Cells and control Revision Notes

Embryonic Stem Cell Function

Embryonic stem cells are found in very early animal embryos. They are pluripotent, which means they can differentiate into almost every cell type in the body. Their primary function is to form all the tissues and organs during embryonic development, leading to the formation of a complete multi-cellular organism.

Adult Animal Stem Cell Function

Adult stem cells are found in some tissues and organs throughout an animal's life. They are multipotent, meaning they can differentiate into a limited range of cell types within specific tissues. Their main function is to replace dead or damaged cells, facilitating tissue repair and maintenance, such as blood cells from bone marrow stem cells.

Meristem Function in Plants

Meristems are regions in plants containing meristematic cells, which are plant stem cells. These cells are totipotent, meaning they can differentiate into any plant cell type. Meristems are responsible for the plant's continuous growth, forming new stems, roots, leaves, and flowers throughout its lifespan. Examples include apical meristems at shoot and root tips, and lateral meristems for girth.

Potential Benefits of Stem Cell Use

Stem cells hold significant promise for treating various diseases and injuries. They can differentiate into specialized cells, allowing for the repair or replacement of damaged tissues. Examples include treating spinal cord injuries, Parkinson's disease, Alzheimer's disease, heart disease, stroke, burns, and diabetes. Stem cells may also be used to grow organs for transplantation, reducing reliance on organ donors and the risk of immune rejection. Additionally, they are valuable for drug testing and studying disease mechanisms in a laboratory setting without harming patients.

Potential Risks and Ethical Concerns

Despite the benefits, stem cell use carries risks. One major concern is the potential for stem cells, especially embryonic stem cells, to form tumours (teratomas) if their growth and differentiation are not precisely controlled. There's also a risk of immune rejection if the patient's body identifies the transplanted cells as foreign, which can be mitigated by using a patient's own adult stem cells, but remains a concern for embryonic or donor-derived cells. Transmission of diseases, although rare with proper screening, is another potential risk if cells are not sourced and handled appropriately. Ethical concerns surround the destruction of human embryos to obtain embryonic stem cells, prompting debate about the moral status of an embryo. While adult stem cells avoid this particular ethical issue, they are harder to obtain and have more limited differentiation potential.

Cerebral Hemispheres

The cerebral hemispheres form the largest part of the brain. They are responsible for intelligence, memory, language, and conscious thought. They also control sensations and voluntary actions across the body. The cerebrum is divided into two hemispheres, left and right, which are connected by a band of nerve fibres.

Cerebellum

Positioned at the back of the brain, below the cerebrum, the cerebellum plays a vital role in motor control. Its functions include coordinating muscle movements, maintaining balance, and regulating posture. Damage to the cerebellum can lead to problems with coordination and movement.

Medulla Oblongata

The medulla oblongata is located at the base of the brain, connecting to the spinal cord. It regulates involuntary life-sustaining functions. These include the control of breathing, heartbeat, blood pressure, and reflexes such as vomiting, coughing, and sneezing. It forms part of the brainstem.

Integrated Brain Function

While each part has specialised roles, the brain's regions work together. For instance, the cerebral hemispheres initiate a voluntary movement, the cerebellum refines its coordination, and the medulla oblongata ensures vital functions like breathing continue unimpeded during the action. This interconnectedness allows for complex physiological and cognitive processes.

Challenges of Brain Access

Directly examining brain tissue inside the skull is highly invasive and carries significant risks due to the brain's delicate nature and its vital functions. Surgical access can lead to infection, haemorrhage, or damage to critical brain regions, hence non-invasive methods are preferred. The skull itself provides a strong protective barrier, making direct observation impossible without intervention.

CT Scans: Structural Insights

CT (Computed Tomography) scans use multiple X-ray beams from different angles to create detailed cross-sectional images of the brain. These images show the brain's structure, allowing identification of abnormalities like tumours, strokes, or trauma. They are primarily used for diagnosing structural problems rather than functional activity. CT scans are quicker and cheaper than MRI, but involve ionising radiation.

PET Scans: Functional Insights

PET (Positron Emission Tomography) scans detect brain activity and function. A radioactive tracer (often a glucose analogue) is injected; active brain cells uptake more glucose. The tracer emits positrons which release gamma rays detected by the scanner. This creates images showing metabolic activity, highlighting areas of the brain that are more active during specific tasks. PET scans are valuable for studying neurological disorders and cognitive processes.

Comparison and Complementary Use

CT scans provide structural 'snapshots' of the brain, while PET scans illustrate its functional activity. Neither method requires direct surgical access to brain tissue. Often, both techniques are used together to gain a comprehensive understanding of a neurological condition, combining anatomical detail with metabolic function. This non-invasive approach significantly reduces risk to patients while maximising diagnostic and research capabilities.