How do contractions start in a cat? - briefly
Contractions in cats are primarily initiated by hormonal signals from the fetuses themselves. Once the fetus reaches a certain stage of development, it begins to produce hormones that stimulate the mother's uterus to contract. These contractions help to expel the kittens from the womb during the birthing process.
How do contractions start in a cat? - in detail
Contractions in cats, also known as labor or parturition, are a complex process involving multiple physiological and hormonal changes. This process is intricately regulated by the interplay of various neuroendocrine signals, ensuring the safe delivery of kittens.
The initiation of contractions in cats begins with the maturation of the fetuses and the preparation of the uterus for labor. As the pregnancy progresses, the fetal adrenal glands start producing cortisol, which stimulates the production of surfactant by the fetal lungs. This surfactant is crucial for lung development and readiness for postnatal breathing.
Concurrently, the placenta begins to produce progesterone, a hormone that maintains the pregnancy by inhibiting uterine contractions and supporting the growth of the fetuses. Towards the end of gestation, usually around day 63 in cats, the placental production of progesterone decreases, leading to a relative drop in its levels. This decrease in progesterone removes the inhibitory effect on the uterine smooth muscle cells, allowing them to become more responsive to oxytocin and other stimulatory hormones.
The decline in progesterone levels triggers the release of prostaglandins from the placenta. Prostaglandins, particularly PGF2α (prostaglandin F2 alpha), act on the uterine smooth muscle cells to induce contractions. These initial contractions are often weak and irregular but gradually increase in intensity and frequency as more prostaglandins are released.
In addition to prostaglandins, the decline in progesterone levels also stimulates the release of oxytocin from the posterior pituitary gland. Oxytocin is a potent hormone that enhances uterine contractions by acting on specific receptors in the uterine muscle cells. The combination of prostaglandins and oxytocin creates a positive feedback loop, where each contraction stimulates the release of more hormones, leading to stronger and more coordinated contractions.
Throughout this process, the cat's body prepares for labor in various ways. The cervix dilates to allow the passage of kittens, and the uterine muscles become more toned and ready for the effort of delivery. The mother cat may also exhibit behavioral changes such as nesting, increased vocalization, and restlessness, which are signs that labor is imminent.
In summary, the start of contractions in a cat is a well-orchestrated event involving the decline of progesterone levels, the release of prostaglandins and oxytocin, and the subsequent stimulation of uterine smooth muscle cells. This complex interplay of hormones ensures that labor progresses smoothly, leading to the safe delivery of kittens.