Respiratory System

Factoids

• Your lungs contain almost 1500 miles of airways and over 300 million alveoli.

• Every minute you breathe in 13 pints of air.

Primary function

• obtain oxygen for use by body's cells & eliminate carbon dioxide that cells produce

Respiratory system includes:

• airways leading into (& out of) lungs plus the lungs themselves

• Pathway of air: nasal cavities (or oral cavity) > pharynx > trachea > primary bronchi (right & left) > secondary bronchi > tertiary bronchi > bronchioles > alveoli (site of gas exchange)

• The exchange of gases (O2 & CO2) between the alveoli & the blood occurs by simple diffusion

Breathing is an active process

• - requiring the contraction of skeletal muscles. The primary muscles of respiration include:– the external intercostal muscles (located

between the ribs) – and the diaphragm (a sheet of muscle located

between the thoracic & abdominal cavities).

• During inhalation

• -the diaphragm contracts (becomes less dome shaped)

• -the rib muscles contract 

• -the rib cage moves up and out.These movements, enlarge the volume of the thoracic cavity, causing the pressure in the lungs to become lower than air pressure, and air will move into the lungs.

b. During exhalation

• -diaphragm relaxes (becomes more domed shaped)

• -the rib muscles relax

• -the rib cage moves down and in

• These movements decrease the volume of the thoracic cavity, causing the pressure in the lungs to become greater than air pressure and air is forced out of the lungs. 

• The walls of alveoli are coated with a thin film of water & this creates a potential problem.

• Water molecules are attracted to each other - surface tension.

• This surface tension increases as water molecules come closer together, which is what happens when we exhale & our alveoli become smaller (like air leaving a balloon).

• Potentially, surface tension could cause alveoli to collapse. If alveoli collapsed they'd contain no air & no oxygen to diffuse into the blood.

• To solve problem, the lungs produce a substance called surfactant that reduces surface tension.

How the Structure of the Alveoli is Related to its Function

a. Each alveolus is thin (0.1 to 0.2 mm in diameter). Allows for faster exchange of gases.

b. The walls of the capillaries and the alveoli are each made up of a single layer of cells – short distance so gases can be exchanged quickly

c. A film of surfactant (a lipoprotein) covers the alveoli. This lowers surface tension and prevents the alveoli from collapsing. 

d. There is a lot of blood supplied to the alveoli via capillaries. This allows for faster exchange of gases 

e. There are approximately 150 million alveoli. The large number increases surface area.

How are oxygen & carbon dioxide transported in the

blood? • Oxygen is carried in blood:

• 1 - bound to hemoglobin (98.5% of all oxygen in the blood)

• 2 - dissolved in the plasma (1.5%)

Carbon dioxide

• - transported from the body cells back to the lungs as:

• 1 - bicarbonate (HCO3) - 60%

• 2 - carbaminohemoglobin - 30% – formed when CO2 combines with hemoglobin

(hemoglobin molecules that have given up their oxygen)

• 3 - dissolved in the plasma - 10%

• Control of Respiration

• Your respiratory rate changes. When active, for example, your respiratory rate goes up; when less active, or sleeping, the rate  goes down. Also, even though the respiratory muscles are voluntary, you can't consciously control them when you're sleeping.

• Function of the Pleural Membranes- A thin membrane called the pleura surrounds each lung and lines the thoracic cavity.- The pleura secretes a small amount of fluid that lubricates each surface, so that they slide past one another as the lungs expand and contract

• Function of cilia in the respiratory tract-beat continuously , pushing mucus and foreign particles embedded in mucus up towards the pharynx where it is swallowed

Tobacco paralyzes cilia – they cannot sweep debris

out of air passages.

• Cigarette smoke prevents the cilia from beating and stimulates mucus secretion.

• Coughing is necessary to expel excess mucous but it contributes to bronchitis and emphysema.

• Cigarette smoke also kills phagocytic cells in respiratory epithelium. These cells normally help rid the lungs of foreign particles and bacteria.

• Cigarette smoke contains compounds that are modified in the body to form carcinogens.

• Smoking causes 80% of lung cancer deaths.

Cancerous lung