Female Reproductive Cycles PDF

Reproductive System – Oestrous Cycle & Gestation Terminology Oestrous vs oestrus Oestrous = the entire reproductive cycle Oestrus = a stage of the oestrous cycle where the “heat” occurs (sexual receptivity of the female to the male and when ovulation occurs) Oestrous vs estr...

Reproductive System – Oestrous Cycle & Gestation Terminology Oestrous vs oestrus Oestrous = the entire reproductive cycle Oestrus = a stage of the oestrous cycle where the “heat” occurs (sexual receptivity of the female to the male and when ovulation occurs) Oestrous vs estrous, oestrus vs estrus Gestation – pregnancy (period of development of young within the uterus) Parturition – giving birth Lactation – secretion of milk from the mammary glands Serosanguinous – yellowish fluid containing a small amount of blood Oestrous Cycle Time from the start of one “heat” to the start of the next “heat” Cycle is controlled by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) – produced by the pituitary gland These hormones stimulate follicle production (produces oestrogen) and after ovulation corpus luteum formation (progesterone production) Function of the Oestrous Cycle Because females do not continuously produce ova, the success of breeding (fertilisation) depends largely on mating at ovulation (when the ova are mature and available for fertilisation) Behavioural changes and ovarian cycles must align to increase the chances of pregnancy  Cycle Classifications Animals are classified by the type of cycle they have Seasonally polyoestrous – multiple cycles during a certain period of the year eg. cats, horses Dioestrous – animals that have two cycles per year eg. dog Monoestrous - having one oestrous cycle per year eg. foxes and bears  Stages of the Oestrous Cycle Proestrus Oestrus Dioestrus Anoestrus Professional Owners Do Adopt  Proestrus ~9 days (range 0-27) Ovary: Follicles develop in the ovary Hormones: Oestrogen is produced by the follicle, causing physical changes in the reproductive tract Thickening in lining of oviduct, uterine horns, and vagina Epithelium of vagina changes (keratinises) Vulva: swells and serosanguinous discharge appears Behaviour: Disinterested in males – may even be aggressive  Oestrus ~9 days (range 2-24) Commonly called the “heat” stage of cycle Ovary: mature follicle producing lots of oestrogen, about to ovulate Hormone: Oestrogen is at peak levels, LH surge causes ovulation Vulva: Vulvar swelling continues, serosanguinous discharge Behaviour: Female is receptive to male, will “stand” for mating  Diestrus 2 months (56-100 days) Ovary: Ruptured follicle initially fills with blood, then forms a solid structure, the corpus luteum(CL) = “yellow body” Hormones: Progesterone is released from CL – temporarily inhibits new follicular development Vulva: Vulva swelling and discharge decreases  Dioestrus Behaviour: not receptive to mating - period of sexual inactivity Pseudopregnancy may occur in this phase – fatty deposits around the abdomen, mammary enlargement. Reasons for pseudopregnancy unknown.  Anoestrus 4 months (range 60-200) Phase of inactivity Similar to what happens with queens and bitches who are speyed Allows uterus to regenerate for next oestrus Low oestrogen and progesterone levels Anoestrus is induced by time of year, pregnancy, lactation, significant illness, chronic energy deficit and age  Induced Ovulation Some species are “induced ovulators” – must be mated for ovulation to occur (the process of mating initiates the LH surge) Usually requires 3-4 matings in a short period Increases the chance of fertilisation Cats, rabbits, possums  Pregnancy Immediately post-mating, spermatozoa make their way to the uterine tubes/oviducts Once one spermatozoa has entered the ovum, the ovum cell membrane changes to block other sperm from entering Fertilised ovum = zygote (single-celled) The zygote travels down towards the uterine horn for implantation Zygote undergoes rapid cell division to become the embryo  Pregnancy Gestation = pregnancy Gestation period is divided into trimesters: First trimester Period of the embryo – implantation, development of placenta Second trimester Embryo now referred to as foetus (name is based on age) Development of foetus, organ development Third trimester Period of foetal growth  Pregnancy and the Placenta In the early stages, the embryo is supported by progesterone released from the corpus luteum (CL) Progesterone = pro-gestational hormone As the embryo grows, a placenta develops to support life Placenta is a multi-layered structure that attaches the embryo to the lining of the uterus by the umbilical cord Amniotic sac – contains fluid that the embryo sits in  Parturition The birth process Progesterone levels decline Glucocorticoids (steroids) from the foetal adrenal glands trigger oestrogen rise in dam Both of these things increase the sensitivity of the myometrium to oxytocin Oxytocin Hormone that causes uterine contractions Triggers the start of the labour process  Physical stages of labour Stage 1 – Uterine contractions Membrane-covered foetus moves to the cervix, causing cervical dilation Stage 2 – Delivery of foetus Combination of strong uterine contractions, abdominal wall contractions Foetus expelled and rupture of the amniotic sac Stage 3 – Delivery of placenta Placenta separates from uterine wall Dam often eats placenta In multiparous species stages one and two often intermix  Lactation Males and females both have mammary glands (except mice, horses, marsupials – not examined) but only females produce the hormones that make their mammary glands functional Mammary glands produce colostrum and milk Colostrum is typically produced for the first 3 days Contains high amounts of proteins, fats and milk Included in proteins are immunoglobulins (antibodies) Important for the transfer of passive immunity Consumption of colostrum must begin within a few hours of birth – the lining of the newborn intestine changes and is unable to absorb large molecules  Lactation Milk “let-down” is the effect of feeding/nursing offspring – milk moves from high in the gland down to the larger ducts in the gland to make it available Hormones involved are prolactin and oxytocin – released from the pituitary gland Prolactin helps trigger and maintain lactation Oxytocin causes contractions in glands to squeeze milk down Physical pressure on the gland by offspring also sends sensory nerve impulses that trigger the hypothalamus to signal the posterior pituitary to release oxytocin