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14    Control theory in biomedical engineering


          Table 2 Mathematical models of some endocrine systems.
                            Related
          Gland             mathematical model  Reference

          Pancreas          Glucose-insulin     Bergman et al. (1979), Mari (2002,
                              regulation system   Kansal (2004), Boutayeb and
                                                  Chetouani (2006), Makroglou
                                                  et al. (2006), Gani et al. (2009),
                                                  Balakrishnan et al. (2011),
                                                  Ajmera et al. (2013), Palumbo
                                                  et al. (2013)
          Hypothalamo-      Reproductive        Cl ement (2016)
            pituitary-        function
            gonadal (HPG)
            axis
          Thyroid           Thyroid disease     Liu et al. (1994)



          system is to identify and then to eliminate all foreign bodies (Gałach, 2003).
          In fact, the immune response begins when tumor cells are detected as unde-
          sirable cells in the body. Then, the lymphocyte cells are stimulated in order to
          coordinate the counterattack. In the literature, the interaction between tumor
          cells and lymphocyte cells in the immune system looks likes the interaction
          between species in the predator-prey model (Bell, 1973; Ben Saad
          et al., 2019). One of the most basic mathematical models describing
          tumor-immune system interactions is the Bell model proposed in Bell (1973).
          This model is based on the classic Lotka-Volterra model (Volterra, 1928).
          Other simple models can be found in research papers (Mayer et al., 1995;
          Sachs et al., 2001) and in survey papers (Adam and Bellomo, 2012; Weera-
          singhe et al., 2019). Thus, the immune response can be described by the
          following simple mathematical model (Sotolongo-Costa et al., 2003):
                                dX
                              8
                              >
                              <    ¼ aX  bXY,
                                 dt
                                dY
                                   ¼ dXY  fY  kX + u:
                              >
                              :
                                 dt
          where X and Y are the number of tumor and lymphocyte cells, respectively,
          and (a, b, d, f, k, u) are system parameters.
          2.6.3 The cardiovascular system
          The cardiovascular system is composed of the heart and vessels. Its main
          function is to pump the blood in the body in order to supply all tissues
          and organs with oxygen and other nutrients (Quarteroni et al., 2009). In fact,
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