Reproduction and Development spermatogonium primary spermatocyte secondary spermatocytes

Reproduction and Development

spermatogonium primary spermatocyte secondary spermatocytes spermatids Meiosis II sperm Differentiation

(a) HEAD nucleus tail sheath mitochondria flagellum TAIL (b) acrosome MIDPIECE

egg secondary oocyte (egg) oogonium primary oocyte polar body Meiosis II (after fertilization)

(b) (a) fimbriae uterine tube ruptured follicle fimbriae corpus luteum 4 ovulated secondary oocyte (egg) degenerating corpus luteum ovary uterus 3 mature follicle with secondary oocyte 2 developing follicles 1 new follicle containing primary oocyte

progesterone 6 LH 3 9 1 FSH 1 4 estrogen 7 developing follicle 2 corpus ovulation luteum 5 menstruation 8 day of menstrual cycle

secondary oocyte (egg) (a) corona radiata zona pellucida

Stages of development A. Cleavage 1. Zygote divides without an increase in size 2. A solid round ball of cells called the morula is formed 3. The morula develops a cavity producing a hollow blastula B. Gastrulation 1. Blastula cells migrate to form three tissue layers a. Endoderm, ectoderm, and mesoderm 2. Resulting three-layered embryo is called the gastrula

(a) (b) day 3 day 2 day 4 blastocyst day 1 4 cells 2 cells zygote day 7 fertilization embryo day 0 blastocyst implanting muscle layer endometrium ovulated egg uterine walls

Human prenatal development A. Implantation of embryo in endometrium 1. Over half of all embryos fail to implant 2. h. CG (human chorionic gonadotropin), basis of early pregnancy test

morula stage cavity inner cell mass outer cell layer blastocyst (blastula stage) uterine lining (endometrium) embryonic disc (future embryo) yolk sac uterine lining (endometrium) amnion

The opening inside the blastula is the blastocoel. yolk The blastopore is the site at which gastrulation will begin. (a) The blastula just before gastrulation.

future brain primitive gut (e) Further development. The neural tube differentiates into brain and spinal cord. A future mouth is produced when the opening formed by the primitive gut breaks through at the end of the embryo opposite the blastopore. The blastopore is the future anus. spinal cord notochord future mouth blastopore (future anus) remnant of yolk

Stages of animal development C. Organogenesis 1. Induction promotes cells to differentiate into specific organ and tissue types 2. Adult structures develop—programmed cell death a. Some cells die unless they receive a chemical "survival signal" b. Some cells live unless they receive a chemical "death signal"

Human prenatal development B. Early embryonic development 1. Rapid differentiation and growth during first 2 months 2. Placenta develops a) Outer cells of blastula form the chorion, which penetrates the uterine lining and develops into the placenta b) Placenta functions 1) Secretes hormones—estrogen and progesterone 2) Regulates exchange of material between the mother and the fetus

Age (weeks) 1 2 zygote to formation of embryonic disc primitive streak Zygote cleaves; blastocyst implants Two-layered embryo forms; amniotic cavity

pool of fetal chorionic maternal blood capillaries villi arteriole venule fetal umbilical vein umbilical cord fetal umbilical arteries fetal amnion fetal chorion lining of uterus (endometrium) uterine muscle

Human prenatal development The Placental Barrier The placenta provides only partial protection 1) Smoking and pregnancy 2) Fetal alcohol syndrome 3) The impact of drugs on fetal development

Age (weeks) 3 4 embryo 2 -3 mm Gastrulation occurs; notochord and beginning of neural tube form 4 mm Neural tube closes; heart beats; arm buds, tail, and gill grooves

Age (weeks) 6 5 embryo 8 mm Incipient eye parts — retina (as optic cup) and lens (as lens pits) — form; leg buds form; brain enlarges 13 mm Webbed fingers and external ear form; pigment appears in retina; tail and gill grooves disappearing

gill grooves 5 th week 8 mm arm bud leg bud tail (a) umbilical cord brain

Age (weeks) 7 8 embryo 18 mm 30 mm Webbed toes form; bones begin to harden; back straightens; eyelids form Upper limbs bend at elbows; genitalia begin to differentiate; fingers are distinct

30 mm 8 th week umbilical cord placenta (c) amniotic sac

Age (weeks) 9 10 fetus 50 mm 61 mm Toes separate; eyelids develop; major parts of brain are present Chin grows; nostrils separate; face appears human; genitals appear male or female

Human prenatal development C. Fetal development 1. After two months, the major organs have formed and the human form appears 2. Gender development in the third month 3. Last 7 months—protected growth and development period

Age (weeks) 11 12 fetus 73 mm 87 mm Well-defined neck appears; genitalia are complete; sucking reflex appears

Age (months) 4 5 fetus 140 mm 190 mm Blood cells form; all major organs form; head and body hair appear; movements are felt by mother

Age (months) 6 7 fetus 230 mm 270 mm Fetus may be viable if born; eyelids open; lungs and lung circulation develop; may suck thumb; fat deposited under skin

Age (months) 8 9 fetus 300 mm 350 mm Fetus usually viable if born; fat deposits increase; body hair is lost; head hair is well developed; most senses are well developed; fetus turns head down in uterus

1 The baby is oriented head downward, facing the mother’s side. The cervix is beginning to thin and expand in diameter (dilate). 2 The cervix is completely dilated to 10 centimeters (almost 4 inches wide), and the baby’s head has entered the vagina, or birth canal. The baby has rotated to face the mother’s back. 3 The baby’s head is emerging. 4 The baby has rotated to the side once again as the shoulders emerge.

Birth Control Methods of contraception 1. Abstinence— 100% effective 2. Permanent contraception a. Sterilization 1) Vasectomy 2) Tubal ligation 3. Temporary contraception a. Preventing ovulation 1) Birth control pills a) High doses of estrogen/progesterone prevent ovulation b) Extended use—Norplant and Depoprovera b. Preventing sperm and egg union 1) Condoms (male and female) 2) Diaphragm and spermicide 3) Rhythm method (natural family planning) c. Preventing implantation of fertilized eggs 1) Intrauterine device (IUD) 4. Abortion a. Partial birth abortions b. Chemically induced abortion—RU-486, methotrexate

Sexually transmitted diseases (STDs) n A. STD statistics (United States) • • • 1. One in five infected 2. 12 million new STD infections per year 3. Two-thirds of all infections in people under 25 years old, one-fourth of all infections in teenagers

Sexually transmitted diseases B. Bacterial STDs 1. Gonorrhea (Neisseria gonorrheae) a. Infects 2 million per year (United States) b. No immunity to repeat infections c. Can result in sterility 2. Syphilis (Treponema pallidum) a. 43, 000 cases in 1995 (United States) b. Untreated can result in organ and CNS destruction c. Tuskegee Experiment— 1932, Macon County, Ga. 3. Chlamydia (Chlamydia trachomatis) a. Most prevalent of all STDs—over 5 million per year infected (United States) b. Serious reproductive tract complications in women - Sterility and ectopic pregnancy c. A "stealth" infection— 50% of infected are completely asymptomatic

Sexually transmitted diseases C. Viral STDs 1. Genital herpes a. b. c. d. 44 million Americans infected (1 in 5 over 13 years old, United States) No cure, lasts for life Transmitted to infants, causes severe disabilities Increases risk of AIDS 2. Genital warts a. b. c. Human papilloma virus 40 million Americans infected 90% of cervical carcinomas caused by HPV 3. AIDS (acquired immunodeficiency syndrome) a. 4 million diagnosed AIDS cases in past 15 years (worldwide) 1) 400, 000 diagnosed infections (United States), possibly 800, 000 infected

Sexual disorders n A. Infertility • • • 1. One in six couples unable to conceive 2. STD infections (PID) main cause of infertility 3. Reproductive technologies • • a. In vitro fertilization— 26, 000 test tube babies b. Fertility drugs and multiple births