Reproductive Hormones
Male gonads: testes produce male sex cells! sperm Female gonads: ovaries produce female sex cells! ovum The union of male and female sex cells during fertilization produces a zygote which divides to produce an embryo and then a fetus
Male Reproductive System Male sex hormones: androsterone and testosterone Produced in Leydig cells found between the seminiferous tubules in the testes
Testosterone Prominent hormone in males Stimulates spermatogenesis in sertoli cells of seminiferous tubules of testes Influences the development of secondary sexual characteristics at puberty (body hair, growth of larynx, strengthening of muscles, increases secretion of body oils linked to acne and body odour) Stimulates maturation of testes and penis Associated with sex drive
At puberty, the hypothalamus secretes gonadotropic releasing hormone (GnRH) which activates the anterior pituitary gland Pituitary gland secretes gonadotropic hormones: Follicle stimulating hormone (FSH): acts directly on the sertoli cells in the seminiferous tubules producing sperm Luteinizing hormone (LH): stimulate leydig cells to produce testosterone. Once high levels of testosterone are detected by the hypothalamus a negative feedback system is activated GnRH stops being released causing other hormones to stop being released slowing the production of testosterone and sperm FSH also causes the sertoli cells to produce a hormone called inhibin that sends messages to pituitary gland to inhibit the release of FSH
Female Reproductive System Oogenesis and Ovulation Ovaries contain fibrous connective tissue in small groups of cells called follicles The follicles are comprised of two types of cells: Primary oocyte contains 46 chomosomes and undergoes meiosis to transform into a mature ovum Granulosa cells provide nutrients for the ovum
Female ovaries undergo continual decline after the onset of puberty Each of two ovaries contains ~350,000 follicles at puberty Many follicles develop during each cycle but usually only one reaches maturity The remaining developed follicles deteriorate and are reabsorbed by the ovary Between the ages of approx. 12 50, ~380 ova will mature
Menopause Major transition in a woman s reproductive cycle when a woman misses her period for 12 consecutive months Marks the end of the female s reproductive cycle and signals a drop in the production of reproductive hormones
Follicle Development and Ovulation A hormone produced by the pituitary gland controls follicle development As the follicle matures it ruptures releases the ovum out of the ovary and into the fallopian tube This is known as ovulation The surrounding follicle cells remain within the ovary and form the corpus luteum which secretes hormones necessary for pregnancy If no pregnancy the corpus luteum disintegrates in approx. 10 days
Menstrual Cycle Approx. 28 days Divided into 4 phases
1. Flow Phase Shedding of the endometrium (uterine lining) Only stage that can be determined externally Beginning of cycle Approx. 5 7 days
2. Follicular Phase Development of follicles within ovary As follicles develop, estrogen is secreted Takes place from approx day 6 to day 13
3. Ovulatory Phase The egg bursts from the follicle out of the ovary and into the fallopian tube Remaining follicular cells turn into corpus luteum
4. Luteal Phase Development of corpus luteum Estrogen and progesterone are both released by the corpus luteum Preparing body for pregnancy Hormones continue to stimulate the growth of endometrium If fertilization does not occur, the concentration of hormones will decrease causing weak uterine contractions and the lining will pull away from the uterine wall and menstruation will start
Hormonal Controls Onset of puberty is signaled by the release of GnRH from the hypothalamus GnRH activates the pituitary gland to release FSH and LH FSH targets the ovary and allows follicular development to commence Follicles secrete estrogen which initiates the development of endometrium Estrogen also sends negative feedback message to pituitary to turn off secretions of FSH
As estrogen increases, it sends a signal to pituitary gland to release LH LH signals follicle to rupture and ovulation to occur Corpus luteum forms and starts releasing more estrogen and progesterone Stimulates endometrium to further develop As these hormones rise they send negative feedback to pituitary to stop releasing LH and FSH and to hypothalamus to stop release GnRH If there is no pregnancy both estrogen and progesterone levels decrease because corpus luteum disintegrates Without these hormones the endometrium will shed and the hypothalamus will again release GnRH
Similarities between Male and Female Systems Both secrete GnRH Both secrete FSH and LH Testosterone and estrogen can be produced by either gender
Homework Read section 10.7