1. Hypothyroidism means decrease in the secretion of T3 and T4
2. Decrease in T4 , i.e. thyroxine in the blood triggers negative feedback mechanism.
3. The hormone receptors in hypothalamus detect this change and secrete TRE
4. TRF stimulates the pituitary to secrete TSH
5. Thus, Patient suffering from hypothyroidism shows increased level of TSH due to negative feedback control.