Theory of milk synthesis

There are four different theories regarding the synthesis of milk

1. Theory of filtration:

• This theory deals that all constituents of milk are simply filtrated from the blood through the epithelial cell living of the basement membrane of the alveoli.
• But this theory does not satisfy the view of milk synthesis & become failed.

2. Theory of cell degeneration:

• According to this theory, in the alveoli, there is a formation of innumerable epithelial cells in every moment.
• Subsequently these cells degenerated due to fatty degeneration and finally to form the milk.
• There may be one million cells present in the udder but in high yielding animals, there is not possible because large quantity of milk synthesis occurred.
• So this theory also becomes failed.

3.Theory of true cell metabolism:

• This theory tells that the precursors of the milk constituents are presents in the blood, which passes through the udder.
• The epithelial cells of the alveoli are capable of converting the chemical structure of milk precursors in the blood into the milk constituents.

Supporting facts for this theory are: –

(a). Deposited body fat is converted into milk fat due to microbial fermentation with the help of blood acetate.

(b). The lacto globulin present in the milk is similar to that present in the blood casein & lactalbumin are derived from the plasma proteins and blood amino acid.

(c). The glucose present in the milk is same as in the blood.

(d). Minerals found in the milk i.e. mg, ca, k etc. in the milk are in more amount than that in blood.

4. Combined theory:

• Since none of the above theories alone is capable of satisfying the mechanism of milk synthesis, it is believed that perhaps the milk is secreted according to the views stated above with combination of all 3 views.
• So now we can say that all components of milk are derived from the blood either same composition or in different chemical, form as blood precursors.
• In general, the major components i.e. protein, fat, lactose are formed within the epithelial cells through the blood precursors & the minor components such as vitamins, salts, immunoglobulins are synthesized by the selective absorption or by passing of materials without changing any of there chemical form across the epithelial cells in to the lumen along with water.
• During active secretion, the mammary gland utilizes some energy source i.e. glucose acetate for tissue metabolism.