Aetna plans to acquire Humana Inc. for $37 billion in cash and stock, the companies announced Friday. They said the merger would create the nation’s second-largest managed care company, with more than 33 million Medicare, Medicaid, TRICARE and other health plan members. The companies expect the transaction to close in the second half of 2016, subject to shareholder and regulatory approvals. In other news, Centene Corp. plans to acquire Health Net Inc. for about $6.8 billion in cash and stock, the companies announced last week. Centene operates health plans through Medicaid, Medicare and the Health Insurance Marketplace; Health Net operates health plans and government-sponsored managed care programs. They expect the transaction to close in early 2016, subject to shareholder and regulatory approvals, and the combined company to have more than 10 million members. AHA will be reviewing the potential impact of both deals on hospitals and health systems.