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Chapter 25

Reproduction and

Development in

Humans

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(I) Female Reproductive

System

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GametogenesisThe production of gametes (sex cells)Males = spermatogenesis in the testesFemales = oogenesis in the ovaries

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(A) OvariesThe female gonads

1. Located within the lower portion of the body cavity

2. In the ovaries, each egg cell (ovum) is present in a tiny sac called a follicle

3. About once a month, a follicle matures and bursts. The egg is then released and travels into the oviduct (Fallopian tubules)

This is known as ovulation

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4. Fertilization takes place within the Fallopian tubules (oviduct) forming a zygote

5. The zygote then travels down and into the uterus where it implants into the uterine lining and develops

6. When embryonic development of the baby is completed, the cervix dilates (opens) and the baby travels through the birth canal known as the vagina

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7. The ovaries also produce sex hormones known as estrogen and progesterone

a) estrogen- used for the development of secondary sex characteristics like mammary glands (breasts)

b) progesterone- maintains pregnancy

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SACCONE IS THE COOLEST

(II) Menstrual CycleMature egg develops and is releasedBegins at puberty and ends at menopauseHormones involved:

FSH estrogen LH progesterone

Stages involved in order: follicle stage ovulation corpus

luteum menstruation

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1. Follicle Stage10-14 daysFSH is secreted by the pituitary gland which stimulates maturation of egg in the follicleAs the follicle develops, it releases estrogen which stimulates the uterine lining to thicken with blood

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2. OvulationSecretion of LH (lutenizing

hormone) from the pituitary causes a mature egg to be released from the follicle and into the fallopian

tubules (oviduct)

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3. Corpus Luteum Stage

10-12 days

The burst follicle fills with cells forming the corpus luteum, which produces progesterone

Progesterone stimulates further thickening of the uterine lining

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4. Menstruation3-5 days

If the egg is not fertilized, progesterone secretion decreases and the lining of the uterus breaks down

The lining of the uterus is sloughed off and discharged from the body through the vagina as a result (period).

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SACCONE IS THE COOLEST

(III) Fertilization and Implantation

1. Fertilization occurs in the fallopian tubules (oviduct)

2. If the egg is not fertilized within 24 hours after ovulation, it will deteriorate

3. After fertilization, the zygote undergoes cleavage and becomes an embryo

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SACCONE IS THE COOLEST

4. The embryo arrives in the uterus 5-10 days after fertilization

5. The embryo implants into the uterine wall and establishes pregnancy

6. Placenta- nourishes the embryo7. Umbilical cord- attaches the embryo to

the placenta8. Amnion- embryo develops inside the

amniotic sac which contains amniotic fluid that serves as a shock absorber

9. Gestation Period- length of pregnancy (approximately nine months)

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SACCONE IS THE COOLEST

(IV) Multiple Births 1. Identical twins- Develops from one

zygote separating into two during cleavage. One sperm and one egg is involved and therefore the babies will look identical and must be of same sex

                                                                                             

    

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Identical twins do not have identical fingerprints. They are a product of their environment.

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(V) Multiple Births

Fraternal twins- Develop from two separate eggs, each fertilized by separate sperm cells. Therefore, the babies may not look identical and could be of different sex. Simply ciblings!

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(V) Multiple Births

Fertility drugs often cause production of more than one ovum during ovulation. Septuplets = 7 ova + 7 sperm (7 zygotes)

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(VI) Male Reproductive

System

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(A) TestesAre the male gonads

1. Produce sperm2. Sperm is produced in the

seminiferous tubules and stored in the epididymis

3. Sperm then leaves the epididymis through the vas deferens and into the urethra (which is a tube inside the penis)

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4. The penis is a structural adaptation for internal fertilization

5. Prostate Glands secrete a liquid into the urethra which combines with the sperm cells. This liquid serves as a transport medium for the sperm cells and is called semen

6. Testes also produce the male sex hormone called testosterone

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7. Testosterone regulates the maturation of sperm and the development of secondary sex characteristics such as beard development and voice pitch

8. Scrotum- sac in which the testes are located

a) outside the body b) keeps the temperature 1-2 degrees

Celsius cooler than normal body temperature

c) this provides an optimum temperature for sperm production

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Seminal Vesicles- are glands at the base of the bladder and connected to the prostate gland that provide nutrients for the semen.

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The Penis