The Wikipedia page for "Cell (biology)" provides an extensive overview of the fundamental unit of life - the cell.

A heart transplant, or a cardiac transplant, is a surgical transplant procedure performed on patients with end-stage heart failure or severe coronary artery disease when other medical or surgical treatments have failed.

A heart valve is a part of the human heart that controls blood flow by opening and closing as the heart pumps.

HIV, or Human Immunodeficiency Virus, is a retrovirus that attacks the immune system of humans, leading to the acquired immunodeficiency syndrome (AIDS).

Kidney transplant or renal transplant is the organ transplant of a kidney into a patient with end-stage kidney disease (ESRD).

Liver transplantation or hepatic transplantation is the replacement of a diseased liver with the healthy liver from another person (allograft).

A pancreas transplant is an organ transplant that involves implanting a healthy pancreas (one that can produce insulin) into a person who usually has diabetes.