Recognize the cells and organs of the immune system and their functions. The key primary lymphoid organs of the immune system are the thymus and bone marrow, and secondary lymphatic tissues such as spleen, tonsils, lymph vessels, lymph nodes, adenoids, and skin and liver. Leukocytes (white blood cells) act like independent, single-celled organisms and are the second arm of the innate immune system.
Timing. Your dog can come into her first heat any time between 6 and 24 months. According to Webvet.com, small dogs come into heat sooner than larger breeds. Typically she will have two estrus cycles, or heats, a year, and each one lasts for between 18 to 24 days.
All dogs are different, but on average a Poodle heat cycle will last for 3 weeks. The first cycle is not a good indication of how future cycles will be. Once a dog matures and reaches the age of 2 years old, the cycles will begin to become more regular and last for roughly the same amount of time for each one.A canine will enter heat 2 times per year.he first cycle is not a good indication of how future cycles will be. Once a dog matures and reaches the age of 2 years old, the cycles will begin to become more regular and last for roughly the same amount of time for each one. A canine will enter heat 2 times per year.