Chemical mediators <ul><li>Hormones </li></ul><ul><li>Local chemical mediators </li></ul><ul><li>Growth factors </li></ul>
Mammalian hormones are substances that stimulate their target cells via the blood system. This results in slow, long-lasting and widespread responses.
Effect of insulin on glucose uptake and metabolism. Insulin binds to its receptor which in turn activates a secondary messenger called IRS (insulin receptor substrate). This causes Glut-4 transporter proteins to move to and embed into the plasma membrane. Also this activates the enzyme glycogen synthase which catalyses the conversion of glucose to glycogen (glycogenesis)
Tropisms are responses to directional stimuli that can maintain the roots and shoots of flowering plants in a favourable environment.
In flowering plants, specific growth factors diffuse from growing regions to other tissues. They regulate growth in response to directional stimuli. The role of indoleacetic acid (IAA) in controlling tropisms in flowering plants. http://bcs.whfreeman.com/thelifewire/content/chp38/3802s.swf
Histamine and prostaglandins are local chemical mediators released by some mammalian cells and affect only cells in their immediate vicinity. Histamines are chemicals produced by a type of white blood cells called Mast Cells. These cells are located within connective tissue and can be triggered by tissue damage or infection by bacteria. The Histamine molecules diffuse into the surrounding tissue but they do not travel in the blood. They cause inflammation and increase the permeability of the capillaries in the tissue. This enables phagocytes to enter the area from the capillaries more easily
<ul><li>Prostaglandins are another class of chemical mediator that have a similar mode of action to histamines. There are a wide variety of different prostaglandins with a variety of effects on the local tissue. Two very common effects are </li></ul><ul><li>They can cause constriction or dilation in vascular smooth muscle cells (so therefore affect artery / arteriole diameter) </li></ul><ul><li>They can cause activation of platelets </li></ul>