Reproductive Cycle Lecture Notes Flashcards
What is the reproductive cycle?
Initiated at the onset of puberty, it’s a series of events that an organism must undergo to successfully reproduce; physiologic events that occur between successive periods of sexual receptivity (estrus or heat) and/or ovulations, which provide females with repeated chances for pregnancy
What is the reproductive cycle called in different species?
Estrous cycle in domestic animals, menstrual cycle in primates, and ovulatory cycle in birds
What is polyestrous?
Uniform distribution of estrous cycles throughout the year (cow, queen, pig, rodents)
What is seasonally polyestrous?
Displays clusters of estrous cycle that occur only during a certain season (short day: begin to cycle when day length decreases: ewe, doe, elk, nanny) (long day: begin to cycle with day length increases: mare)
What is monoestrous?
Having only one cycle per year (dog, wolf, fox, bear)
What are the phases of the estrous cycle?
Estrous cycle, follicular phase, and luteal phase
What (in general) happens during the follicular phase?
period of follicular development and ovulation
What (in general) happens during the luteal phase?
period of formation and function of corpus luteum
What specific events happen during the follicular phase?
- Pulsatile release of GnRH from the tonic center of the hypothalamus
- GnRH acts on gonadotrophs of the anterior pituitary to secrete gonadotropins, FSH and LH
- FSH and LH act on ovary and induce follicular development and maturation
- low level of estradiol secreted from the growing follicle exerts a negative feedback effect on the hypothalamus and pituitary to reduce FSH secretion
- the mature follicle secretes high levels of estradiol, which exerts a positive feedback effect on the surge center of the hypothalamus
- estradiol positive feedback results in preovulatory LH surge, which acts on periovulatory follicle, causing rupture and release of the oocyte (ovulation)
What specific events occur during the luteal phase?
- corpus luteum formation
- formation and maintenance of mature corpus luteum
- high progesterone secreted by the mature CL exerts negative feedback on the hypothalamus to suppress FSH and LH synthesis
- regression of corpus luteum (luteolysis)
- withdrawal of progesterone
- release of negative feedback of progesterone on hypothalamus and pituitary
What are the four stages of the estrous cycle?
Proestrus, estrus, metestrus, and diestrus
What is proestrus?
Begins when progesterone declines as a result of luteolysis, and terminates at the onset of estrus. Is characterized as a change from a period of progesterone dominance to a period of estradiol dominance (caused by FSH and LH). The antral follicles mature for ovulation.
What is estrus?
Sexual receptivity; well-defined period in which the female allows copulation. Estradiol is the dominant hormone during this stage, which not only induces profound behavioral alterations, but causes major physiologic changes in the reproductive tract. Increased locomotion, phonation, nervousness, and attempts to mount other animals, standing estrus, lordosis.
What is lordosis?
The characteristic arching of the back in preparation for mating.
What is metestrus?
Period of transition from estradiol dominance to progesterone dominance (both are relatively low). Ovulation occurs. Estrogen withdrawal results in metestrus bleeding. CL formation:
What is diestrus?
The longest stage of the menstrual cycle, period of sustained luteal secretion of progesterone, which prompts the uterus to prepare a suitable environment for embryo implantation and successful pregnancy. Ends when the CL is lysed.
What is the major ovarian structure and hormone in the follicular phase?
the follicle and estradiol
What is the major ovarian structure and hormone in the luteal phase?
the corpus luteum and progesterone
What changes does estradiol cause in the oviduct during the estrous cycle?
Enhances spontaneous muscular activity, elevates fluid secretion, and drastically increases epithelial cell elevation (causing ciliation)
What changes does progesterone cause in the oviduct during the estrous cycle?
Imposes quiescence, encourages less serous but some mucous secretion, causes epithelial cell regression and atrophy (decreased cell height and partial de-ciliation).
What changes does estradiol cause in the uterus during the estrous cycle?
Prepares the uterus to facilitate the transport and survival of spermatozoa; causes congestion and edema of the uterine mucosa with a predominance of mucin-filled columnar epithelial cells; increases epithelial, glandular, and stromal cell proliferation; increases sensitivity and amplitude of myometrial contractions (results in a strong myometrial tone and a slightly firm or ‘erect’ uterus); increases rate of infiltration of leucocytes
What changes does progesterone cause in the uterus during the estrous cycle?
Prompts the uterus to prepare a suitable environment for embryo implantation; reduces congestion and edema of the mucosa; increases cell differentiation and glandular secretions; causes a flaccid uterus and reduced myometrial tone (quiescence); reduces infiltration of leukocytes
What changes does estradiol cause in the cervix during the estrous cycle?
Relaxation of cervical folds; congestion and edema; increased cell proliferation; marked increase in the glandular secretion of the clear viscid mucus which is discharged through the vulva
What changes does progesterone cause in the cervix during the estrous cycle?
Cervical canal will be tightly closed; reduced congestion and edema; increased cell differentiation; mucus will become thick and tenacious
What changes does estradiol cause in the vagina during the estrous cycle?
Congestion and edema; increased cell proliferation; keratinization of the epithelium; marked increase in the glandular secretion of the clear viscid mucus which is discharged through the vulva
What changes does progesterone cause in the vagina during the estrous cycle?
Reduced congestion and edema; increased cell differentiation; reduced secretions
What are the two parts of the menstrual cycle?
The ovarian cycle and the endometrial cycle
