RESPIRATORY SYSTEM
GROSS AND MICROSCOPIC ANATOMY
GAS EXCHANGE
PULMONARY VENTILATION
GAS TRANSPORT IN THE BLOOD
UPPER TRACT
PHARYNX: the nasopharynx, the oropharynx and the laryngopharynx. The nasopharynx is directly behind the nasal cavities, the oropharynx is directly in the back of the throat and the laryngopharynx is right above the larynx. Both air and food pass through the pharynx. Any air that flows through the nose or mouth will enter the pharynx and then travel to the lungs from there.
NOSE: Epithelial cells produce mucous. Hairs catch debri and provide minor defense against bacteria and foreign material. Bacteria can be cleaned out by blowing nose.
LOWER TRACT
LUNGS: The lungs are similar to a sponge and have a lot of holes in them. The right lung is made up of 3 lobes whereas the left lung only has 2 lobes. The reason for the left only having 2 lobes is to make room for the heart.
BRONCHIAL TREE: Lungs contain millions of air sacs and bronchial tree is a way of branching from the single trachea to these air sacs. The first two branches off the trachea are called the primary bronchi and one goes to the right lung with the other going to the left lung. Each of these branch into smaller and smaller bronchi: Bronchioles--> no longer contains any cartilage around it and is made up of elastic connective tissue and smooth muscle. These bronchioles branch into the tiny air sacs called the alveoli.
TRACHEA: made up of C-shaped cartilagenous rings and runs in front of the esophagus. The opening to the C is towards the back where the esophagus resides. Contains cilia but the cilia here move in an opposite direction from nasal cavities. Cilia move substances back towards the mouth in order to keep debris and bacteria out of the respiratory tract. Also, mucous cells that produce mucus
ALVEOLI: The alveoli in the lungs are the site for gas exchange. There are 300 million alveoli in each lung. Each alveolus is surrounded by capillaries in order for this gas exchange to occur. Made up of simple squamous epithelial cells
LARYNX: The larynx is also known as the voice box and its main function is for speech and singing. Surrounding the larynx are cartilagenous structures which help to support the larynx (this does not include the epiglottis). Examples are the thyroid cartilage and the coricoid cartilage. At the top of the larynx is a floppy piece of cartilage (epiglottis) usually open for normal breathing but when food or drink is swallowed it snaps closed over the larynx.
TYPE II: Type II alveolar cells are interspersed between the type I cells and produce pulmonary surfactant which is a lipid-based substance that reduces the surface tension of the alveoli. This keeps the alveoli open so they don't collapse
MACROPHAGES: Macrophages move around the inside of the alveoli cleaning up any debris or pathogens that got through.
TYPE I: Type I alveolar cells make up close to 97% of the alveolar cells and are the simple squamous epithelial cells for gas exchange.
EXPIRATION: (INCREASING PRESSURE)
INSPIRATION: (DECREASING PRESSURE)
The external intercostal muscles are between the ribs on the external side. These muscles contract and lift the ribcage out which elevates the sternum. If you take a breath to inhale, you can see how both the diaphragm moves down and the ribs move outward.
The diaphragm is a large muscle between the thoracic cavity and the abdominal cavity. It is made up of skeletal muscle and can contract under voluntary or involuntary control. When the diaphragm is at rest it is curved up towards the thoracic cavity. When it contracts it pulls down and is flattened. Increasing the cavity increases the volume so the pressure would decrease.
Pleural membranes are around the lungs and there is the parietal pleura that is attached to the thoracic wall and the visceral pleura that is firmly attached to the lung itself. Between these two membranes there is an extremely small cavity (pleural cavity). The pleural membranes are serous membranes they secrete a serous fluid which acts to give enough surface tension to the membranes. So they are held together tightly and thus move together with inspiration and expiration. This is how the lungs themselves can expand. .
Basically a passive process unless we need to forcefully exhale. Since the diaphragm is contracted to inhale, it will go back to relaxation without our conscious input. However, it will require energy as the diaphragm is skeletal muscle and if you remember, relaxation requires ATP to remove the myosin heads from the actin molecules. The lungs will decrease in volume by automatic recoil once they are done being stretched (compliance).
If a person needs to forcefully exhale to blow up a balloon, various muscles are used for voluntary expiration. The internal intercostal muscles contract pulling the ribs inward therefore decreasing the volume. The abdominal muscles are also used to push up on the diaphragm. (HEIMLICH)
PULMONARY CAPACITY
VC = IRV + TV + ERV
Inspiratory Reserve Volume (IRV) - this is the maximum amount of air that one can inhale above the tidal volume
Tidal Volume (TV) - this is the normal amount of air one breathes at rest which is usually about 500mL
Expiratory Reserve Volume (ERV) - this is the maximum amount of air that one can exhale above the tidal volume
Residual Volume - this is the amount of air that remains in our lungs after the most forceful exhalation so our lungs don't collapse
In order for gases to move either across the membranes of the lungs and also across the membranes of the cells, we have to look at gas pressures for the individual gases. At sea level, the atmospheric pressure is 760 mmHg. Only some of this is due to oxygen. Air is made up of a combination of gases so the pressure is made up off all the parts; oxygen, carbon dioxide, nitrogen. This means that they each exert a partial pressure in the mixture. The symbols for these are as follows: PO2= partial pressure of oxygen; PCO2 = partial pressure of carbon dioxide. To see how this works, you already learned that oxygen is 21% in atmospheric air. The partial pressure of oxygen would be 0.21 X 760 mmHg = PO2 159.6.
98% of the oxygen that moves across from the alveoli into the bloodstream binds with hemoglobin. The other 2% dissolves in the plasma. The oxygen molecule binds specifically to the iron atom in hemoglobin and when oxygen binds to hemoglobin we call it oxyhemoglobin. If oxygen is not bound to the iron we call it deoxyhemoglobin. As expected, oxyhemoglobin moves in the arteries to the cells and arterial blood is bright red. The veins carry blood that is a darker red due to hemoglobin with low oxygen content. When oxygen binds to hemoglobin it is a loose bond so that the oxygen can readily move from the bloodstream into the cells. Oxyhemoglobin ------------> Deoxyhemoglobin
Oxygen specifically binds to the iron molecule of each heme so one hemoglobin can bind a maximum of 4 oxygen molecules.
In order for oxygen to leave oxyhemoglobin there has to be a lower concentration of oxygen in the cells as the oxygen will move from an area of higher concentration in the blood to an area of lower concentration in the cells. The partial pressure of oxygen in the blood would be higher than the partial pressure of oxygen in the cells.
Oxygen repels the plasma chemically so it stays in the red blood cell. But when it encounters an environment with lower concentration of oxygen, the oxygen breaks the bond and readily moves into the lower partial pressure environment of the cells
The partial pressure of oxygen runs along the horizontal axis and the amount of oxygen that is bound runs along the vertical axis which is called saturation. By looking at this, if half of the oxygen is bound it would be at 50% and if you follow the dotted line across you can then see that the partial pressure when oxygen is 50% saturated is 26.8 mmHg.
The change in pressure and volume links to a law called Boyle's Law. This law states that in a contained vessel as volume increases, pressure will decrease. And the reverse is also true so that as volume decreases, pressure increases. Of course this has to come with an equation: P1V1 = P2V2. Our thorax is a contained vessel in which we fill and empty our lungs this way.