Advances in Biology: Cells, Immunity, and Reproduction
Stem Cells and Differentiation
Stem cells are pluripotent, meaning they can differentiate into any of the approximately 200 cell types that exist in the organism. Their differentiation into a specific cell type depends on chemical signals – substances that induce changes in gene expression, protein production, or other cellular processes. For example, they can become:
- Cardiac cells
- Retinal epithelial cells
- Pancreatic beta cells
Embryonic stem cells are obtained from blastocysts, a very early stage of embryonic development. These cells develop through later stages, including the fetal stage.
Adult stem cells are found scattered throughout various tissues in the body. They are responsible for the natural regeneration of damaged tissues.
Vaccines and Immunity
Vaccines prepare the body to protect against specific diseases. The principle behind vaccines involves antibodies, which are defensive proteins produced by a type of white blood cell (lymphocyte). Antibodies react specifically against an antigen (a substance triggering the immune response).
There are two main types of immunization:
Passive Immunization Vaccines
These preparations contain pre-formed antibodies against the disease-causing agent. Protection is short-term, typically lasting 3 to 6 months.
Active Immunization Vaccines
These vaccines contain dead or attenuated (weakened) microorganisms, or parts of them. They stimulate the body to produce its own antibodies against the disease-causing agent, providing long-lasting immunity, often for several years.
Antibiotics: Microbial Defense
An antibiotic is a substance produced by one microorganism that has the property to kill or inhibit the growth of other pathogenic microorganisms (like bacteria).
Important Note: Antibiotics are not effective against viruses.
The discovery of antibiotics began when Alexander Fleming observed that bacteria did not grow near a specific mold (Penicillium). In 1940, scientists successfully isolated the substance responsible for this growth inhibition and named it penicillin. Penicillin kills many types of bacteria and is relatively harmless to humans, so it became almost a miracle weapon against diseases like syphilis, gonorrhea, etc.
In 1943, streptomycin, the first antibiotic effective against tuberculosis, was discovered. As more natural antibiotics were discovered, a new problem emerged: the increasing frequency of antibiotic-resistant bacteria.
Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis (PGD) is an assisted reproduction technique. It allows for the screening of embryos for specific genetic conditions, such as the gene causing hemophilia, to prevent the transmission of the condition to children.
In Vitro Fertilization (IVF)
In Vitro Fertilization (IVF) is an assisted reproduction technique that involves fertilizing one or more ova (eggs) from the woman with sperm outside the body, in a laboratory setting (‘in vitro’).
Artificial Insemination (AI)
Artificial Insemination (AI) is an assisted reproduction technique that involves depositing sperm directly inside the uterus to facilitate fertilization.
Comparing IVF and AI
Both IVF and AI are assisted reproduction techniques. However, IVF involves fertilization outside the mother’s body, while AI involves introducing sperm inside the mother’s uterus.
Gene Therapy Applications
Gene therapy involves introducing genetic material (such as a functional gene) into a patient’s cells to achieve a therapeutic effect, potentially treating or curing a disease. For example, introducing the gene encoding a necessary coagulation factor could potentially treat hemophilia.
Transplant Rejection Immunology
The immune system recognizes transplanted organs as foreign (‘non-self’) and may attack or reject them. Cell membranes contain molecules that form the complex known as the Major Histocompatibility Complex (MHC).
The more similar these MHC molecules are between the donor and recipient, the greater the compatibility and the lower the chance of rejection will be. People who undergo a medical transplant are typically treated with immunosuppressive drugs to reduce the immune system’s response and prevent rejection.