Respiratory System Notes

Cellular respiration requires oxygen to burn oxygen and glucose to produce ATP energy.
- Carbon dioxide is a waste product that must be removed by the respiratory and circulatory systems.

Occurs in the alveoli of the lungs.
Oxygen passes into the blood, while carbon dioxide leaves the blood.
Blood with oxygen heads to the heart and then circulates through the systemic circuit to the tissues.
Oxygen is delivered to the tissues, and carbon dioxide from the tissues enters the blood.

External Respiration: Gas exchange between the air in the lungs (outside the body) and the blood (entering the body).
Internal Respiration: Gas exchange between the blood and the tissues.

Oxygen and carbon dioxide use simple diffusion to move into and out of the blood.
- Simple Diffusion: Small, nonpolar molecules move with the concentration gradient (from high to low concentration).
Oxygen and carbon dioxide are nonpolar, hydrophobic, and can easily cross the cell membrane.
For gases, concentration is referred to as partial pressure. Gases move along a partial pressure gradient.
For example, oxygen diffuses into the blood because there's a higher partial pressure of oxygen in the lungs and a lower partial pressure in the blood.
If the partial pressure gradient were reversed, oxygen would diffuse out of the blood, which is undesirable. Diffusion is dependent on the partial pressure gradient.

Diffusion stops (or net diffusion stops) when partial pressures reach equilibrium.
Equilibrium doesn't occur in the lungs due to:
- Continuous blood flow: Oxygenated blood is constantly moved away and replaced with deoxygenated blood.
- Continuous breathing: Depleted air is constantly exchanged, allowing for continuous oxygen uptake.

Trachea splits into the primary bronchus, which further splits into secondary and tertiary bronchi within the lungs.
Bronchioles are smaller branches after the tertiary bronchus.

Bronchus has cartilage around it, while a bronchiole does not.
Cartilage rings support the larger bronchi, preventing them from sticking together (like a moist balloon neck).
Terminal bronchioles are found inside the bundle of alveoli.

Includes the terminal bronchiole and alveoli, where external gas exchange occurs.
- Alveoli: Primary function is gas exchange; smallest bronchioles also allow for some gas exchange due to thin membranes (though with less surface area).

Nasal cavity contains nasal conchae, which are fine bony ridges with vascularized tissue.
- Functions:
  - Warming the air to body temperature: Air passes through narrow passages, warming it up rapidly.
  - Immune function: Nasal conchae create a vortex of air, throwing higher-density dust and pathogens onto the mucus to get filtered out.
Pharynx: Back of the nasal and oral cavities, divided into the nasopharynx, oropharynx, and laryngopharynx.
Food and air pathways cross in the pharynx, with the trachea anterior to the esophagus.
Talking while eating/drinking can lead to food/drink going down the wrong path because the epiglottis can't keep up with the opening and closing.

Slightly asymmetrical due to the heart's position on the left.
The left lung has two lobes, while the right lung has three lobes.
Pleural cavity surrounds the lungs (similar to the pericardial cavity around the heart).
- Functions to reduce friction and keep the lungs inflated.

Two membranes:
- Visceral pleura (inner membrane)
- Parietal pleura (superficial membrane)
Space between the two membranes is the pleural cavity.

Intra-alveolar pressure: Air pressure inside the lungs (similar to environmental pressure).
Intrapleural pressure: Air pressure in the pleural cavity (slightly lower than intra-alveolar pressure).
Transpulmonary pressure: Difference between intrapleural and intra-alveolar pressure.
- $Transpulmonary\ Pressure = Intrapleural\ Pressure - Intra-alveolar\ Pressure$
The transpulmonary pressure should be negative, i.e., lower pressure in the intrapleural space.
- The lungs are elastic and tend to collapse. Slightly lower intrapleural pressure helps keep them inflated.
Analogy: Balloon inside a jar. Inflating the balloon can be achieved either by forcing air in or sucking air out of the jar, the vacuum inflating the balloon by pulling it outward.

If the parietal pleura is punctured, the intrapleural pressure equalizes with the environment, and the lungs collapse.

Normal quiet inhale and exhale:
- Inhale: Diaphragm and intercostal muscles contract, expanding the thoracic cavity.
- Exhale: Muscles relax, and lungs passively return to their normal lower capacity.
Forceful exhale: Additional muscles (abdominal muscles) are engaged to forcefully depress the rib cage and expel more air.

Measures lung volume/air expelled.
Normal quiet exhalation capacity: 300-500 mL.
The psychological aspect: Thinking about breathing often leads to deeper breaths than normal.

Bronchioles: Look for hyaline cartilage (present in bronchus, absent in bronchiole).
Alveoli: Tiny sacs that greatly increase the lung's surface area.

Each lung has a surface area of about half a tennis court.
Greater surface area facilitates more external respiratory exchange.
Alveoli appear as small spaces (like a cut sponge) on a slide.
Capillaries and blood vessels appear as filled-in spaces. Larger spaces lined with epithelial tissue are bronchioles or bronchi.

Produced by the fetus to reduce the surface tension of fluid in the lungs.
Essential for the baby to take its first breath and inflate the lungs.
Proper surfactant production is a key determinant in the viability of premature births.
Around 26 weeks is a crucial cutoff for premature births due to surfactant production.