\begin{tikzpicture}[very thick]
  \matrix[
    column sep = 6mm, row sep = 4mm,
  ]{
    &&& \node[rtbox] (D) {\(\mathbf{D}\)}; \\

    \node[rtsplit] (U) {};
      & \node[rtbox] (B) {\(\mathbf{B}\)};
      & \node[rtsum] (dX) {};
        \node[above = 0mm of dX] {\(\dot{\mathbf{x}}\)};
      & \node[rtint] (I) {};
      & \node[rtsplit] (X) {};
        \node[above = 0mm of X] {\(\mathbf{x}\)};
      & \node[rtbox] (C) {\(\mathbf{C}\)};
      & \node[rtsum] (Y) {}; \\[1mm]

    &&& \node[rtbox] (A) {\(\mathbf{A}\)}; \\
  };

  \draw[->]
    (U) -- ++(-1,0) node[left] {\(\mathbf{u}\)}
    (U) edge (B)
    (B) edge (dX)
    (dX) edge (I)
    (I) -- (X)
    (X) edge (C)
    (C) edge (Y)
    (Y) -- ++(1,0) node[right] {\(\mathbf{y}\)}
  ;

  \draw[->] (U) |- (D);
  \draw[->] (D) -| (Y);

  \draw[->] (X) |- (A);
  \draw[->] (A) -| (dX);

\end{tikzpicture}