What Are Secretory Proteins?

Secretory proteins are proteins synthesized within cells and subsequently secreted outside the cell to exert their biological functions.

Types of secretory proteins:

1. Digestive enzymes, such as salivary amylase, pepsin, and trypsin;

2. Peptide hormones (protein-based), including insulin, glucagon, growth hormone, thyroid hormone, and thyroid-stimulating hormone (TSH), among others.

Functions of secretory proteins: After synthesis, these proteins are secreted outside the cell—either directly entering the bloodstream to exert systemic effects or being released into luminal spaces (e.g., digestive tract) to act locally:

1. For example, insulin lowers blood glucose levels; abnormal insulin secretion can lead to diabetes mellitus.

2. For example, thyroid hormone promotes overall growth and development—particularly of bone, brain, and reproductive organs. Deficiency of thyroid hormone during fetal development or early childhood may result in congenital or juvenile hypothyroidism, leading to cretinism. Thus, secretory proteins play indispensable roles in human physiology.