Water is the essential nutrient that is needed for all bodily functions. The human body is composed of 80% water. There is a scientific taught that says that the human body can survive weeks without food but without water for three days it will surely die. The blood that circulates through the body serves as transporter of oxygen to the different parts of the body. It is composed of cells and an aqueous solution (plasma) and our body weight is composed of 8% of the blood.
Answer:
1) cortical epithelial cells; (2) macrophages and dendritic cells
Explanation:
T cells, also known as T lymphocytes, are a fundamental type of cell of the immune system that determines the specificity of the immune response to specific foreign particles (antigens). T cells are produced in the Thymus (it is for that reason that they are called T cells) and then circulate throughout the bloodstream in order to recognize specific antigens in association with major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APC), such as macrophages and dendritic cells. T cells undergo positive and negative selection: 1- positive T-cell selection refers to the process by which T cells bind cortical epithelial cells that express Class I or Class II MHC molecules with enough affinity to get a survival signal; whereas negative selection occurs when T cells bind to macrophages and dendritic cells that express MHC specific receptors with a strong enough affinity to get an apoptosis (programmed cell death) signal.
the practice of exchanging things with others for mutual benefit, especially privileges granted by one country or organization to another..... Here is a sentence.... the Community intends to start discussions on reciprocity with third countries
