Reproductive System

Day 3: Spermatogenesis, oogenesis and the menstrual cycle

Gametes

• reproductive cells (sperm and egg)• haploid (single set of unpaired chromosomes)– In humans we have 23 pairs or 46• chromosomes are packaged DNA

• formed by gametogenesis– spermatogenesis– oogenesis

Mitosis• cell division• undergoes several phases:

– interphase* – prophase – prometaphase* – metaphase – anaphase – telophase – cytokinesis*

• results into two identical daughter cells– IF a diploid cell undergoes mitosis, the result is a diploid cell.

Meiosis

• Cell division• results into two daughter cells with half the

number of chromosomes– IF a diploid cell undergoes meiosis, the resulting

cells are haploid cells– Meiosis only happens in gametes.

Spermatogenesis

Oogenesis

Differences in gametes

sperms• male• Meiosis results in four

sperms.• Sperms are motile.• relatively small • in the millions

ova• Female• Meiosis results in one

mature ovum and three polar bodies

• The ovum is nonmotile.• relatively large• Just one ovum is released

every month.

The Sperm Cell

Parts of a sperm

• head: acrosome– has enzymes to penetrate the egg cell– triggers acrosome reaction• prevents other sperms from fusing with the egg

• midpiece: ATP production (energy)– fructose from seminal fluid

• tail: flagella for movement

The Ovum

Parts of an ovum

• yolk– cytoplasm and nutritive

• germinal vesicle– nucleus

• zona striata or zona pellucida– protection– in between the cytoplasm and corona radiata

• corona radiata– outer protection, 2 or 3 cell layers thick

Menstrual cycle

• monthly cycle ~28 days– In adults 21 to 35– In teens 21 to 45

• “bleeding”– shedding of the endometrium of the uterus– lasts 3 to 5 days

What happens in the menstrual cycle?

• follicle-stimulating hormone (ripening)• increase of estrogen– prepares the uterus for pregnancy– the lining grows and thickens

• luteinizing hormone (release)– Day 14, the ovum is released from the ovary.

• Progesterone prepare and maintain the endometrium• Pregnancy can occur 3 days before or during ovulation.

• IF fertilization does not occur:– ovum breaks– hormones drop– the uterine lining is shed

• IF fertilization occurs– Egg is “planted” in the endometrium– Human chorionic gonadotropian (HCG)• Continues secretion of progesterone

*provide the blood vessels (endometrium)

Complications of the menstrual cycle

• amenorrhea– Lack of menstruation• Excessive weight loss• Stress• Excessive exercising

• dysmenorrhea– painful menstruation, cramps• excess prostaglandin

– contracts and relaxes smooth muscles

Menopause

• the menstrual cycle stops• happens at age 45 -55

What happens at menopause?

Ovulation stops.