Complex sentence: For example, nitroglycerin cannot be swallowed because the the liver would inactivate the medication, but it can be taken under the tongue and thus absorbed in a way that bypasses the portal venous system.
Split into simpler sentences: For example, nitro-glycerin cannot be swallowed, but it can be taken under the tongue. Therefore, nitroglycerin is given in a way that bypasses the portal venous system.