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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

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homeostasis and body organization
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

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

environmental change

Positive feedback – a mechanism whereby the effects from the original

environmental changes are intensified.

homeostasis and body organization positive and negative feedbacks4
Homeostasis and Body OrganizationPositive and Negative Feedbacks

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.

body organization
Body Organization

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

other organs.

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.

Primary Functions?

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:

1. Open

2. Closed


Note: Vertebrates (including humans) have a closed circulatory system

circulation the vertebrate heart
Circulation – the vertebrate heart

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...

circulation the four chambered heart
Circulation – the four chambered heart

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 lungs.

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.

circulation the four chambered heart11
Circulation – the four chambered heart

Electric impulses coordinate

the sequence of contractions

Valves maintain directionality of

blood flow. The valves are “one-way”

circulation the four chambered heart12
Circulation – the four chambered heart

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...

circulation structure and function of blood vessels
Circulation – structure and function of blood vessels

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

nearby tissues.

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

circulation structure and function of blood vessels16
Circulation – structure and function of blood vessels

Change in blood velocity as a function

of circulatory cross section allows for

more efficient transport as well as

gas, nutrient, and waste exchange...

circulation blood
Circulation – blood

Blood components:

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

circulation blood18
Circulation – blood

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...

circulation the lymphatic system
Circulation – the lymphatic system

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.