Reproduction & Development
Human Focus
I. Asexual & Sexual Reproduction
I A. Asexual Reproduction
•	Mitosis
•	No genetic change parent to offspring
•	Cloned offspring
•	Budding, fragmentation

I B. Sexual Reproduction
•	Meiosis and Fertilization
•	Genetic variation from parent to offspring
•	Dioecious or monoecious (hermaphroditic)
•	External or internal fertilization

I C. Asexual and Sexual
•	Some animals can do both asexual and sexual
•	Asexual in “good” conditions: exploitation
•	Sexual in “poor” conditions: genetic variability in offspring

II. Human Female Reproductive Anatomy
•	About 400,000 follicles at birth
•	Only about 400 follicles mature and release egg during reproductive years
•	Ovaries source of eggs and hormones
•	Ectopic pregnancy: not in endometrium of body of uterus
–	1 in 100 pregnancies 
–	Most commonly in fallopian tube (“tubal”

III. Human Male Reproductive Anatomy
•	Scrotum thermoregulatory: keeps testes cooler than abdominal temperature
•	Testes source of sperm and hormones
•	Epididymus: 10 feet coiled tubule, sperm storage and maturation

IV. Gametogenesis
•	Spermatogenesis
•	Hormonal regulation of testes
•	Oogenesis
•	Ovarian cycle and hormones
•	Differences between spermatogenesis and oogenesis

IV A. Spermatogenesis
•	65-75 days duration for one cycle
•	Occurs in seminiferous tubules (hundreds of feet long)
•	Meiotic
•	Spermatogonia  Primary Spermatocyte  Secondary Spermatocytes  Spermatids  Sperm

IV B. Hormonal regulation of testes
•	Regulated by hypothalamus of brain
•	Hypothalamus regulates pituitary to secrete FSH and LH
•	FSH  sperm production
•	LH  androgen production
•	Regulated via negative feedback for “even” hormone levels

IV C. Oogenesis
•	Starts prior to birth, arrests in Prophase I
•	Meiosis I not completed until just before ovulation
•	Meiosis II occurs only if eggs fertilized
•	Oogonia  Primary oocyte  Secondary oocyte and polar body  Ovum and polar body
•	Maximum follicle number at 6 mo development
•	Large die-off prior to birth

IV D. Ovarian cycle and hormones
•	Primary Follicle  FSH (Follicle Stimulating Hormone) stimulates to grow and enlarge to mature, secrete estrogen
•	Ovulation induced by LH surge
•	Corpus Luteum  LH (Luteinizing Hormone) induces ruptured follicle to luteinize, produces estrogens and progestins

IV E. Differences Between Spermatogenesis and Oogenesis

V. Hormones and Menstrual Cycle

V A. Hormones 
•	Releasing Hormones: peptides from Hypothalamus
•	FSH and LH: proteins from pituitary gland
•	Estrogen and Progestins: steroids from follicle cells (and placenta during pregnancy)

V B. Menstrual Cycle
•	Series of events that is about 28 days long
•	Coordinated by brain (via hormones from hypothalamus), affects ovaries
•	Hormones from ovaries affect uterus
•	Hormone levels in blood feedback to brain and help regulate the cycle

Menstrual Cycle (28 day)
•	Menstruation (days 1-5): pre-ovulatory
–	Loss of endometrium, end of previous cycle
–	Pituitary begins FSH secretion, some follicular growth
–	Low levels of sex hormones
•	Follicular phase (days 6-14): pre-ovulatory
–	FSH secretion increases, typically one follicle completes growth and maturation
–	Estrogen levels rise
–	Endometrium thickens
–	Duration quite variable
•	Ovulation (day 14)
–	LH surge
–	Follicle ruptures and releases egg
•	Luteal phase (days 14-28): post-ovulatory
–	LH secretion continues, corpus luteum formation
–	Estrogen and Progesterone levels continue to rise
–	Endometrium thickens
–	After day 20, LH levels decrease, corpus luteum shuts down, steroid hormone levels decrease

V B. Menstrual Cycle
•	Length quite variable
•	Variable cycle to cycle for an individual
•	Variable among individuals
•	Most length variability due to variation in pre-ovulatory phase

Overall Cycle Variability

Individual Variability

VI. STD and Contraception
VI A. STD 
•	Bacterial
•	Viral
•	Yeast (fungal)
•	Protozoal

VI B. Contraception

VII. Fertilization
•	Sperm Structures
VII. Fertilization
•	Acrosomal Reaction: sperm releases acrosome contents, digests thru barriers
•	Sperm binds to receptors on egg
•	Sperm and egg membranes fuse
•	Sperm nucleus enters egg (no mitochondria)
•	Eventual fusion of sperm and egg pronuclei

Human Fertilization
•	Human sperm and egg pronuclei fuse
•	Note polar body
VII. Fertilization
Polyspermy Block
•	Changes in egg to prevent additional sperm from entering
•	Having more than one sperm lethal

VII. Fertilization
•	Ernest E. Just – pioneer in fertilization research in 1910-30’s
•	Born August 14, 1883 in Charleston, SC
•	Age16 received teaching degree from South Carolina State College
•	Ernest Everett Just Middle School, Prince George’s County, MD
•	Annual Ernest E. Just Symposium at MUSC
•	Ernest E. Just Research Award at USC-Columbia (Dr. Prioleau)

VIII. Major Events of Development
•	Cleavage
–	Makes embryo multicellular
•	Gastrulation
–	Cell movement to form 3 layers (ectoderm, mesoderm, endoderm)
•	Organogenesis
–	Formation of major organs
–	Neurulation  formation of neural tube
•	Shaping of Embryo
–	Changes in cell shape (microtubules and microfilaments)
–	Apoptosis (programmed cell death)
•	Embryonic Induction
–	Interactions for form structures such as eye
•	Pattern Formation
–	Chemical signaling 

IX. Human Development
•	Fertilization in Fallopian Tube
•	Fertilization takes place in upper portion of fallopian tube
•	One-quarter billion sperm ejaculated into vagina, but few (a few hundred to a few thousand) reach the egg
•	Takes about 30 minutes for sperm to reach fallopian tube

IX. Human Development
•	Cleavage
•	Blastocyst formation day 5
–	Outer trophoblast
–	Inner Cell Mass
•	Implantation of Blastocyst in endometrium day 7
•	Implantation of trophoblast (ICM side) into endometrium
Formation of four extraembryonic membranes
•	Amnion
•	Chorion
•	Yolk Sac
•	Allantois

•	Chorion and Allantois contribute to placenta

IX. Human Development 3 weeks
IX. Human Development 4-5 weeks
IX. Human Development 5 weeks
IX. Human Development 6 weeks
IX. Human Development 8 weeks
IX. Human Development 14 weeks

X. Childbirth
Hormonal Control
•	Oxytocin
•	prostaglandins

3 major phases:
•	Dilation of cervix
•	Expulsion (delivery)
•	Placental (loss of afterbirth – placenta)

Last updated 1 August 2003