Human Reproduction and Development Fertilization Pregnancy Development Birth

Human Reproduction and Development Sperm

Human Reproduction and Development

3 Steps of Fertilization Capacitating Acidic environment of the female reproductive tract causes small pores to open in the acrosome (“enzyme-loaded” head) of the sperm

3 Steps of Fertilization Acrosome

3 Steps of Fertilization Capacitating Acidic environment of the female reproductive tract causes small pores to open in the acrosome (“enzyme-loaded” head) of the sperm Acrosomal reaction Enzymes released from acrosome digest the outer membrane surrounding the egg cell

3 Steps of Fertilization A single sperm cell fuses with the plasma membrane of ovum Head passes into the cytoplasm Electrochemical reaction in egg Makes membrane impermeable to other sperm

Fertilization Fertilization must occur within a very short window of opportunity. Egg is only fertile for 12-24 hours Sperm can survive up to 5 days in the body Sex (copulation) must occur no more than 5 days before or 1 day after ovulation

Pregnancy If pregnancy is established, menstruation does not occur. Fertilized egg is called a zygote. Once cell division brings the total cell count to around 8, it is called a blastocyst. Takes 3-5 days for blastocyst to travel through oviduct to uterus. Blastocyst must implant into endometrium Occurs 2-4 days after reaching the uterus

Fertilization If pregnancy is established, menstruation does not occur. Fertilized egg is called a zygote. Once cell division brings the total cell count to around 8, it is called a blastocyst. Takes 3-5 days for blastocyst to travel through oviduct to uterus. Blastocyst must implant into endometrium Occurs 2-4 days after reaching the uterus

Fertilization If pregnancy is established, menstruation does not occur. Fertilized egg is called a zygote. Once cell division brings the total cell count to around 8, it is called a blastocyst. Takes 3-5 days for blastocyst to travel through oviduct to uterus. Blastocyst must implant into endometrium Occurs 2-4 days after reaching the uterus

Fertilization If pregnancy is established, menstruation does not occur. Fertilized egg is called a zygote. Once cell division brings the total cell count to around 8, it is called a blastocyst. Takes 3-5 days for blastocyst to travel through oviduct to uterus. Blastocyst must implant into endometrium Occurs 2-4 days after reaching the uterus

Pregnancy During implantation, the blastocyst produces a hormone called HCG Human chorionic gonadotropin Prevents degeneration of corpus luteum Stimulates corpus luteum to increase progesterone secretion Maintains uterine lining Prevents contractions Pregnancy test detects HCG in the urine of women. “Turns the stick blue”

Pregnancy Tissue grows out from the embryo and mingles with endometrium to form placenta A disc-shaped organ Size of dinner plate Weighs less than 1 kg. Contains maternal & fetal blood vessels NO mixing of maternal and fetal blood!! Diffusion of gasses, nutrients, & wastes Continues production of HCG, estrogen, progesterone Maintains endometrium Corpus luteum not needed – dissolves

Pregnancy Progesterone & estrogen have a negative feedback effect on the hypothalamus No secretion of FSH No secretion of LH No new follicles mature Embryo remains firmly attached to placenta by umbilical cord.

Pregnancy Umbilical cord Contains: 2 fetal arteries Fetus to placenta One fetal vein Placenta to fetus

Pregnancy

Childbirth Also called parturition 38 – 42 weeks from conception Average = 40 weeks Three stages of childbirth Labour Delivery Afterbirth

Childbirth Labour Involuntary Rhythmic contractions of the uterus Causes cervix to open Diameter = 10 cm Delivery Involuntary uterine contractions Conscious abdominal contractions Mother forces baby out through cervix and vagina

Childbirth Afterbirth Immediately after delivery Blood vessels in placenta contract Placenta separates from uterine wall Expelled by muscle contractions

Childbirth Why?? Nobody totally knows. Baby plays some role in the timing. Progesterone decreases Allows uterus to contract Oxytocin from posterior pituitary Stimulates stronger uterine contractions Relaxin produced by placenta Causes ligaments of pelvis to loosen Larger passageway for baby

Lactation During pregnancy, high levels of estrogen and progesterone prepare the breasts for milk production Each breast has about 20 milk glands Connect to the nipple by ducts Breast enlarges during pregnancy in preparation for lactation Expulsion of the placenta causes the mother's pituitary to secrete prolactin, Initiates lactation

Lactation Prolactin inhibits the release of LH menstrual cycle is suppressed in nursing mothers The high estrogen and progesterone levels during pregnancy are thought to inhibit release of prolactin

Lactation The first fluid formed by the mammary glands is colostrum, Thick contains lactose and milk proteins, lacks fat after a few days, milk is produced Oxytocin is released from hypothalamus when infant suckles Causes milk to be released from mammary glands

Fetal Development A blastocyst embeds in the uterine wall Consists of cells of the future embryo Surrounded by a sphere of cells Embryonic membrane (extra-embryonic membrane) Support the developing embryo

Fetal Development Amnion Innermost embryonic membrane Next to baby Fluid-filled sac that cushions the baby

Fetal Development Chorion Outermost membrane Part of the placenta Secretes HCG

Fetal Development Umbilical cord Connection between mother and baby Belly-button to placenta Carries baby’s blood to and from placenta

Embryonic Development Placenta (review) A disc-shaped organ Size of dinner plate Contains maternal & fetal blood vessels NO mixing of maternal and fetal blood!! Diffusion of gasses, nutrients, & wastes Continues production of HCG, estrogen, progesterone

Embryonic Development A blastocyst undergoes gastrulation Series of cell movements and shape changes Produces an embryo with 3 cellular layers Ectoderm Outer layer of cells Will become skin and nervous system Mesoderm Middle layer of cells Skeleton, muscles gonads, kidneys, circulatory system Endoderm Inner layer of cells Liver, pancreas, lungs, lining of digestive tract

Gastrulation

Human Gestation 1st Trimester From fertilization to end of 3rd month (0 – 13 weeks) Zygote begins cell division as it moves down oviduct Becomes blastocyst and implants in uterus

Human Gestation 1st Trimester Development of body organs Heart starts beating by week 4 Week 7, testosterone begins to be secreted if a Y-chromosome is present This testosterone causes development of testes.

Human Gestation 1st Trimester By week-8 all major structures of the adult are present (in basic form) Embryo is now called a fetus Embryo is most sensitive during first trimester Due to rapid development Sensitive to radiation and drugs

Gastrulation

Gastrulation 6 weeks

7 weeks Gastrulation

Gastrulation 8 Weeks

8 weeks

10 Weeks

11 Weeks

11 Weeks

14 Weeks

Human Gestation 2nd Trimester Fetus grows rapidly To about 30 cm Quite active Hair begins to develop Cartilage of skeleton is replaced by bone

18 weeks Gastrulation

The Hand Picture May 2, 2000 USA Today

An Amazing Story -- Aug.19, 1999 Samuel Armas' tiny hand grips Dr. Joseph P. Bruner's finger just as Bruner finishes returning him to his mother's womb. Bruner, director of fetal diagnosis and treatment at Vanderbilt University Medical Center (Nashville), was performing a cutting-edge procedure on the 21-week-old fetus. The procedure on Samuel took about an hour.

An Amazing Story -- Aug.19, 1999 Bruner and Samuel's parents hope the surgery will alleviate the effects of spina bifida, a disabling birth defect in one or two of every 1,000 babies born. Because fetuses undergoing this procedure are so young -- Samuel could not survive outside his mother's womb -- this kind of surgery is gaining attention nationwide from the medical community and the media.

An Amazing Story -- Aug.19, 1999 During the procedure, surgeons remove the uterus from the mother, drain the amniotic fluid, perform surgery on the tiny fetus, replace everything and put the entire package back inside the mother. Dr. Bruner said regarding the picture, "The baby did not reach out," Bruner says. "The baby was anesthetized. The baby was not aware of what was going on."

An Amazing Story -- Aug.19, 1999 Bruner says he saw the hand "sort of pop up in the incision" on the womb, and he "reached over and picked it up." Samuel, now nearly 5 months old [may 2, 2000], & is “developing normally and hitting his monthly milestones. He smiles often and is nearly sitting up on his own.” It will take years to know how much difference the surgery made, but Alex Armas [father] says he's happy the photo has been seen by millions.

Samuel Armas 21 weeks

Human Gestation 3rd Trimester Rapid growth of fetus To about 53 cm 3-3.5 kg Fetal activity decreases Less room to move Fully mature Ready for birth

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

Parturition

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Parturition

Reproductive Technologies

Birth Control Sterilization Most effective In males vas deferens is cut off and sealed Only effects sperm content of semen so minimal side effects In females tubal ligation or cutting of the oviducts Disadvantages of sterilization - hard to reverse

Birth Control “The pill" A combination of estrogen and progesterone given for 21 days of the 28 day cycle Effectively shuts down FSH and LH production so follicles do not develop. Many of the early problems have been sorted out but side effects possible

Birth Control Barrier Methods Diaphragms, Cervical Caps, Vaginal Sponges, Condoms Condom fits over the penis and prevents semen from entering the female; Diaphragm which fits over the cervix and prevents semen from entering the uterus both of these methods are more reliable when used in conjunction with a spermicidal foam or jelly

Birth Control IUD Inter-Utarian Device placed in the uterus by a physician, prevent implantation of the blastocyst in the endometrium. Best for women who have had one pregnancy, middle to older and are at low risk for STI’s

Birth Control "Natural family planning" Requires knowledge of the day of ovulation If known, can avoid the 4 days either side of ovulation to account for unusually long -lived sperm or eggs. Women need exceptionally regular cycles to be effective "Basal" body temperature measurements (T rises at ovulation), vaginal pH measurements (more alkaline), mucus thickness can help determine time ovulation.

Birth Control "Morning after pill“ Most are essentially a controlled overdose of normal birth control pills RU-486 now distributed by Planned Parenthood. Blocks progesterone receptors causing uterine lining to slough off taking embryo with it. Many people have ethical problems with these pills since they remove fertilized eggs. i.e. after "conception" has occurred. “abortion pill”

Reproductive Technologies Ultrasound the use of high-frequency sound waves to visualize the fetus Amniocentesis a long needle is used to remove a sample of amniotic fluid from the amniotic sac surrounding the fetus, fetal cells in the fluid are cultured for 2 to 4 weeks and then analyzed for chromosomal defects and other genetic disorders

Amniocentesis

Reproductive Technologies Chorionic Villi Sampling (CVS) a small sample of tissue is removed from the chorion, the fetal part of the placenta. Can be performed earlier in the pregnancy than amniocentesis results can be obtained within a few days greater risk of spontaneous abortion from CVS than from amniocentesis ethical considerations: essentially all detectable fetal disorders remain untreatable in the uterus, and many cannot be corrected even after birth

Reproductive Technologies In Vitro Fertilization ova can be surgically removed from a woman whose oviducts are blocked These are fertilized in a petri dish in a laboratory The resulting embryos can than be inserted into the woman's uterus (or into a surrogate mother's uterus) Ethical considerations: post-menopausal woman can now have children; in surrogacy, who is the legal mother???

STIs You need to know which STIs are bacterial (and therefore curable through antibiotics) and viral (uncurable)

Virus Bacteria HPV (human papilloma virus) – Can cause genital warts, some strains can lead to genital cancers Chlamydia Herpes Gonorrhea HIV (Human immunodefficiency virus) – Can develop into AIDS Syphilis This website has more information on STIs and sexual health