JUSTIFICATIONS

Peristaltic waves of digestive tract regulate swallowing of food. 

Once in the esophagus the food moves towards the stomach by a progressive wave of muscle contraction that proceeds along the esophagus, compressing the lumen and forcing the food ahead. Such waves of contraction in the muscle layers surrounding a tube are known as peristaltic waves. It takes about a second to reach the stomach. Swallowing can occur even if the person is upside down or zero gravity because it is not primarily gravity but the peristaltic wave that moves the food to stomach. The lower esophageal sphincter open and remains relaxed throughout the period of swallowing, allowing the arriving food to enter the stomach. After the food passes, the sphincter closes, resealing the junction between the esophagus and stomach. If large particles does not reach the stomach during the initial peristaltic wave and maintained distension of the esophagus by the particle activates receptors, initiate reflexes causing repeated waves (secondary peristalsis).

Hemoglobin facilitate the diffusion of O2 from alveoli into plasma.

Each hemoglobin molecule is a protein made up of four subunits bound together. Each subunit consist of a molecular group known as heme and a polypeptide attached to heme. The four polypeptides of a hemoglobin molecule are called globin. Each of the four heme group in hemoglobin molecule contains one atom of iron (Fe2+) to which oxygen binds. Because each iron atom can bind one molecule of O2 a single Hb can bind 4 O2 molecules.

The binding of oxygen to these heme molecule breaks some of these bonds between globin units leading to conformations changes that leaves the remaining binding sites exposed. This binding of O2 molecule to deoxyhemoglobin increases the affinity of the remaining sites on the same hemoglobin molecule. After the first oxygen molecule dissociates and is dropped off at the tissues the next O2 molecule dissociates more rapidly. When all four heme sites are occupied the hemoglobin is said to be saturated.

ATP is required for muscle relaxation.

In muscles SERCA (Sarcoplasmic Endoreticulum Calcium ATPase) is responsible for lowering the intracellular calcium concentration and thus bringing about the relaxation of the contractile event. SERCA is an enzyme that functions in coupling the energy from hydrolysis of ATP to the active transporter of key ions across membranes. SERCA is a P type ion channel enzyme. Calcium ions are exported to the luminal side of the sarcoplasmic reticulum membrane and protons are imported to sarcoplasm. 2 Ca2+ are transported for each ATP hydrolyzed. Thus, ATP is required for muscle relaxation.

 Left ventricular dysfunction can lead to pulmonary edema.

Failure of the left ventricle-whether due to diastolic or systolic dysfunction lead to pulmonary edema. The accumulation of fluid in the interstitial space of lung or in the air space themselves, impairs gas exchange. The reason for such accumulation is that the left ventricle fail to pump blood to the same extent as the right ventricle, so the volume of blood in all the pulmonary vessel increases. The resulting engorgement of pulmonary capillaries raises the capillary pressure above its normally very low value, causing filtration to occur at a rate than the lymphatics can remove the fluid. 

Peripheral chemoreceptors control pulmonary ventilation.

Peripheral chemoreceptors are sensory extension of peripheral nervous system into blood vessel where they detect change in chemical concentration, located high in the neck at the bifurcation of the common carotid arteries and in the thorax of the arch of aorta are called carotid bodies and aortic bodies respectively. In both locations they are quite close to, but distinct form, the arterial baroreceptor and are in intimate contact with arterial blood. The carotid bodies in particular are strategically located in monitor oxygen supply to brain. The peripheral chemoreceptor are composed of specialized receptor cell stimulated mainly by decrease in the arterial pO2 and an increase in the arterial H+ concentration. These cells communicate synaptically with neuron terminals from which afferent nerve fiber pass to the brainstem. There they provide excitory synaptic input to the medullary inspiratory neurons. The carotid body input is the predominant peripheral chemoreceptor involved in the control of respiration (pulmonary ventilation).

ECG is a tool for evaluating the electrical currents within the heart.

The electro cardiogram is a tool for evaluating the electrical events within the heart. When action potential occurs simultaneously in many individual myocardial cells, currents are conducted through the body fluids around the heart and can be detected by recording electrodes at the surface of the skin.

The first deflection, the P wave corresponds to current flow during atrial depolarization. The second deflection, QRS complex, occurring approximately 0.15 sec later, is the result of ventricular depolarization. The final deflection, the T wave , is the result of ventricular repolarization. It is usually not evident on the ECG because it occurs at the same time as QRS complex.

A typical ECG makes use of multiple combinations of recording locations on the limbs and chest (called ECG leads) so as to obtain as much information as possible concerning different areas of the heart. ECG is not a direct record of the changes in membrane potential across individual cardiac muscle cells. it is a measure of the currents generated in the extracellular fluid by the changes occurring simultaneously in many cardiac cells. Because many myocardial defects alter normal action potential propagation, and thereby the shapes and timing of the waves, the ECG is a powerful tool for diagnosing certain type of heart diseases.

Osteoblasts are bone forming cells.

The three types of bone cells involved in bone formation and breakdown are osteoblasts, osteocytes and osteoclasts. Osteoblasts are the bone - forming cells. They secrete collagen to form a surrounding matrix, which then becomes calcified, a process called mineralization. Once surrounded by calcified matrix , the osteoblasts are called osteocytes. The osteocytes have long cytoplasmic processes that extend throughout the bone and form tight functions with other osteocytes Osteoblasts convert the cartilaginous tissue at the shaft edge to bone.

Osteoclasts are bone desorbing cells.

Osteoclasts are large, multinucleated cells that break down (resorb) previously formed bone by secreting hydrogen ions , which dissolves the crystals , and hydrolytic enzymes , which digest the osteoid. The osteoclasts are the mediators of the continuous destruction of bone. They occupy small depressions on the bone's surface , called Howship Lacunae: the lacunae are thought to be caused by erosion of the bone by the osteoclast's enzymes.

Hyperventilation leads to alkalosis

Respiratory alkalosis occurs when the levels of CO2 and O2 are not balanced and the concentration of CO2 falls too low. This causes the pH of the blood to rise and become too alkaline as CO2 dissolves in the blood to form Carbonic acid in normal conditions and maintains pH of the body. Hyperventilation is typically the underlying cause of respiratory alkalosis as during hyperventilation, the rate of ventilation - rate of O2 and CO2 increases manifold, resulting in excess of CO2 expulsion from the lungs, in turn leading to abnormally low CO2 levels.