1. Entry slip: What are the tiny alveoli sacs surrounded
by?
Lesson 2.3- Describe how breathing is controlled to
help maintain homeostasis in the human body
(pp338-341) of Biology-McGraw-Hill Ryerson)
I. Homeostasis (p772):
a. The body’s maintenance of a relatively
constant internal environment (i.e. water
content, O2 level, temperature, etc..)
b. In this case of homeostasis, the “internal
environment” that the body wants is one
with O2 available for each cell, and the
smallest amount of CO2 possible.
c. The respiratory system brings oxygen
from the atmosphere to all cells in the

2. body, and takes away the CO2 produced
by them.
II. Control of breathing- the human body uses
two muscular structures to control breathing
a.Diaphram:
i. Inhaling: When relaxed, the diaphram
at the bottom of the lungs is dome-
shaped. When it contracts, it pulls
downward on the lungs, expanding
them and drawing air in.
ii. Exhaling: When the diaphram relaxes,
the muscle moves upwards resuming
its domed shape. Air leaves the lungs.
b.Intercostal Muscles:
i. Inhaling: When the intercostals
muscles contract, they spread all of
the ribs out. This increases the size of
the lungs and draws air in.
ii. Exhaling: When the intercostal
muscles relax, the ribs come back

3. close to each other. The size of the
lungs decreases, forcing air out.
III.Lung Capacity:
a.Tidal Volume: “breathing at rest” -the
volume of air inhaled and exhaled during
normal breathing
b.Inspiratory Reserve: “taking in a BIG
breath” -the maximum amount of air that
you can inhale, beyond a tidal inhalation
c. Expiratory Reserve: “breathing out as
much as possible” -the maximum amount
of air that you can exhale, beyond a tidal
exhalation
d. Vital Capacity: “amount from a BIG breath
to breathing out as much as possible” –
the total amount of air that can be moved
in and out of the lungs. VCvolume = TDvolume +
IRvolume + ERvolume
IV.Demos:
a. http://www.youtube.com/watch?
v=HiT621PrrO0&feature=related

4. b. http://www.youtube.com/watch?v=hp-
gCvW8PRY&feature=related
V. Homework Assignment:
a. You are a soldier in the “Human Anatomy
Army”, Sgt. Homeostasis. A new and
untrained recruit, Private Diaphram
arrives at your body and you have to train
her for her position. What orders/
instructions would you give the Private?
b. Not less than 100 words, due the next
day.