Lesson Background and Concepts for Teachers
(Have available a computer with internet access and a projector to show students the 10-slide
Blood Clots, Polymers and Strokes Presentation
along with the information below, as well as a showing them the 3-D animation and short videos listed in the Additional Multimedia Support section that are helpful in teaching this material. The slides are "animated," so clicking the mouse or space bar brings up the next item. Also, having a real brain for students to see and touch, or a classroom model, is helpful.)
Strokes and the Brain
Every year, approximately 800,000 people experience strokes, the leading cause of adult-onset disability in the U.S. A stroke, also called a brain attack, is a loss of brain function due to an interruption of blood supply to the brain. Lack of adequate blood supply or
, starves the affected region of the brain of nutrients and can cause it to die. The human brain has more than 100 billion neurons and different functions are localized in different regions of the brain. Despite the large number of neurons, the slightest loss of brain tissue can result in catastrophic disabilities.
Different regions of the brain have different functions; therefore, the effects of a stroke are dependent upon its location and severity, that is, how much tissue is deprived of blood and for how long. The major regions of the brain are the cerebrum, cerebellum and brain stem. The consequences of strokes are different for each region (see Table 1). As a general rule, strokes occurring in the left hemisphere of the brain affect the left side of the face and the right side of the body. Likewise, strokes occurring in the right hemisphere affect the right side of the face and the left side of the body.
In each region of the brain, localized areas are responsible for particular functions. For example Broca's area and Wernicke's area, located on the left side of the cerebrum (see Figure 1), control speech and language comprehension, respectively. A stroke occurring in Broca's area leaves a person with an impaired ability to speak, while not affecting his/her language comprehension.
Have ready some resources to inform students about the various regions of the brain (see website URLs in the Additional Multimedia Support section), such as:
An interactive "3-D brain" visual aid provides moveable illustrations of brain regions and information on their functions.
A 2.5-minute animation explains how a stroke happens and the different types of strokes.
A human brain, if available for demonstration. If possible, allow students to touch the brain to observe its texture and consistency.
Using whatever resources are available, point out the different regions of the brain and their corresponding functions. What would occur if certain portions of the brain atrophied? How difficult it would be to go through life lacking these functions and dependent on others?
Ischemic stroke can occur due to a blood vessel blockage as a result of a formed blood clot (thrombosis), or a blood clot or plaque that migrated to block blood flow (embolism). Stroke can also be due to
, called hemorrhagic stroke, which is when a weakened blood vessel ruptures and bleeds. Hemorrhages cause blood to accumulate in surrounding brain tissue, causing damage and compression. Ischemic stroke is far more common, causing 87% of all strokes.
A polymer is a large molecule composed of repeating units covalently bonded to one another. The repeating units are termed monomers, which are composed of collections of atoms. Polymerization is the process of covalently linking together monomers to form long chain polymers, with carbon, oxygen, nitrogen, and silicone commonly found in the backbone. The monomer structure and its connectivity in making the polymer determine the overall polymer properties. Also, separate polymer chains can bind to one another through connections known as cross-links. Cross-links hold polymers together, reducing the ability for polymers to slide past one another, effectively altering their physical properties.
Polymers can be naturally or synthetically created. Synthetic polymers are diverse and widespread, and include nylon, polystyrene and Teflon. In humans, polymers are paramount for life processes; examples include polysaccharides (polymers of sugars), polypeptides (polymers of amino acids), and polynucleic acids (polymers of nucleic acids).
Blood is a fluid composed of plasma, blood cells, platelets, and a variety of dissolved proteins, sugars and minerals. For every cell in the body, blood is essential for the delivery of nutrients and removal of waste. Blood is confined to the blood vessels of the body, pushed through the system by the heart. Loss of blood, even through a small cut, can lead to death if not healed or treated. Blood clots form at the sites of damaged blood vessels in order to stop bleeding.
The process of forming a blood clot is called coagulation. (Show students a two-minute video on how blood clots; see website URL provided in the Additional Multimedia Support section.) Damage to a blood vessel is sensed by platelets, which immediately begin to bind to the damaged tissue and plug the opening. The damage is also sensed by protein molecules floating by in the blood, called clotting or coagulation factors. Through a complex cascade of reactions involving dozens of molecules and proteins, fibrinogen, an important blood-clotting protein, is recruited to the damage site and converted to fibrin. Fibrin then polymerizes to form a meshwork in conjunction with the platelets to form a blood clot. Abnormalities in this process can lead to severe complications; excessive clotting can result in heart attack and stroke, whereas less effective clotting can result in hemorrhage.
Biomedical Engineering Inventions
Generally, stroke treatment consists of a variety of drugs designed to thin the blood and break-down clots, with the end goal to restore blood flow to the ischemic area. Sometimes, clots do not respond to these treatments, and must be physically removed. In response to this need, biomedical engineers have created minimally invasive, catheter-based tools that are inserted into arteries to travel to the blockage sites where they remove or destroy blood clots in order to restore blood flow to the region.
Examples: FDA-approved in 2004, the Merci Retrieval System is a small, long and narrow, corkscrew-shaped device that is fed into the femoral artery in the groin area and navigates to the brain blockage site where it grabs the clot, and slowly pulls it back through the vessels and out of the body. The Penumbra System is designed to "suck up" the clot and remove it from the body. (Show photos and/or short animation videos on both of these devices; see website URLs provided in the Additional Multimedia Support section). Figure 2 shows another example, the Insera SHELTER device.