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IBDP Biology -Temperature Regulation

Chapter 6.6 - Hormones, Homeostasis and Reproduction

· Biology,Homeostasis,hypothalamus,thermoregulation,IBDP BIOLOGY

Temperature Regulation

The hypothalamus controls body temperature in mammals. 

The hypothalamus receives information about body temperature from:

  • Temperature receptors 
  • in the skin
  •  which detect changes on skin temperature and therefore indirectly detect environmental temperature.
  • Receptors in the hypothalamus itself detect changes 

in the blood flowing through it. This reflects the changes in the core body temperature.

Hypothalamus

  • In 

IBDP Biology, control of blood glucose is also regulated by homeostasis.

  • The hypothalamus acts as a 

thermostat. It monitors body temperature and compares the actual temperature against a preset value. (37* in humans). Any significant deviation from this is detected and appropriate responses are initiated. 

  • The 

hypothalamus in the brain is the central control for the body temperature

  • this region of the brain receives a constant input of sensory information about the temperature of the blood and temperature of the surroundings
  • it has 
  • thermoreceptor cells
  •  that continually monitor temperature of blood flowing through it
  • the temperature it monitors is the 
  • core temperature - 

the temperature inside the body that remains very close to the set point (37 degrees C in humans)

  • this temperature fluctuates but is kept within narrow limits by the hypothalamus
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When body temperature is lower than normal

Effector:

1. Vasoconstriction

This conserves heat in the body.

  • Arterioles constricted
  • Shunt vein dilated
  • Little heat radiated

- This means that the majority of blood passes though the shunt vein, close to the fat tissue. This is because the arterioles are constricted so little blood can enter the capillaries near the skin surface. This conserves heat in the body due to little radiation of heat from blood.

2. Shiver

- The in voluntary contraction of skeletal muscles generates heat which is absorbed by the blood and carried around the rest of the body

3. Hairs stand on end

-Muscles at the base of hairs in skin contract to increase the depth of fur so trapping air close to skin. Air is a poor conductor of heat and therefore a good insulator

4. Less sweat

-Reduces the loss of heat by evaporation from the skin surface

5. Increased metabolism

-Increase secretion of adrenaline from the adrenal gland increases the rate of heat production in the liver

-Thyroxine increases metabolic rate, which increases heat production especially in the liver. When temperatures drop, the hypothalamus responds by increasing the release of TSH by the anterior pituitary gland so more thyroxine is released from the thyroid gland.

Behavioral responses:

For example:

  • curling up to reduce surface area exposed to air or huddling together
  • finding source of warmth 
  • putting on warm clothing

When body temperature is higher than normal

1. Vasodilation

This cools the body.

  • Arterioles dilated
  • Shunt vein constricted
  • Much heat radiated

This means that the majority of blood travels through the arterioles to the capillaries near the skin surface, so there is a lot of heat radiated from the skin, cooling the blood and the body.

2. Hairs lie flat

- muscles attached to the hairs relax so they lie flat, reducing layer of insulation

3. More Sweat

-Sweat glands increase the production of sweat which evaporates on skin surface so removing heat from the body

4. Decreased metabolism

- When temperatures start to increase again, the hypothalamus responds by reducing the release of TSH by the anterior pituitary gland so less thyroxine is released from the thyroid gland.

Behavioral responses:

For example:

  • lying down with limbs spread out to increase surface exposed to air
  • turning on fans
  • wearing loose fitting clothing
  • taking cool drinks

This is the end of the topic

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Drafted by Eva (Biology)

Photo References:

  1. http://www.opentextbooks.org.hk/ditatopic/35173

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