Download The Respiratory System

BIO 110
Dr. Ely
Chapter 24.1 Notes – The Respiratory System
I.
II.
III.
Functions of the respiratory system
a. Exchange gases with the blood
i. Oxygen gas (O2) is inhaled into the lungs and diffuses into the blood
ii. Carbon dioxide (CO2) diffuses out of the blood, into the lungs, and is exhaled
b. Creates vocalizations for communication
i. Vibrations of vocal cords in the larynx produce sounds
Upper Respiratory Tract
a. The nasal cavities are chambers within the nose to warm, filter, and humidify inhaled air
i. The nostrils are the opening to the nasal cavities
ii. Nasal cavities are lined with:
1. mucous membranes that secrete the fluid mucus in order to warm and humidify
the inhaled air, and trap small particles
2. hairs that filter larger particles
b. The pharynx (the back of your throat) connects the nasal cavity and mouth to the larynx; it is a
common passageway for both food and air before they separate
c. The larynx, or voice box, is supported by the hyoid bone and broad plates of cartilaginous tissue
that prop it open.
i. The glottis is the opening to the larynx. The epiglottis is a small flap of tissue that is
pushed over the glottis when food is swallowed to prevent food from entering the
respiratory system.
ii. The vocal cords are flexible bands of tissue inside the larynx that vibrate to create sound
Lower Respiratory Tract
a. The trachea, or windpipe, is a stiffened tube connecting the larynx to the bronchi
i. The trachea is held open by C-shaped cartilaginous rings that are flexible but supportive
ii. The trachea divides into the right and left bronchi
b. The primary bronchi (singular: bronchus) are two large tubes that continue to branch into
smaller and smaller bronchioles.
c. Bronchioles terminate in clusters of air-filled sacs called alveoli (singular: alveolus)
i. The alveoli are the structures that exchange O2 and CO2 with blood capillaries
ii. Their round shape greatly increases the surface area for exchange.
iii. Exchange is also enhanced by the closeness of the thin capillary and the cells of the
alveoli – creating a respiratory membrane that quickly exchanges gases
1. O2 – poor / CO2 – rich blood enters the respiratory membrane from the
pulmonary arteriole (tiny artery) from the right ventricle of the heart
2. O2 diffuses into blood and CO2 diffuses out following their concentration
gradients
3. O2 – rich and CO2 –poor blood leaves the capillary in the pulmonary venule (tiny
vein) to return to the left atrium of the heart
BIO 110
Dr. Ely
iv. Emphysema is a condition, most often associated with smoking, which causes
breakdown of the alveolar walls. This creates fewer, larger alveoli and thus less surface
area for gas exchange.
IV.
Negative-pressure breathing
a. Muscles involved with breathing
i. The diaphragm is a muscular sheet of tissue that divides the upper thoracic cavity from
the lower abdominal cavity. At rest, the diaphragm is curved upward.
ii. The intercostal rib muscles are the muscles between the ribs that can contract to
expand the chest.
b. Inspiration (inhalation)
i. The diaphragm contracts, moving downward.
ii. The intercostals contract, which spreads out the ribs.
iii. These two contractions serve to increase the volume of the thoracic cavity. This causes
negative pressure, or a vacuum, that pulls air into your lungs. This is the opposite of
pushing air into the lungs (positive-pressure breathing) like blowing up a balloon.
c. Expiration (exhalation)
i. The diaphragm relaxes, moving upward.
ii. The intercostals relax, which brings the ribs closer together.
iii. These actions serve to push air back out of the lungs as the thoracic cavity gets smaller.
V.
Breathing control
a. The medulla oblongata in the brain stem monitors blood pH to regulate the breathing rate.
i. If you hold your breath, the urge to breathe again is stimulated by a drop in blood pH.
1. CO2 is created by the cells and enters the blood where it mixes with water to
form carbonic acid (H2CO3) which forms the hydrogen ion (H+) and the
bicarbonate ion (HCO3-). The increase in hydrogen ion concentration lowers the
blood pH.
2. In the lungs, the reaction runs backwards and CO2 leaves. But, if the breath is
held, the blood grows steadily more acidic and the brain forces the muscle
contractions that cause inspiration.