Respiratory System
•Normal breathing rate 14-20
breaths/min
•Average person uses about .25 liters
of oxygen/min
•Lungs hold about 4-6 liters of air
•Oxygen is needed to metabolize
glucose and release water and carbon
dioxide
Respiration
3 Components of Respiration
Breathing  entrance/exit of air to/from lungs
2a. External respiration  movement of air to blood
2b. Internal respiration  movement of blood/oxygen
to tissue
Aerobic cellular respiration  production of ATP in
cells from metabolism of glucose
Respiratory Structures
Structure
Description
Function
Nasal Cavity
Hollow space in nose
Filters and warms air
Pharynx
Chamber behind oral cavity
Connection to surrounding
regions
Glottis
Opening to larynx
Passes air into larynx
Larynx
Vocal chords
Sound production
Trachea
Tube that connects larynx
with bronchi
Passage of air to bronchi
Bronchi
Major divisions that
Passage of air to each lung
enter lungs
Bronchioles
Small branched tubes that
lead to alveoli
Lungs
Organs that occupy thoracic Gas exchange
cavity
Passage of air to
alveoli
Lungs
•Right lung has 3 lobes; left lung has 2 lobes
•Lie at either side of the heart
•Base of the lung is broad and concave to fit into the convex diaphragm
•Approximately 300 million alveoli in lungs
•Alveoli increase the surface area of the lung so more oxygen can be taken up
•Alveoli are bathed in surfactant, which reduces their surface tension and
prevents collapse
•Gas filled alveoli are very light; a piece of lung usually floats on water
Ear Lobes
3 lobes 
<---2 lobes
Alveoli
Alveoli
Alveoli with attached arterioles
and venules (Capillaries)
The Anatomy of Breathing
•During ventilation, there is continuous air flow from pharynx
to alveoli
•The rib cage forms the top and sides of the thoracic cavity.
The diaphragm forms the bottom of the thoracic cavity
•The outer pleural membrane is attached to the rib cage
and diaphragm
The Physiology of Breathing
Inspiration
•Respiratory center is located in the medulla oblongata
•Neurons in the RC fire automatically in a rhythmic cycle
•Carbon dioxide levels in blood, lungs, or brain can cause changes in the
activity of the RC
•When carbon dioxide levels rise, receptors in body send message to MO
to increase the firing of respiratory neurons
•MO sends impulses directly to the diaphragm and rib muscles
•In relaxed state the, diaphragm is dome shaped.
•When excited by the MO, the dome falls, intercostal muscles contract,
pushing the rib cage out
•These actions create a vacuum of negative space in the lungs, the
volume of the lungs increases, and air rushes in
•Humans inhale by negative pressure
•Deep inspiration excites stretch receptors in alveoli, which in turn send a
message in MO to stop inhalation
The Physiology of Breathing
Expiration
Diaphragm and rib muscles relax and push upward and inward on the
lungs
Deep expiration excites stretch receptors in alveoli, which in turn send a
message in MO to stop inhalation
Lung Capacity
•Lungs hold about 4-6 liters of air
•Tidal Volume  amount of air moved in and out in 1 breath (.1-.2 liters)
•Vital Capacity  Maximum amount of air taken in 1 breath (3.1 liters)
•Residual Volume After all air is expelled, there is still some air in
lungs (<1 liter)
Healthy Lung
Smoker’s lung
Internal & External Respiration
External Respiration
Alveoli and blood vessels both consist of a thin layer of cells
Both the alveoli and blood vessels allow for the free passage of oxygen, carbon
dioxide
Diffusion ALONE governs the exchange of oxygen and carbon dioxide at the
alveoli
Oxygen diffuses from the O2 rich alveoli to the O2 poor blood vessels
Carbon dioxide diffuses from the CO2 rich blood vessels to CO2 poor alveoli
Oxygen & Hemoglobin
•Breathing at high altitude is less effective than at low
altitudes because the concentration of oxygen is low,
therefore less O2 diffuses into the blood
•Hemoglobin tends to attach to oxygen at cooler
temperatures and tends to release oxygen at warmer
temperatures
Internal Respiration
•Blood that enters the tissues is bright red
because the pigment hemoglobin turns red when
attached to oxygen
•Oxygen diffuses out of the blood and into the
tissues (at the capillaries)
•Carbon dioxide diffuses from the tissue to the
blood (at the capillaries)
•Deoxygenated red blood cells have no oxygen;
turning the RBC blue
•Red blood cells also pick up carbon dioxide and
deliver it to the lungs