer 6

Sweat glands secrete sweat

Question 7

What feedback mechanisms are inhibited when there is an increase in body temperature?

Answer 7

• Contraction of arterioles - this means they are relaxed and dialated
• Hair errector muscles - relax so hair lies flat
• Liver - reduces metabolic rate
• Skeletal muscle - relax so no shivering

Question 8

What feedback mechanisms are stimulated when there is a decrease in body temperature?

Answer 8

• Arterioles contract - this means they constrict, reducing blood flow
• Hair errector muscles contract - hair raises
• Liver - increases metabolic rate
• Skeletal muscles contract - this causes shivering

Question 9

What feedback mechanisms are inhibited when there is a decrease in body temperature?

Answer 9

Sweat glands - no sweat produced

Question 10

How can skin control body temperature?

Answer 10

• Sweating
• Raising or flattening hair
• Route of blood flow via vasoconstriction and vasodilation
• Shivering

Question 11

What is shivering and how does it maintain body temperature?

Answer 11

• Shivering is the uncontrolled contraction of normally voluntary muscles
• Energy is transferred to muscle tissue
• This results in more respiration and therefore heat
• Heat production can increase six-fold

Question 12

Describe what happens in vasoconstriction

Answer 12

• Muscles in the arteriole walls contract
• This means the arterioles constrict, reducing blood flow to the surface capillaries
• The shunt vessel, located further below the surface of the skin, dialates so more blood flows through it
• This means blood is travelling further away from the skin’s surface so less energy is lost via radiation, conduction and convection

Question 13

Describe what happens in vasodilation

Answer 13

• Muscles in the arterioles walls relax so the arterioles dilate
• The shunt vessel constricts, reducing the amount of blood flowing through it
• More blood is travelling closer to the skin’s surface so more energy is lost via radiation, conduction and convection

Question 14

What will happen to metabolic reactions if body temperature falls below or rises above the normal range?

Answer 14

• Low temperatures cause a decrease in metabolic reactions as enzyme-controlled reactions slow
• High temperatures cause an initial rise in metabolic rate but then declines as the enzymes become denatured

Question 15

Name things that must be controlled by the body through homeostasis

Answer 15

• Glucose concentration
• Ion concentration
• CO2 concentration
• Water levels
• pH of blood
• Temperature of the blood

Question 16

What are the homeostasis control mechanisms trying to maintain?

Answer 16

• The norm value of a condition
• This is usually the optimum for that condition

eg body temperature is 37°C

Question 17

What stimulates effectors to return a condition to the norm value?

Answer 17

-Nerve impulses or hormones from the control centre

Question 18

What is negative feedback?

Answer 18

-The mechanism that restores a condition back to the norm value

Question 19

Explain how negative feedback would act to restore a decreasing population to the norm for the environment

Answer 19

• A fall in population below the norm reduces competition
• This increases available food
• The population increases back to normal

Question 20

How are hormone levels controlled?

Answer 20

By negative feedback

Question 21

Describe how testosterone levels are maintained

Answer 21

• A change in testosterone levels is detected by the hypothalamus
• A decrease in testosterone causes gonadotropin-releasing hormone to be produced by the hypothalamus
• This stimulates the pituitary gland to release hormones that stimulate the testes to synthesise testosterone

Question 22

What is positive feedback? Give an example of it occuring in the body

Answer 22

• Output from the control centre moves the condition further from the norm value
• In child birth - there is a constant increase in contractions which increases the pressure in the uterus, until the baby is born

Question 23

How is a clot forming an example of positive feedback?

Answer 23

• Platelets stick to exposed collagen in the wall and each other
• They release chemicals that attract more platelets
• This continues until a clot has formed

Question 24

A marathon runner feels cooler after dousing himself in water. How does this help to cool him?

Answer 24

-Increased energy lost by conduction and evaporation

Question 25

Why does high humidity make marathon running more dangerous?

Answer 25

• Less evaporation occurs
• Less energy lost by sweating
• Harder for athletes to keep their bodies at a safe temperature

Question 26

How does convection play a part in homeostasis?

Answer 26

• Air next to the body will be warned by heat from the skin

- The warm air expands and rises, taking the energy with it, and is replaced by cooler air

Question 27

How does body hair reduce heat loss?

Answer 27

• Hair traps a layer of air next to the skin
• This acts as a thermal insulator
• It reduces the heat lost by convention as the air can not be replaced by cooler air

Question 28

Cats (including the big cats) can only sweat from the skin surface of their paws and nose. What other method might a cheetah rely on for transfer of energy to the environment?

Answer 28

• Evaporation from gas exchange surfaces; panting

- Lowering of body hairs to increase heat lost by radiation, conduction and convection

Question 29

Why is heat normally lost to the surroundings?

Answer 29

Because the human body temperature is usually higher than the surroundings

Question 30

What can happen to core body temperature in very cold environments?

Answer 30

-Decrease as the body loses thermal balance due to excessive cooling

Question 31

What happens when core body temperature starts to fall?

Answer 31

• Hypothalamus detects change

- Tries to regulate internal temperature by increasing metabolic rate and slowing energy loss

Question 32

What would be the major route of energy loss for a cross-channel swimmer?

Answer 32

Conduction

Question 33

Swimming the channel means spending between 10-20 hours in water that is usually between 13-16°C. What mechanisms are used to maintain body temperature and enable survival without a wetsuit?

Answer 33

• Shivering increases metabolism which transfers more energy to body cells
• Nerve impulses to the arterioles in the skin cause vasoconstriction which means blood travels further from the skin surface so less energy is lost by radiation, conduction and convection
• Respiration in muscles transfers more energy to body cells