Organism level systems Study Guide

The brain and other parts of the nervous system, including the spinal cord, are incredibly complex and delicate structures. Damage to these areas, whether from injury or disease, often results in debilitating conditions that are difficult to treat. One major limitation arises from the fact that neurons, the primary cells of the nervous system, have a very limited ability to regenerate or repair themselves once damaged, especially in the central nervous system (brain and spinal cord). Unlike many other cell types in the body, mature neurons typically do not divide, making it challenging to replace lost cells. Furthermore, the brain is protected by the blood-brain barrier, a highly selective physiological barrier that prevents many substances, including therapeutic drugs, from reaching the brain tissue. This barrier is crucial for maintaining a stable internal environment in the brain but poses a significant hurdle for drug delivery. The intricate network of connections between neurons means that even seemingly small damage can disrupt widespread functions. Surgical interventions in the brain are high-risk due to the potential for further damage to vital areas and the complexity of accessing certain regions. The lack of complete understanding of the brain's complex processes and interconnections also limits the development of effective treatments. These factors combine to make treating damage and disease in the nervous system a significant challenge for medical science.

Infertility refers to the inability to conceive naturally. Modern reproductive technologies, especially In Vitro Fertilisation (IVF), frequently utilise hormones to overcome various causes of infertility. Follicle Stimulating Hormone (FSH) is a key hormone used to stimulate the ovaries to produce multiple mature eggs simultaneously. Normally, the female body releases only one egg per menstrual cycle. By administering high doses of FSH, usually through daily injections over several days, several follicles in the ovaries can be encouraged to develop and mature. This 'superovulation' increases the chances of retrieving multiple eggs for fertilisation, which is crucial for IVF success. Following FSH treatment, another hormone, Luteinising Hormone (LH), in the form of a human chorionic gonadotropin (hCG) injection, is often given to trigger the final maturation of the eggs and their release from the follicles. This timing is critical for egg retrieval. After fertilisation and embryo transfer, progesterone is often administered to help thicken the lining of the uterus. This creates a more receptive environment for the embryo to implant and supports the early stages of pregnancy, reducing the risk of miscarriage. These hormonal interventions effectively manipulate the natural menstrual cycle to maximise the chances of successful conception and pregnancy in individuals or couples struggling with infertility. Hormone therapy can also address infertility issues in males, such as low sperm count or poor sperm motility, by stimulating appropriate endocrine pathways, although its application is more common and elaborate in female treatments.