Chapter 12 - Homeostasis

Question 1

Define homeostasis.

Answer 1

Homeostasis is the maintenance of a constant internal environment.

Question 2

How does homeostasis help us?

Answer 2

By ensuring a stable internal environment, homeostasis allows an organism to be independent from changes in the external environment.

Question 3

What are 6 internal conditions that should be kept constant?

Answer 3

1) temperature
2) pH
3) water potential (of blood plasma)
4) concentration of metabolic waste
5) blood glucose concentration
6) carbon dioxide concentration

Question 4

Why must body temperature and pH level be kept constant?

Answer 4

Enzymes require an optimum temperature and pH to function properly. Below the optimum temperature, enzymes are inactive. Beyond the optimum temperature, enzymes are denatured. Drastic changes in pH levels in blood affects activity of enzymes and rate of cellular reactions.

Question 5

Define negative feedback.

Answer 5

A set of corrective mechanism triggered due to a change in the internal environment detected by a receptor. It is to bring about the reverse effect of the stimulus to restore normal conditions.

Question 6

Define corrective mechanism.

Answer 6

It consists of processes that brings about the reverse effect of stimulus.

Question 7

Define receptor.

Answer 7

It is an organ or cell that is able to detect stimuli and transmit impulses to the control centre or regulator, triggering an appropriate response to restore internal environment to the norm.

Question 8

What happens when there is a change in environment? (5)

Answer 8

1) stimulus increases/decreases condition above/below normal
2) receptor detects the stimulus
3) self-regulatory corrective mechanism
4) condition decreases, negative feedback sent to receptor
5) condition decreases, back to normal condition

Question 9

What is the cornified layer?

Answer 9

It is a part of the epidermis, which is the outermost surface of the skin. It consists of dead dry cells with keratin deposits that continuously shed from skin surface.

Question 10

What are the 3 layers of the skin? (Outermost to innermost)

Answer 10

Epidermis, dermis, subcutaneous fat

Question 11

What is the granular layer?

Answer 11

It is in the middle of the epidermis. It consists of living cells that move upwards, which eventually become dry and dead to form the cornified layer.

Question 12

What is the Malpighian layer?

Answer 12

It is the innermost layer of the epidermis, which consists of actively dividing cells that contain melanin.

Question 13

What is the upper part of the dermis?

Answer 13

It is directly below the malpighian layer. It is thrown into ridges or papillae.

Question 14

What is the function of the dermis?

Answer 14

Richly supplied with blood capillaries that supply blood to skin.

Question 15

What is vasodilation?

Answer 15

During vasodilation, arterioles dilate, shunt vessels constrict and more blood flows to the blood capillaries in the skin, causing more heat to be lost from skin by radiation, convection and conduction.

Question 16

What is vasoconstriction?

Answer 16

During vasoconstriction, arterioles constrict, shunt vessels dilate,less blood flows to the capillaries in the skin, causing less heat to be lost by radiation, convection, conduction.

Question 17

What is the function of vasodilation and vasoconstriction?

Answer 17

It regulates body temperature.

Question 18

What are 4 roles of the skin?

Answer 18

1) protective outer covering of the body
2) regulator of body temperature
3) excretory organ
4) sense organ

Question 19

Where is hair produced and where is it found?

Answer 19

Produced by the epidermis, they are embedded in the dermis. The Malpighian layer of the epidermis sinks into the dermis, forming a hollow tub called the hair follicle. Each hair grows inside the hair follicle.

Question 20

What is the hair papilla?

Answer 20

It is a mass of tissue at the base of the hair follicle, which contains blood capillaries and nerves.

Question 21

What is the function of hair papilla?

Answer 21

It forms hair. It is covered with epidermal cells that constantly divide, pushing new cells outwards. The cells that are pushed outwards gradually die and harden to form the hair.

Question 22

What is the hair erector muscle and what is its function?

Answer 22

It is a muscle attached to the hair follicles. When it contracts, the hairs “stand on their ends” and skin around the hair is raised, producing “goose pimples”. This traps a layer of air, which is a poor conductor of heat, keeping the human warm.

Question 23

What are sebaceous glands and what is its function?

Answer 23

They open into each hair follicle. They secrete sebum which lubricates the hair, keeps the skin soft and prevents microbial growth.

Question 24

What is the sweat gland?

Answer 24

It is a coiled tube formed by the downgrowth of the epidermis. It forms a tight knot in the dermis, richly surrounded by blood capillaries.

Question 25

What is the function of the sweat gland?

Answer 25

It secretes sweat which flows through the sweat duct and sweat pore to the skin surface. It is a mean to regulate body temperature.

Question 26

Why is the skin considered as an excretory organ?

Answer 26

The sweat is mainly made up of dissolved salt, water and small amounts of urea. Since it contains small amounts of metabolic waste products, like urea, it is considered an excretory organ.

Question 27

What is in the subcutaneous fat layer and what is its function?

Answer 27

It is beneath the epidermis. It contains several layers of adipose cells where fat is stored. The fat in these cells serves as an insulating layer, reducing heat loss.

Question 28

What are the 5 parts of the skin that are involved in temperature regulation.

Answer 28

1) blood vessels
2) hairs
3) sweat glands
4) thermoreceptors
5) subcutaneous fat

Question 29

How does the body gain heat? (3)

Answer 29

1) metabolic activities in body release heat
2) vigorous muscular exercise
3) being in warm environments/intake of warm foods

Question 30

How does the body lose heat?(4)

Answer 30

1) through the skin surface by conduction (limited), convection, radiation
2) evaporation of water in sweat from skin surface
3) faeces and urine
4) exhaled air from lungs

Question 31

What happens when human body temperature rises? (4)

Answer 31

The hypothalamus is stimulated, then send nerve impulses to bring about following changes:

1) during vasodilation, dilation of arterioles in skin and constriction of shunt vessels allow more blood to flow through blood capillaries in the skin. This allows more heat to be lost through skin surface by radiation, convection, conduction.
2) sweat glands become more active, resulting in increased production of sweat. As more water in the sweat evaporates from the surface of the skin, more LATENT heat of vaporisation is lost from the body. It decreases the blood temperature back to normal and thus the body temperature.
3) decreases metabolic rate reduces the amount of heat released within the body.
4) hair erector muscles relax. Hair lies flat, allowing air to circulate over skin, removing heat.

Question 32

What happens when human body temperature fall? (5)

Answer 32

The hypothalamus is stimulated, then it generates nerve impulses to be sent, bringing about following changes:

1) during vasoconstriction, the constriction of skin arterioles and dilation of shunt vessels allows less blood to flow through blood capillaries in the skin. This reduces the heat loss by convection, conduction and radiation.
2) sweat glands become less active, resulting in decreased production of sweat. As less water in the sweat evaporates from the skin surface, less LATENT heat of vaporisation is lost from the body. It increases the blood temperature back to normal and thus the body temperature.
3) increased metabolic rate increases amount of heat released within body
4) hair erector muscles contract, hair “stand up”, form “goose bumps” and trap an insulating layer of warm air over the skin.
5) when above reactions are insufficient to prevent drop of body temperature, “shivering”, a reflex contraction of the body muscles occurs. The spasmodic contraction of skeletal muscles increase rate of respiration, which releases more heat to increase blood temperature