6. homeostasis v1.0

8/12/2019 6. Homeostasis v1.0

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A day at the sauna

How does the body react to change?


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Saving energy?

Sayid has decided to save energy by staying in bed all day.

Surprisingly, the answer is only about 30%.

How much of his energy do you think this will save?

The other 70% keeps his body temperature at 37C, and

the solutions around his cells at just the right concentration.


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What is homeostasis?

The body uses so much energy, even during sleep, because

it must maintain a constant internal environment.

This process of keeping things

the same is called homeostasis.

A series of automatic control

systems ensures that the body

maintains a constant

temperature, and steady levels

of water, ions and blood sugar.

Homeostasis allows the bodys

cells to work at their optimum.


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Keeping comfortable


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The organs of homeostasis


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Why control temperature?

Environmental temperature is

constantly changing. One minute it

can be very hot, the next very cold.

Even slight changes in body temperature can have a life-threatening effect on health. If body temperature falls too

low, reactions become too slow for cells to survive: too high,

and the bodys enzymes are at risk of denaturing.

Despite this, the body must be kept

at a constant temperature of 37C.

Why?

This is the optimum temperature for

the bodys enzymes.



What is core body temperature?

The vital organs located deep within the body, such as the

heart, liver and kidneys, are maintained at 37C. This is

the core body temperature.

Skin temperature at

the body's extremities,

such as the fingers

and toes, is usually

lower than the core

body temperature.

On a warm day, skin temperature may be just 1C lower

than the core body temperature, but on a very cold day it

could be up to 9C lower.



Finding the right balance

Core temperature is maintained by balancing heat gain

and heat loss.

How can heat be gained?

How can heat be lost?

movementand exercise

shivering

vasoconstriction

wearing extra clothing.

sweating

vasodilation

removing extra clothing.



Too hotor too cold?



Finding the right balance



How is temperature controlled?

Body temperature is monitored and controlled by temperature

receptors in the skin and brain.

hypothalamus

These receptors detect changes

in the temperature of blood

flowing through those areas.

The thermoregulatory centre in the

brain is called the hypothalamus.

If body temperature deviates from 37C, the hypothalamus

and skin receptors send out electrical signals that trigger

actions or behaviours that increase or decrease heat loss.



Whats in skin?



Why do we shiver?

When core body temperature drops, muscles begin to

twitch. This rapid and contraction and relaxation of the

muscles is called shivering.

Shivering generates heat, which raises

body temperature.

Goose bumps involuntarily appear when

a person becomes cold. Goosebumps

are caused by the tiny muscles at the

base of body hairs pulling the hairs erect.

The upright hairs trap an insulating layer

of air, which helps reduce heat loss.



Vasoconstriction and warming up

Why do people go pale when they are cold?

Vasoconstriction is

caused by contraction

of the muscular wall of

the blood vessels.

When core body temperature falls, blood vessels in theskin get narrower. This is called vasoconstriction.

This reduces the volume

of blood flowing near theskin surface, and

reduces the amount of

heat lost from the body.



Vasodilation and cooling down

Why do people turn red when they are hot?

Additional cooling occurs

with the production of

sweat from sweat glands.

Vasodilation allows a larger volume of blood to flow near

the skin surface, transferring heat to the environment.

This cools the body down.

When core body temperature rises, blood vessels in theskin get wider. This is called vasodilation.

As the sweat evaporates

it transfers heat away

from the body.



Responding to change



Temperature control in newborns

Sayid has a baby sister. Samira was born premature and is

too young to control her temperature. An incubator helps to

control her temperature, using negative feedback.

The air around Samira is kept at 32C. Why is it not keep

at 37C?



How do incubators work?


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Thermoregulation: true or false?



Why is water important?

The human body is about 60-70% water.

Water is produced by the body during respiration, andabsorbed from food and drink.

Water is lost from the body in exhaled air, sweat, urine

and faeces.

How is water gained and lost?

Water molecules and ions constantlymove in and out of cells, and are essential

for all life processes.

Dehydration(loss of too much waterfrom the body) damages cells.



Dehydration and its causes

Just a 1% decrease in body weight due to water loss is

enough to cause mild dehydration.

Mild dehydration can cause dizziness, a dry mouth and

concentrated urine. Severe dehydration can cause death.

What causes dehydration?

heavy sweating

low water intake

eating salty food

breathing dry air

caffeine and alcohol

diarrhoea.

C lli l l



Controlling water levels

H d th kid k?


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How do the kidneys work?


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Wh t i bl d l ?


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What is blood glucose?

Glucoseis a type of sugar used

by the body to provide energy.

Sometimes there is too much

glucose in the blood, and

sometimes there is not enough.

How does the body regulate blood glucose levels?

Eatingcauses blood glucose levels to rise.

Vigorous exercisecauses blood glucose levels to fall.

What affects the level of blood

glucose?

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Controlling blood glucose

Between meals, blood glucose levels are topped up from

stored deposits in the liver and muscles.

After a meal, blood glucose rises but quickly returns to

normal. Where does the excess go? Why not leave it in

the blood?

Excess glucose makes the blood plasma and

tissue fluid around cells too concentrated.

This can severely damage cells, for example,

causing crenationin red blood cells.

However, low blood sugar levels can be

equally as dangerous, as it can make cells

swell up and burst. This is called lysis.

Th d bl d l


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The pancreas and blood glucose

Blood glucose levels are

monitored and controlled

by the pancreas.

The pancreas produces

and releases different

hormones depending onthe blood glucose level.

pancreas

Insulinis released when blood glucose levels are

highthe liver stores excess glucose as glycogen.

Glucagonis released when blood glucose levels are

lowthe liver converts stored glycogen into glucose

and releases it into the blood.

M i t i i f l l l


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Maintaining safe glucose levels

M i t i i f l l l


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Maintaining safe glucose levels


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Glossary (1/3)


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Glossary (1/3)

ADHThe hormone released from the pituitary gland thatacts on kidneys and blood vessels to maintain the bodys

water balance.

dehydrationThe loss of too much water from the body.

homeostasisThe constant regulation of the body'sinternal environment.

hyperthermiaDangerously high body temperature.

hypothalamusThe part of the brain that helps to

regulate the body's internal environment.

hypothermiaDangerously low body temperature.

glucoseThe main source of energy for the body.

Glossary (2/3)


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Glossary (2/3)

glucoregulationThe homeostatic control of the bodysblood sugar level.

glycogenA storage form of glucose, found in the liverand muscles.

insulinA hormone involved in the control of blood sugar,

and which is reduced or absent in people with diabetes.

kidneyThe bean-shaped organ that filters the blood andproduces urine.

negative feedbackA stabilizing mechanism thatslowsdown or reverses a stimulus.

Glossary (3/3)


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Glossary (3/3)

osmoregulationThe homeostatic control of the bodyswater and ion balance.

pancreasThe organ that secretes the hormone insulin.

thermoregulationThe homeostatic control of thebodys temperature.

vasoconstrictionThe narrowing of the blood vesselsin the skin in order to reduce heat loss.

vasodilationThe widening of the blood vessels in the

skin in order to increase heat loss.

Anagrams


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Anagrams

Multiple choice quiz


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Multiple-choice quiz

6. homeostasis v1.0

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