The Cows Teat!
The cow’s teat has evolved to allow for efficient suckling by the calf but also to provide some defence against damage and infection from mastitis-causing pathogens.
The teat has a large mass of connecting blood vessels at its base called the erectile venous plexus, which, when the milk let-down stimulus occurs, make the teat become more rigid, allowing the milk to be removed by the calf through sucking, or by the milking equipment, without the teat collapsing on itself.
The teat has nerves in the tissues, this allows the brain to react and initiate milk let-down.
Sore and damaged teats can be predominantly painful. Teats vary in shape and size; the more cylindrically-shaped teats are alleged to be less-susceptible to mastitis.
The epidermis is a thick hairless outer skin, containing a thicker layer of keratin (a substance found in hair and hooves) than is found in normal skin. This gives it a much more rugged structure to cope with the demands of being suckled. It has however no sweat or sebaceous glands to lubricate it like normal skin, and so is more prone to drying and cracking. The epidermis also has a large number of nerve endings.
The dermis is the second layer of the teat wall and carries the nerves and blood vessels.
There is a layer of muscle, giving the teat strength and structure, and a circular sphincter muscle around the teat canal.
The teat cistern is lined with epithelial cells, which are square-shaped and are able to move apart, allowing white blood cells to enter the structure as an immune system response to bacterial infection.
The teat canal is approximately 9mm in length and has a lining comprised of folded epidermal tissue (similar to skin, but containing more keratin), covered by a thin lipidised film. This film is hydroscopic (it repels liquids).
There is also a structure known as the rosette of Furstenberg, which has an important role in detecting bacterial infection and initiating an immune response. :