HOMEOSTASIS AND ITS
FUNCTION IN
ORGANISMS
By: Liam Grinton
Due: 11/26/10
INTRODUCTION:
Fig. 1.1
In order for the cells in the body to maintain their
efficiency and be able to function at their fullest, equilibrium
must be maintained. Homeostasis is a term derived from the
Greek roots Homeo and stasis. The Greek word Homeo means
“similar or like”, and the word stasis meaning “state of being”
A homeostatic negative
feedback system
homeostasis is something that our bodies regulate constantly,
however we do not always think about it. Our bodies contain complex biological tools and
systems to regulate homeostasis and our equilibrium. Because homeostasis works on a cellular
level for the most part, the transport of materials into and out of the cell is important for the
organisms homeostasis. An organism can be described by the analogy of a house, and all of the
systems relating to the well- being of the organisms inside it, wastes and nutrients must be
regulated and other systems must function in order for the cells to be able to work efficiently.1
BODY:
THE IMPORTANCE OF HOMEOSTASIS:
Homeostasis is a mechanism employed by our bodies and the bodies of other organisms
to improve the function of the cells, tissues, organs, and organ systems of the body and their
well-being. Enzymes work best under conditions with a certain temperature, and Ph level. Cells
must maintain a certain water level in relationship to the water level outside the cell in order to
function as well. These are only some of the functions of homeostasis in complex mammals.2
CHANGE SENSORS:
Homeostatic change sensors are a vital part of the well- being of an organism. In the context of a
house a change sensor may act like a thermostat. Through a negative feedback system, the
change is detected by a sensor, then it is measured against a norm by a mechanism called an
integrator, and is finally rectified by the effector. For example, using the analogy of a house,
when you turn the heating system on and the temperature in the house is below that at which the
thermostat is set, the thermostat senses the change and turns on the heater.
When your body is subjected to a cold environment, your body does several things to
maintain its homeostasis. Your nervous system relays a signal that your body temperature is low
to your brain. The nervous system then sends a message to your muscular system to start
shivering to generate heat by friction. Depending on how cold you are your body may send a
signal to the vascular system to contract the blood vessels in the extremities. This decreases the
volume of blood going and coming from the extremities to maintain body heat and core
temperature.4
There are many different types of changes that can take place in the environment around
an organism. The changes that occur usually require that organism’s homeostatic tools to adjust
it to the environment and allow the organism to function. Changes in temperature, solutes, water
and many other environmental factors can cause the body’s mechanisms to regulate and maintain
equilibrium.
There are two types of transport employed by cells to regulate the flow of material in and
out of the cell. These two types are active and passive transport. Transport can go two directions,
against and with a concentration gradient. A concentration gradient is a gradient in concentration
of a solute as a function of distance through a solution; "the movement of a solute down its
concentration gradient is called diffusion"5
Passive transport is one of the two ways that cells regulate their homeostasis. Included
within the realm of passive transport are the mechanisms of diffusion, osmosis, facilitated
diffusion, and diffusion through ion channels.
Diffusion:
Fig. 1.2
Diffusion is the simplest type of passive transport. This process takes place
when molecules travel from an area of high concentration to an area of low
concentration. This difference between the low and high concentration is the
concentration gradient. Picture the high concentration as a spray bottle full of
water, when the trigger is pulled, then the water is misted out, picture the water
droplets as individual molecules. When they leave the sprayer, they diffuse, or
spread out in the area with the lower concentration of water. Diffusion is driven
by the kinetic energy of the molecules. Diffusion, if not regulated n any way, will
An illustration
showing the
process of
diffusion.
create an equal solute concentration throughout the entire available space. Diffusion often takes
place across cell membranes. Some molecules are too large to diffuse through the cell
membrane, but some can. They do this in two ways; the first is by dissolving in the lipids that
form the membrane, and passing through. To dissolve in the lipid, they must be non-polar.
Second, other molecules can pass through the membrane because they are small enough to fit
through the tiny surface pores in it.
Osmosis:
Osmosis is the movement of water or another solvent over a selectively permeable membrane
from a region of high solvent concentration to a level of lower solvent concentration with more
solutes. 6 If the solute levels are equal inside and outside of the cell the outside solution is
isotonic. When a large concentration of polar molecules is present either inside or outside of the
cell membrane, then the polar water molecules interact with it. Because there are less free water
molecules in the side with the solute after the interaction, the more water molecules move down
the gradient and into the solute side. This is osmosis.7 Cells that are exposed to an isotonic
environment usually have no problems maintaining the movement of water through their cell
membranes in balance. Unicellular freshwater organisms usually live in hypertonic
environments; therefore they have problems with water constantly flowing into their cell through
osmosis. They must deal with the excel fluid. Some use contractile vacuoles, which collect the
water, and contract to expel it again. Others use solute pumps, which also remove excess fluids
from the cell.
Facilitated diffusion:
Fig. 1.3
This is a process that takes place in molecules in which diffusion does not take
place rapidly despite of an adequate concentration gradient. Facilitated
diffusion is made possible by special carrier proteins that help molecules pass
through the cell membrane to the lower concentration gradient. The molecules
that use this passage might be too large to dissolve in lipids, or too large to
pass through the cellular pores. Each carrier protein is used only for a
An image illustrating
the facilitated diffusion
of potassium
particular molecule such as a sugar or amino acid. The carrier protein or the cell does not expend
any energy in this process. 8
Diffusion through ion channels:
This is a process that is much like facilitated diffusion. This process allows ions that are
too large to pass through the membrane or dissolve in lipids to pass through the membrane in
channels. Each individual channel will only allow a specific type of ion to pass through. Some
channels are continuously open, as others have “gates” to open and allow passage, or close and
block it.
ACTIVE TRANSPORT SYSTEMS:
Cell Membrane Pumps
Cell membrane pumps, such as the sodium- potassium pump are necessary for the proper
function of cells because they carry positive potassium and sodium ions up their concentration
gradient as opposed to down it. The carrier proteins that operate as sodium - potassium pumps
are much like those that operate in facilitated diffusion. Just like in facilitated diffusion, the
protein first binds to a specific kind of molecule. The protein the shields the molecule from the
hydrophobic inside of the lipid bi – layer and transports it to the inside of the cell. Many animal
cells need a higher concentration of positive sodium ions outside the cell, and a concentration of
positive potassium ions inside the cell. Using ATP as an energy source makes it possible to carry
molecules up a concentration gradient. ATP is adenosine triphosphate; a nucleotide derived from
adenosine that occurs in muscle tissue; the major source of energy for cellular reactions.9
Endocytosis and exocytosis:
Endocytosis is when a cell ingests a large polar molecule, organic fragment, or other cell. It does
this by extending the plasma membrane, and engulfing the particle. After having engulfed it and
sealing the opening, the vessel separates from the plasma membrane and transfers it to the inside
of the cell. The “food” is then broken down my lysosomal enzymes to
Fig. 1.4
be consumed. There are three types of endocytosis. Phagocytosis,
pinocytosis, and receptor mediated endocytosis are the three types of
endocytosis. If the object being consumed is solid or particulate, such as
a bacteria, then the process is called phagocytosis, if the object
consumed is liquid, then the process is called pinocytosis. Receptor
mediated endocytosis is a process in which specific molecules like low
density lipoproteins are brought into eukaryotic cells. Molecules to be
An amoeba feeding by
endocytosis.
transported inside the cell are bound to specific receptors on the cell’s plasma membrane. When
enough proteins have bonded to the receptors, the pit in which the receptors are located deepens
and closes off. This creates a vesicle in which the proteins can be transported into the cell.
Exocytosis is essentially the opposite of endocytosis, it is when wastes are “packaged” in a
vesicle, and then excreted from the cell through the plasma membrane.
CONCLUSION:
Homeostasis is a vital natural tool that our bodies and those of others use to stay alive and
functioning efficiently. Organisms maintain their homeostasis by systems of sensors, integrators
and effectors. Many bodily functions depend on this form of system to work efficiently. Cellular
homeostasis is vital to an organism’s survival. Cells regulate their fluid levels and the materials
traveling in and out of them by both passive and active transport systems. Research has shown
that it is vital for organisms to maintain their homeostasis. If they do not, the concequences are
usually painful or fatal. All animals, and the cells within them need certain things to survive, and
keeping their environment relatively constant is one of the determining factors of survival.
WORKS CITED
1^
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookanimorgsys.html
2^
various sources
4^
http://www.biology4kids.com/files/systems_regulation.html
5^
http://wordnetweb.princeton.edu/perl/webwn?s=concentration%20gradient
6^
http://physioweb.med.uvm.edu/bodyfluids/osmosis.htm
7^
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
8^
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_work
s.html
9^
http://wordnetweb.princeton.edu/perl/webwn?s=atp
10^
Image Credits
Fig. 1.1:
http://www.google.com/imgres?imgurl=http://wps.prenhall.com/wps/media/objects/488/500571/
CDA38_2.jpg&imgrefurl=http://wps.prenhall.com/esm_freeman_biosci_1/7/1955/500605.cw/&
usg=__qzQutWz3TDH7521GIRFQEIDpcSA=&h=250&w=250&sz=11&hl=en&start=3&zoom
=1&um=1&itbs=1&tbnid=A_QI86Tik249iM:&tbnh=111&tbnw=111&prev=/images%3Fq%3D
negative%2Bfeedback%2Bloop%2Bhomeostasis%26um%3D1%26hl%3Den%26rlz%3D1R2GG
IE_enUS378%26tbs%3Disch:1
Fig. 1.2:
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html
Fig. 1.3:
http://www.succeed.ufl.edu/content/abe2062/lect/lect_06/4_20A.GIF
fig. 1.4:
http://plantphys.info/organismal/lechtml/images/amoeba.jpg