Download Respiration The resspiratory system

Respiration
The resspiratory system
The Alveoli
The lungs have about 300 million alveoli, with a total crosssec onal area
of 50–70 m2.. Each alveolar sac is surrounded by blood capillaries. The
walls of the sac is squamous epithelium. Gas exchange occurs between
air in the alveoli and blood in the capillaries. Oxygen diffuses across the
alveolar wall and enters the bloodstream,
and carbon dioxide diffuses from the blood across the alveolar wall to
enter the alveoli The alveoli of human lungs are lined with a surfactant,a
fi lm of lipoprotein that lowers the surface tension of water and prevents
the alveoli from closing. The lungs collapse in some newborn babies—
especially premature infants—who
lack this fi lm. The condition, called infant respiratory distress syndrome,
Inspiration
Inspiration is the active phase of ventilation because this is the phase in
which the diaphragm and the external intercostal muscles contract. In its
relaxed state,the diaphragm is dome-shaped. During inspiration, it
contracts and becomes a fl attened sheet of muscle. Also, the
external intercostal muscles contract, causing the rib cage to move
upward and outward. Following contraction of the diaphragm and the
external intercostal muscles, the volume of the thoracic cavity is larger
than it was before. As the thoracic volume increases, the lungs increase
in volume as well because the lung adheres to the wall of the thoracic
cavity. As the lung volume increases, the air pressure within the alveoli
decreases, creating a partial vacuum. In other words, alveolar pressure is
now less than atmospheric pressure (air pressure outside the lungs).
Air will naturally fl ow from outside the body into the respiratory
passages and into the alveoli, because a continuous column of air
reaches into the lungs
Expiration
Usually, expiration is the passive phase of breathing, and no effort is
required to bring it about. During expiration, the diaphragm and external
intercostal muscles relax. The rib cage returns to its resting position,
moving down and inward As the volume of the bellows decreases, the
air pressure inside increases. Now air fl ows out
. The elastic properties of the thoracic wall and lung tissue help them to
recoil.
Volumes of Air Exchanged During Ventilation
Tidal Volume Normally, when we are relaxed, only a small
amount of air moves in and out with each breath, similar,. This amount
of air, called the dal volume, is only about 500 mL.
Inspiratory and Expiratory Reserve Volume As noted previously,we can
increase inspiration by expanding the chest and also by lowering the
diaphragm to the maximum extent possible. Forced inspiration
(inspiratory reserve volume) usually adds another 2,900 mL of inhal
We can increase expiration by contracting the abdominal and thoracic
muscles. This so-called expiratory reserve volume is usually about 1,400
mL of air. The maximum volume of air that can be moved in plus the
maximum amount that can be moved out during a single breath is called
the vital capacity . Residual Volume It is a curious fact that some of the
inhaled air never reaches the lungs; instead, it fi lls the nasal cavities,
trachea, bronchi, and bronchioles.
Nervous Control of Breathing
Normally, adults have a breathing rate of 12 to 20 ven la ons per
minute. The rhythm of ventilation is controlled by a respiratory control
center located in the medulla oblongata of the brain. The respiratory
control center automatically sends out nerve signals to the diaphragm
and the external intercostal muscles of the rib cage, causing inspiration
to occur.When the respiratory center stops sending nerve signals to the
diaphragm and the rib cage, the muscles relax and expiration occurs.
Sudden infant death syndrome (SIDS),. An infant under one year of age
is put to bed seemingly healthy, and sometime while sleeping, the child
stops breathing. the cause is that respiratory center stops sending out
the impluse that cause breath
Chemical Control of Breathing
working cells produce carbon dioxide, which enters the blood.
There, carbon dioxide combines with water, forming an acid,
which breaks down and gives off hydrogen ions (H+). These
hydrogen ions can change the pH of the blood.
Chemoreceptors are sensory receptors in the body that are
sensitive to chemical composition of body fl uids. Two sets of
chemoreceptors sensitive to pH can cause breathing to speed
up. A centrally placed set is located in the medulla oblongata of
the brain stem, and a peripherally placed set is in the
circulatory system. Carotid bodies, located in the carotid
arteries, and aortic bodies, located in the aorta, are sensitive to
blood pH. These chemoreceptors are stimulated when the
carbon dioxide entering the blood is sufficient to change blood
pH.
Gas Exchange
there are two types of air exchange in the body
1- External respiration refers to the exchange of gases between
air in the alveoli and blood in the pulmonary capillaries
Blood in the pulmonary capillaries has a higher PCO2 than
atmospheric air. Therefore, CO2 diffuses out of the plasma into
the lungs. Most of the CO2 is carried in plasma as bicarbonate
ions (HCO3 −). The enzyme carbonic anhydrase speeds the
breakdown of carbonic acid (H2CO3) in red blood cells
Blood in the pulmonary capillaries is low in oxygen, and alveolar air
contains a higher partial pressure of oxygen. Therefore, O2
diffuses into plasma and then into red blood cells in the lungs .
-2 Internal Respiration
Internal respiration refers to the exchange of gases between
the blood in systemic capillaries and the tissue cells.
Blood entering systemic capillaries is a bright red color
because red blood cells contain oxyhemoglobin. The temperature
in the tissues is higher and the pH is slightly lower (more acidic), so
oxyhemoglobin naturally gives up oxygen.After oxyhemoglobin gives up
O2 , it diffuses out of the blood into the tissues Oxygen diffuses out of
the blood into the ssues because the PO2 of tissue fl uid is lower than
that of blood Carbon dioxide diffuses into the blood from the tissues
.because the PCO2 of ssue fl uid is higher than that of blood