Which substances are secreted into the filtrate as waste products?

1. Most calcium, sodium, glucose and amino acids must be reabsorbed to hold plasma concentrations steady. 2. Urea, potassium, ammonia, creatinine and some drugs travel the other way and are secreted into the filtrate. 3. Secretion adds to what filtration already delivered, so these substances leave faster than filtration alone would manage. 4. Albumin, globulin and platelets never enter the filtrate at all, since they are too large to cross. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.6 Tubular Reabsorption_