HUMAN REPRODUCTION

I. Gametogenesis:
* the production of gametes

A) Male Reproductive System

* carries out spermatogenesis; the production of 4 monoploid sperm from one primary sex cell
* deposits sperm within the female reproductive tract for internal fertilization

1) testes
* produces sperm
* produces testosterone (male sex hormone) which:

a) regulates the maturation of sperm
b) development of secondary sex characteristics such as facial hair and a deeper voice

* the testes are located in the scrotum outside the internal body cavity to keep the testes 1-2 degrees Celsius cooler than the body for the optimum temperature for producing and storage sperm

2) glands and tubes
* sperm are produced in the testes and are stored in the tube called the epididymis
* they are then carried through the abdominal cavity by the tube called the vas deferens which...
* connects with the urethra (leads out of the penis)
* along the way through the tubes, certain glands add fluids to the sperm to nourish them and protect them from the acidic environment of the woman's vagina such as:

a) prostrate gland
b) seminal vesicles
c) Cowper's gland

* these secretions and sperm are referred to as SEMEN as is released during ejaculation

3) penis
* an adaptation for internal fertilization
gets the sperm up into the female's reproductive tract

B) Female Reproductive System

* carries out oogenesis; the production of one viable monoploid (usable) egg and 3 non-viable polar bodies from one primary sex cell
* produces many hormones, including estrogen and progesterone which:

a) control menstrual cycle
b) development of secondary sex characteristics, such as development of mammary glands (breasts) and the broadeneing of pelvis (hips)

responsible for the internal development of offspring!

1) ovaries (2 of them)
* mature eggs in small cavities called follicles (remember FSH-- Follicle Stimulating Hormone)
* all eggs are present by the time the female is born

OVULATION: when eggs are matured and released

2) oviduct
* after ovulation, the egg is transported through the oviduct (a.k.a. Fallopian tubes) heading towards the uterus
* if the egg is to be fertilized, it happens in the oviducts

3) uterus
* where the embryo implants if development occurs
* at the lower end of the uterus is the cervix, which leads to the muscular tube called the vagina
* the vagina is opening between the internal and external environment

Human Reproduction and Development

here is a nice Nova link for the human fertility timeline

II. The Menstrual Cycle
* begins at puberty and ends at menopause (which is a permanent cessation (stoppage)
* usually lasts approximately 28 days
* can vary a great deal due to:

1) age
2) illness
3) pregnancy
4) stress
5) other factors

* there are 4 stages to the menstrual cycle:

A) follicle stage:
* FSH (follicle-stimulating hormone), produced by the pituitary (of the endocrine system) tells the egg to mature
* estrogen is produced from the ovary to build up the uterine lining (blood vessels) in case the embryo implants AND to stimulate ovulation
* ~days 1-14 of the cycle

NEGATIVE FEEDBACK
as the estrogen levels get higher, the pituitary inhibits (slows) its production of FSH and stimulates (speeds up) the production of LH (luteinizing hormone); this leads to...

B) ovulation:
* the mature egg is released from the follicle around day 14
* the high levels of LH (luteinizing hormone) stimulates the ruptured follicle to transform into the corpus luteum

C) corpus luteum stage:
* the newly formed corpus luteum (in the ovary) now secretes progesterone which will prepare the uterine lining for possible fertilization/implantation
* ~days 14-26 of the cycle

NEGATIVE FEEDBACK
if fertilization does not occur, the high levels of progesterone in the blood inhibits the production of LH (luteinizing hormone), which then lowers the progesterone level

D) menstruation:
* if no zygote is implanted into the uterus, the uterine lining breaks down
* the lining of the uterus, together with some blood and mucus, pass out of the body through the vagina
* ~ days 26-28 of the cycle

make sure you know what each hormone does and where it is produced!!!
(more notes and useful graphs are in the graphing activity--The Menstrual Cycle)

Human Reproduction and Development

here is a nice Nova link for the human fertility timeline

III. Fertilization in Humans

* happens internally
* after ovulation, fertilization usually occurs in the oviduct (Fallopian tubes)
* if not fertilized within ~24 hours, the egg deteriorates and can no longer be fertilized
* cleavage begins in the oviduct
* ~ 6-10 days later, the developing embryo (now a blastula) may be implanted in the lining of the uterus
* gastrulation and differentiation occur after the embryo has been implanted in the uterine walls


* if more than one egg is produced, you can have more than one embryo

FRATERNAL TWINS result when 2 eggs are fertilized by 2 different sperm cels

IDENTICAL TWINS result with 1 egg gets fertilized by 1 sperm; during cleavage, the zygote breaks off into two completely separate cells

* external fertilization- fusion of gametes OUTSIDE the mother's reproductive tract as in...
* in vitro fertilization- where an egg (ovum) and sperm are fused externally and the embryo is then implanted artificially into the mother (test tube baby)

Human Reproduction and Development

here is a nice Nova link for the human fertility timeline
Tim and Moby review reproduction

IV. Human Development
* the time between fertilization and birth is referred to as the gestation period
* in humans, the gestation period is about 9 months
* at the end of the gestation period, the secretion of progesterone from the ovary decreases and another hormone from the pituitary gland causes the females body to go into labor

A) Pre-Natal Development

* development before birth
* the first 2 months are the most important--this is when the cells become specialized--differentiation
* MANY THINGS CAN GO WRONG!!!
* there is a 5% chance that the developing embryo/fetus can have some sort of DEVELOPMENTAL DISABILITY automatically, without any other influences
* the number can go up depending on many factors such as:

1) genetic problems
* defective genes and/or chromosomes that often runs through families
* these are present at conception (fertilization)

2) acquired problems
* problems that can be prevented!

a) drug, alcohol, and tobacco abuse
* leads to low birth weight (less than 5 pounds at birth), which is the leading cause of developmental disability--lots of problems
* possible cerebral palsy, seizure disorders (epilepsy), immature organs (heart, liver, kidney), RDS (respiratory distress syndrome), non-developed immune system

THIS CAN BE PREVENTED! IF YOU ARE PREGNANT, DON'T LET CHEMICALS GET INTO YOUR BLOOD WHICH CAN THEN GET INTO YOUR DEVELOPING CHILD'S BLOOD

b) maternal/paternal factors
c) STD's (sexually transmitted diseases)
d) mother nature
e) poor prenatal care
* mother doesn't go to the doctor
* bad diet (caffeine and any other chemicals)
f) teenage parents
* your bodies are not fully developed yet, so what are the chances that the children of the children will be healthy?

B) Post-Natal Development

* development after birth
* happens at different rates until the person is a mature adult, where it slows down, until eventually death...? what about telomeres? or aging genes turned off? ...who wants to live forever?

aging-- the complex developmental changes that occurs naturally, with the passage of time

Human Reproduction and Development

here is a nice Nova link for the human fertility timeline