2.10.1 Homeostasis

Question 1

What is Homeostasis

Answer 1

Homeostasis is the control or regulation of the internal conditions of a cell or organism

Question 2

Give 5 examples of internal conditions of a cell or organism

Answer 2

1. Water content (of an individual cell or of the body fluids of an organism)

Question 3

Why is it important for an organism to keep internal conditions within set limits

Answer 3

to ensure they stay healthy and to maintain optimum conditions to allow the organism to function in response to internal and external changes

• If these limits are exceeded, the organism may die

Question 4

What does Homeostasis maintain?

Answer 4

optimal conditions for enzyme action and all cell functions

Question 5

What does homeostasis maintaining optimal conditions ensure

Answer 5

that reactions in body cells can function and therefore the organism as a whole can live

Question 6

Give two examples of homeostasis in humans

Answer 6

1. The control of body temperature

Question 7

What is the core body temperature of humans

Answer 7

humans is kept close to 37°C

Question 8

Why is human temperature so tightly controlled

Answer 8

in core body temperature of more than 2°C can be fatal, such a temperature change would stop essential enzymes from functioning optimally

• For this reason, the human body must be able to make a coordinated response to any rise or fall in body temperature

Question 9

Body temperature is monitored and controlled by what?

Answer 9

the thermoregulatory centre in the base of the brain as blood passes through it

Question 10

What does the thermoregulatory center contain?

Answer 10

receptors that are sensitive to the temperature of the blood

Question 11

What also contains temperature receptors

Answer 11

The skin also contains temperature receptors and sends nervous impulses to the thermoregulatory center

The brain then coordinates a cooling or heating response, depending on what is required

Question 12

(Cooling mechanisms in humans) Describe what Vasodilation of skin capillaries is

Answer 12

1. Heat exchange (both during warming and cooling) occurs at the body’s surface as this is where the blood comes into closest proximity to the environment

Conclusion; This is why pale-skinned people go red when they are hot

Question 13

(Cooling mechanisms in humans) Sweating

Answer 13

1. Sweat is secreted by sweat glands

Question 14

(Cooling mechanisms in humans) Flattening of hairs

Answer 14

1. The hair erector muscles in the skin relax, causing hairs to lie flat

Question 15

What is Shivering?

Answer 15

This is a reflex action in response to a decrease in core body temperature

Muscles contract in a rapid and regular manner

The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature

Question 16

What is an Erection of hairs

Answer 16

The hair erector muscles in the skin contract, causing hairs to stand on end

This forms an insulating layer over the skin’s surface by trapping air between the hairs and stops heat from being lost by radiation

Question 17

What is a Vasoconstriction of skin capillaries

Answer 17

• One way to decrease heat loss is to supply the capillaries in the skin with a smaller volume of blood, minimising the loss of heat to the environment via radiation
• During vasoconstriction, the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries
• Vasoconstriction is not, strictly speaking, a ‘warming’ mechanism as it does not raise the temperature of the blood but instead reduces heat loss from the blood as it flows through the skin

Question 18

If the water content of the blood falls below a certain level, what happens?

Answer 18

1. The blood is too concentrated

Question 19

If the water content of the blood rises above a certain level, what happens?

Answer 19

1. The blood is too dilute