Final answer:
The protein in milk is broken down by stomach acid and pepsin into shorter chains and further digested into amino acids in the small intestine. These amino acids are absorbed into the blood, contributing to the body's amino acid pool and hence to the synthesis of new proteins.
Step-by-step explanation:
When you drink a cup of milk, the protein in the milk is initially acted upon by hydrochloric acid (HCl) and an enzyme called pepsin in the stomach. This is the beginning of protein digestion, where proteins start to break down into shorter chains. Following this, as the proteins further move into the small intestine, they encounter additional enzymes that break them down into individual amino acids. These amino acids are then absorbed into the bloodstream through the intestinal walls. This absorption of amino acids into the blood does not typically stimulate an immune response; thus, they can be utilized for the body's protein synthesis and various other functions.
The proteins we ingest form the structure of our body, become antibodies, or control and regulate cell activities. The amino acid pool in the body is replenished with these new amino acids from dietary proteins, and this pool is available for new protein synthesis as part of the continuous bodily process of protein turnover. It's important to note that almost all the proteins in the body are degraded and replaced within a span of 6 to 9 months.