Duct system:

a) Alveoli :-

• The alveoli are composed of single layer of epithelial cells.
• The functions of these cells are to remove nutrients from blood, transform them into milk and discharge the milk into lumen of each alveolus.
• Surrounding of each alveolus is a capillary which supplies blood containing nutrients and hormones for milk system and removes waste products from the alveolar cells.
• The myoepithelial cells get contract in response to oxytocin that forces the milk from the lumen of the alveolus into ducts and gland cistern and teat cistern.

b) Gland cistern:

• The teat cistern joins the glad cistern at limited storage space for milk as it trickles down from secretary tissues.

c)Teat – teat cisterns

I. Continuous after gland cistern

ii. The teat cistern is separated from the gland cistern by an annular fold.

iii. At the base of the teat is streak canal through which milk must be drawn to exterior. The streak canal is usually 8-12 mm long and is surrounded by a true sphincter muscle, which remains constricted and prevents leakage and external injury. The teat cistern is located immediately above the streak canal.

d) Mammary duct:

• Branching of the gland cistern are 12-50 or more duct, which branches many times and finally form a terminal duct and drains each of alveolus.