Chapter 43

Reproduction and Development

Male Reproductive System- Testes: two typically egg shaped organs that produce

sperm (gametes).- Located in the scrotum- Form inside the body, but “drop” shortly after birth- Typically about 3 degrees color than normal body

temperature- Nec. For sperm to develop (98.9 is to hot)

- Sperm production begins in adolescence (puberty)- Seminiferous tubules: tightly coiled tubules (packed into

thousands of compartments) where sperm is produced via meiosis.

- Luteinizing hormone (LH): stimulates secretion of the sex hormone testosterone

- Follicle-stimulating hormone (FSH): with testosterone, stimulate the production of sperm.

Maturation and storage- Several hundred million sperm are created each day- Produced in the seminiferous tubules- They will travel through several tubes (can’t swim yet)- Will then enter the epididymis, where they mature and become

capable of moving- Sperm are also stored here- Vas Deferens: long tube where sperm move to reach the urethra

(also how sperm exit the body).

Semen- In urethra, sperm are mixed with fluids by three glands.

Nourish and aid in passage in the female- Seminal vesicles: produce a fluid rich in sugar- Prostate gland: secretes an alkaline fluid to neutralize

acids in the female reprod. System- Bulbourethral gland: secrete an alkaline fluid that

neutralizes traces of acidic urine- The mixture of all these is called semen.

- Semen exits body via the penis (male reproductive organ)

The Female reproductive systemThe ovaries- A mature egg is produced each month- Ovaries: two egg shaped organs found in abdominal cavity

- Gamete producing organs of the female- At birth, contain about 2 million immature eggs, have begun first

division of meiosis, but not completed it. They are stalled in prophase 1.

- After reaching puberty, sex hormones enable meiosis to resume. But, only one egg matures at a time, each month (usually).

- Only 300-400 eggs will mature in the lifetime of a female- A mature egg is called an ovum (and is released about every 28

days).

Structures of the female reproductive system- Fallopian tube: a mature egg that has been released is

swept (via cilia) into the FT which leads to the uterus.- Usually takes 3-4 days.- If not fertilized within 24-48 hours it dies.- Uterus: hollow, muscular organ about the size of a fist. If

fert. Occurs, development will take place here.- Vagina: where sperm are deposited during intercourse. It is

a muscular tube that leads to the entrance of the uterus called the cervix. (during pregnancy the cervix must open to 10 cm for the child to be able to be delivered).

The Ovarian Cycle- The events of the release of an ovum. The release of an ovum from

the ovary is ovulation.- Two distinct phases: follicular and luteal phasesFollicular: (a follicle is a cluster of cells that surround an immature egg and provide it with nutrients), hormones regulate the completion of the egg (maturing). - Beginning of the ovarian cycle- Pituitary releases FSH (follicle stimulating hormone) and Luteinizing

hormone (LH) into blood stream.- FSH causes follicle to develop- The follicle produces estrogen

Ovulation- A small amount of estrogen prevents further release of FSH and LH (negative

feed back loop), however as follicle approaches maturity, it begins to secret large amounts of estrogen. The anterior pituitary responds by greatly increasing the production of LH, causing the egg cell to complete meiosis and the ovary to rupture (positive feed back loop).

Luteal phase- Follows follicular phase- LH causes the ruptured follicle to grow, forming a corpus luteum (mass of

cells that function like endocrine gland, secreting hormones directly into their surroundings)

- LH now causes the corpus luteum to secrete more estrogen and progesterone (another sex hormone).

- The two hormones inhibit the release of FSH and LH (negative feed back loop) so that no more development of new follicles can occur during the luteal phase.

Preparation for Pregnancy- Progesterone is the hormone that signals the body to prepare for

fertilization- If occurs, corpus luteum continues producing it- If does not occur, it slows then stopsMenstrual cycle (series of changes to prepare uterus for pregnancy each month)- Changes occurring in the uterus are also taking place- Lasts about 28 days- Influenced by the levels of estrogen and progesterone- Lining of uterus thickens- If pregnancy does not occur, hormone levels drop causing the

lining of the uterus to shed, marking the end of the cycle

Menstruation- Lining of the uterus is shed- Blood vessels break and bleeding occurs- Blood and discarded tissue have to leave the body- Roughly 14 days after ovulation- Hormone levels are low at the end of this, negative

feed back loop, and process starts again- Between 45 and 55 (usually but not always) women

stop menstruation, called menopause.

DevelopmentFertilization- If a sperm is present with in a few days of ovulation, fert. Can occur.- A sperm must swim to a fallopian tube, where fert. Occurs.- A sperm releases enzymes to break down the jellylike outer layer of the

ovum.- The head enters the ovum, and the nuclei of the sperm and ovum fuse, now

called a zygote.Cleavage and implantation- First week after fert. Zygote undergoes a series of internal divisions called

cleavage, producing many smaller cells (exponentially)- Zygote continues to move towards uterus.- When zygote reaches uterus it is now a hollow ball of cells called a

blastocyst.- After about 6 days the blastocyst burrows into the lining of the uterus…

implantation.

Pregnancy- Uterus provides protection and nourishment for the developing

zygote- Gestation: “pregnancy” in humans is about 9 months long- Divided into 3 trimesters, or 3 month periods.- For the first 8 weeks the developing human is called an embryo.First Trimester- Most crucial time of development- Embryo grows rapidly- Placenta develops from the chorion through which the mother

nourishes embryo- Nutrients diffuse through membranes- Waste products pass into mother for removal- Everything is shared, so if mommy takes drugs, baby gets it as well.

Continued….- Fetal alcohol syndrome has been very prevalent in the past few years due to

mothers drinking during this time frame.- As embryo develops, three primary tissue layers form:

- Endoderm- Mesoderm- Ectoderm

- By 3rd week, blood vessels and the gut begin to develop, embryo is about 2mm long

- By 4th week, arms and legs begin to form, and more than doubles, 5mm long- By the end of the 4th week, all the major organs begin to form, and heart

begins to beat.- During 2nd month final stage of embryonic development takes place, arms

and legs take shape, major organs or evident, by the end embryo is about 22 mm.

Continued….- 8th week until birth, developing human is now called a fetus.- By the end of the 1st trimester the sex of the fetus can be

determined.

2nd and 3rd Trimesters- Fetus grows rapidly- Organs become functional- After 9 months fetus can function outside on its own- Labor: can last several ours, walls of the uterus contract, expelling

fetus.- The placenta and umbilical cord are expelled after the baby is

born.

STD’S- Diseases spread by sexual contact.Bacterial STD’s- Most caused by bacteria are treatable- Most are not detected very early, increasing transfer rates- Three major types:

- Gonorrhea: causes painful urination, discharge from penis in males.- In females often has no symptoms- May lead to infertility- Causes pain and scaring as spreads

- Syphilis: a serious bacterial STD that usually begins with the appearance of a small, painless ulcer called a Chancre.- If not treated it may cause fever, swollen lymph glands, or rashes.- Symptoms disappear without treatment.- Years later however, it may cause destructive lesions on the nervous system, blood

vessels, bones, and skin.- Can be passed to fetus, thus may be stillborn or suffer serious organ damage.

- Chlamydia: most common in the US- Similar symptoms to mild gonorrhea- Often not detected- More likely than gonorrhea to cause scaring, leading to infertility

Viral STD’s- Can not be treated or cured with antibiotics- AIDS and genital herpes are two common viral diseases.- Other common viral STD’s include genital warts and hepatitis B.- AIDS: fatal disease caused by HIV.

- Destroys the immune system by attacking white blood cells.- People don’t die from HIV, but rather from other infections because the body can’t

fight them- Genital herpes

- Caused by the HSV. Two types HSV-2 (70%), rest HSV-1 (cold sores, fever blisters, around and inside the mouth)

- Other symptoms are flu like symptoms, blisters in genital region, not life threatening, but increase possiblilites of certain cancers, can be passed to fetus, which often will die.

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