Homeostasis and Body Organization. What is homeostasis?. “constancy” or “steady state” maintained within the organisms’ bodies. Whereas the environment can be highly variable, organisms incorporate internal control mechanisms to oppose the forces that would change their
What is homeostasis?
“constancy” or “steady state” maintained within the organisms’ bodies.
Whereas the environment can be highly variable, organisms incorporate
internal control mechanisms to oppose the forces that would change their
internal physiological equilibrium.
The organisms’ internal state can be described as being in dynamic
equilibrium, because the body needs to be constantly adjusting to the
This regulation occurs in two basic ways:
Negative feedback – most important means of maintaining homeostasis,
negative feedback creates a counter-effect to the outside
Positive feedback – a mechanism whereby the effects from the original
environmental changes are intensified.
It should be noted though that there are many systems involved in organisms’
Body, and that they all need to interact with each other to maintain homeostasis.
Different systems working independently could end up working against each other,
but since the body has systems that move substances and signals from one part of the
body to the next, all the different body parts remain “connected”.
This coordination is achieved via chemical (hormones) and/or electrical
(nervous) communication between tissues that elicits appropriate responses.
The body is organized at different levels:
Tissues: includes structurally similar cells that act together to perform a
particular function. (e.g. muscular, nervous, epithelial, etc.)
Organs: the next higher level of organization, tissues come together to form
organs. (e.g. stomach, kidneys, liver, etc.)
Organ systems: the different organs that work together towards a particular
function come together to create organ systems. (e.g. digestive system
which is composed of the stomach, small intestine, large intestine, and
You are responsible to read pages 526 – 533. Learn the basic structure and function
of the major vertebrate organ systems outlined in table 26-2 on page 532.
Why do we even need a circulatory system?
Simple diffusion is too slow to serve the needs of “larger” organisms.
1. Gas exchange
2. Distribution of nutrients
3. Waste removal
Other functions in vertebrates (and some invertebrates)?
4. Distribution of hormones
5. Regulation of body temperature
6. Protection of body from bacteria and viruses – circulation of
antibodies and white blood cells.
All circulatory systems have 3 major components:
1. A fluid “blood” that serves as a medium of transport
2. A system of channels (blood vessels) that transport the blood
throughout the body.
3. A “heart” that acts as a pump and keeps the blood circulating.
Animals have one of two types of circulatory systems:
Note: Vertebrates (including humans) have a closed circulatory system
There is an increased level of complexity associated with vertebrate evolution. This
increased complexity has created more efficient circulatory systems that have allowed
for greater diversity of form and function in different environments.
This is not of course
the only solution,
squids for example
have three hearts...
The mammalian and avian hearts consist of two pumps in one.
One pump is responsible for pulmonary circulation – consisting of the right
atrium and ventricles, this pump is responsible for sending blood to
The other pump is responsible for systemic circulation – consisting of the left
atrium and ventricles, this pump is responsible for sending oxygenated
blood to the body.
Electric impulses coordinate
the sequence of contractions
Valves maintain directionality of
blood flow. The valves are “one-way”
The atria and ventricles of the heart need to pump in a coordinated fashion. The
alternating contraction and relaxation of the heart chambers is called
the cardiac cycle.
The contraction of the ventricles is called the systole and the relaxation is called the diastole
The nervous system and hormones influence heart rate...
Arteries and Arterioles – Thick-walled vessels that carry
blood away from heart
arterioles can control the distribution of blood
by muscular contractions – they are influenced
by nerves, hormones, and chemicals produced in
Capillaries – Microscopic vessels that allow blood and body
to exchange gas, nutrients, and waste
Veins and Venules – Carry blood back to the heart
Valves direct flow of blood in veins
Change in blood velocity as a function
of circulatory cross section allows for
more efficient transport as well as
gas, nutrient, and waste exchange...
Plasma – the “fluid” part of the blood, it is composed of 90% water along
with proteins, hormones, nutrients, gases, salts, and wastes...
Specialized cells – these are cells suspended in the plasma and include red blood
cells, white blood cells, and platelets.
Red blood cells are primarily involved in transport of oxygen
White blood cells are primarily involved in the immune system
Platelets are primarily involved in blood clotting
Red blood cells contain a large,
iron-containing protein called
Each hemoglobin can bind to four
oxygen molecules and is involved
in picking up oxygen in the lungs
and transferring it to the body...
A network of lymph capilaries and large vessels
that empty into the circulatory system. Function
1. Removal of excess fluids and dissolved
substances that leak from capillaries.
2. Transport of fats from the small intestine
to the blood stream.
3. Defense of the body by exposing bacteria
and viruses to white blood cells.