The Mechanics of Breathing

Breathing The mechanism by which mammals ventilate their lungs Air will flow from a region of higher pressure to a region of lower pressure There are two muscular structures that control air pressure inside our lungs

Muscles involved in breathing: Intercostal Muscles Diaphragm

Intercostal Muscles Muscles associated with the ventral surface of the rib cage These muscles are found between the ribs There are two kinds

Intercostal Muscles Internal Intercostal Muscles Located in the inside of the ribcase External Intercostal Muscles Located in the outside of the ribcase

Intercostal Muscles

X-Section of Intercostal Muscles

Diaphragm A muscle layer that separates the thoracic cavity (region of the lungs) from the abdominal cavity (region of the stomach and the liver)

Diaphragm Found in all mammals Prime function: to assist in the ventilation of the lungs Works simultaneously with intercostal muscles To produce breathing-related movements

How breathing works Inhalation vs. Exhalation Lungs Diaphragm

HOW BREATHING WORKS- Inhalation To inhale, the external intercostal muscles contract Intercostal muscles expand the rib cage, lifting it up and out

HOW BREATHING WORKS- Inhalation the diaphragm contracts and pulls downward in the thoracic cavity This increases the volume of the thoracic cavity, causing the lungs to expand. How?

How Lungs Expand The thoracic cavity is relatively airtight An increase in its volume, produces a decrease in air pressure within the cavity This decrease in pressure draws the flexible walls of the lungs outward into the thoracic cavity Therefore, the lungs expand

HOW BREATHING WORKS- Inhalation As a result of this expansion, the air pressure within the lungs is lower than the air pressure in the external environment Recall: Air will flow from a region of higher pressure to a region of lower pressure Therefore, air enters the lungs

HOW BREATHING WORKS- Exhalation The diaphragm relaxes, returning to a dome- shaped curve

HOW BREATHING WORKS- Exhalation To exhale, the external intercostal muscles relax But the internal intercostal muscles contract to help pull the ribcage back to its original shape and position

HOW BREATHING WORKS- Exhalation These changes create a higher pressure in the thoracic cavity This causes the lungs to shrink, which results in a higher pressure in the lungs Air then moves out through the trachea

Inhalation and Exhalation Intercostal muscles contract, lifting rib cage up and out Diaphragm contracts and pulls downward The lungs expand, air is sucked in Intercostal muscles relax Diaphragm relaxes The ribs fall downward and inward Diaphragm back into dome shape, squeezing lungs and pushing air out

Exchange of Gases Review Capillary network and gas exchange

Composition of inspired and expired air under normal conditions 16.49% Oxygen 4.49% Carbon Dioxide 79.02% Nitrogen and Trace gases 20.94% Oxygen 0.04% Carbon Dioxide 79.02% Nitrogen and Trace gases

Lung Capacity The different volumes of air drawn in or pushed out by the lungs are distinguished

The volume of air inhaled and exhaled in a normal breathing movement Tidal Volume The volume of air inhaled and exhaled in a normal breathing movement

Inspiratory Reserve Volume The additional volume of air that can be taken in, beyond a regular or tidal inhalation

Expiratory Reserve Volume The additional volume that can be forced out of the lungs, beyond a regular or tidal exhalation

The total volume of gas that can be moved in or out of the lungs Vital Capacity The total volume of gas that can be moved in or out of the lungs VC=Tidal volume+IRV+ERV

The residual volume never leaves the respiratory system The amount of gas that remains in the lungs and the passageways of the respiratory system even after a full exhalation The residual volume never leaves the respiratory system If it did, the lungs and the respiratory passageways would collapse It has little value for gas exchange, because it is not exchanged with air from the external environment

Residual Volume

Respiratory Efficiency In mammals, the rate at which oxygen can be transferred into the blood stream for transport to the rest of the body There are factors that affect the respiratory efficiency Other animals have respiratory systems with special adaptations to help increase respiratory efficiency One adaptation is facilitated diffusion

The Respiratory System in Fish The gills of fish utilize counter-current flow A very effective mechanism for removing the maximum amount of oxygen from the water flowing over them

Gills & Gas Exchange: Counter-current Flow Oxygenated blood Deoxygenated Blood During counter-current flow, two types of fluids (blood and water) with different concentrations flow in opposite directions past one another

Counter-current Flow These two fluids (water and blood) are separated by thin membranes

Counter-current Flow Fish gills consist of a series of filaments supported by bony gill arches Each filament is covered with thin folds of tissue called lamella Blood flows across each lamella within a dense network of capillaries Filament Gill arch Gill arch High O2 Filament Lamellae Low O2

Counter-current Flow Water is deflected over the lamellae in a direction opposite the flow of blood in the capillaries Thus, the most highly oxygenated blood is brought close to the water that is just entering the gills and that has an even higher oxygen content than blood Vein-Oxygen poor blood Artery-Oxygen rich blood Low Oxygen High Oxygen Water flow Low Oxygen High Oxygen Blood flow

Counter-current Flow As the water flows over the lamellae, gradually losing its oxygen to the blood, it encounters blood that is also increasingly low in oxygen In this way, the gradient encouraging oxygen to move from the water into the blood is maintained across all the lamellae. Vein-Oxygen poor blood Artery-Oxygen rich blood Low Oxygen High Oxygen Water flow Low Oxygen High Oxygen Blood flow

Counter-current Flow Vein-Oxygen poor blood Artery-Oxygen rich blood Low Oxygen High Oxygen Water flow Low Oxygen High Oxygen Blood flow

Current vs. Counter-current Flow

Counter-current Flow Within each lamella, Counter-current flow enhances diffusion by maintaining a concentration gradient of oxygen between the water (relatively high in oxygen) and the blood (lower in oxygen) Countercurrent flow is so effective that some fish extract 85% of the oxygen from the water that flows over their gills.

Gas Exchange in Mammals In the mammalian lung, the oxygen gradient between the respiratory medium in the lungs and the blood in the capillaries is steadily reduced as oxygen passes across the alveoli wall The blood may take up about 50% of the oxygen in the respiratory medium entering the lungs

Gas Exchange in Fish In a countercurrent exchange system, the oxygen gradient is maintained over the whole of the gill The blood may take up as much as 80% of the oxygen carried in the respiratory medium entering the gill

The Respiratory System in Birds Respiration in birds is much different than in mammals. Birds do not have a diaphragm; instead, air is moved in and out of the respiratory system through pressure changes in the air sacs

Avian Respiratory System Anterior air sacs Inhalation: When the bird breathes in, the air sacs expand Most of the inhaled air passes into the posterior air sacs Some flow from there into the lungs At the same time, the air that was in the lungs moves into the anterior air sacs Posterior air sacs Anterior air sacs Lungs

Avian Respiratory System Anterior air sacs Exhalation: When the bird exhales, all the air sacs contract, forcing the air in the posterior air sacs into the capillary- lined tubes of the lungs Gas exchange takes place in the lungs Then, the air from the anterior air sacs is forced out through the trachea Posterior air sacs Anterior air sacs Lungs