Homeostasis and Control of body temperature

what is homoeostasis

process of keeping the internal body environment in a steady state.

reactions that take place in the body are catalysed by what and give an e.g.,

enzymes. For enzymes to work at their optimum rate, the body must keep several factors in a steady state

Name a factor that is tightly maintained by homoeostatic mechanisms

body temperature

what is normal body temperature

37’c even a few degrees change above or blow have serious consequences for body

name examples of states maintained by homoeostasis

body temperature
blood glucose concentration
blood water potential

all mechanisms of homoeostasis rely on

negative feedback

what does negative feedback mean

when there is a change away from the normal set point, corrective processes take place to return the change back to normal

All negative feedback mechanisms involve:

• a receptor which detects the change away from normal

• an input pathway which sends signals to the control centre

• a control centre which coordinates a response to reverse the change

• an output pathway which takes signals from the control centre to the effector

• an effector which carries out a response to reverse the change.

draw the negative feedback loop used to maintain homoeostasis in the human body

see notes

define Thermoregulation

maintenance of normal body temperature – around 37oC

what does a failure of thermoregulation lead to

hypothermia

factors that lead to high body temperature include

heat exhaustion where severe dehydration and reduced sweating

causes the temperature to rise excessively and fluid loss caused by medications such as diuretics.

Prolonged exposure to temperatures above 40oC can result in heat stroke.

Heat stroke disrupts thermoregulation because

compensatory mechanisms such as sweating are lost and the core body temperature soars. This is an extremely serious condition which causes blood pressure to fall and respiratory function to weaken. If the body temperature remains high, neurological damage will occur causing

confusion, delirium and eventually, coma. Urgent steps must be taken to reduce the core body temperature otherwise death will result.

where is body temperature control coordinated by the thermoregulatory centre

in the hypothalamus of the brain

where does the thermoregulatory centre receives input signals from

two sets of receptors which detect changes in temperature. called thermoreceptors.

The hypothalamus itself contains thermoreceptors which monitor

the temperature of the blood as it passes through the brain thus monitoring the body’s core temperature.

Thermoreceptors in the skin monitor

the temperature of peripheral regions of the body

The thermoregulatory centre sends signals to a range of different effectors in response to

increased or decreased temperatures

The heat loss centre of the hypothalamus is stimulated when you

too warm (heat needs to be lost) and the heat gain centre of the hypothalamus is

stimulated when you get too cold (heat needs to be gained)

draw Negative feedback control of body temperature

see notes

what is the first response to a change in temperature is a

voluntary behavioural action.

e.g., of voluntary behavioural action.

If it gets too cold, you

may put on a jumper or move indoors. If it gets too warm, you may take layers of clothing off or move

to the shade. If these corrective mechanisms are not enough, then the thermoregulatory centre will act

to initiate appropriate response

draw Homeostatic control of an increasing body temperature

see notes

Arteries divide into smaller blood vessels called

arterioles

Arterioles contain a layer of smooth muscle which allows the arterioles to

dilate and constrict and therefore alter the diameter of the lumen in order to regulate the flow of blood into capillary beds in the tissues.

what is vasoconstriction. , vasoconstriction occurs meaning that

When this smooth muscle contracts, the lumen of the blood vessel is constricted (the blood vessel narrows) and less blood flows through the body tissues;

When body temperature falls does vasoconstriction still happen

yes meaning less heat is transferred away from the body core and so less heat is lost.

what happens when the body temperature rises with the smooth muscle in the arteriole walls and the vasodilation

When body temperature rises, the opposite occurs. The smooth muscle in the arteriole walls relaxes

and vasodilation occurs. More heat is carried from the core to the surface of the body where it can be

lost to the external environment.

what happens to the sweat glands when the body temperature increases

sweat glands in the skin secrete sweat onto the

skin where it evaporates. The evaporation of water requires a relatively large amount of energy and

so sweating is an effective way of cooling down.

what happens to the erector pili muscles in the skin when the body temperature falls

the hairs that can be found covering the surface of the skin have muscles attached to them. When body temperature falls, signals from the heat gain centre cause

these muscles to contract. This causes the hairs to stand on end, allowing them to trap an

insulating layer of air close to the skin. This is not an effective heat gain mechanism in humans

since much of the body hair has been lost through evolution

what happens to the skeletal muscle when

the heat gain centre of the hypothalamus can send signals to

skeletal muscles to cause them to contract and relax repeatedly. This is shivering. Heat is generated

from the increased rate of respiration needed to supply the ATP for the contractions to take place.

the adrenal gland is responsible for the secretion of the hormone

adrenaline

thyroid gland is responsible for the secretion of the hormone

thyroxine

what happens to the adrenal and thyroid glands

Secretion of both hormones by their respective gland is increased to raise the body’s metabolic rate. This generates heat. When the body temperature decreases the glands stop secreting adrenaline and thyroxine

When the body temperature changes, the hypothalamus works to restore

temperature to normal

what is not able to cope with extreme changes in temperature

homeostatic mechanisms

what if body core temperature falls below 35°C

hypothermia occurs

Hypothermia can be caused by

exposure to a cold environment or from something that causes decreased heat production or increased heat loss such as alcohol intoxication or low blood sugar.

Hypothermia can cause

shivering, drowsiness, unconsciousness and ultimately death if left untreated.

Other cold related conditions that can

occur at the same time as hypothermia include:

• chilblains

• frostbite

what is chilblains

cold causes permanent damage to the small blood vessels in the skin resulting in

redness and itching

what is frostbite

tissue, usually of the extremities including fingers and toes, freezes and is destroyed.

This can result in permanent nerve damage and gangrene. Often amputation of the affected area is

needed to prevent gangrene from spreading which can be fatal.

If body core temperature increases greater than 37.5 – 38.3 °C, what occurs

hyperthermia occurs

Hyperthermia is also known as

heat stoke

when does hyperthermia occur

It occurs when there is an excess production of heat due to exercise, an increase in the temperature of the environment or ineffective heat loss. It occurs when the body is unable to cool down using the normal homeostatic mechanisms.

Symptoms of hyperthermia

sweating, rapid breathing, vomiting, headaches, unconsciousness, organ failure and eventually death if left untreated.

Excess heat can also cause injury to the skin resulting in burns. Depending on the extent of damage,

burns can heal within a few days or weeks or can require amputation or even result in death.