Reproduction

• asexual reproduction: a single organism reproduces by itself

• sexual reproduction: organs called gonads produce haploid sperm or eggs through meiotic cell division

• Eggs develop without fertilization
• Ex. male honeybees develop from unfertilized haploid eggs and remain haploid; their diploid sisters develop from fertilized eggs

Some parthenogenetic fish, amphibians, and reptiles produce diploid offspring by doubling the number of chromosomes in the eggs, either before or after meiosis

• The female gonad, produces haploid eggs

• The male gonad, produces small, motile haploid sperm

• the union of sperm and egg, forms a diploid zygote

• Some can fertilize their own eggs while others still engage in sex, with two individuals exchanging sperm

• the sperm swim to reach the eggs
• must synchronize their reproductive behaviors both temporally (male and female spawn at the same time) and spatially (male and female spawn in the same place)

• Sperm are placed within the female’s moist reproductive tract, where the egg is fertilized
• Usually occurs by copulation, in which the male deposits sperm directly into the female’s reproductive tract
• males of some species package their sperm in a container called a spermatophore

• gonadotropin-releasing hormone (GnRH),
• stimulates the anterior pituitary to produce

• luteinizing hormone (LH) and
• follicle-stimulating hormone (FSH)
• (both essential in males and females)
• stimulate the testes and ovaries to produce

• testosterone and estrogen

• stimulated by the anterior pituitary system
• (both essential in males and females) stimulate the testes and ovaries to produce testosterone and estrogen

conducts semen from vas deferens and urine from the urinary bladder to tip of the penis

seminal vesicles, prostate glands, bulbourethral glands

Spermatogonia, spermatocytes, and spermatids

• produced by anterior pituitar
• LH stimulates the interstitial cells of the testes to produce testosterone
• FSH with testosterone stimulates the Sertoli cells and promotes spermatogenesis

• Testosterone inhibits the release of GnRH, LH, and FSH, which limits further testosterone and sperm development
• Sertoli cells, stimulated by FSH and testosterone, secrete a hormone called inhibin, which inhibits FSH
• This complex feedback process maintains relatively constant levels of testosterone and sperm production

• comprises about 60% of the semen
• This fluid is rich in fructose
• Its slightly alkaline pH (urine, vagina)
• prostaglandins which stimulate uterine contractions

• produces an alkaline, nutrient-rich secretion that comprises about 30% of the semen volume
• includes enzymes that allow the sperm to swim more freely

• secrete a small amount of alkaline mucus into the urethra, neutralizing remaining traces of acidic urine

• opening at the uterine tube
• bear cillia that sweep the egg into the oviduct

• conducts the egg to the uterus.
• site of fertilization

nearly closes off the outer end of the uterus

• the formation of egg cells
• ~6th week of embryonic development Oogenesis starts with diploid cells called oogonia
• ~9th - 20th weeks, oogonia become primary oocytes
• ~20th week primary oocytes have begun meiosis , but stop at prophase of meiosis I

• layer of smaller cells surrounding the oocyte and the oocyte
• Roughly every month after puberty, the hormonal changes of the menstrual cycle stimulate the development of about a dozen follicles
• The small follicle cells multiply, providing nourishment for the developing oocyte
• In response to hormones secreted by the anterior pituitary, they also release estrogen into the bloodstream

• Ovulation occurs when the follicle erupts through the surface of the ovary, releasing its secondary oocyte
• From this point, the ovulated secondary oocyte can be considered an egg
• Some of the follicle cells accompany the egg, but most of them remain in the ovary, where they enlarge, forming a temporary gland called the corpus luteum

• secretes both estrogen and a second hormone called progesterone
• These hormones stimulate the development of the uterine lining and play crucial roles in controlling the menstrual cycle
• If fertilization does not occur, the corpus luteum degenerates a few days later

• Accessory structures include the uterine tubes, uterus, and vagina
• Each ovary nestles within the open end of a uterine tube (also called the oviduct or Fallopian tube), which is fringed with ciliated “fingers” called fimbria that nearly surround the

• : inner uterine lining, is richly supplied with blood vessels and with glands
• will form the mother’s contribution to the placenta

• : outer muscular wall of the uterus, contracts during childbirth, expelling the infant out of the uterus

• The outer end of the uterus
• holds the developing baby in the uterus, then expands during labor

• opens to the outside
• receptacle for the penis and sperm duringintercourse and as the birth canal

• Developing follicles secrete estrogen (stimulates the endometrium to become thicker and grow an extensive network of blood vessels and glands)
• After ovulation, corpus luteum releases estrogen and progesterone to further stimulate endometrium
• egg not fertilized: corpus luteum disintegrates, estrogen and progesterone levels fall, endometrium disintegrates
• uterus contracts (menstrual cramps) squeezes out the excess endometrial tissue, menstruation