Download File

Biology 12
11.1 The Respiratory System
The main function of the respiratory system is to allow oxygen
from the air to enter the blood and carbon dioxide from the
blood to exit into the air.
Ventilation, another term for breathing, includes both inspiration
(inhalation) and expiration (exhalation).
• Air is conducted toward or away from the lungs by a
series of cavities, tubes, and openings
The respiratory system works with the circulatory system in the
following homeostatic functions:
• External respiration: exchange of gases (oxygen and
carbon dioxide) between the air and blood
• Transport of gases to and from the lungs and tissues
• Internal respiration: exchange of gases between the
blood and tissue fluid
The Respiratory Tract
Inspiration: air is filtered, warmed, and moistened as it moves along
the respiratory tract
• Filtered by hairs in the nostrils, and by cilia in the mucus of
nasal cavities and airways
• Warmed by heat given off by blood vessels close to the lining
of the airways
• Moistened by the wet surface of airways
Expiration: air cools and loses its moisture as it moves out of the
respiratory tract
• Deposits moisture on the lining of the trachea and nose
The Nose
The nose is the only external portion of the respiratory system.
• Air enters the nose through the nostrils
• Air is moistened and warmed in two nasal cavities that
are lined with mucous membranes
• Nasal cavities are separated from the mouth by the
palate, which is composed of the hard palate and soft
palate
Biology 12
The Pharynx
The pharynx is also known as the “throat.”
• Connects the nasal and oral cavities to the larynx
• Contains lymphatic tissues called tonsils that contain lymphocytes that protect against
pathogens
• Allows for the passage of air and food
The Larynx
The larynx is called the voice box since it contains the vocal cords.
• Connects the pharynx to the trachea
• Composed of cartilage and dense connective tissue
• Allows for the passage of air (the glottis allows air into the larynx)
• A flap of tissue above the larynx, the epiglottis, prevents passage of food into lower
respiratory tract
The Trachea
The trachea is commonly called the
windpipe.
• Connects larynx with bronchi
• Composed of C-shaped cartilaginous
rings
• Allows for the passage of air to
bronchi
• Cleans, warms, and moistens air
• Mucous membrane lining contains
goblet cells (produce mucus) and
ciliated cells (sweep mucus and
debris toward the pharynx)
Biology 12
The Bronchial Tree
The trachea divides into the bronchi, which
lead into the lungs.
• The bronchi branch into secondary
bronchi that lead to bronchioles
• Each bronchiole leads to thin-walled
air sacs called alveoli (site of gas
exchange between air and blood)
• The components of the bronchial tree
beyond the primary bronchi make up
the lungs
The Lungs
The lungs are paired, cone-shaped organs
that contain alveoli, airways, and blood
vessels.
• At the base of the lungs is the diaphragm, a muscle involved in inspiration and
expiration
• Each lung is covered with a thin membrane called a pleura
o Secretes fluid so that it can slide freely against the pleura of the chest wall and
diaphragm during inspiration and expiration
• During inhalation, air enters the lungs by way of the bronchial tree and moves to the
alveoli
• Gas exchange occurs between the air in an alveolus and the blood in the capillaries
Biology 12
o Alveoli are covered with pulmonary surfactant, a film of lipoprotein that
prevents the alveoli from closing so that inhaled air can enter