MATLAB four compartment pharmacological model with regular mass intake

CompartmentModel.m

sol = ode45(@CompartSysFunc, [0 10], [1.8 0 0 0]);
t = transpose(getfield(sol, 'x'));
y = transpose(getfield(sol, 'y'));
plot(t, y(:,1), 'r', t, y(:,2), 'g', t, y(:,3), 'b', t, y(:,4), 'y')
range = 10:5:30;
for i = 2:5;
    sol(i) = odextend(sol(i-1), @CompartSysFunc, range(i), [sol(i-1).y(1,end)+2 sol(i-1).y(2,end) sol(i-1).y(3,end) sol(i-1).y(4,end)]);
    t1 = transpose(getfield(sol(i), 'x'));
    y1 = transpose(getfield(sol(i), 'y'));
    hold on;
    plot(t1, y1(:,1), 'r', t1, y1(:,2), 'g', t1, y1(:,3), 'b', t1, y1(:,4), 'y')
end
legend('Gut', 'Central Tissues', 'Peripheral Tissues', 'Bladder')

CompartSysFunc.m

function s = CompartSysFunc(t, x)
    ka = 5;
    kc = 2;
    kp = 2;
    ke = 0.4;
    s1 = -ka.*x(1);
    s2 = ka.*x(1) -(kc + ke).*x(2) + kp.*x(3);
    s3 = kc.*x(2) -kp.*x(3);
    s4 = ke.*x(2);
    s = transpose([s1 s2 s3 s4]);
end