Victoria Booth
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A system of defences that the body has against infections and cancer. The immune system is composed of a variety of cell types – for example lymphocytes, macrophages, and antigen-presenting cells – that patrol the tissues and look for signs of invading organisms or cells that are transforming into cancer cells. When a problem has been identified, the immune cells react by producing antibodies or going into cell-to-cell combat with the source of the problem. The immune system is part of a more extensive network of defences that the body possesses. Several organs are involved in the immune system – the spleen, thymus, tonsils, and lymph nodes being among them.
Approximately a week after fertilization the conceptus has become a blastocyst and has reached the uterus, where it attaches to the lining – the endometrium – and begins to bury itself in the maternal tissue. This process is called implantation and takes approximately a week to complete.
This has so many nuances, but generally means knowledge, an observation, or a signal of some kind that can be transmitted and received. The term can be used effectively when talking about cells, systems, or people, not to mention computers.
The system of the body that includes the skin and structures derived from the skin such as the hair, nails, sweat glands, and sebaceous glands.
