Homeostasis - 15.1-15.3

Question 1

Define homeostasis?

Answer 1

A dynamic equilibrium within the body that experiences small fluctuations over a narrow range of conditions.

Question 2

What does a receptor do?

Answer 2

Sensory receptors detect changes in the internal and external environment and can lead to changes being arranged by the body’s feedback system.

Question 3

What is an effector?

Answer 3

Muscles or glands that react to the motor stimulus and being about a change in response to a stimulus

Question 4

Describe a negative feedback system?

Answer 4

A small change in one direction is detected by sensory receptors, as a result effectors work to reverse the change and restore conditions to their base level. They work to reverse the initial stimulus.

Question 5

Describe a positive feedback system?

Answer 5

A change In The internal environment is detected by sensory receptors and effectors are stimulated to reinforce that change and increase the response. Eg the blood clotting cascade or during childbirth.

Question 6

Name some receptor cells?

Answer 6

Chemoreceptors 
Baroreceptors 
Photoreceptors 
Mechanoreceptors
Thermoreceptors
Osmoreceptors

Question 7

What are some possible causes of gains in heat in an organism?

Answer 7

Waste heat from cell respiration

Conduction from surroundings

Convection from surroundings

Radiation from surroundings

Question 8

Name some causes of loss of heat in organisms?

Answer 8

Evaporation of water
Conduction to surroundings
Convection to surroundings
Radiation to surroundings

Question 9

What are ectotherms?

Answer 9

Use their surroundings to heat their bodies, core body temp heavily influenced by their environment.
Include all invertebrate animals, fish, amphibians, and reptiles.

Many ectothermic living in water do not need to thermoregulate, due to the high heat capacity of water meaning the temp doesn’t change much.

Ectotherms that live on land have a much bigger problem as there is no constant to the environment on land, very subject to changes.

Question 10

What is an endotherm?

Answer 10

Organisms that rely on their internal metabolic processes to warm up and maintain a stable core temperature regardless of the environment.
They have adaptations which enable them to maintain body temp. And take advantage of warm environment.

Keeping warm in the cold and keeping cool in the heat are active processes.

Metabolic rate in endotherms is 5x higher than in ectotherms

Question 11

Behavioural responses of ectotherms?

Answer 11

Basking in the sun to warm up

Maximising sunlight by orienting towards the sun

Pressing their body to the ground and ectothermic body reactions

Opposite of these to cool down.

Question 12

Physiological responses to warming?

Answer 12

Colder climates animals tend to be darker in colour to absorb more radiation.

Alteration of heart rate to increase or decrease their metabolic rate.

Ectotherms eat less food than endotherms as they use less energy regulating their temp and where they live food can be in short supply.

Question 13

Describe some adaptations of the Namaqua chameleon?

Answer 13

Black in the morning

Orientates body sideways to the sun

Increases heart rate early in morning when basking in sun.

Inflates it’s body early in morning

Presses body against sand in the morning

During the day it deflates its body

Becomes Pale grey in day

Heart rate slows down in day

Pants in the middle of the day to increase evaporation

Question 14

How are temperature changes detected?

Answer 14

Homeostatic receptors detect these changes. Temperature receptors kiln the hypothalamus detect the temperature of the blood deep in the body.

Temp of skin is likely to be changed by external environment / conditions

Question 15

What do endotherms do to keep them warm?

Answer 15

Use their internal exothermic metabolic activities to keep them warm and energy requiring physiological responses to help them to cool down.
There are also passive ways of heating up and cooling down their bodies.

Question 16

What methods to endotherms use to cool down?

Answer 16

Vasodilation

Increased sweating

Reducing the insulating effect of hair or feathers.

Question 17

How does vasodilation cool the body down?

Answer 17

Arterioles near skin surface dilate when the temperature rises.
The vessels between arterioles and venues constrict forcing blood through capillary networks close to the surface of skin.
The skin flushes red, and this increases radiation, therefore cooling the skin.

Cooling can also occur if skin is pressed against cool surfaces via conduction.

Question 18

How does increased sweating cool the body down?

Answer 18

Sweat spreads out across surface of the skin, as sweat evaporates off the surface of the skin, heat is lost, thus cooling the blood below the surface.
Where this cannot happen easily ( eg in furry animals) animals will often pant and when they get hot, losing heat as water evaporates

Question 19

How does reducing the insulating effect of hair or feathers cool down mammals?

Answer 19

Erector pilli muscles in the skin relax, hair or feathers lie flat to the skin, which avoids trapping an insulating layer of air - has little effect in humans.

Endotherms that live in hot environments also have anatomical adaptations to adapt to their environment. These minimise the effect of high temperatures and maximise the ability of the animal to cool down through the surface area of the body. These include a relatively large SA:V ratio to maximise cooling (large ears and wrinkly skin) and pale fur or feathers to reflect radiation.

Question 20

What ways can the body control warming up?

Answer 20

Vasoconstriction

Decreased sweating

Raising body hair or feathers

Shivering

Question 21

How does vasoconstriction heat the body?

Answer 21

Arterioles near the surface of the skin constrict, ateriovenous shunt vessels dilate so very little blood flows through the capillary network close to the surface of the skin. If skin looks pale there’s very little radiation, and warm blood is kept well below the surface.

Question 22

How does decreases sweating warm you up?

Answer 22

Reducing sweating reduces the cooling by the evaporation of water from the surface of the skin, although some evaporation from the Lungs still continues.

Question 23

How does raising body hairs or feathers warm the body up?

Answer 23

Erector pilli muscles in the skin contract, pulling the hair or feathers of the animal erect. This traps a layer of air and reduces cooling from the skin. The effect can be quite dramatic and is a very effective way to reduce heat loss to the environment.

Question 24

How does shivering warm the body up?

Answer 24

Rapid involuntary contraction and relaxation of large voluntary muscles in the body. The metabolic heat from exothermic reactions warm up the body instead of moving it - an effective way of increasing core temp

Question 25

Name some examples of anatomical adaptations in endotherms in cold environments?

Answer 25

Small SA:V (small ears etc)
Blubber
Hibernation

Question 26

What activates the heat loss centre?

Answer 26

When the temperature of blood flowing through the hypothalamus increases. It sends impulses through the autonomic motor neurone to effectors in the skin and muscles, triggering responses that act to reduce core temperature.

Question 27

When is the heat gain centre activated?

Answer 27

When the temperature of the blood flowing through the hypothalamus decreases . It sends impulses through the autonomic nervous system to effectors in the skin and the muscles, triggering responses that act to raise the core temp.