Homeostasis is the maintenance of a constant internal
environment by the combination of bodily functions. Cells, the basic unit in
all living things depend on the body environment to survive and perform their specific
functions. Homeostasis ensures cells get the conditions they need. If poor
conditions are present, processes such as osmosis and proteins such as enzymes
won’t be able to fulfil their function. Disasters can then be caused such as
heatstroke, hypothermia, hypercalcemia, obesity or diabetes. Homeostasis is involuntary;
we don’t need to know anything from birth to make it work to help us survive.
Homeostasis works in feedback loops, negative feedback to bring a condition
back to its normal state and positive feedback for a condition to go further
away from its normal state.
The endocrine system comprises of glands that secrete
hormones into the bloodstream. Hormones are chemical messengers that cause
changes in the body. Hormones are involved in negative feedback loops to ensure
conditions are normal. One condition is blood glucose concentration. Blood
glucose concentration rises after eating food high in carbohydrates, or falls
after exercise. The pancreas – an organ in the endocrine system – detects when
blood glucose concentration is too high or too low. If too high, beta cells
secrete insulin and alpha cells stop secreting glucagon. If too low, beta cells
stop secreting insulin and alpha cells secrete glucagon. In both cases, the
secreted hormone binds to liver cells. Insulin converts excess glucose to
glucagon in high blood glucose concentration. Glucagon is converted into
glucose for low blood glucose concentration. Blood glucose levels then revert
to normal. Insulin and glucagon are secreted by islets of Langerhans. Under
great stress or during exercise blood glucose concentration can get very low,
therefore, adrenaline is released from the adrenal glands. Adrenaline binds to
receptors in liver cells, and increases the blood glucose concentration. It activates
the breakdown of glycogen to glucose and inhibits the synthesis of glycogen
from glucose. It also activates glucagon secretion and inhibits insulin
secretion. Blood glucose concentration is then brought back to normal via a
negative feedback loop.
A second example of homeostasis is temperature control. Body
temperature is usually kept at 37oC ± 0.5oC. If body
temperature is too high or too low enzymes can become denatured or enzyme
activity can be reduced. Metabolic reactions are then less efficient.
Therefore, the body detects when the temperature is too far away from 37oC.
Effectors then respond to either decrease or increase the temperature. To decrease
the temperature, sweat glands produce sweat which increases heat loss by
evaporation. Hairs also lay flat so heat can escape. To increase the
temperature, hairs stand up to trap air. Humans also shiver which generates
heat. In both cases, temperature returns to normal, again via a negative
A third example of homeostasis is calcium levels. 99% of
calcium is in our teeth and bones, the 1% is in the blood. Too low or too high
calcium levels can result in either hypocalcaemia or hypercalcaemia respectively,
weakening bones, wheezing or even causing kidney stones. The parathyroid glands
release parathyroid hormone to increase the amount of calcium in bloodstream if
calcium levels are too low. If calcium levels are too high the thyroid gland
releases calcitonin which increases bone calcium content, decreasing the amount
of calcium in the blood.
All major organ systems work together like an orchestra to
keep the human body functioning. The
excretory system contains kidneys which are made up of lots of tiny structures
called nephrons. The glomerulus in each nephron filters oxygenated blood from
the heart in the cardiovascular system, removing excess water and waste
products. That blood can then go to the rest of the body concentrated of
oxygen, therefore no waste will affect the ability for oxygen to work in the body.
Without the cardiovascular system, the kidney won’t have the oxygenated blood
to perform its many functions. The cardiovascular system also links to the
digestive system. In the digestive system, food is broken down by chemical and
mechanical digestion. Food contains minerals, nutrients, salts and more. When
the food is broken down, these minerals etc are absorbed into the bloodstream.