Blood pressure measurements are expressed as a fraction. The bottom number of this fraction indicates what?

A. Interferons:Interferons are signaling proteins produced by virus-infected cells that warn neighboring cells of infection. They stimulate the production of antiviral proteins in surrounding cells, limiting viral replication and spread, and enhancing the innate immune response.

B. Granzymes:Granzymes are proteolytic enzymes secreted by NK cells and cytotoxic T cells to induce apoptosis in infected or cancerous cells. They act directly on target cells rather than alerting neighboring cells.

C. Complement system globulins:Complement proteins help lyse pathogens and promote opsonization, but they do not act as signaling molecules to warn uninfected cells of viral threats. Their action is primarily destructive, not protective for nearby healthy cells.

D. Perforins:Perforins form pores in target cell membranes to allow granzymes entry. They are involved in direct cytotoxicity and do not provide antiviral signaling to surrounding cells.

E. Pyrogens:Pyrogens induce fever by acting on the hypothalamus and are part of systemic inflammatory responses, but they do not protect neighboring cells from viral infection directly.

A. Pulmonary artery:The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. It branches extensively into capillaries that surround each alveolus, allowing for efficient gas exchange of oxygen and carbon dioxide.

B. Inferior vena cava:The inferior vena cava returns deoxygenated blood from the lower body to the right atrium. It does not supply blood to the alveolar capillaries.

C. Vena cava:Both the superior and inferior vena cava return systemic venous blood to the heart but do not directly supply the lungs or alveoli with blood for gas exchange.

D. Aorta:The aorta carries oxygenated blood from the left ventricle to the systemic circulation. It is unrelated to the pulmonary capillary network surrounding alveoli.

E. Pulmonary vein:The pulmonary veins carry oxygenated blood from the lungs back to the left atrium. They collect blood from alveolar capillaries but do not supply the capillaries themselves.

F. Superior vena cava:The superior vena cava returns deoxygenated blood from the upper body to the right atrium. It does not participate in supplying blood to alveoli.