Nullcline plot shows too many nucllines

Hi, I'm trying to plot my nullcline for differential equations which depend on parameters alpha1 and alpha2. I want to see how the plot varies depending on these parameters values so I use for loops. However, for some of the plots extra nullclines appear.

here is my code:

clear all
beta = 2; 
gamma = 2; 
U = 0:0.1:10; 
%dvdt = (alpha2./(1+u.^gamma)) -v; 
%dudt = (alpha1./(1+v.^beta)) - u;

for i=1:1:5 
    
    alpha1 = i;
    
    for j=1:1:5
        
        alpha2 = j; 
        
        clear nullclineU
        clear nullclineV 
        nullclineU =@(u) sqrt(u./(alpha1-u)); 
        nullclineV =@(u) (alpha2.*u.^2)./(1+u.^2); 
        
        figure(i*j) 
        
        plot(U, nullclineU(U), 'b'); 
        hold on
        plot(U, nullclineV(U), 'r');
        grid on
        title(['alpha2 = ', num2str(alpha2), 'alpha1 = ', num2str(alpha1)], 'FontSize', 8);
    end

end