Answer to Question 1
Answer: Sexual maturity starts at puberty when the hypothalamus secretes releasing hormones that act on the pituitary to secrete gonadotrophins from the anterior pituitary. The same two hormones are released in the male and in the femalefollicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones induce the gonads (testesmale; ovariesfemale) to secrete steroid hormones. For a female, this would be estradiol and for a male this would be androgens. Estradiol elicits the secondary sex characteristics of the female (breast development, uterine lining growth, maturation of the genitals) while androgens stimulate genital and muscle growth in the male and lower his voice. Adrenal androgens stimulate axially and pubic hair growth.
Answer to Question 2
Answer: The anterior pituitary starts the cycle by the secretion of FSH, which acts on the ovarian follicles to secrete estradiol into the blood stream. Increasing estradiol levels act on the anterior pituitary to produce a surge of luteinizing hormone (LH), which causes a follicle to rupture, thereby releasing the ovum. The ruptured follicle (corpus luteum) secretes estradiol and progesterone, which prepare the uterine lining for implantation of the ovum (if fertilized). If no implantation occurs, then estradiol/progesterone secretion stops, and the uterine lining is shed, thus resulting in blood flow (menstruation).
Male (Bull) Roosevelt Elk at Northwest Trek, Washington, USA
Male giraffes will engage in necking to establish dominance.
Normal female karyotype
Structural basis for Ras activation by GTP