Animal Reproduction Chapter 46

Reproduction in the Animal Kingdom Sexual Asexual  Fission  Budding  Fragmentation & Regeneration  Parthenogenesis  egg develops without being fertilized

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

Reproductive Cycles and Patterns Most animals exhibit cycles in reproductive activity  Often related to changing seasons Reproductive cycles  Are controlled by hormones and environmental cues

Fertilization Plays an important part in sexual reproduction Joining of egg & sperm  external usually aquatic animals  internal usually land animals

Patterns of Sexual Reproduction External fertilization, external development Internal Fertilization, External Development Internal Fertilization, Internal Development

Hermaphrodites Certain Organisms seldom encounter a mate Solution  hermaphroditism  In which each individual has both male and female reproductive

Sequential Hermaphroditism An individual reverses its sex during its lifetime Figure 46.4

Male Reproductive System

Testicles  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

Male reproductive system Sperm production  over 100 million produced per day!  ~2.5 million released per drop! Testes & epididymis  sperm production & maturation Glands  seminal vesicles, prostate, bulbourethal produce seminal fluid = nutrient-rich

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

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

Female Reproductive System

Oogenesis Meiosis 1 completed during egg maturation Meiosis 2 completed triggered by fertilization ovulation What is the advantage of this development system?

The reproductive cycle of the human female The Ovarian Cycle The Uterine (Menstrual) Cycle Menopause

Female Hormones FSH & LH  release from pituitary  stimulates egg development & hormone release  peak release = release of egg (ovulation) Estrogen  released from ovary cells around developing egg  stimulates growth of lining of uterus  lowered levels = menstruation Progesterone  released from “corpus luteum” in ovaries cells that used to take care of developing egg  stimulates blood supply to lining of uterus  lowered levels = menstruation

The Ovarian Cycle In the ovarian cycle  Hormones stimulate follicle growth, which results in ovulation Following ovulation  The follicular tissue left behind transforms into the corpus luteum

Figure 46.13a–e Control by hypothalamus Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen Inhibited by low levels of estrogen Hypothalamus Anterior pituitary GnRH FSH LH Pituitary gonadotropins in blood LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle Growing follicle Mature follicle Corpus luteum Degenerating corpus luteum Estrogen secreted by growing follicle in increasing amounts Progesterone and estrogen secreted by corpus luteum Follicular phase Luteal phaseOvulation Ovarian hormones in blood Peak causes LH surge Estrogen Progesterone Estrogen level very low Progesterone and estro- gen promote thickening of endometrium Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 1 (a) (b) (c) (d) (e)

The Uterine (Menstrual) Cycle Occurs when the endometrium is shed Three Phases  Mentrual Flow Phase  endometrium is shed and mentrual bleeding occurs  Proliferative Phase  endometrium regenerates & thickens  Secretory Phase  endometrium thickens, if an embryo has not implanted by the end of this phase  A new menstrual flow commences

Menopause After about 450 cycles, human females undergo menopause  The cessation of ovulation and menstruation

Fertilization

Placental Mammals Human Chorionic Gonadotropin  Secreted by embryo; acts like LH to maintain the Corpus Luteum  Excreted in urine Parturition  Birth; in late pregnancy; estrogen increases  This stimulates oxytocin receptors  Oxytocin from fetus and mother stimulate contractions

Hormonal Control of the Male Reproductive System Testosterone and other androgens  Are directly responsible for the primary and secondary sex characteristics of the male

Androgen secretion and sperm production  controlled by hypothalamic and pituitary hormones Stimuli from other areas in the brain Hypothalamus GnRH from the hypothalamus reg- ulates FSH and LH release from the anterior pituitary. FSH acts on the Sertoli cells of the seminiferous tubules, promoting spermatogenesis. LH stimulates the Leydig cells to make testosterone, which in turn stimulates sperm production. Anterior pituitary Negative feedback Leydig cells make testosterone Primary and secondary sex characteristics Sertoli cells Spermatogenesis Testis Figure 46.14

Conception, Pregnancy and Birth Blastocyst Implants by burrowing; endometrium grows over Provides nutrients first 2-4 weeks

Placenta  Derived from both maternal and fetal cells  produce progesterone Materials exchange across membranes

Human fetal development The fetus just spends much of the 2 nd & 3 rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid Week 20

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

Human fetal development 30 weeks (7.5 months) umbilical cord

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

Birth Hormone induction positive feedback

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

The end of the journey!

Mechanisms of some contraceptive methods

RU486 Progesterone analog Blocks progesterone receptors in uterus; lining is shed Prostaglandins also taken

Reproductive Technologies Ultrasound Amniocentesis Chorionic Villi Sampling (CVS) In Vitro Fertilization (IVF) or GIFT