Circulatory and Respiratory Systems - NCLEX-PN

Gas exchange in the lung occurs exclusively in the alveoli, the tiny grape-like clusters of sacks at the terminus of the bronchioles of the lung. The gas contained in the larger structures of the lung - the trachea, bronchi, and bronchioles, is termed "dead space" as it does not participate in gas exchange.

Gas exchange in the alveoli occurs by the process of simple diffusion. The blood that enters the lung capillaries is relatively low in oxygen and high in , in comparison to the room air that is drawn into the alveoli during respiration. The separation between the capillaries and the alveolar epithelium is thin enough that these gasses can exchange across their pressure gradients by the process of simple diffusion.

The main trigger for the impulse to breathe is high carbon dioxide (decreased blood pH). In response to a decrease in blood pH, the medullary respiratory center triggers the diaphragm and the external intercostal muscles to increase breathing rate.

Myoglobin, an oxygen-binding protein in the muscle tissue, can bind with one molecule of oxygen. Hemoglobin, the main oxygen-binding metalloprotein in red blood cells, can bind four molecules of oxygen.

While hyperventilation or tachypnea may be triggered by various forms of acidosis, they will not cause a decrease in blood pH, but rather push the blood into a more alkaline state. This occurs due to loss of carbon dioxide during respiration, followed by a compensatory decrease in bicarbonate ions. The result is in an elevation in the pH of the blood. This condition is known as respiratory alkalosis.

Dead space is the volume of air that remains in the trachea, bronchi, and bronchioles during respiration. It does not enter the alveoli and so does not participate in gas exchange. In the average adult, the amount of air left in the dead space after expiration is .

Tidal breathing is the term for relaxed inhalation and exhalation (as opposed to maximum inspiration and forced exhalation). The average volume of air breathed into and out of the respiratory system during tidal breathing is .

Carbon dioxide has paracrine effects in the airway, causing the smooth muscle of bronchioles to relax. When the partial pressure of carbon dioxide in the alveoli increases, the bronchioles dilate. This allows for increased ventilation.

There are many factors that can cause bronchioconstriction. Some of them are normal physiological responses, such as parasympathetic input or decreased partial pressure of carbon dioxide in the alveoli. Other causes are pathological, such as allergic bronchioconstriction or asthma triggered by cold air.

The diaphragm is innervated by the phrenic nerve. This nerve exits the spine at C3-C5. In the case of spinal cord trauma, if injury occurs above C3, the diaphragm is no longer able to function on its own and breathing assistance is generally required.

Vital capacity is the maximum volume of air a person can exhale after maximum inhalation. Residual volume is the air that remains in the lung after forced exhalation, while functional residual capacity is the volume of air that remains in the lung after a relaxed exhalation.

The only chamber of the upper respiratory tract that is shared by both the respiratory and the digestive systems is the pharynx. The pharynx is the part of the throat that is immediately posterior to the mouth and the nasal cavity, and superior to the trachea, larynx, and esophagus.

The pharynx is made up of three divisions: the laryngopharynx, the oropharynx, and the nasopharynx. There is no portion of the pharynx called the sinopharynx.

Depolarization is able to travel in a uniform wave through myocardium due to the presence of gap junctions. These junctions allow the depolarizing current to be transmitted directly from cell to cell in the heart. Striation in cardiac muscle is a feature of contraction, created by overlapping thick and thin contractile filaments. Desmosomes are strong fiber-like anchors between myocardial cells, and T-tubules, while an important part of depolarization, are not responsible for the rapid inter-cellular communication that occurs as a result of the presence of gap junctions.

The only anucleate blood cells are erythrocytes, or red blood cells. These cells are created with nuclei, but each daughter cell will then lose its nucleus in order to create more suface area for hemoglobin to bind oxygen and for easier passage through narrow capillaries.

Monocytes, the largest of all the leukocytes, make up just 2-10% of the average white blood cell count. These white blood cells will mature into macrophages to phagocytose foreign matter.

Macrophages consume bacteria, cancer cells, and cellular debris via phagocytosis. Once these elements are within the cell, the macrophage is able to use lysosomes to break them down and prepare them for release into the blood as waste, which will eventually be excreted.

Platelets are small cell fragments that play an important role in hemostasis, or clot formation. Once activated, platelets release clotting factors that recruit more platelets till a clot is formed and bleeding stops.

Diapedesis, also known as leukocyte extravasation, is the process by which white blood cells move into and out of blood vessels. This process includes four stages: chemoattraction, rolling adhesion, tight adhesion, and endothelial transmigration. This process is integral in the delivery of white blood cells to sites of infection and in their return into the blood stream to mobilize and facilitate the excretion of waste.