Homeostasis refers to the
maintenance of a constant internal
This refers to the conditions within the body of the
In humans, this includes the blood and tissue fluids.
Therefore, homeostasis is the process which ensures
that the composition of bodily fluids is kept within
By ensuring a relatively stable internal environment,
homeostasis allows organisms to be independent from
changes in the external environment (the
surroundings) This external environment is the
environment in which an organism lives.
Homeostasis also involves a
process called negative feedback:
In homeostasis control, your body reacts to bring
about changes that are opposite to the changes that are
If the system (you body) is disturbed, the disturbance
sets in motion, a sequence of events that restores the
body to its original state.
This is called the negative feedback process.
In a negative feedback control loop, there must
A normal condition or set-point to be maintained
A stimulus; which is a change in the internal
A receptor that can detect the stimulus and sends
signals to the control centre
A corrective mechanism, which brings about an
opposite effect of the stimulus
A feedback to the receptor when the set-point is
reached, causing the corrective mechanism to stop.
Temperature homeostasis (Thermoregulation)
basically refers to the regulation of body
temperature, which in turn means the process of
maintaining the temperature of the human body at
a constant, acceptable rate.
The body regulates temperature by balancing the
amount of heat lost and heat produced from and by
Animals that maintain a constant body temperature
are called endotherms.
Animals that have a variable body temperature are
Endotherms: Normally maintains their body
temperature at 35-40 degrees, and hence known as
warm-blooded creatures (e.g. Birds and mammals)
Ectotherms: Known as cold-blooded creatures these
animals can also warm themselves in the day by
basking in the sun, etc. (E.g. bumblebees and tuna)
We humans use both mechanisms!
Uses internal corrective mechanism to
regulate temperature (the maintenance
of temperature occurs inside the body)
Uses behavioural mechanism to regulate
temperature (E.g. lying in the sun when
cold, moving into the shade when hot)
Heat is produced in the body when processes such as
cellular respiration (when cells respire) occurs.
High levels of cellular respiration occurs in the liver
and muscles. As a result, large amounts of heat is
released in these organs, and then distributed evenly
throughout the body via the bloodstream.
The body can gain extra heat through:
Vigorous muscular exercise
The consumption of hot food
Being in warm environments (e.g. being outdoors on a
very hot day.
The body can lose heat through:
The skin by radiation –the transfer of heat in the form
of waves without the use of a medium, convection –the
transfer of heat through a medium in the for of
currents, and to a limited extent, conduction-the
transfer of heat from one object/medium to another.
By evaporation of water in sweat at the surface of our
In the faeces and urine, including the air that we
How does you body regulate
The hypothalamus (a portion of your brain that
contains a small number of nuclei, that performs a
variety of functions) in your brain monitors and
regulates your body temperature.
The hypothalamus receives information about
temperature changes from two sources:
1) the thermo receptors in your skin which detect
temperature from the environment, and
2) the thermo receptors of the hypothalamus which
detect the temperature of the blood
What happens when human body
temperature begins to rise?
When one performs rigorous exercise, a large amount
of heat is produced. This heat accumulates in the
body, causing a rise in blood temperature. This change
is detected by the hypothalamus, causing it to send out
nerve impulses to the relevant body parts to bring
about changes such as:
Dilation of tiny arteries called arterioles in our skin, and the constriction of vessels
called shunt vessels which connects the skin arterioles to the skin venules-tiny
veins. This allows more heat to be lost through radiation, convection and
Sweat glands become more active, resulting in more sweat being produced. As more water
evaporates from the sweat on the skin surface, more heat is lost.
There is also a decreased metabolic rate, thus reducing the amount of heat produced in the
What happens when human body
temperature begins to fall?
On a cold day, the rate of heat loss increases, especially
at the skin surface. This drop in temperature
stimulates the temperature receptors to rapidly send
nerve impulses to the hypothalamus. The
hypothalamus with then send nerve impulses to the
relevant body parts to bring about these changes:
Constriction of skin arterioles and dilation of shunt vessels so that less blood flows
through the blood capillaries in the skin, thus reducing heat loss by conduction,
convection and radiation.
Sweat glands become less active, resulting in decreased production of sweat. Less water
evaporates from the body, and thus less heat is lost.
Increased metabolic rate, to increase the amount of heat released within the body.
When the above are insufficient, ‘shivering’, a reflex action occurs. This contraction of the
It is the balance of the hormones insulin & glucagon to
maintain the concentration of glucose in the blood at a
This is controlled to provide the cells with a constant
supply of energy.
The cells in our bodies require glucose (a sugar) for
What is it?
Insulin is a hormone which plays a key role in the
regulation of blood glucose levels. It is secreted by the
beta cells of the pancreas in response to high blood
Glucagon is a hormone which also plays a major role in
maintaining normal concentrations of glucose in the
blood. It is secreted by the alpha cells of the pancreas
when the blood glucose levels are low.
Insulin & Glucagon
Insulin is released from pancreatic beta cells in the
Islets of Langerhans.
The uptake of glucose is stimulated, the cells absorb
glucose more quickly
Excess glucose is converted into glycogen in the liver,
this is caused by the hormone insulin.
The excess glucose which was converted to glycogen is
then stored for a later date in the liver.
Hence, the concentration of glucose in the blood is
When Glucose Levels Are Too
The hormone glucagon is secreted by the alpha cells in
the Islets of Langerhans in the pancreas.
During starvation or after intense exercise, glucagon
promotes the conversion of the stored glycogen in the
liver to glucose.
The glycogen which has been converted to glucose
enters the bloodstream.
Thus, the concentration of glucose in the blood
When Glucose Levels Are Too Low
What is blood Pressure?
the pressure of the blood against the inner walls of the blood vessels,
varying in different parts of the
body during different phases of contraction of the heart and under
different conditions of health
It is also the pressure of the blood in the circulatory system, often
diagnosis since it is closely
related to the force
and rate of the
and elasticity of the
Regulation of blood pressure
The circulatory system plays a major role in the
regulation of temperature, body fluids, glucose
The blood transports hormones , gases and
nutrients and allows for heat gain or loss.
The pressure at which the blood is pumped
and distributed is also controlled by a homeostatic
What’s the purpose of regulating
blood pressure ?
Changes in blood pressure are routinely made in order
to direct appropriate amounts of oxygen and nutrients
to specific parts of the body. So if we are exercising,
then more blood is sent to the muscles. Having eaten,
more is sent to the gut to aid absorption.
How is Blood Pressure Controlled
Blood Pressure is controlled by homeostasis through
the use of sensory receptors and hormonal secretions.
A barorecetor reflex is a homeostasis mechanism
which uses sensory receptors in the heart to send
messages to the brain to regulate blood pressure.
Homeostasis also works via adrenal secretions to
control blood pressure.
A diagram on Blood Pressure
It shows the contribution of vasopressin and vasopressin
receptor type V1a and V2 in the regulation of blood
A HOMEOSTATIC IMBALANCE IS THE
DISTURBANCE OF THE HOMEOSTASIS IN
THE HUMAN BODY. THIS RESULTS IN AN
UNSTABLE INTERNAL ENVIRONMENT THAT
INCREASES THE RISK OF ILLNESS. IT IS
RESPONSIBLE FOR MANY DISEASES AND
PHYSICAL CHANGES IN OLD AGE.
• Insulin is a hormone responsible for regulating
carbohydrates and fats in the body. It causes the cells in the
body to absorb glucose from the blood.
• Diabetes mellitus can be caused by the body’s failure to
produce insulin or when cells fail to use insulin properly.
• Due to the body’s failure to regulate the carbohydrate and
fat metabolism in the body, this results to homeostatic
imbalance, Diabetes Mellitus. Diabetes mellitus is the
failure to keep blood glucose concentration within the
Dehydration is the excessive loss of body water.
• Fluid balance is maintained through a process called ‘water
• When a person is dehydrated, the amount of water in the
circulation is low and this is detected by the brain. A hormone
is then released by the pituitary gland to ensure that the
amount of water being released, in the form of urine, is
HYPOGLYCaEMIA / HYPERGLYCAEMIA
Hypoglycaemia is the condition in which a person has low
blood glucose level.
Hyperglycaemia is the condition in which a person has high
blood glucose level.
The causes of hypoglycaemia are the excessive insulin
produced in the body, hormone deficiencies and organ
failures. While, the cause of hyperglycaemia is the
inadequate insulin production.
When too much insulin is produced, the release of
glucagon is inhibited. Glucagon is a hormone that converts
glycogen to glucose.
When glucagon is not released, needed glucose is also not
released, therefore resulting in hypoglycaemia. When too
much glucagon is released, too much glucose is released
resulting in hyperglycaemia.
Gout is caused by the high levels of uric acid in the
* Uric acid is a metabolic product that causes a person
to get sick when contained in high levels.
Gout causes painful inflammation in muscle joints.
When there is a high level of uric acid, crystals of uric
acid may form and typically collect in a joint, causing
the joints to be irritated and hence the person
experience a ‘gout attack’.
An inability to maintain homeostasis may lead to death or
a disease condition known as homeostatic imbalance.
Medical intervention can help restore homeostasis and
possibly prevent permanent damage to organs.