Introduction:

• Milk, the normal secretion of the mammary gland is an emulsion of fat in watery solution of sugar and mineral salts, and with protein in colloidal suspension.
• The principal components of milk are; water; fat; solid not fat (SNF), which are made up of protein, lactose, and minerals; vitamins and several types of cells, i.e. bacteria, leukocytes, and mammary secretary cells.

Alveolar secretary cell

It includes the following:

a) Nucleus:

• It transmit the genetic information contained in the genes for the synthesis of proteins and for certain enzymes, which catalyze the many bio-chemical reaction in the mammary cell.
• DNA (Deoxy-ribose nucleic acid) transcribes genetic information to messenger RNA (Ribo-nucleic acid).
• The messenger RNA then leaves through the pores of nuclear membrane to the endoplasmic reticulum.

b) Endoplasmic Reticulum:

• It is the site of protein synthesis.
• This organelle consists of a system of canals located in the basal two-third of the cytoplasm of the mammary cell.
• It helps to specify the amino acid sequence for the synthesis of specific proteins and enzymes.

c) Lysosome:

• These are the membrane bound particles, which contain the enzymes which when released from within the lysosomal membranes cause degradation of the cell.
• Lysosomes are particularly active during involution of mammary tissue such as that which occurs in the early dry period or during mastitis.

d) Mitochondria:

• The mitochondria are numerous in metabolically active tissue.
• Alveolar secretary cell being one of the most active ones has a large number of them during lactation.
• But their number diminishes drastically during the non-lactating state.

e) Plasma membrane:

• It helps in selective and active transport of various chemicals into the cell and into various components within the cell.
• Due to this, some nutrients from blood enter the cells through the plasma membrane with ease and even get concentrated.
• Other nutrients in the blood are excluded.

f) Cytoplasm:

• It helps in anaerobic break down of glucose.
• It consists of large portion of the mammary cell.
• Much of the material in this fraction, which includes some enzymes, nutrients, and macromolecular products, is soluble.