chapter 15 p2

Question 1

Principles of thermoregulation in endotherms:

Answer 1

• Endotherms use their internal exothermic metabolic activities to keep them warm, and energy-requiring physiological responses to help them cool down.
• They also have passive ways of heating up and cooling down, to reduce the energy demands on their bodies.

Question 2

behavioural responses for thermoregulation in endotherms:

Answer 2

• basking in the Sun, pressing themselves to warm surfaces, wallowing in water and mud to cool down, and digging burrows to keep warm or cool.
• Some animals even become dormant through the coldest weather (hibernation) or through the hottest weather (aestivation is a period of prolonged or deep sleep similar to hibernation but occurs in summer or during dry seasons to avoid heat stress rather than cold).
• Humans have additional behavioural adaptations to help control body temperature - clothes are worn to stay warm, houses are built, and then heated up or cooled down to maintain the ideal temperature.

Question 3

however, endotherms still what?

Answer 3

• In spite of these behavioural responses, endotherms mainly rely on physiological adaptations to maintain a stable core body temperature, regardless of the environmental conditions or the amount of exercise being done.
• These adaptations include the peripheral temperature receptors, the thermoregulatory centres of the hypothalamus, the skin, and muscles.

Question 4

Cooling down:

Answer 4

If the core body temperature increases it is important for an animal to cool down.
There are a number of rapid responses to a rise in the core temperature that are common to all endotherms. These include:
Vasodilation:
Increased sweating:
Reducing the insulating effect of hair or feathers:

Question 5

Vasodilation:

Answer 5

• The arterioles near the surface of the skin dilate when the temperature rises.
• The vessels that provide a direct connection between the arterioles and the venules (the arteriovenous shunt vessels) constrict.
• This forces blood through the capillary networks close to the surface of the skin.
• The skin flushes, and cools as a result of increased radiation.
• If the skin is pressed against cool surfaces, then the cooling results from conduction.

Question 6

diagram of vasodilation

Answer 6

Question 7

Increased sweating:

Answer 7

• As the core temperature starts to increase, rates of sweating also increase.
• Sweat spreads out across the surface of the skin.
• In some mammals, including humans and horses, there are sweat glands all over the body.
• As the sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface.
• In some animals, the sweat glands are restricted to the less hairy areas of the body such as the paws.
• These animals often open their mouths and pant when they get hot, again losing heat as the water evaporates.
• In human beings, around 1 dm’ of sweat is lost by evaporation on a normal day.
• If the conditions are very hot and dry or the person is exercising very hard, up to 12 dm of sweat a day can be lost.
• Kangaroos and cats often lick their front legs to keep cool in high temperatures.

Question 8

Reducing the insulating effect of hair or feathers:

Answer 8

• As the body temperature begins to increase, the erector pili muscles (the hair erector muscles) in the skin relax - as a result, the hair or feathers of the animal lie flat to the skin.
• This avoids trapping an insulating layer of air - It has little effect in humans.
• Endotherms that live in hot climates often have anatomical adaptations as well as the behavioural and physiological adaptations already described.
• These minimise the effect of high temperatures and maximise the ability of the animal to cool down through the surface area of the body.
• They include a relatively large surface area: volume (SA:V) ratio to maximise cooling (e.g., include large ears and wrinkly skin), and pale fur or feathers to reflect radiation.

Question 9

Warming up in endotherms

Answer 9

If the core temperature falls it is important for an animal to warm up and prevent further cooling.
There are a number of rapid responses to a fall in the core temperature that are common to all endotherms.
Vasoconstriction:
Decreased sweating:
Raising the body hair or feathers:
Shivering:

Question 10

Vasoconstriction:

Answer 10

The arterioles near the surface of the skin constrict.
The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin.
The skin looks pale, and very little radiation takes place.
The warm blood is kept well below the surface.

Question 11

Vasoconstriction diagram

Answer 11

Question 12

Decreased sweating:

Answer 12

As the core temperature falls, rates of sweating decrease and sweat production will stop entirely.
This greatly reduces cooling by the evaporation of water from the surface of the skin, although some evaporation from the lungs still continues.

Question 13

Raising the body hair or feathers:

Answer 13

As the body temperature falls, the erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect.
This traps an insulating layer of air and so reduces cooling through the skin.
The effect can be quite dramatic and it is a very effective way to reduce heat loss to the environment in many animals.
In humans this has little effect although you can observe the hairs being pulled upright.

Question 14

Shivering:

Answer 14

• As the core temperature falls the body may begin to shiver.
• This is the rapid, involuntary contracting and relaxing of the large voluntary muscles in the body.
• The metabolic heat from the exothermic reactions warm up the body instead of moving it and is an effective way of raising the core temperature.

Question 15

Endotherms living in cold climates often have additional anatomical adaptations to help them keep warm.

Answer 15

• Many have adaptations that minimise their SA: V ratio to reduce cooling (e.g., small ears).
• Another common adaptation is a thick layer of insulating fat underneath the skin, for example, blubber in whales and seals.
• Some animals hibernate - they build up fat stores, build a well-insulated shelter, and lower their metabolic rate so they pass the worst of the cold weather in a deep sleep-like state.

Question 16

example of of endotherms keep warm in cold conditions

Answer 16

• Polar bears demonstrate many of the ways in which endotherms can survive in extremely cold conditions.
• They have small ears and fur on their feet to insulate them from the ice.
  The fur and skin of polar bears work together.
• The hairs are hollow so trap a permanent layer of insulating air.
• The skin underneath is black, so it absorbs warming radiation.
• They have a thick layer of fat under the skin.
• Polar bears are so well insulated that their external surfaces are similar in temperature to the snow and ice on which they live.
• Females dig dens in the snow and remain in them, warm and insulated, for months while they give birth to their cubs, only emerging when the cubs are large enough to survive the cold.
• Polar bears are so well adapted to life in temperatures down to -50°C in the Arctic that they can overheat at temperatures over 10°C.

Question 17

Controlling thermoregulation:

Answer 17

The physiological responses of endotherms to changes in the core temperature are the result of complex homeostatic mechanisms involving negative feedback control from the hypothalamus.
There are two control centres:
The heat loss centre:
The heat gain centre:

Question 18

The heat loss centre:

Answer 18

This is activated when the temperature of the blood flowing through the hypothalamus increases.
It sends impulses through autonomic motor neurones to effectors in the skin and muscles, triggering responses that act to lower the core temperature.

Question 19

The heat gain centre:

Answer 19

This is activated 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 temperature.
The interaction of the sensory receptors, the autonomic nervous system, and the effectors in a sophisticated feedback system enables endotherms to maintain a very stable core body temperature regardless of environmental conditions or activity levels.

Question 20

diagram of Controlling thermoregulation:

Answer 20

Question 21

Many of the chemical reactions of metabolism that take place in

Answer 21

the cells of the body produce waste products that are toxic if they are allowed to build up.

Question 22

Excretion

Answer 22

the removal of the waste products of metabolism from the body.

Question 23

The main metabolic waste products in mammals are:

Answer 23

Carbon dioxide
Bile pigments
Nitrogenous waste products (urea)

Question 24

Carbon dioxide

Answer 24

one of the waste products of cellular respiration which is excreted from the lungs.

Question 25

Bile pigments

Answer 25

formed from the breakdown of haemoglobin from old red blood cells in the liver. They are excreted in the bile from the liver into the small intestine via the gall bladder and bile duct. They colour the faeces.

Question 26

Nitrogenous waste products (urea) -

Answer 26

formed from the breakdown of excess amino acids by the liver. All mammals produce urea as their nitrogenous waste. Fish produce ammonia while birds and insects produce uric acid. Urea is excreted by the kidneys in the urine.

Question 27

The liver: p1

Answer 27

The liver is one of the major body organs involved in homeostasis. It is a reddish-brown organ which makes up about 5% of the total body mass - the largest internal organ of the body. It lies just below the diaphragm and is made up of several lobes. The liver is very fast growing and damaged areas generally regenerate very quickly. The liver has a very rich blood supply - about I dm^3 of blood flows through it every minute.

Question 28

blood flow in The liver

Answer 28

- Oxygenated blood is supplied to the liver by the hepatic artery and removed from the liver and returned to the heart in the hepatic vein. - The liver is also supplied with blood by a second vessel, the hepatic portal vein. - This carries blood loaded with the products of digestion straight from the intestines to the liver and this is the starting point for many metabolic activities of the liver - Up to 75% of the blood flowing through the liver comes via the hepatic portal vein.