Systole heart beats—is cued by messages from the brain, reflecting the brain's responses to conditions of the body, such as pain, emotional stress, level of activity, and to ambient conditions including external temperature, time of day, etc. Electrical systole opens voltage-gated sodium, potassium and calcium channels in cells of myocardium tissue. Subsequently, a rise in intracellular calcium triggers the interaction of actin and myosin in the presence of ATP which generates mechanical force in the cells in the form of muscular contraction, or mechanical systole. The contractions generate intra-ventricular pressure, which is increased until it exceeds the external, residual pressures in
Cooperative Human Tissue Network Cooperative Human Tissue Network The Collaborative Human Tissue Network (the CHTN) was established in 1987 by the National Cancer Institute in response to an increase in the demand for high quality biospecimens for cancer research. The purpose of the CHTN is to stimulate, for the good of the public, cooperative efforts to collect and distribute human biospecimens and to thereby facilitate research utilizing those specimens. These activities are expected to encourage basic and developmental studies in many areas of cancer research, including molecular biology, immunology and genetics. The CHTN is not intended to be a human tissue bank, but instead