Anatomy/Respiratory System

Respiratory System
<Anatomy

Mechanics
The Respiratory system is controlled in mammals by the diaphragm muscle. When the diaphragm relaxes, the thoracic cavity decreases in size. However, when the muscle contracts, it pulls downward, adding size to the thoracic cavity. While this happens, the intercostal muscles pull upwards on the ribcage, adding more space to the thoracic cavity. When the diaphragm relaxes, it pushes upward on the lungs, along with the intercostal muscles pushing downward on the ribcage. These muscles decrease the volume while increasing their internal pressure. When the diaphragm contracts, the lungs gain volume and lose pressure, causing a partial vacuum. Having no choice at this point but to follow the laws of nature, air follows the pressure gradient and rushes into the lungs.

There are two main breathing patterns: quiet breathing and forced breathing.

In quiet breathing, muscles contract voluntarily to let air in the lungs, but exhalation is passive.

In forced breathing, muscles contract voluntarily in both inspiration and expiration.



Measures of Pulmonary Ventilation
Minute ventilation 	= tidal volume * respiratory rate

the total volume of gas entering the lungs per minute.

Alveolar ventilation 	= (tidal volume - dead space) * respiratory rate

the volume of gas per unit time that reaches the alveoli, the respiratory portions of the lungs where gas exchange occurs.

Dead space ventilation 	= dead space * respiratory rate

the volume of gas per unit time that does not reach these respiratory portions, but instead remains in the airways (trachea, bronchi, etc.).

Control of Breathing
Unlike digestion, pupil contraction, and the beating of your heart, breathing is controlled both unconsciously and consciously. Few other actions are like this, blinking being another example. When you are not thinking about your breathing, such as when you are at rest, you will unconsciously regulate your air intake. However, when performing activities such as exercise, talking, or swimming, you are consciously deciding when to breathe. When not being actively controlled, breathing is controlled by the brain stem. The brain stem will automatically regulate breathing as needed by the body. For instance, when you exercise, you need ATP for muscle contraction to occur. When you strength train, you enter the zone called anaerobic exercise. This triggers anaerobic metabolism, which causes a buildup of lactic acid in the body. This lowers blood pH, which can be fatal. The brain stem then increases the rate of breathing.

Gas Exchange and Transport
Gas exchange

1. Oxygen in air dissolves into fluid lining the alveolus and diffuses through alveolar wall and capillary wall. 2. Oxygen enters blood plasma inside capillary. Gas exchange occurs in the capillary beds. 3. Oxygen binds to oxyhemoglobin in red blood cells. 4. Carbon dioxide diffuses out of blood plasma and into air in alveolus. 5. Oxygenated blood leaves heart and circulates through capillaries to tissue. 6. Red blood cells arrive at tissue, rich in oxygen that binds to the hemoglobin in the tissue. 7. Oxygen leaves hemoglobin in red blood cells and diffuses across blood capillary walls and into tissue cells. 8. Carbon dioxide diffuses out of tissue into blood plasma, which carries red blood cells into lungs. Completely dissociated hemoglobin enters the lung in red blood cells ready to be oxygenated.

Transport of gases in the blood is essential to life. The gases are carried in the blood in one of two ways: in the blood plasma or combined with hemoglobin.