Chapter 16: The reproductive system

(Slides by Jennifer Wade, modified by Paul Nagami)

The reproductive system• The main organs of the reproductive system

are the gonads: ovaries and testicles• The gonads make gametes: eggs & sperm• Most human cells have 46 chromosomes (two

sets of 23 chromosomes each, one set from each parent).

• Gametes only have one set of 23 chromosomes, which are passed down to offspring

• Meiosis is a special term for the cell division that gives rise to gametes

3

Sexual reproduction in diploid organisms

• Cells that give rise to gametes are called germline cells

• The letter n is used to indicate the number of copies of each chromosome a cell in an organism has. n = 23 in humans.

Testes are the male gonads

• Housed in the scrotum• Seminiferous tubules are

where meiosis actually occurs to make sperm

• They travel to the epididymis where they mature (takes about 20 days)

• Mature sperm leave the testis through the vas deferens

• The spermatic cord attaches the testis to the body, as well as housing the vas deferens & blood vessels and nerves

• Vas deferens empties into the ejaculatory duct, surrounded by smooth muscle

• The seminal vesicles, prostate, and bulbourethral glands make fluids that help the sperm move and survive. Semen is sperm + seminal fluid.

• The urethra delivers semen, as well as urine, to the outside of the body

Signals from the anterior pituitary, controlled by the hypothalamus,

trigger sperm development

In males, FSH and LH trigger testosterone release and sperm production. Too much testosterone blocks FSH/LH production!

Female reproductive anatomy

• Ovaries are the female gonads, where eggs (ova) develop. They then travel through the fallopian tubes

• Fertilization usually occurs in the fallopian tubes; the ovum migrates to the uterus, where it implants in the endometrium

Female reproductive anatomy

• The cervix separates the uterus from the vagina• Females also have a urethra, but unlike in males, it plays

no reproductive function

Oogenesis: Making EggsOo = eggGenesis = makingOogenesis = making eggs

Oogenesis begins before birth; women make their supply of primary oocytes early. One matures per month (usually) and women run out at menopause.

The monthly cycle & menstruation

• Fertile women undergo a series of hormonal changes each month; these changes help prepare the body for pregnancy if the ovum is fertilized after ovulation.

• Main hormones: FSH and LH from anterior pituitary, and estrogen and progesterone from the gonads.

Hormones from the anterior pituitary control the cycle

FSH triggers maturation of the follicle and egg.

FSH + LH spike triggers ovulation (release of the egg)

Maturation of the ovum

After meiosis produces the egg and the follicle ruptures, the remains of the follicle become the corpus luteum, which releases hormones.

Estrogen and progesterone are made in the ovaries

Rising estrogen triggers FSH + LH release

Progesterone + estrogen prepare the body for pregnancy

Fall in progesterone triggers menstruation

Changes in the endometrium

The buildup of the endometrium provides a safe “landing zone” for the fertilized zygote to implant and grow. Blood vessels give nutrients to the growing embryo. In absence of pregnancy, this lining breaks down.

Fertilization usually happens in the fallopian tube, and leads to a series of rapid divisions, of cleavage, in the developing zygote. The resulting hollow ball of cells that implants in the uterus is called a blastocyst.

The uterus expands during pregnancy