Editing Haemodynamic response (section)

===Reduced haemodynamic response diseases===

==== Alzheimer's disease ====
In this disease, there is a build of the [[amyloid beta]] protein in the brain. This ultimately leads to a reduction in the haemodynamic response and less blood flow in the brain. This reduced cerebral blood flow not only kills neuronal cells because of shortages in oxygen and glucose but it also reduces the brain's ability to remove amyloid beta. In a healthy brain, these protein fragments are broken down and eliminated. In Alzheimer's disease, the fragments accumulate to form hard, insoluble plaques which reduce blood flow. Two proteins are involved in this accumulation of amyloid beta: [[serum response factor]] or [[serum response factor|SRF]] and myocardin.<ref>"Blood Flow In Alzheimer's Disease." ScienceDaily. ScienceDaily, 29 June 2009. Web. 04 Nov. 2012. https://www.sciencedaily.com/releases/2009/06/090624211135.htm</ref> Together, these 2 proteins determine whether smooth muscle of blood vessels contract. SRF and myocardin are more active in the brains of people with Alzheimer's disease. When these proteins are active, they turn on SREBP2 which inhibits LRP-1. LRP-1 helps the brain remove amyloid beta. Therefore, when SRF and myocardin are active, there is a buildup in amyloid beta protein which ultimately leads to less blood flow in the brain because of contracted blood vessels.<ref>"Doc Blog." Cardiovascular System Proteins Play a Role in Alzheimer's. N.p., n.d. Web. 04 Nov. 2012. http://www.docblog.org/cardiovascular-system-proteins-play-a-role-in-alzheimers.html</ref>

====Ischemia====
A decrease in circulation in the brain vasculature due to [[stroke]] or injury can lead to a condition known as [[ischemia]]. In general, decrease in blood flow to the brain can be a result of thrombosis causing a partial or full blockage of blood vessels, [[hypotension]] in systemic circulation (and consequently the brain), or cardiac arrest. This decrease in blood flow in the cerebral vascular system can result in a buildup of metabolic wastes generated by neurons and glial cells and a decrease in oxygen and glucose delivery to them. As a result, cellular energy failure, depolarization of neuronal and glial membranes, [[edema]], and excess [[neurotransmitter]] and calcium ion release can occur.<ref>Arcinlegas, David B., MD. "Hypoxic-Ischemic Brain Injury | Internationalbrain.org."Hypoxic-Ischemic Brain Injury | Internationalbrain.org. International Brain Injury Association, Mar. 2010. Web. <http://www.internationalbrain.org/?q=node/131></ref> This ultimately ends with cell death, as cells succumb to a lack of nutrients to power their metabolism and to a toxic brain environment, full of free radicals and excess ions that damage normal cell organelle function.