Estrus cycle

Question 1

ovarian (follicular ) phase

Answer 1

• follicular matures and is ovulated
• estrogen dominates
• short (20%)

Question 2

uterine (luteal phase )

Answer 2

• uterus prepares for pregnancy (building wall for protection )
• progesterone dominates (corpus luteum)
• long (80%)

Question 3

follicular phase

Answer 3

• maturation of the follicle and ovulation
• primary follicles recruited for maturation by follicle-stimulating hormone (FSH)
• secreted from anterior pituitary
• stimulated by GnRH which is released from hypothalamus
  -granulosa cells proliferate to form several layers
• secrete thick gel to form the zona pellucida, which create gap junctions connect granulosa cells to oocyte
• thecal cells differentiate from ovarian connective tissue
• follicular cells = granulosa + thecal cells
• secrete estrogen
• secondary follicle

Question 4

formation of the antrum

Answer 4

• fluid filled sac surrounded by follicular cells
• antral follicle
• follicular cells produce estrogens (estrodiol (most species), estrone (pig)
• rapid follicular growth(mostly due to expansion of the antrum
• antral follicle count - number proportional to total follicular pool

Question 5

dominant follicle

Answer 5

• for those who are monoovulatory
• multiple dominant follicles in multi-ovulatory species (preovulatory or Graafian follicle)
  greater number of FSH receptors
  atresia of remaining antral follicles
• zona pellucida is surrounded by a layer of granulosa cells
• they bulge on the surface of the follicle

Question 6

ovulation

Answer 6

• follicular cells secrete enzymes to breakdown the follicular wall
• follicle is still expanding (pressure causes weak spot in wall)
• follicle bursts and the secondary oocyte is swept into the infundibulum along with the follicular fluid

Question 7

follicular wave

Answer 7

• multiple waves of follicular development occur in each cycle
• ovulation only occurs when progesterone drops

Question 8

luteal phase

Answer 8

• remaining follicle transforms into corpus luteum (starts as corpus hemorrhagicum)
• granukosa and thecal cells become luteal cells (cells hypertrophy, accumulate beta-carotene in lipid droplets)
  highly vascularized
• secrete large amounts of steroid hormoned (primarily progesterone, some estrogen)

Question 9

corpus luteum

Answer 9

• is embryo implants (pregnancy)
• CL is maintained throughout the pregnancy
• significant increase in progesterone production
• if no implantation occurs (not pregnant)
• prostaglandins secreted from endometrium, signals to degenerate
  luteolysis - lysis corpus luteum, forms corpus albicans (white body that indicated of a previous cycle
• end of luteal phase

Question 10

estrous cycle phases

Answer 10

follicular phase:
- proestrous - development of the follicles
- estrus (heat) - sexual receptivity, leading up to ovulation
Luteal phase:
- metestrus - development of the CL after ovulation
- diestrus - functional CL secretes steroid horones until it regresses

Question 11

hormone regulation

Answer 11

• hypothalamus produced GnRH
• stimulates the pituitary to release ( FSH and LH)
• follicular cells produce estrogen and inhibin
• corpus luteum produces progesterone

Question 12

hormone regulation in ovulation

Answer 12

• rapid increase in estrogen secretion by dominante follicle
• positive feedback increases frequency of GnRH pulses
• increases sensitivity of LH producing cells in anterior pituitary to GnRH (stimulates FSH and LH)

Question 13

LH surge

Answer 13

• stops estrogen synthesis by follicle
• initiates oocyte meiosis
• triggers ovulation (24 hours later)
• triggers luteinization

Question 14

luteal phase

Answer 14

• tonic LH secretion stimulates CL development
• increasing progesterone as CL develops
• progesterone inhibits GnRH pulses from the hypothalamus (inhibits LH secretion, prevents another LH surge and ovulation)
• progesterone also controls timing of PGF2a secretion (luteolysis )

Question 15

follicular phase

Answer 15

• luteolysis causes a drop in progesterone (removes inhibition of LH secretion by progesterone)
• increases frequency of LH pulses ( promotes maturation of the dominant follicle)
• dominant follicle increases secretion of estrogen and inhibin ( inhibits FSH)
• when estrogen concentration reaches the threshold, it triggers a surge of LH and FSH
• FSH recruits new wave of follicular development

Question 16

estrogen

Answer 16

• striumlates growth and maintenance of reproductive tract
• development of secondary sex characteristics
• stimulates growth of endmetrium
• stimulates development of progesterone receptors in endometrium
• high estrogen = thin, clear cervical mucus ( facilitates passage of sperm
• increases bone growth and desity

Question 17

progesterone

Answer 17

• promotes endometrial angiogenesis
• reduces contractility of the myometrium
• makes cervial mucus thick and sticky ( impedes passage of sperm
• formation of mucous plug

Question 18

estrus detecion

Answer 18

• estrus (heat) - period of sexual receptivity (24 hours total, 12 hours of max fertility)
• behavioural changes (standing to be mounted (standing heat), bellows, increased activity/restlessness )
• estrus detection ( visual observation), teaser animals (gomer bulls) and detection aid

Question 19

estrus detection in pigs

Answer 19

• strong standing heat response, presence of bore (nose to nose)
• matrix (alternogest) - synthetic progestin, 14 day treatment, heat 4-9 days after

Question 20

estrus detection in cattle

Answer 20

• heat patches
• tail paint electronic patch ( pressure sensor, records mount time, transmits data wirelessly)
• padometer (as an animal approaches heat she walks a lot more)

Question 21

estrus synchronization

Answer 21

• increase success of AI
• synchronize breeding
• tightens caving window
• GnRH, progesterone and PGF2a

Question 22

progesterone delivery

Answer 22

• CIDR - controlled internal drug release
• PRID - progesterone releasing intravaginal device