32-2-503. Application of sections. The provisions of 32-2-501 through 32-2-503 shall apply only to loans, advances of credit, charges, investments, purchases, sales, contracts for insurance of mortgages and advances of credit and accounts of members, and other contracts made in connection with and incidental to loans secured by mortgages and to advances of credit, insured or to be insured, and accounts, insured or to be insured, under the provisions of said National Housing Act and amendments thereof duly passed and approved.