The structure of the respiratory system

what are the two main functions of the respiratory system?

1. pulmonary ventilation; the inspiration (breathing in) and expiration (breathing out) of air

2. gaseous exchange

   a. external respiration: movement of oxygen into the blood stream and carbon dioxide into the lungs

   b. internal respiration: the release of oxygen to respiring cells for energy production and collection of waste products

what is inspiration?

drawing of air into the lungs

what is expiration?

expelling of air from the lungs

pathway of air through the respiratory system

• air is drawn into the nasal cavity through the nose and travels down the pharynx, larynx and trachea

• trachea divides into the left and right bronchi as they enter the lung cavity

• bronchi subdivide into smaller bronchioles and end in alveolar ducts

• air enters into the alveoli for gaseous exchange

the passageways of the pharynx, larynx and trachea

has a mucous membrane and ciliated cells (covered in tiny hairs) which moisten, warm and filter the air before entering the lungs

alveoli definition

clusters of tiny air sacs covered in a dense network of capillaries which together serve as the external site for gaseous exchange

features of the alveoli

• walls are one cell thick and lined with fluid to accommodate gaseous exchange

what is gaseous exchange?

the movement of oxygen from the alveoli into the blood stream and carbon dioxide from the blood stream into the alveoli

how does the alveoli and surrounding capillary beds create the perfect conditions for gaseous exchange?

very slow blood flow and very thin, moist walls that are in extremely close contact - oxygen moves from the alveoli into the blood stream and carbon dioxide moves from the blood stream into the alveoli to be expired

the pathway of air diagram

simplified pathway of air

• nasal cavity/mouth

• pharynx

• larynx

• trachea

• bronchi

• bronchioles

• alveoli

what is the blood made up of?

45% cells

55% plasma

what is oxygen?

an essential gas required for aerobic energy production in the muscle cells. the greater the efficiency to inspire, transport and use oxygen, the greater the aerobic capacity to perform for long periods of low-intensity activity

two ways oxygen can be transported

1. carried with haemoglobin (Hb) in the red blood cells (approx. 97%) - to form oxyhaemoglobin. Hb + O2 = HbO2

2. carried with blood plasma (approx. 3%)

how many molecules of oxygen can each haemoglobin molecule combine with?

4

what is carbon dioxide?

the waste product of aerobic energy production in the muscle cells, must be removed from the respiring tissues and transported to the alveoli if effective performance is to be maintained

three ways carbon dioxide can be transported

1. dissolved in water and carried as carbonic acid (approx. 70%)

2. carried with haemoglobin (approx. 23%) → Hb + CO2 = HbCO2 / carbaminohaemoglobin

3. dissolved in blood plasma (approx. 7%)