Gas Exchange and Respiratory Systems

• Gas exchange involves the uptake of oxygen for cellular respiration and the elimination of carbon dioxide.

Gas Movement and Pressure

• Gas movement relies on diffusion, influenced by gas pressure, which relates to concentration.
• Partial pressure describes the pressure and concentration of each gas in a mixture like air.
• Gases move between environments based on relative partial pressures; oxygen moves from high to low pressure.
• Extracting oxygen from water is more challenging than from air due to its lower concentration (about 30 times less).

Types of Respiratory Systems

• Respiratory surfaces facilitate gas exchange with the environment, requiring moist plasma membranes.

Respiratory Surfaces

• Small organisms with low metabolic demands use body surfaces for respiration, for example, earthworms and some amphibians.
• The dense capillary network beneath the body surface enables direct exchange.

Gills

• Gills are outfoldings of the body surface that increase surface area for exchange.
• Gills are prevalent in aquatic organisms with high oxygen demands.
• Ventilation, moving water over gills, is necessary to maintain partial pressure gradients.
• Fish use a countercurrent exchange system to maximize the differences in partial pressure.

Tracheal Systems

• Tracheal systems consist of branching air tubes within the body.
• These tubes bring air in contact with moist epithelium for internal gas exchange.

Lungs

• Lungs have maximized surface area for gas exchange via capillaries.
• The circulatory system is essential for transporting gases to and from tissues.

Breathing Mechanisms

• Breathing ventilates the lungs, bringing in oxygen and removing carbon dioxide.
• Surfactant, a lipoprotein, reduces surface tension in the alveoli to prevent lung deflation.

Positive Pressure Breathing

• Amphibians lower their oral cavity floor, close their mouth and nostrils, and raise the floor to force air into the lungs; exhalation results from lung recoil.
• Birds use two inhalation/exhalation cycles for complete air exchange.
• On the first inhalation, air fills posterior air sacs; on the first exhalation, air is forced into the lungs.
• On the second inhalation, air passes from the lungs to the anterior air sacs; final exhalation pushes air out of the body.

Negative Pressure Breathing

• Humans flare the rib cage and contract the diaphragm, increasing thoracic volume and decreasing pressure.
• Air moves from high (outside) to low pressure (inside the lungs) during inhalation.
• Relaxing the rib cage and diaphragm decreases volume, increases pressure, and forces air out during passive exhalation.

Human Lung Volumes

• Lung volumes are monitored in diseases like asthma and COPD to assess disease progression and treatment effectiveness.
• Tidal Volume is about 500ml and measures the air exchanged during a normal breath.
• Inspiratory Reserve Volume (IRV) is the amount of air forcefully inhaled after a normal breath.
• Expiratory Reserve Volume (ERV) is the amount of air forcefully exhaled after a normal breath.
• Vital Capacity is the total air available for exchange.
• Residual Volume is the air that remains in the lungs to ensure inflation.
• Total Lung Capacity equals vital capacity plus residual volume and varies by height.

Human Breathing Control

• Breathing is controlled by monitoring blood pH; a drop due to carbon dioxide triggers the medulla oblongata.
• The medulla signals rib and diaphragm muscles to contract faster and more completely, increasing breathing rate and depth.
• Drugs like anesthesia and alcohol can suppress the breathing centers, decreasing or stopping breathing.

Respiratory Gasses in Humans

• Gas exchange in the bloodstream, tissues, and lungs is based on relative partial pressures.
• Gasses follow partial pressure gradients, moving to lower pressure.