Systems Biology and Tissue Types - MCAT Biological and Biochemical Foundations of Living Systems

During depolarization, voltage-gated sodium channels open and allow a rapid influx of sodium ions. The membrane voltage rises from its resting potential of -70 mV to 35 mV. Depolarization is not associated with endocytosis of neurotransmitters.

When blood passes from the right atrium into the right ventricle, it must pass through the tricuspid valve.

The mitral, or bicuspid, valve separates the left atrium and ventricle. The semilunar valves are the aortic and pulmonary valves. The aortic valve separates the left ventricle and aorta, while the pulmonary valve separates the right ventricle and pulmonary arteries.

The pulmonary arteries bring deoxygenated blood from the body into the lungs, where carbon dioxide is exchanged for oxygen. The oxygen-rich blood leaves the lungs to return to the heart through the pulmonary veins. This is the only occurrence in which arteries carry oxygen-poor blood and veins carry oxygen-rich blood.

The thoracic aorta supplies the bronchi, esophagus, pericardium, chest wall, and diaphragm with oxygenated blood. The inferior vena cava collects deoxygenated blood from the lower extremities and transports it to the heart. In the upper limbs, superficial veins merge to form the axillary vein. These empty into the superior vena cava, and then into the heart.

The glycoproteins , , and are responsible for the A, B, and O blood types in humans, respectively.

and are dominant to , meaning that blood types A and B are dominant to O. Additionally, and can be co-dominant, giving the AB blood type. The person in the question has and glycoproteins, giving the patient the A blood type, as is dominant to . Genotypically, they will carry alleles for both A and O blood type, but their phenotype will be only A.

Hemoglobin displays the unique property of cooperativity, meaning that once one molecule of oxygen has bound to the hemoglobin molecule, adding the three next molecules is easier. This gives the hemoglobin binding curve the typical sigmoidal oxygen dissociation curve.

Cooperativity helps hemoglobin bind four oxygen molecules in the lungs and maintain the bonds until it enters a region of very low oxygen partial pressure. The most energy is required to remove the first oxygen; the next three are easier because the cooperativity has been lessened. As hemoglobin travels, it is able to selectively distribute oxygen the areas of the body that need it most because of this property.

Several factors are capable for shifting the oxygen dissociation curve. A decrease in pH or an increase in carbon dioxide partial pressure indicates a need to remove carbon dioxide wastes from the system. Hemoglobin affinity for oxygen will decrease under these conditions in order to accommodate the carbon dioxide for removal. Decreased carbon dioxide partial pressure will increase the affinity for oxygen rather than decrease it.

Increased temperature and increased 2,3-bisphosphoglycerate will also decrease the hemoglobin affinity for oxygen.

A decrease in binding affinity shifts the oxygen dissociation curve to the right, while an increase shifts the curve to the left.

Antibodies are not responsible for the removal of pathogens, only the binding and/or tagging foreign materials for destruction by other immune cells. Antibodies are released into the blood stream and bind to matching antigens on the surface of infectious cells. By binding and tagging foreign materials, antibodies enhance the ability of other immune cells (such as macrophages) to engulf or phagocytose the foreign material, leading to its destruction and removal.

Antibodies themselves cannot remove pathogens; they only aid in the removal of pathogens by immune cells.

Active immunization is that which occurs as a result of the immune response of the affected individual. Passive immunization is the passing of antibodies from one entity to another, such as a pregnant mother who passes antibodies through the placenta to the fetus. Artificial immunization occurs when one is exposed to the antigen of the infection without having to experience the infection. The antigen can be a weakened or dead form of the microbe. Natural immunity is achieved when one is infected by a live form of the microbe. In both natural and artificial immunity, the immune system generates antibodies and memory cells to fight off future infections.

Calcitonin lowers plasma calcium, while parathyroid hormone (PTH) increases it. Insulin and glucagon are responsible for blood glucose, not calcium.

Microvilli surround villa which line the small intestine. These structures greatly increase the surface area (and therefore nutrient absorption capability) of the small intestine.

Homeostasis, or "steady-state" physiology, is the system of feedback loops that enables an organism to create a stable, adaptive environment. For example, the pancreas and the brain together work to regulate the blood sugar levels via the hormones insulin and glucagon.

Compact and spongy bone have similar chemical and structural compositions and are both hard and resistant to compression; however, due to the fact that compact bone is denser, nutrients are delievered through canals called Haversian systems in compact bone; spongy bone is less dense and lacks these specialized canals.

Blood pressure tends to be the greatest near the heart, and decreases as blood flows to the capillaries. The pressure is greatest at the aorta and gradually decreases as blood moves from the aorta to large arteries, smaller arteries, and capillaries. The pressure is lowest in the venous system, which is why blood can pool in the veins and act as a "blood reservoir". Veins contain valves that allow them to pump blood back to the heart.

Carbon dioxide is usually circulated in human blood in the form of , or bicarbonate. This is an important part of the blood buffering system, as the bicarbonate ion is the conjugate base of carbonic acid.

The lower esophageal sphincter separates the esophagus from the stomach. When stomach acid and contents leak through the lower esophageal sphincter, the acid irritates the esophagus and can lead to pain around the area of the heart. The heart is not actually affected.

During inhalation, the external intercostal muscles and diaphragm both contract to help expand the thoracic cavity and draw in air. The internal intercostal muscles are involved in exhalation, and compress the thoracic cavity during contraction.

Cellular respiration is more active during running than during walking, producing more carbon dioxide. The carbon dioxide will enter the carbonic anhydrase reaction, producing more protons in the blood and lowering the pH. To counter this drop in pH, runners will naturally increase their breathing rate. This serves to deliver more oxygen to the muscles, as well as to remove more carbon dioxide wastes and prevent acid from building in the blood.

The two muscles that help with breathing are the diaphragm and the external intercostal muscles. The diaphragm pulls the thoracic cavity downward and the external intercostal muscles expand the cavity outward. This expansion of the thoracic cavity leads to a decrease in pressure and allows air to be drawn into the lungs.

The plasma portion of the blood is the extracellular matrix that suspends the erythrocytes and lymphocytes traveling through circulation. The plasma contains water, proteins (chiefly albumin), electrolytes, and clotting factors (such as thrombin). Whole blood contains the cells, as well as thx extracellular plasma. Blood serum refers to blood plasma that has had the clotting factors removed.