AP Biology Animal Reproduction Chapter 46

AP Biology Sexual & asexual reproduction  Asexual  offspring all have same genes (clones)  no variation  Sexual  gametes (sperm & egg)  fertilization  mixing of genes  variation

AP Biology Parthenogenesis  Development of an unfertilized egg  honey bees  drones = males produced through parthenogenesis  haploid  workers & queens = females produced from fertilized eggs  diploid queenworkerdrone

AP Biology Different strokes… parthenogenesis in aphids sex-change in fish

AP Biology Hermaphrodites flat worm earthworms mating  Having functional reproductive system of both sexes

AP Biology Fertilization  Joining of egg & sperm  external  usually aquatic animals  internal  usually land animals

AP Biology Development  External  development in eggs  fish & amphibians in water  soft eggs= exchange across membrane  birds & reptiles on land  hard-shell amniotic eggs  structures for exchange of food, O 2 & waste  sharks & some snakes  live births from eggs  Internal  placenta  exchange food & waste  live birth

AP Biology Adaptive advantages?  What is the adaptive value of each type of sexual reproduction  number of eggs?  level of parental care  habitat?

AP Biology Human Reproduction: Reproductive hormones  Testosterone  from testes  Functions  Prenatal development of male genitalia  sperm production  2° sexual characteristics  Maintenance of sex drive  Estrogen  from ovaries  functions  egg production  prepare uterus for fertilized egg  2° sexual characteristics LH & FSH testes or ovaries

AP Biology Sex hormone control in males Hypothalamus Pituitary Testes Body cells GnRH FSH & LH testosterone

AP Biology  Sperm production  over 100 million produced per day!  ~2.5 million released per drop! Male reproductive system

AP Biology Male reproductive system  Testes  produces sperm & hormones  Scrotum  sac that holds testicles outside of body  Epididymis  where sperm mature  Vas deferens  tubes for sperm to travel from testes to penis  Prostate, seminal vesicles, Cowper’s (bulbourethal) glands  nutrient rich fluid to feed & protect sperm  buffer to counteract acids in vagina

AP Biology Male reproductive system  Testes & epididymis  sperm production & maturation  Glands  seminal vesicles, prostate, bulbourethal  produce seminal fluid = nutrient-rich seminiferous tubule sperm spermatocytes

AP Biology Spermatogenesis  Spermatogenesis occurs within each testis in small tubules called seminiferous tubules This light micrograph shows a cross section of seminiferous tubules, blood vessels and the interstitial Leydig cells. Leydig cells are responsible for the production of testosterone.

AP Biology Spermatogenesis Mitosis and meiosis may be taking place at any time in the spermatogonia. Mitosis replenishes numbers of cells, meiosis produces actual sperm (spermatozoa) Sertoli cells help nourish sperm cells during meiosis

AP Biology Spermatogenesis Epididymis Testis Coiled seminiferous tubules Vas deferens Cross-section of seminiferous tubule Spermatozoa Spermatids (haploid) 2° spermatocytes (haploid) 1° spermatocyte (diploid) Germ cell (diploid) MEIOSIS II MEIOSIS I

AP Biology Hormonal control of sperm production  LH (Leutinizing hormone) stimulates Leydig cells to produce testosterone  FSH (follicle- stimulating hormone) and testosterone stimulate meiosis in spermatogonia to produce spermatozoa

AP Biology Role of epididymis, seminal vesicles, and prostate in semen production Sperm cells were produced in seminiferous tubules, carried thru the lumen, and sent to the epididymis. They are stored briefly in the epididymis. On sexual arousal, millions of sperm cells are moved from the epididymis into the vas deferens. Seminal vesicles add large volume of fluid which has a high conc. of fructose for energy for the sperm cells to swim (approx. 70% of the fluid in semen is added by the seminal vesicles.) The prostrate adds more fluid: alkaline which helps the sperm survive the acidic environment in a female’s vagina.

AP Biology Female reproductive system

AP Biology Female reproductive system  Ovaries  produces eggs & hormones  Uterus  nurtures fetus; lining builds up each month  Fallopian tubes  tubes for eggs to travel from ovaries to uterus  Cervix  opening to uterus, dilates 10cm (4 inches) for birthing baby  Vagina  birth canal for birthing baby

AP Biology Female reproductive system

AP Biology Menstrual cycle  Starting at puberty, human females begin a hormonal cycle called the menstrual cycle. Each cycle lasts (on average) 28 days.  The purpose is to time the release of an egg (ovum) for possible fertilization and later implantation into the inner lining of the uterus (endometrium) The implantation must occur when the endometrium is rich with blood vessels. The breakdown of the blood vessels leads to menstrual bleeding (menstruation); a sign that no pregnancy has occurred

AP Biology Hormones Hypothalamus Pituitary Ovaries Endometrium of uterus GnRH FSH & LH estrogen progesterone regulatory center for the menstrual cycle. The hypothalamus produces a hormone called GnRH (gonadotrophin-releasing hormone). The target tissue of GnRH is the anterior pituitary gland, which results in the pituitary producing and secreting 2 hormones into the bloodstream: FSH and LH. The target tissues for these 2 hormones are the ovaries

AP Biology Effects of FSH and LH on the ovaries  To increase the production and secretion of estrogen by the follicle cells of the ovary  Estrogen enters the bloodstream  Its target tissue is the endometrium of the uterus  Result is growth of lining (increase in blood vessels)  Stimulates egg development in ovaries

AP Biology Egg maturation in ovary  A spike in levels of FSH and LH leads to ovulation (release of oocyte from the follicle)  The outer ring of follicle cells begin to divide and fill in the ‘wound’ area left by ovulation which forms a corpus luteum. The corpus luteum produces progesterone for days after ovulation.  Progesterone (hormone) maintains the thickened endometrium  If no pregnancy, the corpus luteum eventually breaks down = less estrogen and progesterone

AP Biology LH FSH egg development ovulation = egg release corpus luteum estrogen progesterone lining of uterus days Menstrual cycle … as estrogen and progesterone levels fall, the highly vascular endometrium can no longer be maintained. The capillaries begin to rupture and menstruation begins. The drop in progesterone and estrogen also signals the hypothalamus to begin secreting GnRH and another menstrual cycle begins.

AP Biology Oogenesis Meiosis 2 completed triggered by fertilization ovulation In ovaries, cells called oogonia go thru mitosis repeatedly to build up numbers of cells. Then those oogonia grow into larger cells (primary oocytes) and start meiosis, but the process stops at Prophase I, until puberty. Then FSH periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis I and start meiosis II

AP Biology Comparison of spermatogenesis and oogenesis  Millions of sperm produced every day  4 gametes for every cell that begins meiosis  Very small  Occurs in testis  Released during ejaculation  Haploid nuclei  Continues throughout all of life, starting at puberty  One egg is ovulated per menstrual cycle  One gamete is produced for each cell that begins meiosis (plus polar bodies)  Eggs are ‘large’  Occurs in ovaries  Released during ovulation  Haploid nuclei  Ovulation starts at puberty, occurs with each menstrual cycle, then stops at menopause SpermatogenesisOogenesis

AP Biology Fertilization

AP Biology Fertilization Enzymes from acrosome are released at the zona pellucida. Sperm head enters egg, plasma membranes fuse together. This initiates the cortical reaction.

AP Biology Fertilization and the cortical reaction As soon as the sperm reaches the nucleus, the cortical granules fuse with the cell membrane and release their enzymes to the outside, making it impermeable to any other sperm cells.

AP Biology Early human embryonic development: Cleavage  Fertilization triggers the zygote to start repeated mitotic divisions as it moves down the Fallopian tube toward the uterus  By the time the embryo reaches the uterus, it is approx. 100 cells and is ready to implant into the endometrium of the uterus. At this point, it’s a hollow ball of cells called a blastocyst.

AP Biology A few days later, the embryo imbeds itself in the uterine lining. At this point, a woman's body begins to secrete a pregnancy hormone known as HCG. This hormone maintains production of progesterone from the ovary, a crucial factor in maintaining a pregnancy.

AP Biology HCG specifics  HCG = Human Chorionic Gonadotrophin.  It enters the bloodstream of the mother  its target tissue is the corpus luteum. HCG acts to maintain the secretory functions of this gland beyond the length of time typical of a normal menstrual cycle. The corpus luteum continues to make both estrogen and progesterone and the endometrium is maintained.  Later on in pregnancy, the placenta will take over estrogen and progesterone production.

AP Biology Organogenesis Umbilical blood vessels Chorion Amnion Yolk sac Allantois Fetal blood vessels Maternal blood vessels Bird embryo Mammalian embryo Placenta

AP Biology Placenta  Materials exchange across membranes

AP Biology Role of the Placenta When fully formed, 2 fetal blood vessels within the umbilical cord carry fetal blood to the placenta. The blood is deoxygenated and carries waste products (CO2, urea, hormones). This fetal blood exchanges materials (not blood) with the maternal bloodstream. Another fetal blood vessel returns the ‘clean’ blood to the fetus (has oxygen and nutrients, hormones) At no time do the 2 bloods actually mix When the corpus luteum stops producing estrogen and progesterone, the placenta starts producing and secreting them.

AP Biology Role of the amniotic fluid  Amniotic sac extends all the way around the fetus  The fluid within it is called amniotic fluid  Several functions:  Provides cushioning effect if something happens to mom’s abdomen Provides safe environment where fetus has free movement and can exercise its developing muscles and skeleton Provides temperature stability

AP Biology Human fetal development 7 weeks4 weeks

AP Biology Human fetal development 10 weeks

AP Biology Human fetal development 12 weeks20 weeks

AP Biology Human fetal development  24 weeks (6 months; 2nd trimester) fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix

AP Biology Human fetal development  30 weeks (7.5 months) umbilical cord

AP Biology Getting crowded in there!!  32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

AP Biology Birth Hormone induction positive feedback

AP Biology Intestine Placenta Umbilical cord Wall of uterus Vagina Cervix Birth (36 weeks) Bladder

AP Biology The end of the journey!