How Homeostatic Mechanisms Operate in the Maintenance of

UNIT 5 -TOPIC 3

How Homeostatic Mechanisms Operate in the Maintenance of an Internal Environment.

Learning Outcome:

By the end of this topic you will:

Understand how Homeostatic Mechanisms Operate in the Maintenance of an Internal Environment.

Topic 3

There is a glossary at

the back of your

booklet for keywords

and their meanings, fill

it in as we go along,

adding any more that

are new to you.

This includes:1. Homeostasis2. Homeostatic Mechanisms for Regulation of Heart Rate3. Homeostatic Mechanisms for Regulation of Breathing

Rate4. Homeostatic Mechanism for Regulation of Body

Temperature5. Homeostatic Mechanisms for Regulation of Blood Glucose

Levels

Assessment Objectives:

By the end of this topic you will be able to:

Explain the concept of homeostasis. (P5)

Discuss the probable homeostatic responses to

changes in the internal environment during

exercise. (M1)

Evaluate the importance of homeostasis in

maintaining the healthy functioning of the body.

(D1)

TASK 3

What is homeostasis?


Homeostasis is the mechanism inside our bodies that regulates and

maintains a stable and constant internal environment.

In other words it keeps our body working within a delicate balance.


Homeostasis ensures that cells of the body are in

the environment that meets their needs and

allows them to function normally despite

external changes.

This does not mean that there are no changes.

On the contrary, there are continuous

fluctuations brought about by variations in

internal and external conditions, such as

changes in temperature, pH and water

potential.


These changes, however, occur

around a set point.

Homeostasis is the ability to return to

that set point and so maintain

organisms in a balanced

equilibrium.

Activity

What body functions do you think homeostasis is responsible for?

Make a list using the spider diagram

There are 6, so try and think of as many as you can.

Homeostasis is responsible for…

Body temperature

Heart rate

Blood pressure

Breathing rate

Water levels

Glucose levels

Waste products must be removed from the body in order to

main a stable body environment

If they are not removed they can interfere with chemical

reactions and damage the body.

Waste products include Urea and Carbon dioxide

Waste Products

Homeostasis clip

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/homeo/h

omeosts.shtml

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/homeo/homeosts.shtml

NEGATIVE FEEDBACK SYSTEM

Homeostasis is described as a negative feedback system

This means that corrective action is taken to maintain the

constant environment

So when an important variable like the pH of blood and tissue

fluid, deviates from the accepted range of limits, it triggers

responses that return the variable to within normal range.

Negative feedback system

What features should a control

mechanism have?

Like a Thermostat

Your body works in a similar way to how your central heating system

works to control the temperature in your house.

The system is controlled by a thermostat, which regulates the

temperature and is similar to the Hypothalamus in the brain.

The Hypothalamus monitors and controls our internal environment.

How do control mechanisms work?

The control of any self-regulating system involves a series of stages that feature:

1. The set point, which is the desired level, or norm, at which the system operates. This monitored by a …

2. Receptor, which detects any deviation from the set point and informs the …

3. Controller, which coordinates information from various receptors and sends

instructions to an appropriate …

4. Effector, which brings about the changes needed to return the system to the set point. This return to normality creates a …

5. Feedback loop, which informs the receptor of the changes to the system brought about by the effector.

How do control mechanisms work?

How are control mechanisms

coordinated?

Systems normally have many

receptors and effectors.

It is important to ensure that the

information provided by receptors is

analysed by the control centre

before action is taken.

Receiving information from a

number of sources allows a better

degree of control.

How are control mechanisms

coordinated?

For example, temperature receptors in the skin may signal that the skin itself is

cold and that the body temperature should be raised.

However, information from the temperature centre in the brain may indicate

that blood temperature is already above normal. This situation could arise

during strenuous exercise when blood temperature rises but sweating cools the

skin.

By analysing the information from all the detectors, the brain can decide the

best course of action – in this case not to raise the body temperature further.

In the same way, the control centre must coordinate the action of the effectors

so that they operate harmoniously. For example, sweating would be less

effective in cooling the body if it were not accompanied by vasodilation.

Homeostatic Mechanisms for

Regulation of Heart Rate

What is the autonomic nervous system?

The autonomic nervous system controls the

involuntary (subconscious) activities of

internal muscles and glands.

It has two divisions:

1. The sympathetic nervous system

2. The parasympathetic nervous system

Which of part of the nervous system (somatic

or autonomic) would be responsible for each

response in the following examples:

A tiger walks into class- Your heart rate increases

You decide to move your arm and fingers to pick up your pen- You pick up the pen

Whilst walking barefoot you stand on a pin- You quickly move your foot away (withdrawal reflex)

Stimulus –response—integration—effect---feedback—response slows down

What causes the heart to beat?

How does the autonomic nervous system control heart rate?

Changes to the heart rate are controlled by a region

of the brain called the medulla oblongata.

How does the autonomic nervous

system control heart rate?

The medulla oblongata has two centres:

1. A centre that increases heart rate, which is linked to the sinoatrial node by the

sympathetic nervous system.

2. A centre that decreases heart rate, which is linked to the sinoatrial node by the

parasympathetic nervous system.

What changes occur to the blood

during exercise?

How does the autonomic nervous

system control heart rate?

Which of the two centres is stimulated

depends upon the information they receive

from two types of receptor:

1. Chemical (pH) changes in the blood

2. Pressure changes in the blood.

What role do chemical receptors play

in the process?

Chemoreceptors are found in the wall

of the carotid arteries (the arteries that

serve the brain) and aortic bodies.

They are sensitive to changes in the pH

of the blood that result from changes in carbon dioxide concentration.

What role do chemical receptors play

in the process?

http://highered.mcgraw-

hill.com/sites/0072943696/student_view0/chapter13/animation__chemoreceptor_reflex_control_of_

blood_pressure.html

What role do pressure receptors play in the process?

Pressure receptors occur within the walls of the carotid arteries and the aorta.

When blood pressure is higher than normal they transmit a nervous impulse to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which decreases the rate at which the heart beats.

When blood pressure is lower than normal they transmit a nervous impulse to the centre in the medulla oblongata that increases heart rate. This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heart beats.

What role do pressure receptors play in the process?

http://highered.mcgraw-

hill.com/sites/0072943696/student_view0/chapter13/animation__baroreceptor_reflex_control_of_blood_pr

essure.html

3. Homeostatic Mechanisms for

Regulation of Breathing Rate

How is ventilation controlled in

humans?

Ventilation of the respiratory system in humans is primarily controlled by the breathing centre in a

region of the hindbrain called the medulla oblongata.

The ventral portion of this centre controls inspiratory movements and is called the inspiratory

centre; the remainder controls breathing out and is called the expiratory centre.

How is ventilation controlled in

humans?

As the lungs expand during inspiration, stretch receptors in their walls are stimulated

and impulses pass along the vagus nerve to the expiratory centre in the medulla.

This automatically ‘switches off’ the inspiratory centre, the muscles relax and

expiration takes place.

The stretch receptors are no longer stimulated, the expiratory centre is ‘switched off’ and the inspiratory centre ‘switched on’. Inspiration takes place again.

How is ventilation controlled in humans?

Control also relies on

chemoreceptors in the

carotid and aortic bodies

of the blood system.

These are sensitive to the

minute changes in the concentration of carbon dioxide in the blood.

How is ventilation rate increased in humans?

When the carbon dioxide level rises, increased ventilation of the respiratory

surfaces is required.

Nerve impulses from the chemoreceptors stimulate the inspiratory centre in the

medulla.

Nerve impulses pass along the phrenic and thoracic nerves to the diaphragm and intercostal muscles.

Their increased rate of contraction causes faster inspiration.


Regulation of Body Temperature

Activity

What actions do we take in order to either warm ourselves up or cool ourselves

down?

How is body temperature

regulated in humans?

Within the hypothalamus there is a thermoregulatory centre

consisting of two parts:

A heat gain centre, which is activated by a fall in blood

temperature. This controls the mechanisms that increase body

temperature.

A heat loss centre, which is activated by a rise in blood

temperature. This controls the mechanisms that decrease body

temperature.



The hypothalamus monitors the temperature of the blood passing

through it.

In addition, the thermoreceptors in the skin measure skin temperature.

These thermoreceptors send impulses along the autonomic nervous

system to the hypothalamus. They provide information on the

environmental temperature and so give advanced warning of

potential changes in core body temperature. The animal can therefore

take measures to conserve or lose heat as appropriate, before the core

temperature is affected.



The two sets of thermoreceptors (in the

hypothalamus and the skin) interact to

control temperature.

Of the two, it is the core temperature,

measured in the blood passing through

the hypothalamus, which is most

important.

Why do organisms regulate their body

temperature?

If an organism’s body temperature is too low, the rate at which enzyme-controlled reactions take place may be too slow for the organism to function properly.

Equally, if the body temperature is too high, enzymes may be denatured and the organism may cease to function altogether.

Therefore, in order to survive, many animals need to regulate their body temperature – a process called thermoregulation.

How do humans lose heat in

response to a warm environment?

Rapid responses that enable heat to be lost when the

environmental temperature is high include:

Vasodilation

Increased sweating

Lowering of body hair



Vasodilation. The diameter

of the arterioles near the

surface of the skin become

larger. This allows warm

blood to pass close to the

skin surface through the

capillaries. The heat from this

blood is then radiated away

from the body.



Increased sweating. To evaporate water from the skin surface requires energy in

the form of heat. In relatively hairless mammals, such as humans, sweating is a

highly effective means of losing heat.

Lowering of body hair. The hair erector muscles in the skin relax and the elasticity

of the skin causes them to flatten against the body. This reduces the thickness of the insulating layer and allows more heat to be lost to the environment when the

internal temperature is higher than the external temperature.

body temperature normal

hair lies flat on the skin

the muscle is relaxed

body temperature falls

hair stands up and a

goose bump appears

the muscle contracts



Regulation of core body temperature in humans is an example of

homeostasis.

In this case, the stimulus (a change in body temperature) is detected

by receptors (thermoreceptors), which pass the information to a

coordinator (the hypothalamus) in the brain, which then causes an

effector (the skin) to produce the appropriate response (an increase or

decrease in core temperature).


Regulation of Blood Glucose Levels

Why do we need to regulate

blood glucose levels?

It is essential that the blood of mammals contains a relatively constant level of glucose for respiration.

If the level falls to low, cells will be deprived of energy and die – brain cells are especially sensitive in this respect because they can only respire glucose.

If the level rises too high, it lowers the water potential of the blood and creates osmotic problems that can cause dehydration and be equally as dangerous.

What is the role of the pancreas in

regulating blood glucose?

The pancreas is a large, pale-coloured gland that is situated in the upper abdomen, behind the stomach.

It produces enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose.

What is the role of the pancreas in


When examined microscopically, the pancreas is made up of largely of the cells that produce its digestive enzymes.

Scattered throughout these cells are groups of hormone producing cells known as islets of Langerhans.

The cells of the islets of Langerhans are of two types: α cells, which are the larger and produce the

hormone glucagon

β cells, which are smaller and producer the hormone insulin.

What are the role of glucagon in


The α cells of the islets of Lanagerhans detect a fall in blood glucose and respond by secreting the hormone glucagon directly into the blood plasma.

Only the cells of the liver have receptors that bind to glucagon so only liver cells respond.

They do this by:

Activating an enzyme that converts glycogen to glucose

Increasing the conversion of amino acids and glycerol into glucose (=gluconeogenesis).

The overall effect is therefore to increase the amount of glucose in the blood and return it to normal level. This raising of the blood glucose level causes the α cells to reduce the secretion of glucagon (= negative feedback).

What is the role of glucagon in


What is the role of adrenaline in


At times of excitement or stress, adrenaline is produced by

the adrenal glands that lie above the kidneys.

Adrenaline raises the blood glucose level by:

Activating an enzyme that causes the breakdown of glycogen to

glucose in the liver

Inactivating an enzyme that synthesises glycogen from glucose.

Why is homeostasis important?

Look at the

following slides and

discuss why the

people died?

Titanic – 1,502 died – WHY?

It was 2:20 am on Monday 15th April 1912. The Titanic had collided with an iceberg at 11:40 pm on 14th April and had floundered 3.5 hours later. About 650 passengers were lowered in lifeboats capable of holding 1178; the remaining passengers entered the sea as the Titanic sank. Hundreds of people thrashed about in water that was less than -2 degrees, well below freezing point. It was 4:10am before another ship arrived to collect the survivors. Only 705 of the 2207 survived - 1502 died.

Many of the passengers had life jackets and there was a lot of debris to hang onto. It was a calm and still night. Why did they die?

People die on underground trains all over the

world during the hot summer months – WHY?

An elderly couple died in bed after forgetting to switch their gas

hob off in the kitchen. No fire broke out, there was no evidence

of fire damage. Just two dead bodies ........ WHY?

After the London Flora Marathon.

Why did this man collapse?

Why is this tri-athlete more likely to get

hyperthermia when wet?

Four asylum-seekers die in a tragedy. Police have discovered the bodies of four suspected asylum-seekers in a container. The four, all young men are believed to be have been Romanian. The bodies were found in a container load of tiles bound for the UK. The grim discovery was made when police noticed seals had been broken on the container and investigated. WHY did they die?

What is the importance of

homeostasis?

Homeostasis is essential for the proper functioning of organisms for the following reasons:

1. The enzymes that control the biochemical reactions within cells, and other proteins, such as channel proteins, are sensitive to changes in pH and temperature. Any change to these factors reduces the efficiency of enzymes or may even prevent them working altogether, for example, by denaturing them. Maintaining a constant internal environment means that reactions take place at a constant and predictable rate.


homeostasis?

Homeostasis is essential for the proper functioning of organisms for the following reasons:

2. Changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand (even to bursting point) as a result of water leaving or entering by osmosis. In both instances the cells cannot operate normally. The maintenance of a constant blood glucose concentration is essential in ensuring a constant water potential. A constant blood glucose concentration also ensures a reliable source of glucose for respiration by cells.


homeostasis?

Homeostasis is essential for the proper functioning of organisms for the following reasons:3. Organisms with the ability to maintain a constant internal

environment are more independent of the external environment. They have a wider geographical range and therefore have a greater chance of finding food, shelter, etc. Mammals for example, with their ability to maintain a constant temperature, are found in most habitats, ranging from hot arid deserts to cold, frozen polar regions.

Factor Controlled by Homeostasis

Consequence if factor falls too low

Consequence if factor increases too

high

Temperature Hypothermia Hyperthermia

Blood Glucose Concentration

Hypoglycaemia Hyperglycemia

Respiratory GasesHypoventilation Hyperventilation

Blood Pressure Hypotension Hypertension

ASSESSMENT:

You should complete this assessment by yourself and are not allowed to ask for help. You can use your workbook and any other research you can find. Please remember to reference any books or websites that you have used.

Explain the concept of homeostasis. (P5)

Discuss the probable homeostatic responses to changes in the internal environment during exercise. (M1)

Evaluate the importance of homeostasis in maintaining the healthy functioning of the body. (D1)

You should present your work in the form of a essay, include pictures and diagrams to illustrate the points you are making.

TASK 2

Documents

How Homeostatic Mechanisms Operate in the Maintenance of