property of cells, tissues,
and organisms that allows the maintenance and regulation of the
stability and constancy needed to function properly. Homeostasis is a
healthy state that is maintained by the constant adjustment of
biochemical and physiological pathways. An example of homeostasis is
the maintenance of a constant blood pressure in the human body
through a series of fine adjustments in the normal range of function
of the hormonal, neuromuscular, and cardiovascular systems. These
adjustments allow the maintenance of blood pressure needed for body
function despite environmental changes and changes in a person's
activity level and position. Other homeostatic mechanisms, for
example, permit the maintenance of body temperature within a narrow
range. The human body manages a multitude of highly complex
interactions to maintain balance or return systems to functioning
within a normal range.
An inability to maintain
homeostasis may lead to death or a disease, a condition known as
homeostatic imbalance. For instance, heart failure may occur when
negative feedback mechanisms become overwhelmed and destructive
positive feedback mechanisms take over. Other diseases which result
from a homeostatic imbalance include diabetes, dehydration,
hypoglycemia, hyperglycemia, gout and any disease caused by the
presence of a toxin in the bloodstream. Medical intervention can help
restore homeostasis and possibly prevent permanent damage to the
organs.All of the body's systems
work together to maintain balance in the body, but various systems
do have specific roles. Two of the most important systems for
maintaining homeostasis are the nervous and endocrine systems.Basic bodily functions such
as heart rate and breathing may be stimulated or slowed under neural
control. The nervous system helps regulate breathing and the urinary
and digestive systems, and it interacts with the endocrine system.Homeostasis and systems:
(i)Digestive:
Breaks down food and send to cells.
(ii)Respiratory: Oxygen
and carbon dioxide exchange between blood and lungs
(iii)Urinary:
Liver removes toxin from blood and converts them into chemicals that
can be removed
from the body by the
kidney.
The concept of homeostasis
is widely used, in physiology and psychology, to identify what seems
to be a general attribute of living organisms: the tendency to
maintain and restore certain steady states or conditions of the
organism. Homeostasis is the purposeful maintenance of a stable
internal environment maintained by coordinated physiologic processes
that oppose change.
The physiologic control
systems that oppose change operate by negative feedback mechanisms
that are composed of a sensor that detects a change, an
integrator/comparator that sums and compares incoming data with a set
point, and an effectors system that returns the sensed function to
within the range of the set point. Homeostasis does not occur by
chance, but is the result of organized self-government.
In summary, physiologic and
psychological adaptation involves the ability to maintain the
constancy of the internal environment (homeostasis) and behaviour in
the face of a wide
range of changes in the
internal and external environments. It involves negative feedback
control systems that regulate cellular function, control life’s
processes, regulate behaviour, and
integrate the function of
the different body systems.
The above diagram states the
negative feedback control mechanisms using blood glucose.
1. The decreased insulin
release and addition of glucose has been added to the blood.
2. The glucose has been
increased in blood.
3. The glucose serves as the
sensor in beta cells.
-Beta cells store
and release insulin, a hormone that controls the level of glucose in
the blood. The liver maintains the base-line glucose level, but the
beta cells can respond quickly to spikes in blood glucose by
releasing some of its stored insulin while simultaneously producing
more. The response time is very quick.
4. The Insulin is made to
increase in blood and the glucose are removed from the system.
5. As soon as the glucose
has removed from the body, decrease in blood glucose occurs.
6. The returned Glucose
sensors in the beta cells.
-
The b-cells must sense and respond suitably to postprandial increases
of blood glucose, and perturbation of glucose-sensing in these cells
can lead to hypoglycaemia or Hyperglycaemias and ultimately
diabetes. Here, we review b-cell glucose-sensing with a particular
focus on the regulation of cellular excitability and exocytose.
hen blood passes thru blood
vessels near the skin surface heat is lost by radiation. Arterioles
(small arteries) have muscles in their wall, when we are too hot,
these muscles relax, creating a wide lumen through which lots of
blood can pass( the skin of a hot person may look red). This is
called vasodilatation. More heat is radiated, so we cool down. When
we are too cold, the muscles contract, creating a narrow lumen thru
little blood can pass (the skin of a cold person may look very pale )
this is called vasoconstriction less heat is radiated to conserve
heat.
Blood glucose levels: when
the glucose level is too high the liver secretes insulin by
converting glucose into glycogen for storage in liver, if the glucose
content in too low a hormone named glucagon is secreted which
converts glycogen in the liver to glucose increasing the glucose
content in blood.
Heart rate: heart rate
increases due to tension and pressure, adrenaline is secreted which
increases the blood pressure and so fast flow of glucose and oxygen
to the muscles. Resulting in aerobic respiration, bronchioles relax
causing much air flow into lungs, and increase in tissue respiration.
All of the body's systems
work together to maintain balance in the body, but various systems
do have specific roles. Two of the most important systems for
maintaining homeostasis are the nervous and endocrine systems. Basic
bodily functions such as heart rate and breathing may be stimulated
or slowed under neural control.
A familiar domestic example
is the thermostat which controls a central heating system. If the
temperature of the room falls below the setting on the thermostat, an
electrical circuit is completed which switches on the boiler and pump
to circulate hot water through the system. When the desired
temperature is reached.