\begin{tikzpicture}[
    bloco/.style={
        draw, 
        rectangle, 
        minimum height=3em, 
        minimum width=3em, 
        fill=blue!10, 
        line width=1.2pt
    },
    somador/.style={
        draw, 
        circle, 
        minimum size=7mm, 
        line width=1.2pt
    },
    vetor/.style={
        ->, 
        >=Stealth, 
        line width=1.2pt
    },
    % Distâncias reduzidas para compactar o diagrama
    node distance=1.0cm and 1.2cm
]

    % Nós
    \node (input) {$u(t)$};
    \node [bloco, right=of input] (B) {$B$};
    \node [somador, right=of B] (sum) {$+$};
    \node [bloco, right=of sum] (int) {$\int$};
    \node [bloco, right=of int] (C) {$C$};
    \node [right=of C] (output) {$y(t)$};
    \node [bloco, below=of int] (A) {$A$};

    % Conexões
    \draw [vetor] (input) -- (B);
    \draw [vetor] (B) -- (sum);
    \draw [vetor] (sum) -- node[above] {$\dot{x}$} (int);
    \draw [vetor] (int) -- node[above, name=x] {$x$} (C);
    \draw [vetor] (C) -- (output);
    
    % Realimentação
    \draw [vetor] (x) |- (A);
    \draw [vetor] (A) -| (sum);

\end{tikzpicture}