1. Regulating the Internal Environment
Homeostasis is the maintenance of the
body’s multicellular environment with the
body’s external environment or any changes
in activity caused.
The bodies homeostatic response controls water
concentration in the blood, body core temperature,
blood glucose levels and heart rate by a process
called negative feedback control.

2. Receptors and Effectors
Any change to the environment will be detected by receptors found in the sensory organs and glands
Effectors
The receptor sends a message to the effector which alters the bodies response and returns it back to normal. Gland and muscular contraction, hormone and enzyme production are all effector responses.

3. Negative Feedback Control (Fig. 24.1)

4. Control of Heart Rate Although the pacemaker initiates heartbeats,
the rate of heart beating is not fixed and can
be altered as a result of nervous or
hormonal activity.
The autonomic nervous system regulates the
heart, blood vessels, lungs, alimentary canal and
sweat glands. This is when the body work
automatically without the individual having
to think about making the body do certain jobs.

5. Autonomic Nervous System (ANS)

6. Cardio Accelerator Cardio Inhibitor Centre Centre
Medulla of Brain
Cardio Accelerator Cardio Inhibitor
Centre Centre
Sympathetic Parasympathetic
cardiac nerves cardiac nerves
Antagonistic response
Increase in Decrease in
nerve impulses nerve impulses
Increase in heart rate Decrease in heart rate

7. Hormonal Control of Heart Rate
Adrenaline
Adrenaline is produced in
the adrenal glands which
are situated above the
kidneys. The sympathetic
nervous system in a
situation which would
required adrenaline e.g.
fight of flight situation, stimulates
the adrenal glands to release
adrenaline into the blood system.
When it reaches the pacemaker it
increases the heart rate

8. Exercise and Heart Rate
When we exercise the muscle cells which
are working are at a higher metabolic rate
and therefore require a higher levels of
oxygen and glucose. As a consequence
they also produce higher levels of carbon
dioxide. This all needs to be balanced.

9. Distribution of Blood During Exercise
During exercise the heart rate (pulse) increases, the volume of blood
(stoke volume) pumped through the heart in each contraction increases
cardiac output = heart rate X stoke volume
This increase in heart rate and stoke volume increases the rate of
oxygen delivery to working cells and tissues. Not all organs require an
increase in blood during exercise, only the ones which are doing the
extra work:
Increase in blood flow to tissue during exercise would be in the heart
cardiac muscle, skeletal muscle and the skin where excess heat is lost.
To help with this increase arteries and arterioles vasodilate to allow
A larger volume of blood to pass through at a faster rate
Decrease in blood flow to tissue during exercise would be in the kidneys,
stomach, intestines etc.. The function of the kidneys to purify blood and the
function of the intestine to digest and absorb nutrients are processes that can
wait until exercise is complete. This decrease in blood is as a result of
vasoconstriction of the arteries and arterioles carrying blood to these organs.

10. Control of Blood Sugar Levels
Glucose is essential to
all living cells as energy
is released from
Glucose. The liver
stores excess glucose
as glycogen so when it
is needed there is a
reserve.

11. The Pancreas and Sugar Levels
Cells in the pancreas called the
Islets of Langerhans produce
two hormones – insulin and
glucagon which help control blood
glucose levels. These levels are controlled through negative feedback mechanisms.
Insulin
Glucose Glycogen
Stored in liver
Glucagon
Glycogen Glucose

12. Diabetes Diabetes mellitus is a disorder in
people and animals who do not
have or have less functional
insulin secreting cells in the
pancreas. As a result of having
little or no insulin, their blood
glucose levels increase and are
not stored in the liver. This can be
detected in their urine as there is
so much glucose in the blood that
it is not reabsorbed but excreted
in the urine. This used to be a fatal
disease but with controlled
administration of insulin by injection
daily, their glucose levels can be
maintained.

13. Control of Body Temperature
The hypothalamus is the
bodies temperature
monitoring centre. Heat and
cold thermoreceptors in the
skin convey information to
the hypothalamus. A body
core temperature from the
blood and body shell
temperature form the skin
triggers a response to
return the temperature back
to normal .

14. Sweat Glands Skin Arterioles Hair Erector Muscles Skeletal Muscles
Hypothalamus
Hypothalamus
Receiving
Information
Core Blood Skin
Temperature Thermoreceptors
Sweat Glands Skin Arterioles Hair Erector Muscles Skeletal Muscles
Sweating Vasodilatation ‘Goose bumps’ Shivering
Vasoconstriction

15. Temperature Control in Infants
Brown Fat
Babies have a relatively large
surface area to volume ratio and
therefore loose heat more rapidly
than an adult. When a baby is
born its thermoregulation mechanisms are not fully
developed. When it gets cold it
involuntarily responds by
vasoconstriction and brown fat
generates heat as it is supplied
with blood vessels.

16. Preterm babies, infants
Hypothermia
Hypothermia is when
someone's body
temperature is below
what is considered a
normal level.
Preterm babies, infants
and the elderly are at
risk.