Lungs

Lungs

When doing dissections of fetal pigs or other organisms, lung tissue is characteristically squishy. This is owing to its porous nature, much like a sponge. We already know from looking at the secondary bronchiBranches from the primary bronchi that lead to each lung lobe. Also called segmental bronchi of each lung. The left lung is smaller than the right lung because of the cardiac notchA concave space on the left lung that accommodates the heart.. This cardiac notch is the space that the heart occupies. Lungs and their alveolar clusters are the site of a process called external or alveolar respirationThe process of gas exchange, including ventilation, external and internal respiration.. Sometimes we get to a quiz or a test. Students will approach me, saying they don’t remember the term external or alveolar respiration. They ask, what is this? Should I know this? I think these two words may have a previous meaning for you. Their combined effect here is somewhat lost. The term respiration specifically applies to the exchange of gases across a membrane. Here in the lungs is external or alveolar respiration. This is because what is in your alveoliMicroscopic air sacs in the lungs where gas exchange occurs between air and blood. is not yet in your body. We have the same situation with the digestive system. The contents of your GI tract are not in your body. They are outside until they diffuse through the cellsThe basic structural and functional units of life. lining your small intestine. Then they enter the hepatic portal system.

Speaking of vascularization your lungs are vascularizedTo invade a tissue with blood capillaries. by two different circuits with two different purposes. Bronchial circulation involves arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr and veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge serving the lungs. They function as if the lungs were any other tissue in the body. Therefore, the arteries carry oxygen-rich blood. It goes to the simple squamous cells and the alveolar great cells in your lungs. The veins of bronchial circulation carries the oxygen poor blood back to the vena cava. There was also another circuit called the pulmonary circuitThe circulation of blood between the heart and the lungs, where blood is oxygenated.. This circuit carries blood directly from the right ventricle of the heart. The blood flows through the pulmonary artery and into the lungs for oxygenation. This blood is not used by the cells of the lungs. This blood returns to the left atrium of the heart and is oxygen rich. It then leaves the aorta and is distributed through the systemic circuitThe part of the circulatory system that carries oxygenated blood from the heart to the body and retu and oxygenates peripheral tissues.

Pleura

The pleuraThe double-layered membrane surrounding the lungs and lining the thoracic cavity. of the lungs is a serous membrane similar to that of the pericardiumThe membrane surrounding the heart.. There are two layers. The parietal layer is superficialNear the surface of the body.. The visceral layer is deepAway from the surface of the body.. Between them is the intra pleural cavity. The visceral pleura dips into the interlobar fissures. The septa is just connective tissue separating each lobe of the lungs. We now have our first picture. It shows us very clearly the three lobes of the right lung. It also shows the two lobes of the left lung.

The intrapleural cavity of each lung holds only about 1/4 cup of fluid. The fluid is somewhat straw colored owing to albuminA plasma protein that helps maintain osmotic pressure and transport substances. concentration and resembles the lipid like texture of melted butter. If you consider 1/2 a stick of butter melted down, it is not a lot of fluid. It is insufficient to lubricate each lung. The generalized term given to inflammation of the pleura is pleurisy. This can be bacterially caused or caused by other things like autoimmune diseases. Pleurisy effectively eliminates the intrapleural cavity. It causes the visceral and parietal pleuraThe outer layer of the pleura that lines the thoracic cavity. to rub against each other with each breath. I know this because I’ve had it it feels like there’s an elephant sitting on your chest.

The pleura and the fluid-filled intrapleural space reduce friction as the lungs expand and contract in ventilation. They work like any serous membrane. The pleura are also for containment.  As with other important organs in the thoracic cavityThe body cavity housing the heart and lungs., we don’t want infection in one organ to seep into another.  This is why the esophagusThe muscular tube that transports food from the pharynx to the stomach via peristalsis. and trachea have adventitiaThe outermost connective tissue layer of an organ, such as the esophagus, which binds it to surround and the heart and lungs have these serous membranesThin tissues that line body cavities and secrete fluid..  The pleura play one last but very important role in creating a pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. gradient in pulmonary ventilation.

Bronchopulmonary Segments

As mentioned previously, the trachea separates into the primary bronchiThe first branches of the trachea that lead into the lungs. Also called lobar bronchi which each lead to one lung left or right.  The secondary bronchiThe large airways that branch from the trachea into the lungs, dividing into smaller bronchioles. can also be called segmental bronchi. In this diagram of both lungs, the broncopulmonary segmentsThe subdivisions of lung lobes, supplied by tertiary bronchi. are diagrammed and listed by name. The corresponding secondary bronchi are labeled with the same number as the broncopulmonary segment they serve. During developmentThe process of growth and differentiation., both lungs have 3 lobes at first. As the heart becomes established, it is one of the first organs to become established. It carves out the cardiac notch in the left lung. This process reduces it to two lobes. Although reduced to two lobes, the left lung retains the same 10 bronchopulmonary segmentsFunctional units of the lungs, each served by its own tertiary bronchus and blood supply. that the right lung has.

Pneumothorax & Pleural Effusion

The common term collapsed lung usually is referring to a pneumothorax. In this situation, alveoli and the visceral pericardium have been breached. This breach allows air to seep into the intrapleural space with each breath. Alternatively, the superficial chest wall and parietal pleura have been breached. Because there’s no outlet to the intra pleural cavity pressure builds up and pushes back against the squishy squishy lung. The pressure cannot expand the pleural cavity outward the ribsCurved bones forming the rib cage; articulate with thoracic vertebrae and most with the sternum. prevent that from happening. One of my favorite movies is 3 kings a movie made back I think in 1999. The film includes Mark Wahlberg in one of his first roles as an actor. At that time, he was still being referred to as Marky Mark. In the movie, he gets shot in the lung. He has a pneumothorax, and they tap the pleural space with a valve. This allows him to let the pressurized pleural space lose some air and consequently some pressure. This process allows the lung to reinflate. Although not a permanent fix it did the job in the movie at least.

Pleural effusion has the same end result as a collapsed lung. However, pleural effusionFluid accumulation between the layers of the pleura around the lungs. refers to the fluid build-up in the intrapleural cavity. The same thing happens as with a pneumothorax.  The increased pressure in the intrapleural cavity pushes back on the squishy and porous alveoli of the lungs. This condition can result from low pressure conditions in the atmosphere. For example, at the highest elevations on Everest, the air pressure is extremely low. It is so low that it actually wicks fluids out of your body. The atmosphere is doing that over the surfaces of the alveoli in your lung. This leads to the pooling of the fluid in the intrapleural cavity. Yes, you can tap that cavity to reduce the fluid build-up. You can deliver a big shot of corticosteroidsSteroid hormones from the adrenal cortex, including glucocorticoids and mineralocorticoids.. Alternatively, you can just climb down the mountain and live at a reasonable elevation.