TOPICS COVERED IN THESE NOTES:

• (a) The Structure of the Respiratory System

• (b) Respiratory Dynamics

The Functions of the Respiratory System

The three main functions of the respiratory system are to:

• supply O2 to the blood

• remove CO2 from the blood

• regulate blood pH (acid-base balance)

IMPORTANT TERMS

External Respiration • External respiration refers to the processes that occur within the lungs involving the exchange of O2 and CO2. Internal Respiration •

Internal respiration refers to the exchange of gases at the tissue level, where O2 is delivered and CO2 is removed.

Cellular Respiration • Finally, cellular respiration is the process in which the cells use O2 to generate energy in the mitochondria of cells.

The Structure of the Respiratory System

The respiratory system can be divided into two main zones — the^^“conductive zone”^^ and the$“respiratory zone.”$

• The conductive zone transports filtered air to the lungs. This zone consists of the mouth and nose; pharynx; larynx; trachea; primary and secondary bronchi; tertiary bronchioles and terminal bronchioles.

• Therespiratory zone is where gas exchange occurs. Bronchioles, alveolar ducts, and alveolar sacs are all structures of the respiratory zone that are involved with the exchange of gases between inspired air and the blood.

The Mechanics of Breathing The combination of inspiration and expiration together is known as “ventilation.”

•Inspiration is an active process, requiring the contraction of various respiratory muscles and therefore the expenditure of significant amounts of energy.

•Expiration, on the other hand, maybe passive, as in quiet breathing (which may not require much energy), or active (as in forced breathing).

Inspiration and Expiration

Inspiration: Air flows into the lungs due to increased lung volume following the contraction of the diaphragm and intercostal muscles.

Expiration: Air is expelled from the lungs due to the relaxation of the diaphragm and the intercostal muscles.

The Control of Ventilation Breathing results from the contraction and relaxation of the inspiratory muscles and the expiratory muscles. The contraction of muscles is dependent on stimulation from the central nervous system (CNS).

• All aspects of breathing are closely associated with the overall need for O2, metabolic processes, muscle activity, and the production of CO2.

• Control of breathing is very complex and involves many different forms of feedback from specialized sensory systems to the neural control centers within the brain.

Gas Exchange

The average person’s lungs have about 300 million alveolar sacs (that is about a tennis court’s worth), each of which is surrounded by a web of capillaries. The walls of each capillary are one cell thick, which provides a very short distance for gases to diffuse.

Diffusion

The primary factor that mediates gas exchange both in the lung (where blood becomes oxygenated and CO2 is removed) and in the tissue (where O2 is delivered for metabolism and CO2 is removed) is diffusion.

• Diffusion is the movement of a gas, liquid, or solid from a region of high concentration to a region of low concentration through random movement.

• Diffusion can only occur if a difference in concentration exists, and such a difference is called a concentration gradient.

IMPORTANT TERMS

O2 Transport

• The process by which O2 is absorbed in the lungs and carried to the peripheral tissues.

CO2 Transport

• The process by which CO2 in the blood is moved into the alveoli and then exhaled from the body.

a-vO2 diff

• The difference between the amount of O2 in the artery and vein reflects the amount of O2 that was delivered to the muscle.

SUMMARY

The respiratory system does many things such as

• supplies O2 to the blood, removes CO2 from the blood and regulates blood pH (acid-base balance). All aspects of breathing are closely associated with the overall need for O2, metabolic processes, and muscle activity.

• External respiration occurs within the lungs and involves the exchange of O2 and CO2.

• Internal respiration refers to the exchange of gases at the tissue level.

• Cellular respiration is the process in which the cells use O2 to generate energy.